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G R A H A M'S
CHEMICAL AND PHYSICAL
RESEARCHES.
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f a 0 m A PHOTO C R A PH BY M A J L L & Cº.

CHEMIC A. L.
AND
PHYSICAL RESEARCHES
BY
THOMAS GRAHA M,
D.C.L., F.R.S.,
CORRESPONDING MEMBER OF THE INSTITUTE OF FRANCE, ETC. ETC.
COLLECTED AND PRINTED FOR PRESENTATION ONLY.
PREFACE AND ANALYTICAL CONTENTS
f{Y
DR. R. A.ING US SMITH.
EDINBURGH, MIDCCCLXXVI.
PRINTED BY T. AND A. CONSTABLE, PRINTERS TO HER MAJESTY,
AT THE EDINBURGH UNIVERSITY PRESS.
Chem
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PR E FA C E.
-O-
GRAHAM AIND OTHER ATOMIST.S.
ATOMS and eternal motion are amongst the first known
scientific ideas. We find them discussed with full keenness
of insight by the earliest Greeks of whom we have received
definite accounts. If the opinions did not spring from Hellenic
soil they certainly found themselves in a land well fitted for
their development; but so many of the thoughts of men have
come from the East that it is natural to suppose that both
had their origin there. India has had several atomic systems
and acute discussions on atoms and matter. I shall leave it
to others to decide at what time the earliest known were
written, but it is at least clear that the subject was thought
out in a peculiar method, with occasional logic of the
keenest known, moving forward into regions where reasoning
is difficult and mysticism reigns. There we may find thoughts,
the same apparently as led to the centres of force of Bosco-
vich and original fluid or universal ether, as well as the
various atoms of the Greeks, or the clearest ideas of moderns,
too clear at times to be sufficiently comprehensive. It is said
that Leucippus obtained his opinions from a Phoenician called
Moschus (and Mochus), and it is pleasant to think of this
earlier name of an atomist to whom it seems unnatural to deny
existence, even if he be little known. And although Zeller"
tells us that the roots of the ideas lay in the earlier Greek
mode of thought, this scarcely is sufficient for separating the
1 In Die Philosophie der Griechen, p. 688.
279996
vi PREFACE.
East and the West, since tradition in very remote times led
to the belief in frequent and interesting communication. Such
names are not forged, and when characters are invented we
find them rarely to be men of science. Still, the accounts are
vague, and Indian literature waits arrangement. Although
Kapila as a philosopher is almost lost as a personality, his
system" shows a long train of successfully cultivated thought.
How and when did Cánáde's notion arise that an atom was the
sixth part of a mote in a sunbeam 2 If, however, we turn to
the second idea, namely, “eternal motion,” we must claim
for it decidedly an Eastern origin, and perhaps it is still to
be found among the remnants where Chaldaeans or Acca-
dians may have recorded their thoughts, when their astrono-
mers and astrologers sought wisdom out of the heavens.
Science seems to have begun amongst the heavenly bodies,
and even amongst the Greeks Anaximander brought forward
his mystic idea of the immeasureable, before the smaller
movements in matter were considered. To follow a late
writer,” even the idea of eternal motion, as held by that
early Greek speculator, referred only to the motion of the
stars and the unceasing changes of the sun and moon.
When Leucippus gave his mind to the study of atoms
he saw there also the need of movement, and the restless-
ness of all creation in detail was thus early expressed by
him. It was the result of a process of reasoning, begun
by observing objects that strike all men unceasingly, and
ending amongst those too small to be visible; it began with
what to us is infinitely great, and ended with what to our
senses is infinitely small. Leucippus seems to have concluded,
as so many thinkers have since done, that arguments con-
cerning the infinite divisibility of matter must end in empty
words, or in thoughts of awe regarding the unlimited, which
* Colebrooke's Essays on the Religion and Philosophy of the Hindus.
* Gustav Teichmuller, Studien der Geschichte der Begriffe. Berlin, 1874,
PREFACE. vii
was to take a basis of thought; without such a foundation
where would he stand to observe the building up of the
world ! The assumption, if it be one, formed the atom of
science, and its study, although without a distinct advance for
ages, has richly rewarded the student of the present century,
giving us the basis of a rational view of matter, as the atoms
are the basis of the matter itself. In the mind of this early
Greek, first or not, the action of the atom, as one substance
taking various forms by combinations unlimited, was enough
to account for all the phenomena of the world. By separation
and union, with constant motion, all things could be done.
These great thoughts, the oneness of matter and the power
of motion and combination, were given to gifted men of the
early days, and, like some other great thoughts, they have
been misunderstood or neglected to a very late time. It is
because Graham took a similar view, and advanced the idea
of atomic motion with unity of material to that which
might be fairly called its utmost limit, that he is brought
forward here with Leucippus. The Greek told us that all was
in motion. | Graham conceived the idea that the diversity in
the motion was the only basis of the diversity of the material,
or, in other words, that an atom constituted an element of a
special kind, according to rate or peculiarity of its movements.
To the study of the motion of atoms, or at least of molecules,
the practical atom of our chemistry, or that which although in
a sense divisible is not known to be divided, Graham gave all
the leisure of a thoughtful life. When he came to the subject
it had advanced far beyond the early stage, notably by the
thoughts of Dalton and the chemists of the earlier part of this
century. To pass over more than two thousand years in a bound
is apparently to forget the effect these thoughts had on man-
kind; but it cannot be denied that no important results
followed for the human race, and only a few men seemed seri-
viii PREFACE.
ously to think on the subject until very modern times. A
glance at a few of the more striking halting-places will help
us to see better the relative position of Graham as an atomist
and a philosopher, words which suit his character better than
chemist, although chemistry was his profession and the source
of all his speculations and reasoning.
Leucippus was soon almost forgotten, until a time came
when men gladly treasured the little that was remembered of
him; but his successor was better known, and Democritus has
obtained much of the honour of the acute thoughts that taught
us atomic motion. It is said that Xerxes himself stayed, when
at Abdera, with the father of Democritus, who was very
wealthy, and that the magi in the great king's train taught
the theory of atoms to the young man. It may be true, for
the East ever appears at the beginning of things, and the fresh
minds caught up the richest crops as they showed themselves
on the face of the creation, expanding before men's eyes.
A few words, quoted from Lange,' give the position of Demo-
critus so far as we are here concerned:— -
“The difference of substances arises from the difference in
the number, size, shape, and arrangement of the atoms. The
atoms have no internal conditions; they act by pressure and
percussion only.”
These words express the early theory with great beauty
and precision. We do not say here with Aristotle, “Matter
cannot move itself,” and so inquire further into the subject;
for us it is enough to remember the physical theory. So far
as is apparent, Democritus left the pure physical theory of
oneness of atom, and he makes many varieties, so that at last
it is said that “the soul consists of round atoms, fine and
smooth like those of fire, and by their motion, which penetrates
the whole body, the whole phenomena of life are produced.”
But although this theory leaves the oneness of atoms, it keeps
* F. A. Lange, Geschichte des materialismus. 1873.
\
\
PREFACE. ix
closely to the idea of motion as the only one phenomenon
conceivable for matter or mind, and it is without much doubt
the origin of the saying that life is motion, the great thought
of Heraclitus. All life consists of this constant moving,
nothing is but as a movement. If we car (to view the subject
very strictly, we may say that the simplicity of the atom is
gone even at this early stage; but if the simplicity of the
atom is gone, the age of the molecule commences, a body com-
posed of bodies not to be separated; and although the atom
of Democritus is spoken of as one in quality, its diversity of
size gives it a composite character, and one might even choose
to find in him the germ of an opposition to the theory show-
ing itself during the very building." The peculiar soul-atoms”
destroy even the supposed qualitative uniformity of atoms;
but Leucippus is said to have had the same opinion. At
best this early atom is a practical one, like that of Newton's,
not an intelligible one, an idea that has still to be imagined
in a reasonable manner. This difficulty produces the non-
atomists, but the atomist may see it quite as clearly, and leave
the reasoning for a stage, since he cannot proceed with any
firmness of step. A consistent atomist of the Dalton type
may be a thorough non-atomist when he breaks up in his
mind the present elements.
We do not find that anything fitting our present purpose
was added to the theory of atoms until the time of Lucretius, if
indeed he can be said to have added anything. He, however,
as the only full expositor of the doctrine among the ancients,
must be viewed with attention. As a philosophic poet,
Lucretius is interesting, it ought rather to be said interesting
for the time in which he lived, but he contradicts himself more
than the early Greeks in his theories, and his explanations,
that are so satisfactory to himself, seem to many men to ex-
plain little. Nevertheless he deserves a full share of honour.
l Zeller, vol. i. 699; Aristotle quoted in the note, 2 P. 729.
X PREFACE.
If it is attempted to give by quotations from Lucretius a
good idea of his system, we get rather into confusion. The
reason probably is, that he had not thought out the details
clearly in his own mind, and indeed every man who has
attempted consistency in this department has failed; but it
may be said that his atoms are solid and eternal, with some
unalterable motion, and a tendency downwards as well as to
the side, easily agitated also by many forces. They are made
of parts, which parts cannot exist by themselves, the atoms
are partly like our molecules, but the parts seem hypothetical
existences, conceived apparently in order to bridge over the
distance between nothing and something, a difficulty frequently
attempted by those who reason outside the atomic idea.
Motion is to him everything that can be found in life and
thought, which are only the clashing of atoms, light or heavy,
round or smooth, made by more or fewer of the combinations
of small points that do not exist by themselves. This theory
allows of any shape of molecules, even hooked ones, which
are spoken of as explaining combination both in Lucretius
and more modern writers, and to which the name of atom is
applicable only with suitable explanation.
In reality, Lucretius sometimes loses the clear meaning
of the atom he admires; as he loses also and objects to
the idea of centres in the universe, preferring up and down
as fundamental ideas. After the first great thoughts are
uttered, the rudest ideas come into play, and the carpenter
and hammer seem to be set to do the whole work as was
done by his predecessors, and which his successors continue
to admire.
The alchemists got rid of this, but lost also the idea of
atoms. They retained, however, the one fundamental matter
of which they were composed; with a loss of clearness they
gained in breadth. Roger Bacon, so much superior to the
most, may be looked on as an ideal one. He says logically:
PREFACE. xi
“The elements are made of ylá." Barley is a horse by possi-
bility, that is occult nature, and wheat is a possible man, and
man is possible wheat.”—De Arte Chymiae.
If, however, we come to the atom which has done most
good work in modern chemistry, we are after all obliged to
turn back to one of the descriptions of it by Lucretius in one
of his best moments, and after it has been modified by the
powerful hand of Newton, and freed from connecting obscuri-
ties. Lucretius says, book i. line 603, “Primordial bodies are
solid in their simplicity, and consist of the smallest parts
closely united, not combined by a union of others, but rather
endowed with eternal simplicity: from them nature allows
nothing to be taken away or to be diminished, reserving them
as seeds for bodies.”
Newton's well-known words may be quoted, since they
form an era in the theory of atoms, not so much by new ideas
as by distinctness, and the elimination of much confusion —
“It seems probable to me that God in the beginning framed
matter in solid, massy, hard, impenetrable, moveable par-
ticles, of such sizes and figures, and with such other properties,
and in such proportion to space, as most conduced to the end
for which He formed them; and that these primitive particles
being solid, are incomparably harder than any porous bodies
compounded of them; even so very hard as never to wear or
break in pieces; no ordinary power being able to divide what
God himself made one in the first creation. While these
particles continue entire, they may compose bodies of one and
the same texture in all ages; but should they wear away, or
break in pieces, the nature of things depending on them would
1 Or the one original matter.
* “Sunt igitur Solida Primordia simplicitate, -
Quae minimis stipata cohaerent partibus arcte;
Non exullorum conventu conciliata,
Sed magis aeterna pollentia. Simplicitate:
Unde neque avelli quicquam, neque diminui jam
Concedit natura, reservans semina rebus.”
xii - IPREFACE.
be changed. Water and earth composed of old worn particles
would not be of the same nature and texture now with water
and earth composed of entire particles in the beginning. And,
therefore, that nature may be lasting, the changes of corporeal
things are to be placed only in the various separations and
new associations and motions of these permanent particles;
compound bodies being apt to break, not in the midst of solid
particles, but where those particles are laid together, and only
touch on a few points.” * t *
Here, then, is the real atom of the chemist—explaining
a mode of combination which Bergman, Wenzel, and Richter
laboriously tried to understand, which Higgins reached but
did not see with vigour—the atom with which Dalton made
his fertile discovery—the atom which has built up the modern
science of chemistry, and from which our most precise ideas
of the constitution of matter have been acquired, one which
must remain probably without fundamental alteration until
a new mode of analysis is found, and one which probably
is in principle true even at stages considerably below that
which contains our unaltered elements. This atom, how-
ever, is by no means of necessity indivisible in every sense;
it is only indivisible by us, although some chemists may
have different views. It may be in a strict sense a molecule,
but it is much better to keep that word for a combination of
atoms of known bodies rather than of hypothetical existences,
a double atom of hydrogen or other element being our simplest
molecule. w
When we arrive at this point we pass to the next important
stage, namely, the motion of gaseous molecules, if not of atoms,
and the beginning of the attempt to define it precisely. The
first definite ideas are by D. Bernoulli. They are explained in
his Hydrodynamics," which, although published in Strasburg
1 Danielis Bernoulli, Joh. Fil., Med. Prof. Basil. Hydramania. sive de viribus et
motibus fluidorum Commentarii (Argentorati, 1738), p. 200. Sectio decima:—
“Fluida nunc elastica consideraturis licebit nobis talem is affingere constitutionem,
PREFACE. xiii
in 1738, were previously worked at when he was Professor in
St. Petersburg.
D. Bernoulli says, “The chief peculiarities of fluids are
these : 1st, they are heavy; 2d, they expand in all directions
unless they are confined; and 3d, they allow themselves to
be compressed more and more, according to the increased force
applied.” Speaking of a vessel of air with a weighted cover,
and which he illustrates with a diagram, he says, “So the
minute bodies, whilst they impinge on the cover EF, keep it
up by their continually repeated strokes, and form an elastic
fluid, which expands itself when the weight is removed or
diminished.” “We shall consider the corpuscles enclosed
in the hollow of the cylinder as infinite in number, and when
they occupy the space ECDF we shall say that they consti-
tute the natural air.”
Davy and Count Rumford entered the field when this
theory of gaseous motion was forgotten, and inaugurated a
new theory of heat founded on molecular activity. That
heat is immaterial was no rare opinion last century, or since
Lord Bacon spoke of it as motus et nihil aliud. However,
atomic motion ceased from the time of Rumford to be a vague
idea. Davy" spoke definitely when, without calling in the aid
of forces, he supposed that in solids the particles are in a vibra-
tory motion, the particles of the hottest bodies moving with
greatest velocity and through the greatest space; that in
quae cum omnibus adhuc cognitis conveniat affectionibus, ut sic ad reliquas etiam nondum
satis exploratas detur aditus.”
* “Fluidorum autem elasticorum praecipuae affectiones in eo positae sunt : 1°, ut sint
gravia; 2", ut se in omnes plagas explicent, nisi contineantur, et 3', ut se continue
magis magisque comprimi patiantur crescentibus potentiis compressionis: ita compa-
ratus est ačr, ad quem potissimum presentes nostrae pertinent cogitationes.”
2 << Sic corpuscula dum impingunt in operculum E Fidemque suis sustinent
impetibus continue repetitis fluidum componunt elasticum quod remoto aut diminuto
pondere P sese expandit 33
* “Corpuscula cavitati cylindri inclusa considerabimus tanquam numero infinita,
et cum spatium E CDF occupant, tunc ačrem illa dicemus formare naturalem.”
* Collected Works, vol. iv. p. 67.
xiv. PREFACE.
fluids and elastic fluids, besides the vibratory motion, which
must be considered greatest in the last, the particles have a
motion round their own axes with different velocities, the
particles of elastic fluids moving with the greatest quickness;
and that in ethereal substances the particles move round
their own axes and separate from each other, penetrat-
ing in right lines through space. Temperature may be
conceived to depend on the velocity of the vibrations, in-
crease of capacity on the motion being performed in greater
Space, etc. -
This is evidently the work of Rumford and Bernoulli, with
additions after passing later through an original and powerful
mind. - -
We may take the next step to Herapath." At p. 15, vol. i.,
he says:— -
“Theory of Gases.—From these considerations it follows
that if a number of small bodies be inclosed in any hollow
body, and be continually impinging on One another, and on
the sides of the inclosing body; and if the motions of the
bodies be conserved by an equivalent action in the sides of
the containing body, then will these small bodies compose a
medium, whose elastic force will be like that of air and
other gaseous bodies; for if the bodies be exceedingly small,
the medium might, like any aeriform body, be compressed into
a very small space; and yet if it had no other tendency than
what would arise from the internal collision of its atoms, it
would, if left to itself, extend to the occupation of a space of
almost indefinite greatness. And its temperature remaining
the same, its elasticity would also be greater when occupying
a less, and less when occupying a greater space; for in a com-
pressed state the number of atoms striking against a given
portion of the containing vessel must be augmented, and the
space in which the atoms have to move being less, their
1 Mathematical Physics, etc., by John Herapath. 2 vols. 8vo, 1847.
PREFACE. XV
motions or periods must be shorter, and the number of them
in a given time consequently greater; on both of which
accounts the elasticity is greater the greater the compression.
Besides, when other things are the same, the elastic force
augments with an augmentation of temperature and diminishes
with a diminution; for an increase of temperature, according
to our theory, must necessarily be attended with an increase
of velocity, and therefore with an increase in the number of
collisions.”
Joule took up the subject immediately after Herapath,
and says: “Since the hypothesis of Herapath, in which it is
assumed that the particles of a gas are constantly flying about
in every direction with great velocity, the pressure of the gas
being owing to the impact of the particles against any surface
presented to them, is somewhat simpler, I shall employ it
in the following remarks on the constitution of elastic fluids,”
etc." Dr. Joule continued the subject, and introduced it into
the region of experiment and observation, or, in other words,
to the science of modern times.” Joule might have added
that the view he adopted is not only in accordance with
the known laws of the elasticity of gases, but conforms to
the ratio of the specific heats of gases. The mathematical
development continued to make progress in the hands of
Clausius, Clerk Maxwell, Holtzmann, and others, taking
us to new fields, and outside the region of Graham's
activity.
Graham is as strict an atomist as perhaps can be found.
We have seen how difficult it has been to hold the doctrine
pure, how even Democritus looked on the atoms as containing
parts, and to get rid of the difficulty, Lucretius makes the
parts incapable of existence per se,_thus introducing the
inconceivable; even, with Newton, and decidedly with
* Memoirs of Lit. and Phil. Soc. of Manchester, vol. iv. 1851, p. 111. Read in 1848.
* See Math. Physics, vol. i. p. 264.
Xvi PREFACE.
Dalton, hitherto the greatest of atomists, because his system
has had the most substantial results, the atoms are either
compounded of matter, besides many properties which for
want of a better name we might call metaphysical, or aſ
surrounded with forces which act very independently, and
attach themselves to the atoms doing apparently most of
the work.
It was a true movement in the direction of atomism, when
Davy gave his ideas; and one may almost say that it was the
object of Graham's life to find what the movement of an atom
\was. Davy does not define his vibratory motion, which could
scarcely be imagined in an unconfined space unless the body
had parts; for fluids he gives a motion of rotation making
thereby a definite boundary; but we do not see in his opinions
what an atom, say of iron, would do when alone. He would
probably in such a case give it the same revolving motion as
he gives the parts of gas. Graham avoids picturing the
most primitive motion in all its character, but he seems to
indicate one of revolution as he brings in the similarity to the
orbit of a planet, and in this way with Davy connects in an
interesting manner the very first speculations on the eternal
motion of the heavens with those movements the smallest
conceivable of atoms.
He has, however, advanced further, when he adopts the
theory of one kind of matter, each atom being distinguished
by the extent of its motion, one primordial impulse for
each kindy This movement is an unalterable one, unaffected
even by heat. These atoms do not come to us free, but are
believed to be congregate, forming the compound atom or
molecule, whose movements have of late been more carefully
studied, and which form, in fact, the elements as the chemist
finds them. And then, in his cautious manner, he adds that
they have a singular relation connected with equality of
volume. Equal volumes can coalesce and form a new atomic
PREFACE. xvii
group, retaining the whole or the half, or some simple propor-
tion, of the original movement and consequent volume. This
is chemical combination.
It is therefore clear that Graham was a true descendant
bf the early Greeks, his mind altered, of course, by inter-
vening thinkers; but in one point he differs from most, if not
all, known to us, in that he devoted his whole life to the
study of this subject, -
In all his work we find him steadily thinking on the ulti-
mate composition of bodies; he searches after it in following
the molecules of gases when diffusing; these he watches as
they flow into a vacuum or into other gases, and observes care-
fully as they pass through tubes, noting the effect of weight
and of composition upon them in transpiration. He follows
them as they enter into liquids and pass out, and as they are
absorbed or dissolved by colloid bodies, such as caoutchouc, he
attentivelyinquires if they are absorbed by metals in a similar
manner, and finds the remotest analogies, which, by their
boldness, compel one to stop reading and to think if they be
really possible. He follows gases at last into metallic com-
bination, and the lightest of them all he makes into a com-
pound with one of the heavier metals, chasing it finally through
various lurking-places until he brings it into an alloy and
the form of a medal, and puts upon it the stamp of the Mint.
Indeed, he is scarcely satisfied even with this, and he finds
in bodies from stellar spaces—in meteoric iron—this same
metallic hydrogenium, which he draws out from its long
prison in the form of a gas.
It was a wonderful, and one may say romantic, ending to
a series of inquiries, to the eyes of most men the most unin-
teresting. His works are full of care, but not of joy. He
slowly collected figure after figure, never idle with his theories,
but never venturing without a reason.
b
xviii PREFACE.
If we examine his work on Salts and on Solutions we have
a similar train of thought. One might have slighted the
importance which he attached to the water of salts and
the temperature at which it was reduced, but in his hands it
was a revelation of some of the most mysterious internal
phenomena of these bodies. Although the inquiry was made
without reference to the new position which hydrogen takes
in acids, it was entirely on a track of preliminary necessary
thought; the modern view he received favourably at an early
period in his system of chemistry. Other advanced ideas
were stimulated by him in the 1st vol. of the publications of
the Cavendish Society, a Society established mainly by his
influence.
A chemist must take great pleasure in following Graham
when he seeks the laws of the diffusion of liquids, and traces
their connections, especially when they lead to such results
as he has expressed by dialysis, a process founded on a new
classification of substances, and promising still the most valu-
able truths. We see in the inquiry how carefully Graham
thought on the internal constitution of bodies, by examining
the motion of the parts, and from the most unpromising and
hopeless masses under the chemist's hands—amorphous pre-
cipitates of alumina or of albumen—brought out analogies
which connected them with the most interesting phenomena
of organic life. Never has a less brilliant-looking series of
experiments been made by a chemist, whilst few have been so
brilliant in their results or promise more to the inquirer who
ollows into the wide region opened.
It is easy to see that, however various the subject on the
surface of his writings, Graham's inquiries all led to one end,
namely, the condition and motion of the molecule or atom.
In using the word atom chemists seem to think that they
bind themselves to a theory of indivisibility. This is a mis-
take. The word atom means that which is not divided, as easily
PREFACE. xix
as it may mean that which cannot be divided, and indeed the
former is the preferable meaning. Even when Lucretius speaks
of primordial bodies that cannot be divided, he does not deny
that they have parts, although these, as we have seen, cannot
exist by themselves, and Graham, as well as other atomists,
give a similar opinion, that is, that the original atom may be
far down. Graham speaks of this in more than one place.
There comes to us a something indivisible by us, and it is
consistent to call it an atom, as it is consistent to call the
smallest particle of alum, with its twenty-four equivalents of |
water, an atom, simply because it is the smallest possible
portion of alum, which to divide would be to destroy.
Some have preferred to leave the atom without believing
in infinite divisibility, and it is strange that when we come
to the point of deciding on the existence of atoms the mind
insists on going further and finding of what the atom is com-
posed. | By doing this the atomist often ends by being a
º and probably this is the necessary double con-
clusion: we believe in atoms because Nature seems to use
them, and we break them up continuously because we know
not when to stop. / There are various methods of spanning the
distance from nothing to something. Boscovich, by his centre
of force, forms an atom, but it differs in nowise from Newton's
but in name. Newton and Dalton, and all others, would allow
all the forces that Boscovich can desire. Sir W. Thomson
has made a vortex atom in the perfect fluid described by
Helmholtz, and some such, fluid is much required for the
exp \nation of many phenomena.
In 1868 Graham acknowledged the possibility of the vortex
atom when he said, “We may imagine the same result from
atoms and from a fluid medium to a position of which a special
rate of pulsation is imparted, enlivening that portion of matter
into an individual existence and constituting it a distinct
substance or element.” -
XX & PREFACE.
Davy's revolving atom has been more fully considered by
Czirnianski, but our real success is confined to the fuller deve-
lopment of the idea of motion in gases and in solutions.
We see, then, that Graham advances the idea of atomic
motion, and teaches us also how to observe it. The accuracy
of his method, as well as of his work, is proved by the results;
and it is not without reason that he is placed in that chain of
eminent thinkers which has been represented by such as
Leucippus, Lucretius, Newton, Higgins, and Dalton.
In Graham's lifetime chemistry had been enriched with
inquiries into atomic volumes, the volumes of compound mole-
cules, and the specific heat of the atom, or the relation of heat
to the atomic weight. The relations in which the atoms of a
compound stand to each other have been viewed very differ-
ently by chemists, and given rise to a certain change in
the names, whilst the idea of atomicity has been developed
more fully. To some of these Graham contributed his part
in his inquiries on Salts, but to the mechanics and statics
of the molecule, so to speak, he gave his special attention;
and although new names have already arisen of men who have
carried the subject in directions not followed by Graham, it
is still true that his own mode of thought is peculiar, and he
has left no one who can be called a successor.
His Elements of Chemistry form two admirable volumes,
where the kernels of thought could be obtained free from
shell, and where the student was led up to the newest
opinions. As a text-book, however, time has removed much
of its value.
It is not intended to give here any account of Graham's
life. That, if done well, cannot fail to be an interesting picture
of a mind devoted to the study of nature, and entirely free
from display. It may be interesting, however, to note down
the date of his birth and of his death, and the chief periods
PREFACE. xxi
which affected his outer life. He was born in Glasgow
on December 21st, 1805—studied Chemistry with Dr. Hope
in Edinburgh—was made Lecturer in the Andersonian Institu-
tion in Glasgow in 1830—was made Professor of Chemistry
at the London University (now University College) in 1837
—and succeeded Sir John Herschel as Master of the Mint
in 1855. He died in London on the 16th September 1869.
R. ANGUS SMITH,
Ph.D. : F.R.S.
MANCHESTER, November 1875.
THIS collection of Memoirs is presented to the friends of Professor
Graham and to chemists in various parts of the world. The works are
exactly of that class which are most liable to be forgotten by the general
public, and to become difficult of access to men of science.
It is hoped that the Analysis of the Contents may save some of the
reader's time.
Eloquent and careful accounts of Graham's life and works have appeared;
one by Professor Hofmann, read to the Chemical Society of Berlin; another
by Professor Odling, being a lecture delivered at the Royal Institution.
Shorter notices have been published by Professor Williamson and others;
one of these was written for the Royal Society by the writer of this preface,
but there is room for something fuller.
GRAHAM’S
CHEMICAL AND PHYSICAL RESEARCHES.
C O N T E N T S.
PREFACE,
CONTENTS,
CONTENTS ANALYTICALLY,
GASES.
\ 1. ON THE ABSORPTION OF GASES BY LIQUIDS, .
2. ON THE FINITE EXTENT OF THE ATMOSPHERE,
3. AN ACCOUNT OF LONGCHAMP’S THEORY OF NITRIFICATION,
WITH AN EXTENSION OF IT,
4. EXPERIMENTS ON THE ABSORPTION OF WAPOURS BY
LIQUIDS,
5. ON THE INFLUENCE OF AIR IN DETERMINING THE
CRYSTALLIZATION OF LIQUIDS,
6. A SHORT ACCOUNT OF EXPERIMENTAL RESEARCHES ON
THE DIFFUSION OF GASES THROUGH EACH OTHER, AND
THEIR SEPARATION BY MECHANICAL MEANS,
7. OBSERVATIONS ON THE OXIDATION OF PHOSPHORUS, .
8. NOTICE OF THE SINGULAR INFLATION OF A BLADDER,
9. CHEMICAL OBSERVATIONS ON THE APPLICATION OF SPONGY
PLATINUM TO EUDIOMETRY,
\ 10. ON THE LAW OF THE DIFFUSION OF GASES,
PAGE
xxiii
xxvii
17
24
28
36
40
41
44
xxiv. CONTENTS.
ll.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
2
4.
5.
ON PHOSPHURETTED HYDROGEN,
ON A NEW PROPERTY OF GASES,
ON THE COMPOSITION OF THE FIRE-DAMP OF THE NEW-
CASTLE MINES, .
ON THE MOTION OF GASES. PART I., .
ON THE MOTION OF GASES. PART II.,
ON THE MOLECULAR MOBILITY OF GASES,
ON THE ABSORPTION AND DIALYTIC SEPARATION OF
GASES BY COLLOID SEPTA,
ON THE OCCLUSION OF HYDROGEN GAS BY METEORIC
IRON, . .
ON THE OCCLUSION OF HYDROGEN GAS BY METALS,
ON THE RELATION OF HYDROGEN TO PALLADIUM, AND OF
HYDROGENIUM,
SPECULATIVE II) EAS CONCERNING THE CONSTITUTION OF
MATTER,
SALTS AND SOLUTIONS.
. ON EXCEPTIONS TO THE LAW THAT SALTS ARE MORE
SOLUBLE IN HOT THAN IN COLD WATER, WITH A NEW
INSTANCE, &
. AN ACCOUNT OF THE FORMATION OF ALCOATES, DEFINITE
COMPOUNDS OF SAILTS AND ALCOHOL ANALOGOUS TO
THE HYDRATES,
. RESEARCHES ON THE ARSENIATES, PHOSPHATES, AND
MODIFICATIONS OF PHOSPHORIC ACID,
ON HYDRATED SALTS AND METALLIC PEROXIDES; WITH
~ OBSERVATIONS ON THE DOCTRINE OF ISOMERISM,
ON WATER AS A CONSTITUENT OF SALTS,
PAGE
71
84
85
88
l62
210
281
283
290
299
302
309
CONTENTS.
XXV
10.
ll.
- 12.
13.
14.
15.
16.
17.
. ON THE WATER OF CRYSTALLIZATION OF SODA-ALUM,
. INQUIRIES CONCERNING THE CONSTITUTION OF SALTS OF
OXALATES, NITRATES, PHOSPHATES, SULPHATES, AND
CHLORIDES,
. ON THE THEORY OF THE VOLTAIC CIRCLE,
. ON THE CONSTITUTION OF THE SULPHATES AS ILLUSTRATED
DY LATE THERMOMETRICAL RESEARCHES,
EXPERIMENTS ON THE HEAT DISENGAGED IN COMBINA-
TIONS. PART I.,
EXPERIMENTS ON TEIE HEAT DISENGAGED IN COMBINA-
TIONS. PART II.,
ON THE DIFFUSION OF LIQUIDS, .
SUPPLEMENTARY OBSERVATIONS ON THE DIFFUSION OF
LIQUIDS, .
ADDITIONAL OBSERVATIONS ON THE DIFFUSION OF LIQUIDS,
ON THE APPLICATION OF LIQUID DIFFUSION TO PRODUCE
DECOMPOSITIONS, .
ON THE CONCENTRATION OF ALCOHOL IN SöMMERING'S
EXPERIMENTS,
LIQUID DIFFUSION APPLIED TO ANALYSIS,
ON CAPILLARY TRANSPIRATION OF LIQUIDS IN RELATION
To CHEMICAL COMPOSITIONS, * .
ON THE PROPERTIES OF SILICIC ACID AND OTHER ANALO-
GOUS COLLOIDAL SUBSTANCES,
UN CLASSIFIED PAPERS.
. ON THE HEAT OF FRICTION, .
ALCOHOL DERIVED FROM THE FERMENTATION OF BREAD, .
PAC, E
365
400
402
496
531
544
5
5
2
601
61S
xxvi CONTENTS.
3. EFFECTS OF ANIMAL CHARCOAL ON SOLUTIONS,
4. NOTE ON THE PREPARATION OF CHLORATE OF POTASH,
5. LETTRE DE M. GRAHAM A M. DUMAS,
6. NOTE ON THE USEFUL APPLICATIONS OF THE REFUSE-LIME
OF GAS-WORKS,
7. NOTE ON THE EXISTENCE OF PHOSPHORIC ACID IN THE DEEP-
WELL WATER OF THE LONDON BASIN, .
8. OBSERVATIONS ON ETHERIFICATION, .
INDEX,
PLATES.–
PAGE
630
634
636
643
645
646
65]
EFFUSION AND TRANSPIRATION OF GASES, . & ... at the end.
EFFUSION OF MIXED GASES,
TRANSPIRATION OF MIXED GASES,
>
~
~
GRAHAM'S
CHEMICAL AND PHYSICAL RESEARCHES. .
CONTENTS ANALYTICALLY.
GASES.
I.—ABSORPTION OF GASES BY LIQUIDS.—1826.
PAG C
Liquids miscible in all degrees, as alcohol and water, or in limited degrees,
as ether and water. Some mixtures exhibit chemical union. Water
impairs the volatility of alcohol. Gases may be considered volatilized
liquids, and such bodies may have the common properties of liquids, . 1
It is assumed then that gases liquefied by pressure or other means will mix
with liquids in some proportion. Sulphuric acid, at boiling, or 600°F.
(316°C.), will liquefy steam of the same temperature, although it would
require to pass down to boiling point to be condensed. Gases may
owe their absorbability to their capability of being liquefied, . ... 2
Gases, already liquefied by Faraday, easily absorbed, . e . 3
The sp. gr. of the liquids formed, and of their solutions, are confirmatory.
Dr. Henry's law, that absorption is directly proportional to pressure at
variance, ex. gr. in muriatic acid, but may be approximately true when
absorption is small, . & º e º º *
By diminishing temperature we diminish the absorption of a gas, not in the
same but in much greater proportion. Amount of gas absorbed by a
liquid depends on the gaseous residue or amount of gas exposed to the
liquid. This is deducible from the gases being liquefied. Analogous
instances occur with liquids, . tº º wº e ſº
Finally, absorption of gases is in the same class as miscibility of liquids, .. 6
II.-ON THE FINITE EXTENT OF THE ATMOSPHERE.—1827.
Wollaston's opinion that the limit of the atmosphere would be arrived at
on mechanical principles. Faraday's illustration. But it may be that
by being cooled down to —284°C. it becomes liquid or solid. If the air
cools 1 degree for 300 feet, it will lose its elasticity at 27.27 miles,
and temperature occasion a limit to diffusion, . e * . 6,
7
xxviii CONTENTS ANALYTICALLY.
III.—LONGCHAMP's THEORY OF NITRIFICATION, WITH AN EXTENSION
OF IT.-1827.
Reason to doubt Glauber's theory, the prevailing one, that “saltpetre is
formed by the decomposition of mineral and vegetable substances,”
The solution of lime by free carbonic acid of the air enables the oxygen and
" azote to act on each other more effectually,
IV. —EXPERIMENTS ON THE ABSORPTION OF WAPOURS BY
LIQUIDS.—1828.
Saturated solution of chloride of sodium absorbs water in a position where
water evaporates, and where the crystals do not deliquesce, at 57° F.,
14°C., º º & © º
Do., of muriate of ammonia and sulphate of magnesia, º e
Water lost 23 grains. A solution of chloride of sodium, 1 in 4 of water,
gained 39 grains. Carbonate of potash, 1 in 4 of water, gained 6-5.
Table of gain of water in 6 days and in 14 days in ten solutions of salts.
Not only deliquescent but even efflorescent salts absorb water when in
solution, Saturated solutions being used, except in the case of carbonate
of potash and chloride of calcium, & º * º e
All saline solutions just as readily inhale as exhale vapours, according to
the atmosphere. Column of boiling points. Index of the invaporating
powers of the solutions. Liquids invaporate when they take in vapour,
and evaporate when they give it out. Gain in five days with chloride of
sodium. Loss with sea-water, . º © º Q e
Examples of solutions which boil at the same point. Absorption of water
by muriatic acid, at temperature not above 55° (13°C.) giving out acid
and absorbing vapour till the strength is 1-0960,
Sulphuric acid absorbs the vapour of alcohol,
Absorption of alcohol vapour by camphor, e & & e
Absorption of carbonate of ammonia. Passage of dry subcarbonate into
water,
V.—ON THE INFLUENCE OF AIR IN DETERMINING THE CRYSTALLI-
ZATION OF SALINE SOLUTIONS.—1828.
Various opinions. Solutions of Glauber's salts might be kept in tubes in-
verted over mercury in a trough without crystallizing, if the mercury
were heated first, and the whole allowed to cool gradually, o e
Sometimes solutions did not crystallize by introducing a bubble of air, at
temperature not exceeding 150° or 170° F.; in all successful cases
crystallization commenced around the bubble of air. Effect may be by
absorbing air, the smallest increase causing a change in saturated solu-
tions. The most absorbable gases had the greatest effect,
PAGE
10
15
17
18
19
20
21
22
23
24
25
26
CONTENTS ANALYTICALLY. xxix
Ammonia and sulphurous acid act vigorously. Hydrogen less influential
than common air. Minute quantities of foreign liquids soluble in water
act well. The solution does not expand as water does in freezing.
Expansion temporary caused by rise of temperature of 20°–30° F.
(11–17° C.),
WI.—A SHORT ACCOUNT OF EXPERIMENTAL RESEARCHES ON THE
DIFFUSION OF GASES THROUGH EACH OTHER, AND THEIR SEPARA-
TION BY MECHANICAL MEANS.—1828.
Law that gases diffuse, developed by Dalton. Berthollet's results,
Diffusion of the different gases into atmospheric air, gº *
Evident that the diffusion of gases is inversely as some function of their
density—apparently the square root. Diffusion of mixed gases into atmo-
spheric air, . º © o * e tº &
Of mixed gases the more diffusive gas leaves the receiver in greater pro-
portion than in solitary diffusion, and the less diffusive in less proportion
than in its solitary diffusion, . g e * t e
By taking advantage of diffusion a light gas may be eliminated from
others by a species of rectification—so of a denser gas by a converse
PAGE
28
29
30
31
method, © tº tº 31-33
Diffusion of gases into other atmospheres than common air. Examples—
hydrogen and olefiant gas, etc., º & g g
§ 5. Concentration of alcohol by spontaneous evaporation of water. It is
conceivable that imperceptible pores, or orifices of excessive minuteness,
may be altogether impassable (by diffusion) by gases of low diffusive
power, that is, by dense gases, and passable only by gases of a certain
diffusive energy,
VII.—OBSERVATIONS ON THE OXIDATION OF PHOSPHORUS.—1829.
Some curious properties of phosphorus mentioned. The presence of a
minute quantity of certain gases and vapours entirely prevents the usual
action of phosphorus upon the oxygen of common air, . t o
1-400th of olefiant gas in common air in July and August prevented the
smallest oxidation over water. With 1-20th of olefiant gas in three
months the phosphorus never became luminous. Essential oils prevent
luminosity, so also 4 per cent. of chlorine in the surrounding medium,
also 20 of sulphuretted hydrogen. Alcohol also at about 80°. Not so
vapours from camphor, sulphur, iodine, benzoic acid, carbonate of
ammonia, iodide of carbon, at 67°. Muriatic acid increases, nitric
diminishes it. Phosphorus therefore cannot take oxygen from mixtures
of olefiant gas, & tº e ę e tº &
In 1 of air and 1 of olefiant gas luminosity begins at 200°F. ; 3 of air and
2 of ether vapour luminosity, begins at 215°; 111 of air to 1 naphtha at
170°; 166 of air and 1 of vapour of turpentine at 186°. Luminous in
34
85
XXX CONTENTS ANALYTICALLY.
air, with 50 per cent, olefiant gas under pressure of half an inch of mer-
cury. Table of luminosity at different pressures and proportions,
Potassium oxidation retarded by vapour of ether or olefiant gas. Perhaps
allied to the property olefiant gas has of preventing explosion of hydrogen
and oxygen,
VIII.-NOTICE OF THE SINGULAR INFLATION OF A BLADDER.—1829.
A bladder filled with coal gas became inflated in carbonic acid gas standing
over water, . º o © e º ſº º
The outer portion of the bladder would be moist, and absorb carbonic acid.
The water would pass the bladder, and the carbonic acid would evaporate
within it, as nothing but the presence of carbonic acid within could pre-
vent the disengagement of that gas,
IX. —ON THE APPLICATION OF SPONGY PLATINUM TO EUDIOMETRY.
—1829.
Olefiant gas, which had been found to prevent the oxidation of hydrogen
and oxygen, was found to lose this power when sedulously washed with
caustic potash. Then the ball with platinum acts in a few minutes,
and the heat is so great that some of the olefiant gas is oxidized, and
carbonic acid always appears. The same with vapours of naphtha and
essential oils. With sulphuretted hydrogen the latter gas only oxidized,
and little of the free hydrogen. Sulphurous acid also hinders the oxida-
tion of free hydrogen. The action of these gases is therefore unlike the
action of the same gases and vapours in protecting phosphorus from
oxidation. The action not influenced by diminishing barometric pres-
PAGE
38
39
40 .
41
Sure, . - • e - s - wº 41-43
X.——ON THE LAW OF THE DIFFUSION OF GASES.—1838.
The object is to establish with numerical exactness the following law of the
diffusion of gases. “The diffusion or spontaneous intermixture of two
gases in contact is effected by an interchange of position of indefinitely
minute volumes of the gases, which volumes are not necessarily of equal
magnitude, being in the case of each gas, inversely proportional to the
square root of the density of that gas,” º -> e
The volumes may be called equivalent volumes of diffusion :-air 1,
hydrogen 37947, carburetted hydrogen 13414, water-vapour 12649,
nitrogen 1-0140, oxygen 0.9487, carbonic acid 0-8091, chlorine 0.6325.
Gases being separated by a screen, with apertures of insensible magni-
tude, the interchange of “equivalent volumes of diffusion” is effected
by a force of the highest intensity; if the gases are of unequal density,
there is an accumulation on the side of the heavy gas. The process of
exchange continues till both sides are equalized. Doebereiner's explana-
44
CONTENTS ANALYTICALLY. xxxi
* PAGE
tion, viz., the capillary action of the fissure in the case of a broken jar,
is improbable; hydrogen is condensed and absorbed by porous bodies,
according to Saussure, with greatest difficulty, and we have no reason to
suppose that its particles are smaller than those of other gases. When
hydrogen escapes, air always enters, . e tº * . 45
Better than broken jars are Wedgewood stone-ware tubes, unglazed. But
these are superseded by gypsum, ſe º . 46
A diffusion-tube—a glass-tube open at one end, and with a plug of gypsum
at the other, was filled with hydrogen over mercury, when that liquid
rose 2 inches in three minutes: with water it is striking, the rise in a
tube 14 inches long is 6 to 8 inches in as many minutes, e . 47
Amount of five gases absorbed in the pores of the stucco, oxygen, hydro-
gen, nitrogen, carbonic oxide, olefiant gas, and coal gas not in sensible
proportions. Vacuities of the stucco one-third of the volume. Experi-
ments on the diffusion of hydrogen into air. Wet and parched plugs of
stucco. Some anomaly in the action of hydrogen, gº * > 48–53
The more dense and compact plugs the best. When the plug is loose, the
return air is notably diminished in the case of hydrogen. Passage of
gases into a vacuum in time through a stucco plug. Not in direct pro-
portion to pressure, . g e tº † g . 54
Tables of the times. The kind of gas in the receiver did not alter the
velocity with which hydrogen entered under a certain pressure, 55-56
Dry sound corks answer well as a substitute for stucco-plugs. This pas-
Sage of hydrogen is against Dalton's opinion that one gas is vacuum to
another. Diffusion of carbonic acid. The gas confined over a solution
of common salt, ſº & * e & * . 57
Chlorine, ſº & & tº & * º . 59
Sulphurous acid. Protoxide of nitrogen. Cyanogen, . * . 60
Muriatic acid. Ammoniacal gas. Sulphuretted hydrogen, e . 61
Oxygen, ge & © e tº ſe e 62
Nitrogen. Olefiant gas. Carbonic oxide, iº 63
Carburetted hydrogen of marshes. General table. In the volumes of
Oxygen, nitrogen, and carbonic oxide, theory and experiment agree as
closely as could be desired, . fe & * e . 64
Density of any gas diffused into air, both being in the same state as to
©
/ A \ 2
aqueous vapour, is obtained by the formula D=[. ; where G is the
volume of the gas diffused and A the returned air. It is possible to
come within 100th part of the specific gravity by operating on a cubic
inch of gas, . e © > º * ſº . 65
Nitrogen and carbonic oxide diffused without contraction on either side.
Same density. Inequality of density not essential requisite in diffusion.
Plugs not used for some days did not diffuse. Hydrogen opened a pass-
age in a few minutes, and they went on as before. Heat also restored
the action,-dust the cause of stoppage. Evaporation may be explained
on the principle of diffusion, . ga * & . 66
xxxii CONTENTS ANALYTICALLY.
Mechanism of respiration. Carbonic acid being carried out from the air-
cells, oxygen is carried in, & e te wº e
Heavy carbonic acid exchanged for a larger amount of oxygen, and may
explain inflation of the minute tubes. To insect respiration most dis-
tinctly perceived applicable. Diffusion takes place by interchange of
position of indefinitely minute volumes of the gas, not between sensible
masses. The law not provided for in the corpuscular philosophy of the
day,
SUPPLEMENTARY OBSERVATIONS ON THE LAW OF DIFFUSION OF GASES.
Some gases mix more rapidly than others, still keeping in conformity
with the law. This is connected, in the case of hydrogen, with the
apparent deviation from the law of diffusion, mentioned p. 53. It is
there shown that more hydrogen passes out than the exact quantity pro-
portioned to the return air,
XI.-ON PHOSPHURETTED HYDROGEN.—1835.
Spontaneously inflammable, prepared by heating phosphorus, lime, and
water; not spontaneously inflammable when allowed to stand over water
twenty-four hours, or when made by heating hydrated phosphorous acid.
The peculiarity attributable to something adventitious. Not free phos-
phorus presumably, because that is less accendible than the hydrogen
compound. Loss of accendibility over water caused by rise of oxygen
from air in the water. Free hydrogen unexpectedly rendered the gas
self-accendible, but not if quite pure,
Caused by nitrous acid vapour, . & * e
Spontaneity destroyed by charcoal, caustic potash, phosphorous acid,
Strong arsenic acid, essential oils, and most hydrocarburets,
Alcohol, olefiant gas slowly and potassium, ſº e tº *
Spontaneous action restored by small quantities of nitrous acid, not by a
large amount, between 1 and 10 to 10,000 of phosphuretted hydrogen, .
Nitric oxide acts only when nitrous acid is in it, . & º te
In the reaction there is a spontaneous formation of compounds of phos-
phorus and oxygen, . ſº º º ſº tº º
The gas obtained by ordinary processes probably owes its peculiarity to a
minute trace of such a compound, analogous to nitrous acid,
XII.-ON A NEW PROPERTY OF GASES.—1845.
The passage of gases into a vacuum. Speed of effusion. Proposal to find
the density by the speed of effusion. Passage of gases through porous
bodies, called transpiration. Air more rapid than oxygen. ... Carbonic
acid more rapid also, and under low pressure more rapid than air,
PAGE
67
68
69
71
74
76
77
78
80
83
83
84
CONTENTS ANALYTICALLY. xxxiii
XIII.-ON THE COMPOSITION OF THE FIRE-DAMP’OF THE NEW-
CASTLE COAL MINES.—1845.
PAG [.
Only carburetted hydrogen, nitrogen, and oxygen found. The power of
resisting oxidation remarkable in light carburetted hydrogen, cause of
its being found in coal mines. Resists the action of platinum black, but
permits other gases to be oxidated, e º e - 85, 87
XIV.-ON THE MOTION OF GASEs. PART I.— 1846.
Necessary to keep apart the phenomena of the passage of a gas through a
small aperture in a thin plate and its passage through a tube of sensible
length. Rate of discharge independent of the material of the tube, . 89
Rate of discharge of gases by tubes has no uniform relation to the density of
the gases. Passage of gas through a thin plate. Effusion tube. Tran-
spiration, e e º e º e - . 90
PART I.—EFFUSION OF GASES.–Effusion of hydrogen into a vacuum by a
glass jet, - g tº - e & . 90
Do. of oxygen and nitrogen; of carbonic oxide ; of carburetted hydrogen;
of marsh gas, . & º º - 92
Do. of carbonic acid and nitrous oxide; of olefiant gas, e . 93
Effusion into a vacuum by a perforated brass plate A, with results. Different
gases pass through minute apertures into a vacuum in times which are as
the square roots of their specific gravities, e o º 94, 95
For a proper effect the plate ought to have no sensible thickness, . . 96
Tubularity of the opening quickens the passage of carbonic acid and nitrous
oxide in reference to air, they being more transpirable and less diffusive
than air. Effusion of nitrogen and oxygen, and of mixtures of these
gases under different pressures, by a second perforated brass tube B.
Table of effusion of air, nitrogen, oxygen, and mixture, - . 97
Effusion of air, carbonic acid, oxygen, and mixture, at different pressures,
by plate B, . e º º - º º . 99
Effusion of carbonic acid, air, and of mixtures of carbonic acid and air at
different pressures, by plate B, b e º & . 100
Effusion of mixtures containing hydrogen, - e º . I 01
Effusion into a sustained vacuum by platinum plate E, . e . 102
Effusion of air of different elasticities or densities by brass plate B. The
effusion time of air of two atmospheres falls below that of air of one atmo-
sphere, . 104
Effusion of air of different temperatures, by plate F, º e . 107
Effusion time of air of different temperatures is proportional to the square
root of its density at each temperature. Moist air, great effect in opening
fissures, º º & º º & e ... 108
PART II.-TRANSPIRATION OF GASEs.—Transpiration of air of different
densities or elasticities, by a glass capillary tube E, . º . 108
C
xxxiv. CONTENTS ANALYTICALLY.
PAGE
For equal volumes of air of different densities, the times of transpiration are
inversely as the densities. Transpiration of air of different temperatures, 110
Preliminary experiments on the transpiration of different gases, by capill-
ary A, e g º © e e º . 111
Do. by capillary B, º e - e e e . 114
Do, by capillary C, 1 inch long, . - º e & . 118
Do. by capillary C, 2 inches long, º e * - . 119
Do. by capillary C, 4 inches long, * © º & . 120
Transpiration by capillary H, 22 feet long, of glass into vessels of different
sizes, . . 121
Transpiration by capillary H, with cupped ends. By cupping the end of
ingress the passage of air became slender in the proportion of 509 to
496 : cupping the egress caused no further change, pressure being be-
tween 28:5 and 23.5 inches, . º e g - . 127
Transpiration of different gases by a capillary tube of copper. Tube 11
feet 8 inches, diameter 0.0114 inch, . e º º . 129
Transpiration of different gases by a glass capillary E. This was 20 feet
long and 0-0187 in diameter, . e º e º . 135
All these tubes give the same coefficient of transpiration to each gas, . 138
A certain length of tube most favourable, e e º . 139
A certain interference supposed to depend on friction, . & . 139
Theory of transpirability, that it is a kind of elasticity depending upon the
absolute quantity of heat, latent as well as sensible, and more imme-
diately connected with specific heat than any other property of gases, . 140
Transpiration of olefiant gas, e • : º * . 140
Do. of nitrous oxide, e -> - e & º . 142
Do. of sulphuretted hydrogen, . º e º - . 143
Conclusions drawn from Tables XLII. to T.V., . & º . 145
Tables of the observed transpiration of gaseous mixtures, .. e 147-161
XV.—ON THE MOTION OF GASES. PART II.-1849.
The velocities of gases attain a particular ratio with a certain length of
tube and resistance; after attaining this the passage of gases becomes
slower, . * & e G. g s © . 162
Transpiration velocity of hydrogen double that of nitrogen. That of car-
bonic oxide and nitrogen the same. Velocity of nitrogen and oxygen
inverse to the densities, equal weights and not equal volumes being
transpired, Q - & & . 163
Points demanding attention. Capillary tubes for transpiration, . . 164
Transpiration by capillary H reduced to 237.875 inches. Transpiration of
equal volumes by capillary H of different lengths, º . 165
Transpiration of all gases does not become normal for the same length of
tube or resistance, tº º tº e º . 166
Use of a thermometer tube of fine flat bore, capillary K, 52% inches, . 166
CONTENTS ANALYTICALLY. XXXV
PAGE
K shortened to 39-375 inches, . e * gº † . 167
Do. 26.25 , sº . 168
Do. 13:125 , e e * * * . 168
Do. 875 . & * * ſº * . 169
Do. 6:4375 , * & e e g . 170
Do, 4:3125 171-173
7) te g &
Use of capillary M 524 in thermometer tube, as above, bore cylindrical.
K and M have 50 times the resistance of E and H. Capillaries of
extreme resistance recommended, º g & * . 171
Capillary P a compound one, formed of 30 capillary tubes, each 4 inches
in length, in a sheaf, 400 times the resistance of K and M. Gases com-
plessed instead of being drawn into a vacuum, . tº . 173, 174
Results obtained by this sheaf of capillaries of extreme resistance the most
uniform of all, . ſº º tº g jº . 178
In carbonic acid the carbon gives velocity to the oxygen, showing the im-
portant chemical bearing of transpirability, . & * * . 179
Transpiration of various gases and vapours:—
Protocarburetted hydrogen, . e º & tº . 179
Olefiant gas, . º sº e e * . 181
Ammonia, . * ſº * tº & º . 184
Cyanogen. Hydrocyanic acid, º * & º . 187
Hydrosulphuric acid, © tº e e * . 188
Bisulphide of Carbon. Sulphurous acid, . g ge . 190
Sulphuric acid, tº te & º g & . 191
Chlorine, . sº & & & * & . 192
Bromine. Hydrochloric acid, e * e sº . 194
Ether, Ç wº e e * e & . 195
Methylic ether, e e te gº * * 197
Chloride of methyl, . e g tº & * . 198
Water, * º gº & º & . 199
Alcohol. Naphtha and coal gas, . & ë ſº . 200
Transpiration of air of different densities or elasticities, . * , 201
Transpiration of air and other gases at different temperatures, . . 203
Do. of equal volumes at different temperatures, . te e . 204
Do. of air under pressure (into air) at different temperatures, we . 207
General results of the inquiry, . g e © º . 208
XVI.—ON THE MOLECULAR MOBILITY OF GASES.—1863.
The passage of gases under pressure through a thin porous plate or septum, 210
Description of the graphite diffusiometer. Pores so small that molecules
only can pass, not gases in mass. Sole motive agency the intestine
movement of molecules. The hypothesis of the movement of gaseous
particles, by Bernoulli, revived in recent times by J. Herapath, . 211
The passage of gas through a graphite plate agrees with the times of diffu-
sion, not of transpiration, te * § * $ . 214
xxxvi CONTENTS ANALYTICALLY.
PAGF.
Diffusion tube with pressure of 100 mms, of mercury, - º . 215
Diffusion tube described to obtain a Torricellian vacuum, - . 216
Movement through graphite and stucco plates, . ſº © . 219
Stucco under pressure gives mixed diffusion and capillary transpiration.
Movement through biscuit ware, º . 220
Passage through graphite closely proportional to pressure. Passage of a
mixture of air and hydrogen, . º e * º . 221
Time neither diffusion nor transpiration. Gas altered in composition.
Each gas impelled by its own molecular force. Separation is a conse-
quence of the movement being molecular, . 222
Permeation through the graphite plate into a vacuum, and the diffusion into
a gaseous atmosphere due to the same inherent mobility of the gaseous
molecule. The diffusive mobility is a property of matter fundamental
in its nature, . o w & e º & . 223
The physical basis is the molecular mobility, g e º . 224
Diffusion of mixed gases into a vacuum, with partial separation.—Atmolysis, 224
Oxygen and hydrogen, amount of separation in proportion to the pressure, 224
Oxygen and nitrogen, separation of, *G. e e & . 225
All porous masses will have some effect in separating mixed gases. The
tube atmolyser—a clay tube within a glass or metal one, to increase
rapidity, º o e * * - º . 228
Separation of oxygen from hydrogen and nitrogen, º - 229-232
Interdiffusion of gases—double diffusion. Remarks on Bunsen's results, 232
Interdiffusion without an intervening septum, º o º . 233
A portion of carbonic acid travelled at an average rate of 73 millimetres
per minute, of hydrogen a third of a metre in one minute, * . 234
. XVII.-ON THE ABSORPTION AND DIALYTIC SEPARATION OF
GASES BY COLLOID SEPTA.—1866.
PART I.—ACTION OF A SEPTUM of CAouTchouc.—Dr. Mitchell's experi-
ments, ſº e * g º º e . 235
Important to remember the complete suspension of the gaseous function
during the transit through colloid membrane, . • º . 236
Passage of gases through caoutchouc, e © . 237
The relation not that of diffusion. The first absorption of the gas by the
rubber must depend on a kind of chemical affinity, e º . 239
A film of caoutchouc has no porosity, and resembles a film of liquid in its
relation to gases, . tº e ** º • º . 240
Liquids and colloids have an unbroken texture, and afford no opportunity
for gaseous diffusion. Penetration of varnished silk, . º . 241
Absorption of gases by a block of caoutchouc. Dialytic separation of
oxygen from atmospheric air (1.) by means of other gases; (2) by
means of a vacuum, 6 tº & . 242
Dialytic action of caoutchouc in various forms, . º • , 246
CONTENTS ANALYTICALLY. xxxvii
l
PAGE
Dialytic action of silk cloth, varnished with caoutchouc on one side, slightly
Vulcanized, . gº º tº * & {º} . 250
Percolation of air through gutta percha and other septa, . & . 253
PART II—ACTION of METALLIC SEPTA At A RED HEAT-Platinum.
Porosity when heated. Deville, * & * g . 253
Platinum tube 1:1 millim. in thickness. Not permeable to hydrogen till of
a red heat, and then more permeable than caoutchouc. Is the difference
of temperatures the cause ? . ge te tº * tº
Heated platinum, with oxygen and nitrogen, not sensibly permeable. Car-
bonic acid, penetration incalculably small, de * iº . 256
Heated platinum, with chlorine not sensibly penetrating. Hydrochloric
acid, do. Vapour of water, do. Ammonia, do. Carbonic oxide, marsh
255
gas, and olefiant gas not penetrating, e º e . 257
Hydrosulphuric acid, not penetrating. Table of above results, . . 258
Absorption and detention of hydrogen by platinum, g e . 260
A new property in platinum to absorb and retain hydrogen at a red heat.
Occlusion of hydrogen, G tº e & * . 263
379 vols. for wrought platinum, . s tº * . 264, 265
Palladium, ſº 266
Occlusion of hydrogen 643.3 vols. Hydrogen absorbed at natural tem-
perature in vacuo, e g * wº * * . 267
Action of the occluded hydrogen on salts, ſº & is . 268
Palladium, its absorptive power for liquids. Alloy of silver and palladium, 269
Conclusions regarding the absorption by palladium. Hydrogen taken up
as a highly volatile liquid, g tº * * wº . 270
Separation of pure hydrogen from a gaseous mixture. Passage of ether
through palladium, . e & º & ſe . 271
Speculations on the pores of metals, and the excess obtained in the diffusive
coefficient of hydrogen, caused by a small amount of liquefaction.
Osmium-iridium. No absorbent power. This is consistent with its
crystalline character, . * tº e & & . 272
Copper—occludes 0.306 vol. hydrogen. Gold. Occlusion of nitrogen,
oxygen, carbonic acid and oxide, hydrogen, . e e . 273
Silver. Occlusion of above gases, * * e te . 275
Iron. Penetration by hydrogen, e * & º . 278
By carbonic oxide, 4:15 vols. Acieration and carbonic oxide, . . 280
XVIII.—ON THE OCCLUSION OF HYDROGEN GAS BY METEORIC
IRON.—1867.
That of Lenarto yielded 2.85 vols. of gas, with 86 per cent. of hydrogen, 282
XIX.—ON THE OCCLUSION OF HYDROGEN GAS BY METALS.—1868.
A thin plate of palladium in contact with zinc, which is giving off hydrogen
in sulphuric acid, occludes that gas. Still more, when the plate is
xxxviii CONTENTS ANALYTICALLY.
PAGE
the negative electrode to a Bunsen battery of six cells. This gas is not
given out in a vacuum; it is taken out by heat, or by reversing the posi-
tion of the palladium in the cell, and evolving oxygen on the surface.
Palladium charged with hydrogen apt to heat spontaneously in air, . 284
Platinum charged with hydrogen by voltaic action. Soft iron occluded
0.57 vols. hydrogen, . § º & º & . 285
Explanation by the electro-chemical theory, v s & * . 286
Precipitated palladium occluding 982:14 vols, of hydrogen, ge . 287
Penetration by hydrogen and carbonic acid. Liquid diffusion explains
the passage of hydrogen through a soft colloid metal, . e . .289
“Solution affinity” of metals confined to hydrogen and carbonic oxide, . 290
XX.—ON THE RELATION OF HYDROGEN TO PALLADIUM, AND ON
HYDROGENIUM.–1869.
Properties of occluded hydrogen, which, if metallic, would have to be called
hydrogenium. Palladium charged with hydrogen is lowered in density.
Emits bubbles when in water, so that the density is obtained best by
measurement and calculation, g * ge & . 290
A piece of palladium wire 609-144 millims, long, charged with 936 vols.
of hydrogen, was increased to 618-923 millims., showing increase of
9-779 millims. (or 23982 inches gained 0-385 inch); increase in length
100 to 101-605, and in cubic capacity from 100 to 104-908, . , 291
Alloy —Palladium, 95.32
Hydrogenium, 4-68
100 giving density of hydrogenium, 1708, . 292
The palladium wire lost when heated 9.7 millims, below original length :
gravity less: length only was contracted. Mobility of metallic particles.
Combustion of the wire. Another experiment, hydrogenium 1898 specific
gravity, and a third 1977, . § e ſe tº . 294
Further trials, highest number 2:055, retraction of the wire continues in
four experiments, º & & * tº . 294
Loses its power to occlude hydrogen, and after six times occluded only 320
and 330-5 volumes. Power restored partly by heat and wholly by
extracting the hydrogen by electrolysis in an acid fluid, e . 295
Tenacity of palladium being 100, that of palladium and hydrogen was 81.29.
Electrical conductivity, copper 100, palladium 8:10, palladium and hydro-
gen 5.99, & * * & º wº . 296
Hydrogenium a magnetic metal. Slight absorption of hydrogen at a high
temperature. Speed of movement through palladium 1 millim. in thick-
ness is 4 millims. per minute, . & & $ { } , 298
Alloy contains about 20 volumes of palladium and 1 of hydrogenium. An
approach to equivalents. Summary, . tº tº * . 299
CONTENTS ANALYTICALLY. xxxix
XXI.—SPECULATIVE IDEAS CONCERNING THE CONSTITUTION OF
MATTER.—1864.
It is conceivable that the various kinds of matter may possess one and the
same ultimate or atomic molecule in different conditions of movement.
One substance, © tº e o e º
Ponderable matter and a common atom. The atom is not at rest. Mo-
tion due to primordial impulse. This gives rise to volume. The more
rapid the movement the greater the space occupied by atoms. Matter
of different density forms different substances. This not applied to
known gases, which are composed of molecules or groups of atoms.
There may be infinite repetitions of such steps. Molecular volumes of
different elementary substances have the same relation to each other as
the subordinate atomic volumes of the same substances, º
Volumes uniting retain a portion of the original movement and volume.
This is chemical combination. The same result attained by hypothesis
of a fluid medium caused to undulate. A special rate of vibration or
pulsation imparted to a portion of the fluid medium. No incompati-
bility between the liquid, solid, and gaseous states. Possibility of
something like an undeveloped condition of matter connecting two
states, . e o e º º º 4.
Molecular mobility has an obvious bearing on the communication of heat to
gases. The impact of the gaseous molecule, when more rapid, produces
more frequent contact. A hot object in hydrogen is touched 3-8 times
more frequently than in air. Dalton ascribes this to mobility. Hydro-
gen in an air-engine favours the alternate heating and cooling of a confined
volume of gas, .
SALTS AND SOLUTIONS.
I.—ON EXCEPTIONS TO THE LAW THAT SALTs ARE MORE SOLUBLE IN
HOT THAN IN COLD WATER, WITH A NEW INSTANCE-1827.
Phosphate of magnesia prepared by precipitation. Efflorescent. Solution
cloudy at (120° F.) about 50° C. Precipitate like anhydrous phosphate.
774 parts water dissolve 1 at 7°2, and
1151 ?? 1 at 100°, .
Time required to dissolve, e cº & º e
Mere continuance of heat did not increase the precipitate. A solution
once precipitated by heat did not precipitate more except by greater heat.
Efflorescence in hydrates shows a weak affinity for water,
PAGE
. 299
. 301
. 302
Xl CONTENTS ANALYTICALLY.
PAGE
As all the hydrates of salts lose water by heat there is a point at which
every salt diminishes in solubility, º & ū . 307
Some substances insoluble in water whilst the hydrates are soluble, such as
silica, . * & gº p e g & . 308
II.—AN ACCOUNT OF THE FORMATIQN OF ALCOATES, DEFINITE COM-
POUNDS OF SALT AND ALCOHOL ANALOGOUS TO THE HYDRATES.
—1831.
Mode of concentrating alcohol by quicklime. Quicklime absorbs a small
quantity of alcohol vapour, & º & & e . 311
Sulphuric acid absorbs the vapour of absolute alcohol, as of water, . 312
Chloride of calcium absorbs it. Compound described, . º . 314
Alcoate of nitrate of magnesia, . * e e ge . 316
Do. of lime, * & gº º * º g . 317
Do. of protochloride of manganese, tº te iº & . 318
Do. of chloride of zinc : chlorides of magnesium and iron, º , 319
Absorption of deut-oxide of azote by protochloride of iron and alcohol,
more than by the salt alone, . wº . 320
Absorption by the iron salt may show a tendency to deliquesce in an atmo-
sphere of that gas, the retaining power being equal to the absorbing
power, . ſº * > e e g tº ſº . 321
III.-RESEARCHES ON ARSENIATES, PHOSPHATES, AND MODIFICATIONS
OF PHOSPHORIC ACID.
I.—SUBSALTs, . * g ſº g * * . 321
Description of subarseniate and subphosphate of soda, . * . 322
Explanatory hypothesis that phosphoric acid is disposed to unite with three
atoms of base, common phosphate of soda being phosphate of soda and
water. For the water another base may be substituted, as an atom of
soda in the subphosphate, or an atom of silver in the corresponding
salt. Pyrophosphate produced by heating phosphate, not by subphos-
phate, as it leaves an excess of base. Phosphoric acid by burning
phosphorus, . G º
e g º * * 323
Water in the crystals of Subarseniate of soda, probably 24 atoms, differing
from the neutral arseniate by an atom of soda substituted for water, .. 324
Subphosphate dried, heated, fused with protoxide of lead. Calcined with
exposure to carbonic acid, º tº tº º g . 328
Subsesquiphosphate formed, * g tº © tº . 329
Subphosphates and subarseniate of potash, e tº * . 330
Barytes, lime, and lead salts, º ſº ſº º * 331-33
II, NEUTRAL PHOSPHATES AND PYROPHOSPHATES.—Clark on the action of
heat on the phosphate of soda, and removal of the last atom of water, . 334
CONTENTS ANALYTICALLY. xli
PAGE
Phosphate of soda has three atoms base—two soda, one water; added to
earthy and metallic salts, gives precipitates, with three atoms base : one
may be water, the basic function of which is essential to the phosphate
of soda. The pyrophosphate has two atoms base, and gives accord-
ingly bibasic precipitates. Unusual appearance of the crystals after
long boiling of the solution, . º gº º * . 335
III.-OF THE SUPERPIIoSPHATEs.-1st, Of the biphosphate. Remarkable
body. Its dimorphism. Crystals contain four atoms of water, and lose
two at 212°F. (100° C.), and no more till 375° F. (191° C.), . . 336
Two atoms essential to the salt—one atom soda, two water, and a double
atom of phosphoric acid, these three atoms replaceable by three of oxide
of silver. Second variety of bipyrophosphate of soda. The biphosphate
heated to 400°F. (204°C.), rapidly semifuses, and one atom of water
comes off in ebullition, * tº # g & . 337
Salt still soluble, but altered. Precipitates silver white, and with two
atoms to a double atom of the acid, pyrophosphate of silver, . . 338
Third variety of the biphosphate of soda. The above biphosphate heated
between 400° and 470°F. (204° and 243°C.) for several days. Small
part insoluble nearly, see p. 341. Solution exactly neutral. Probable
composition, . * & º tº * $ g
Fourth or insoluble variety of biphosphate of soda. If sufficient heat-
ing were possible, water would probably be incapable of acting on it.
Reasons for this. Fifth variety of biphosphate of soda. The preceding
insoluble variety heated to low redness, iº 340–41
Description of its properties. Metaphosphate.—Not crystallized, changed.
The acid coagulates albumen. The glacial acid was supposed to be
pyrophosphoric. The hydrated salt retains one atom water heated to
400° F. (204° C.), becoming bipyrophosphate. The anhydrous fused
metaphosphate is not changed by heating for several days, change effected
by water: dried sharply, or with sufficient alkali, becomes common sub-
phosphate, g iſ ſº g g * * . 342
Metaphosphate of Barytes.—Insoluble even by washing in hot water, but on
long boiling is decomposed and dissolved, biphosphate of barytes being
in the solution, e & * º g gº . 344
Metaphosphate of Lime, . * º † & * . 345
339
IV.-ON THE MoDIFICATIONS OF PHOSPHORIC ACID.—Acid in common
phosphate of soda has three atoms of base to the double atom of acid.
Does not affect albumen. Other modifications pass into it in solution,
after some days in water or boiling, on fusion with three proportions of
fixed base. Pyrophosphoric acid of the fused phosphate forms salts
with two atoms base. Does not disturb albumen, or make a precipitate
in muriate of barytes, . tº tº t te te . 345
The metaphosphoric acid disposed to form salts, with one atom of base to
the double atom of acid. Made by heating the other modifications
per se, or with only one atom of certain fixed bases. These three acids,
xlii CONTENTS ANALYTICALLY.
even when free, have still their usual proportion of base, and that base
is water, or they are a terphosphate, a biphosphate, and a phosphate of
water, o º • e e º e
Table of oxygen in the salts. Loss of water by heating phosphoric acid.
Possible hydrates of the acid. Binarseniate of soda does not undergo
the same changes as biphosphate,
IV.-ON HYDRATED SALTS AND METALLIC OXIDES; WITH OBSERVA-
TIONS ON THE DOCTRINE OF ISOMERISM.–1834.
Certain salts mentioned, with five or seven atoms of water, retain one in
more intimate union than the others. Sulphate of zinc loses six atoms
at 65° F. (18°2 C.), and retains one up to 410°F. (210°C.). This salt
may be viewed as a sulphate of zinc and water, with six atoms of water
of crystallization. This last atom discharges a basic function, explain-
ing the disposition of the salt to form double sulphates. Sulphate of
potash may take the place of this water, and form the double sulphate of
zinc and potash. Sulphate of lime, peculiarity, º e
Protochlorides and cyanides. Tin. Two oxides. Different hydrates.
Various peroxides and some salts obtained as débris of hydrates by
heating. Incandescent on heating to redness. Isomerism, which has
been proposed to explain the change of character in bodies of the same
apparent composition, may often be explained by certain differences in
composition, when carefully examined ; eac. gr., 1. The water of the
phosphoric acids. 2. Some bodies are mere débris of chemical com-
pounds. 3. The proximate constitution may be very different when
the ultimate is the same. No evidence of cyanogen in fulminic acid.
Tartaric acid and racemic probably have as little relation to each other
as any two vegetable acids which could be named; certainly contain
different radicles. 4. A minute trace of adventitious matter may affect
PAGE
, 346
, 347
. 349
a body. See Phosphuretted Hydrogen, s º . 350, 351
W.—ON WATER AS A CONSTITUENT OF SALTS.—1836.
Water in salts of ammonia. Water of crystallization, feeble affinity.
Water in the caustic alkalies has the function of an acid, e
The inseparable water of acids, as of sulphuric acid, has been held to be
basic, and that acid to be a sulphate of water and bisulphate or bitar-
trate of potash, a double salt. Development of this view in the Memoir
on the Phosphates. Now finds water to exist in a different state, replace-
able by Salt. The tendency of phosphate of soda to unite with more
soda was traced to the existence of basic water in the former. The
question arose,_1)0es an analogous provision exist in such salts as form
double salts 7
. 352
. 353
CONTENTS ANALYTICALLY.
xliii
In the sulphates of magnesia, zinc, iron, manganese, copper, nickel, and
cobalt, an atom of water seems essential. In sulphate of zinc and potash,
one of the seven atoms of water in the first salt is replaced by sulphate
of potash, and the six atoms of water remain as water of crystallization,
Supersulphates, double salts.-Second atom of water in sulphuric acid re-
placed by sulphate of potash, but the first replaceable only by a true
base. The sulphuric acid hydrate, therefore, has an atom of basic and
an atom of Saline water, just as the hydrous sulphate of zinc is a sulphate
of zinc with saline water. No supersulphates of magnesia, etc., because
the sulphate of water and sulphate of magnesia, etc., are analogous in
constitution, and do not tend to combine. Sulphate of water with saline
water.—The primary sulphate. Specific gravity 1-78. The dilute acid
may be concentrated at a temperature not exceeding 380° F. (193° C.),
without loss of acid, the water reduced to two atoms. At 400° or
410°F. (204°-210°C.) this hydrate begins to be decomposed, .
Sulphate of water and sulphate of potash. Bisulphate of potash, without
Water of crystallization, º º º º e
Sulphate of potash, Sulphate of soda-Of the ten atoms of water in
crystals of sulphate of soda, none essential to its constitution, crystallizes
anhydrous from a hot solution, º º & -
Sulphate of zinc with saline water. Heated above 410° F (210°C.), loses
the last atom of water, but regains it with evolution of heat when mois-
tened. Sulphate of zinc and potash. Retains the six atoms with more
force than the sulphate of zinc alone. The sulphate of potash does not
neutralize the acidity, e º - º &
Sulphate of zinc and soda.-Not obtained merely by crystallizing together
the mixed salts, but from a solution of bisulphate of soda and sulphate
of zinc in a day or two, & & & e
Sulphate of copper and saline water.—Loses its fifth or saline atom above
430° F (221°C.) Takes it up with evolution of heat. Sulphate of
copper and potash. Table of water at different temperatures,
Sulphate of copper and soda, e & º o e
Sulphate of manganese, with saline water, five atoms of water reduced to
one, at 410° F (210°C.) Table of water at different temperatures.
Sulphate of iron with saline water.—The saline atom of water retained to
the temperature of 535° F (27.9°C.), e º •
Sulphate of iron and potash.-Sulphates of nickel, as well as sulphate of
iron, when combined with sulphate of potash, retain water at a higher
temperature than the corresponding double salt of zinc. Sulphate of
magnesia. One atom of water retained up to 460°F. (238°C.) It has a
disposition like the lime sulphate to retain two atoms. Table of water
at several temperatures. Sulphate of magnesia and ammonia lost six
atoms of water at 270°F. (132°C.), . e tº º e
Hydrated sulphate of lime.—A sulphate with one atom of water obtained
by heating the hydrate over sulphuric acid in vacuo at 212°F. (100°C.)
The salt can be made anhydrous at 300°F. (149°C.) Table of water
PAGE
354
. 355
356
. 357
. 359
. 360
. 361
. 362
363
xliv CONTENTS ANALYTICALLY.
PAGE
at different temperatures. Monohydrate does not adhere like stucco.
This power retained to 270° F (132°C.) The heated sulphate—the
débris of the hydrate, not to be confounded with anhydrate, . , 364
Anhydrous gypsum may be written with a — or minus after it, to show
that something is wanting. Anhydrate requires no –, as it takes up no
water. Sulphuric acid and other salts may be equally represented. This
view of the constitution of sulphates must not be hastily applied to other
classes of salts, as each has its own peculiarities to be studied, s . 365
VI. —ON THE WATER OF CRYSTALLIZATION OF SODA-ALUM.—1836.
Of soda-alum. This alum, like potash alum, has octohedral crystals, but is
said to contain two atoms more water than the latter. No proof of iso-
morphism of soda and potash, but rather that soda plus two atoms water
is isomorphous with potash. . e tº o º . 365
Mode of preparation. Efflorescent. Contains, like potash alum, twenty-
four atoms of water, . te * * g e . 366
VII.-INQUIRY RESPECTING THE CONSTITUTION OF SALTs, OF OXA-
LATES, NITRATES, PHOSPHATES, SULPHATES, AND CHLORIDES.—
1837.
From the paper on water in salts would be inferred an analogy between any
hydrated acid and its magnesian salt. So the oxalate and nitrate of
water resemble the oxalate and nitrate of magnesia. In certain subsalts
of the magnesian class of oxides the metallic oxide replaces the crystalli-
Zation water. As in the case of sulphates, an atom of water seems to be
replaced in the oxalates, so as to form double oxalates, . g . 367
I.—OF THE OxALATES.—Oxalate of water, or hydrated oxalic acid. Three
atoms of water one basic. The two others may be termed constitutional,
and are found in the magnesian oxalates. By drying two atoms are lost,
or none, * tº º tº º e . 368
Oaxalate of zinc.—Retains its two atoms water strongly. Ovalate of mag-
nesia.-Retains these two atoms still more strongly. Oxalates of iron,
nickel, and cobalt, not obtained pure, as they appear to carry down part
of the precipitant. No binoxalate of magnesia, e & . 369
Ocalate of lime.—Contains two atoms of water, lost readily. Ocalate of
barytes.—One atom of water, and thus differs from preceding, . . 370
Owalate of potash.--Crystallizes with one atom water. Binoacalate of potash.
—Contains three atoms. The constitutional water of the neutral oxalate
displaced by oxalate of water, which has two atoms, . & . 371
Quadrocalate of potash.-The two atoms of the preceding salt replaced by
two of hydrated oxalic acid. Has seven atoms of water, four of which it
loses at 240°F. (116°C.), being the two atoms of water of the two atoms
oxalic acid, {} tº * * º & tº , 372
CONTENTS ANALYTICALLY.
xlv.
Owalates of ammonia.-Agree with those of potash. There is also a
quadroxalate as well as binoxalate, º º º e
Owalate of soda.—Least soluble of soda salts. Anhydrous. With oxalic
acid forms a binoxalate. No quadroxalate. Absence of water probably
shows an indifference for further combination, . º º
Bönow.alate of soda.-Three atoms of water. Like the potash salt, loses only
two at 300°F (147°C.), º -> e © º
Double oxalates.—One member of the magnesian class of oxides, namely
copper, forms binoxalates with an alkaline salt, . ©
Owalate of copper and potash.-One form of crystal has two, the other four
atoms of water. The second loses two by efflorescence. The oxide of
copper is substituted for the basic water of the binoxalate,
Owalate of chromium and potash.—With six atoms water,
Ocalate of peroxide of iron and potash,
Do. do. soda, º e º º -
These three salts occupy the same important position among the oxalates
as the alums among the sulphates.
II.-OF NITRATES.–1. Hydrated nitric acid, the nitrate of water.—This has
one atom of water as base and three held less powerfully. 2. Nitrate of
copper.—Two crystals. The prisms contain three, the rhomboids six
atoms of water and lose three readily; the other three cannot be expelled
without loss of acid, . o
3. Submitrate of copper, . © º º e e º
Thinks the single atom of water to be the base, and the three atoms of
oxide of copper in place of the constitutional water of the nitrate
of water, e & e º e &
4. Nitrate and submitrate of bismuth.-The neutral nitrate contains three
atoms of water like the nitrate of copper, * º ©
5. Nitrate of zinc.—Contains six atoms of water, which cannot be reduced
below three without loss of acid. 6. Nitrate of magnesia.-Contains six
atoms of water. At heat of melting lead reduced to one atom. This
intimate combination of one atom does not indicate a disposition to form
a double salt, and is probably the result of a new arrangement of the
constituents at a high temperature. No proof of the existence of super-
nitrates,
III.-OF PHosphaTEs, . & © e º º ©
Table of Phosphoric acid and salts. Nomenclature—monobasic, bibasic,
and tribasic, . º tº * & e º tº
1. Tribasic phosphate of soda, ammonia, and water.—The name expresses
the view of the constitution of the salt, . t º -
2. Tribasic phosphates containing oxides of the magnesian class.-Tribasic
phosphate of zinc and water.—Has two atoms of water difficult to dispel,
besides one basic. Tribasic arseniate of magnesia and water has fifteen
atoms of water, of which three—one being basic—are retained at
212° F (100° C.),
PAGE
. 373
. 373
. 373
. 373
. 382
. 387
xlvi CONTENTS ANALYTICALLY.
3. Tribasic phosphate of magnesia and water.—Has fifteen atoms of water,
reduced at 212° F (100° C.) to seven atoms, one of which is basic, . 889
4. Tribasic phosphate of magnesia and ammonia.-This not a double phos-
phate, but formed from the tribasic phosphate of magnesia and water by
the substitution of oxide of ammonium for the basic water of that salt, 390
IV.—SULPHATES.—(CHROMATES.) See former paper, . g , 392
As to the suggestion that bisulphate of potash is a double sulphate of water
and potash, and therefore really neutral in composition ; if all bisalts are
neutral in composition, what explains the condition of the bichromate 2
The vapour of anhydrous sulphuric acid is absorbed by sulphate of
potash and chloride of potassium, without decomposition. Chromic
acid forms analogous compounds; with neutral chromate, it forms the
red chromate, and with chloride of potassium Peligot's salts analogous to
but more permanent than Rose's sulphates. The red chromate may then
belong to a new order of combination, te º e , 393
Subsulphates hold water with remarkable force. That of copper retains
its four atoms at 212°F. Alum an alkaline sulphate with sulphate of
alumina attached, - e º e . . ſº . 451
W.—CIILORIDES.—Hydracids have weak affinity for water, . e 394
The law seems to be that the chlorides of the magnesian class have two
atoms of water pretty strongly attached. Some have two or four more,
advancing by twos, . & * te º & . 395
1. Chloride of copper, two atoms water, sº - e . 395
2. Chloride of manganese, four atoms water, . - & , 395
3. Protochloride of iron, four atoms water, . - º , 396
4. Chloride of magnesium, six atoms water, . e & . 396
5. Chloride of calcium, six atoms water, reduced in vacuo over sul-
phuric acid to two, tº º º e º . 396
6. Double chloride of copper and ammonium, with two atoms water, . 396
The disposition of the protocyanide of iron and of the cyanide of copper to
combine with two atoms of cyanide of potassium may depend upon the
cyanides of iron and copper possessing two atoms of constitutional water, 397
VIII.—ON THE THEORY OF THE VOLTAIC CIRCLE.—1839.
The polar molecules of a salt contain negative and positive, or rather
chlorous and zincous affinities, called also halogenous and basylous.
(Graham's Elements of Chemistry, 1850, p. 239, etc.) Explanation of
the apparent travelling of hydrogen to the copper plate, by a series of
transferences, beginning with the first partially freed atom of hydrogen
(in the case of hydrochloric acid), i.e. by a propagation of a decom-
position through a chain of particles of the acid. (See also Elements of
Chemistry, p. 272, etc.), * -> e º s . 398
CONTENTS ANALYTICALLY. xlvii
*
IX. —ON THE CONSTITUTION OF THE SULPHATES As ILLUSTRATED BY
LATE THERMOMETRICAL RESEARCHES.—1842.
fº PAGE
No heat evolved in uniting sulphate of magnesia with sulphate of potash,
some with sulphate of ammonia, but on stirring the latter when the
double salt fell the temperature rose 5°40 F. (3°C.), and fell on reso-
lution. No heat of combination, because sulphate of potash and water
are equicalorous in the constitution of such salts (see also p. 422), . 400
X.—EXPERIMENTS ON THE HEAT DISENGAGED IN COMBINATIONS.
PART I.-1842.
Sulphuric acid, . e - º - e -> . 404
Hydration of magnesian sulphates, . - e - . 407
Sulphates and chromates of the potash family, . & - . 412
Double sulphates, º º & g e . 417
Table of heat absorbed by equivalent quantities of crystallized salts on dis-
solving in water, ſº º & º e e . 422
Simple relations observed between the heat disengaged by the sulphates of
magnesia and zinc, which appear to belong to one class, whilst the sul-
phates of water, copper, and manganese belong to another, * . 423
XI.-EXPERIMENTS ON THE HEAT DISENGAGED IN COMBINATIONS.
PART II.-1843.
Neutralization of various acids by hydrate of potash, tº e . 424
1. Neutralization of potash by nitric and hydrochloric acids, . . 424
2. Neutralization of potash by sulphuric acid, * e . 431
3. Do. of bichromate of potash by hydrate of potash, . - . 437
4. Do. of acetic acid by do., * * e ſº . 437
5. Do. of oxalic acid by do., e - * e . 438
6. Do. of bicarbonate of potash by do., - e º . 441
7. Do. of arsenic and phosphoric acids by do., * º . 441
XII.—ON THE DIFFUSION OF LIQUIDS.—1849.
Any substance in solution is diffused uniformly through the mass of the
solvent by a spontaneous process, . 444
The subject has been obscured by the experiments being made with a mem-
brane which imbibes the substance and produces endosmose, not connected
with diffusibility. A diffusibility like that of gases would afford means
of separating bodies, and present a scale of densities for substances in
solution analogous to vapour densities. Gay-Lussac's theory. Chemical
xlviii CONTENTS ANALYTICALLY.
PAGE
combination attended with heat, solution with cold, dissimilar bodies
combine, whilst soluble substances and their solvents are like, or analo-
gous. Solubility is not the same as the intensity of the solvent force, the
gradations of which may depend on unequal diffusibility, º 444-5
Diffusion of liquid or dissolved carbonic acid slow compared with gaseous, 446
Mode of experimenting without a diaphragm, g e º . 448
Solutions of salts of the same density diffuse unequally, . g . 449
1. Characters of liquid diffusion. Diffusion of chloride of sodium. Quan-
tity diffused closely proportioned to the quantity of salt, e . 450
Diffusion increases with the temperature. Nearly the same for eight
days, but diminishing, te e º 3 e e . 451
2. Diffusion of various salts and other substances. 20 salt to 100 water, at
60°-5 (15.8° C.), for eight days. Salts, sugar, gum, albumen, . . 452
Sugar less than half of the diffusibility of chloride of sodium, . 453
The diffusion of albumen very much lower than of saline bodies.
Chloride of sodium appears 20 times more diffusible; actually more
so, as nearly one-half the matter diffused from the first consists of
inorganic salts. Value of this low diffusibility in retaining serous
fluids in the blood-vessels, & º º g . 453
Diffusion of solutions of 10 salt to 100 water, at 59°5 F. (15°-3 C.), . 454
Do. do. do. at 37°.5 F. (3°05 C.)
Near equality of certain isomorphous salts, - © . 455
Diffusion of acid solutions, 4 acid to 100 water, at 59°3, (15°1 C.)
Considerable latitude in the diffusibility, . • e . 456
3. Diffusion of ammoniacal salts of copper, º º e . 457
4. Diffusion of mixed salts, º • o e . 458
Inequality of diffusion is not diminished but exaggerated in mixtures.
Same observed of mixed gases, . tº e e . 461
5. Separation of salts of different bases by diffusion. The potash salts more
diffusive than the soda salts. Experiments. Sea-salt. Slowness of
diffusion, e º º º e e º . 463
In the sea-salt does magnesium exist as a chloride or sulphate? Will
diffusion show this by taking out the most diffusible? Or will the
most diffusible, the chloride, form because of its opportunities to
diffuse 2 Liquid diffusion, as well as gaseous evaporation, can pro-
duce decomposition, g e e e e . 463
6. Decomposition of salts by diffusion. Bisulphate of potash. Potash alum.
Ammoniated sulphate of copper. Alkaline salts with lime, e . 464
7. Diffusion of double salts. A mixture of sulphate of magnesia and sul-
phate of potash gave in diffusion the sum of the separate diffusions. The
salts probably not combined immediately on dissolving, . * . 467
8. Diffusion of one salt into the solution of another salt, . e . 468
Chloride of sodium does not resist carbonate of soda diffusing into it. Sul-
phate of soda does. Nitrate of potash is not resisted by nitrate of
ammonia although isomorphous. They are inelastic to each other, like
two gases, e º ſº * º º e . 469
CONTENTS ANALYTICALLY. xlix
PAGE
At a certain pressure attraction impairs the elasticity of a gas, so at a
certain Saturation the salt molecules tend to crystallize. Further analogy
between liquid and gaseous diffusion, . g * g . 470
Diffusion of salts of potash and ammonia. Vials for diffusion holding 2080
grains (13474 grammes), outside vessel or water atmosphere 87.50
grains (or 571-1 grammes). Density 2, 4, 63, and 10 to 100 water by
Weight. Some at two temperatures, . g g * . 471
Diffusion of carbonate of potash, sulphate of potash, and sulphate of ammonia.
Sensibly equal except at the densest point, º & & . 472
Diffusion of chromate of potash and acetate of potash. Close correspondence,
even to the 10 per cent. solution, g & C tº . 474
Diffusion of bicarbonate of potash and bichromate of potash. Close ap-
proximation : so that equality is not confined to isomorphous salts, . 475
Diffusion of nitrate of potash and nitrate of ammonia. A slight superiority
in the latter, . º t º * § & g
Diffusion of chloride of potassium and chloride of ammonium. Agree well:
related to the preceding nitrates. Crystallizing attraction in strong solu-
tions resisting diffusion, * o g tº * . 47
Diffusion of chlorate of potash. Inferior to the nitrate. Its less solubility
may be connected with a tendency to crystallize, uniformity of diffusion
greater in weak solutions, & * e * e . 478
Diffusion of Salts of the sulphate of potash class. Diffusion of 1 per cent.
solutions. Ferrocyanide and ferricyanide of potassium, e . 479
Diffusion of salts of the nitre class, * e e e . 480
Nitrate of potash and carbonate of potash, º tº . 482
Times of equal diffusion. A 4 per cent. solution of nitrate of potash dif.
fused for 7 days, the same amount of carbonate of potash in 9.9 days, or
as 1 to 1.4142, the square root of two. Leading to the idea of solution
densities, and further analogy with gases. Further trials, g , 483
Hydrate of potash. Compared with nitrate and sulphate, e . 486
Diffusion of salts of soda, & ſº e g w , 488
Diffusion of sulphate and carbonate of soda. Nitrate of soda, . . 489
Relation of salts of potash to salts of soda. Times of equal diffusibility as
the square root of 2 to that of 3, * g tº & . 490
Diffusion of sulphate of magnesia, g * . 491
Has half the diffusibility of sulphate of potash, and one-fourth that of the
hydrate at 52°F. (122°C.) Sulphate of zinc differed from sulphate of
magnesia 4 per cent, although isomorphous, . tº t . 493
Table of solutions of 1 and 2 salt to 100 water —
Summary of results:—Diffusion a property of a fundamental character.
Supplies the densities of a new kind of molecules. Relations in diffusion
refer to equal weights, not to atomic weights, or to larger molecules, if not
of equal weight, of weights with a simple relation to each other. Classes
of equidiffusive substances. Division of salts of potash. Separation of
salts by diffusion. Decomposition by diffusion. Use in the study of
endosmose, . * te * tº t $ . 494
d
l CONTENTS ANALYTICALLY.
Supplementary Observations on the Diffusion of Liquids (1850),
Effect of time, * ſº & & &
Diffusion of hydriodic acid, hydrobromic acid, and bromine,
Diversity of physical properties compatible with equal diffusibility in
stances which are isomorphous,
Hydrocyanic acid. Nitric acid,
Sulphuric acid. Chromic acid,
Acetic acid. Sulphurous acid,
Ammonia,
Alcohol, .
Nitrate of baryta, ſe
Nitrate of Strontia. Nitrate of lime,
Acetate of lead. Acetate of baryta,
Chloride of barium. Chloride of strontium,
Chloride of calcium,
Chloride of manganese. Nitrate of magnesia. Nitrate of copper,
Brotochloride of iron. Sesquichloride of iron,
Sulphate of magnesia,
Sulphate of zinc,
Sulphate of alumina, e
Nitrate of silver. Nitrate of soda,
Chloride of sodium,
Chloride of potassium, . & º
Iodides and bromides of potassium and sodium,
Chloride of ammonium,
Dichloride of copper. Diffusion diminished by excess of hydrochloric acid
Same effect of acid on chloride of sodium. Effect of acids,
Bicarbonate of potash. Bicarbonate of ammonia,
Bicarbonate of soda,
Hydrochlorate of morphine,
Hydrochlorate of strychnine. Observations in this paper favour the exist-
ence of a close similarity or equality in diffusibility between certain
classes or substances. Chlorides and nitrates and their acids show this,
isomorphous salts also, .
Additional Observations on the Diffusion of Liquids (1851). In the follow-
ing the salts of potash and soda only are used, and in four different pro-
. 531
. 532
. 533
. 534
. 535
. 537
. 538
portions. Hydrate of potash, .
Hydrate of soda, e
Carbonate of potash,
Carbonate of soda, tº * e
Comparison of potash and soda. Sulphate of potash,
Sulphite of potash, tº G e ſº & te
Sulphite of soda. Hyposulphite of potash. Hyopsulphite of soda,
Sulphovinate of potash. Sulphovinate of soda. Oxalate of potash,
Sulphate and oxalate compared. Oxalate of soda,
PAGE
. 496
Diffusion of hydrochloric acid. One of the most diffusive substances.
. 497
499
. 500
. 501
. 503
, 504
. 505
. 506
. 507
, 508
. 509
. 510
. 512
. 513
. 514
. 515
. 516
. 517
. 518
. 519
. 520
. 523
524
. 525
. 527
. 528
529
530
539
. 540
CONTENTS ANALYTICALLY. li
PAGE
Acetate of potash. Sulphate and acetate compared, wº º . 541
Acetate of soda. Acetates of soda and potash compared, . º . 542
Tartrate of potash, © e ſº º . 542
Tartrate of soda. Tartrate of potash and soda compared. Double tartrate
of potash and soda decomposed by diffusion. . In nine pairs of potash and
soda salts, the potash salts uniformly exceed the soda in diffusibility, the
ratio sensibly the same ; the hydrates not included, . º . 543
XIII.—ON THE APPLICATION OF LIQUID DIFFUSION TO PRODUCE
DECOMPOSITIONS.—1849.
Observations made on the spontaneous diffusion into pure water of several
salts already dissolved in 100 times their weight of water. Apparatus as
before : the water of the water-jar is an atmosphere into which the salts
diffuse, from the solution phial within. Together they form a diffusion-
cell. Time seven days, unless stated otherwise. Temp. 50° F (10° C.), 544
Salts diffused from a 1 per cent. solution in equal times, . 545
Decomposition of sulphate of potash by lime in diffusion-cells, e . 546
Decomposition of sulphate of soda. Potash salt most decomposed, . 547
Alkaline chlorides very slightly decomposed. Decomposition of sulphates
by lime in dilute solutions, which cannot deposit sulphate of lime.
Decomposition of sulphates by carbonate of lime, o g . 548
Effect in the soil. No decomposition in saturated solutions of chlorides, .. 549
An agency in the soil by which the alkaline carbonates required by plants
may be formed from the chlorides of potassium and sodium, as well as
from the sulphates. This brought into action by top-dressing with lime, 551
XIV.-ON THE CONCENTRATION OF ALCOHOL IN SöMMERING's
EXPERIMENTS.–1854.
The alcohol was, by Sömmering, concentrated in a bladder; it was here
shown that gelatine had the same effect, e * º . 551
W.—LIQUID DIFFUSION APPLIED TO ANALYSIS.—1861.
Wolatility a means of separating bodies. Diffusion similar in character.
Hydrate, sulphate of potash, etc., “volatile ” as regards diffusion. The
fixed class are silicic acid, albumen, gums, etc.; crystalline bodies the
type of first; gelatine the type of colloids. Distinction intimate molecular.
The crystalloid state is statical, the colloid dynamical, . º . 552
Colloidal has energia. The source of force in vital phenomena, . . 554
Colloid substances assisting diffusive separations. Starch and pectin greatly
resist passage of less diffusive substances, and entirely cut off colloid sub-
stances. A mere film of jelly is enough, e § * . 554
lii CONTENTS ANALYTICALLY.
PAGl.
Instances with sized paper. Not as a filter. Only molecules permeate,
and not masses. The water of the colloid is in a state of combination,
although feeble, and cannot be used as a medium for diffusion. The
crystalloid can separate the water, molecule by molecule, and make its
way through the gelatinous septum. This action called dialysis, . 555
Vegetable parchment or parchment-paper, made by M. Gaine. Unsized
paper dipt in sulphuric acid. Dialysing vessel or saucers of paper.
Jar-diffusion explained, e e e º e . 556
Diffusion of 10 per cent. solutions of chloride of sodium, sugar, gum, and
tannin in fourteen days, at 10°C., © tº e tº . 558
Diffusion of sulphate of magnesia, albumen, and caramel for fourteen days, . 559
Diffusion of chloride of sodium in different times, tº * . 560
Diffusion of a 10 per cent. solution of cane-sugar in different times, . 561
Hydrochloric acid compared with salts, sugar, and albumen, tº . 562
Diffusion in alcohol of iodine and acetate of potash. Diffusion of alcoholic
Solution of resin, {º * * ſº . 563
Diffusion of 5 per cent. solution of chlorides of potassium and of sodium, , 565
Diffusion of 5 per cent. solution of chloride of sodium and sulphate of soda,
at 10°C., for seven days, g * º © . 566
Same for fourteen days. Can two unequally diffusive metals be separated
by varying the acid 2 . tº tº e e e . 567
Diffusion of 5:12 per cent. chloride of potassium and 4.88 of sulphate of
soda for seven days, at 14°C., e ę (* & , 568
Diffusion of 4:01 per cent, chloride of sodium and 5.99 of sulphate of potash
for seven days, at 14° C. Effect of temperature on diffusion, . . 569
Dialysis, . e . 571
Diffusion of a 10 per cent. solution of chloride of sodium in the jelly of
gelose for eight days, at 10° C. A crystalloid passes through a firm jelly
with little or no abatement of velocity, & ſº & . 572
Heat. The effect of heat increasing diffusion is diminished in dialysis.
Bell-jar. Bulb-dialyser, tº & w & . 573
Effect of volume of liquid in the dialyser. Effect of acids, & . 574
Dialysis through parchment-paper during twenty-four hours, at 10°–15° C., 575
Do. animal mucus during twenty-five hours, do.” . 576
Do. parchment-paper during twenty-four hours, at 12°, . 576
Purification of colloid substances by dialysis. Crystalloids eliminated by
diffusion. Soluble silicic acid. Hydrochloric acid and chloride of
sodium removed from it in a hoop dialyser in four days. Pure solution
of silicic acid, limpid and colourless, preserved a few days, * . 577
Coagulated by earthy or alkaline carbonates and carbonic acid, precipitated
on calcareous stone without penetrating: acid like carbonic acid : pre-
cipitated by certain other colloids. (Ordinary silicate of soda not colloidal.)
Soluble silicic acid forms a peculiar class of compounds also colloidal, . 578
Silicate of gelatine. Colli-silicates or cosilicates, & & . 579
Cosilicic acid. Albuminic acid. Soluble alumina made by placing on the
dialyser a solution of alumina in chloride of aluminium. Very unstable.
CONTENTS ANALYTICALLY. liii
PAGE
Coagulated by extremely minute amounts of salts. Colloidal alumina
has a high atomic weight, like cosilicic acid, . e s . 580
Soluble metalumina. Crum's discovery. Heating a binacetate to the
boiling point of water, and keeping it thus for several days; also by
dialysing an acetate of alumina that has been altered by heat : not a
mordant. Soluble peroxide of iron. Preparation, & * . 581
Solution of the peroxide in the chloride goes on for months. Slow action
characteristic of colloids. Very unstable solution. Separation by
diffusion, © e © º & e . 582
Soluble metaperoxide of iron. Ferrocyanide of copper, . s . 583
Neutral Prussian blue, e & e º º . 584
Ferrocyanide of iron soluble in oxalic acid and binoxalate of potash.
Sucrate of copper. Sucrate of peroxide of iron, & e . 585
Sucrate of peroxide of uranium. Sucrate of lime. Soluble chromic oxide.
Hydrated uranic oxide and glucina. It appears that the hydrated per-
oxides of the aluminous type, when free, are colloid bodies; two species
exist, of which alumina and metalumina are the types, . e . 586
The double type, in fibrin of blood, º tº º & . 587
Peroxide of tin. Metastannic acid. Titanic acid, e 587
Dialysis of organic colloid substances.—Tannin diffuses at most 200 times
less than chloride of sodium. Gum 400 times less diffusive than chloride
of sodium, e e te © e g . 588
Gummic and metagummic acids. Gummate of gelatine, tº: . 589
Dextrin, Caramel, varieties of Cane-sugar, º e t . 590
Albumen, e © e º º º e . 591
Emulsin. Coagulated albumen. Gelatinous starch. Extract of flesh.
Separation of arsenious acid from colloidal liquids, º e . 592
95 per cent. of the arsenious acid diffused out in twenty-four hours.
Amount with albumen and gum, º e º e . 593
Arsenious acid with other organic substances, 594
Colloidal condition of matter.—Colloids and crystalloids different worlds
of matter, distinct as the material of a mineral and the material of an
organized mass. Colloids may be soluble or insoluble. Easily thrown out
of solution by crystalloids. Crystalloids sapid, colloids insipid, . . 595
Tendency to change in colloids. Colloid equivalents high. Possibly a
collection of crystalloid molecules, g . 596
Gelatine an important colloidal base, * e * te . 597
Ice.—Colloid and crystalline. No abrupt transitions, . g . 598
Osmose.—Caused by hydration and dehydration of the membrane. Outer
surface being with pure water is most hydrated. With full hydration
through the membrane osmose is checked. Weak alkalis swell the
colloids and cause extreme osmotic sensibility, . º e 598-600
liv CONTENTS ANALYTICALLY.
XVI.—ON CAPILLARY TRANSPIRATION OF LIQUIDS IN RELATION TO
CHEMICAL COMPOSITION.—1861.
PAGE
Poiseuille.—Greatest retardation of alcohol is with 6 equivalents of water, . 600
Nitric acid.--Retardation greatest with three atoms water, * , 602
Sulphuric acid.—Twenty-four times slower than water. Least transpira-
bility in the crystallizable hydrate, or one atom of water added to SHO.
Transpiration-time of water 109 seconds, 6 te . 604
Acetic acid.—The hydrate C.H.0,--2HO has a transpiration-time 2-7 times
longer than water, © e * * e , 605
Butyric acid.—With 3 equivalents water greatest retardation, . . 606
Valerianic acid.—Retarded most by 2 equivalents water, . g . 607
Formic acid does not follow the same rule, tº º Q . 607
Hydrochloric acid.—Its retardation indicates a 12-hydrate. No appear-
ance of a point indicating a 16-hydrate, (e tº * . 608
Alcohol.—Poiseuille's fundamental discovery confirmed by numerous expe-
riments. Methylic alcohol, 6-hydrate of Amylic alcohol, . 609-61.1
Ethers.—Formiate, acetate, butyrate, and valerianate of ethyl, give trans-
piration-times progressively rising: this may be connected with the in-
creased weight of the molecule, © & * * . 611
Acetone.—Time greatest with 12 equivalents of water, . * . 612
Glycerine.—No point of retardation found, * gº gº . 613
Importance of observing transpiration. Retardation of hydrates may be
caused by the increased size of the molecules, but it is possible to con-
ceive a decomposition caused by the friction of passage and the propelling
power lost by conversion into heat, . " tº te e 614-5
Table of the transpiration of water at different temperatures, ū . 616
Do. of alcohol at do., g e . 617
XVII.—ON THE PROPERTIES OF SILICIC ACID AND OTHER ANALOGOUS
COLLOIDAL SUBSTANCES.—1864.
Hydrate of silicic acid soluble according to hydration. A jelly with 1 per
cent. of silicic acid gives a solution with one of that acid in 5000. Time
alone may cause coagulation, which is opposed by concentration and
warmth, e e d º g º tº . 618
Pectization by pounded graphite. No crystallization. Colloids transpire
slowly. The particles aggregate, ſº * & tº . 619
Alcohol and silicic acid, . * te wº . 620
Ether and silicic acid. Glycerine and silicic acid, o e , 621
Sulphuric acid and acetic acid, e & & . 622
Restoration of the liquid from the pectose state. Liquid stannic and meta-
stannic acids, . * & tº e . tº . 623
Liquid titanic acid, Liquid tungstic acid, * tº © . 624
Molybdic acid, . g e § e * g . 625
CONTENTS ANALYTICALLY. Iv
UNCLASSIFIED PAPERS.
I.—ON THE HEAT OF FRICTION.—1826.
PAGE
A speculation on the separate existence of heat, . º * . 626
II.-ALCOHOL DERIVED FROM THE FERMENTATION OF
BREAD.—1826.
There was found alcohol equal to 0-3 to 1 per cent of the flour employed, . 629
III.-EFFECT OF ANIMAL CHARCOAL ON SOLUTIONS.—1830.
Here it is shown by several instances, chiefly of metallic salts, that the char-
coal removes more than mere colouring matter from solution, . . 630
IV.—NOTE ON THE PREPARATION OF CHLORATE OF
POTASH.-1841.
Loss of oxygen by acting with chlorine on carbonate of potash alone. Re-
commends addition of hydrate of lime. The chlorine attacks the potash,
and the lime takes the carbonic acid at the same time: similar result of
secondary action found when sulphate of soda is added to lime, which
mixture takes up two equivalents of sulphuretted hydrogen to one of lime, 634
V.—LETTRE DE M. GRAHAM A M. DUMAS.—1842.
Some ideas arising from the law of substitution—even an isolated element
such as a metal, held to be made up of several parts. Combination the
natural state of matter. Electro-chemical theory, and mode of writing
the symbols under this theory. A view of the constitution of several
molecules of compound bodies, e * † * . 636
WI-NOTE ON THE USEFUL APPLICATIONS OF THE REFUSE LIME
OF GAS-WORKS.—1845.
By exposure to air refuse lime becomes quickly oxidized, and one-sixth of
its weight has been taken from it as crystallized hyposulphite of lime by
a single crystallization, & & & e te . 643
VII.—NOTE ON THE EXISTENCE OF PHOSPHORIC ACID IN THE DEEP
WELL WATER OF THE LONDON BASIN.—1845.
Deposits carbonate and phosphate of lime. Green confervae grow readily.
Does the value of water for irrigation depend on the phosphoric acid 2 . 645
lvi CONTENTS ANALYTICALLY.
VIII.-OBSERVATIONS ON ETHERIFICATION.—1851.
PAGE
The most direct method of preparing ether is to add 4 to 8 of alcohol to one
of strong sulphuric acid of 83 per cent, and to heat to 320°F. (160° C.)
under pressure. No distillation or sensible formation of sulphovinic
acid necessary. Action of the acid compared to that on the essential
oils. A polymerizing action, . © e & & . 646
INDEX, º e t e e t © . 651
G. A S E S.
I.
ON THE ABSORPTION OF GASES BY LIQUIDS.
From Annals of Philosophy, xii. 1826, pp. 69-74.
1. LIQUIDS are in general miscible with one another, in all propor-
tions as water and alcohol, or in a limited degree as ether and water;
ether agitated with water taking up one-tenth of its weight of that
liquid.
2. Frequently the mixing of liquids exhibits the closeness of chemical
union, among other points, in the manner in which the volatility of the
compound liquid is affected. Thus the vapour from pure alcohol at
170 Fahr. supports a column of mercury of 30 inches, but by mixing
the alcohol with a quantity of water, we impair the volatility of the
alcohol; and we may form mixtures which require a temperature of
upwards of 200° to produce vapour capable of supporting such a column.
In the same way portions of water are retained with so great force by
sulphuric acid as to require, in order to drive them off, a degree of heat
greatly higher than the boiling point of water. From these, and other
instances of this affinity, we learn that, in a mixture of a volatile and
more fixed liquid, the tendency of the more volatile ingredient to pass
into vapour may be checked in a considerable degree by its connexion
with the other liquid.
That many reputed gases, at a low temperature, or under great pres-
sure, assume the liquid form, has been demonstrated by Mr. Faraday."
The researches of that ingenious chemist on gaseous liquefaction strongly
impress the doctrine, that in the physical states of gas, liquid and solid,
there is nothing of absolute permanency, and that any body may assume
consecutively all these forms. Hence it follows that those bodies
which, at the temperature of the atmosphere, we experience to be gases,
may be considered without impropriety as volatilized liquids; and we
may predicate of such bodies the common properties of liquids. Of
* Philosophical Transactions, 1823.
2) - A
2 ON THE ABSORPTION OF GASES BY LIQUIDS.
these properties, two have been mentioned, which alone will be applied
to the elucidation of the phenomena of absorption.
It is then assumed that the gases, if liquefied (by pressure or any
other means), would in general mix in some proportion or other with
such ordinary and reputed liquids as we had it in our power to present
to them ; and that they would be retained in part by these liquids,
through the agency of the mutual attraction evinced in liquid mixture,
even although the pressure under which the union took place were con-
siderably reduced, and the temperature raised. In this way there might
result a mixture of a liquefied gas and a common liquid in reduced pro-
portions, at the ordinary atmospheric pressure and temperature.
But it is not necessary to suppose that the gaseous bodies, whose
absorption by liquids it is attempted to explain, be presented in a
liquefied state. Analogy will lead us to expect that the mere injection
into our absorbing liquids of such gases, in their elastic state, will occa-
sion their liquefaction, and consequently bring into play the affinities of
liquids, and the concomitant diminution of volatility, on which the
explanation is founded. t
Thus sulphuric acid, concentrated as much as it can be, boils at
about 620°. Let a quantity of sulphuric acid so concentrated be heated
to 600°, and kept at that temperature, and let the steam of water
previously raised to the same temperature be conducted into it, we
would predict, without the least hesitation, as the result, the detention
and absorption of the steam, notwithstanding its high elasticity, until
the boiling point of the acid was reduced by the dilution to 600°.
Here then we have an instance of the absorption of a gaseous body
(steam at 600), by a liquid at the same temperature; yet, in order
to liquefy the gaseous body absorbed, in the ordinary way, it would
be necessary to cool it down through the long space of nearly 400°,
or to 212° Fahr. Such a reduction below the degree of temperature
at which the absorption took place would be productive, in all pro-
bability, of liquefaction in the case of the most refractory of the gases.
Now a composition of sulphuric acid and water, the same in every
respect, might be obtained more directly by simply mixing together
the ingredients, both being in the liquid state. This case of the ab-
Sorption of a gaseous body by a liquid is, therefore, dependent upon
the affinity which occasions the miscibility of liquids, and is, in fact,
an instance of the mixture of two liquids. Many similar illustrations
might be adduced if required.
We are, therefore, authorized in concluding that gases may owe their
absorption by liquids,--to their capability of being liquefied, and to the
affinities of liquids (apparent in their miscibility), to which they become
in this way exposed. These properties may, therefore, be considered as
ON THE ABSORPTION OF GASES BY LIQUIDS. 3
the proximate or immediate causes of the absorbability of the gases.
Upon this supposition, solutions of gases in liquids are mixtures of a
more volatile with a less volatile liquid; and to them may be extended
the laws which hold in such mixtures.
Several circumstances are favourable to this view of the absorption
of gases. v.
1. The cause assigned is one which we know to exist, and to be in
operation. It is no supposititious cause of the existence of which we
can adduce no other evidence than its conveniency in explaining certain
phenomena. We possess evidence that almost all the gases may be
condensed into liquids. They are, therefore, necessarily under the in-
fluence of those causes which we have supposed to occasion gaseous
absorbability. ' Thus Mr. Faraday condensed sulphurous acid gas into
a liquid, and found that its vapour possessed an elasticity which was
balanced by the weight of about two atmospheres at 45° Fahr. Here
then is a liquid which, from the frequency of the intermiscibility of
liquids, might be expected to possess the property of mixing so inti-
mately with certain of our reputed liquids as to admit of being detained
by them in considerable quantity at the ordinary pressure and tempera-
ture. And, accordingly, sulphurous acid is absorbed and detained in
large proportions by sulphuric acid and by alcohol, and in a consider-
able measure by water.
2. It is a coincidence which appears more than accidental, that the
gases which yielded to Mr. Faraday are, generally speaking, of easy
absorbability. This will appear from the following table of the gases
which were liquefied by that experimenter, of the pressure of their
vapours in atmospheres, and of the amount of their absorption by water
and alcohol at 60°, according to the experiments of Thomson, Henry,
Dalton, and Saussure :—
Pressure of I Vol. Water 1 Vol. alcohol
Gases Liquefied. vapours in absorbs in absorbs in
atmospheres, VOlS. at 60°. vols. at 60°.
Ammoniacal, . . . . 6-5 at 50° 780 tº - G
Sulphurous acid, . . 2 at 45 43-78 115-77
Muriatic acid, . . . 40 at 50 516 tº ºr tº
Cyanogen, . . . . . 37 at 45 4-5 23
Chlorime, . . . . . 4 at 60 2 - tº gº
Sulphuretted hydrogen, 17 at 50 l 6'06
Carbonic acid, e e 36 at 32 I 1-86
Nitrous oxide, . . . 50 at 45 l 1-53
Euchlorine, tº @ tº e º 8 tº ſº e
With the exception of fluosilicic and fluoboric gases, all the gases
absorbed in considerable quantity by water are contained in the fore-
4 ON THE ABSORPTION OF GASES BY LIQUIDS.
going table. While the other gases, such as oxygen, hydrogen, etc.,
which are condensed into liquids with great difficulty, are absorbed by
water in very minute quantities indeed. This, however, is more than
the theory requires.
3. Mr. Faraday was enabled to give approximations to the specific
gravities of some of the liquids into which the gases were reduced.
Now it would be an objection to the hypothesis, if there were an exces-
sive discordance between the specific gravities obtained by Mr. Faraday,
and the specific gravities which these liquids maintain in mixture, or
when in solution with water, etc. For although the specific weight of
a mixture of two liquids is rarely the mean of the weights of the liquids,
yet in general the variation from the mean is not excessive. There
exists, however, no such discordance. Indeed, a comparison of these
specific weights, which I have made, remarkably confirms the theory.
In addition to these facts, this hypothesis has in its favour all those
circumstances which are thought to recommend the chemical theory of
the absorption of gases, so ably illustrated by Berthollet, Thomson, and
Saussure. Indeed, the account here given may be considered as a
development of that theory.
By the latent heat which becomes sensible in the condensation of
vapours, and also by the heat which is frequently evolved in the mixing
of liquids, that increase of temperature, which always marks the absorp-
tion of gaseous bodies, is explained. The same liquid absorbs different
quantities of different gases, and different liquids absorb unequal quan-
tities of the same gas, from the attraction between the absorbing liquids
and the gases when liquefied being variable, as is the case among ordi-
nary liquids. Diminution of pressure or increase of temperature uni-
formly lessens the quantity of a gaseous body retained by a liquid,
because the absorbed gas is itself then in a liquid state ; and the vola-
tility of all liquids, whether by themselves or mixed with others, is
dependent upon pressure and temperature. The law, however, which
Dr. Henry deduced from his experiments upon carbonic acid, viz., that
the quantity of a gas which water absorbs is directly proportional to the
pressure, is at variance with this theory. It is not likely that Dr.
Henry would have come to the same conclusion had he experimented
upon the more absorbable gases. In the case of muriatic acid gas, for
instance, it is unlikely that he would have succeeded in impregnating
water with a double portion by doubling the pressure. There may,
nevertheless, be an approximation to such a law when the quantity of
gas absorbed is inconsiderable, as it is the case of carbonic acid gas;
our knowledge of the laws by which a volatile is retained by a more
fixed liquid being too superficial to enable us at present to decide the
point in question. The existence, however, of a general mechanical law
ON THE ABSORPTION OF GASES BY LIQUIDS. 5
of that description is incompatible with any chemical theory which can
be given. Supposing such a law to hold, it is remarked by Dr. Thom-
son, that “the proportion of the ingredients in this case is entirely
regulated by the bulk, whereas in chemical combinations it is regulated
by the weight.” Dr. Thomson, notwithstanding this admission, attempts
ingeniously to reconcile such a law to his modification of the chemical
theory."
The same objections are applicable to the analogous mechanical law,
that the quantity of a gas absorbed, estimated by the bulk, is unaffected
by variations in temperature. Such a law would be agreeable to the
theory illustrated, if it were true that the pressure of vapours from
liquids is exactly proportional to the temperature. But we know that
the elasticity of vapours, over their liquids, increases in a much higher
ratio than the temperature. Hence we are led to propose a different
law, viz., that by increasing the temperature of a liquid we diminish its
capacity to absorb any gas, not in the same but in a much greater
proportion.
Dr. Henry and Mr. Dalton have proved that the amount of any gas,
absorbed by a quantity of water in a vessel, depends greatly upon the
gaseous residue. This fact is deducible from the supposition that the
gases are liquefied when absorbed. For all liquids continue to evapo-
rate until they are pressed upon by an atmosphere of their own vapour,
equal in elasticity to that which they are capable of evolving at the
temperature of the experiment. In a solution of carbonic acid in water,
we ought, therefore, to expect carbonic acid to be given out or to evapo-
rate till an atmosphere of that gas be formed of elasticity sufficient to
counteract the tendency to assume the gaseous form of the remaining
liquid carbonic acid. If the solution be freely exposed to the air, the
whole of the carbonic acid will in a short time assume the gaseous
form, from the impossibility of forming such an atmosphere. But if the
solution be exposed to a limited quantity of any foreign gas, the carbonic
acid will cease to evaporate, when the elasticity of the gaseous portion
can counteract the volatility of the liquefied part. The greater the
quantity of the foreign gas with which the solution is in free communi-
cation, the less carbonic acid will be detained, or would be taken up,
were the absorption but commencing. Hence the influence of the
gaseous residue, as it is called.
To the partial displacement of one gas absorbed by a liquid by
another gas, parallel cases may be adduced from the mixture of liquids.
Thus, if alcohol, holding a volatile oil in solution, be poured into water,
the greatest part of the oil separates, while the alcohol unites with the
water.—The simultaneous absorption of several gases by a liquid be-
* System of Chem., vol. ii. p. 61.
6 ON THE FINITE EXTENT OF THE ATMOSPHERE.
longs to this class of appearances. From Mr. Dalton's theory it follows
that two gases absorbed into a liquid should really occupy always the
same room as they would occupy, if each of them had been absorbed
singly, at the degree of density which it has in the mixture. This law
is inconsistent with the explanation given here; but it has been fully
disproved by the subsequent experiments of Saussure.
It may be stated, in conclusion, that all that is insisted upon in the
foregoing sketch is, that when gases appear to be absorbed by liquids,
they are simply reduced into that liquid inelastic form, which other-
wise (by cold or pressure) they might be compelled to assume. That
their detention in the absorbing liquid is owing to that mutual affinity
between liquids, which is so common. An affinity which occasions the
miscibility of liquids affects the bulk or density of the mixture, and
frequently impairs the volatility of the more easily vaporized liquid in
the mixture. In this way the phenomena of the absorption of gases
are brought into the same class as those of the miscibility of liquids.
II.
ON THE FINITE EXTENT OF THE ATMOSPHERE.
From Philosophical Magazine and Annals of Philosophy, i. 1827, pp. 107-109.
Edinburgh, December 14, 1826.
To Dr. Wollaston we owe a satisfactory reason for a limit to the
atmosphere, even upon mechanical principles. The idea that the mere
weight of the matter of gaseous substances might afford, at a certain
degree of rarefaction, a balancing resistance to further expansion is
certainly beautiful, a conception worthy of that Sagacious philosopher.
Mr. Faraday, with his usual felicity in experimental research, has endea-
voured to adduce instances of this equilibrium between the expansive
power of gaseous matter and its clogging gravity—to give an experi-
mental demonstration of the hypothesis.
Admitting, as we do without hesitation, that the cause assigned
would be fully adequate to produce the effect, the question still remains,
—but is it really the cause which does produce the effect 2 The atmo-
sphere may possess some well-known property which necessarily ren-
ders it limited, and the proposal of any supposititious cause may be
therefore unnecessary.
Such a property we believe the atmosphere does possess, although
ON THE FINITE EXTENT OF THE ATMOSPHERE. 7
We are not aware of its having been noticed with this view previously.
he law of the expansion of gaseous bodies by heat and their con-
raction by cold involves a curious consequence, which has attracted
the attention of several philosophers. Bodies cannot exist in that state
below a certain temperature. Let us direct our attention to a volume
of air at 32° Fahr. It is a well-established law, that for every degree
Fahrenheit which the volume of air is heated above that temperature, it
increases 1-480th part ; and also for every degree which it is cooled
below 32°, it is reduced 1-480th part of what it was at that tempera-
ture. Hence if it should be cooled down 480°, and reduced by so
many parts, it would be reduced into a volume infinitely small —it
would really be annihilated. To avoid this absurdity, we are con–
strained to believe that all gases would be reduced into the liquid or
Solid state by a fall of temperature which does not amount to 480°
below the freezing point of water. The proposition, therefore, that the
earth's atmosphere cannot exist in the gaseous state at a temperature
below — 480°,+ 32” – – 448° Fahr. is susceptible of demonstration ad
absurdum.
Now meteorologists have discovered a law in the atmospheric tem-
perature which makes this fact available in elucidation of our subject.
It has been found that the temperature of the atmosphere decreases as
we ascend, and that with considerable regularity. The observations
which we possess upon this subject indicate a decrease of 1 degree for
every elevation of about 300 feet. This brings us rapidly to a limit to
the height of the atmosphere. Supposing the temperature of the sur-
face of the earth 32°, the air would lose its elastic state at a height
which would be less than 480 times 300 feet, or under 27.27 miles.
However, without questioning the continuance of this decrease of tem-
perature at great elevations, it is probable that in the higher regions of
the atmosphere it is by no means so rapid as in the lower regions,
where the law has been verified by observation. For the great source
of the heat of the atmosphere is its contact with the surface of the
earth, and not in the calorific rays of the sun which it arrests in their
progress. Hence the lower strata of the atmosphere will possess a com-
paratively high and extraordinary temperature, and the fall of tempera-
ture as we ascend will appear for Some time rapid. But at a certain
elevation, the effect of this adventitious supply of heat will be greatly
diminished.
The increase of capacity for heat in gases, attendant upon increase
of bulk, accounts in a satisfactory manner for reduction of temperature
in a mass of air as it is elevated and less compressed. The Superior
stratum of the atmosphere we may suppose to expand from its unre-
strained elasticity: its temperature is thereby lowered, till at last it

8 ON THE FINITE EXTENT OF THIE ATMOSPHERE,
arrives at that point which involves the loss of its elastic state. As the
liquid state is a physical state of bodies, which implies pressure and a
power to maintain the evolution of vapour (certainly in all non-metallic
bodies), the cooled and uncompressed superior air will be at once re-
duced from the gaseous to the solid state. In this way may tempera-
ture occasion a limit to the diffusion of the atmosphere.
From the length of time during which the sun's rays continue to be
reflected back upon the earth by the superior parts of the atmosphere,
after he has sunk beneath the horizon, there is reason to believe that
the atmosphere extends in a state of great tenuity to a very consider-
able height above the surface of the earth, and therefore that the theatre
of this condensation is considerably removed. Let us suppose that it
is so, and inquire whether its existence would be indicated by any
notable effect.
We know well that in ordinary cases the reduction of a body from
the gaseous to the liquid or solid state is attended with a considerable
extrication of heat. Light, too, has been observed in condensation
following sublimation, particularly in the case of benzoic acid. Now,
the superior and condensing strata of the atmosphere are of a tenuity
incomparably greater than that of the vapours whose condensation we
generally witness. But this tenuity has been arrived at at the expense
of the previous absorption of much more heat; or, in other words, the
latent heat of vapours, which is emitted upon their condensation, is in
proportion to their tenuity. Hence it is probable that the condensation
of the elastic air into solid particles would be attended with the emis-
sion of accumulated stores of light and heat. Would not air, too, it
might be asked, emit light upon its complete condensation and loss of
physical state, while it may be made to do so by mere mechanical com-
pression ? Here, perhaps, we have the cause of that degree of lumi-
nosity which is generally associated with the upper regions of the
atmosphere, and which has induced Professor Leslie, with that daring
originality which frequently characterizes his beautiful speculations, to
attribute to them a phosphorescent property.
These luminous appearances will be more frequent and striking at
the polar regions, from the temperature there approaching more closely
to the condensing point of the gaseous substances constituting the
atmosphere. Their proper sites will be the thermal poles, or points on
the earth's surface of lowest temperature. From late observations, the
thermal poles of the earth appear to coincide with its magnetic poles.
Let us suppose a determination to condensation to take place in the
superior regions of the atmosphere at the thermal pole, the surrounding
elastic air would rush in, and expand, to fill the vacuity occasioned by
the condensation. But this rarefaction, with its attendant fall in tem-


ACCOUNT OF M. LONGCHAMP's THEORY OF NITRIFICATION. 9
perature, would frequently be productive of condensation and deposition
in these masses of air themselves. In this way the tendency to con-
densation, originating perhaps at the thermal pole, would be widely and
rapidly propagated, and the attending streams of light would appear to
shoot from that point. Here we recognise the brilliant phenomena of
the aurora borealis.
It evidently follows from this theory that the atmosphere will be
of different altitudes over different parts of the earth, according to their
temperature. Within the tropics it will be higher than over the polar
regions. Hence the higher parts of the equatorial atmosphere will tend
to fall back upon the poles, a disposition which will co-operate with
the inferior current in an opposite direction, to produce a grand circula-
tion of the atmosphere, and to impress a general character upon winds.
III.
AN ACCOUNT OF ML LONGCHAMP’S THEORY OF NITRIFI-
CATION, WITH AN EXTENSION OF IT.
From Philosophical Magazine and Annals of Philosophy, i. 1827, pp. 172-180.
M. LONGCHAMP, in a memoir read some time ago before the Academy
of Sciences, and published lately in the Annales de Chimie et de Physique
(t. xxxiii. p. 1), has developed a theory of the natural production of
nitre in various soils, and superficially upon certain rocks. This theory,
in its full detail, is, perhaps, not altogether new ; for several of the
opinions of which it consists have been advocated, or at least broached,
by preceding chemists. But M. Longchamp has certainly the merit of
confidently displaying these opinions in their full force, and of method-
izing them into a consistent system. Of this theory we propose to give
an account, as nearly as possible in the words of the author, and to
subjoin certain speculations with the view of supplying a material
deficiency in the theory of M. Longchamp. a
It may be premised that M. Longchamp confines himself to the pro-
duction of the acid of the native nitrous Salts, and very properly avoids
any supposition of the production of their base previously existing, as
fact and reason point out that it must be, and, unlike the nitric acid of
these salts, incapable of a synthetic formation. .
There is reason to doubt the original proposition of Glauber, and
which, as far as regards the nitric acid, has been the prevailing theory
I 0 AN ACCOUNT OF M. LONGCHAMP's THEORY OF
to the present day, that “saltpetre is formed by the decomposition of
animal and vegetable substances;” for nitrates form and are found in
materials and in places which contain no vegetable or animal matter,
and which have never been exposed to the emanations of animals.
Persons engaged in the production of nitre know well that earths
taken from caves furnish nitrates by lixiviation, and that earths, re-
placed in the same circumstances, yield again, after eight or ten years,
new quantities of saltpetre. This fact cannot be denied ; but some
have attempted to weaken its force by the reflection that, in general,
the nitrous materials are not completely deprived of their salts by the
washing to which they are subjected; while these materials, exposed
again to the air, become dry, and as the water does not evaporate except
at their surfaces, it deposits there all the nitre which it held in solution.
This objection would be of weight, if it were true that only a small
quantity of nitre could be obtained from materials which had been
replaced ; but it is well known that if earth from a cave has given, by
the first lixiviation, 100 parts of nitric acid, saturated with the different
bases, the whole mass, being returned to the same place, will yield
again, after eight or ten years, the nitrates which represent the same
quantity of acid. It is not, therefore, only the nitre which the mate-
rials have retained which is obtained by the second lixiviation ; but
besides, and for the greater part, what is formed anew upon replacing
the earth in the circumstances which had induced its first nitrification.
Moreover, the same materials twice lixiviated, returned again to the
same cave, will yield, after eight or ten years, the same quantity of
nitre which they furnished at each of the two former lixiviations; and
the nitrification is perpetuated without a limit, provided that the re-
turned earth possess a sufficient portion of the base, which commonly
solicits the formation of the nitric acid, and absorbs that acid as it is
produced. y *
Lavoisier took from the quarry a great number of specimens of
chalk, at Roche Guyon and Mousseaux, and all when washed yielded a
small quantity of nitrate of potash, mixed with much nitrate of lime.
These specimens were frequently taken at a distance of many hundred
toises from any habitation, and from parts of the rock exposed to the
rain and all vicissitudes of weather; and he has drawn this consequence
from the facts related in his memoir: “the nitric acid does not pre-
exist in the chalk of Roche Guyon, but is formed by the action of the
air.”* It is remarkable that this chalk was often richer in nitre than
the best nitrous soils. The quantity of nitre which any specimen con–
tained was found to depend most upon its vicinity to the surface. As
the organic remains of these rocks do not retain their animal matter,
* Mémoires Etrangères de l'Académie des Sciences, xi. P. II. p. 565.
NITRIFICATION , WITH AN EXTENSION OF IT. 11
no influence can be attributed here to the decomposition and putrefac-
tion of animal substances in contact with the air.
But nitric acid forms in the open air, and in materials which con-
tain no vestige of animal or vegetable matter. An experiment is related
by one of the competitors for the French prize,” in which a quantity of
earth from the fields, washed with great care, dried by exposure to the
Sun, and afterwards kept moist by occasional watering for a year, afforded
by lixiviation a saline solution, in one case of one degree of the areo-
meter, and in another of half a degree. Thouvenel, too, who has pro-
duced nitric acid by exposing chalk to the gases evolved from the
putrefaction of animal or vegetable substances, mixed with common
air, likewise obtained this acid when the chalk was in contact with
nothing but atmospheric air.” It is true that in the experiment which
he relates, the materials exposed to the atmospheric air, loaded with
putrid gases, yielded fifteen parts of nitrate of lime; while those which
were in contact with pure atmospheric air afforded no more than six
parts of the salt. Thouvenel concludes, “It is demonstrated by our
experiments that atmospheric air possesses all that is necessary to serve
for nitrification, as well as the air which emanates from putrescent
bodies, provided it finds matter capable of absorbing the materials.”
M. Longchamp having thus shown how ill-founded the proposition
is, that the materials proper for nitrifying never nitrify in the air, with-
out the concurrence of animal matter, attempts, in the next place, to
prove that the nitric acid is formed exclusively from the elements of
the atmosphere.
It is admitted, he observes, that the animal matters do not require
to be in contact with the earths, but that their emanations are sufficient
for the production of nitre. Could it be through the instrumentality of
azote, which animal matter might disengage during putrefaction ? But
chemists know that the products of this putrefaction are ammonia, car-
bonic acid, carburetted hydrogen, and perhaps some carbonic oxide and
water, but no azote; and even if this gas were produced, how would it
combine with the carbonate of lime 2 There are instances of extraordinary
combinations of gases in the nascent state, but the azote is not presented
in that state in the case referred to, since the putrescent blood was at
the distance of two feet from the carbonate of lime, which it is pre
tended that it nitrified." -
1 Mémoires Etrangères de l'Académie des Sciences, xi. P. I. p. 160.
2 Ibid. P. II. p. 124. 3 Ibid. p. 89.
4 The commissioners of the Academy, among whom was Lavoisier, took a quantity
of the carbonate of lime, which they carefully washed in boiling water to extract all
the salts; they placed the washed carbonate of lime in baskets, which were hung at
the distance of two feet from a quantity of blood in a state of putrefaction.—Mém.
Etrang. de l'Acad., xi. P. I. p. 126,
12 AN ACCOUNT OF M. LONGCHAMP's THEORY OF
Might it arise from some combination of azote, which these emana-
tions bore along with them? But it is known that in the putrefactions
of blood, urine, and similar matter, all the azote goes to form ammonia:
admitting, however, that a part of the azote escapes the hydrogen, and
enters into some combination hitherto unobserved; why, it may be
asked, does it exhibit no nitrifying power without the co-operation of
carbonate of lime? For if directed against caustic lime, magnesia,
alumina, etc., no nitric acid is formed, or at least a scarcely sensible
quantity, and only after a long lapse of time; while if potash, caustic or
carbonated, be presented, not an atom of nitre is formed."
Might it be through a reaction of the putrid emanations upon the
atmosphere? But, besides that this reaction is difficult to conceive,
and that otherwise it would be the azote of the air which formed the
nitric acid, and not that of the animal matters, it may still be asked,
Why is the carbonate of lime the only body which solicits this
reaction ?
Considering it as proved, that animal substances do not nitrify by
means of their emanations, M. Longchamp believes that insuperable
difficulties attend the supposition, that putrescent bodies, in contact with
carbonate of lime, contribute in any measure to the production of nitric
acid. For there is no chemical fact which entitles us to suppose, that
urine or blood would yield by their putrefaction, other products when
they are mixed with calcareous earths, than when they putrefy without
the admixture. Provided, too, that the animal matters remained in the
solid state, their action upon the solid calcareous matter would be very
much circumscribed, extending only to the particles in immediate con-
tact with their surfaces. Even supposing that the animal matter was
liquid, and would thereby become diffused more generally through the
mass, still its action would be limited, to a great degree, by the total
insolubility of the carbonate of lime. From a review of these circum-
stances, Mons. L. considers himself entitled to conclude, that animal
matters, whether solid or liquid, do not concur by their azote to the for-
mation of the nitric acid. He then proceeds to the development of his
own theory, or to show how atmospheric air, without the concurrence of
any vegetable or animal matter, may form nitric acid.
It is universally admitted that nitric acid is not formed in sheltered
situations, unless a certain degree of humidity prevails, and the air
circulates through all the parts; for in places where the air cannot be
renewed, there is no formation of acid. Thus, Lavoisier observed at
Roche Guyon that in the caverns or pits, which were very deep and
had but one issue, nitric acid did not appear in the deep parts, but only
at the entrance. The same observation was made by that celebrated
* Thouvenel, Mém. Etrang. de l'Acad., xi. P. II. p. 119.
NITRIFICATION, WITH AN EXTENSION OF IT. 13
philosopher in the tufa quarries of Touraine. The nitric acid is formed
only in places which contain porous rocks or light soils, possessing car-
bonate of lime, moisture, and a constant circulation of air.
Tufa, light earths and chalk, act chiefly as absorbents. Chevraud
met with compact chalks, which did not nitrify. Hence we never find
marble, whether in the quarry exposed to the atmosphere, or in our
houses, to exhibit any tendency to the formation of nitre ; while tufa
and chalk, which differ from it only in porosity, nitrify with ease.
It is upon water that chalk and tufas exert their absorbing power.
But these substances in contact with water produce no nitric acid when
atmospheric air is withheld. But the water brings air with it, and the
nitrifiable materials, possessed of humidity, continue to absorb air by
means of that humidity.
Chemists have long known that all kinds of water contain air; but to
MM. Gay-Lussac and Humboldt' we are indebted for a fact, which has
more recently been confirmed by the latter philosopher and M. Pro-
vençal,” that the air in water contains more oxygen than atmospheric
air does. The mean of ten experiments made by Humboldt and Pro-
vençal on air derived from water gives the proportion of oxygen as
####. The previous researches of Gay-Lussac and Humboldt made
llS acquainted with a still more interesting fact, that if aerated water be
exposed to heat, and if we divide the air procured into any number of
equal portions, the first portions contain less oxygen than the last, as is
exhibited in the following table :-
Oxygen in 1000 parts of 1st portion of air, 24.0
32 22 2d 33 , 26-8
22 25 3d 33 , 29-6
33 33 4th , ,, 33-0
29 32 5th , , 34'8
M. Longchamp's application of this fact I shall give in his own
words, without abridgement, the more so, as I consider it not altogether
correct. “According to M. Berzelius, protoxide of azote contains 36-07
parts oxygen; the last portion, therefore, of the air obtained in the
experiments of Gay-Lussac and Humboldt, contained almost as much
oxygen as the oxide of azote possesses; and we perceive that water
exercises such an action upon the oxygen and azote, as tends to combine.
these gases in a more intimate manner than they exist in the atmosphere.
But if any other force should unite with that of the water, is it not reason-
able to think that the molecular action of the gases will acquire more
energy, and that there will result from these united forces a combination
which will be nitric acid; whether this acid is formed in following out
1 Journ. de Phys., lx. 129. * Mém. d’Arcueil, ii. 359.
14 AN ACCOUNT OF M. LONGCHAMP's THEORY OF
the whole chain of compounds known and unknown of oxygen and azote,
or is formed immediately by the first action of these gases? Now, the
body which in nitrification seconds the action of the water, is the lime
of the chalk. So then, tufa, chalk and nitrifiable materials act in nitri-
fication both as absorbents of water and air, and as presenting a base
which solicits the formation of nitric acid; and water acts as an absorb-
ent of oxygen and azote, and in commencing the combination of these
gases.”
The greater portion of oxygen absorbed depends without doubt
simply upon the greater absorbability of that gas than of azotic gas, and
not, as Mons. L. supposes, upon water exerting “such an action upon the
azote and oxygen as tends to unite them in a more intimate manner
than they exist in the atmosphere.” We embrace, however, M. Long-
champ's fundamental proposition,-that it is from the action of the
oxygen and azote, held in solution by water, upon the carbonate of lime,
that the nitrate of lime results. All bodies, when in the liquid state,
possess their powers of combination most energetically. Now I have
formerly shown" that oxygen and azotic gases, when absorbed by water,
are really in the liquid state; there is, therefore, some reason for that
activity with which our theorist has invested them.
Such is the theory of M. Longchamp; and it appears to me to be, as
far as it goes, a true explanation of the phenomena. The process of
nitrification is constantly going on in nature, and in circumstances
where no other agents appear to be employed, except carbonate of lime
and the elements of the atmosphere. Hence, in circumstances in which
animal matter is superadded to these agents, it is reasonable to think
that the latter does not contribute, in any essential way, to the nitrifica-
tion. Where nitrate of potash is the ultimate result, it appears to be
established that nitrate of lime pre-existed, and that the nitrate of
potash resulted from the decomposition of the nitrate of lime by some
salt of potash.
But it cannot be denied that the nitrification of calcareous sub-
stances is greatly promoted by the contact, or, more generally, by the
proximity, of putrescent vegetable and animal matter. The experiment
of Thouvenel, to which M. Longchamp refers above, abundantly proves
this ; and the constant and universal practice in the formation of arti-
ficial nitre-beds strongly confirms it. This fact appears, therefore, to
weigh heavily against the theory of M. Longchamp : it is however,
in our opinion, susceptible of an explanation without any mutilation
of that theory; and to this extension of the hypothesis we now
proceed.
We are disposed to attribute the beneficial effect in nitrification of
* Annals of Philosophy, N. S. vol. xii. p. 69.
NITRIFICATION, WITH AN EXTENSION OF IT. 15
the decomposition of animal and vegetable matter to the plentiful supply
of an element which exists at all times in the atmosphere in a percep-
tible proportion–carbonic acid gas. The free carbonic acid renders a
portion of the carbonate of lime soluble in the water or moisture, which must
Öe present, and thereby enables the carbonate of lime to act more effectually
ºpon the oxygen and azote, which the water has absorbed. The oxygen,
azote, and carbonate of lime are all liquefied, and in solution in the
Water; they are therefore in circumstances most favourable to their
mutual action.
Carbonate of lime is altogether insoluble in pure water, while water
Saturated with carbonic acid dissolves 1-1500th part. According to
Dr. Thomson : * “when carbonate of lime is rendered soluble in water
by means of carbonic acid a bi-carbonate is formed, which seems only
capable of existing in solution.” That carbonic acid is one of the most
considerable products of the putrefaction of both animal and vegetable
Substances is well known.
Water in ordinary circumstances absorbs rather more than an equal
volume of carbonic acid gas.
Now Thouvenel, without any view to this point, performed and has
registered a series of experiments, which render it exceedingly probable
that, of the products of putrefaction, it is the carbonic acid alone which
contributes to the nitrification ; inasmuch as when these products were
deprived of their carbonic acid, by being passed through caustic potash
or lime-water, before acting upon the chalk, their nitrifying power was
lost; while otherwise their nitrifying power was sufficiently notable. I
shall give Thouvenel's experiments, as reported by Messrs. Aikin in
their Chemical Dictionary, which is still the best work we possess upon
the chemical manufactures:– e
“Having charged a retort with putrefying materials, Thouvenel con-
nected with it three receivers in the manner of Woulfe's bottles, the last
of which terminated in a tube communicating with a pneumatic appara-
tus. Four different sets of this apparatus were employed at the same
time. In the first of these the two receivers nearest the retort were
charged with four ounces of chalk diffused in distilled water, while the
third receiver contained a solution of caustic potash. In the second set
the two first receivers contained distilled water, and the last was charged
with washed chalk. In the third set the two first receivers contained
lime-water: and in the fourth set a solution of caustic potash; the third
receiver in both cases holding the chalk. They were all equally exposed
to the same temperature, namely, from 7 4° to 80° Fahr., for six months,
and the changes which their contents had undergone were then
examined.
* First Principles, ii. 296.
I 6 LONGCHAMP's THEORY OF NITRIFICATION.
“The chalk in the first apparatus afforded 26 grains of nitrate of
lime mixed with a little nitrate of ammonia; the potash in the third
receiver had become saturated with carbonic acid, and had partly Crys-
tallized on the side of the receiver, but contained no nitre.
“In the second apparatus the water of the two first receivers had
acquired a very putrid smell from the gas which had passed through it,
and contained a little ammonia, but afforded no nitrous salt on evapora-
tion: the chalk in the third receiver afforded by lixiviation no more
than 4 grains of nitrated lime.
“In the third apparatus the lime-water had deposited its earth in
the state of carbonate, and the supernatant fluid had a strong odour
resembling ammonia and putrid garlic : by evaporation it yielded 5 or
6 grains of nitrated ammonia. The chalk in the third receiver gave
only a slight trace of nitrate of lime.
“In the fourth apparatus the potash was crystallized, but contained
no nitre : with sulphuric acid it effervesced strongly, giving out a very
pungent and highly fetid gas: the chalk in the third receiver gave no
$ndications whatever of the presence of any nitrous salt.
“The gas remaining in the receivers, and collected in the pneumatic
apparatus, was in all the four experiments found to be slightly inflam-
mable, although, when rising from the putrefying materials, it extin-
guished a taper immersed in it. This putrid inflammable gas was
incapable by itself of nitrifying chalk; but when mixed with washed
atmospheric air, carbonic acid soon made its appearance, and then
the gas became capable of impregnating chalk with nitrous acid as
at first.” "
These experiments of Thouvenel, and particularly the last observa-
tion, point out carbonic acid as the important agent in nitrification,
at least as distinctly as could be expected of experiments of this
nature.
It has all along been observed in the management of artificial nitre-
beds, that although free exposure to the atmosphere be indispensable to
the progress of nitrification, yet a strong current of air is exceedingly
prejudicial. The rapid circulation of the atmosphere would be attended
with the quick dissipation of the carbonic acid gas, upon which we have
supposed the superiority of these nitre-beds to depend.
The atmosphere at all times and places abounds in carbonic acid gas,
as the exposure of lime-water would quickly indicate. In those chalks
and calcareous Soils, in which the spontaneous production of nitrous
salts is observed, the activity Öf the carbonate of lime may, therefore,
equally depend upon its dissolution, effected by the absorption of mois-
* Aikins' Chemical Dictionary, vol. ii. 160. From Mém. Elrang. de l'Acad. des Sciences,
tom. xi. 503. gº
EXPERIMENTS ON THE ABSORPTION OF WAPOURS. 17
ture and carbonic acid from the atmosphere. It would still, however,
be a curious subject of inquiry—whether these soils and chalks do not,
in Some cases, contain within themselves the carbonic acid necessary
in conjunction with water to effect their partial solution, and be thus
enabled to act to a greater extent upon the absorbed oxygen and azote
—the elements of nitric acid :
Should this theory of the instrumentality of carbonic acid, in nitrifi-
cation, be eventually substantiated, several improvements, in the artificial
production of nitre, might evidently be deduced from it.
IV.
EXPERIMENTS ON THE ABSORPTION OF WAPOURS By
LIQUIDS.
From Edin. Journ. of Science, xvi. 1828, pp. 326-335. [Schweigger, Journ. liii.
(=Jahrb. xxiii.) 1828, pp. 249-264.]
FROM theoretical considerations I was led to institute the following
experiment —Into a deep cylindrical jar as much water was poured as
covered the bottom of it to the depth of half an inch. Within the jar,
and an inch above the surface of the water, a porcelain basin, three
inches in diameter, was supported, containing 500 grains of a saturated
solution of chloride of sodium of the temperature 57°, which was ob-
served to be also the temperature of the water below and of the air
without. The mouth of the jar was finally covered over by a glass plate,
and made nearly air-tight by means of lard. It was intended by this
arrangement to preserve the solution of chloride of sodium in an atmos-
phere Saturated, or nearly so, with aqueous vapour, to be supplied by the
water at the bottom of the jar. For comparison another arrangement of
a similar nature was made at the same time, with the only difference,
that the porcelain basin contained 500 grains pure water instead of a
saline solution. The two jars were set aside in a quiet place, not subject
to great variations in temperature, and a specimen of the dry chloride
of sodium made use of, was exposed freely to the air in their neighbour-
hood. At the expiration of six days the whole were examined: the
Salt exposed to the air did not present the slightest appearance of deli-
quescence. The basin of pure water in the second jar had lost three
grains in weight, but the Solution of chloride of sodium had increased in
weight by 63 grains. This solution possessed no power to absorb and
condense vapour from a temperature originally lower than that of the
* Read before the Royal Society of Edinburgh, March 3, 1828, then communicated
to the Edin. Journal of Science.
B
18 - EXPERIMENTS ON THE ABSORPTION OF
water near it; while the circumstance of a loss, rather than an increase
of weight, occurring in the other case, renders it improbable that any
inequality of temperature took place during the continuance of the
experiment, and operated in this way. The plain inference from the
experiment was, that the chloride of sodium employed, although by itself
not deliquescent, or incapable of absorbing vapour, yet possessed that
property in a considerable degree when in solution, seeing that in six
days it had absorbed nearly half its weight of water, the quantity of Salt
in solution being 143 grains, and the increase of weight 63 grains.
In a second preliminary experiment there were two cases similar to
the preceding, and besides, the same quantities of Saturated solutions of
muriate of ammonia and of sulphate of magnesia were enclosed in jars
containing a little water in a similar manner. The temperature on
closing the jars was about 58°, and very equable during the experiment.
In four days the basin of pure water was found to have lost 2.5 grains,
but the solution of muriate of ammonia had increased 34 grains, of
chloride of sodium 37 grains, and of sulphate of magnesia 8 grains. The
increase in the case of sulphate of magnesia was the least, although it
contained most saline matter.
In the further investigation of this subject, instead of separate jars,
low tin canisters were employed, in which several vessels with solutions
might be arranged at the same time. The vessels rested on a support
of wire-cloth an inch from the bottom of the canister, the lowest part of
the canister being occupied with water to the depth of half an inch. The
canisters were provided with lids, which could be made air-tight. . It
had been found that Wedgewood porcelain basins unfailingly absorbed a
portion of the water or of the saline solution which they contained,
varying from one to twelve grains. The use of them was therefore dis-
continued, and hemispheres or capsules of glass three inches in diameter,
and blown as like each other as possible, were employed in their place.
1. Solutions were formed of one part chloride of sodium in four parts
water, and of anhydrous carbonate of potash and water in the same pro-
portions. The carbonate of potash, which is deliquescent, was obtained
by keeping the Sesquicarbonate in a red heat till the excess of acid and
the water which it contains were wholly expelled. Three of the glass
capsules were placed in contact on the wire-cloth support of a small tin
canister, with water below, but not in contact with them. These capsules
contained respectively, 500 grains water, 500 grains of the solution of
chloride of sodium, and 500 grains of the solution of carbonate of
potash. They were less than half full. The observation being made
that no inequality of temperature existed within the canister, its lid
was applied, and the joinings made air-tight with lard. Upon exami-
nation at the expiration of six days, the capsule of water was found to
WAPOURS BY LIQUIDS. 19
have lost 23 grains; that of the solution of chloride of sodium to have
gained 39 grains; and the solution of carbonate of potash was found to
have gained only 6.5 grains. Here it is evident that the solution of
chloride of sodium had drawn vapour not only from the water below,
but likewise to a large extent from the adjoining capsule of water, and
most probably to a small extent from the solution of carbonate of potash,
likewise in contact with it. The solution of chloride of sodium appears,
therefore, to possess a manifest superiority in absorbing power over a
similar solution of the deliquescent carbonate of potash.
2. In a large tin canister or box, eighteen inches long, nine broad,
and four deep, with a wire-cloth support and water under it, precisely
as in the foregoing case, ten capsules containing various solutions were
arranged at the same time. To prevent the liquids from influencing each
other, they were separated by temporary screens of pasteboard, so that
each capsule was contained in a cell by itself; but all communicated
equally, through the apertures of the wire-cloth, with the reservoir of
water below. The results of this experiment are thrown into the form
of a table. In the first column the composition of the solutions is given,
of which 700 grains were always employed. When the proportion of
salt in the Solution is not expressed, it is to be understood that the solu-
tion was a Saturated one at the temperature of the atmosphere, which
varied during the experiment from 55° to 42°. In the second column
the increase or loss of weight undergone by the different solutions, after
being enclosed for six days, is expressed; and in the third column the
additional increase or loss of weight, after further confinement for four-
teen days. In a fourth column the boiling points of the solutions are
subjoined, for a purpose which shall be presently explained.

Solutions. §. º
Grs. Grs.
1. Chloride of sodium, & ſº te 35 66 224°
2. Sulphate of magnesia, . sº * 7 16 214-5
3. Sulphate of soda, . iº & gº 0 2 213
4. Carbonate of soda, . te tº tº 2 7 214
5. Nitrate of potash, . ſe * * 2 8 214
6. Muriate of ammonia, . * t 29 39 221
7. 1 carbonate of potash, 2 water t 22 45 22]
8. 1 chloride of calcium, 2 water, . 53 105 230-5
9. 1 chloride of calcium, 5 water, e 17 33 216.5
10. Water, . e & tº tº te — 5 –3 212
From the experiments of this table, and from other experiments yet
to be detailed, it is evident that not only the solutions of salts, which
are deliquescent, but that the solutions of salts which are persistent in
the air, and even of efflorescent salts, are capable of absorbing vapour in
20 EXPERIMIENTS ON TEIE ABSORPTION OF
an atmosphere nearly saturated with it. Some of the results are curious.
It appears from the table that a saturated solution of common salt,
which contains less than a third of its weight of a saline substance,
which is not deliquescent, absorbs vapour much more powerfully than a
solution of the deliquescent carbonate of potash in twice its weight of
water. In fact, it appears that all saline solutions just as readily inhale
as exhale vapour, according to the state of the atmosphere in which they
exist. It is this proposition in all its generality which I wish to estab-
lish. As the powers to absorb and to emit vapour appear to be neces-
sarily conjoined and of equal importance, it may be allowed us to say,
that liquids invaporate when they take in their vapour, as they are said
to evaporate when they give it out.
The column of boiling points is an index of the invaporating powers
of the solutions. The superior invaporating power of chloride of sodium
is distinctly connected with the high temperature at which it boils.
We see that the power of water to emit vapour at these high tempera-
tures is diminished in various degrees by the saline matter in solution.
At low temperatures it is probably diminished according to the same
rate; and saline solutions, unable to give out vapour of the tension of
that in the atmosphere around them, necessarily become absorbents of
that vapour, as is proved by these experiments.
3. The following table exhibits the weight acquired by solutions of
the same salt, viz. chloride of sodium, in various proportions, and also
by sea-water, by enclosure for five days. 500 grains of each solution
were employed. The boiling points of the solutions are likewise sub-
joined. -
Gain in Boiling
5 Days. Points.
Grs.
1. Saturated solution, chloride of sodium, 33 224°
2. 2 do. + 1 water, º e e 23 220
3. 2 do. + 2 water, & wº ſº 17 217.5
4. 2 do. + 4 water, ſº wº º 10 216
5. Sea-water, * e e o 3 213
A capsule of pure water enclosed at the same time, instead of increas-
ing in weight, lost 4 grains. The curious inference is deducible from
this experiment, that sea-water is capable of absorbing moisture from
air, perfectly Saturated with it at the same temperature. The experiment
with sea-water was several times repeated, and it always exhibited a
slight invaporating power, while a capsule of pure water placed beside
it lost weight.
4. Several Saline solutions and acid liquors were formed, all of which
boiled at one temperature, viz. 224”. 700 grains of each were employed,
WAPOURS BY LIQUIDS. 21
and they were retained for five days in the tin vessel. In the second
column the weight is expressed which each liquid acquired during that
period. These liquids were afterwards withdrawn from the tin vessel
and freely exposed to the air, that they might evaporate, in order that
the connexion between their evaporating and invaporating power might
be observed. The loss of each liquid by evaporation during twenty-four
hours is placed against it in a third column.
Solutions. ºr ºr
1. Chloride of sodium, e & + 32 grs. – 8:5 grs.
2. Chloride of calcium, • , , + 34 – 8:0
3. Carbonate of potash, e e + 30 — 8-6
4. Tartaric acid, . e * g + 31 – 8:4
5. Sulphuric acid (1:221), . º: + 34 – 8:1
6. Muriatic acid (1:125), g * } + 113 + 2*l
7. Muriatic acid (1.089), . sº + 61 — 2-3
8. Nitric acid (1206), . tº e + 59 — 2-9
A capsule of pure water was allowed to evaporate spontaneously for
the same time as the cases in the table. It lost 13.9 grains. The
temperature of the air did not exceed 45°. The similarity of the point
of ebullition seems to be attended with an analogous increase from in-
vaporation and loss by evaporation in the Saline solutions and in tartaric
and sulphuric acids. The difference of the results in these cases is so
Small that it might depend on slight variations of the form of the cap-
Sules, or other accidental circumstances. But the absorbing power of
the two cases of muriatic acid and of nitric acid, which boil at the same
temperature, are exceedingly different. The stronger muriatic acid also
actually gained weight when exposed to the air, instead of sustaining
loss by evaporation, like the other cases. The weaker muriatic acid and
the nitric acid likewise lost less by evaporation, as they gained more by
invaporation than the saline solutions. The invaporating powers of
liquids appear to be reciprocally proportional to their evaporating
powers, as might be expected. This was observed very distinctly on
exposing to the air various saline solutions of dissimilar absorbing
power, when those which invaporated in the least degree evaporated
most rapidly, and vice versa.
It has not, I believe, hitherto been noticed that muriatic acid is ever
capable of increasing in weight when exposed to the air, as sulphuric
and nitric acids are known to do, and as occurred in the case of the
stronger muriatic acid in the foregoing experiment. But I have fre-
quently observed muriatic acid, of all degrees of strength, intermediate
between 1190 and 1:100, to increase in weight by the absorption of
hygrometric moisture, when the weather was damp and the temperature
22 EXPERIMENTS ON THE ABSORPTION OF
not above 55°. When the acid is strong it emits muriatic acid gas at
the same time that it absorbs aqueous vapour, till it becomes of specific
gravity 1-0960. But when acid, diluted to any degree below that
strength, is exposed in a dry atmosphere, no material quantity of the
acid gas is emitted, but the acid concentrates by the emission of aqueous
vapour, till its specific weight rises to 1-0960. The boiling point of
muriatic acid is at a maximum when of that strength, as was observed
by Mr. Dalton; and it consists of exactly one atom acid and sixteen
atoms water, as Dr. Thomson remarked.
As evidence of the power of muriatic acid to absorb moisture from
an atmosphere not particularly dry, and to increase in weight, I may be
allowed to state one experiment, made lately in the month of January.
Three small porcelain basins, each containing 200 grains of liquid, were
exposed together, with paper covers, in a room in which there was no
fire. The liquid in No. 1 was muriatic acid of specific gravity 1-185.
In No. 2 the same, diluted with half its weight of water. In No. 3
pure water. It had been previously ascertained that the muriatic acid
contained no sulphuric acid. The basins were weighed every twenty-
four hours, and the following results obtained :-
Weight in Grains.
No. 1. No. 2. No. 3.
200 200 200
209 204 194
219 216 187
227 224 160
235 220 133
242 223 105
2.47 221 93
245 210 70
244 200 50
5. The capacity of liquids of dissimilar composition to absorb the
vapours of each other is also exceedingly general. We may always
presume with Safety, that, if two liquids are miscible in all proportions,
the more fixed liquid is capable of absorbing the vapour of the more
volatile liquid. Yet the only instances of such absorption which have
been attended to are the absorption of aqueous vapour by sulphuric
acid, and of the same vapour by nitric acid.
6. Alcohol and water are miscible liquids, of which water is the
more fixed; and I find water to absorb the vapour of alcohol at the
temperature of the atmosphere with considerable avidity.
Sulphuric acid also absorbs alcohol vapour with avidity, as was
stated in a former communication. The following experiment was per-
VAPOURS BY LIQUIDS. - 23
formed with the view of ascertaining the relative intensity with which
Water absorbs the vapour of alcohol, and sulphuric acid the vapours of
water and of alcohol.
(1) A small Wedgewood basin, one inch and a half in diameter,
containing 200 grains water, was supported over Sulphuric acid in a
cylindrical vessel, and closed in. Upon opening the jar after twelve
hours, the water was found to have lost eleven grains. (2) The acid
was stirred up, and, instead of the water, 200 grains absolute alcohol
were introduced into the basin, and the whole closed in as before. In
twelve hours the alcohol was found to have lost sixty grains, and the
sulphuric acid had acquired a reddish tinge. (3) The Sulphuric acid
was now withdrawn from the jar, and pure water substituted as the
absorbing liquid. The quantity of absolute alcohol in the basin being
again increased to 200 grains, and the lid carefully luted down, in
twelve hours the alcohol lost 45 grains, and the water below had
acquired the taste of alcohol very sensibly. The vapour of sulphuric
ether is absorbed with great avidity by alcohol, and with much less
force by water.
The vapour of alcohol is likewise absorbed by castor oil, especially
after some alcohol has been previously mixed with it, although with a
very feeble force. Retained over alcohol for ten days 200 grains castor
oil became 273 grains. Bichloride of mercury deliquesces in alcohol
vapour, although slowly when in hard crystals. Twenty grains of the
crystals (not reduced to powder), Suspended in a capsule over alcohol,
became in six days 29 grains, a portion being dissolved by the alcohol
absorbed. A solution of bichloride of mercury in alcohol likewise
exhibits an invaporating power when in an atmosphere of alcohol
vapour.
It would be curious to know whether alcohol is capable of absorbing
the vapour of water, as well as water is capable of absorbing the vapour
of alcohol. It is difficult to determine the point directly, as the quan-
tity of water absorbed might be very minute; but I am inclined to
believe, from an indirect experiment, that alcohol does not possess such
an absorbing power. A crystal of Sulphate of Soda was suspended over
a small quantity of absolute alcohol very carefully prepared, by a thread,
which was attached to the cork of the phial for a period of six months,
without undergoing the slightest alteration in appearance. Now, if
alcohol had possessed the power to absorb aqueous vapour, and to keep
the atmosphere above it in a dry state, so far as aqueous vapour is con-
cerned, the crystal would certainly have effloresced and fallen into
powder. - º
The phenomena presented when pieces of camphor are placed at a
little distance from alcohol are very remarkable. A number of small
24 ON THE INFLUENCE OF THE AIR IN DETERMINING
pieces in a gauze bag were suspended within a glass jar which contained
a little alcohol. In a few hours the camphor began to run into a liquid,
which fell in drops, and in twenty-four hours the whole camphor had
left the bag in that manner. It is evident, therefore, that solid cam-
phor with relation to alcohol vapour is deliquescent. Forty grains cam-
phor were suspended over alcohol, as in the previous case, with the
difference that the camphor was contained in a little glass capsule.
Five days afterwards the capsule contained a solution of camphor in
alcohol weighing 105 grains. A little camphor, however, had passed
down to the alcohol below, to which it communicated its taste and
smell; but the quantity was so small that the alcohol, on being diluted
with water, became only slightly opalescent. The temperature of the
atmosphere during these experiments averaged about 55°.
The salt subcarbonate of ammonia is known to be possessed of con-
siderable volatility, and also to be soluble in water. Enclosed with
water in separate vessels it quickly passes over into the water. Thirty
grains of dry subcarbonate reduced to powder were suspended in a glass
capsule over a considerable quantity of cold water, the whole being con-
tained in a close vessel as usual. Upon examination after five days,
the capsule, instead of 30 grains of the dry salt, was found to contain
12 grains of a solution of it, the greater part of the salt having passed
over into the reservoir of water below, to which it had imparted its taste
and properties. The habitudes of subcarbonate of ammonia in an atmo-
sphere Saturated with aqueous vapour are therefore exceedingly different
from those of any other salt, as, instead of attracting water or remaining
unaffected, it is itself attracted by water and dissolved.
Such are the principal facts which have presented themselves in the
investigation of the absorption of vapours by liquids.
V.
ON THE INFLUENCE OF THE AIR IN DETERMINING THE
- CRYSTALLIZATION OF SALINE SOLUTIONS.
From Edin. Roy. Soc. Trans. xi. 1831, pp. 114-118, author's reprint. [Phil. Mag. iv.
1828, pp. 215-218 ; Silliman, Journ. xvii. 1830, pp. 373-374.]
THE phenomenon referred to has long been known, and popularly
exhibited in the case of Glauber's salt, without any adequate explana-
tion. A phial or flask is filled with a boiling saturated solution of
sulphate of soda or Glauber's salt, and its mouth immediately stopped
THE CRYSTALLIZATION OF SALINE solutions. 25
by a cork, or a piece of bladder is tied tightly over it, while still hot.
The solution, thus protected from the atmosphere, generally cools with-
out crystallizing, although it contains a great excess of salt, and con-
tinues entirely liquid for hours, and even days. But upon withdrawing
the stopper, or puncturing the bladder, and admitting air to the solu-
tion, it is immediately resolved into a spongy crystalline mass, with the
evolution of much heat. The crystallization was attributed to the
pressure of the atmosphere suddenly admitted, till it was shown that
the same phenomenon occurred when air was admitted to a solution
already subject to the atmospheric pressure. Recourse was likewise
had to the supposed agency of solid particles floating in the air, and
brought by means of it into contact with the solution ; or it was Sup-
posed that the contact of gaseous molecules themselves might determine
crystallization, as well as solid particles. But although the phenomenon
has been the subject of much speculation among chemists, it is gene-
rally allowed that no satisfactory explanation of it has yet been pro-
posed. -
In experimenting upon this subject, it was found that hot concen-
trated solutions, in phials or other receivers, might be inverted over
mercury in the pneumatic trough, and still remain liquid on cooling;
and thus the causes which determine crystallization were more readily
examined. For this purpose, it was absolutely necessary that the mer-
cury in the trough should be previously heated to 110° or 120°; for
otherwise that part of the solution in contact with the mercury cooled
so rapidly as to determine crystallization in the lower part of the
receiver long before the upper part had fallen to the temperature of the
atmosphere. In such cases, crystallization beginning on the surface of
the mercury, advanced slowly and regularly through the solution.
Above, there always remained a portion of the solution too weak to
crystallize, being impoverished by the dense formation of crystals
below. It was also necessary to clean the lower and external part of
the receivers, when placed in the trough, from any adhering solution,
as a communication of saline matter was sometimes formed between
the solution in the receiver and the atmosphere without. When these
precautions were attended to, saline solutions over mercury remained as
long without crystallizing as when separated from the atmosphere in
the usual mode.
Solutions which completely filled the receivers when placed in the
trough allowed a portion of mercury to enter by contracting materially
as they cooled. A bubble of air could thus be thrown up without
expelling any of the solution from the receiver, and the crystallization
determined without exposing the solution directly to the atmosphere.
The first observation made was, that solutions of Sulphate of soda
26 ON THE INFLUENCE OF THE AIR IN DETERMINING
sometimes did not crystallize at all upon the introduction of a bubble
of air, or at least for a considerable time. This irregularity was chiefly
observed in solutions formed at temperatures not exceeding 150° or 170,
although water dissolves more of the sulphate of soda at these inferior
temperatures than at a boiling heat. Brisk ebullition for a few seconds,
however, rendered the solution upon cooling amenable to the usual in-
fluence of the air. In all successful cases, crystallization commenced
in the upper part of the receiver around the bubble of air, but pervaded
the whole solution in a very few seconds. A light glass bead was
thrown up into a solution without disturbing it.
It occurred to me that, since the effect of air could not be accounted
for on mechanical principles, it might arise from a certain chemical
action upon the solution. Water always holds in solution a certain
portion of air, at the temperature of the atmosphere, which it parts with
upon boiling. Cooled in a close vessel after boiling, and then exposed
to the atmosphere, it reabsorbs its usual proportion of air with great
avidity. Now, this absorbed air appears to affect in a minute degree
the power of water to dissolve other bodies, at least a considerable part
of it is extricated upon the solution of salts. When a bubble of air is
thrown up into a solution of sulphate of soda, which has previously
been boiled and deprived of all its air, a small quantity of air will cer-
tainly be absorbed by the solution around the bubble. A slight reduc-
tion in the solvent power of the menstruum will ensue at the spot
where the air is dissolved. But the menstruum is greatly overloaded
with saline matter, and ready to deposit; the slightest diminution of its
solvent power may therefore decide the precipitation or crystallization
of the unnatural excess of saline matter. The absorption of air may in
this way commence and determine the precipitation of the excess of
sulphate of soda in solution. -
Here, too, we have an explanation of the fact just mentioned, that
solutions of sulphate of soda, which have not been boiled, are less
affected by exposure to the air than well-boiled solutions; for the former
still retain the most of their air, and do not absorb air so eagerly on
exposure as solutions which have been boiled.
But the theory was most powerfully confirmed by an experimental
examination of the influence of other gases, besides atmospheric air, in
determining crystallization. Their influence was found to be precisely
proportionate to the degree in which they are absorbed or dissolved by water
and the saline Solutions.
To a solution of Sulphate of Soda over mercury, which had not been
affected by a bubble of atmospheric air, a bubble of carbonic acid gas
was added. Crystallization was instantly determined around the bubble,
and thence through the whole mass. Water is capable of dissolving its
THE CRYSTALLIZATION OF SALINE SOLUTIONS. 27
own volume of carbonic acid gas, and a solution of sulphate of soda, as
strong as could be employed, was found by Saussure to absorb more
than half its volume.
In a solution of sulphate of soda, which was rather weak, both
Common air and carbonic acid gas failed to destroy the equilibrium;
but a small bubble of ammoniacal gas instantly determined crystalli-
zation.
When gases are employed which water dissolves abundantly, such
as ammoniacal and sulphurous acid gases, the crystallization proceeds
most vigorously. It is not deferred till the bubble of gas reaches the
top of the receiver, as always happens with common air, and frequently
with carbonic acid gas, but the track of the bubble becomes the common
axis of innumerable crystalline planes, upon which it appears to be
borne upwards ; and sometimes before the ascent is completed, the
bubble is entangled and arrested by crystalline arrangements which
precede it.
The number of gases which are less soluble in water than atmo-
spheric air is not considerable, but of these hydrogen gas was found
to be decidedly less influential in determining crystallization.
Minute quantities of foreign liquids soluble in water likewise dis-
posed the saline solution to immediate crystallization, as might be
expected, and none with greater effect than alcohol. It is known that
alcohol can precipitate sulphate of soda from its aqueous solutions. The
soluble gases I suppose to possess a similar property.
These facts appear to warrant the conclusion that air determines
the crystallization of supersaturated Saline solutions by dissolving in
the water, and thereby giving a shock to the feeble power by which the
excess of salt is held in solution.
Before concluding, I may be allowed to make a remark on the usual
description of the sudden congelation of the solution of sulphate of soda
upon the admission of air. It is said that the solution expands in
solidifying, in the same way as water does in becoming ice. But the
expansion which takes place is merely temporary, and not due to such
a cause, but entirely to a momentary dilatation of the whole contents of
the phial, both liquid and solid, by the evolution of heat, which occurs
on the instant of crystallizing, and which always amounts to 20° or 30°.
That the salt does not permanently expand on crystallizing is easily
proved by the sinking of a crystal in the densest solution of the salt
which can be formed.
28 EXPERIMENTAL RESEARCHES ON THE DIFFUSION OF GASES,
VI.
A SHORT ACCOUNT OF EXPERIMENTAL RESEARCHES ON
THE DIFFUSION OF GASES THROUGH EACH OTHER,
AND THEIR SEPARATION BY MECHANICAL MEANS.
From Quart. Journ. of Science, ii. 1829, pp. 74-83. [Poggend, Annal. xvii. 1829,
pp. 341-347; Schweigger, Journ, lvii. (=Jahrb. xxvii.) l829, pp. 215-227.]
FRUITFUL as the miscibility of the gases has been in interesting
speculations, the experimental information we possess on the subject
amounts to little more than the well-established fact, that gases of a
different nature, when brought into contact, do not arrange themselves
according to their density, the heaviest undermost, and the lightest
uppermost, but they spontaneously diffuse, mutually and equably,
through each other, and so remain in an intimate state of mixture for
any length of time. The beautiful illustrations of Mr. Dalton, by which
this law was first developed, have rendered it familiar to every one.
The subsequent experiments of Berthollet were made with uncommon
care, and in most favourable circumstances, yet it is difficult to, draw
more from them than the same general fact; unless perhaps that hydro-
gen is much more penetrating and diffusive than any of the other gases.”
It is sufficiently evident, however, from Berthollet's experiments, that,
in cases of gaseous mixture which are exactly similar, corresponding
results may be expected, or that the diffusion is not accidental, but sub-
ject to fixed laws.
In the prosecution of further inquiry into the laws of the diffusion
or miscibility of gases, much use was made of a cylindrical
glass receiver A, 9 inches in length, and 0.9-inch internal
diameter, divided into 150 equal parts, and provided with a
stopper B, fitted into the mouth of the receiver by accurate
grinding. The stopper was perforated longitudinally, cavity
cylindrical, 0.34-inch in diameter, and 1:8 in length. (Into
the cavity of the stopper there was again ground a short
piece of stout tube, having a bore of 0:07, or nearly 14.5 inch,
and bent into a right angle in the middle; such as C. These
were the dimensions of tube A ; but after several experi-
ments that tube was laid aside, and a second and a wider
tube, of 0-12-inch bore and 2 inches in length, was ground
into the aperture of the large stopper B, and bent in the
middle, like tube C.
ſil*—sº|
* Berthollet's experimental paper is contained in the Mém. d’Arcueil, vol. i. p. 463; but
the whole experiments are given in a tabular form in Dr. Thomson's System, vol. iii. p. 33.

AND THEIR, SEPARATION BY MECHANICAL MEANS. 29
I. On the Diffusion of the different Gases into Atmospheric Air.
The receiver, above described, was filled in succession with various
gases in a state of purity, and sup-
ported in a horizontal position upon
a frame within a box, with the end
of the bent tube pointing upwards,
when the contained gas was heavier
than air (fig. 1), and downwards,
when the gas was lighter (fig. 2),
to avoid any tendency of the gas
to flow out of the receiver. After
the gas had been allowed to diffuse
FIG. I.
G-2) ſh
-E"
into the air through the tube for a certain time, the receiver was trans-
ferred to the pneumatic trough, and the quantity of air which had
entered, and gas that remained, ascertained. Two or three and some-
... times more experiments were made on each gas, and the results found
to be regular, or to vary within moderate limits.
(1.) After diffusion for ten hours, through tube I, there was found in
the receiver, of which the capacity = 150 parts—of
Hydrogen gas (sp. gr. 0-0694), . o © &
Carburetted hydrogen of marshes (sp. gr. 0-5555), 56
8.3 parts.
Ammoniacal gas (sp. gr. 0-59027), 61
Olefiant gas (sp. gr. 0-9722), 77-5
Carbonic acid (sp. gr. 15277), . © ... 79.5
Sulphurous acid (sp. gr. 2'2222), º º ... 81
Chlorine (sp. gr. 2:5), • * * & . 91
(2) After diffusion for four hours through tube I—in 152 parts
there was found—of
Hydrogen gas, &
Carburetted hydrogen,
Ammoniacal gas,
Olefiant gas,
Carbonic acid, .
Sulphurous acid,
Chlorine, e e
There have, therefore, left the receiver in the same time—of
Hydrogen gas, . e
Carburetted hydrogen,
Ammoniacal gas,
Olefiant gas,
Carbonic acid gas,
Sulphurous acid,
Chlorine,
28-1
86
89
99
104
110
116
1239 parts.
66
63
53
48
42
36

30 EXPERIMENTAL RESEARCHES ON THE DIFFUSION OF GASES,
In deducing the comparative diffusiveness of the different gases from
the table above, it is necessary to keep in mind the diminishing rate,
according to which the latter portions of the gas leave the receiver. It
was determined, with precision, in the case of olefiant gas, that that gas
continues to leave a receiver, by diffusion, according to the same dimin-
ishing rate which holds in mechanical exhaustion by the air-pump.
Hence the initial diffusions of the gases are even more varied than the
numbers of the table. As much hydrogen gas left a receiver in two
hours, as of carbonic acid in ten hours. Hence the former gas is five
times more diffusive than the latter. In all cases the gases were neces-
sitated to diffuse in opposition to the solicitation of gravity. Yet car-
buretted hydrogen and ammoniacal gases left the receiver in greater
proportions than olefiant gas did, although the diffusion of the former
gases was more opposed by mechanical causes.
It is evident that the diffusiveness of the gases is inversely as
some function of their density—apparently the square root of their
density. .
The results, however, are much influenced by the mechanical resist-
ance arising from gravity, which is not constant in gases of
different densities, the position of the receiver remaining the
same. The effect of the position of the receiver may be con-
ceived from an experiment on hydrogen gas. The receiver,
filled with hydrogen gas, was placed in an upright instead of
a horizontal position (see figure). Other circumstances being
the same as in the experiment of table (1), of 150 parts hydro-
gen 22:1 were found remaining in the receiver after diffusion
for ten hours, instead of 83 parts, as in that experiment.
Although the stoppers fitted precisely, the additional pre-
caution of luting the joinings was attended to. The properties
of the receiver, too, were found not to be peculiar to it.
II. On the Diffusion of mixed Gases into Atmospheric Air.
In the case of an intimate mixture of two gases, I was anxious to
learn if each gas left the receiver, independently of the other, in the
proportion of its individual diffusiveness—which would be a step gained
in the solution of the important problem of the analysis of mixed gases .
by mechanical means.
For this purpose, the receiver was filled with 75 vols. hydrogen + 75
vols, olefiant gas, agitated and allowed to stand over water for 24 hours,
that the mixture might be as perfect as possible. The receiver being
then placed in the usual position, the mixed gases were allowed to

AND THEIR SEPAIRATION BY MECHANICAL MEANS. 31
diffuse into the air for ten hours. The receiver thereafter was found to
contain
Hydrogen gas, . o e e e 3.5
Olefiant gas, º g º º © 56-6
Air, e º º e e º 89-9
I 50-0
There have left the receiver—of
Hydrogen gas, e º º 71.5 out of 75 parts.
Olefiant gas, © © º 18°4 75
The more diffusive gas has, therefore, separated from the other, and left
the receiver in greatest proportion.
Now, when the receiver contains nothing but pure olefiant gas, 72-5
parts of that gas leave the receiver in the circumstances of the preceding
experiment. Hence, when the receiver is half filled with olefiant gas,
we would expect the half of 72-5 parts, or 36:25 parts, to leave the
receiver, and this happens when the complementary 75 parts are common
air. But instead of 36:25 parts, only 18.4 olefiant gas leave the receiver
in the last experiment. The disparity between the diffusion of each of
the mixed gases, in that experiment, is actually greater than the disparity
between the solitary diffusions of the same gases.
In the case of mixed gases, the law is—that the more diffusive gas
leaves the receiver in a greater proportion than in the case of the solitary
diffusion of the same gas, and the less diffusive gas in the mixture in a
less proportion than in its solitary diffusion—a law of the diffusion of
mixed gases, which was confirmed in upwards of forty experiments on
diverse gaseous mixtures. Some of these experiments I shall subjoin.
(1.) The receiver was charged with
Carbonic acid, e e e 75 U_
Hydrogen, . e º & 75 } = 150
which were allowed to mix intimately over night. The mixture was
afterwards allowed to diffuse into the air through the tube for ten hours.
Position horizontal, mouth of tube downwards. Thereafter contained,
Carbonic acid, . tº tº º e 45
Hydrogen, º o ge © © 4-65
Air, . . . . . . 100-35
150-00
In this experiment, a portion of the carbonic acid may have flowed out,
for at the end of the experiment the density of the gaseous mixture was
greater than that of the atmosphere, while the mouth of the tube opened
downwards.
32 EXPERIMENTAL RESEARCHES ON THE DIFFUSION OF GASES,
(2) Receiver charged with
Carbonic acid, . tº ... 102 = 15.2
Hydrogen, & gº © 50 ſ T
With tube II. Position of receiver horizontal, mouth upwards. After
diffusing into the atmosphere for four hours, contained
Carbonic acid, . § o 76
Hydrogen, & te e 10-3
Air, . © s & tº 65-7
152
(3) Receiver charged with
Carbonic acid, . * e 76 152
Carbur. hydrogen (of marshes), 76 ſ T “”
Tube II, mouth upwards. After four hours, contained
Carbonic acid, . tº we 57
Carbur. hydrogen, * e 35-3
Air, . © tº gº * 59-7
152
Have left the receiver,
Carbonic acid, . e tº 19
Carbur. hydrogen, ſº tº 40-7
or, twice as much carburetted hydrogen as carbonic acid has left the
receiver. Of these gases individually, there left the receiver in the
Same circumstances,
Of Carbonic acid, * © 48
Carburetted hydrogen, . 66
(4) Receiver charged with
Carbonic acid, . º e * ! =158
Carburetted hydrogen, . 100 ( ~ ***
Position, etc., as in preceding experiment. After four hours, contained
Carbonic acid, . * * 39
Carbur, hydrogen, e ſº 51-6
Air, . de e wº te 61°4
152
IIave left the receiver,
Carbonic acid, . * & 13
Carbur. hydrogen, e ſº 48°4
(5) Receiver charged with
Carbonic acid, . te g 31 l 152
Carbur. hydrogen, & 121 i = 10
AND THEIR, SEPARATION BY MECHANICAL MEANS. 33
Position, etc., as above. After four hours,
Carbonic acid, . e is 23
Carbur, hydrogen, e e 71
Air, . * • * * 58
152
Have left the receiver,
Carbonic acid, . g & 8
Carbur. hydrogen, g º 50
These three last experiments form a series. Suppose we had a
mixture of two gases, of the same densities as carbonic acid and car-
buretted hydrogen, in equal volumes, but which could not be separated
from each other by chemical means. Allow this gaseous mixture to
diffuse for a certain time, as in Experiment 3, into a gaseous or vaporous
atmosphere, which may afterwards be absorbed or condensed with
facility. On condensing this atmosphere, there would remain a mix-
ture, consisting of two parts of the light and one of the heavy gas.
By a similar diffusion of the mixture thus obtained, we would pro-
cure a third mixture, consisting of four parts of the light and one of
the heavy gas (Experiment 4).
By a third diffusion, a mixture would be obtained of six or seven of
the light and one of the heavy gas (Experiment 5).
In this way a specimen of the light gas would at last be eliminated,
by a species of rectification, in a state of tolerable purity.
On the other hand, if a specimen of the dense gas be desired, a
converse series of operations must be pursued. What remains in the
receiver after diffusion must be preserved, accumulated, and submitted
again and again to diffusion.
(6.) Receiver was charged with
Olefiant gas, tº º O - 76
Carburetted hydrogen, . © #& =1 52
After four hours, contained,
Olefiant gas, º º ë 47.75
Carbur. hydrogen, & ſe 41°40
Air, . . . . . 62°85
152
Have left the receiver,
Olefiant gas, ſº * e 28-25
Carbur. hydrogen, & & 34-60
34 EXPERIMENTAL RESEARCHES ON THE DIFFUSION OF GASES,
III. Diffusion of Gases into other Atmospheres than Common Air.
(1) A phial, A, of 52 cubic inches, provided with a perforated cork,
was filled with an intimate mixture of olefiant and hydrogen gases in
equal proportions. The phial being held with its mouth undermost, a
glass tube of 0-12 inch bore was thrust through the cork, and likewise
quickly inserted into the perforated cork of another bottle, B, of 37
FIG. I. FIG, 2.
cubic inches, containing carbonic acid gas. The whole was then sunk
in water till the surface of the water, a, a (fig. 2), rose above the
joinings. After ten hours, the upper phial was removed, and its con–
tents washed with lime-water. There remained a mixture, consisting of
Olefiant gas, & * } e 12
Hydrogen, . & ( ; wº 3-1
There can be no doubt that the olefiant gas would have been obtained
in a state of greater purity had not the diffusion of the hydrogen gas
been greatly impeded, 1st, from the direction in which it took place
downwards; and, 2dly, from the density of the medium into which it
diffused.
Had the mixture of olefiant gas and hydrogen been allowed to
diffuse upwards, and into an atmosphere of specific gravity intermediate
between that of its constituent gases—into steam or ammoniacal gas,
for instance,—circumstances would have been most conducive to the
unequal diffusion and separation of the mixed gases.

AND THEIR SEPARATION BY MECHANICAL MEANS. 35
(2) Hydrogen gas, in a tall receiver, is expanded by sulphuric
ether, I find, four times more rapidly than common air. Mr. Leslie
had already observed, that ice evaporates twice as rapidly in hydrogen
gas as in common air; and he and Mr. Dalton found the cooling
powers, or mobility of the different gases, to be inversely as their
density.
(3) Gases permeate with increased facility in both directions
through the pores of porcelain tubes at high temperatures (Priestley),
because, I believe, their tendency to diffusion, which is inversely as
their density, is vastly increased by their rarefaction, and not from any
dilatation of the pores of the porcelain, which must be utterly trivial
in the most intense heat.
(4.) A tall receiver was #ths filled with a mixture of 2 hydrogen
+ 1 oxygen, which had remained mixed for three weeks, but was found
sensibly pure before the experiment. A little ether being thrown up
into the receiver, the experimental mixture rapidly expanded. The first
bubble projected from the receiver by the expansion was received,
deprived of all ether-vapour by washing, and, being exploded, left half
its bulk of pure hydrogen gas.
(5.) The vapour of water appears, from the following experiment, to
be more diffusive than the vapour of alcohol, as might be expected from
the densities of these vapours. Of dilute alcohol (0-964), three ounces
were exposed to spontaneous evaporation in a cylindrical jar two inches
deep, and the same quantity in a jar six inches deep, but otherwise
similar, the mouths of both jars being loosely covered with paper.
When each of the vessels had lost half an ounce by evaporation, the
remaining liquor was examined and found to contain sensibly more
alcohol in the case of the deep than of the shallow jar. The difference,
however, was altogether insufficient to enable us to account for the well-
known experiment of the concentration of alcohol in a bladder, by
referring it to the superior diffusiveness of water-vapour. But it is con-
ceivable, and the subject is at present under investigation, that imper-
ceptible pores, or orifices of excessive minuteness, may be altogether
impassable (by diffusion) by gases of low diffusive power, that is, by
dense gases, and passable only by gases of a certain diffusive energy.
Hydrogen gas certainly escapes from a bladder more rapidly than any
other gas, and probably from diffusion, as the place of the hydrogen
is found occupied by common air. But to these investigations, and
to certain theoretic considerations, I hope again to recur in a future
paper.
36 OBSERVATIONS ON TEIE OXIDATION OF PHOSPHORUS.
VII.
OBSERVATIONS ON THE OxTDATION OF PHOSPHORUS.
From Quart. Journ. of Science, ii. 1829, pp. 83-88. [Poggend, Annal. xvii. 1829,
pp. 375-380; Schweigger, Journ. lvii. (=Jahrb. xxvii.) 1829, pp. 230-240.]
WE are at present in possession of several curious facts respecting
the insensible combustion of phosphorus at low temperatures.
1. In pure oxygen gas, under the atmospheric pressure, and at tem-
peratures below 64", the usual white smoke is not seen around phos-
phorus in daylight, and it is not luminous in the dark. No absorption
of oxygen takes place.
2. A slight expansion of the oxygen gas, produced by diminishing
the pressure upon it two or three inches below the usual pressure of the
atmosphere, occasions phosphorus to be acted upon by pure oxygen, and
to undergo slow combustion.
3. By diluting oxygen with certain gases, such as hydrogen, azote,
protoxide of azote, carbonic oxide, carbonic acid, etc., the oxygen
becomes capable of supporting the slow combustion of phosphorus
even under the atmospheric pressure, as well as when rarefied by
reduced pressure. Hence phosphorus is luminous in common air.
The proportion of foreign gas necessarily varies according to the nature
of the gas.
4. Certain other gases do not qualify oxygen to act upon phosphorus
at low temperatures, in whatever quantity they may be added to it.
This is the case with olefiant gas, and with azote obtained by the action
of a paste of sulphur and iron on common air. -
The first and third of these facts have been known for a long time;
the second was discovered by M. Bellani de Monza; and the fourth
appears to have been first observed by M. Thénard (Traité de Chimie,
t. i. p. 236, where the subject is treated at length).
In experimenting upon this subject, another curious fact was noticed.
The presence of a minute quantity of certain gases and vapours entirely
prevents the usual action of phosphorus upon the oxygen of common
air. Thus the slow combustion of phosphorus does not take place at
all, at the temp. of 66°, in mixtures of
Wolumes of air.
1 volume olefiant gas and e e e 450
1 ditto vapour of sulphuric ether and . e 150
1 ditto vapour of naphtha and . e . 1820
1 ditto vapour of oil of turpentine and . 4444
OBSERVATIONS ON THE OXIDATION OF PHOSPHORUS. 37
A stick of phosphorus was repeatedly left for upwards of twenty-
four hours over water in air containing only one four-hundredth part of
its bulk of pure olefiant gas, during the hot weather of July and August
1828, thermometer frequently above 70°, without diminishing the bulk
of the air in contact. A slight expansion, amounting sometimes to
+&oth part, occurred on Several occasions. A stick of phosphorus, with
a few drops of water, was corked up in a large retort, 213 cubic inches
in capacity, and containing common air, with which ºoth of its bulk of
pure olefiant gas had been mixed. During three months the phos-
phorus never became luminous, although its surface was gradually
covered with a thin white crust. The water present was found to have
become slightly acidulous.
The influence of a minute quantity of ether-vapour, in extinguishing
the combustion of phosphorus at low temperatures, may be exhibited
in a striking manner. Introduce two or three moist sticks of phos-
phorus into a pint-stoppered phial, into which, when filled with the
white fumes, pour a little ether-vapour from the ether bottle. In a few
seconds the fumes entirely disappear, and the air around the phosphorus
becomes perfectly transparent. If the bottle is now stopped, white
fumes do not again appear in it till the ether has passed entirely into
acetic acid by combining with oxygen, which requires a few days.
Phosphorus is not luminous in the dark in air slightly impregnated
with any other essential oil, as well as oil of turpentine. In an open
two-ounce phial, phosphorus will appear brightly luminous in the dark;
but the moment the phial is stopped with a cork, which has formerly
confined an essential oil, and still sensibly retains its odour, the light
begins to fade, and disappears entirely in a few seconds. The light
from phosphorus in air at 63" F. is extinguished by the addition of four
per cent. of chlorine gas, or twenty per cent. of sulphuretted hydrogen.
The vapour from strong alcohol of about 80° in temperature extinguishes
luminous phosphorus. But the vapours from camphor, Sulphur, iodine,
benzoic acid, carbonate of ammonia, iodide of carbon, do not produce
that effect—thermometer 67. Held in the mouth of a bottle contain-
ing strong muriatic acid, phosphorus appears to become more brilliant.
But this is not the case with nitric or nitrous acids, which sensibly
impair the light. The vapour from the liquor condensed in the vessels
of the Portable Oil Gas Company, and coal gas, protect phosphorus from
oxidation.
It is evident, from these experiments, that phosphorus cannot be
used to withdraw oxygen from gaseous mixtures containing olefiant gas,
or the different compounds of carbon and hydrogen allied to that gas.
It may be employed as a test of their presence even in very minute
quantity.
38 OBSERVATIONS ON THE OXIDATION OF PHOSPHORUS.
The influence of those gases in preventing the oxidation of phos-
phorus in air appears even at elevated temperatures. Phosphorus may
be melted and kept for any length of time at 212°, without alteration,
in air containing an equal volume of olefiant gas. In three parts air,
with two parts sulphuric ether, phosphorus became faintly and transi–
ently luminous in the dark at 215°—weak lambent flashes, which dis-
appeared entirely at 210°, and were repeatedly revived and extinguished
by alternately elevating and lowering the temperature between these
limits. A pretty strong combustion occurred at 240°. The following
table exhibits the temperature at which phosphorus first becomes
faintly luminous in the dark in air containing different gaseous
Substances:— * *
In 1 volume of air and 1 volume of olefiant gas, at . © 200°F.
3 22 2 ” vapour of ether, at . 215
I 11 52 1 * vapour of naphtha, . 170
166 55 1 » vapour of turpentine, at 186
The manner in which the influence of these gases is modified by
barometric pressure is the most curious part of the subject. The pro-
portion necessary to prevent combustion depends entirely upon the
Jensity of the gases. Thus, although less than one four-hundredth part
of olefiant gas prevents the combustion of phosphorus—barometer 29
inches—phosphorus has been observed in a luminous state, under the
pressure of half an inch mercury, in air containing so much as an equal
volume of that gas.
In the following table, the first column of fractions expresses the
largest proportion of olefiant gas, in a mixture of air and that gas,
which allows phosphorus to be luminous under the pressure placed
against it. A greater proportion, of olefiant gas extinguishes at that
pressure.

PHOSPHORUS LUMINOUS.
Proportion of Olefiant Gas. | Olefiant Gas + Air Barometric Pressure.
# 1. + 2 1:4 inches.
# 1 + 4 2-3
To 1 + 9 3.2
3%, 1 + 19 5.0
#5 1 + 29 10.3
z's 1 + 39 12.1
º, 1 + 49 16-5
ris 1 + 99 25.5
zºo 1 + 199 26-4
ZTB Ö 1 + 449 29:0
OBSERVATIONS ON THE OXIDATION OF PHOSPHORUS. 39
Thermometer at 70°. When phosphorus is luminous above the mer-
curial column in a barometer tube, at the greatest pressure possible
for a particular mixture, a slight inclination of the tube from its vertical
position, which has the effect of condensing the gas, extinguishes the
light; while, on bringing back the tube to its vertical position, the
phosphorus again becomes luminous.
The influence of other vapour on the oxidation of phosphorus, at
various pressures, did not present any material differences from that of
olefiant gas just detailed.
Naphtha and turpentine vapours appeared to lose their negative
influence very rapidly as the pressure was reduced.
Carburetted hydrogen of marshes impedes to a certain degree,
but does not altogether prevent, the oxidation of phosphorus. Its
effect vanishes over a mercurial column of a few inches, a circumstance
which will be attended to with advantage in removing, by means of
phosphorus, the Small portion of oxygen generally found in that gas.
The Sulphuret of phosphorus and phosphuretted hydrogen gas are
likewise protected from oxidation, to a certain extent, by olefiant gas,
sulphuric ether, etc., although less powerfully than phosphorus, in pro-
portion to their higher accendibility.
The oxidation of potassium appears likewise, from several com-
parative experiments, to be considerably retarded in dry air contain-
ing a fourth or fifth of its bulk of ether-vapour or olefiant gas,
particularly of the latter. A piece of potassium, about the size of a
pea, confined for a month in dry air, containing a fifth of its bulk of
olefiant gas, was merely covered by a thin coating of grey oxide; while
another piece of potassium, in similar circumstances, with the excep-
tion of the olefiant gas, was deeply penetrated with fissures of a kernel
white.
The interference of those gases in preventing the oxidation of phos-
phorus, etc., is probably allied to the influence of the same and several
other gases in preventing the accension of the explosive mixture of
oxygen and hydrogen by the electric spark, first observed by Sir H.
Davy (Essay on Flame), and since confirmed and investigated by Dr.
Henry (Phil. Trans, 1824), and Dr. Turner (Edin. Phil. Journal, vol. xi)
Olefiant gas was found to act most powerfully, half a volume preventing
the combustion of the explosive mixture, that is, defending the hydrogen
from oxidation; and here, as in the case of phosphorus, the olefiant gas
seemed to suspend the usual action between the supporter and com-
bustible, without undergoing any change itself. If the nature of this
(nfluence of olefiant gas is the same in both cases, it forms a singular
and interesting subject of inquiry, readily accessible in its most minute
details in the case of phosphorus.
40 NOTICE OF THE SINGULAR INFLATION OF A BLADDER.
VIII.
NOTICE OF THE SINGULAR INFLATION OF A BLADDER.
From Quart. Journ. of Science, ii. 1829, pp. 88, 89. [Schweigger, Journ. lvii.
(=Jahrb. xxvii.) 1829, pp. 227-229.]
IN the course of an investigation respecting the passage of mixed
gases through capillary openings, the following singular observation
was made.
A sound bladder with stopcock was filled about two-thirds with coal
gas, and the stopcock shut; the bladder was passed up in this flaccid
state into a bell-jar receiver, filled with carbonic acid gas, and standing
over water. The bladder was thus introduced into an atmosphere of
carbonic acid gas. In the course of twelve hours, instead of being in
the flaccid state in which it was left, the bladder was found distended
to the utmost, and on the very point of bursting, while most of the car-
bonic acid gas in the receiver had disappeared. The bladder actually
burst in the neck in withdrawing it from under the receiver. It was
found to contain 35 parts of carbonic acid gas by volume in 100. The
substance of the bladder was quite fresh to the Smell, and appeared to
have undergone no change. The carbonic acid gas, remaining without
in the bell-jar, had acquired a very little coal gas.
The conclusion is unavoidable, that the close bladder was inflated
by the insinuation of carbonic acid gas from without.
In a second experiment, a bladder containing rather less coal gas,
and similarly placed in an atmosphere of carbonic acid gas, being
fully inflated in fifteen hours, was found to have acquired 40 parts
in 100 of this latter gas. A small portion of coal gas left the bladder
as before. -
A, close bladder, half filled with common air, was fully inflated in
like manner in the course of twenty-four hours. The entrance of car-
bonic acid gas into the bladder depends, therefore, upon no peculiar
property of coal gas. The bladder, partially filled with coal gas, did
not expand at all in the same bell-jar containing common air or water
merely.
M. Dutrochet will probably view, in these experiments, the discovery
of endosmose acting upon aeriform matter, as he observed it to act upon
CHEMICAL OBSERVATIONS ON SPONGY PLATINUM. 41
bodies in the liquid state. Unaware of the speculations of that philo-
sopher at the time the experiments were made, I fabricated the follow-
ing theory to account for them, to which I am still disposed to adhere,
although it does not involve the new power.
The jar of carbonic acid gas standing over water, the bladder was
moist, and we know it to be porous. Between the air in the bladder
and the carbonic acid gas without, there existed capillary canals through
the substance of the bladder filled with water. The surface of water
at the outer extremity of these canals being exposed to carbonic acid, a
gas soluble in water would necessarily absorb it. But the gas in solu-
tion, when, permeating through a canal, it arrived at the surface of the
inner extremity, would rise, as necessarily, into the air in the bladder
and expand it. Nothing but the presence of carbonic acid gas within
could prevent the disengagement of that gas. The force by which
water is held in minute capillary tubes might retain that liquid in the
pores of the bladder, and enable it to act in the transit of the gas, even
after the pressure within the bladder had become considerable.
IX.
CHEMICAL OBSERVATIONS ON THE APPLICATION OF
SPONGY PLATINUM TO EUDIOMETRY.
From Quart. Journ. of Science, ii. 1829, pp. 354-359. [Erdm. Journ. Tech. Chem. viii.
1830, pp. 20-27.]
IN explaining the action of cold spongy platinum in disposing the
union of mixed oxygen and hydrogen gases, it seems necessary to Sup-
pose that hydrogen is really accendible at common temperatures, but
that its point of accension is unnaturally elevated in ordinary circum-
stances when it is not in contact with highly-divided matter, just as the
boiling point of water and other liquids is elevated in smooth glass
vessels. This view may be correct, although it only shifts the difficulty;
for we have still to explain why hydrogen, if so accendible, does not
take fire at superior temperatures when out of contact with minutely-
divided matter. But there is an apparent analogy between the circum-
stances of the suspension of the combustion in the one case, and of the
42 CHEMICAL OBSERVATIONS ON THE APPLICATION
ebullition in the other, on which the mind can rest with some satisfac-
tion.
Soon after the discovery of Doebereiner, it occurred to both Dr.
Henry and Dr. Turner to apply the principle to the analysis of mixed
gases. But they immediately found that hydrogen could not at all
times be withdrawn from a gaseous mixture by the action of Spongy
platinum, although the required addition of oxygen was made, as
the action of that substance was paralysed or entirely suspended
by the presence of certain gases in the mixture. The following
table of Dr. Henry's exhibits the sum of our information on this
subject.
“The first column exhibits the number of volumes of each gas
required to render one volume of an explosive mixture of hydrogen and
oxygen (in the usual proportion of two hydrogen to one oxygen) unin-
flammable by the discharge of a Leyden jar; while the second column
shows the number of volumes of each gas necessary, in some cases, to
render one volume of an explosive mixture insensible to the action of
the sponge, and in other cases indicates the number which may be added
without preventing immediate combination.
“In the first column, the numbers marked with an asterisk
were determined by Sir H. Davy: the remaining numbers in that
column, and the whole of the second, are derived from my own
experiments:—
One volume of explosive mixture was rendered in- Effect of adding the same gases to one
capable of being inflamed by electricity when volume of explosive mixture on the
mixed with action of the sponge.
f —A- -N /- –2– —y
About *8 vols. of hydrogen . ... not prevented by many vols.
22 6 , nitrogen . . ditto.
, *9 , oxygen . ... not prevented by 10 vols.
, *11 , nitrous oxide . ditto.
59 1.5 , cyanogen . ... prevented by 1 vol.
, *1 , carbonized hydr. not prevented by 10 vols.
, 4 , carbonic oxide . prevented by # vol.
, *0:5 , olefiant gas ... prevented by 1-5 vol.
, *2 , muriatic acid . not prevented by 6 vols.
, 2 , ammoniacal ... not prevented by 10 vols.
2, 3 s, carbonic acid . ditto.
From other observations of Dr. Henry, carbonic oxide appears to
retard the combustion of hydrogen, by taking the precedence of the
latter in uniting with oxygen, from superior inflammability. This I
found to be much more strikingly the case with sulphuretted hydrogen
OF SPONGY PLATINUM TO EUDIOMETRY. 43
gas, which Dr. Turner found to suspend the action of the sponge, when
present even in the most minute proportion. When mixed with oxygen,
this gas slowly disappeared under the influence of a dried clay pellet,
containing spongy platinum; the hydrogen only uniting with the oxygen,
and the sulphur being deposited in the ball, which was soon thereby
rendered inactive, but not, till it had destroyed two or three hundred
times its bulk of sulphuretted hydrogen in the course of twenty-four
hours. In a mixture of sulphuretted hydrogen, hydrogen and oxygen
gases in equal volumes, the oxygen united in twenty-four hours to the
hydrogen of the sulphuretted hydrogen, nearly to the entire exclusion
of the free hydrogen; but the union of the last with the remaining
oxygen was determined in a few seconds by throwing up a fresh
platinum ball.
Sulphurous acid gas is as efficient in this way as sulphuretted
hydrogen (Turner); yet, upon trial, the sponge had no effect in deter-
mining the union of oxygen and sulphurous acid, even with the presence
of moisture.
Olefiant gas in my hands was at first as powerful in preventing the
combustion of explosive mixture as it was found to be by both Henry
and Turner; but on washing that gas more sedulously with caustic
potash, its interference was found to depend on a trace of impurities, for
the ball always acted on explosive mixture within a few minutes, how-
ever largely diluted with this gas, if properly purified. Indeed, I had
frequent occasion to separate hydrogen from olefiant gas, and found
cold spongy platinum most effectual for the purpose. Neither did
sulphuric acid vapour retard the action of the platinum; indeed, the
other allowed the action to go on so rapidly, that from the elevation
of temperature it was itself slightly acted upon, carbonic acid always
appearing. The same was the case with the vapours of naphtha and
the essential oils.
The action of these gases here, therefore, is unlike the action of the
same gases and vapours in protecting phosphorus from oxidation.
The influence of sulphurous acid and sulphuretted hydrogen is not
impaired by diminishing the barometric pressure.
44 ON THE LAW OF THE DIFFUSION OF GASES.
X.
ON THE LAW OF THE DIFFUSION OF GASES."
From Phil. Mag. ii. 1833, pp. 175-190, 269-276, 351-358. [Poggend, Annal. xxviii.
1833, pp. 331-358; Edin. Roy. Soc. Trans. xii. 1834, pp. 222-258.]
IT is the object of this paper to establish with numerical exactness
the following law of the diffusion of gases:—
“The diffusion or spontaneous intermixture of two gases in contact.
is effected by an interchange in position of indefinitely minute volumes
of the gases, which volumes are not necessarily of equal magnitude,
being, in the case of each gas, inversely proportional to the Square root
of the density of that gas.”
These replacing volumes of the gases may be named equivalent
volumes of diffusion, and are as follows:—air, l; hydrogen, 3.7947;
carburetted hydrogen, 1.3414; water-vapour, 12649; nitrogen, 1:01.40;
oxygen, 0.9487; carbonic acid, 0-8091 ; chlorine, 0.6325, etc.—numbers
which are inversely proportional to the square roots of the densities of
these gases, being the reciprocals of the square roots of the densities, the
density of air being assumed as unity.
If the two gases are separated at the outset by a screen having aper-
tures of insensible magnitude, the interchange of “equivalent volumes
of diffusion” takes place through these apertures, being effected by a
force of the highest intensity; and if the gases are of unequal density,
there is a consequent accumulation on the side of the heavy gas, and
loss on the side of the light gas. In the case of air, for instance, on the
one side of the screen, and hydrogen gas on the other, a process of
exchanging 1 measure of air for 37947 measures of hydrogen, through
the apertures, is commenced, and continues till the gases on both sides
of the screen are in a state of uniform mixture. Experiments on this
principle can be made with ease and precision, as will appear in the
sequel, and afford an elegant demonstration of the law.
There is a singular observation of Doebereiner, which chemists seem
to have neglected as wholly inexplicable, on the escape of hydrogen gas
by a fissure or crack in glass-receivers, which belongs to this subject,
and from which I set out in the inquiry. Having occasion, while
engaged in his researches on spongy platinum, to collect large quantities
of hydrogen gas, he accidentally made use of a jar which had a slight
crack or fissure in it. He was surprised to find that the water of the
pneumatic trough rose into this jar one and a half inches in twelve
1 Read before the Royal Society of Edinburgh, Dec. 19, 1831, and now reprinted
from the Edin. Phil. Trans, with an Appendix communicated by the author.
ON THE LAW OF THE DIFFUSION OF GASES. 45
hours, and that, after twenty-four hours, the height of the water was
two inches two-thirds above the level of the water-trough. During
the experiment, neither the height of the barometer nor the temperature
of the place had sensibly altered. -
In other experiments, he substituted glass vessels of very different
forms, tubes, bell-jars, flasks, all of which had fissures. In every one
of these vessels, filled with hydrogen, the water rose, after some hours,
to a certain height. On covering one of these vessels, containing hydro-
gen, by a receiver—or on filling the vessel with atmospheric air, oxygen,
or azote, instead of hydrogen—he never observed a change in the original
volume of the gas. He thinks it probable that the phenomenon is due
to the capillary action of the fissure, and that the hydrogen only is
attracted by the fissures, and escapes through them on account of the
extreme smallness of its atoms."
This explanation is rendered improbable by the circumstance, that
hydrogen, of all the gases, was condensed and absorbed with greatest
difficulty, and in Smallest quantity, by charcoal and the other porous
substances, tried by Saussure. And we have no reason to suppose that
the particles of hydrogen are smaller than those of the other gases.
On repeating Doebereiner's experiment, and varying the circum-
stances, it appeared that hydrogen never escapes outwards by the fissure
without a certain proportion of air returning inwards. In the experi-
ment, however, as originally performed, it is evident, that, as soon as the
water rises in the jar above its outer level, air will begin to be forced
into the jar mechanically through the fissure, by the pressure of the
atmosphere, independently of what we shall suppose enters by diffusion.
But if we press down the jar of hydrogen to a certain depth in the
water-trough, so that the level of the water without is kept constantly
higher than the level of the water within the jar, then, on the contrary, a
portion of the hydrogen will be forced out mechanically by the pressure
to which the gas is subject. In the last circumstances, however, no air
can enter by the fissure, and mix with the hydrogen, except by diffu-
sion, or in exchange for hydrogen. Now, in a great number of experi-
ments of this kind, the air which entered by diffusion amounted to
between one-fifth and one-fourth of the hydrogen, which left the
receiver at the same time. But when the circumstances were reversed,
and the column of water allowed to rise in the jar above the level of
the water-trough, the quantity of air which entered by diffusion was
increased by a portion which entered mechanically; and varied from a
third to a fourth part of the hydrogen, which escaped at the same time.
The results, therefore, oscillate, as they should do, about our theoretical
“Sur l’Action capillaire des Fissures, etc.” Annales de Chimie et de Physique, t. 24,
pp. 332-334, 1823. -
46 ON TELE LAW OF THE DIFFUSION OF GASES.
number. One volume air should replace 37947 volumes hydrogen; or
the whole hydrogen, on escaping from the jar, should be replaced by
little more than one-fourth of its bulk of air, and a very great contrac-
tion ensue.
But it is unnecessary to detail experiments made with the jar with
the fissure, as with every precaution they were not precise, although at
all times compatible with, and indeed illustrative of, the law. Thus a
sensible contraction always took place in the bulk of the gaseous con-
tents of the jar when filled with carburetted hydrogen of marshes, or
with coal-gas, which, like hydrogen, are lighter than air, and ought
therefore to be replaced by less than equal volumes of air. With
olefiant gas and carbonic oxide, which approach closely to the density
of air, no contraction was perceptible, not attributable to other causes,
although the gases as usual wholly escaped. In the case of carbonic
acid, which is heavier than air, a slight, but positive, expansion appeared
to take place, the experiment being performed over mercury. w
But the same fissure or opening never allows the process of diffusion
to go on with the same degree of rapidity in two successive experiments,
principally, I believe, from its size changing with variations in its con-
dition in regard to humidity. The fissures appear to be extremely
minute, for we cannot cause either air or the gas employed to flow
through them mechanically, at the same rate as it passes by the agency
of diffusion, without the application of considerable pressure. Artificial
chinks, such as that obtained by pressing together ground glass-plates,
or in phials fitted with accurately ground glass-stoppers, allow gas to
pass through under the slightest pressure, and do not answer for the
experiment.
The effects were made much more striking, in some respects, by the
discovery that Wedgewood stoneware tubes, such as are used in furnace
experiments, admit from their porous structure, of being substituted,
instead of jars with fissures. When shut at one end, as they are some-
times made, they may be managed like other cylindrical gas receivers.
Those which are unglazed are most suitable; but do not answer the
purpose, if either very dry or too damp, being permeable by a gas under
the slightest pressure in the one case, and perfectly air-tight in the
other. The following experiment illustrates the force and rapidity with
which diffusion proceeds. A stoneware cylinder was entirely filled with
hydrogen gas over water, and transferred to the mercurial trough : in
forty minutes the mercury rose to a height of 2% inches in the receiver
above the level of the mercury in the trough; half of the hydrogen had
escaped, and had been replaced by about a third of its volume of air.
But these modes were superseded by the use of Paris-plaster as the
porous intermedium. -
ON THE LAW of THE DIFFUSION OF GASES. 47
A simple instrument, which I shall call a diffusion-tube, was con-
structed as follows. A glass-tube open at both ends was selected, half
an inch in diameter, and from six to fourteen inches in length. A
cylinder of wood, somewhat less in diameter, was introduced into the
tube, so as to occupy the whole of it, with the exception of about one-
fifth of an inch at one extremity, which space was filled with a paste of
Paris-plaster of the usual consistence for castes. In the course of a few
minutes the plaster set, and, withdrawing the wooden cylinder, the tube
formed a receiver closed with an immoveable plug of stucco. The less
water employed in slaking the Paris-plaster the more dense is the plug,
and the more suitable for the purpose. In the wet state the plug is
air-tight; it was therefore dried, either by exposure to the air for a day,
or by placing the instrument in a temperature of 200°F. for a few hours;
and thereafter was permeable by gases, even in the most humid atmos-
phere, if not positively wetted. The tube was finally graduated by
means of mercury into hundredths of a cubic inch, and the notation, as
is usual with gas-receivers, counted from the top. -
When such a diffusion-tube, six inches in length, was filled with
hydrogen over mercury, the diffusion, or exchange of air for hydrogen,
instantly commenced, through the minute pores of the stucco, and pro-
ceeded with so much force and rapidity, that within three minutes the
mercury attained a height in the receiver of upwards of two inches
above its level in the trough. Within twenty minutes the whole of the
hydrogen had escaped.
In conducting such experiments over water, it was necessary to
avoid wetting the plug. With this view, before filling
the diffusion-tube with hydrogen, the air was with-
drawn by placing the tube upon the short limb of an
empty syphon (see figure), which did not reach, but
came within half an inch of the plug, and then sinking
the instrument in the water-trough, so that the air
escaped by the syphon, with the exception of a small
measure, which was noted. The diffusion-tube was
then filled up, either entirely, or to a certain extent,
with the gas to be diffused.
The ascent of the water in the tube, when hydrogen
is diffused, forms a striking experiment. In a diffusion-
tube fourteen inches long, the water rises six or eight inches in as many
minutes. The column of water attains in a short time its maximum
height, at which, however, it is never long sustained; for, as in Doebe–
reiner's experiment, air is all along entering mechanically through the
porous plug, in such circumstances, from the pressure of the atmosphere;
and after the diffusion is over, the water subsides, in the course of

48 ON THE LAW OF THE DIFFUSION OF GASES.
several hours, to the general level. In experiments made with the
purpose of determining the proportion between the gas diffused and the
return-air, it was therefore necessary to guard against any inequality
of pressure, which was managed much more easily when the tube Was
standing over water than over mercury.
The capacity of a mass of stucco to absorb and condense in its pores
the various gases was made the subject of experiment, as this property
might interfere with the results of diffusion. The mass was previously
dried at 200°F. It absorbed at the temperature of the atmosphere,
which at the time was 78°.
6-5 volumes ammoniacal gas,
0-75 , sulphurous acid gas,
0.5 92 Cyanogen,
0.45 , sulphuretted hydrogen,
0-25 , carbonic acid.
Oxygen, hydrogen, nitrogen, carbonic oxide, olefiant gas, coal-gas were
not absorbed in a sensible proportion, even when the temperature was
58". It is evident, therefore, that the absorbent power which stucco
enjoys, as a porous substance, is inconsiderable. Placed in humid air,
the same mass of stucco absorbed 1% per cent. of hygrometric moisture.
In setting, 100 parts of the stucco had retained twenty-six parts water
uncombined, which escaped on drying at a moderate temperature, so as
to avoid decomposing the hydrated sulphate of lime. It can be shown
from this, that the vacuities must have amounted to one-third of the
volume of the mass.
I shall treat in succession of the escape of the different gases from a
diffusion instrument into air. As the contained gas bears no proportion
in quantity to the external air, the gas escapes entirely, and is wholly
replaced by air. It is of the utmost importance to determine the pro-
portion between the volume of gas diffused, and the replacing volume
of air eventually found in the instrument. We thus obtain the equiva-
lent diffusion-volume of the gas, which it will be convenient to state in
numbers with reference to the replacing volume of air as unity. I shall
begin with hydrogen gas, although attended with peculiar difficulties,
as it introduces in a distinct manner to our notice several circumstances
which may slightly modify the results of diffusion.
I. Diffusion-volume of Hydrogen Gas.
I shall in this paper adopt the specific gravities of the gases gene-
rally received in this country. Of hydrogen the specific gravity is
ON THE LAW OF THE DIFFUSION OF GASES. 49
0-0694 (air= 1), of which number the square root is 0.2635. Now,
according to our law, 1 volume hydrogen should be replaced by 0.2635
air. But to have the replacing volume of air= 1,
0.2635 : 1 : : 1 : 37947;
1 dº
Or, g-87947 ; that is, 1 air should replace 37947 hydrogen.
With the specific gravity of hydrogen adopted by Berzelius, namely,
0-06885, the equivalent diffusion-volume of hydrogen is 38149.
In a diffusion-tube standing over water, temperature 65°, 88 volumes
hydrogen were replaced by 26 air; 84 hydrogen by 25 air; and in
another tube, 130 hydrogen by 38 air. The quantity of return-air is
here related to the hydrogen diffused, as 1 to 3:38, 3:36, and 3:42, num-
bers which approach to, but fall short of, the theoretical diffusion-volume
of hydrogen, namely, 3-79. But the hydrogen in these experiments was
Saturated with vapour at 65°, which would make its density 0.0809, and
reduce its diffusion-volume to 3:5161; while the air without, being
comparatively dry, would be somewhat expanded after it entered the
diffusion-tube, by the ascent of vapour into it. This would occasion
the quantity of return-air to appear greater than it should be; but it
is difficult to find elements for a proper correction, as not only the
quantity of vapour in the atmosphere must be taken into account, but
also the hygrometric state of the plug itself. The increased return-
air, however, evidently lowers the diffusion-volume of the hydrogen
gaS.
With the view of increasing the capacity of the instrument, and the
number of its divisions, and of obviating the interference A
of vapour, the mode of performing the experiment was
varied. On a tube, four-tenths of an inch in diameter, a
bulb of two inches in diameter was blown, as in figures
A and B. The tube above and below the bulb, in the
case of A, was graduated into two-hundredths of a cubic
inch. The upper end of the tube was closed by stucco, as
in the case of the simple diffusion-tube. The general
mode of proceeding will be best conceived from the
recital of the details of a particular experiment.
The diffusion-instrument employed in the following experiment con-
tained 855 measures, and was of the form A. The stucco plug was
unusually large, being 0-6 inch in length, which occasioned the diffusion
to be slow. At the commencement of the experiment the thermo-
meter stood at 68°, and the barometer 29.73 inches. The bulb being
sunk in water with the air-syphon in it, the whole air was withdrawn,
with the exception of 12 measures, and the instrument filled up
D

B
50 ON THE LAW OF THE DIFFUSION OF GASES.
with newly made hydrogen gas. So that at the outset we had in the
instrument,
Air with its vapour, . e * > Q . 12.
Hydrogen, . g e ‘ • . . 823-83
Vapour (accompanying the hydrogen at 68%) 19:17
855.00
As soon as it was filled, it was placed in a glass-jar, of about the
same height, with a little water left in the bottom, and in proportion as
the water rose in the tube of A, from the subsequent contraction, the jar
was filled up by repeated additions of water, so as to keep the surface
of the water, within and without the tube, as nearly as possible at the
same level. With the view of having the external air in a constant
state in regard to humidity, means were taken to saturate it. A small
cone of damp paper was inverted, like an extinguisher, over the upper
part of the instrument; the jar containing the instrument was placed
on the shelf of the pneumatic trough, and a bell-jar with an opening at
the top, which could be shut at pleasure, inverted over the whole. The
return-air must therefore have been in the same state, in regard to
humidity, as the hydrogen itself. Aqueous vapour would diffuse neither
outwards nor inwards, as it existed in the same proportion on both sides
of the plug; but dry hydrogen only would be exchanged for dry air, in
the proportion of their equivalent diffusion-volumes.
In the first thirty-four minutes, the gaseous contents of the bulb
were diminished by 95 measures, and ultimately, in twenty-six and a
half hours, they were reduced to 227 measures, which were common air.
The contraction in this and other cases, in which the water rose into
the bulb, was determined by weighing, at the end of the experiment, the
water which had entered; a mode which admits of even greater nicety
than measuring the bulk of residuary gas in a graduated vessel.
With the view of obtaining elements for a correction for any change
in the bulk of the gas, which might take place during the continuance
of the experiment, from changes in temperature, pressure or
from solution of the gas in water, a receiver was made of the
same tube, with a bulb of nearly the same capacity as the dif-
fusion-instrument, but close at the top. This receiver was also
nearly filled at the commencement of the experiment with
hydrogen gas, and the quantity of gas noted, the tube being
graduated. The hydrogen in this standard receiver contracted ºnd part
during the experiment. We have therefore to increase the quantity of
air found ultimately in the diffusion-receiver by gºnd part. In this way
the residuary air is increased to 2298 measures, 12 of which, or, more
correctly, 11.85 (= 12–;(1 2)), were present from the beginning. -
ON THE LAW OF THE DIFFUSION OF GASES. 51
The temperature was also 68° at the end of the experiment, the same
as at the beginning. The ultimate contents of the diffusion-instrument
may be stated with sufficient accuracy as follows:—
Air and vapour originally present, ge tº 11.85
Dry air which has entered, & & . .212°84
Vapour in ditto, * > $º g * & 5'11
229'80
The conclusion is, that 823.83 measures dry hydrogen have been
replaced by 21284 dry air. Now,
823'83
212°84
The diffusion-volume of hydrogen comes out above the theoretical
number in this experiment, but an addition of not more than 2 per cent.
to the quantity of return-air would reduce it below the theoretical
number. The quantity of vapour which was supported by the hydrogen
at the commencement of the experiment was 19:17 measures, but at the
end of the experiment we find only 5'11 measures vapour; the difference
has condensed from the loss of a permanently elastic fluid necessary to
support it.
As the quantity of hydrogen and of return-air is amplified in the
same proportion by vapour, provided the temperature be the same at
the beginning and end of the experiment, it is unnecessary to know the
absolute quantity of vapour in either case in determining the diffusion-
volume of hydrogen. We may smply divide the gross amount of
hydrogen gas diffused by the gross amount of return-air; the quotient
is the diffusion-volume of hydrogen.
Ea:periment 2.—The thickness of the stucco-plug in the instrument
used above was reduced from six-tenths to two-tenths of an inch, by
cutting away the upper portion. The instrument, of the same capacity
as before, was now entirely filled with hydrogen gas. This was effected
by first filling up with hydrogen, leaving a small quantity of air in the
upper part of the instrument, as in the previous experiment, then with-
drawing this impure hydrogen by the air-syphon, and filling up a second
or third time with the same gas, whereupon the proportion of air remain-
ing ceased to be appreciable. The apertures of the plug were closed,
by pressing the finger upon its upper surface; and in this manner any
diffusion of the hydrogen was carefully guarded against till the process
of filling was completed. The diffusion was so rapid in the case of the
thin plug that this additional precaution was absolutely required. Care
was taken to have the return-air saturated with moisture in this and every
other experiment of the same kind, and inequality of pressure was avoided.
At the beginning of the experiment, the instrument contained 855
=387 = diffusion volume of hydrogen.
52 ON THE LAW OF THE DIFFUSION OF GASES.
measures hydrogen, saturated with vapour at 62°; in three minutes a
contraction of 95 measures took place, and in the course of an hour the
diffusion was sensibly at an end. The instrument, however, was exposed
for two hours longer, that the diffusion might certainly be complete.
During intervals so short, uniformity of temperature might be counted
upon, with certain precautions; and the variations in atmospheric pres-
sure were generally so minute, that they might be neglected with im-
punity. Corrections for temperature and pressure might therefore be
dispensed with, which was a great advantage. 855 measures hydrogen
were found eventually to be replaced by 226.5 measures air, both Satu-
rated with vapour at 62°.
855
226'5
is somewhat below the theoretical diffusion-volume, 3-79, while the
preceding determination was in excess.
Eageriment 3–Another diffusion-instrument of the form B, with
a dense plug, one-tenth of an inch in thickness, was filled with water,
which was then poured into a counterpoised phial, and found to weigh
1085-7 grains. When filled over water, 1085-7 grain-measures of gas
are therefore introduced into this instrument, and in this way we express
most correctly its capacity. The instrument, after the plug was dried,
was entirely filled with hydrogen gas, as in the preceding experiment,
thermometer 61°. The bulk of the diffusion appeared to be over in an
hour and a half, but five hours were allowed to the experiment. There-
after the water, which had entered the instrument, was poured into a
counterpoised phial, and found to weigh 800-6 grains. This last quan-
tity represents the contraction, and subtracting it from 10857, we have
the return-air equal to 285:1 grain measures. Now,
1085.7
285.1
Eaperiment 4.—Same bulb, circumstances the same, but thermo-
meter 62°. Time allowed for the diffusion four hours.
1085.7 measures hydrogen were replaced by 286.1 measures air.
1085.7
286' 1
Ea'periment 5–Same bulb, etc., thermometer 61°. Time five hours.
1085.7 measures hydrogen were replaced by 278.4 measures air.
1085.7
278°4.
Baperiment 6–Same bulb, but in this and the succeeding experi-
ment the bulb was attached to the end of a balance, and counterpoised,
so that it adjusted itself spontaneously in the jar filled with water, in
which it floated. Thermometer 60°.
= 3774 – diffusion-volume of hydrogen. This determination
=3-808 = diffusion-volume of hydrogen gas.
= 3-795 = diffusion-volume of hydrogen.
= 3900 = diffusion-volume of hydrogen.
ON THE LAW OF THE DIFFUSION OF GASES. 53
10857 measures hydrogen were replaced by 27.9:1 measures air.
1085.7
279-1
Baperiment 7–Same repeated. Thermometer 61°.
1085.7 measures hydrogen were replaced by 2822 measures air.
1085.7
282-2
The results of these five last experiments, with the same instruments,
are, in One view,
= 3890 = diffusion-volume of hydrogen.
=3-847 = diffusion-volume of hydrogen.

Measures of man Diffusion-volume of
Air. Hydrogen.
285.1 3-808
286-1 3-795
278-4 3'900
279-1 3-890
282-2 3-847
Mean, 282-2 Mean, 3.848
New hydrogen gas was made for each experiment by the moderate
action of dilute sulphuric acid on zinc, and it was collected in the diffu-
Sion-instrument from the beak of the retort. The observations could
not be made with so much accuracy as to entitle us to place any reliance
on more than two decimal places of the calculated diffusion-volumes.
A great variety of experiments were performed on the diffusion of
hydrogen with the diffusion-bulbs employed above, and several others
of similar construction, principally with the view of discovering the
cause of the slight variations in the results, and why the quantity of
return-air was pretty uniformly somewhat less than the theoretical
quantity, which has the effect of increasing the proportion of the
hydrogen diffusion-volume.
It appears that when the stucco-plug is in a parched state, the
Quantity of return-air is uniformly greater than it should be. Thus
3.65 and 3:69 were the diffusion-volumes of hydrogen deduced from an
experiment, in the one case with a plug which had been dried at 100°,
and subsequently exposed for several hours to the air, and in the other
case with a plug merely dried in air, temperature 68°. The obvious
cause of this is, that the air is dried in passing through the plug, and is
Subsequently expanded while in the diffusion-instrument by the ascent
of vapour into it. Hence, the first time a diffusion-bulb is tried, it
generally gives the diffusion-volume of hydrogen below the truth.
On the other hand, I apprehend that, when the pores of the stucco
54 º
ON THE LAW OF THE DIFFUSION OF GASES.
are saturated with hygrometric moisture, which, from the circumstances
of the experiments, must be almost always the case, the hydrogen, in
making its way through the plug, actually avails itself to a small
extent of this moisture, inducing it to vaporize, and exchanging places
with it instead of air. Hydrogen, which escapes in this way, will not
be represented by return-air, the quantity of which is thus diminished.
This process, however, is extremely intricate, and has not yet been fully
investigated. Its effect is insensible in the case of the other gases, of
which the diffusion-volumes approach more closely to that of air.
The more dense and compact the plaster-plug, the more correct
appear to be its general indications. On this account I compress the
plug, while moist, before it sets. When the plug is of a loose structure,
and probably contains sensible vacuities in its substance, diffusion goes
on with increased rapidity; but I have observed that the proportion of
return-air is notably diminished in the case of the diffusion of hydrogen.
Thus, in a set of experiments with a diffusion-bulb, having a plug of
this description, and little more than one-tenth of an inch in thickness,
I obtained, as the diffusion-volume of hydrogen, 4-05, 4'04, and 4:00.
This plug had been somewhat thicker at one time, and then gave 3.93
as the diffusion-volume of hydrogen. These experiments exhibit an
extreme case of this deviation. It appears to depend upon some
physical property of hydrogen gas which is peculiar to it. To obtain
light upon this subject, I was led to investigate the rate at which air,
hydrogen, and the other gases flow through the stucco-plug into a
vacuum under the influence of mechanical pressure.
A small bell-jar, with an opening at top, was used, which opening
was closed with a plug of Paris-plaster of half an inch in thickness,
over which a brass cap and stopcock were fitted and cemented. This
receiver was placed on the plate of an air-pump in perfect order, and
exhausted. When the stopcock of the receiver was closed, nothing
entered the exhausted receiver; but on opening it, either air entered,
forcing its way through the pores of the stucco, or any gas which might
be conducted to it, by means of a flexible tube from a proper magazine.
The time was noted in which the mercury of the gauge-barometer,
in communication with the receiver, fell two inches, always setting out
with gas of the tension of one inch mercury in the receiver, and stop-
ping exactly when it attained a tension of three inches.
Air entered, according to eight or ten experiments made on different
days, in within ten seconds, Imore or less, of ten minutes, and so whether
the air was Saturated with aqueous vapour or dry.
The same volume of different gases entered in the times expressed
in the following table, under the same pressure, or beginning at a pres-
sure of 29 inches mercury, and terminating with a pressure of 27
inches:—
ON THE LAW OF THE DIFFUSION OF GASES. 55
Minutes. Seconds.
Air, dry, . * tº e wº - 10 0
Air, saturated with moisture at 60°, . 10 0
Carbonic acid, . © g * ... 10 0
Nitrogen, . & º i.e. º . 10 O
Oxygen, . tº tº ſº e . 10 0
Carbonic oxide, . wº * ſº . 9 30
Olefiant Gas, tº te * e ... 7 50
Coal Gas, e * cº tº ... 7 O
Hydrogen, 4 0
In repetitions of the experiments, the numbers oscillated 10, or 12,
sometimes 20 seconds, on either side of the numbers given in the table,
from circumstances which could not easily be appreciated. As the mer-
cury in the gauge fell not continuously, but by leaps, from adhesion to
the glass, the experiments are not susceptible of the greatest accuracy.
The greater the pressure the more rapidly are gases forced through
the pores of the plug; but the quantity of gas which penetrates in any
given time is not exactly proportional to the pressure, at least in the case
of air and hydrogen. By doubling the pressure, we do not quite so much
as double the quantity of gas forced through ; or a fixed quantity of gas
does not enter in half time under double pressure, as will be evident from
the following table of observations. Pressure of atmosphere 30 inches.

Height of Gauge AIR. HYDROGEN.
Barometer in Inches of Interval of Time in falling | Interval of Time in falling
Mercury or Pressure. one inch by Gauge. one inch by Gauge.
Minutes. Seconds. Minutes. Seconds.
29 O 0 O O
28 5 O I 50
27 5 23 2 0
26 5 15 1 55
25 5 30 1 55
24 5 35 2 O
23 5 45 2 2
22 6 0. 2 13
21 6 5 2 10
20 6 30 2 35
19 6 35 2 30
I 8 7 3 2 40
17 7 12 2 50
I 6 7 35 $ 10
15 8 10 3 30
l4 8 40 3 35
13 9 10 4 5
12 9 S5 4 10
| 1 11 O 4 15
10 11 40 4 30
9 12 30 5 20
8 14 15 7 40
56 ON THE LAW OF THE DIFFUSION OF GASES.
The ratio of the times, in hydrogen and air, is not greatly different
at different pressures. Thus the mercurial column was depressed 18
inches, or from 29 to 11 inches.
By air, in 7283 seconds,
By hydrogen, in 3025 seconds,
348 tº
4.- 2:408 =ratio of hydrogen,
1 = rate of air.
It was found that the kind of gas in the receiver made no difference
on the velocity with which hydrogen entered under a certain pressure.
Hydrogen entered as rapidly against hydrogen in the receiver of a cer-
tain tension, as against air of the same tension. Thus,

Hydrogen entered
against Hydrogen.
(From preceding Table.)
Hydrogen entered
Barometer Gauge. against Air.
Height.
Time. Time.
Inches. Min. Sec. Min. Sec.
15 0 0 0 O
14 3 37 3 35
13 3 56 4. 5
It is evident from this, that the air does not diffuse out against So
strong a pressure and the inward current of hydrogen.
When this jar, of which the capacity was 65 cubic inches, was used
as a diffusion-instrument, and filled over water with hydrogen, one-
fourth of the hydrogen which it contained escaped by diffusion into air
in the first hour. Now, we find by the table (p. 55), that hydrogen
penetrates the plug with greater velocity when passing into a vacuum
or into the exhausted receiver. The exhausted receiver was filled one-
fourth in about fifteen minutes; hence a certain quantity of hydrogen
passed through the same porous plug, by the pressure of the atmosphere,
into a vacuum in fifteen minutes; by spontaneous diffusion into air in
sixty minutes; or the velocity of diffusion was one-fourth the velocity
of mechanical pressure.
This was a dense and excellent plug; and in others of a looser
texture, the velocity of diffusion was much less than a fourth.
Dried bladder answers for showing the diffusion of hydrogen when
stretched over the open end of the tube receiver. The diffusion, how-
ever, through a single thickness of bladder, is effected at least twenty
times more slowly than through a thickness of one inch of stucco.
While, on the other hand, either air or hydrogen, under mechanical
pressure, passes more readily through bladder than a great thickness
of stucco. Goldbeaters' skin is even more permeable by gases under a
slight pressure than bladder, and less suitable for diffusion.
ON THE LAW OF THE DIFFUSION OF GASES. 57
The superior aptitude of stucco for exhibiting the unequal diffusion
of gases of different densities, seems to depend upon its pores being
excessively numerous, but exceedingly minute, making in the aggregate
a considerable channel. In the bladder, or goldbeaters' skin, the pores
I suppose to be few in number but wide, making, however, when added
together, but a small channel. Air passes through them but little
impeded by friction. t *
Dry and sound cork answers exceedingly well as a substitute for the
stucco-plug. The diffusion takes place slowly, but is not apt to be
deranged by a slight mechanical pressure. So do thin laminae of many
granular minerals, such as the flexible magnesian limestone, etc.; char-
coal also, and woods, if not too porous, may be applied to the purpose.
It might occur, in explanation of our experiments with the diffusion-
instrument, to take Mr. Dalton's hypothesis, and suppose, in the case of
hydrogen, the external air to be a vacuum to the hydrogen, and the
hydrogen a vacuum to the air, and that the inequality of the diffusion
depends upon the hydrogen being least resisted in passing through the
plug. The experiments on the permeability of the stucco by gases
under pressure, above detailed, were projected with a view to settle this
point among others; and they are evidently incompatible with such an
application of the theory, for hydrogen passes 2:4 times more swiftly,
and not 3-8 times, as in the diffusion experiments. Carbonic acid, too,
permeates the plug, under pressure, as rapidly as air does, or even some-
what more rapidly, for our results inclined to this side rather than to
the other; whereas carbonic acid diffuses through the plug more slowly
than air does, or is replaced by more than an equal volume of air, as
will presently appear.
Those experiments, previously narrated, are perhaps sufficient to
establish the law in regard to hydrogen, particularly when we find it
hold in the case of other gases.
As hydrogen is a very light gas, I was anxious to establish the law
also in regard to a heavy gas, such as carbonic acid.
II. Diffusion of Carbonic Acid Gas.
The most satisfactory experiments with carbonic acid gas were per-
formed by confining it over a solution of common salt, Saturated in the
cold, which absorbs this gas very slowly, and, instead of the diffusion-
instrument with bulb, a long diffusion-tube was found most suitable.
Experiment 1.—Thermometer 64 : dew-point 53°. Barometer 30:13.
Left in diffusion-tube 17 air, and filled up over brine to 197 with carbonic
acid gas, which gives 180 carbonic acid. As brine boils at 222° or 224°,
that is 11° or 12” above the boiling point of water, we may suppose it
58 ON THE LAW OF THE DIFFUSION OF GASES.
to be proportionally less vaporous at low temperatures, and take the
tension of its vapour at 64° to be that of water at 53°, which was also
the dew-point. This was confirmed by confining 847 volumes of atmos-
pheric air over brine at the time; the air was not expanded by vapour
rising into it from the brine, nor did it contract.
The initial contents of the diffusion are therefore,
Air and vapour, . * tº tº 17.
Carbonic acid gas, ſº ſº . 177-6
Vapour, tº dº º º e 2-4
197:0
An expansion took place of 4 measures in ten minutes, and of 40
measures in five hours. A standard tube of the same diameter as the
diffusion-tube, sealed at the top, had been filled with carbonic acid and
placed over brine, to mark the absorption of the gas. One measure of
gas was absorbed during the continuance of the above experiment. The
expansion, therefore, in the diffusion-case has really been 41 and not 40,
or, probably even more than 41, as undoubtedly a greater absorption of
gas by the brine occurred in the diffusion-tube than in the standard-tube,
from the motion of the liquid in the former during the course of the
expansion of its gaseous contents, while the liquid in the other was
quite at rest, and 1776–1, or 1766 carbonic acid gas only have been
exposed to diffusion. The diffusion was allowed to take place into the
open air, which had the same proportion of vapour as the carbonic acid.
The specific gravity of carbonic acid gas is 1:527, of which the square
root is 1:2360, and the reciprocal of the square root 0-8091. Hence one
volume air should replace 08091 carbonic acid gas, which is the theo-
retical diffusion-volume of this gas.
In the experiment, 1766 carbonic acid are replaced by 217.6 air.
Here, the expansion upon 1766 carbonic acid being replaced by air
is 41 + parts by experiment, while it is 41.68 parts by theory.
The diffusion-volume of carbonic acid gas is,
0-812 by experiment,
0.809 by theory.
Eageriment 2–In another experiment, conducted in the same
manner, thermometer 64", barometer 30:00, the initial contents of the
diffusion-tube were,
Carbonic acid and vapour, 201.
The final contents,
Air and vapour, gº 245.
Correcting for loss of gas by absorption, the final contents would be,
Air and vapour, º 246.
As the proportion of vapour in the gas at the first, and in the air
ON THE LAW OF THE DIFFUSION OF GASES. 59
finally is the same, we may say that carbonic acid is replaced by air in
the proportion of 201 to 246.
201 is zºº & tº ſº
246 T 0-813 = diffusion-volume of carbonic acid.
O
Eageriment 3.—In a third experiment over brine, thermometer 62°,
barometer 29'65, carbonic acid and vapour, e 4. 169
Replaced by air and vapour, . © e ſº 205
Or, allowing for absorption, by air and vapour, . 206
169 º es e
206 Tº 0-816 = diffusion-volume of carbonic acid.
But extreme accuracy is quite out of the question in the case of
carbonic acid, from the vagueness of the small correction for absorption
of the gas by the brine, and from the absorbent action of the plug, which
affects, more or less, all the condensible gases.
The experiment in the case of this gas had been performed repeatedly
over water itself, in different diffusion-tubes, and always with an even-
tual increase to the gaseous contents of the tube of within 2 per cent. of
the theoretical quantity; but this mode, and the corrections for absorp-
tion, are decidedly inferior in precision to the preceding.
3. Chlorine.—This gas, from its high density, should afford a good
illustration of the law, were other circumstances equally favourable, as
the specific gravity of chlorine is about 2:5, of which the square root is
1-5811, and the reciprocal of the square root 0.6325. 100 measures of
chlorine should be replaced by 158'11 air; or 1 air should replace 0.6325
chlorine, which is its diffusion-volume.
Ea'periment—Thermometer 64". To a diffusion-tube over water,
with 5 measures air, 80 chlorine gas were added, making together 85
measures, which, diffusing into damp air, expanded 3 measures in the
first eight minutes, 18 measures in eighty-two minutes, and, finally, 19
measures in one hundred and six minutes; but the same gas, in a close
standard tube of the same diameter, contracted, owing to absorption of
the gas by water, 5 measures in eight minutes, 15 measures in thirty-
three minutes, and 18 measures in thirty-nine minutes, the rate of
absorption diminishing evidently from the water in the tube becoming
saturated and abiding in it. But the absorption of gas by water in the
two experiments cannot be well compared; for, in the diffusion experi-
ment, the chlorine is rapidly diluted with return-air, which protects it
from absorption, and, indeed, before the end of the experiment, must
occasion a portion of the dissolved chlorine gas to reassume the gaseous
form, vaporizing away from the water which held it in solution, and
rising into the upper part of the tube. The absorption in the diffusion-
case would certainly be overrated at one-half of what occurred in the
comparative experiment in the same time. At the outset, however, we
60 ON THE LAW OF THE DIFFUSION OF GASES.
may presume that the same absorption took place in both cases. Hence
the expansion in the diffusion experiment would be 3 + 5, or 8 measures
to the first eight minutes. The absorption, however, would tell two
ways in lessening the expansion; first, so much gas has disappeared by
absorption, the quantity to be added to the expansion; Second, so much
less chlorine has really been submitted to diffusion; 80 parts have not
been diffused, but 80 diminished by this quantity.
Merely adding the observed absorption in the first thirty-nine
minutes, namely, 18 measures to the expansion observed of 19 measures,
we have an expansion from diffusion of 37 measures, which approaches,
as near as we can expect from the method, to 45 measures, the theoreti-
cal expansion on 78 measures dry chlorine. We may therefore presume
that the diffusion of chlorine is not incompatible with the law.
4. Sulphurous Acid Gas—Over mercury. To diffusion-tube with 7
measures air, 66 dry sulphurous acid gas were added, which were allowed
to diffuse into dry air. An expansion occurred of
5 measures in 9 minutes,
13 25 23 ,
30 25 85 ,
31 , 108 ,
at which last expansion it remained steady.
Assuming the specific gravity of Sulphurous gas at 2:222, its square
root is 1:4907, of which the reciprocal is 0-6708.
67-08 sulphurous gas should be replaced by 100 air.
We have 66 sulphurous gas, and expansion 31, or,
66 sulphurous acid are replaced by 97.00 air, by experiment;
66 35 25 35 98.39 air, by theory.
The diffusion-volume of sulphurous acid gas is,
0-68 by experiment,
0.67 by theory.
5. Protozide of Nitrogen.—In an experiment with this gas, dry, over
mercury, allowing for a quantity of nitrogen which it contained, 51
measures were replaced in ninety minutes by 62 dry air. Taking the
specific gravity of this gas at 1:2577, its root is 1:2360, of which the
reciprocal is 0-8091.
Diffusion-volume 0-82 by experiment,
55 , 0.81 by theory.
6. Cyanogen.—Also over mercury. First deprived of hydrocyanic
acid by peroxide of mercury, and dried, an expansion always resulted
from diffusion, but it never amounted to the theoretical quantity. Taking
18105 as the specific gravity of cyanogen, the square root is 1:3456, and
the reciprocal of the square root 0-7432. N
Hence, 1 cyanogen is replaced by 1:3456 air; and }
1 air replaces, 0-7432 cyanogen.
ON THE LAW OF THE DIFFUSION OF GASES. 61
1st, 83 cyanogen were replaced by 99% air; 2nd, 75 cyanogen by
90 air; 3d, 50 cyanogen by 63 air. The last experiment is the most
favourable. But 100 cyanogen are replaced, according to that experi-
ment, by 126 air only, instead of 134. This deviation from the law
depends on the property of the plaster-plug, which it shares with all
porous bodies, to absorb and condense a portion of all those gases which,
like cyanogen, are easily liquefied. It is evident, that if a portion of the
cyanogen is withdrawn in this way, a certain contraction is occasioned,
and again really less of the gas is submitted to diffusion; and from both
causes, the expansion is less than it ought to be. It is possible, also,
that the cyanogen may have contained a little nitrogen.
7. Muriatic Acid Gas.-Specific gravity 128472; square root, 1-1334;
reciprocal of square root 0.8823. Hence,
1 muriatic acid should be replaced by 12847 air; and
1 air should replace 08823 muriatic acid.
In the case of this gas, the expansion from diffusion was overpowered
by the absorbent property of the plug.
94 measures contracted to 88 in ten minutes, and remained at that
quantity for nine minutes, and then expanded to 90 measures in twenty-
five minutes more. The plug, upon a subsequent examination, appeared
to be injured, and rendered too permeable, by a chemical action of the
muriatic acid upon the hydrated sulphate of lime.
8. Ammoniacal Gas. – Density 0-5902. Square root 0.76825;
reciprocal of square root 1:3016. Hence,
1 ammoniacal gas should be replaced by 0.76825 air; and
1 air should replace 1:3016 ammoniacal gas.
But in the case of this gas, as with muriatic acid, the result of diffu-
sion is altogether deranged by condensation of gas in the porous plug,
which, in these experiments, was half an inch in thickness. It is
remarkable, however, that when the tube was filled with ammoniacal
gas in the usual way, the final contraction was by no means excessive,
indeed, never quite so great as it should have been from diffusion alone,
independently of the contraction from absorption. This was found
to arise from the absorption by the plug being so rapid, that, during
the progress of filling the tube with gas, the plug became nearly
saturated with gas, taking up ten or twelve times its bulk, and con-
sequently, a great deal more gas was introduced into the tube than its
capacity. t
9. Sulphuretted Hydrogen Gas—Prepared from sulphuret of anti-
mony, by the action of muriatic acid. Density, 1-1805. Root, 1.0855.
Reciprocal of root, 0.9204.
In the case of this gas, 69 measures were replaced by 73 air. In this
experiment, 100 air replaced 95 instead of 92 sulphuretted hydrogen.
62 ON THE LAW OF THE DIFFUSION OF GASES.
But we may refer the diminution to the absorption of the gas by the
plug, and to its partial decomposition, as the mercury exposed to the gas
became black. The air which entered contributed to this decomposi-
tion.
As carbonic acid is one of the gases condensed by the plug, like the
preceding examples, but to a less extent, we can now understand why
the return-air was always a little under the theoretical quantity, in the
careful experiments on that gas, of which an account was formerly
given.
In the case of the gases which follow, the specific gravity approaches
so closely to that of air, that their accordance with the law requires
every precaution.
10. Oaxygen Gas—Specific gravity, 1111. Square root, 10541.
Reciprocal, 0.9487.
100 oxygen should be replaced by 105:41 air; and
100 air should replace 94.87 oxygen.
When confined in a straight diffusion-tube, there is uniformly an
expansion; but it is unnecessary to recount experiments performed with
the straight tube, as the divisions are not minute.
Eageriment 1.—Thermometer 64". Barometer 29.82 inches. Diffu-
sion-instrument with bulb, divided into two hundredths of a cubic inch ;
also standard bulb and tube, close at top, to afford corrections for
changes in temperature and pressure, as before explained. . Both diffu-
sion-instrument and standard were filled with pure oxygen from chlorate
of potash, and placed in glasses over water, covered by a bell-jar, of
which the inside was moistened. A few minutes were purposely allowed
to elapse before the quantity of gas in either instrument was noted, as
the quantity Oscillated for a little. The diffusion-instrument contained
7.95 measures oxygen, and the standard 828 at the outset. In two hours
the expansion in diffusion-instrument, corrected from the standard, was
6 measures; in four hours and a half, 13 measures; in fifteen hours, 29
measures; in twenty hours, 34 measures; in twenty-nine hours, 41
measures; in thirty-eight hours, the expansion was at a maximum,
namely, 43 measures. In explanation of the long duration of this and
the following experiments, it may be stated, that the plug was fully half
an inch in thickness.
795 measures oxygen and vapour have therefore been replaced by
838 measures air and vapour.
795 tº zºº &
8387 0.9487 = diffusion-volume of oxygen by experiment.
This is the exact theoretic number; a coincidence, however, which
we must view as accidental.
Ea'periment 2. In a careful repetition of this experiment with another
ON THE LAW OF THE DIFFUSION OF GASES. 63
Specimen of oxygen gas, the results approached very closely to the ple-
ceding; but the return-air was in slight excess above the theoretical
quantity. Thus,
1 oxygen was replaced by 1.056 air, by experiment.
I 29 52 1054 air, by theory.
Oxygen, therefore, affords a most striking confirmation of the law.
11. Nitrogen.—Prepared by burning an excess of phosphorus in a
confined portion of air, and allowing the residuary gas to stand over
water for several days.
Specific gravity, 0-9722. Root, 0.9860. Reciprocal of root, 1-0140.
100 nitrogen should be replaced by 98-60; and 100 air should replace
101'40 nitrogen.
Thermometer 66°. Barometer 29:23. Diffusion into moist air as
in the preceding experiments.
836 measures contracted 3 measures in two hours and forty minutes,
as corrected by standard ; and 13 measures in eighteen hours, which
was the maximum contraction; for in twenty-three hours and a half
from the beginning of experiment, a contraction of 12 measures was
indicated. Taking the last as the true result,
836 & º
8347 1.0143 = diffusion-volume of nitrogen by experiment.
1-0140 = diffusion-volume of nitrogen by theory.
12. Olefiant Gas—Specific gravity likewise 0-972, etc., as in nitro-
gen. The gas was carefully made, collected in a low receiver, allowed
to stand over water for twenty-four hours, and finally washed with
caustic ley.
Thermometer 59°. Barometer 29.83. 800 measures of this gas
were replaced by 785 measures of air, in twenty-five hours, correcting
from standard.
80 e º
800 = 1.0191 = diffusion-volume of olefiant gas, by experiment.
785
The contraction in this experiment is a little above the theoretical
quantity. In another experiment with different gas, the contraction
was even greater, indicating a diffusion-volume = 1.0303; but the pre-
sence of a minute quantity of carburetted hydrogen, or Some lighter
hydro-carburet, was suspected, from the rapidity of the contraction in
this case.
13. Carbonic Oaside.—Specific gravity, 0-9722, etc., as in the case of
nitrogen. Gas prepared by the action of sulphuric acid on crystallized
oxalic acid, well washed with caustic ley.
On 803 measures carbonic oxide and vapour, a contraction of 11
measures in fifty hours, 12 measures in eighty-nine hours, 12 measures
in ninety-seven hours; or 803 became 791. The diffusion was slower
64 ON THE LAW OF THE DIFFUSION OF GASES.
than usual, from the plug having been partially wetted in filling the
instrument with gas.
815
803– 10149 = diffusion-volume of carbonic oxide, by experiment.
1-0140 = diffusion-volume of carbonic oxide, by theory.
In the case of the last three gases, when the experiment was per-
formed over water in a diffusion-tube, with free exposure to the dry
atmosphere, instead of any contraction ensuing, a positive expansion
generally occurred, which was to be attributed to the return air, which
was comparatively dry, being expanded after entering the receiver.
14. Carburetted Hydrogen of Marshes.—Specific gravity, 0-555.
Diffusion-volume, 13414.
In an experiment with this gas, deducting a small quantity of air
which it contained, 252 measures were replaced by 187 air.
252
187 = 1.344 = diffusion-volume, by experiment.
1.341 = diffusion-volume, by theory.
These are all the permanent gases which could conveniently be
submitted to diffusion. Vapours cannot be rigidly examined, as they
are all condensible in the pores of the stucco. The following Table
exhibits a summary of the results:—
Table of Equivalent Diffusion-volumes of Gases; Air = 1.

By Experiment. By Theory. Spec. Gravity.
Hydrogen, . . . . . . . 3-83 3-7947 0-694
Carburetted Hydrogen, . . . 1-344 1°3414 0°555
Olefiant Gas, • e º e - 1-019.1 1-0140 0-972
Carbonic Oxide, . . . . . 1:01.49 1-0140 0.972
Nitrogen, . . . . . . . 1.0143 1-0140 0-972
Oxygen, . . . . . . . . 0-9487 0-9487 0-111
Sulphuretted Hydrogen, . . 0.95 0-9204 I'l 805
Protoxide of Nitrogen, . . . 0-82 0-8091 I-527
Carbonic Acid, . . . . . O'812 0-8091 1.527
Sulphurous Acid, . . . . . 0-68 0-6708 2-222
In the diffusion-volumes of oxygen, nitrogen, and carbonic oxide,
the correspondence between theory and experiment is as close as could
be desired. Indeed, admitting our law, I believe that the specific gravity
of these gases can be determined by experiments on the principle of
diffusion, with greater accuracy than by the ordinary means. But, to
be of value, experiments performed with this important object in view,
would require to be conducted with extreme care, in the most favourable
circumstances, as regards uniformity of temperature, and to be frequently
repeated. The diffusion-bulbs might also be considerably increased in
ON THE LAW OF THE DIFFUSION OF GASES. 65
size, and a greater minuteness of observation attained. Even in the
most successful experiments recited in this paper, we cannot depend
upon the absolute accuracy of the third decimal figure. In the case of
carbonic acid gas, protoxide of nitrogen, Sulphuretted hydrogen, and
sulphurous acid, the process of diffusion is interfered with in a greater
or lesser degree by the absorbent action which all porous bodies exer-
cise upon gases. Fortunately, however, the absorbent power of stucco
is very low in degree.
The density of any gas diffused into air, both being in the same state
as to aqueous vapour, is obtained by the formula
..)
D =(#).
where G is the volume of gas submitted to diffusion, and A the volume
of return-air. In operating upon gases lighter than air, the most useful
instrument is a bulb of about two inches in diameter blown upon half-
inch tube, of which about an inch may be left on either side of the bulb.
The capacity of the instrument, used as a gas-receiver over water, is most
simply determined by filling it with water, and weighing the water
which it contains, and which can be poured from it into a counterpoised
phial. Then, after any experiment, the return-air may be found from
the weight of the water which has entered the instrument, determined
in the same manner. By proceeding in this way, we avoid wetting the
stucco after every experiment. A hood of damp paper may be inverted
over the upper tube while the diffusion is going on, and the whole
counterpoised in a tumbler of water, being suspended from one of the
arms of the beam of a balance, the scale on that side being removed.
An experiment with the bulb will generally occupy several hours. But
with a plain diffusion-tube, a much shorter time will suffice.
A peculiar advantage of this mode of taking the specific gravity of
gases, besides its simplicity, is, that we can operate upon a most minute
quantity of gas: it is possible to come within 100th of the specific
gravity, operating upon no more than one cubic inch of gas.
It is to be regretted that this method is not so fully available in the
case of coal-gas as might be expected. The density of that gaseous
mixture appears to depend, in no inconsiderable measure, upon the
presence of a small quantity of the heavier hydro-carburets, such as
naphtha-vapour; and these are apt to be absorbed and withdrawn in
part by the water during the continuance of a diffusion experiment. I
have observed coal-gas to contract tºoth of its bulk by standing over
water, without agitation, for forty-eight hours, and from the loss of the
denser portion of it. But in the case of this gas, the experiment should
succeed over brine, which absorbs much less of the gas than water
does.
E
66 ON THE LAW OF THE DIFFUSION OF GASES.
The process of diffusion may be managed so as to demonstrate
relations in density. The short upper tubes of two diffusion-bulbs,
not closed by plaster, but open, were connected by means of thick
caoutchouc adopters, with the two ends of a short piece of straight tube,
in which there was a diaphragm of plaster #th of an inch in thickness,
and equidistant from either end of the tube. The apparatus being
proved air-tight, and the plug in a proper condition for diffusion, one of
the diffusion-bulbs was filled with nitrogen gas, and the other with
carbonic oxide, and the bulbs placed upright in separate contiguous
glasses containing water. The quantity of gas in each was carefully
observed at the beginning of the experiment; and after the expiry of
twenty-four hours, when it was found to be identically the same as at
first ; at least, if a contraction or expansion took place, it was the same
in both bulbs, and therefore entirely due to changes in temperature or .
pressure. Now, the gases were found by analysis to be uniformly dif-
fused through both bulbs; so that nitrogen and carbonic oxide are of
the same density, or at least do not differ more than #6th part, which
was the limit of the observation in the case of these experiments. It
appears, also, that inequality of density is not an essential requisite in
diffusion.
I had occasion to remark, more than once, a singular accident to the
stucco plugs. After being disused for some days or weeks, and left in
the interval exposed to the air, which might be either dry or damp at
the time, the plugs occasionally, on a new trial, did not permit diffusion
to take place through their pores, at least immediately. Hydrogen,
however, always opened a passage in the course of two or three
minutes, and then the diffusion proceeded as rapidly as ever. Carbu-
retted hydrogen, and the other gases, often required a longer period.
A slight heat restored the action of the plug. The obstruction could
not be attributed to moisture, nor to anything but dust. .
It may be mentioned that there was nothing peculiar in a mixture
of two gases in the proportion of the numbers expressing their diffusion-
volumes;–nothing that could be considered an indication of mutual
Saturation. •
Evaporation, or the elevation of vapour from a liquid into air, or
any other gas, comes now to be explained on the principles of diffusion.
The powerful disposition of the particles of different gaseous bodies to
exchange positions may as effectually induce the first separation of
vapour from the Surface of the liquid, as a vacuum would do. Once
elevated, the vapour will be propagated to any distance by exchanging
positions with a train of particles of air, according to the law of diffusion.
The length to which this diffusion proceeds, in a confined portion of air,
is limited by a property of vapour, namely, that the particles of any
oN THE LAW OF THE DIFFUSION of GASEs. 67
vapour condense when they approximate within a certain distance.
Hence, the quantity of vapour which rises into air has the same limit
as that which rises into a vacuum, and is the same.
I may be allowed to mention an application of the law of dif-
fusion, in explanation of the mechanism of respiration. The cavity
into which air enters during respiration consists, first, of a large tube,
the windpipe ; secondly, of Smaller tubes, into which the windpipe
diverges; and, thirdly, of a series of still smaller tubes, diverging
from the last, themselves ramifying to an indeterminate extent, till
at last the tubes cease to be of sensible magnitude, but are believed
to terminate in shut sacs. The capacity of the whole cavity cannot
easily be determined, but we may estimate it at 300 cubic inches.
In a natural expiration, about 20 cubic inches, or Hºth of the con-
tents, are thrown out from the application of a general pressure to
the whole. But it is evident that these twenty cubic inches will be
the twenty cubic inches nearest the outlet, or the contents of the larger
tubes. The contents of the second-sized tubes will advance at the
same time into the largest tubes, but no further, and will recede again
into their original depositories on the next inspiration, which will fill
the larger tubes with fresh air; which identical quantity will again
be expelled in the next expiration. This illustration is perhaps too
strongly stated; but it is evident that, in ordinary respiration, the slight
mechanical compression will have little or no effect in emptying the
most distant tubes, or the ultimate air-cells, of their contents. The bulk
of the air, also, is not altered during respiration, although, for a quantity
of oxygen, carbonic acid gas is substituted. This substitution, which is
the great end of respiration, undoubtedly takes place most abundantly
in the minute and distant air-cells, which present the largest surface to
the blood; and the carbonic acid there produced must be moved along
the smaller tubes by the diffusion process (which we know to be ex-
tremely energetic, and also inevitable), till it is thrown into the larger
tubes, from which it can be expelled by the ordinary action of respira–
tion. But the action of diffusion is always twofold; at the same time
that carbonic acid is being carried outward from the air-cells, oxygen is
carried inward in exchange, and thus the necessary circulation kept up
throughout the whole lungs.
Further, by a forced expiration, from 160 to 178 cubic inches may
be expelled, after which there still remain in the lungs about 120 cubic
inches, which are not under the control of the respiratory action.
There can be no doubt that much of this quantity occupies con-
stantly and permanently the most minute tubes and air-cells, for it can
scarcely be withdrawn by means of the air-pump. Now, the question
has arisen, how these ultimate tubes and air-cells are so powerfully
68 ON THE LAW OF THE DIFFUSION OF GASES.
inflated; for they are not distended by the action of muscular fibre, of
which they are known to be destitute. This state of distention must
be highly useful by exposing surface, and the law of diffusion enables us
to account for it. The heavy carbonic acid which these minute cells
may contain is not merely exchanged for oxygen, but for a larger volume
of oxygen, in the proportion of the diffusion-volumes of carbonic acid
and oxygen, namely, 81 carbonic acid are replaced by 95 oxygen. The
resistance to passage through the most minute tubes is overcome by the
diffusion action, as in the case of the pores of the stucco-plug, and there
follows a tendency to accumulation on the side originally occupied by
the carbonic acid. This accumulation is limited by the increased facility
with which the air-vessels can empty themselves mechanically of a
portion of their contents from their distended state.
In the law of diffusion of gases, we have, therefore, a singular pro-
vision for the full and permanent inflation of the ultimate air-cells of
the lungs.
But it is in the respiration of insects that the operation of this law
will be most distinctly perceived. The minute air-tubes accompanying
the blood-vessels to every organ, and like them ramifying till they cease
to be visible under the most powerful microscope, are kept distended
during the most lively movements of the little animals, and the neces-
sary gaseous circulation maintained, wholly, we may presume, by the
agency of diffusion.
In regard to the terms of the law of diffusion: “The diffusion, or
spontaneous intermixture of two gases in contact, is effected by an
interchange in position of indefinitely minute volumes of the gases.” My
experiments, published on a former occasion, on the diffusion of mixed
gases (Quarterly Journal of Science, p. 28, Sept. 1829), afford the first de-
monstration of the fact that diffusion takes place between the ultimate
particles of gases, and not between sensible masses, and therefore that
diffusion cannot be the result of accident. For, in the case of a mixture
of two gases escaping from a receiver into the atmosphere, by apertures
of 0-12 and 0.07 inch in diameter, it was not so much of the mixture
which left the receiver in a given time, but a certain proportion of each
of the mixed gases, independently of the other, corresponding to its
individual diffusiveness. The same separation of mixed gases occurred
in diffusion through the pores of stucco, or the fissure of a cracked jar.
“Which volumes are not necessarily of equal magnitude, being, in
the case of each gas, inversely proportional to the square root of the
density of that gas.” This may be demonstrated when different gases
communicate by very narrow channels, or by very small apertures, and
and when inequality of pressure is guarded against. In the case of a
gas communicating with the air by a wide aperture, on the other hand,
ON THE LAW OF THE DIFFUSION OF GASES. 69
although the diffusion or intermixture takes place precisely in the same
Way, still the result is different; for where a contraction takes place.
from the process of diffusion, the air flows in mechanically through the
aperture, wholly unresisted, and makes up the deficiency. A gas, how-
ever, of large diffusion-volume escapes, in these circumstances, in a
shorter time than a gas of small diffusion-volume. Indeed, it was the
conclusion of the former paper, that gases diffuse more or less rapidly
according to some function of their densities, “apparently inversely
as the square root of their densities.” The advantage, in illustrating
the process of diffusion of minute apertures or channels of commu-
nication, such as we have in the stucco-plug, depends upon the
circumstance that, when a contraction or expansion takes place in the
gaseous contents of a diffusion-instrument, any current in an outward
or inward direction is prevented by frictional resistance; so that the
simple result of diffusion is exhibited, not complicated by the effect of
any other force.
The law at which we have arrived (which is merely a description of
the appearances, and involves, I believe, nothing hypothetic) is certainly
not provided for in the corpuscular philosophy of the day, and is alto-
gether so extraordinary that I may be excused for not speculating further
upon its cause, till its various bearings, and certain collateral subjects,
be fully investigated.
SUPPLEMENTARY OBSERVATIONS
ON THE LAW OF THE DIFFUSION OF GASES.
It is curious that intermixture takes place more rapidly in the case
of some gases than in that of others, although still in conformity with the
law of diffusion. Thus the process goes on with much greater activity
in the case of hydrogen, olefiant gas, and coal gas diffusing into air, than
in the case of chlorine, carbonic acid, carbonic oxide, etc., diffusing into
the same medium. This is very observable on comparing the times as
stated in describing the experiments on each gas.
The circumstance of the apertures being in the upper part of the
diffusion-instruments, and opening upwards, may be supposed to give
the light gases an advantage in diffusing; but I am disposed to attri-
bute little of the inequality in question to this cause. From a diffusion-
bulb, in which the upper tube was curved and bent downwards,
hydrogen gas was found to escape with its wonted rapidity.
This inequality in the velocity of diffusion is strikingly illustrated
in the following results, obtained from experiments with different gases,
70 ON THE LAW OF THE DIFFUSION OF GASES.
submitted in turn to diffusion from the same instrument. In a certain
time, the same in all the experiments, a quantity of air entered, by dif-
fusion, which varied with the gas diffusing.
In a given time,
With chlorine in the diffusion-tube 0.302 vol. air entered.
With carbonic acid . º ... 0-623 35
With hydrogen e º . . 1277 35
It appears, then, that the process of diffusion into air through stucco
is four times more rapid in the case of hydrogen than in that of chlorine,
and twice as rapid in the case of the former gas as in carbonic acid.
The process of diffusion might be said to proceed at a uniform rate, if
the same quantity of air entered the instrument in the same time, what-
ever gas was diffused, and although the quantity of gas which escaped was
variable of course, and proportional to the respective diffusion-volume
of the gas. But this exchange of diffusion-volumes takes place more
rapidly, it appears, in the case of Some gases than of others.
A table of experiments is given in the body of the paper (p. 55)
on the rate of passage of different gases through the pores of stucco
under the influence of pressure. The rate appears to be the same in the
case of air, nitrogen, oxygen, and carbonic acid, from which carbonic
oxide deviates in a small degree. But hydrogen, and, it is remarkable,
olefiant gas and coal gas, which contain hydrogen, are less resisted than
the preceding class. Upon reconsideration, I am inclined to connect with
this fact the apparent deviation of hydrogen from the law of diffusion,
which is noticed in the paper. It is there shown that more hydrogen :
passes out than the exact quantity proportional to the return-air. The
same deviation from the law may be remarked in the experiments
detailed on olefiant gas. It is also very noticeable in the case of coal
gas. But these are gases which, like hydrogen, are less resisted than
common air in their passage through stucco. There appears to exist an
inaptitude on the part of a stucco intermedium to exhibit the exact
effect of diffusion, in the case of gases, on either side of it, which are
not capable of permeating through it with equal facility; that gas which
experiences least frictional resistance diffusing through in a quantity
somewhat greater than it should do.
There can be no doubt that the velocity of diffusion noticed above is
likewise influenced by the variable resistance which the gases experi-
ence in passing through the stucco. But I am not prepared to say
that the variation depends entirely on this cause, and is therefore acci-
dental to the mode in which the diffusion takes place. The diffusion
or intermixture of light gases appears to take place in all circumstances
with greater rapidity than that of heavy gases. -
THOMAS GRAHAM.
GLAsgow, Sept. 7, 1832.
ON PHOSPEIURETTED HYDROGEN. 71
XI.
ON PHOSPHURETTED HYDROGEN."
From Edin. Roy. Soc. Trans. xiii. 1835, pp. 88-106. [Phil. Mag. v. 1834, pp. 401–415;
Erdm. Journ. Prak. Chem. iii. 1834, pp. 400-416.] -
FEw substances have been made the subject of experimental inquiry
more frequently than the compounds of phosphorus and hydrogen, and
no subject is so remarkable for the various and conflicting results which
it has presented to chemists of the greatest acuteness and practical
skill. The obscurity which long hung over the subject has been dis-
pelled, however, in a great measure, by the recent investigations of
Henry Rose of Berlin. Although baffled in his early researches, that
philosopher returned again and again to the subject, and at last suc-
ceeded in determining the chemical functions and true constitution of
phosphuretted hydrogen. He has shown it to be analogous to ammonia
in chemical character and composition. But hitherto two compounds
of phosphorus and hydrogen had generally been admitted to exist,
which were believed to differ in composition, as they do in properties,
one being spontaneously inflammable in atmospheric air, and the other
not so. Rose establishes beyond all doubt that these gases are essen-
tially of the same composition, and of the same specific gravity; and,
indeed, that they are mutually convertible, each into the other, without
any addition or subtraction of matter that could be perceived. In
explanation of their possessing different properties, under the same
composition, allusion is made by Rose to Isomerism, or the doctrine that
two bodies may exist identical in composition, but differing in properties.
Certainly the existence of two gases, constituted alike, and yet possessing
different properties, if established, would afford a firm basis for this
doctrine.
It was the importance of the theoretical results which might be
looked for, that induced me to attempt to continue the investigation
beyond the point to which it had been carried by Rose.
Holding the general doctrine of Isomerism as problematical, my
inquiries were directed to the discovery, in one or other of the gases, of
some adventitious matter, to the presence of which the peculiarities of
the species might be attributed.
It is to be understood that the spontaneously inflammable gas made
use of in my experiments was prepared by the well-known process of
heating phosphorus, lime, and water together. This gas is spoken of
as “the self-accendible gas,” or as “the gas from phosphuret of lime.”
The other gas, which is not spontaneously inflammable, was prepared by
1 Read before the Royal Society of Edinburgh lst Dec. 1834.
72 ON PHOSPHURETTED HYDROGEN.
heating hydrated phosphorous acid, or by allowing the preceding species,
contained in low receivers, to stand over water for twenty-four hours. It
is described as “the non-accendible gas,” the gas from phosphorous acid.
The accendibility of the gas was judged of by allowing it to escape in
bubbles into the air from the receiver containing it, either over water or
mercury. The experiments were all made when the temperature of the
atmosphere was between 60° and 70° Fahrenheit.
1. In the process by which the self-accendible gas is procured, free
phosphorus distils over, of which a trace, in the state of vapour, may
well be supposed to remain in the gas for some time. Hence the idea
has generally presented itself, that the free and highly accendible phos-
phorus present may be the cause of the spontaneous inflammability of
the gas. Dr. Dalton, who all along maintained the opinion, which has
finally been established by Rose, that the two gases are of the same
composition, was in the habit of referring the spontaneous inflamma-
bility of the one species to this cause. The speedy loss of the property
in question, in the case of gas confined over water, seemed to favour
this view. I find, however, that if a small quantity of phosphuretted
hydrogen, when not self-accendible, be added to a confined portion of
air, sticks of phosphorus introduced into that air do not smoke, that
phosphorus has no disposition to combine with oxygen when phosphu-
retted hydrogen is present. In a transparent mixture of one volume
phosphuretted hydrogen with one thousand volumes, or any smaller
proportion of air, sticks of phosphorus remain unaffected, but the phos-
phuretted hydrogen itself always undergoes a slow oxidation. In a
mixture of one volume phosphuretted hydrogen and two thousand
volumes air, phosphorus Smoked strongly for some time ; but at a cer-
tain period the action ceased, long before the oxygen of the air was
exhausted. A minute proportion of phosphuretted hydrogen is, there-
fore, sufficient to protect phosphorus from oxidation, in which respect
this gas resembles the hydrocarburets and essential oils, which have been
shown to be equally efficacious in protecting phosphorus from oxidation.
All these bodies appear to act in this respect in one way, namely, by
taking the precedence of phosphorus in the process of oxygenation.
Phosphorus therefore being less oxidable than phosphuretted hydrogen
itself, cannot be supposed to take fire and to inflame the gas, or to be
the cause of the accendibility of the gas at low temperatures.
On Sending electric sparks through non-accendible phosphuretted
hydrogen itself, phosphorus is deposited, but the gas, when still cloudy
from the phosphorus suspended in it, proved to be non-inflammable on
passing it into air.
The loss of accendibility in the case of gas confined over water is
certainly wholly unconnected with the deposition of any free phos-
ON PHOSPHURETTED HYDROGEN. 73
phorus from the gas, which may occur, but is due to the rise of oaygen
from the water into the gas. It was observed that water, which had
been boiled to deprive it of all air, and which was then passed up to
self-accendible gas confined over mercury, did not affect the gas in the
course of forty-eight hours. In this case, moreover, the gas was agitated
with the water. The gas continues in general spontaneously inflam-
mable over mercury for forty-eight hours, and sometimes for three or
four days, but ceases to be so in a very short time after the admission
of a small proportion of air, particularly if the air be added in a gradual
manner. Thus, if to the gas be passed up one-twentieth part of its
bulk of cork or of dry stucco, containing air in its pores, a white smoke
appears in the gas, and it ceases to be spontaneously inflammable in the
course of a few minutes. The same mass of stucco, warmed before
being passed up into the gas, so as to expel the air it contained, did not
produce the same effect. The Self-accendible gas always deposits on
standing a solid matter, containing phosphorus, of a lively yellow colour,
but in quantity too minute for analysis. This matter is not acted on
by any of the ordinary solvents, such as alcohol, ether, alkalies, or
muriatic acid, but is destroyed by chlorine-water, and by nitric acid.
The precipitation of this matter is most rapid in the case of gas over
water, and is indicative of deterioration of the gas.
2. The self-accendible gas procured from phosphorus, water, and
lime is always mixed with free hydrogen, varying in quantity from
25 to 50 per cent. ; while the non-accendible gas from phosphorous acid
contains no hydrogen gas, but is pure. Rose concludes that the spon-
taneous inflammability of the first species cannot depend upon this
hydrogen, for the other species is not made self-accendible by the addi-
tion to it of any proportion of free hydrogen. On trying the experiment,
however, I obtained a different result. A quantity of gas had lost its
self-accendibility by standing over water for two or three hours; to my
surprise, the addition to this gas of hydrogen, in any proportion from
one-third of a volume to three volumes, restored the self-accendibility
of the gas. Spontaneous inflammability was likewise communicated, in
Some cases, to the gas procured from phosphorous acid merely by adding
hydrogen to it. It was early perceived, however, in the course of the
investigation, that hydrogen did not uniformly communicate the pro-
perty in question, and that its influence depended on something acci-
dental and not essential to the gas. For instance, the hydrogen which
comes over almost pure towards the end of the process for phosphuretted
hydrogen had none of this property, nor did it appear in hydrogen
obtained from the following sources:—from the electric decomposition
of water, from the decomposition of steam by iron, from the action of
water on amalgam of potassium, or from the action of muriatic, arsenic,
74 ON PHOSPEIURETTED HYDROGEN.
or phosphoric acid on zinc. Even in the case of the action of Sulphuric
acid on zinc or iron, which had first afforded hydrogen possessing the
property in question, it turned out that only the hydrogen evolved at
an early period of the action is efficient, while the gas evolved after the
vivacity of the action is impaired is nearly, and sometimes entirely,
destitute of any influence. The activity of the hydrogen was in short
traced to a slight impregnation of nitrous acid vapour, which it pos-
sessed. The sulphuric acid of commerce always contains a small por-
tion of some acid of nitrogen, probably the hyponitrous, from which, I
find, it cannot be freed by boiling or concentration continued for any
length of time. On quickly mixing sulphuric acid with two or three
volumes of water, the presence of nitrous acid is attested by its peculiar
Odour, and almost certainly by the appearance of brown fumes. That
the hydrogen did not owe the property in question to a trace of nitric
oxide, which, combining with oxygen, might, by a slight consequent
evolution of heat, have an effect in kindling the phosphuretted hydrogen,
was proved by the fact that the property in question could not be
imparted to hydrogen by any proportion of nitric oxide; but to this
point there will be occasion to recur.
At an earlier stage in the inquiry, some experiments were made
upon the effect of other gases than hydrogen upon phosphuretted
hydrogen. None, with the exception of sulphuretted hydrogen (evolved
by the action of sulphuric acid on sulphuret of iron, and which therefore
contains free hydrogen), appeared to favour the accendibility of the gas.
On the contrary, the addition of all others, and even of hydrogen and
Sulphuretted hydrogen themselves above a certain proportion, distinctly
impeded or destroyed the accendibility of this gas. Thus, one volume
phosphuretted hydrogen ceased to be spontaneously inflammable when
mixed with the following proportions of different gases:–
With 5 volumes hydrogen,
, carbonic acid,
, nitrogen,
volume olefiant gas, -
, Sulphuretted hydrogen,
, nitric oxide,
, muriatic acid,
, ammoniacal gas.
22
25
It is to be remarked, however, in reference to the preceding table,
that some specimens of phosphuretted hydrogen appear to be more
highly accendible than others, and that there is considerable latitude
in the proportion of foreign gas, which may be requisite for destroying
the spontaneous inflammability of a given specimen. Often a much
Smaller portion suffices than is stated in the table. I have found half
ON PHOSPHURETTED BIYDROGEN. 75
a volume of carbonic acid or of nitrogen to produce the effect. Of
course the introduction of any trace of air, with the gases, must be
carefully guarded against. Nitrous acid, when present in hydrogen in
too small a proportion to enable that gas to communicate spontaneous
inflammability to phosphuretted hydrogen, or to be perceived by the
smell, may be detected by the effect of the hydrogen upon a prepared
mixture of non-accendible phosphuretted hydrogen and air, which mix-
ture may be had quite free from white smoke and transparent. The
addition of hydrogen to this mixture occasions the immediate appear-
ance of a dense white smoke, the oxidation of the phosphorus being
partially induced, if even an infinitesimal proportion of nitrous acid exist
in the hydrogen. Although the oxidation of the phosphorus takes place
at the expense of the air present, and only when air is present, yet the
nitrous acid appears to be speedily consumed; the fumes soon ceasing
but appearing again on every subsequent addition of active hydrogen,
till several volumes have been added, or till the oxygen of the air
present is exhausted.
That the influence of hydrogen was referable to the nitrous impreg-
nation appeared also from the fact that phosphuretted hydrogen, which
had lost its spontaneous inflammability, was rendered as actively
inflammable as ever by passing it, bubble by bubble, into an inverted
receiver filled with sulphuric acid, recently diluted with three measures
of water and cooled. The gas was now capable of igniting spontane-
ously, when passed into air, without the intervention of hydrogen. The
same diluted acid lost the smell of nitrous acid by exposure to air in a
shallow vessel for a few hours, and thereafter was found unfit for the
purpose in question. Phosphuretted hydrogen, which had acquired
spontaneous inflammability from a nitrous impregnation, appeared to
retain that property as long as the phosphuretted hydrogen, which is
spontaneously inflammable as first prepared.
Hydrogen gas, too, which had received a nitrous impregnation by
being passed through a diluted Sulphuric acid, retained, in one case,
after being confined for twenty-four hours over water, the power of
rendering phosphuretted hydrogen spontaneously inflammable. From
the preceding results and other considerations, it seemed not unlikely
that the spontaneous inflammability of phosphuretted hydrogen may
be an accidental property, and depend upon the Occasional presence
of some foreign body in minute quantity. The inquiry suggests
itself, Is there a peculiar principle in the self-accendible gas, and what
is it 2
3. It was very soon found that a peculiar principle is withdrawn
from the gas by porous absorbents, such as wood, charcoal, and baked
clay, which substances are capable of destroying the inflammability of
76 ON PHOSPEIURETTED HYDROGEN.
several hundred times their volume of gas. Thus, in one experiment,
to 500 measures of highly accendible phosphuretted hydrogen, one
measure of charcoal, recently heated to redness, and cooled under the
surface of mercury, was passed up. In the course of five minutes a
contraction of eight or ten measures occurred, without any oxidation of
the gas, for no air was introduced with the charcoal. The gas was still
spontaneously inflammable, but ceased to be so in the course of half
an hour. It was found, in fact, by different experiments, that wood-
charcoal can absorb about ten times its volume of phosphuretted
hydrogen gas itself; that the phosphuretted hydrogen and the peculiar
principle are absorbed indiscriminately at first by the charcoal, but
that by-and-bye the peculiar principle comes to be entirely absorbed
by the charcoal, without any further absorption of phosphuretted
hydrogen.
When the phosphuretted hydrogen did not exceed fifty or sixty
times the bulk of the charcoal, the peculiar principle was entirely with-
drawn in five minutes, and the gas ceased to be self-accendible. Char-
coal, which had been drenched in water, was without effect upon the
gas. On heating the charcoal saturated with gas, in a retort filled with
water, phosphuretted hydrogen was given off, which, however, was not
self-accendible, and all my attempts failed to isolate the peculiar prin-
ciple by separating it from the charcoal. It was quite clear that the
peculiar principle formed but a very small proportion of the volume of
the phosphuretted hydrogen, evidently much less than one per cent. of
the bulk of the gas.
Spongy platinum introduced into the gas did not exercise any sen-
sible absorbent effect, and no quantity of it seemed sufficient to with-
draw the peculiar principle from a small bulk of the phosphuretted
hydrogen.
Stucco, likewise, was without effect upon the gas, at least when
access of air was guarded against at the same time. But both of these
substances are known to possess a very low absorbent power.
4. Phosphuretted hydrogen transferred to a receiver over mercury,
the inside of which is moistened by a strong solution of caustic potash,
always loses its spontaneous accendibility, although by no means rapidly,
several hours being generally required.
5. Certain acids appear to have a remarkable power in withdrawing
the principle of inflammability from phosphuretted hydrogen.
Let phosphuretted hydrogen be transferred into a jar inverted over
mercury, of which jar the inner surface has been moistened with con-
centrated phosphorous acid. A small quantity of a milk-white matter
immediately appears in the acid where exposed to the gas, and in two
or three minutes the gas has ceased to be spontaneously inflammable
ON PHOSPHURETTED HYDROGEN. 77
without any appreciable diminution of its volume having occurred.
This white matter, although very sensible to the eye, exists only in the
most minute quantity. It is not crystalline, and perhaps is not even
solid. The introduction of concentrated phosphoric acid into the gas
was attended by similar phenomena, and the gas lost its spontaneous
inflammability in the course of half an hour.
A strong solution of arsenic acid acts as rapidly in withdrawing the
peculiar principle as phosphoric acid does, but the arsenic acid soon
begins to react upon the phosphuretted hydrogen itself, a dark copper-
coloured incrustation soon forming upon the surface of the gas-receiver,
which matter is probably a phosphuret of arsenic. Concentrated sul-
phuric acid is capable of absorbing phosphuretted hydrogen itself, which
the preceding acids are not, but even sulphuric acid appears to absorb
the peculiar principle, in the first instance, by a more active affinity
than it exerts upon the gas itself. Dilute phosphorous, phosphoric, and
arsenic acids, react in the same manner upon phosphuretted hydrogen,
but not so rapidly as the concentrated acids do.
6. The following liquids are capable of dissolving the quantity of
phosphuretted hydrogen gas placed against their names, at 65° Fahr.
Alcohol (sp. gr. 850), º & \ ſº # volume.
Sulphuric ether, e e tº sº 2
Oil of turpentine, tº wº º tº 3#
The essential oils and most of the hydroearburets appear to withdraw,
or to negative the peculiar principle in spontaneously inflammable
phosphuretted hydrogen in a rapid manner. If a jar be moistened, in
the slightest degree, with oil of turpentine, coal-tar naphtha, or by the
liquid distilled from Caoutchouc, and then be used as a receiver for con-
taining self-accendible gas, either over water or mercury, the gas is
found to lose its spontaneous inflammability in a very few minutes.
White fumes often appear in the gas at the same time, but these I am
satisfied are due to the evolution of some gaseous oxygen from the
liquids, and appear in the case of the portion of gas which is first
brought into contact with the liquid, but do not occur in the case of
subsequent additions of gas, although the liquid remains capable of
destroying the spontaneous accendibility of many portions of gas, suc-
cessively exposed to it. It is not easy to decide whether the vapours
destroy irrecoverably the peculiar substance of spontaneous inflam-
mability, or merely negative the action of that principle by their
presence.
I am inclined to think, however, that they destroy that principle,
for the action is not so rapid as the diffusion of the vapour through the
gas, the impregnation appearing to be fully accomplished, and yet the
78 - ON PHOSPEIURETTED HYDROGEN.
loss of inflammability not occurring sometimes for two or three minutes
afterwards, particularly in the case of naphtha, a portion of that pure
liquid, in which potassium had been preserved, being used in the experi-
ment. A small addition of ether-vapour also destroys the inflamma-
bility of phosphuretted hydrogen, although a distinct interval must
elapse before the change occurs, such as a quarter or half of an hour.
The action of alcohol vapour is much slower, generally requiring two
or three hours. Pure olefiant gas, containing no air, added in the
proportion of 10 or 20 per cent, eventually destroys the spontaneous
inflammability, but requires a period of not less than twenty or thirty
hours.
Olefiant gas has a negative influence of quite a different character,
which has already been alluded to, and which is in action the
moment the gases are mixed, but which does not appear unless the
proportion of olefiant gas be very considerable. It is probable that
ether-vapour and the gaseous hydrocarburets likewise have an influence
of the same kind. An astonishingly minute quantity of an essential
oil suffices to destroy the inflammability of the gas over mercury, if
allowed an hour or two to act. Hence it is very difficult to preserve
gas in the inflammable condition, in the mercurial trough, if any portion
of the mercury has been soiled by an essential oil.
7. The action of potassium on the peculiar principle is equally
remarkable. A most minute quantity of this metal, or of its amalgam,
destroys the self-accendibility of the gas in a few minutes, without
occasioning any sensible reduction of volume that could be measured.
The fact is, potassium, or its amalgam, is without effect upon phos-
phuretted hydrogen itself, at the temperature of the air, neither absorb-
ing nor decomposing the gas; but upon the peculiar principle the action
of this metal is rapid and certain. One grain of potassium, amalgamated
with fifty pounds of mercury, rendered that large quantity of mercury
quite unfit for retaining gas over it, in the self-accendible condition, for
more than a few minutes. In such experiments the interference of
naphtha vapour was perfectly excluded. Zinc and tin, either by them-
selves or in the state of amalgam, have no sensible effect upon self-
accendible gas, at least in a period of five or six hours. Protoxide of
mercury speedily withdraws the peculiar principle, but afterwards also
reacts slowly upon the gas itself. On the other hand, the peroxide of
the same metal is nowise injurious to the self-accendible gas. Arsenious
acid in powder acts in the same manner as protoxide of mercury. The
solution of proto-sulphate of iron, if previously boiled to deprive it of
air, is without effect upon the gas. - -
The extraordinary action of potassium, and that also perhaps of the
essential oils, seemed to point to the existence of an oxygenated prin-
ON PHOSPEIURETTED HYDROGEN. 79
ciple, as the cause of the spontaneous inflammability of phosphuretted
hydrogen.
It is sufficiently evident that the proportion in which this principle
exists to the whole gas, is exceedingly small, too minute to afford any
hope of isolating that principle. The nitrous impregnation, too, which
was found adequate to render gas spontaneously inflammable, shows to
how minute a quantity of matter the spontaneous inflammability of
phosphuretted hydrogen may at times be owing. It seemed within the
bounds of possibility that the gas might owe its spontaneous inflamma-
bility, in ordinary circumstances, if not to nitrous acid, at least to some
other principle analogous to that substance. This led to a careful
examination of the properties of phosphuretted hydrogen made inflam-
mable by means of nitrous acid; a subject of much interest, as illus-
trating the effect of a most minute and almost infinitesimal quantity
of foreign admixture, in communicating so striking a property as
spontaneous inflammability to a chemical body, independently of the
light which it may throw upon the constitution of ordinary phosphu-
retted hydrogen.
8. Phosphuretted hydrogen, which had lost all trace of spontaneous
inflammability by standing a day or two over water, or the gas from
hydrated phosphorous acid, might be impregnated with nitrous acid,
and made spontaneously inflammable in various ways. It was ascer-
tained that the gas obtained, by either process, was affected in the same
way. Such gas only, entirely destitute of spontaneous inflammability,
was employed in the following experiments:—
(1) The nitrous acid of Dulong may be added directly to the gas
over mercury, a glass spherule, or the bore of a short piece of thermo-
meter tube being filled with the liquid, and passed up to the gas. When
nitric acid is brought into contact with the gas in this manner, a violent
action occurs; but with nitrous acid the evolution of white fumes is very
slight. The nitrous acid is absorbed in part by the mercury, but this
absorption is slow, provided the quantity of gas be considerable with
which the acid vapour is mixed. If the quantity of gas primarily im–
pregnated with nitrous acid, in the manner described, be small, or the
impregnation of nitrous acid considerable, the gas exhibits no disposi-
tion to smoke or to take fire, when passed into air. It has not become
spontaneously accendible. On diluting the gas with a large proportion
of unimpregnated phosphuretted hydrogen, no reaction is indicated, but
the whole becomes spontaneously accendible in a high degree. In fact,
it was discovered that the gas is not accendible when the nitrous acid
exceeds a certain proportion, which is by no means considerable.
(2) Allow a single drop of nitrous acid to fall into a dry glass jar,
which may be of small dimensions. Fill the jar with mercury, and
80 ON PHOSEPHURETTED EIYDROGEN.
invert it without loss of time in the mercurial trough, a bubble őf gas
will collect in the upper part of the jar, which bubble is chiefly nitrous
acid vapour. One cubic inch or so of phosphuretted hydrogen, or of
hydrogen itself, may then be added to the gas in the jar, and this is
our nitrous impregnating mixture. Suppose this mixture to contain
one-twentieth of its bulk of nitrous acid vapour. The addition of it,
in any proportion, to phosphuretted hydrogen, is not attended by the
slightest production of white fumes; in fact no reaction appears to take
place. But the addition of a single bubble of this mixture, not exceed-
ing one-tenth of an inch in volume, to five or six cubic inches of phos-
phuretted hydrogen, will render the whole highly accendible, so that
every bubble passed into the air will take fire. .
(3.) In the above arrangement, a drop of the strongest nitric acid
may be substituted for the nitrous acid, in the preparation of the im–
pregnating mixture. The nitric acid acts on the mercury, and nitric
oxide, charged with nitrous acid, is collected, which may be diluted with
hydrogen as above. -
The preceding processes uniformly afford a nitrous impregnating
mixture which may be depended upon; but when the experiment is
attempted over water, there is not the same certainty of the impregna-
tion being successful. I have often, however, made hydrogen highly
suitable for the purpose, by passing it through a column of fluid com-
posed of nitric acid recently diluted with water, provided that the acid
had been fuming from the presence of nitrous acid; or by passing
hydrogen through recently diluted sulphuric acid, as has already been
stated. §
In regard to the proper proportion of nitrous acid vapour to the
phosphuretted hydrogen, I am satisfied that the proportion most effica-
cious is somewhere between 1 part nitrous acid to 1000, and 1 to 10,000
phosphuretted hydrogen. One volume nitrous acid vapour to 100 gas,
or to less gas, is never accendible, but becomes so on diluting it with
enough of phosphuretted hydrogen. 3.
I was anxious to discover how far nitric oxide interferes in the
phenomenon. The nitrous acid is never free from, but always accom-
panied with, a certain proportion of this gas.
9. Action of Nitric Oaxide—In a table formerly given, nitric oxide
is set down as incompatible with the accendibility of the good gas from
phosphuret of lime, when the proportion of the first is so great as one-
tenth of the whole mixture.
In fact, the best inflammable gas, when mixed with nitric oxide,
in quantity from two volumes to one-tenth of a volume, exhibited no
symptoms of spontaneous inflammability. The nitric oxide forms red
fumes when the mixture meets the air, but the phosphuretted hydrogen
ON PHOSPHURETTED HYDROGEN. 81
does not even smoke, so that the oxidation of the nitric oxide has not a
kindling effect upon the phosphuretted hydrogen, but the very reverse.
A mixture of one volume nitric oxide, with twenty volumes good phos-
phuretted hydrogen (self accendible per se), is still self-accendible; the
bubble, however, does not take fire the instant it bursts in the air, but
after rising to a little height, and then explodes with a puff like loose
grains of gunpowder, and not with the usual snap, the oxidation of
the nitric oxide preceding the oxidation of the phosphuretted hydro-
gen by a sensible interval. Nitric oxide, in a considerably smaller
proportion than one-twentieth volume, exhibits a sensible effect in
retarding the combustion of self-accendible gas, but does not altogether
prevent it. In the case of phosphuretted hydrogen, which was not
Self-accendible, small additions of nitric oxide, such as 1 to 100, to 500,
to 1000, or to 2000 volumes phosphuretted hydrogen, did not induce
Self-accendibility, when the nitric oxide employed had been previously
washed with caustic alkali. The experiment was tried with three
different specimens of washed nitric oxide. But nitric oxide, which
had not been washed with alkali, particularly if it resulted from a
turbulent action of the nitric acid on copper, and came overcharged
with red fumes, and was withal newly collected, was pretty often effi-
cient in making the gas self-accendible. The proper proportion of such
nitric oxide for this purpose was found to be 1 volume to a quantity
between 1000 and 2000 volumes of phosphuretted hydrogen. A greater
or a less proportion of the nitric oxide failed to produce the desired
effect. All these experiments with nitric oxide were made over
Water.
It is well known that a mixture of phosphuretted hydrogen and
nitric oxide may be exploded by a bubble of oxygen gas, a method of
firing these gases first practised, I believe, by Dr. Thomson. But pure
nitric oxide was found by Dr. Dalton to oxygenate phosphuretted
hydrogen in a gradual manner, when the two gases are left together.
It is probable, therefore, that it is by acting itself upon phosphuretted
hydrogen that nitric oxide prevents atmospheric air from acting upon
that gas in our experiments. It is conceivable that the oxygenating
action of nitric oxide upon phosphuretted hydrogen, like that of air
upon the same gas, may be promoted by the presence of nitrous acid,
which will explain Dr. Thomson's experiments.
The impregnating nitrous mixture of the foregoing experiments was
not destitute of nitric oxide, but what proves that the efficiency of the
mixture did not depend upon the last-mentioned ingredient, is the cir-
cumstance, that the mixture lost its virtue by standing Over mercury
for a week, during which period the acid-vapour was absorbed by the
mercury, but the nitric oxide remained, as appeared on admitting air
F
82 ON PHOSPHURETTED HYDROGEN.
to the gaseous mixture. Hence we may conclude that when nitric
oxide acts in producing inflammability in phosphuretted hydrogen, it is
from the nitrous acid which it occasionally contains.
It is certainly, however, very curious that nitric oxide is not quite
equivalent to nitrous acid, in producing the change in question upon
phosphuretted hydrogen, seeing that the nitric oxide passes immediately
into nitrous acid upon meeting air. Whether the negative influence of
nitric oxide upon really accendible gas is sufficient to account for this
anomaly, I am doubtful. It may be thought that nitrous acid and phos-
phuretted hydrogen, when in contact for a short time, react upon each
other, with the production of some entirely new and highly accendible
body. But this supposition seems not to quadrate with the fact, that
the impregnating mixture requires to be diluted by so large a propor-
tion of phosphuretted hydrogen, before the whole becomes spontaneously
accendible. Nor is it supported by any visible signs of reaction between
the nitrous acid and phosphuretted hydrogen. Indeed, nitrous acid-
vapour appears to be compatible with phosphuretted hydrogen, to an
extent which could not have been anticipated.
Again, that nitrous acid, or at least Some acid compound of nitrogen,
continues to exist in what we may now call the nitrous phosphuretted
hydrogen gas, appears to be corroborated by the properties which this
self accendible gas is found to possess.
10. Properties of nitrous phosphuretted hydrogen.
(1.) This gas loses its self-accendibility when kept over mercury, in
a period varying from six to twenty-four hours, according to the amount
of nitrous impregnation.
It is remarkable that this gas continues, in general, inflammable for
a longer time when confined over water than over mercury, which is
the reverse of what occurs with the gas from phosphuret of lime.
(2.) The factitious gas is deprived of its spontaneous inflammability
by charcoal and other porous absorbents, by essential oils and hydro-
carburets, and by amalgam of potassium, and quite as rapidly as is its
natural prototype.
(3) Phosphorous acid, and concentrated sulphuric acid, appear like-
wise to withdraw the nitrous principle, although phosphoric acid does
not. The agency of these acids probably exemplifies the disposition of
nitrous acid to combine with other acids. The action of potassium and
of essential oils upon nitrous acid, requires no explanation. Potassium
has, I find, no action upon pure nitric oxide in the cold.
(4.) A cubic inch of this gas, passed up into a receiver, of which the
inside was moistened with caustic alkali, had its accendibility sensibly
impaired in fifteen minutes, but not completely destroyed in less than
an hour.
ON PHOSPHURETTED HYDROGEN. gº 83
In conclusion, the statement of the above properties is abundantly
sufficient to prove that a strong analogy subsists between our nitrous
phosphuretted hydrogen and the self-accendible gas, which has been so
long in the hands of chemists. The peculiar principle of the last may
therefore possibly be an oxygenated body. That principle cannot be
nitrous acid, but it may be a compound of phosphorus and oxygen, P.
analogous to nitrous acid. In all the reactions by which self-accendible
phosphuretted hydrogen is produced, we have the simultaneous forma-
tion of compounds of phosphorus and oxygen, such as hypophosphorous
and phosphoric acids. The compound P is hypothetical, however, and
has not yet been formed directly. Its existence is only surmised from
the parallelism which appears to be established between nitrogen and
phosphorus, and between their compounds; phosphuretted hydrogen
itself corresponding with ammonia, phosphoric, and phosphorous acids,
with nitric and hyponitrous acids. The peroxide of chlorine of Davy
and Stadion Öl, corresponds with nitrous acid, and with our hypothetical
oxide of phosphorus, which we may speak of as the peroxide of phos-
phorus.
The peroxide of phosphorus would appear to resemble the peroxide
of chlorine, in being acted on more slowly by mercury and by alkalies,
than is the case with nitrous acid. It is to be admitted, however, that
I did not succeed in producing an inflammable phosphuretted hydrogen
by the agency of peroxide of chlorine—that there is no chlorous phos-
phuretted hydrogen. The reason is, that peroxide of chlorine is incom-
patible with phosphuretted hydrogen, reacting upon that gas the instant
of mixture.
As to the mode in which nitrous acid vapour, in a proportion so
minute, contributes to the accendibility of phosphuretted hydrogen, I
have been able to form no distinct idea. The most likely conjecture is,
that the nitrous acid, or resulting hyponitrous acid, combines with some
product of the oxygenation of phosphuretted hydrogen, and thereby
disposes or promotes the occurrence of that change. The oxygenation
of pure hydrogen itself, under the influence of a clean plate of platinum,
is not promoted in a sensible degree by any nitrous impregnation.
Sulphurous acid and muriatic acid gases, and vapour of acetic acid,
appeared to contribute nothing to the accendibility of phosphuretted
hydrogen.
It appears, then, that the two phosphuretted hydrogens are not
isomeric bodies, but that the peculiarities of the spontaneously inflam-
mable species depend upon the presence of adventitious matter:
That the vapour of some acid of nitrogen, which, in the present state
of our knowledge of that class of compounds, seems to be the nitrous
84 ON A NEW PROPERTY OF GASES.
acid, is capable of rendering phosphuretted hydrogen spontaneously
inflammable, when present to the extent of one ten-thousandth part of
the volume of the gas:
That the last gas has a general resemblance to phosphuretted
hydrogen, as obtained in the spontaneously inflammable state by ordi-
nary processes, which, it is probable, owes its ready accendibility to the
presence of an equally minute trace of a volatile compound of phosphorus
and 02:ygen, analogous to nitrous acid. .
XII.
ON A NEW PEOPERTY OF GASES.
From Report of Brit. Assoc. for the Advancement of Science, 1845 (Part ii.), p. 28.
AFTER explaining the law which regulated the diffusion of gases, and
stating the fact, that the lighter gases diffused themselves much more
speedily than the more dense ones—the velocity of their diffusion
being equal to the square root of their densities—he proceeded to relate
his experiments on the passage of gases into a vacuum. To this passage
the term effusion has been applied. The velocity of air being 1, the
velocity of oxygen was found to be 0.9500 by experiment, and by calcu-
lation 0-9487. Carbonic acid being much heavier than air, gave the
number 0.821, the theoretical number being 0-812. Carburetted hydrogen
gave 0-1322 as the velocity of its effusion, the theoretical number being
1341. Hydrogen gave as the velocity of effusion 3-613 by experiment,
which was nearly the amount given by theory (0-379). The interference
of friction, even of minute orifices, was then described, and shown to
admit of easy correction. Some useful applications were mentioned;
as in the manufacture of coal-gas, where it is desirable to ascertain the
quality, as well as the quantity of gas manufactured. As the gas will pass
the orifice on its way to a vacuum the quicker the lighter it is, and the
more slowly as it increases in density, and as the superior carburetted
hydrogen is heaviest, it would be easy to construct an instrument to
register this velocity, and thus mark at once the required quality and
quantity of gas. It was also proposed that an instrument might be
used in mines to detect the presence of light carburetted hydrogen
(fire-damp). The passage of gases under pressure through porous bodies
was termed, by Prof. Graham, transpiration. The mode adopted in
experiment was, to take a glass receiver, open at the top, which was
ON COMPOSITION OF FIRE-DAMP OF NEWCASTLE COAL MINES. 85
closed with a plate of stucco. This was placed on an air-pump, and the
air exhausted by the pump, the velocity with which the air passed
through the stucco being marked by the mercurial gauge of the pump.
The transpiration of atmospheric air was found to be more rapid than
that of oxygen. Carbonic acid is found to be more transpirable than
oxygen, or even, under low pressure, than atmospheric air. The tran–
spiration of hydrogen is one-third more rapid than that of oxygen. The
applicability of this process of experimenting to the explanation of
exosmose and endosmose action in the passage of fluids through porous
bodies was pointed out.
XIII.
ON THE COMPOSITION OF THE FIRE-DAMP OF THE
NEWCASTLE COAL MINES.
From Memoirs of Chem. Society, iii. 1845-48, pp. 7-10.
SOME years ago I examined the gas of these mines with the same
result as Dr. Henry, Davy, and Dr. Turner had previously obtained,
namely, that it contains no other combustible ingredient than light
carburetted hydrogen. But the analysis of the gas of the coal mines in
Germany, subsequently published, showing the presence of other gases,
particularly of olefiant gas, has rendered a new examination of the gas
of the English mines desirable. The gases were—1, from a seam named
the Five-Quarter seam, in the Gateshead colliery, where the gas is col-
lected as it issues, and used for lighting the mine; 2, the gas of Heb-
burn colliery, which issues from a bore let down into the Bensham
Seam—a seam of coal which is highly charged with gas, and has been
the cause of many accidents; and 3, gas from Killingworth colliery, in
the neighbourhood of Jarrow, where the last great explosion occurred.
This last gas issues from a fissure in a stratum of sandstone, and has
been kept uninterruptedly burning, as the means of lighting the horse-
road in the mine, for upwards of ten years, without any sensible dimi-
nution in its quantity. The gases were collected personally by my
friend Mr. J. Hutchinson, with every requisite precaution to insure their
purity, and prevent admixture of atmospheric air.
The usual eudiometrical process of firing the gases with oxygen was
sufficient to prove that they all consisted of light carburetted hydrogen,
with the exception of a few per cent. The results were as follows:—
S6 ON THE COMPOSITION OF THE FIRE-DAMP
Gateshead Gas—Specific gravity 0-5802.
Carburetted hydrogen, e tº º . 94.2
Nitrogen, . º & e º º e 4'5
Oxygen, ſº © e & e º e 1-3
100'0
The density of such a mixture is, by calculation, 0:5813.
Killingworth Gas.-Specific gravity 0-6306.
Carburetted hydrogen, e <e º . 82°5
Nitrogen, e e º e º ... 1
Oxygen, º º º º e º e 1-0
100'0
The theoretical density of this gas, deduced from its composition, is
0-6308.
The Hebburn gas was of specific gravity 0.6327.
Seventy-nine measures of the Killingworth gas, mixed with an equal
volume of chlorine, left in the dark for eighteen hours, and afterwards
washed with alkali, were reduced to seventy-five measures, from which
the presence of four measures of olefiant gas might be inferred. But in
a comparative experiment made at the same time on 253 measures of
pure gas of the acetates, mixed with an equal volume of chlorine, a con-
traction occurred of 1-3 measure ; that is in exactly the same proportion
as with the fire-damp. -
It was observed that phosphorus remains strongly luminous in these
gases, mixed with a little air, while the addition to them of one-four-
hundredth part of olefiant gas, or even a smaller proportion of the vola-
tile hydrocarbon vapours, destroyed this property. Olefiant gas itself,
and all the allied hydrocarbons, were thus excluded.
Another property of pure light carburetted hydrogen, observed by
myself, enabled me to exclude other combustible gases, namely, that the
former gas is capable of entirely resisting the oxidating action of pla–
tinum black, and yet permits other gases to be oxidated, which are
mixed with it even in the Smallest proportion, such as carbonic oxide
and hydrogen the first slowly and the last very rapidly; air or oxygen
gas being, of course, also present in the mixture. Now platinum black
had not the Smallest action on a mixture of the gas from the mines with
air. No moisture appeared or Sensible contraction, and no trace of
carbonic acid could be discovered after a protracted contact of twenty-
four hours; while, with the addition of one per cent of hydrogen, the
first effects were conspicuously evident in three minutes, and with the
same proportion of carbonic oxide, the gas became capable of affecting
lime-water in half an hour. These experiments were repeated upon each
of the three specimens of fire-damp.
OF THE NEWCASTLE COAL MINES. 87
Potassium fused in the fire-damp did not become covered with the
green fusible compound of carbonic oxide, nor occasion any contraction.
Indeed, however carefully the heat was applied to the potassium by
means of an oil-bath, a slight permanent expansion always ensued.
The same thing occurred in pure gas of the acetates. It appeared that
potassium could not be heated above 300 Fahr. in pure carburetted
hydrogen, without causing a decomposition and the evolution of free
hydrogen gas.
The gas was also inodorous, and clearly contained no appreciable
quantity of any other combustible gas than light carburetted hydrogen.
The only additional matters present were nitrogen and oxygen; the
specimen collected in the most favourable circumstances for the exclu-
sion of atmospheric air, namely, that from the Bensham seam, still con-
taining 0.6 per cent. of oxygen. The gases also contained no carbonic
acid.
It is worthy of observation that nothing oxidable, at the tempera-
ture of the air, is found in a volatile state associated with the perfect
coal of the Newcastle beds. The remarkable absence of oxidability in
light carburetted hydrogen appears to have preserved that alone of all
the combustible gases originally evolved in the formation of coal, and
which are still found accompanying the imperfect lignite coal of Ger–
many, of which the gas has been examined. This fact is of geological
interest, as it proves that an almost indefinitely protracted oxidating
action of the air must be taken into account in the formation of coal, air
finding a gradual access through the thickest beds of superimposed
strata, whether these strata be in a dry state or humid.
In regard to measures for preventing the explosion of the gas in coal
mines, and of mitigating the effects of such accidents, I confine myself
to two suggestions. The first has reference to the length of time which
the fire-damp, from its lightness, continues near the roof, without mixing
uniformly with the air circulating through the workings. It was found
that a glass jar, of six inches in length and one inch in diameter, filled
with fire-damp, and left open with its mouth downwards, continued to
retain an explosive mixture for twenty minutes. Now it is very desir-
able that the fire-damp should be mingled as soon as possible with the
whole circulating stream of air, as beyond a certain degree of dilution it
ceases to be explosive. Mr. Buddle has stated, “that immediately to
the leeward of a blower, though for a considerable way the current may
be highly explosive, it often happens that after it has travelled a greater
distance in the air-course, it becomes perfectly blended and mixed with
the air, so that we can go into it with candles; hence, before we had
the use of the Davy lamp, we intentionally made ‘long runs, for the
purpose of mixing the air.” It is recommended that means be taken to
88 ON THE MOTION OF GASES.
promote an early intermixture of the fire-damp and air; the smallest
force is sufficient for this purpose, as a downward velocity of a few
inches in the second will bring the light gas from the roof to the floor.
The circulating stream might be agitated most easily by a light portable
wheel, with vanes, turned by a boy, and so placed as to impel the air in
the direction of the ventilation, and not to impede the draft. The gas
at the roof undoubtedly often acts as an explosive train, conveying the
combustion to a great distance through the mine, while its continuity
would be broken by such mixing, and an explosion, when it occurred,
be confined within narrower limits.
Secondly, no effective means exist for succouring the miners after
the occurrence of an explosion, although a large proportion of the deaths
is not occasioned by fire, or injuries from the force of the explosion, but
from Suffocation by the after-damp, or carbonic acid gas, which diffuses
itself afterwards through all parts of the mine. It is suggested that a
cast-iron pipe, from eight to twelve inches in diameter, be permanently
fixed in every shalt, with blowing apparatus, above, by which air could
be thrown down, and the shaft itself immediately ventilated after the
occurrence of an explosion. It is also desirable that, by means of fixed
or flexible tubes, this auxiliary circulation should be further extended,
and carried as far as practicable into the workings.
XIV.
OF THE MOTION OF GASES.1 PART I.
From Phil. Trans. iv. 1846, pp. 573-632; ii. 1849, pp. 349-362.
THE spontaneous intermixture of different gases, and their passage
under pressure through apertures in thin plates and by tubes, form a
class of phenomena of which the laws have been only partially estab-
lished by experiment. The separation of two gases by a porous screen,
such as a plate of dry stucco, will prevent for a short time any sensible
intermixture arising from slight inequalities of pressure, but such a
barrier is readily overcome by the diffusive power of the gases, which is
fully equal to their whole elastic force. Hence a cylindrical glass jar
With a stucco top, filled with any gas and standing over water, affords
the means of demonstrating the unequal diffusive velocities of air and
the gas, by the final contraction or expansion of the gaseous contents of
the jar, after the escape of the gas is completed. Compared with the
* Received June 18; Read June 18, 1846,
ON THE MOTION OF GASES. 89
volume of air which has entered, the volume of gas which has passed
simultaneously outwards is found to be in the inverse proportion of the
square root of the specific gravity of the gas. The diffusive velocities
therefore of different gases are inversely as the square root of their
densities; or the times of diffusion of equal volumes directly as the
square root of the densities of the gases.” -
Such is also the theoretical law of the passage of gases into a vacuum,
according to the well-known theorem that the molecules of a gas rush
into a vacuum with the velocity they would acquire by falling from the
summit of an atmosphere of the gas of the same density throughout;
while the height of such an atmosphere, composed of different gases, is
inversely as their specific gravities. This is a particular case of the
general law of the movement of fluids, well established by observation
for liquids, and extended by analogy to gases. The experiments which
have already been made upon air and other gases, by M. P. S. Girard”
and by Mr. Faraday,” are sufficient to show that the discharge of light
is more rapid than that of heavy gases; and are interesting as first
approximations, although incomplete and lending a very imperfect sup-
port to the theoretical law. Indeed some results obtained by these
experimenters and others, appear wholly inconsistent with that law,
such as Mr. Faraday's curious observations of the change of the relative
rates of hydrogen and olefiant gases in passing through a capillary tube
under different pressures; and my own observation, that carbonic acid
gas is forced by pressure through a porous mass of stucco as quickly or
more so than air is, although more than a half heavier; and that other
gases pass in times which have no obvious relation to their diffusive
velocities.”
In studying this subject, I found that it was necessary to keep
entirely apart the two cases of the passage of a gas through a small
aperture in a thin plate and its passage through a tube of sensible
length. The phenomena of the first class then became well-defined and
simple, and quite agreeable to theory. Those of the second class also
attained a high degree of regularity, where the tubes were of great
length, or being short were of extremely small diameter. Capillary
glass tubes, which varied in length from twenty feet to two inches, were
found equally available and gave similar results, where a sufficient resist-
ance was offered to the passage of the gas.
The rate of discharge of different gases from capillary tubes appears
to be independent of the nature of the material of the tube, in so far as
1 On the Law of the Diffusion of Gases; Transactions of the Royal Society of Edin-
burgh, vol. xii. p. 222; or Phil. Mag., 1834, vol. ii. pp. 175, 269,351. See ante, p. 44.
2 Annales de Chimie, etc., 2de Sér., t. 16, p. 129.
3 Quarterly Journal of Science, vol. iii. p. 354; and vol. vii. p. 106.
* Edinburgh Transactions, xii. 238. (Paper at p. 44, ante.)
90 ON THE MOTION OF GASES.
the rates were found to be similar for tubes of glass and copper, and even
for a porous mass of stucco. But while the discharge by apertures in
thin plates is found to be dependent in all gases upon a constant function
of their specific gravity, the discharge of the same gases from tubes has
no uniform relation to the density of the gases. Both hydrogen and
carbonic acid, for instance, pass more quickly through a tube than
oxygen, although the one is lighter and the other heavier than that gas.
I shall assume then for the present, that in the passage of gases through
tubes we have the interference of a new and peculiar property of gases;
and on the ground of a radical difference in agency speak of the two
classes of phenomena under different names. The passage of gases into
a vacuum through an aperture in a thin plate I shall refer to as the
Effusion of gases, and to their passage through a tube as the Transpira–
tion of gases. The determination of the coefficients of effusion and
transpiration of various gases will be the principal object of the following
paper.
PART I.-EFFUSION OF GASES.
1. Effusion into a Vacuum by a glass jet.
The glass jet was formed from a short piece of a capillary thermometer
tube, of which the bore was cylindrical, to which a conical termination
was given by drawing it out when softened by heat and breaking the
point. The aperture at the point of the jet was cylindrical, in a flat
surface, and so small that it could only be seen distinctly by means of a
magnifying-glass; its size, compared with other apertures, may be
expressed by the statement that one cubic inch of air of the usual tension
passed into a vacuum through this aperture in 2:18 seconds. By means
of a perforated cork this glass jet was fixed within a block-tin tube,
through which the gas was to be drawn; with the point of the tube
directed towards the magazine of gas, so that the gas in passing towards
the vacuum entered the conical point of the jet instead of issuing from it.
This form of the aperture reduced the rubbing surface of glass to a thin
ring, or made it equivalent to an aperture in a very thin plate; but the
mode of placing the jet, or direction in which the current passed through
the aperture, was found afterwards to be of little consequence.
The gas for an experiment was contained in a glass jar, of an ellip-
tical form, balanced like a gasometer over water, and terminated at top
and bottom with two short hollow cylindrical axes, of an inch in diameter;
its capacity between two marks, one on each of the cylindrical ends,
being 227 cubic inches. From this gasometer the gas was conveyed directly
into a U-shaped drying tube, 18 inches in length and 0.8 inch in dia-
meter, filled in some cases with fragments of chloride of calcium, in
ON THE MOTION OF GASES. 91
others with fragments of pumice-stone soaked in oil of vitriol; the pumice,
when used, having been first washed with water, to deprive it of soluble
chlorides. From the drying tube, the gas entered the tin tube occupied
by the glass jet, one end of that tub being connected with the drying
tube, and the other with an exhausted receiver on the plate of an air-
pump. The apparatus described is exhibited in fig. 1 of Plate XXXIII.,
with the exception of the elliptical gasometer, the place of which is
occupied there by the counterpoised jar A in the water trough. The
gas was thus forced through the minute aperture by the whole atmos-
pheric pressure. In making an experiment with any other gas than
atmospheric air, a considerable quantity of the gas was first blown
through the drying tube, from the gasometer, to displace the air in the
former; and to do this quickly an opening was made into the air-channel
beyond the drying tube, at G, by which gas might be allowed to escape
into the atmosphere without proceeding further or being drawn through
the glass aperture into the vacuum. This side aperture was closed by
a brass screw and leather washer. In making an experiment, the gaso-
meter was filled with the gas to be effused, and then connected with the
air-pump receiver, in which a constant degree of exhaustion was main-
tained by continued pumping. The interval of time was noted in
seconds, which was required for the passage of a constant volume of gas,
amounting to 227 cubic inches, namely, that contained between the two
marks in the elliptical gasometer. Or, the volume of gas effused was
more strictly 227 cubic inches, minus the volume of aqueous vapour
which saturates air at the temperature of the experiment; the vapour
being withdrawn from the gas, after it left the elliptical measure and
before it reached the effusion aperture. It is scarcely necessary to add
that great care is necessary during these and all other experiments on
gases, to maintain a uniform temperature. The use of a fire or stove
in the room in which the experiments were conducted was therefore
avoided, and such arrangements made that the temperature was kept for
five or six hours within a range of a single degree of Fahrenheit's scale.
Hydrogen.—In the experiments first made with air and hydrogen the
temperature was 59° Fahr., and the height of the barometer 30:14 inches;
a uniform exhaustion was maintained in the air-pump receiver of 29.3
inches, as observed by the gauge barometer attached.
The constant volume of dry air passed into the vacuum, or was
effused, in three experiments, in 494, 495, and again in 495 seconds.
The constant volume of dry hydrogen was effused, in two experi-
ments, in 137 and again in 137 seconds. Calculating from 495 seconds
as the time for air, we have—
Time of effusion of air,
Time of effusion of hydrogen,
*
s
7
7
92 - ON THE MOTION OF GASES.
Or, the result may be otherwise expressed, taking the reciprocals of the
last numbers:
Velocity of effusion of air, . © e • 1
Velocity of effusion of hydrogen, 3°613
The specific gravity of hydrogen gas, according to the most recent
and exact determination, that of Regnault, is 0.06926, referred to air
as unity; of which the square root is 0.2632, and the reciprocal of the
square root 37994; to which the numbers for the time and velocity of
hydrogen above certainly approximate.
Oaxygen and Nitrogen.—Temperature 60°; exhaustion maintained at
29-3 inches. The constant volume of air was effused in 494 seconds,
of oxygen in 520 seconds, and of nitrogen in 486 seconds, in one experi-
ment made upon each gas. Hence the following results:

Time temion, sº | W:#" |*:::::::::::::"
Air, l I l l
Oxygen, . 1'053 1-0515 0.9500 0-95.10
Nitrogen, 0°984 0-9856 1.0164 1 * 0.146
The densities made use of are those of M. Regnault, namely, 1.10563
for oxygen, and 0.97.137 for nitrogen. It will be observed, that the times
of effusion of these two gases correspond as closely with the square roots
of their densities as the mode of observation will admit of ; the times
observed being within one second of the theoretical times. :
Carbonic Oaside.--This gas was prepared by the action of oil of vitriol
upon pure crystallized Oxalic acid, and subsequent washing with alkali.
The temperature during the effusive experiment was 60°3; the usual
exhaustion was maintained. The time of effusion of air was 494 seconds;
of the same volume of carbonic oxide 488 seconds:

Time of effusion, | Square root of Velocity of Reciprocal of square
air = 1. density. effusion. root.
Carbonic oxide, . 0.987 0-9838 1.01.23 1:01.65
The effusion-rate of this gas approaches therefore very closely to the
theoretical number. In the calculations the density of carbonic oxide is
taken at 0.96779, as found by Wrede.
Carburetted Hydrogen, CH,-This was the gas of the acetates, pre-
pared by heating a mixture of acetate of Soda with dry hydrate of potash
and lime.
The temperature of the gases effused being 59°5, and the exhaustion
29-3 inches; the constant volume of air passed through the aperture in
493 seconds, of carburetted hydrogen in 373 seconds :
ON THE MOTION OF GASES. 93

Time, air = 1. Theoretical time. Velocity. Theoretical velocity.
Carburetted hydrogen,
0-756 0.7449 1.322 l'3424
The density of carburetted hydrogen is taken at 0:5549 in the cal-
culations.
Carbonic Acid and Nitrous Oxide. —In the first experiment with
carbonic acid, the gasometer with the gas was floated as usual over
water; thermometer 58°5. The effusion of air took place in 495 seconds,
of carbonic acid in 595 seconds. To diminish the loss of the latter
gas occasioned by its solubility in water, a second experiment was
made over brine : the time required by the carbonic acid was now 603
seconds. The velocity of effusion of carbonic acid is by the first experi-
ment 0-832; by the second it approaches more nearly the theoretical
number, calculated from 152901 (Regnault) as the density of this gas,
as appears below:

Time, air = 1. Theoretical time. Velocity. Theoretical velocity.
Carbonic acid, . . I-218 1-2365 0.821 0-8087
The observation on nitrous oxide was made on a different occasion,
with a temperature of 62°5. The time of effusion of air was then 488
seconds; of nitrous oxide 585 seconds, the gas being collected over
Water :

Time, air, – 1. Theoretical time. Velocity. Theoretical velocity.
Nitrous oxide, . . 1-199 1 -2365 0-834 0-8087
The specific gravity of nitrous oxide is assumed in the calculations
to be the same as that of carbonic acid. The time of effusion of both of
these gases is shortened by the loss of a portion of the gas, by solution
in the water of the pneumatic trough during the period of the experi-
ment, and falls below the theoretical number. In carbonic acid over
brine, where the injury is least from this cause, the observed velocity
is, however, still within one-seventieth part of that calculated from the
specific gravity of the gas.
Olefiant Gas—When this gas is prepared by heating sulphuric acid,
of specific gravity 1-6, with strong alcohol at the temperature of 3209,
in the proportion of six parts of the former to one of the latter, it appears
94 ON THE MOTION OF GASES.
to come off at first very pure, as it is entirely absorbed by the perchloride
of antimony, and contains therefore no carbonic oxide. But it is really
contaminated, I find, by a portion of another heavier gas or vapour (not
ether vapour), which cannot be entirely removed from it by washing
with alkaline water, oil of vitriol, or strong alcohol, and which may
raise the density of the gas above that of air. As the evolution of gas
proceeds, the proportion of the heavy compound diminishes, and it
finally disappears, and the gas attains its theoretical density; but it is
then again contaminated with more or less carbonic oxide. The latter
gas, however, being of sensibly the same density as olefiant gas, is not
likely to exert any influence upon its effusion rate. But before these
facts were ascertained this jet became unserviceable from an accident,
and the experiments made with it were all made upon the dense olefiant
gas, and gave an effusion time which slightly exceeded that of air.
2. Effusion into a Vacuum by a perforated brass plate A.
A minute circular aperture was made by means of a fine drill in a
thin plate of sheet brass 3; sth of an inch thick, and the opening still
further diminished by blows from a small hammer, of which the surface
was rounded. A small disc of the brass plate was then punched out,
having the aperture in the centre, which was soldered upon the end of
a short piece of brass tube, of quill size, so as to close the end of the
cylinder. This brass tube was then fixed, by means of a perforated
cork, within the tin tube, used as formerly, for conveying the gas from
the gasometer jar to the air-pump receiver; so that the gas should
necessarily flow through the small aperture in its passage, as before
through the glass jet. The aperture was of an irregular triangular
form, in consequence of the hammering of the plate. One cubic inch
of air of usual tension passed into a vacuum through this aperture
in 12:56 seconds. The volume of gas effused in an experiment was the
same as before, and the other arrangements similar, but the aperture in
the brass plate being Smaller than that of the glass jet, the effusion was
considerably slower.
The constant volume of 227 cubic inches of the following gases
passed into a vacuum of 293 inches by the attached mercurial gauge,
at the temperature of 63°3, in the following times:–
(1) Air in 47° 32", or 2852 seconds.
(2) Nitrogen in 46' 47", or 2807 seconds.
(3.) Oxygen in 50' 1", or 3001 seconds.
(4) Hydrogen in 13' 8", or 788 seconds.
(5) Carbonic acid (over brine) in 56' 54", or 3414 seconds.
oN THE MOTION OF GASEs. 95
These results, referred to air as unity, are as follows:—

Time of effusion. Theoretical time. Vººr Tººl
Air, . . . . . . . . 1 l I I
Nitrogen, . . . . . 0-9842 0-9856 1.0160 1:01.46
Oxygen, . . . . . I •0502 1:05.15 0.9503 0-95.10
Hydrogen, . . . . . . 0-2763 0.2632 3.607 3-7994
Carbonic acid, . . . 1-1971 1.2365 0-8354 0-8087
The experimental results of the velocity of effusion of nitrogen and
oxygen accord very closely with theory, the velocity of the first being
only 0-0014 in excess, and the second 0-0007 in deficiency. Indeed the
differences fall within the unavoidable errors of observation in deter-
mining the specific gravity of these gases, unless conducted with the
greatest precautions. Of hydrogen, the velocity of effusion observed is
3:607 times instead of 380 times greater than air. It thus suffers a
small but sensible reduction of its velocity, which can be referred, as
will afterwards appear, to the thickness of the plate and the aperture
being in consequence Sensibly tubular. A portion of the carbonic acid
gas must have been absorbed by the brine during the long continuance
of the experiment, nearly an hour; to which the quickness of the rate
of that gas may be referred; the velocity of its passage being thus
apparently increased from 0-81 to 0-835.
The experiment was varied by observing the time in which gas
entered a vacuous receiver upon the plate of the air-pump, in quantity
sufficient to depress the gauge barometer from 28 to 23 inches. An
exhaustion was always made at first of upwards of 29 inches, and the
instant noted at which the mercury passed the 28th and 23rd inches of
the scale. The times of effusion were as follows, the temperature
being 66° — -

Experiments. Velocity of effusion.
* 1. 2. | 3. Mean. || Observed. Calculated.
Air, . . . . . . . . 474 474 & º & 474 I I
Oxygen, . . . . . 501 502 499 || 500-7 || 0-9467 || 0-95.10
Nitrogen, . . . . . . 468 || 469 ... 468°5 || 1:01.17 || 1:01.46
Olefiant gas, . . . . . 467 469 tº º e 468 1.0128 || 1:01.47
Carburetted hydrogen, . 357 e e º ... 337 1°3278 || 1:3369
Carbonic acid, . . . . 573 573 ... [ 573 0-8272 || 0-8087
The same close correspondence is manifest here between the
observed and calculated velocities.
The whole results leave no doubt of the truth of the general law,
that different gases pass through minute apertures into a vacuum in times
which are as the square roots of their respective specific gravities; or with
96 ON THE MOTION OF GASES.
velocities which are inversely as the square roots of their specific gravities;
that is, according to the same law as gases diffuse into each other.
It appears that the proper effect of effusion can only be brought out
in a perfect manner when the gas passes through an aperture in a plate
of no sensible thickness, for when the opening becomes a tube, however
short, the effluent gas meets a new resistance which varies in the dif-
ferent gases according to an entirely different law from their rates of
effusion, namely, the resistance of transpiration. The deviation is most
considerable in hydrogen, which rapidly loses velocity if carried through
a tubular opening, when compared with air. This was illustrated by
experiments made upon the glass jet of the former observations; which
was operated upon in four different conditions as to length. The point
had been drawn out rather long at first, so that it admitted of portions
of 0.2 inch, 0.1 inch, and 0.07 inch, being broken off successively before
it was reduced to the form of a blunt cone, which it had when used in
the experiments already detailed. Air and hydrogen were effused from
this jet into the exhausted receiver till the mercurial gauge fell from 28
to 4 inches, with the jet in the different states described.
When the glass jet was of greatest length, the time of air was 335
and 337 seconds in two experiments, and of hydrogen 120 seconds in
two experiments; which give 2:800 as the velocity of effusion of
hydrogen. -
After the first portion was broken from the point, by which of
course the aperture was enlarged, the time of air was 175 seconds in
two experiments, of hydrogen 55 and 56 seconds; giving 3-153 for the
effusive velocity of hydrogen. - *
After the second abridgment in its length, the time of passage of
air by the jet was 110 seconds in two experiments, of hydrogen, 33, 32.
and 33 seconds in three experiments; giving 333 for the velocity of
hydrogen.
When still further reduced in length, a larger jar being used as the
vacuous receiver, the time of air was in two experiments 408 and 410.
seconds; of hydrogen in three experiments, 122, 120 and 122 seconds,
giving 338 for the velocity of hydrogen. Thus, as the jet was pro-
gressively shortened, the relative velocity of the passage of hydrogen
continually rose, passing through the numbers 2:8, 3:153, 3:33 and 3:38.
By reversing the direction of the stream of gas through the aperture in
its last condition, the effect of friction was still further diminished, and
the velocity of hydrogen raised to 3.61, as in the experiments previously
recorded, which were made with this jet in an inverted position. It
may be fairly presumed, therefore, that if the length of the tube or
thickness of the plate containing the aperture was still further
diminished, the effusive velocity of hydrogen, compared with air, would
ON THE MOTION OF GASES. 97
be increased, and approximate more nearly to 380, the theoretical
number.
The tubularity of the opening quickens, on the contrary, the passage
of carbonic acid and nitrous oxide in reference to air; for these gases are
more transpirable than air, although less effusive; hence their observed
time of effusion is always sensibly less than their calculated time.
3. Effusion of Nitrogen and Oaygen, and of mixtures of these Gases under
different pressures, by a second perforated brass plate B.
This brass plate was of the same thickness as the last (#sth of an
inch); the aperture was circular and also ºsth of an inch in diameter,
as measured by a micrometer; and the velocity with which air of the
usual tension passed into a vacuum by the aperture, one cubic inch in
6:08 seconds. The rate of passage was therefore rather more than twice
as quick as by the first perforated plate A.
A two-pint jar was used as the air-pump receiver, or aspirator-jar,
as it may be called; and the capacity of the vacuous space into which
the gas effuses, including the tubes and channels of the air-pump as well
as the jar, was found to be 72.54 cub. in. An exhaustion was always
first made of about 29 inches by the gauge barometer of the pump, and
then the gas allowed to enter from a counterpoised bell-jar over water
(fig. 1, Plate XXXIII). The instant was noted at which the mercury
fell to 28 inches, when the observation began, and again at 20 and 12
inches, or after two intervals of 8 inches each; and again at 4 and 2
inches by the gauge barometer. The experiments were made suc-
cessively on the same day in the order given, with the barometer at
29.34 inches and thermometer at 49". A small thermometer placed
within the aspirator-jar was observed to rise 1. Fahr. very uniformly
during the continuance of an experiment. The effusion of air is
repeated at the close of the experiments to determine whether or not
any change of rate had occurred during their continuance.

TABLE I.—Effusion.
Gauge barometer Air. Nitrogen. Oxygen. 50 mitºgº.
in inches.
I. II. I. II. I. II. I. II.
28 ô ô Ö Ö ô 6 Ö Ö
20 120 120 119 119 126 126 122 122
12 123 122 120 120 128 130 125 125
8 68 68 67 67 72 72 70 69
4 84 84 83 83 89 88 85 S6
2 57 57 55 54 59 59 57 57
452 451 444 444 || 474 475 459 459
98 ON THE MOTION OF GASES.
TABLE II.-Effusion.

Gauge barometer 25 nitrogen + 75 oxygen. 75 nitrogen + 25 Oxygen. Air.
in inches.
I. II. I. II.
28 4/ al fi au £1
20 122 122 122 121 120
I2 125 125 122 122 123
8 70 69 68 68 68
4 85 86 85 85 83
2 57 57 56 56 57
459 459 453 453 451
The near approach to equality in the times from 28 to 20, and from
20 to 12 inches throughout the whole of these experiments, is very
remarkable. Under an average pressure of 24 inches in the former
portion of the scale and of 16 in the latter, the gases effuse with nearly
equal velocities; which confirms the observation of MM. de Saint-
Venant and Wantzel, on the passage of air through a minute aperture,
namely, that above two-fifths of an atmosphere, the further increase of
the pressure is attended with a very slight increase in the velocity of
passage." In the experiments above with an increase of pressure from
16 to 24, or of one-half, the increase in velocity is not in general more
than one-sixtieth part. -
In the table which follows the average times are given, which the
gauge barometer required to fall from 28 to 12 inches, and from 12 to 4
inches, taken from the preceding table, for air, nitrogen, and oxygen,
and also the ratio between the times of these gases, that of air being
taken as unity, with their relative velocities, also referred to the
velocity of air.

Time in seconds. Time of air =1. Velocity of air =l.
Gauge barometer.
- Air. Nitrogen. Oxygen. Nitrogen. Oxygen. Nitrogen. Oxygen.
From 28 to 12 in., 242.5 239 255-0 || 0'9855 || 1:0515 || 1:01.46 || 0-95.10
From 12 to 4 in., 152-0 150 1605 || 0-9868 || 1:0558 || 1:01:33 || 0-9470
These results do not indicate any material difference between the
ratios of effusion of these gases at different pressures. At the low as
well as the high pressure, the velocities are in close accordance with
the law of effusion; indeed they correspond as closely as the short-
ness of the time of observation justifies any inference; the small devia-
tions observable being quite within the amount of errors of observation.
* Journal de l'Ecole Royale Polytechnique, tome xvi., 27 Cahier, 1839, p. 85. This
memoir contains a valuable mathematical discussion of the velocities with which air
flows into a receiver at different degrees of exhaustion.
ON THE MOTION OF GASES. 99
The results for the mixtures of oxygen and nitrogen are as follows,
for similar divisions of the scale — -

Time in Seconds. Time, air =l.
barometer.
Gauge I II. III. I. II. III.
50N+500.|25N+75 O.75 N+250. Mixture. Mixture. Mixture.
From 28 to 12 in., 247 252 243.5 1.0185 | 1-0391 || 1:004]
From 12 to 4 in., 155 157 153 1.0.197 | 1.0329 || 1:0066
In these instances as well as in the unmixed gases, the results do
not justify the inference of any difference in the ratios of effusion at low
from the ratios which hold at high pressures.
It appears, on comparing the times observed of the mixtures with
the times calculated from the unmixed gases, that they sensibly agree.
Thus the mean rate or time of 50 nitrogen + 50 oxygen, or square root
of the specific gravity of that mixture, is 1-0191, the observed rate
1.0185; of 25 nitrogen + 75 oxygen, the mean rate is 1.0354, the
observed rate 1:0391; of 75 nitrogen + 25 oxygen, the mean rate is
1.0025, the observed time 1-0041, in the range between 28 and 12
inches of the gauge barometer. Lastly, the particular mixture forming
atmospheric air has already been seen to have the rate corresponding
with its specific gravity or its composition. It may hence be inferred
that any mixture of oxygen and nitrogen will possess the average rate of
effusion of its constituent gases.
4. Effusion of Air, Carbonic Owide, Oxygen, and of a mixture of Carbonic
Owide and Oaxygen at different pressures, by Plate B.
The carbonic oxide was prepared according to Mr. Fownes's process,
by heating oil of vitriol upon ferrocyanide of potassium : the gas was
collected, as a measure of precaution, over alkali.
The arrangements were similar to the last; barometer at 29:29
inches, thermometer 52°.

TABLE III.-Effusion.
Gauge barometer Air. Carbonic oxide. Oxygen. bºn
in inches.
I. II. I. II. I. II. I. II.
28 Æ £f &M Aft *. Aj Aff £i
20 118 119 116 117 125 126 12] I2]
12 120 120 118 I 17 126 126 123 122
8 67 66 66 66 71 71 68 68
4 81 82 80 81 86 86 83 83
2 56 56 55 55 60 60 58 58
442 || 443 435 | 436 468 469 453 452
100
ON THE MOTION OF GASES.
The passage of the gases is somewhat quicker throughout than in
the preceding experiments with the same plate, but the ratio between
their velocities remains constant.
Comparing again the same portions of the scale, we have—

Gauge barometer.
Time in seconds.
Time, air =l.
Air. Cº. G Oxygen. Mixture. C.ic Oxygen. Mixture.
From 28 to 12 in., 238.5 234 251-5 243 0-9811 | 1.0545 || 1:0188
From 12 to 4 in., 148 146.5 157 151 0.9898 || 1:0608 || 1:0202
Taking 0.96779 as the specific gravity of carbonic oxide, the Square
root is 0.9838, which corresponds closely with the observed time above,
being intermediate between the times for the two different portions of
the scale. º
The time of effusion also of the mixture of carbonic oxide and
oxygen in equal volumes is obviously the square root of the density of
the mixture of the two gases:
Observed time of mixture,
Calculated time of gases, .
1-0.188
1.0182
**
The observed time of effusion of the mixture being within one thousandth
part of the calculated time.
5. Effusion of Carbonic Acid, Air, and of mixtures of Carbonic Acid and
Air, at different pressures, by Plate B.
The arrangements continued the same as in last experiments;
barometer 29'58 in.; thermometer 49".
TABLE IV.-Effusion.


Gauge Air, Carbonic acia. | Fºº |º] ſº
barometer
in inches.
I. II. I. II. I. II. I. II. I. II.
28 4A 4t Af ** &A Ö Aſº ô AA - MA
20 121 12] 145 146 141 140 135 134 128 128
12 123 123 150 149 143 143 137 137 131 131
8 69 70 83 84 81 80 76 77 74 73
4 85 84 103 103 98 99 95 94. 90 90
2 58 59 7] 70 68 67 64 64 6] 61
456 457 552 552 531 529 507 506 484 483
ON THE MOTION OF GASES.
101
Comparing again the times in the two divisions of the scale adopted
in the preceding tables:
Time in Seconds.

| Gauge barometer. Air. Carbonic acid. Mixture I. Mixture II. | Mixture III.
From 28 to 12 in., ...... 244 295 283'5 271-5 259
From 12 to 4 in., ...... 154 187 179 171 163-5.
Time of Effusion, time of Air = 1.
Carbonic acid. Mixture I. Mixture IL Mixture III.
Gauge barometer.
Observed. | Calculated. Observed. | Calculated. Observed. | Calculated. Observed. | Calculated.
From 28 to 12 in.., | 1.2090 1-2365 || 1:1618 11818 || 1:1127. I-1245 | 1.0618. 10647
From 12 to 4 in.., | 1:2143 l'?365

The calculated number for carbonic acid (1-2365) is the theoretical
time, or square root of the density of the gas; the calculated times for
the mixtures are also the square roots of the respective gravities of those
mixtures.
The times of effusion of carbonic acid compared with air do not
therefore differ more than the numbers 1-209 and 1214, in the two
divisions of the scale; or 1 part in 242, a deviation which may be con-
sidered as within the errors of observation.
The mixtures of carbonic acid and air have also the mean times of
the pure gases.
6. Effusion of mixtures containing Hydrogen.
*[I was induced to examine the effusion of mixtures of hydrogen
and other gases very minutely, in order to elucidate if possible certain
singular peculiarities which were observed in the transpiration of these
mixtures by tubes. A new plate E was employed, composed of thin
platinum foil régth of an inch in thickness, with a circular aperture
głoth of an inch in diameter, as measured by Mr. Powell by means of
a micrometer. It was desirable to simplify the experiment at the same
time by operating upon a constant volume of gas, measured before
effusion, and drawn into an aspirator-jar which was maintained vacuous,
or as nearly so as possible, by uninterrupted exhaustion. The gas was
measured in a globular jar, to which more particular reference will be
made hereafter. It contained 65 cubic inches between two marks, one
upon each of its tubular axes, and was supported vertically over the
water of a pneumatic trough. * —
1 The passages and tables in this paper, which are enclosed in brackets, as the follow-
ing to p. 103, have been added during the progress of the paper through the press, and
the date of the addition is in each case noted at the end of the last paragraph.—S. H. C.
102 ON THE MOTION OF GASES.
The littlebrass tube upon which the perforated plate is fixed (a.in fig. 5,
Plate XXXIII) was now made to screw upon the end of one of the stop-
cocks, namely, L (fig. 1), which is immediately attached to the aspirator-
jar, and projected upwards within the block tin tube H. The perforated
plate was fixed to the end of its brass tube by means of soft solder.
The results thus obtained I consider superior in value to those already
detailed, from the longer periods of observation, the time for air generally
amounting to 800 or 900 seconds; from the new plate being thinner and
its aperture of a regular circular form ; and from the greater simplicity
of the conditions of the experiment, namely, the passage of the gases into
a sustained vacuum under the whole atmospheric pressure.
The series of experiments is divided into five sections, each contain-
ing the experiments of one day, to which the height of the barometer
and the temperature are added. Two observations were made of the
time of effusion in seconds for each gas, which are given under the
columns of experiments I. and II., and the mean of the two experiments
is added in a third column. This mean is expressed in the column
which follows, with reference to the time of oxygen as 1. The addi-
tional column headed “calculated times of mixtures, oxygen = 1,”
contains times of the mixtures, calculated from their specific gravities,
being the square roots of the densities of the respective mixtures. The
observed times of the hydrogen mixtures will be seen to correspond very
closely with these calculated numbers, the maximum divergences not
exceeding that of pure hydrogen itself.
TABLE V-Effusion into a Sustained Vacuum by Platinum Plate E.

I. II. Mean. Oxygen-1. §º. Barometer. º g
SECTION I. O
Oxygen, . & . 909 || 909 909 1:0000 tº º tº 30-396 | 68
Air, . e º . 866 || 865 | 865-5 || 0-9521
Hydrogen, ſº . . 242 242 242 0-2662
Carburetted hydrogen, 624 622 || 623 0-6853
Carbonic oxide, . | 849 || 850 | 849-5 || 0-9345
Nitrogen, . g . 850 | 851 850°5 || 0°9356
Air, . º ſº . 864
Carbonic acid, . . 1053 || 1051 |1052 1-1573
SECTION II.
Oxygen, . sº . 912 912 912 1.0000 tº $ tº 30°288 66
y • & & . 868 || 867 867-5 || 0-9512
Hydrogen, gº . 240 240 240 0.2631
25H + 75 Air, . . 756 756 756 0-8289 || 0-8328
50H +50 Air, . , 633 || 633 || 633 0-6940 || 0-6951
75H+25 Air, . , 483 || 483 || 483 0.5296 || 0-5224
80H +20 Air, . . . 444 || 444 || 444 0°4868 || 0-4805
90H + 10 Air, . . | 358 || 358 358 0-3925 || 0-3830
95H + 5 Air, . . 309 || 309 || 309 0-3388 || 0-3296
Air, . * g g 864
ON THE MOTION OF GASES.
103
TABLE W.-continued.

I. II. Mean. Oxygen-1. Śº. Barometer. ºtº
SECTION III. O
Oxygen, . © 912 910 911 1-0000 30°219 66
Air, . tº e 867 865 866 0-9506
Hydrogen, {} 239 241 240 0-2634
12.5H + 87.50, . 853 855 854 0-9374 || 0-9396
25 H + 75 O, . 796 || 796 || 796 0-8737 || 0-8750
37.5H + 62:50, . 733 | 733 | 733 0.8046 0-7990
50 H + 50 0, . 661 | 661 | 661 0-7255 || 0-7289
62.5H + 37-50, . 586 586 585-5 0.6427 0-6435
75 H + 25 O, . 501 || 501 || 501 0-5499 || 0:5449
80 H +20 O, . 460 || 461 || 460°5 || 0'5055 || 0:5000
90 H + 10 O, . 368 || 368 368 0.4039 || 0-3954
95 H + 5 O, . 312 || 312 || 312 0°3424 || 0°3309
Air, . & 860.
SECTION IV.
Oxygen, . & 914 || 913 913-5 1:0000 29-673 64
Air, . g iº 870 869 869-5 || 0-9518
Carbonic oxide, . 854 853 | 853-5 0-9343
Hydrogen, 238 239 238°5 || 0:2610
25H + 75CO, 749 || 748 || 748-5 0.8193 || 0-8199
50H + 50CO, 626 || 626 626 0-6852 0-6848
75H+25CO, 478 || 478 478 0.5231 || 0-5155
80H +2000, 445 445 || 445 0°4871 || 0:4745
90H + 10CO, 360 360 || 360 0-3940 || 0-3793
95H+ 5CO, 314 || 314 || 314 0.3437 || 0-3213
Air, . 870
SECTION V.
Oxygen, 915 914 || 914°5 l'0000 29'500 | 63
Air, . & 870 869 869-5 0-9508
Nitrogen, . 855 | 854 || 854-5 || 0-9344
Hydrogen, 241 24] | 241 0-2635
25H +75N, 753 || 753 || 753 0-8234 0-8213
50H + 50N, 631 631 631 0-6899 || 0-6859
75H+ 25N, 480 478 || 479 0°5238 || 0-5163
80H + 20N, 442 442 || 442 ()-4833 0°4752
90H + 10N, 359 359 || 359 0-3925 || 0-3797
95H + 5N, 309 || 310 || 309.5 || 0:3379 || 0.3215
Hydrogen, 24]
Air, . tº 869
The principal results of the preceding table, and also the results of
two series of experiments or mixtures of hydrogen with carburetted
hydrogen (CH2) and with carbonic acid, are exhibited by means of the
curves projected in Plate XXXIV., for the purpose of comparing with
them the results of the transpiration of the same mixtures exhibited in
Plate XXXV., which I have not yet succeeded in reconciling with any
physical law. Feb. 1846.]
The numbers at the top and bottom of the Plate, which apply to the
vertical lines, express the times of effusion, the time of oxygen being
104 ON TEIE MOTION OF GASES.
taken as 100; while the numbers to the right of the table, and which
apply to the horizontal lines, express the volumes of hydrogen in 100
volumes of the mixture. Thus the curves all terminate above in a
common point, 26-3, the time of 100 hydrogen; and each terminates
below with the proper time of the particular gas which is mixed with
hydrogen, the proportion of hydrogen being then 0, and that of the other
gas 100; that is, the curve of the carburetted hydrogen mixtures at
72:32; the curve of the nitrogen mixtures at 93-5; that of the air
mixtures at 95.1; that of the oxygen mixtures at 100, and that of the
carbonic acid mixtures at 116.
7. Effusion of Air of different Elasticities or Densities, by brass plate B.
In all the experiments hitherto described, the air or gas effused was
under the atmospheric pressure, which varied only within narrow limits.
It was desirable to know whether the time remained constant for the
passage into a vacuum of equal volumes of air of all densities, which
the theory of the passage of fluids into a vacuum requires.
The air was drawn into the receiver of an air-pump (fig. 2, Plate
XXXIII.), maintained vacuous by continued pumping, from the globular
gas receiver a, placed in a deep glass basin half-filled with water and
used as a pneumatic trough; this basin and the globular vessel being
placed on the plate of a second air-pump under a large bell-jar in which
a partial exhaustion could be maintained during the continuance of the
experiment. The vessel a had tubular openings at top and bottom; its
capacity between the marks b and c in these necks was 65 cubic inches;
the lower tube was expanded under the mark b into an open funnel;
the upper tube was cylindrical with a flange or lip, and had a Sound
cork fitted into it. A short brass tube d, of quill size, soldered to the
end of the stopcock e, descended into the bell-jar and passed through
the cork of a, which was perforated. The vessel a having thus an air-
tight communication with the exhausted receiver v of the first air-pump,
by the tube F, the drying tube U and the tube H.; a measured quantity
of air (65 cubic inches) could be drawn from it by observing the time
which the water of the trough took to rise from the mark b to c. The
perforated brass plate, through which the gas had to pass, was attached
to the stopcock L, as before, and was therefore within the tube H. It
is represented of one-fourth of its linear dimensions in fig. 5, Plate
XXXIII.
When the large bell-jar over a was not exhausted, the gas in the
latter was of the atmospheric tension. With the barometer at 29-28
inches, and thermometer at 54°, the air was withdrawn from the globe
a, in 388 seconds in one experiment, and in 389 seconds in another.
ON THE MOTION OF GASES. 105
The pressure upon the air in a was then reduced to three-fourths of
an atmosphere, by exhausting so that the gauge barometer stood at 7:32
inches from the bottom of the scale, which is one-fourth of the whole
pressure of 29:28 inches. The globe a was thus occupied by air of the
tension of three-fourths of an atmosphere, or 21'96 inches. It was in
this state connected with the vacuous receiver v of the air-pump, and
the time required for the effusion of the constant volume of 65 cubic
inches of air, measured in its rarefied state, between the marks b and c,
observed. The effusion of this volume of air of three-fourths density
was effected in two experiments in 389 and 392 seconds.
Again, the air in a being made of 14.64 inches tension, or half an
atmosphere, the constant volume was effused into a vacuum in 411 and
408 seconds. -
Lastly, with the air in a of 7:32 inches tension, or one-fourth of an
atmosphere, the time of effusion was 438 and 439 seconds. The results
therefore of the effusion of a constant volume are as follows:—
Time of effusion.
Air of 1 atmosphere . . 388°5 seconds . . 1"
Air of 0.75 atmosphere . . 390-5 seconds . . 10051
Air of 0-5 atmosphere . . 409:5 seconds , , 1.0541
Air of 0.25 atmosphere . . 438.5 seconds . . 1-1287
It thus appears that the effusion of air into a vacuum is very little
affected by a moderate change of density; air of 1 atmosphere and of
0-75 atmosphere passing in nearly the same time. The effect therefore
of the ordinary changes of the barometer on the effusion of air must be
small, if at all sensible. A retardation occurs in the effusion of air of
diminished density, which amounts to an excess of gºoth of the time,
on air of 0.75 tension; of ºoth on air of 0-5 tension, and ºth on air of
0.25 tension.
Experiments were also made on the effusion of air of higher density
than 1 atmosphere. The air was drawn of any required tension from 1
to 2 atmospheres from a strong globular vessel A (fig. 3, Plate XXXIII.),
provided with a gauge barometer and mercury, by which the tension of
the compressed air within it was observed. Before its admission into
this vessel the air was previously condensed in another vessel D by a
syringe, to a higher degree of density than was required in A, and the
supply of compressed air, regulated by the adjustment of an intermediate
stopcock, so as to keep the gauge of A at a constant elevation, which
could easily be done within ºth of an inch.
In experiments with compressed air, the latter was allowed to flow
into the two-pint jar exhausted on the plate of the air-pump, and the
time observed which the gauge barometer required to fall through its
range from 28 to 2 inches. During the following experiments the height
106 ON THE MOTTON OF GASES.
of the barometer was 29-3 inches, which is the value of 1 atmosphere,
and the thermometer 53°. -
TABLE VI.-Effusion of Air of different Densities.

Air of 1 || Air of 1-25 | Air of 1:5 | Air of 1°75 Air of 2 Air of 1
Height of w * h
gauge barom. atmosphere.jatmosphere. atmosphere.] atmosphere. atmospheres. |atmosphere.
in inches.
I. II. I. II. I. II. I. II. I. | II III. IV.
If || il II II il º, il il II il II
28 0 || 0 || 0 || 0 || 0 || 0 || 0 || 0 || 0 -
20 | 116 II6 90 91 || 76 || 75 65 65 56 || 55 117 | 117
12 || 118 118 92 || 91 || 76 || 76 || 64 || 64 56 || 56 || 118 || 118
8 65 65 47 || 48 38 38 33 || 33 30 29 | 66 67
4 79 80 50 50 41 40 || 33 || 32 26 28 80 80
2 54| 54| 26 ||25 |18 |18 || 16 || 17 | 14 || 13 54|| 53
432 || 433 305 |305 (249 (247 (211 |211 182 181 || 435 || 435
In these experiments the depression of the gauge barometer is not
produced by a constant volume of the compressed air, but by a volume
which is inversely proportional to the density of the compressed air;
half a volume of air of 2 atmospheres being equal in the aspirator-jar,
on the plate of the air-pump, to a whole volume of air of 1 atmosphere.
Correcting the times of the preceding table, we have the passage of
equal volumes of air of different densities, between the gauge height of
28 and 12 inches, as follows:— Time of effusion of equal volumes. -
Air of 1 atmosphere . . 234°5 seconds . . 1.
Air of 1:25 atmosphere . . 227-5 seconds . . 0-9701
Air of 1:5 atmosphere . . 227-2 seconds . . 0-9688
Air of 1.75 atmosphere . . 2252 seconds . . 0-9603
Air of 2 atmospheres. . 223 seconds . . 0-9510
It appears then that air of different densities between 1 and 2 atmos-
pheres is effused in nearly equal times, the time of effusion diminishing
slightly, not more than 5 per cent, with air of double tension. Taking
the whole range of the preceding and present results, we have air vary-
ing in density from 0.25 to 2 atmospheres, or from 1 to 8, while the
extreme variation in the time of the effusion of equal volumes is from
0.9510 to 1-1287, or from 1 to 1-1868.
In the lower part of the scale a more sensible inequality is perceived.
Thus, with an exhaustion of from 8 to 4 inches in the aspirator-jar, the
passage of equal volumes of air of different densities takes place in the
following times :— Time of effusion of equal volumes.
Air of 1 atmosphere . . 145 seconds . . 1.
Air of 1:25 atmosphere . . 1219 seconds . . 0-8407
Air of 1:5 atmosphere . . 117-7 seconds . . 0-8117
Air of 1.75 atmosphere . . 114-6 seconds . . 0-7903
Air of 2 atmospheres. . 113 seconds . . 0-7793
ON THE MOTION OF GASES. 107
Here the time of effusion of air of 2 atmospheres falls about 22 per
cent, below that of air of 1 atmosphere, while in the upper part of the
scale the difference was only 5 per cent.
[8. Effusion of Air of different Temperatures, by Plate F.
This plate was a portion of thin platinum foil, with an aperture of
an irregular hatchet form, of which the two greatest cross diameters
were a #0th and sºoth of an inch. The perforated plate was attached
to the end of the little brass cylinder by means of soft solder. A two-
pint jar, giving a cavity of 72.54 cubic inches, was used as the aspirator-
jar, and the time of the fall of the gauge barometer was observed from
28-5 to 23.5 inches, with the admission of dry air at different tempera-
tureS.
1. The temperature of the room being 41°Fahr., and the height of
the barometer 29'616 inches, dry air entered the aspirator-jar in three
experiments in 533, 532, and 530 seconds, of which the mean is 53166
seconds. The room being afterwards heated up to 52°, the time of
effusion of an equal volume of air was found to be, in three experiments,
525, 527, and 526 seconds, of which the mean is 526 seconds; or, a rise
of 11° in temperature has shortened the time of effusion by 5-66 seconds.
Taking the density of air at 32° as 1, at 41° it will be 0.9820, of which
the square root is 0.9909; and at 52° it will be 0.9609, of which the
square root is 0.9802. Now the relative times of effusion observed,
namely, 531-66 and 526 seconds, are as 0.9909 to 0-9803, numbers
which all but coincide with the square roots of the densities, 0-9909
and 0.9802, at the two different temperatures. -
2. With the barometer at 30-186 to 30:150 inches, experiments were
again made on the effusion of the same volume of dry air at 38', 48’’,
and 58”, four hours elapsing between each set of experiments, which
were required to bring up the room and apparatus to a uniform and
steady temperature. In three experiments at each temperature,
The time of effusion at 38° was 526, 527, and 526 seconds: mean 526.33
The time of effusion at 48° was 520, 521, and 520 seconds: mean 520:33
The time of effusion at 58° was 515, 516, and 515 seconds : mean 515:33
Here the first rise of 10° shortens the time of effusion 6 seconds,
and the second rise of 10° shortens the time 5 seconds more. The
density of dry air being 1 at 32°, it is at 38°, 0.9879; at 48’’, 0.9684;
and at 58°, 0.9497, of which three last densities the square roots are
0.9939, 0.9841, and 0.9745 respectively. Now the three mean times
of effusion observed are in the proportion of the numbers 0.9939, 0-9826,
and 0.97.31, which correspond more closely with the preceding Square
IOS ON THE MOTION OF GASES.
roots than could be expected from the nature of the experiments. It
appears then that the effusion time of air of different temperatures is pro-
portional to the square root of its density at each temperature. The
velocity of the effusion will be inversely as the square root of the air's
density. Hence two volumes of air which have not the same tempera-
ture, are, in regard to effusion, like different gases possessing the densi-
ties of the air at the two temperatures.
As the velocity of the effusion of air does not increase at a rate So
rapid as the direct proportion of its expansion by heat, it follows that
the flow of air under pressure, through a small aperture, is retarded by
heating the air; that is, the same absolute quantity or weight of air will
take a longer time to pass, when rarefied by heat, than when in a dense
state.
I have made several experiments on the influence of aqueous vapour
upon the effusion of air. When dry air was effused into an aspirator-
jar with the gauge barometer attached, and immediately afterwards air
saturated with moisture at the same temperature, the latter passed
through in sensibly the same time with comparatively large apertures,
but in a shorter time with small apertures, although in general without
much uniformity in successive experiments. Thus the time for dry air
being constant at 524 seconds with plate F of small aperture, barometer
29-812, and thermometer 49°; with moist air, the time gradually fell,
till at last it appeared to settle at 506 seconds, that number being
obtained in three successive experiments; the temperature in the mean-
time having risen to 51°. There is here an acceleration of 18 seconds,
of which not more than 2 seconds are accounted for by the diminished
density of the moist air, and 1 second more by the rise in temperature.
The moist air seemed also to have an extraordinary effect in opening
and enlarging fissures, and very soon rendered more than one platinum.
plate useless, which was fixed by brazing, by that action. Nov. 1847.]
PART II.-TRANSPIRATION OF GASES.
1. Transpiration of Air of different Densities or Elasticities, by a Glass
Capillary Tube E.
(a) The same arrangements were adopted as in the effusion of air of
different densities, lately described, the capillary tube being interposed
in the place of the perforated plate. The apparatus employed is repre-
sented in fig. 4, Plate XXXIII.
With barometer 29:28, and thermometer 54°, 65 cubic inches of dry
air of the atmospheric density were transpired from the globular vessel
a (fig. 2), into a good vacuum sustained by continued pumping, through
ON THE MOTION OF GASES. 109
a capillary glass tube E, twenty feet in length; the same volume of air
of 0.75 atmosphere and 0-5 atmosphere, measured at these pressures,
were also transpired by the same capillary. The times were as
follows:—

I. II. Mean.
Transpiration of air of 1 atmosphere, . 79% - 800 795.5
Transpiration of air of 0.75 atmosphere, . 1049 1051 1050
Transpiration of air of 0-5 atmosphere, . 1545 1542 1543.5
It is obvious that the times approach the inverse ratio of the ten-
sions, as will appear more clearly on comparing the times observed with
those calculated on that principle.

Time observed. | Time calculated. |
!
|
|
Transpiration of air of 1 atmosphere, l l
Transpiration of air of 0-75 atmosphere, . H 3133 1.3333
Transpiration of air of 0-5 atmosphere, I '9306 2
With air of higher tension than 1 atmosphere, the same apparatus for
compression was also employed as in the effusion experiments (fig. 3).
The capillary E communicated with the two-pint aspirator-jar (capa-
city 72'54 cubic inches), which was fully exhausted on the plate of the
air-pump. The air being then allowed to pass into the capillary, the
instant of time was noted when the gauge barometer fell to 28 inches,
and the other points described below. The external barometer stood
at 29-08 inches; thermometer at 53°.
TABLE VII-Transpiration of Air of different Densities.

Air of 1 Air of 2 - Air Of I-75 Air of 1:5 Air Of 1:25 Air Of 1
Gauge barometer atmosphere. atmospheres. |atmosphere, atmosphere. atmosphere. atmosphere.
in inches. - -
I. II. I. II. I. II. I. II. I. II. III.
28 s Ö Ö - Ö - Ö - Ö fi MI Il 1. II fi
20 253 254 66 67 85 86 114 || 114 | 162 | 161 255
12 310 || 310 70 69 91 90 123 124 182 179 311
8 220 220 37 37 49 49 69 70 110 || 109 221
4 349 352 39 40 53 53 78 77 132 134 346
2 328 || 328 20 19 29 28 41 4l 78 79 229
1460 ||1464 232 || 232 305 |306 || 425 || 426 | 664 | 662 1462
The times of transpiration in the preceding table require to be
&
110 ON THE MOTION OF GASES.
corrected, as they represent the passage of equal volumes of air measured
after and not before the transpiration. Thus the same depression of
the gauge barometer would be produced by half a volume of air of 2
atmospheres, as by a whole volume of air of 1 atmosphere; and it is
necessary therefore to double the times observed of air of the former
density, to obtain the time of passage of a whole volume. For the
transpiration of equal volumes, in the gauge-range from 28 to 20 inches,
which is most nearly equivalent to the action of a vacuum, we have—

Equal volumes. Observed time of transpiration. Calculated time.
Air of 1 atmosphere......... 254 seconds......... l I
Air of l'25 atmosphere......... 2019 seconds......... 0-7949 0-8000
Air of 1-5 atmosphere......... 171 seconds......... 0-6732 0.6666
Air of l'75 atmosphere......... 149-6 seconds......... 0-5890 0.5714
Air of 2 atmospheres ....... 133 seconds......... 0.5236 0.5
The calculated times of the last column are the reciprocals of the
tension, or number of atmospheres in the first column; they represent
the observed times within a sufficient degree of approximation, to prove
that for equal volumes of air of different densities, the times of transpira–
tion are inversely as the densities. The velocity of transpiration will
therefore be directly in proportion to the density of the air, air of
double density being transpired into a vacuum in half time.
This at once separates the action of a capillary tube from that of a
minute aperture; for air of all densities, it will be remembered, passes
into a vacuum by effusion with equal velocity, -
A consequence of this law immediately appears in conducting tran-
spiration experiments, in the marked influence of the height of the
barometer on the time of transpiration; the higher the barometer and
the denser the air, the more quickly does a constant volume of it pass
through a capillary tube into a väcuum.
This appears also to separate transpiration from the ordinary action
of friction; for the denser the air, the more should its passage be
retarded by friction. -
[2. Transpiration of Air of different Temperatures.
Dry air was transpired by a glass capillary tube K, of fine bore, 39.4
inches in length, into a two-pint jar till the gauge barometer fell from
28'5 to 23-5 inches, in 796, 794 and 794 seconds, in three successive
experiments, made at the temperature of 41°Fahr., and with the baro-
meter at 30.052 inches. Four hours afterwards, the air and all the
apparatus having been for some time at 58", an equal volume of dry
air was transpired twice in 814 seconds. A difference of 17 degrees
ON THE MOTION OF GASES. 111
of temperature has made a difference of 19 seconds in the time of tran-
spiration, and the dense cold air is transpired most rapidly. The times
are nearly in the inverse ratio of the Square root of the densities of air
at the two temperatures. - -
The transpiration of air in the first experiments which are made in
the morning is often observed to be more rapid than in those which
follow, owing I believe to the low nocturnal temperature being retained
for some time by the glass capillary. January 1847.]
3. Preliminary Eageriments on the Transpiration of different Gases by
t Capillary Tubes, A, B, and C.
The times of transpiration of the gases will be expressed in the
sequel with reference to the time of oxygen as unity instead of that of
air. Assuming what is now almost universally conceded, that the
atomic weights of the following elements are exactly expressed by
entire numbers, namely, oxygen by 8, nitrogen by 14, carbon by 6, and
hydrogen by 1, and that, while the equivalent proportion of the first
affords one volume of gas, that of each of the others affords two volumes,
we obtain the following theoretical densities for these elements, and
several of their gaseous compounds. The experimental determinations
which appear to be of most value are subjoined.
TABLE of Specific Gravities of Gases.
Air=1. Oxygen–l and 16.
Calculated. Observed. Calculated. Observed. -
Oxygen, . . . . 1-1099° 1'10563 Regnault. I I6 ||
Nitrogen, . . . . . 0-9712 0-97137 Regnault. 0-875014 (0.8785 Regnault.
Air, . . . . . . . . 1 l 0-901014-416 0.9038 Regnault.
Hydrogen, . . . . . 0-06937 0-06926 Regnault. 0.0625. I 0.0626 Regnault.
Carbon, . . . . . 0.4162 gº tº º tº £ tº ... 0-3750 6
Carbonic acid, . . . 1–5261 l'52901 Regnault. 1.3750/22 1:3830 Regnault.
Nitrous oxide, . . I-5261 tº ſº º e a º ... 1-3750/22 - -
Nitric oxide, . . . 1-0405 * * * tº a º ... 0.9375]15
Carbonic oxide, . . . 0-97.12 0.9678 Wrede. 0-875014 |0°8754 Wrede.
carburetted hydrogen, |0.5849 0.558.”* 0.5000 8 0:00, #.”
Olefiant gas, . . . . 0-97.12 (0.9852 Saussure. 0-875014 |0°8904 Saussure.
Sulphuretted hydrogen, | 1:1793 || 49.2% .#. } * 107664 §:
* Assigning the theoretical densities of 14 and 16 to nitrogen and oxygen, and
assuming air to be composed of 792 volumes of the first, and 20:8 volumes of the
second, the density of air will be expressed by the intermediate number 14:416; or,
with the density of air=1, the density of oxygen becomes 1:1099, and the density of
nitrogen 0-9712, both as given above. Hydrogen is calculated in the same column as
Path of oxygen (1.1099), carbon as ºths, carbonic acid and nitrous oxide as each ##ths;
nitric oxide as the mean of nitrogen and oxygen, carbonic oxide and olefiant gas as #ths
of oxygen; carburetted hydrogen as āths, and sulphuretted hydrogen as #ths.
112 ON THE MOTION OF GASES.
With the exception of the recent valuable determinations of M. Re-
gnault and Baron Wrede, the calculated specific gravities are probably
nearer the truth and more to be depended on than the experimental
results found in books, which are old, and generally not made with that
degree of precision which the science now requires.
Capillary A—This glass tube was thirty inches in length, and of a
fine cylindrical bore; it allowed 1 cubic inch of air of the usual tension
to pass into a vacuum in about 13 seconds. A pint-jar was exhausted,
of which the capacity, including the vacuous spaces of the air-pump,
was 41'64 cubic inches. The gas entered into this space, passing through
the capillary, and depressed the attached gauge barometer in the times
stated in the following Tables — - -
‘t
TABLE VIII.-Transpiration by Capillary A into a One-Pint Jar.
Barom. 29.55 in. Temp. 61°.
Air. Oxygen. Hydrogen.
Gauge barometer in inches.
I. II. I. II. I. II.
f/ Aſ M/ f/ M/ f/
28 0 0 0 0 | O 0 °
20 150-5 150 166-5 166 71 70.5
12 181-5 182 | 201 2015. 87 87
4 321 321 354'5 354 156 155
2 * * - • g e 213.5 215.5 94-5 94.5
From 28 to 4 inches . 653 653
From 28 to 2 inches . tº º e 935-5 937 408°5 407
Mean Results.
Gauge barometer. Air. - Hydrogen.
º Time in seconds ......... 150-25 70-75
From 28 to 20 inches; i...— ... O'9037 0.4255
tº Time in seconds ......... 181-75 87
From 20 to 12 inches Time of oxygen = 1 ...... 0-9031 0-4322
-> Time in seconds ......... 321 155-5
From 12 to 4 inches; i. of oxygen-1 ...... 0-9061 0.4389
© Time in seconds ......... tº º e 94'5
From 4 to 2 inches Time of oxygen = 1 ...... e e ºr 0°4405
-> Time in seconds ......... 653 313.25
From 28 to 4 inches Time of oxygen = 1 ...... 0-9047 0°4340
- Time in seconds ......... 407.75
From 28 to 2 inches } Time of oxygen = 1 ...... 0.4355

ON THE MOTION OF GASES. 1 H3
TABLE IX-Transpiration by Capillary A into a One-Pint Jar.
Barom. 29.5. Temp. 58°5.
Air. Oxygen. Carburetted Hydrogen. Carbonic Acid.
Gauge barometer
in inches.
I. II. I. II. I. . II. I. II.
- 28 // ſ/ f Z/ 6 6 M/ A/
20 150 150 | 166°5 166 94'5 94.5 | . 131 131
12 182°5 | 182 202 201'5 118.5 II9 158 158
4 318:5 318 || 359'5 357 198'5 198 272 271
2 1905 || 192 217 216 119 118 159 159
From 28 to 2 inches | 841.5 | 842 945.5 | 940.5 | 530-5 529-5 720 719
Mean Results.
Gauge barometer. Air. º Cºle
- Time in seconds ......... 150 94-5 13]
From 28 to 20 inches } Time of oxygen = 1 ...... 0-9022 0.5684 0.7879
º Time in seconds ......... 182°25 118.75 158
From 20 to 12 inches } Time of oxygen = 1 ...... 0-9033 || 0:5886 || 07831
-> Time in seconds ......... 318:25 198.25 271-5
From 12 to 4 inches } Time of oxygen = 1 ...... 0-8914 || 0:5505 || 0-7600
º Time in seconds ......... 191-25 118.5 159
From 4 to 2 inches } Time of oxygen = 1 ...... 0-8833 || 0:5473 || 0-7344
º Time in seconds ......... 841-75 530° 719.5
From 28 to 2 inches } Time of oxygen = 1 ...... 0.8928 0-5622 || 0-7633



It will be observed that the proportion between the times of oxygen
and air is subject to a variation at different parts of the scale, but is so
small as to be within the errors of observation; while this nearly con-
stant ratio of their times coincides almost with that of their specific
gravities (1 to 0.9038 Regnault),
The time or rate of hydrogen varies to the extent of 0.015 at different
parts of the scale, the passage of that gas being relatively quicker at
high than at low pressures. It is a question how far this variation in
the ratio is owing to the action of effusion; the time of effusion of this
gas being only 0:25, referred to oxygen as unity, while its time of tran-
spiration is 0.4355. The influence of effusion upon the rate of passage
is likely to be most considerable when the pressure is greatest; and
that of transpiration, on the contrary, most considerable when the resist-
H
114 - ON THE MOTION OF GASES.
ance to the passage of the gas is greatest and the pressure least, that is,
in the lower part of the scale.
It may be observed that the transpiration time of hydrogen does not
differ far from 0.4375, which is one-half of the transpiration time of
nitrogen, calculated from the experiment on air, or Seven-sixteenths of
that of oxygen.
Carbonic acid appears to be much more quickly transpired than
oxygen, although denser than that gas in the ratio of 11 to 8; but the
effusion time of carbonic acid being slow, any influence of effusion will
increase the time of transpiration of this gas, the reverse of what occurs
with hydrogen. The transpiration time of carbonic acid varies con-
siderably at different pressures, being slower by 0.0535 at the upper than
the lower part of the scale. An approach to 0-75, or twelve-sixteenths
of the time of oxygen, may be noted at present in the rate of this gas.
The transpiration rate of carburetted hydrogen appears to be affected
by an error of observation in the middle part of the scale; but its rate
is slower at the upper part than at the lower, to the extent of 0.02.11.
This is also in accordance with the assumed influence of effusion, the
effusion time of this gas being greater than its transpiration time.
The transpiration time of carburetted hydrogen is not in direct pro-
portion to its gravity, which is 0.5, or one-half of that of oxygen : it
approaches more nearly to 0:5625, which is nine-sixteenths of the time
of oxygen.
Capillary B.-This glass tube was 31-5 inches in length, of a round
bore, but decidedly conical. It was first placed so that the gas entered
the tube by the large and escaped by the small opening. When so
arranged this tube allowed 1 cubic inch of air to pass into a vacuum in
34-3 seconds, or the transpiration was nearly three times slower than
by A. -
TABLE X.—Transpiration by Capillary B into a Half-Pint Jar (21:26
cubic inches). Barom. 29.17. Temp. 68°.

Oxygen. Nitrogen. Carburetted hydrogen.
Gauge barometer in inches.
I. II. I. II. I. I. II.
28 6 || 6 || 6 || 6 || 6 f/ Z/
20 235.5 || 235'5 | 209 205 || 205 133 133
12 289 290°5 || 252 253 tº º º 162-5 163
4. 521 521 451.5 453-5 | ... 290.5 290°5
2 290.5 290.5 258 255°5 ... 164 I65-5
From 28 to 2 inches ...|1336 |1337 |II'70-5 |1167 205 750 752
ON THE MOTION OF GASES.
115
Mean Results.

Gauge barometer. Nitrogen. º
º Time in seconds......... 206.3 133
From 28 to 20 inches; T. j. oxygen = 1 . 0-8760 0-5647
sº Time in seconds......... 252.5 I62-7
From 20 to 12 inches; ii. of jºi". 0-8716 0°5618
F 12 to 4 inch Time in seconds......... 452-5 290.5
rom 1% to *** Time of oxygen-1 ... 0-8685 0.5576
F 4 to 2 inch Time in seconds........, 256-7 1647
TODOl 9 * * Time of oxygen-1 ... 0-884.5 0.5677
& Time in seconds......... 1168-7 751
From 28 to 2 inches } Time of oxygen = 1 ... 0-8740 0.5619
TABLE XI.-Transpiration by Capillary B into a Half-Pint Jar.
Barom. 292.

Gauge barometer Oxygen. Hydrogen. Carbonic acid.
in inches.
- I. IL III. I. II. III. I. II. III.
62° 62°-5 64°-5 65° 65° 65°-5 | 66° 66° 66°
2 0” 0” 0” O” 07 O' f 07 0” 0”
20 234 234. 234°5| 103 103 103 174:5| I?4 173
I2 285 287.5 288-5 126-5 126 126'5| 212 211-5 212
4. 516 || 516 516.5| 229-5 228 228 376 379.5| 376
2 290 292.5 288:5| 129 126 132 ... + 213 212°5
629.5 64° 64°-5 65° 65-5 e 66° 66°
From 28 to 2 in. |l325 |1330 |1328 588 583 || 589-5 978 974
Mean Results.
Gauge barometer. Hydrogen. Carbonic acid.
º Time in seconds......... 103 173-8
From 28 to 20 inches; i.e., 0°4398 0-7424
tº Time in seconds......... 126-3 211-8
From 20 to 12 inches} iſ...}"...] “...aos 0.7385
- Time in seconds......... 228.5 377-3
From 12 to 4 inches Time of oxygen = 1 0.4425 0.7310
- Time in seconds......... 129 212-75
From 4 to 2 inches Time of oxygen = 1 0-4443 0.7327
º Time in seconds......... 586-8 976
From 28 to 2 inches } Time of oxygen = 1 ... 0-4413 0-735]


Taking the higher part of the scale, from 28 to 20 inches, which
approaches nearest to transpiration into a vacuum, we obtain the fol-
I 16 ON THE MOTION OF GASES.
lowing times of transpiration :-Oxygen 1, nitrogen 0-8760, hydrogen
0.4398, carburetted hydrogen 0-5647, carbonic acid 0-7424; which
almost coincide with the numbers lately mentioned in relation to these
gases, with the exception of carbonic acid, which is 0-7424, instead of
0-75. With the great resistance of this tube, the variation in ratio at
different parts of the scale has also become very small, being only 00045
for hydrogen and 0:0097 for carbonic acid. The disturbing influence
of effusion appears therefore to be in a great measure eliminated. It is
also worthy of remark, that the time of passage of carbonic acid into a
perfect vacuum would certainly approach still more nearly to 0-75; for
the rate of transpiration of that gas appears, in the case of the present
capillary, to become slower with the increase of pressure. It will be
seen hereafter that the gases deviate very sensibly at low pressures
from the empirical coefficients of transpiration which have been named,
becoming slower in their passage with reference to oxygen, as is here
observed of carbonic acid. This deviation appears to be connected with
excessive resistance, whether arising from the Smallness of the capillary
opening or diminished pressure.
With the view of observing the effect of alterations in the position
and dimensions of a capillary, experiments were now made with this
tube, (1) in an inverted position, so that the gas entered by the narrow
and escaped by the wide end, and (2) after being reduced to half its
Original length.
Capillary B reversed.—The passage of gas through this tube was
nearly three times more rapid in the new direction, 1 cubic inch being
now transpired into a vacuum in 12-6 seconds. The length of the tube
and resistance to passage through it are therefore nearly the same as
in capillary A; but while the latter was of uniform bore, the present
capillary is highly conical.
TABLE XII.-Transpiration by Capillary B reversed into a One-Pint
Jar. Barom. 30:13.

Air. Oxygen. Hydrogen. Carbonic acid.
Gauge barometer
in inches.
I. II. III. I. II. III. I. II. I. II. III.
59° F. 59° F.] 59° F. 61° F. 61°-5F.61°-5F. 62°F. 62°F.
28 0” 0” 0', 07 0” 0” ()” 0” 0” 0” O”
20 149-5 144-5 145 | 160 160 | 160 69 69 | 127 | 126 126
12 173-5 177.5| 178 198 || 196 | 196 86 85-5 154 | 153 | 152
4 318 || 318 317 | 352-5| 353'5' 353-5 157.5 157.5 268.5 267-5, 268-5
2 190 | 189'5| 192 5 216 || 216.5| 215 96 96° 5' 154°5 155 | 156' 5
From 28 to 12 in. 323 322 || 323 358 || 356 356 155 154-5 281 279 || 278
From 28 to 2 in. 831 || 829'5| 832°5 926'5| 926 || 924.5| 408.5 408.5 704 || 701-5. 703
ON THE MOTION OF GASES. 117
Mean Results.
Gauge barometer. Air. Hydrogen. Carbonic acid.
* Time in seconds .........] 322 154.75 279-33
From 28 to 12 inches } Time of oxygen = 1...... 0-9024 || 0:4338|| 0-7831
- Time in seconds .........] 317-7 157-5 268-16
From 12 to 4 inches Tijºnºi...]”83994 "o 1459| "oºps
- Time in seconds......... 1907 96.25 155-33
From 4 to 2 inches; Tiji...] "o.3836|| "o 4.59| "ºig'ſ
- * Time in seconds ......... 831 408'5 702-83
From 28 to 2 inches } Time of oxygen = 1...... 0-8978 || 0-4413 || 0-7594

The coefficients of air and hydrogen, although still corresponding
very closely with the numbers 0.9038 and 0.4375, begin to exhibit a
sensible variation in different parts of the scale.
bonic acid is considerable, amounting to 0.0634, and the divergence
is on both sides of the empirical number 0-75. w
Capillary B shortened.—The tube was preserved in its last position,
but its length reduced to 14.5 inches.
The variation in car-
It now allowed 1 cubic inch of
air to pass into a vacuum in 64 seconds; or twice as rapidly as when
entire.
TABLE XIII-Transpiration by Capillary B (14% inches long) into a
One-Pint Jar.
Barom. 30°12.

& Y: Carburetted Carbonic
Air. Oxygen. Nitrogen. r Hydrogen. *
Gauge barometer - 8 c hydrogen. acid.
in inches.
I. II. III. I. II. III. I. IL I. II. III. I. II. III. L II.
62°F. 62°F. 62°F. 63°F. 68°F. 62°F. 61°F. 62°F.62°F.62°F. 62°F.62°F. 62°F.
28 07 07 07 07 0” 07 07 07 07 07 07 0” 07 07 0” 07
20 75 75 75-5 82.5 83.5 82 72 72 48 48 48 34°5 || 34 34 69 69
12 89.5 | S9°5 | 89.5 99°5 99-5 iO0 87°5 || 88 57 57 57 41°5 || 41 °5 || 41'5| 81 80°5
4 158 157 |157.5175 1755 1745 152-5|152.5| 98 98 98 75 75 75 |137:5 136-5
2 9] ‘5 91 92 102 ||103 102.5, 91 S9-5 56 56 55-5 || 45°5 45°5 45 77 77.5
From 28 to 12 in. 164°5 |164°5 |164-5 182 183 182 159 5 160 |105 |105 |105 76 75-5 75-5 150 [149-5
From 28 to 2 in. 414, 412-5 414-5 459 |461-5 459 |403 |402 |259 |259 |258-5 1965 ise 195'5|364 |363-5
Mean Results.
& * Carburetted Carbonic
Gauge barometer. Air. Nitrogen. hydrogen. Hydrogen. acid.
- Time in seconds ..] 164°5 159-75 105 75'66 149-7
From 28 to 12 in. Hºllº |lºſº | }º ſº ºn
º ime in seconds . ‘5 52-5 9S 75 37
From 12 to 4 in. { Time of oxygen-1 || 0:9000 || 0-87.14 0-5600 0 °42S5 0.7828
From 4 to 2 in Time in seconds .. I 5 90-25 55-83 45°33 77-25
* R Time of oxygen=l 0°S926 0 °8804 0°54'47 0°4325 0-7546
- - Time in seconds ...| 413-7 402°5 25S°83 196 363-75
From * to * in 3 time of oxygen-i | "...#999 || 03755 "jºgg2 | "...#263 0-7912

118 ON TEIE MOTION OF GASES.
The times are now too short for accurate numerical determinations,
but it is obvious that while the relative times of air and nitrogen are
little changed, particularly from 28 to 4 inches, the times of hydrogen
and carbonic acid are sensibly affected by effusion, and most so in the
upper part of the scale; the coefficient of hydrogen falling to 0°41'50;
while that of carbonic acid rises to 0.8211. From 4 to 2 inches, the
rates are 0.4325 and 0.7546; numbers which still diverge a little from
the empirical coefficients, but both in the direction of the effusion
influence. - -
Reduced to 7 inches in length, and now allowing 1 cubic inch of air
to pass into a vacuum in 3:4 seconds, this capillary was found to be still
less adapted for transpiration. In a series of observations, which are
not of sufficient importance to be particularly detailed, the coefficients
of the gases in the range from 28 to 12 inches, were, air 0-9194,
nitrogen 0-8983, carburetted hydrogen 0-6029, carbonic acid 0.9028, and
hydrogen 0-3930: numbers which demonstrate an increasing interfer-
ence of effusion. In the range from 12 to 4 inches, the coefficients
were, air 0.9114, nitrogen 0.8851, carburetted hydrogen 0.5764, car-
bonic acid 0.8303, hydrogen 04180. -
Of this last portion of capillary B, 5-5 inches were found to contain
2.78 grains of mercury; which gives the tube a mean diameter of 0.0137,
or 7'3d of an inch.
Capillary C.—This was a tube of exceedingly fine bore; 8.3 inches
of the tube containing only 0.65 grain of mercury; which gives a
diameter of 0.00539 inch, or about Těath of an inch. Experiments were
made with portions of this tube of different lengths; and first with a
portion only 1 inch in length, in which it was expected that the influence
of effusion would be considerable, from its approach to an aperture in a
thin plate.
TABLE XIV.-Transpiration by Capillary C (1 inch long) into a
One-Pint Jar. Barom. 28.81. Temp. 60°.

Air. Oxygen. Hydrogen. Carbonic
Gauge barometer - acid.
in inches.
I. II. I. II. I. II. I.
28 4/ ſ/ A A &/ w/ Aſ
20 248.5 || 249 273 271-5 108 108 237.5
12 283 281°5 || 308'5 308'5 126 127 261
8 186°5 | 185.5 204-5 | 206 87 87 167
4 284 286 315°5 || 314 136 137 244
2 270-5 266.5 301 302 133 132 227
From 28 to 2 in. 1272°5 | 1268'5 || 1402.5 || 1402 590 591 1136'5
ON THE MOTION OF GASES. ^
119
Mean Results.
Gauge barometer. Air. Hydrogen. Cºle
g Time in seconds 248.75 108 237.5
From 28 to 20 in. } Time of oxygen = 1 || 0-9138 || 0-3967 || 0-8725
tº Time in seconds 531 234.75 498'5
*** **in ii.; jºi". “og139|| “...ao "o;94
* Time in seconds 282-25 126'5 261
*** **in i. i*| "dºi10 || “...100 || “...sago
g Time in seconds 186 87 167
From 12 to 8 in. } Time of oxygen = 1 || 0-9063 || 0:4238 || 0-8138
ſº Time in seconds 285 136-5 244
From 8 to 4 in. } Time of oxygen=l 0.9054 || 0:4339 0.7751
* * Time in seconds 268.5 132°5 227
From 4 to 2 in. } Time of oxygen = 1 || 0-8905 || 0:4374 0-7529
º Time in seconds 1270-5 590:5 1136-5
F gº
rom 28 to 2 in. } Time of oxygen = 1 || 09060 || 0:4211 || 0-8104

TABLE XV-Transpiration by Capillary C (2 inches long) into a
Half-Pint Jar. Barom. 29.32.
Air. Oxygen. Hydrogen.
Gauge barometer
in inches. t s
I. II. I. II. | I. II. |
28 &M Z/ Af Aſ 47/ &
20 211.5 211.5 234 234 101-5 102
12 254 254 281-5 281 124°5 124
8 176.5 176.5 196 197 88 88
4 280.5 280.5 321-5 320 141-5 138
2 273 272 301 302 141 l46
From 28 to 2 in. 1195-5 1196 1334 1334 596-5 598
Mean Results.
Gauge barometer. Air. Hydrogen.
ge Time in seconds ...... 2.11-5 101.75
From 28 to 20 inches Time of oxygen = 1... 0-9038 0°4348
e Time in seconds ...... 254 124-25
From 20 to 12 inches {i}... i. “ogosi 0-4417
* Time in seconds ...... 176.5 88
From 12 to 8 inches Time of oxygen-1...] 0-898] 0.4478
tº Time in seconds...... 28.1-25 139-75
From 8 to 4 inches Time of oxygen-1... 0-8768 0.4357
* Time in seconds ...... 272-5 I43°52
From 4 to 2 inches Time of oxygen-1... O'9038 0.4759
* & Time in seconds ...... 1195.75 597.25
From 28 to 2 inches } Time of oxygen = 1... 0.8964 0.4476


120 ON THE MOTION OF GASES.
TABLE XVI—Transpiration by Capillary C (4 inches long) into a
Half-Pint Jar.
Air. Oxygen.
Gauge barometer in inches.
I II. I
65° 65° 65°
28 O” 0” 0”
24 205 205 228
20 214 } 419 || 3i. | 419 239 } 467
16 234 236 262
12 276 | 510 278 | 510 § { 575
10 166 ), 163 183
8 195 ! 361 197 ; 360 3.0 403
6 248 245 273
5 145 ), 570 151 W 580 169 ), 648
4 177 184 206
3 241 238 265
2 333 573 jo 568 ... 659
From 28 to 2 inches...... 2433 2439 2752
Mean Results.
Gauge barometer. Air.
e Time in seconds ...... 205
From 28 to 24 inches } Time of oxygen = 1... 0.8991
º Time in seconds ...... 4.18
From 28 to 20 inches } Time of oxygen = 1... 0-8951
º Time in seconds ...... 512
From 20 to 12 inches } Time of oxygen = 1... 0.8904
º Time in seconds ... ... 360°5
From 12 to 8 inches } Time of oxygen = 1... 0.8945
e Time in seconds ...... 575
From 8 to 4 inches } Time of oxygen = 1... 0-8657
º Time in seconds...... 570-5
From 4 to 2 inches }}. of oxygen = 1... 0-8657
ſº Time in seconds ~. 2436
From 28 to 2 inches } Time of oxygen = 1... 0°8852

The velocity with which air passed into a vacuum was, by C 1 inch,
1 cubic inch in 21'26 Seconds; by C 2 inches, 1 cubic inch in 35:43
Seconds; and by C 4 inches, 1 cubic inch in 70 seconds.
C 1 inch exhibits (Table XIV) great variation in its rate of tran-
spiration at different pressures, as was to be expected. At the head of
the scale, the rate of air is 0-9138, of hydrogen 0-3967, and of car-
ON THE MOTION OF GASES. + 121
bonic acid 0.8725; which all indicate a great interference of effusion.
At the bottom of the scale, on the other hand, where the pressure is
small and the resistance to passage consequently great, the rate of air
is 0.8905, of hydrogen 0.4374, and of carbonic acid 07529, or nearly
normal.
With C 2 inches (Table XV), the rates of air are pretty uniform at
different parts of the scale, and sufficiently normal; the deviation from
8 to 4 inches appears to be an accidental anomaly. The rate of hydrogen
also is never distant from 0°4375, except at the very bottom of the scale.
This appears to be the length of a tube of so small a bore which gives
the most uniform results at different pressures:
For with C 4 inches (Table XVI.), where the resistance is excessive,
air has a rate corresponding sufficiently with its specific gravity at the
head of the scale, but diverging rapidly in the lower part of the scale,
the time of transpiration becoming rapid as compared to that of oxygen.
With a tube then like the present, the relation between the times of
transpiration is only to be looked for within a limited range, and that
at a high degree of pressure approaching to a whole atmosphere.
4. Transpiration by Capillary Tube H.
As the existence of any simple numerical relation among the gases,
such as the preceding experiments on transpiration render probable,
would be a point of fundamental importance in their history, I was
induced to try new capillary tubes and to multiply experiments, varying
the circumstances in which they were made, and taking additional
precautions against the interference of disturbing causes. The arbi-
trary nature of the coefficients of transpiration indeed produces a
more than usual necessity for strong evidence and numerous confir–
mations, as the numbers themselves have no a priori probability in
their favour.
It appeared desirable to try capillary tubes of larger diameter than
those already employed, and of great length; partly to vary the con-
ditions of the experiment, and partly because extreme shortness of tube
appears, in the experiments made with C, to be unfavourable to unifor-
mity of rate at different pressures.
Several portions of capillary tube, of which the bore was as nearly
equal as could be judged of by the eye, were accordingly selected and
cemented together at the blowpipe, so as to form a continuous tube 22
feet in length, which was bent up into coils for convenience in using it,
as represented in figure 4, Plate XXXIII. The extremities of this
capillary were connected with the block-tin tubes proceeding from the
122 ON THE MOTION OF GASES.
drying tube and air-pump jar respectively, by means of thick caoutchouc
adopters, which diminished the rigidity of the arrangement and protected
the glass tube from the effect of the shocks, which are unavoidable in
working the air-pump. This capillary (H) allowed 1 cubic inch of air
to pass into a vacuum in 15:64 seconds. Two inches of the tube were
found to hold 2.65 grains of mercury, which gives a diameter of 0.0222
inch, or Täth of an inch. The tube, however, may have been more
contracted at the bendings.
Air-pump jars of greater size were also employed, so as to protract
the time of passage, and give larger numbers. Of these vessels, which
I have termed aspirator jars, the capacity of the “three-pint jar” was
103-56 cubic inches, and that of the “six-pint jar” 201:78 cubic inches;
the vacuous channels of the air-pump and connecting tubes being in-
cluded in these measurements.
The temperatures recorded are those of the interior of the aspirator
jar, observed by a very small mercurial thermometer, containing no
more than 50 or 60 grains of mercury, and therefore highly sensitive.
It will be remarked that the temperature within the receiver always
rises, and in general about half of a degree Fahrenheit during the con-
tinuance of an experiment: this is owing to the compression of the gas
already in the receiver by that which enters. The change of temperature
due to this cause becomes less considerable with large aspirator jars,
which are preferable to small jars for this and other reasons.
As it appears that the relation between the coefficients of transpira-
tion is only to be looked for at high pressures, attention should be more
directed to the rates of transpiration in the upper than in the lower part
of the scale. The inquiry will therefore be directed with the view of
solving the question, What are the coefficients of transpiration of the
different gases into a vacuum, or under considerable pressures 2
TABLE XVII.-Transpiration by Capillary H. into a Three-Pint Jar.
Barom. 30°324.

Air. Oxygen. Hydrogen. | Hyd. 95-F5 air. | Carbonic acid.
Gauge barometer
in inches.
I. II. I. II. I. II. I. II. I. II.
61°-5 |61°5 ||61°-5 61°-5 61°5 61°5 | 61°-5 | 61°-5 | 61°-5 | 61.95
28 O't 0'ſ 07 0” ()” 0// 0” O't O't O't
24 213 || 213 236 || 237 || 104 || 104 || 125 | 124 || 178 || 177
20 227 227 254 253 || 111 || 111 || 132 132 | 188 188
12 549 549 || 611 611 268 269 321 321 454 || 455
8 389 || 388 435 435 | 192 192 || 227 227 | 321 || 320
61°75 61°75 61°-75 61°75 61°75 61°.75 61°.75 (61°75 61°.75.61°.75
From 28 to 8 inches | 1378 || 1377 | 1536 | 1536 675 676 805 || 804 || 1141 1140
ON THE MOTION OF GASES. 123
Mean Results.

Gauge barometer. Air. Hydrogen. 95 Hº: ** | Carbonic acid.
& Time in Seconds...... 213 104 124.5 177.5
From 28 to 24 inches: Time of ... gº 0.4397 || 0-5264 0-7505
& ºf \ { Time in seconds...... 2 188
From 24 to 20 inches; Time of ... * 2: ºrs 0.5206 0-7416
e Time in seconds...... - 321 454-5
From 20 to 12 inches; †º sº.” | 1.4% gº 0-7438
- Time in seconds...... - 227 320-5
From 12 to 8 inches: Time of oxygen-1...] 0-8931 || 0:4413 || 0-5218 0.7368
º Time in seconds...... 1377.5 675-5 864.5 1140°5
From 28 to 8 inches: Time of oxygen-1...] 0.8968 0.4397 0.5237 0-7425
The numbers for air, hydrogen, and carbonic acid accord well with
those obtained by the other capillaries. The small addition of 5 per
cent. of air to hydrogen has a surprising effect in retarding the transpira-
tion of that gas. The mean rate of Such a mixture, calculated from the
rates of air and hydrogen separately, is 04625, whereas the actual rate
is 0.5264. The rate of the mixture should only be increased by 0.0228,
whereas it is really increased by 0-0840. Hence the effect of 5 per
cent. of air in retarding the rate of hydrogen is nearly four times
greater than it should be by calculation. The experiment shows the
effect which a small amount of impurity must have in deranging the
transpiration rate of that gas. I shall return again to this point under
the subject of the transpiration of mixed gases.
TABLE XVIII.-Transpiration by Capillary H into a Three-Pint Jar.
Barom. 30°3—30'242.

Oxygen. Nitrogen. Carbonic oxide. Air.
Gauge barometer in inches.
I. II. I. II. I. II. ' I. II.
619.5 |619.5 |619.5 | 61°-5 || 61°-5 61°-5 61°-5 61°-5.
2 8 07 0” 0” 0 // 0” 0” 07 0”
24 238 239 208 208 207 207 214 || 214
20 253 253 220 22I 220 220 229 229
12 614 614 536 533 532 533 552 550
8 434 || 434 378 376 376 377 389 392
61°.75|| 61°-75 62° 62° 62° 62° 62° 62°
From 28 to 8 inches | 1539 || 1540 | 1342 | 1339 1335 | 1337 || 1384 || 1385
124
ON THE MOTION OF GASES.
Mean Results.

Gauge barometer. Nitrogen. Carbonic oxide. Air.
From 28 to 24 inches Time in seconds ... 208 207 214
Time of oxygen = 1 0-8721 0.86.79 0.8972
From 24 to 20 inches Time in seconds ... 220:5 220 229
Time of oxygen = 1 0-8715 0.8695 0-9051
From 20 to 12 inches Time in seconds ... 534-5 532°5 551.
- Time of oxygen = 1 0.8705 0-8673 0.8974
e Time in seconds ... 377:5 376.5 390-5
From 12 to 8 inches { Time of oxygen = 1 || 0:8698 0-8675 0-8998
g Time in seconds ... 1340-5 1336 1384.5
From 28 to 8 inches } Time of oxygen = 1 || 0-8707 0-8678 0-8993
In the preceding table, a comparison is made between two gases,
nitrogen and carbonic oxide, of which the theoretical specific gravities
are the same, namely, 0-8750, while the mean rate of nitrogen, from 28 to
12 inches, proves to be 0-8707, and that of carbonic oxide 0:8678, which
is a pretty close approximation. In several other experiments with these
gases, a slight difference in their coefficients of transpiration was observed,
carbonic oxide having always the smaller number : the difference gene-
rally approached 0-0040. It is not at all impossible, however, that these
gases may really differ quite as much in specific gravity; the specific
gravity of carbonic oxide found by Wrede being 0-8754, on the oxygen
scale, while that of nitrogen by Regnault is 0.8785.
TABLE XIX-Transpiration by Capillary H into a Three-Pint Jar.
- Barom. 30.232. -

. Air. Oxygen. Carburetted hydrogen.
Gauge barometer in inches.
I. II. I. II. I. II.
65°-25 || 65°-2 66° 66° 66° 66°
28 0" 0" 0" 0" 0" O"
24 215 216 239 || 240 131 131
20 229 230 255 || 256 141 141
12 555 553 617 | 616 || 338 338
8 393 393 439 437 240 240
66° 66° 66° 66° 66°-25 | 66°-25
From 28 to 8 inches... 1392 1392 1550 | 1549 || 850 850
ON THE MOTION OF GASES. 125
Mean Results.

Gauge barometer. Air. Carburetted hydrogen.
* § Time in seconds ...... 215.5 13]
From 28 to 24 inches; †. oxygen = 1...] 0-8997 0.5474
º Time in seconds ...... 229-5 141
From 24 to 20 inches; ii., ii...] "jºgs? 0°5518
• Time in seconds ...... 554 338
From 20 to 12 inches; ii. i. “o.sgsg 0.5482
º Time in seconds ......] 393 240
From 12 to 8 inches; it. . . .i...] "...s072 0.5479
wº Time in seconds...... 1392 850
From 28 to 8 inches { Time of oxygen = 1... 0-8983 0.5485
TABLE XX-Transpiration by Capillary H into a Six-Pint Jar.
Barom. 30°196—30-174.

Carburetted
O Hydr º Air.
Gauge barometer in inches. Xygen. hydrogen. yorogen II.
I. II. I. II. I. II. I. II.
66°-75 | 66°-75 | 66°-75 | 66°.75 | 66°.75|662.75 67° 679
28-5 0" 0" 0" 0" 0" 0" 0" 0"
26.5 228 232 126 128 102 IOI 207 204
24.5 235 233 130 128 102 104 || 212 || 211
23'5 121 121 66 67 54 54 || 108 || 110
67° 67° 67° 67° 679 679 67° 679
From 28°5 to 23-5 inches...| 584 586 322 || 323 258 259 527 525
Mean Results.

Gauge barometer. º: Hydrogen. Air.
º • R & Time in seconds ...... 322.5 258-5 526
From 28°5 to 23-5 inches } Time of oxygen = 1...| 0:5512 || 0-4418 0.8991
Tables XIX, and XX. exhibit the transpiration rates of carburetted
hydrogen and hydrogen, the former of which approaches to 0:55, which
is certainly a sensible deviation from 0.5625. The number for hydrogen
(0-4418), on the other hand, is but very little removed from 0.4375.
126 ON THE MOTION OF GASES.
TABLE XXI-Transpiration by Capillary H into a Six-Pint Jar.
Barom. 30'158—30. 138.

Gauge barometer Oxygen. Carbonic Oxide. Nitrogen. Nitrous oxide. Carbonic acid.
in inches.
I. II. I. II. III. I. II. I. II. I. II.
67° 67° 67° 67° 67° |67°.75|67°.75|| 68° | 68° | 68° | 68°
28 •5 O” O” 07 0” 07 O” 07 07 0” 0” 0”
26.5 230 231 | 202 | 200 201 || 202 | 202 || 173 || 173 || 173 173
24-5 237 235 | 202 203 204 || 205 205 || 176 175 174 176
23.5 121 | 121 | 107 || 107 || 106 || 108 || 108 91 91 92 92
67° 67° |67°25' 67°25' 67°-25 | 68° 68° 68° 68° 68° 68°
From 28°5 to 23-5 in. 588 587 || 511 || 510 || 511 || 515 || 515 || 440 || 439 || 439 || 441
Mean Results.

Gauge barometer. Carbonic oxide. Nitrogen. Nitrous oxide.|Carbonic acid.
g .E. s. ſ Time in seconds...| 510:5 515" 439-5 440
From 28'5 to 23°5 in. { Time of oxygen-1| 0-8689 0-8766 || 0-7480 0-7455
In the preceding table carbonic oxide and nitrogen are again com-
pared, and also another remarkable pair of gases having the same theo-
retical density, namely carbonic acid and nitrous oxide. The two latter
exhibit an extraordinary parallelism in their rates of transpiration in all
experiments which were made upon them, provided due attention was
paid to the purity of the nitrous oxide. The solution of nitrate of
ammonia should always be filtered, and the salt crystallized, as the pre-
sence of a very minute quantity of solid matter may cause a change in
the mode of decomposition of the Salt by heat, and the evolution of a
very sensible quantity of free nitrogen. t
The carbonic oxide of experiments 1 and 2 was obtained by the
action of oil of vitriol on pure oxalic acid; that of experiment 3 was
prepared by the process of Mr. Fownes, namely, heating oil of vitriol
upon the ferrocyanide of potassium, avoiding a violent reaction by a
proper regulation of the temperature. The gas of both processes was
washed with alkali, although this precaution is scarcely required with
the gas of the last process. The transpiration results are exactly the
same with the gas prepared in both ways.
ON THE MOTION OF GASES. 127
TABLE XXII-Transpiration by Capillary H (with cupped ends) into a
Six-Pint Jar. Barom. 29:39. Temp. 51°.

- Olefiant * Carburetted
Gauge barometer Nitrogen. Oxygen. gaS. Air. hydrogen.
in inches.
I. II. I. II. I. II. I. II. I. II. III. IV.
28'5 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6
26.5 203 || 204 || 233 235 | 122 121 211 || 211 || 129 || 129 | 129 129
24-5 206 207 || 236 236 122 122 212 212 129 || 131 || 130 || 130
23.5 104 || 104 || 121 | 120 | 62 | 63 108 || 108 || 67 | 66 | 66 | 66
From 28-5 to 23.5 in. 513 || 515 || 590 591 306 || 306 || 531 531 || 325 | 326 325 || 325
Mean Results.
|
Gauge barometer. Nitrogen. oº:nt Air. º
© • K . Time in seconds ... 514 306 531 325-25
From 28°5 to 23-5 inches | Time of oxygen-1 osſo owlsº oºooo oasis

For the experiments of the preceding table the form of the capillary
H was so far altered, that a funnel-form was given to the apertures of
the tube. This was done by softening the tube in the blowpipe flame,
within an inch of each extremity, and expanding the bore into a small
ball of about one-tenth of an inch in diameter; the ball was afterwards
cut across the middle, and left the tube of course with a cup-shaped
termination. This change in the condition of the capillary seems to
have no effect on the comparative rates of transpiration of the different
gases.
It was found that the passage of air became a little slower by cup-
ping the end of the tube by which the gas obtains ingress, in the pro-
portion of 509 to 496; but cupping the point of egress occasioned no
further change in the rate, the experiments being made within the
pressures of 28:5 and 23.5 inches.
The transpiration rate of olefiant gas differs entirely from that of
nitrogen and carbonic oxide, of which gases it possesses the theoretical
Specific gravity, and is a great deal more rapid, the transpiration coeffi-
cient being so low as 0.5182. The specific gravity of the gas made use
of was found to be 0.9840, and it was absorbed by the perchloride of
antimony to the extent of 96.5 per cent. The determination of the
true coefficient for this gas is attended with unusual difficulty, from its
constant and I believe unavoidable impurity, as prepared by the action
of sulphuric acid upon alcohol.
128 ON THE MOTION OF GASES.
TABLE XXIII-Transpiration by Capillary H (with cupped ends) into
- a Six-Pint Jar. Barom, 29-91. Temp. 54°.

* Carburet. Carbonic | Carbonic
Gauge barometer Air. Oxygen. Hydrogen. §: oxide. acid.
in inches.
I. II. I. II. I. II. I. II. I. II. I. II.
28-5 6|| 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6
26.5 212 212 234 233 || 105 || 105 || 133 133 206 || 204 || 175 176
24.5 212 || 212 235 || 236 105 || 106 || 134 || 132 204 205 || 176 174
23.5 108 107 121 || 119 53 53 | 66 67 106 106 || 90 | 90
From 28-5 to 23.5 in. 532 531 590 ||588 263 264 || 333 332 || 516 || 515 441 440
Mean Results.
Gauge barometer. - Air. Hydrogen. §. Cºlº Cºle
From 28°5 to ( Time in seconds...] 531-5 263.5 332.5 515-5 440-5
23.5 inches Time of oxygen-1| 0-9024 0.4473 0-5645 0.8752 07479|

The results of the preceding table are remarkable as approaching
more closely to the empirical numbers than any preceding results
obtained by the same capillary. The same observation applies to the
results of the table which immediately follows. In the one table, the
number for carbonic oxide is 0.8732, in the other 0-8752; the numbers
for carbonic acid are 0.7479 and 0.7466, and for carburetted hydrogen
0°5645.
TABLE XXIV.-Transpiration by Capillary H into a Six-Pint Jar.
Barom. 29.63. Temp. 55°.

Air. . Oxygen. Carbonic oxide. Carbonic acid.
Gauge barometer in inches.
- I. II. I. II. I. II. III. I. II.
2 8 e 5 A Z/ // Z/ Z/ &/ Z/ Af Æ
26.5 212 || 212 || 236 235 | 214 || 214 || 213 175 176
24.5 214 214 || 237 239 203 205 || 205 || 178 177
23.5 110 | 110 | 121 | 120 | 100 | 101 || 101 90 91
From 28°5 to 23-5 inches ... 536 536 594 594 || 517 | 520 || 519 || 443 || 444
Mean Results.
Gauge barometer. Air. Carbonic oxide. Carbonic acid.
- • B : Time in seconds ...] 536 518.7 443’5
From 28-5 to 23:5 inches | Time of oxygen – 1 || 0:9023 || 0:8732 || 0-7466

ON THE MOTION OF GASES. 129
5. Transpiration of different Gases by a Capillary Tube of Copper.
It appeared desirable to have experiments on the passage of gases
through tubes of different materials, in order to ascertain how far the
coefficients of transpiration observed are peculiar to glass. After some
trials, a capillary tube of copper was constructed, of a fine smooth bore,
not wider than an ordinary thermometer tube, and indeed less in diameter
than the preceding glass capillary H. This tube was formed by first
drilling a cylindrical hole in the axis of a solid copper rod, 4 or 5 inches
in length, and extending the latter afterwards by drawing it through a
wire-plate. An iron wire, or triplet, was placed within the copper
tube and drawn through the wire-plate at the same time, in order to
keep the interior surface of the copper tube smooth and uniform. It
was necessary to pull out the iron wire always after the copper was
drawn through the plate, to prevent the former being fixed. The iron
wire was then extended somewhat separately, and again introduced into
the copper tube, and the operation of drawing out the latter repeated.
In this way the copper tube was extended to a length of 11 feet 8 inches.
It was found to be perfectly sound and air-tight; and allowed 1 cubic
inch of air to pass into a vacuum in 22°12 seconds. Of the iron wire,
upon which the copper tube was last drawn, 927 inches weighed 18:30
grains; or 1 inch 0-1974 grain. Taking the specific gravity of iron at
7-7, this gives as the diameter of the copper tube 0.0114 inch, or gºth
of an inch. When used as a transpiration tube it was coiled up into
circles of about 10 inches in diameter, and the ends joined by soldering
to two block-tin tubes provided with screws by which they could be
attached to the aspirator-jar and drying tube.
The experiments were conducted precisely in the same way as with
a glass tube, except that oil of vitriol was avoided and chloride of calcium
only used in the drying tube. The following series of results were
obtained with the copper capillary:
TABLE XXV-Transpiration by a Copper Capillary Tube into a One-
Pint Jar. Barom. 29.97. Temp. 58°.
Gauge barometer Air. Oxygen. Nitrous oxide. Carbonic acid. Air.
in inches.
I. II. I. II. I. II. I. II. I.
28 6 6 £/ 6 J/ (/ Ö £/ 6
20 234 233 260 261 198 || 198 || 199 || 199 || 234
I2 291 || 292 || 324 324 244 244 245 245 292
8 206 205 228 228 170 | 1.70 || 171 || 170 204
4 333 || 335 | 372 373 275 277 276 276 || 336
2 342 344 387 | 390 283 285 287 288 344
From 28 to 4 in. 1064 1065 1184 1186 887 | 889 | 891 | 890 | 1066

130
ON THE MOTION OF GASES.
Mean Results.

Nº. Gauge Barometer. Air. Nitrous oxide. Carbonic acid.].
e Time in seconds ...... 233.5 198 199
From 28 to 20 inches Time of oxygen = 1... 0-8963 0-7601 sº
e Time in seconds ...... 291.5 244
*rom 20 to 12 inches it. . . .] “à:007 || "oſsal || Toºls31
From 12 to 8 inches } Time in seconds...... 205.5 170 170.5
Time of oxygen = 1...] 0-9000 0-7456 0.7478
From 8 to 4 inches Time in Seconds ...... 334 276 276
Time of oxygen = 1... 0-8966 0.7410 0.7410
From 4 to 2 inches Time in seconds ...... 343 284 287
Time of oxygen – 1...] 08831 0.7310 0.7400
g Time in seconds ...... 1064'5 888 890
From 28 to 4 inches } Time of oxygen–l... 0-8983 || 0-7493 || 0-7514
It will be observed that the numbers do not differ materially from
those obtained with glass tubes, particularly with H. This is a capillary
of great resistance, and therefore a deviation from uniformity of ratio
may be looked for in the lower part of the scale. A little irregularity
in the rate of air, probably accidental, appears in the upper part of the
Scale; but as with capillary H, the coefficient for air never varies far
from 0.9, at least between 28 and 4 inches.
Carbonic acid and nitrous oxide exhibit the usual parallelism of rate;
but in the upper part of the scale the excess of the coefficient above
0-75 is rather considerable. Other experiments were made on the tran-
spiration of carbonic acid into different aspirator jars, as the size of the
jar and duration of the experiment appeared to have some influence on
the ratios.
TABLE XXVI-Transpiration by Copper Capillary into a One-Pint Jar.
Barom. 29.07. Temp. 56°.

- Oxygen. Carburetted hydrogen.
Gauge barometer in inches.
I. II. I. II.
28 6 6 A Aſ/
20 273 274 151 151
12 338 336 186 186
8 237 236 129 130
4 383 385 210 2II
2 391 400 214 213
From 28 to 4 inches.., | 1231 1231 676 678
ON THE MOTION OF GASES. I31
Mean Results.

Gauge barometer. Carburetted hydrogen.
- Time in seconds ...... 151
From 28 to 20 inches } Time of oxygen=1... 0.5521
º Time in seconds ...... 186
From 20 to 12 inches Time of oxygen – 1... 0.5519
e Time in seconds ...... 129-5
From 12 to 8 inches; i.f.i. 0-5475
º Time in seconds ...... 210.5
From 8 to 4 inches Time of oxygen = 1... 0°5482
º Time in seconds ...... 213.5
From 4 to 2inches; iii.;...i. 0.5398
* Time in seconds ...... 677
From 28 to 4 inches } Time of oxygen = 1... 0.5500
The coefficient obtained for carburetted hydrogen in the preceding
experiments never varies much from 0:55, which is the mean between
28 and 4 inches. The result is similar to that given by glass capillary
H for the same gas.
TABLE XXVII.-Transpiration by Copper Capillary into a Two-Pint Jar.
Barom. 29°49. Temp. 56°5.
Air. Oxygen. Nitrogen. Cºle Air. Hydrogen.
Gauge barometer *
IIl IIlCIlêS.
I. II. I. II. I. II. I. II. III. I. II.
28 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6
20 421 || 419 || 467 || 466 405 || 407 || 405 | 404 || 419 || 206 || 205
12 515 514 572 574 501 || 500 496 || 498 || 516 || 255 254
8 360 | 363 402 || 404 || 351 351 || 348 348 || 361 179 179
From 28 to 8 in. 1296 || 1296 || 1441 1444 1257 1258 1249 | 1250 | 1296 || 640 638
Mean Results.
Gauge barometer. Air. Nitrogen. Carbonic oxide. Hydrogen.
& Time in seconds ... 406 404-5 5-5
From 28 to 20 in {}::... it *goog. “...sos 0-8670 0°4405
From 20 to 12 i Time in seconds •5 500-5 497 4-5
OIſl ZU UC) LZ IIl. {#. of oxygen-1 || 0:8979 0-8734 0-8673 0°4441
From 12 to 8 i Time in seconds 61:5 348 179
OIIl O & IIl. { Time of oxygen=l 0.8970 0-8709 0-8635 0°4441
F 28 to 8 i Time in seconds ...|1296 1257-5 I249-5
TOIn Zö 5O & IIl. {#. of oxygen–1 || 0-8984 0.8717 0-8662 0-4429


132 ON TEIE MOTION OF GASES.
The great resemblance which these results bear to those of the last
glass capillary is most surprising. The rates of air, nitrogen, carbonic
oxide, and hydrogen, may be considered as identical with these two
capillaries, although they differ in substance, and also in the time of
passage, which is slower in the copper capillary than in H, in the
proportion of 22:12 to 15.64. Carbonic oxide, it will be observed, is
still sensibly more rapid in its passage than nitrogen.
The experiments in the preceding and all other tables are put down
in the order in which they were made. The observation with air is
occasionally repeated, to find whether the rate of the capillary remains
COnstant.
TABLE XXVIII.-Transpiration by Copper Capillary into a Three-Pint
Jar. Barom. 29.73. Temp. 57*.

Gauge barometer Air. Oxygen. Nitrogen. Hydrogen. Carbonic acid.
in inches.
I. II. I. II. I. II. I. II. I. II.
28 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6 || 6
20 595 595 | 663 | 660 575 577 287 287 || 500 || 502
12 736 | 735 | 818 819 || 713 || 713 358 357 | 616 || 613
8 516 || 517 | 575 577 500 || 501 || 251 252 426 428
Erom 28 to 8 in. 1847 1847 2056 2056 1788 1791 | 896 || 896 1542 | 1543
Mean Results.

Gauge barometer. Air. Nitrogen. : Hydrogen. Carbonic acid.
& Time in seconds...... 595 576 287 501
From 28 to 20 in. { Time of oxygen–l 0-8994 0-8707 0.4339 0-7573
& Time in seconds...... 735-5 357-5 614'5
From 20 to 12 in. {#. of oxygen-1 || 0-8986 0.8711 0.4369 0-7507
g Time in seconds...... 516.5 500.5 251-5 427
From 12 to 8 in. {#. of oxygen-1 || 0-8967 0-8689 0°4366 0.7413
... ( Time in seconds......|1847 1789.5 896 1542-5
From 28 to 8 in. {#. of oxygen–1 || 0-8984 0-8704 0°4358 0-7502
The preceding results with air and nitrogen might be confounded
with those obtained with capillary H. The rate of hydrogen is sensibly
faster, while that of carbonic acid is decidedly slower; both gases
diverging sensibly from their empirical rates 0.375 and 0.75, on the side
of effusion, but the former very slightly.
ON THE MOTION OF GASEs.
133
TABLE XXIX-Transpiration by Copper Capillary into a Six-Pint Jar.
- Barom. 30:14. Temp. 58°.


Air. Oxygen. Hydrogen.
Gauge barometer in
inches.
L II. I. II. I. II.
47 // z/ wº AA Af
28 ()
24 º e e e tº º e - e. 614 269 27]
20 1139 1139 1268 654 290 290
12 1413 ; 1413 ; 1570 1573 698 699
8 994 993 1109 I 110 494 495
From 28 to 8 inches...] 3546 || 3545 3947 || 3951 I751 I755
Mean Results.
Gauge barometer. Air. Hydrogen.
se Time in seconds ...... 1139 560
From 28 to 20 inches}#. . . .] “...sgsg O'4416
* Time in seconds ...... 1413 698°5
From 20 to 12 inches}#...] “àsgol 0'4445
fº Time in seconds ...... 993-5 494-5
From 12 to 8 inches; i.i...] "...a55 0.4457
* Time in seconds ...... 3545-5 1753
From 28 to 8 inches } Time of oxygen = 1... 0-8978 0.4439

In these experiments with a large aspirator-jar and long times, the
rate of air continues very nearly 0.9, and that of hydrogen approaches
0.44. The rates at the upper part of the scale are to be particularly
attended to, as most uniform, and as representing pretty nearly transpi-
ration into a vacuum.
TABLE XXX-Transpiration by Copper Capillary into a Six-Pint Jar.
Barom. 30.23. Temp. 58°5.
Air. Oxygen. Carbonic acid.
Gauge barometer in inches.
I II. I II. I. II.
59° 59° 59°-25 59° 59°-5 59°-75
28 0” 0” O” 0” 0” 07
24 550 550 611 612 469 468
20 . 590 589 655 655 498 499
12 * - e. * * * 1570 1570 1183 1183
8 | 103 1104 824 825
From 28 to 8 inches... 3939 394] 2974 2975

134 ON THE MOTION OF GASES.
Mean Results.
Gauge barometer. Air. Carbonic acid.
From 28 to 24 inches †. . tº: *son, “ºn
From 24 to 20 inches}}. tº: * | *%io
From 20 to 12 inches}#:::::::... . . * *
From 12 to 8 inches}}...] ..., | *s
From 25 to sinches}}...i...] ... *;sº
The preceding table contains an experiment on carbonic acid tran-
spired into a large jar. The coefficient of that gas still considerably
exceeds 0-75 in the upper part of the scale.
It appears then that the rates of transpiration are similar through
glass and copper tubes, for air, oxygen, nitrogen, hydrogen, and car-
buretted hydrogen; whilst the passage of carbonic acid is subject to a
retardation in the upper part of the scale of the copper capillary, by
which its rate increases so much as from 0-75 to 0-7661, in the last series
of experiments. The rate of carbonic acid indeed exhibits a want of
steadiness with this capillary, which is not observed in the other gases
enumerated. Thus we find it in the upper part of the scale 0-7639 by
Table XXV. ; 0.7573 by Table XXVIII.; and 07661 by the last table.
I may add, that in a preliminary experiment which was made with this
gas, and also in an experiment made subsequently to those recorded,
and after the tube had been some weeks out of use, so high a coefficient
was given for carbonic acid as 0-78. It is impossible to say whether
this irregularity is properly referable to the material of the tube, or is
peculiar to this individual capillary, as it is the only instrument of the
same metal which was used.
The copper tube has no advantage over the glass capillary for experi-
ments on transpiration, while it is liable to the objection that it cannot
be used at all with certain gases which have a chemical action on copper,
and would tarnish the surface of the tube. The experiments made with
it, however, have their value in demonstrating that the rates of transpi-
ration of different gases are essential properties of these gases, and not
regulated by the material of the transpiring tube. Indeed there is no
more reason to suppose that the coefficient of transpiration of a gas
would vary with the substance of the tube, than that the specific gravity
ON THE MOTION OF GASES. 135
of the same gas would be found different according as it was observed
in a glass or copper vessel.
6. Transpiration of different Gases by a Glass Capillary Tube E.
This was another long capillary glass tube, resembling H, but some-
what shorter. The extreme length of capillary E was 20 feet; it allowed
1 cubic inch of air to pass into a vacuum in 12-03 seconds. One inch
of this tube at either end was found to contain 1 grain and 0.94 grain
of mercury; the smallest of which admeasurements gives 0.0187 inch
as the diameter of the tube; that is, about ###th of an inch.
The following table contains a series of experiments on various gases,
which were made on one occasion, and in the order in which they are
given.
TABLE XXXI.-
TABLE XXXI.—Transpiration by Capillary E into a Six-Pint Jar. Barom. 30.340–30-288.
Gauge barometer Air. Oxygen. º Hydrogen. Carbonic oxide. Nitrogen. Nitrous oxide. Carbonic acid. Air.
in inches. r
I. II. I. II. I. II. I. II. I. II. I. II. I. II. I. II. I. II.
- 72°| 72°| 72° | 72°-25 | 72°.75 |72°.75||72°.75||72°75||72°75 |72°.75||72°.75||72°.75||72°.75||72°.75||72°.75 | 72°.75 72°.75||72°-75
2 8 º5 0” 0 // 07 O” 07 0” 0% 0% 0” 0” 0% 0” 0” 0% 0” 0” 0” 0”
26-5 153 |153 172 | 170 93 93 75 74 150 149 150 149 I29 129 || 130 130 154 154
24°5 156 |156 173 || 175 97 97 75 76 150 151 151 153 133 133 || 132 132 158 158
23.5 84 || 84 || 92 || 92 52 50 41 40 80 80 81 80 70 70 70 70 84 84
From 28'5 to 23.5 in, 393 ||393 || 437 || 437 24.2 240 191 190 380 380 382 382 332 332 332 332 396 396
º Mean Results.
Gauge barometer. Air. º Hydrogen. Carbonic oxide. Nitrogen. Nitrous oxide. Carbonic acid. Air.
From 285 { Time in seconds 393 241 190.5 380 382 332 332 396
to 23-5 in. Time of ox. = 1 0-8993 0.5515 0°4359 0.8696 0-8741 0-7597 0-7597 0-9062
:


ON THE MOTION OF GASES. 137
This table exhibits the transpiration of the gases by E, in the upper
part of the scale or into a vacuum nearly, the condition in which the
subject is studied with most advantage. The coefficients exhibit a
close correspondence with those found by the two preceding capillaries.
The number for air is 0-8993 at the beginning, and 0.9062 at the end of
the experiments; a variation of rate to which this capillary appeared
more liable than the others. The number for nitrogen, 0.8741, again
slightly exceeds that for carbonic oxide, 0.8696. Nitrous oxide and
carbonic acid have the same number 0-7597, which is in excess com-
pared with 0.75; while the number for hydrogen, 0.4359, is slightly
deficient compared with 0:4375. Carburetted hydrogen has the number
0.5515, and is wonderfully constant with all these long capillaries.
As the time of transpiration in these experiments appeared rather
short for exact results, a larger aspirator-jar was employed, and the
experiment repeated with carbonic acid; air and oxygen being added
to give standards of comparison.
TABLE XXXII.-Transpiration by Capillary E into a Nine-Pint Jar.
Barom. 30.136. Temp. 74°5.

Air. Oxygen. Carbonic acid,
Gauge barometer in inches.
- I. II. I. II. I. II.
A/ &/ 4/ A Af A/
28.5 -
26.5 229 229 254 254 190 191
24°5 233 232 259 258 195 195
23.5 121 121 135 135 104 103
From 28°5 to 23:5......... 583 582 648 647 489 489
Mean Results.
Gauge barometer. Air. | Carbonic acid.
ſº • K : Time in seconds ...... 582-5 489
From 28-5 to 23.5 inches } Time of oxygen = 1 ... 0-8996 0-7550

As the result for carbonic acid differed sensibly from the experiment
of the preceding table, it was considered desirable to return to the sub-
ject on the following day. In the meantime the barometer had fallen
considerably, which accounts for the comparative slowness of transpira-
tion in the following repetition of the last experiments.
138 t ON THE MOTION OF GASES.
Repetition of the last Experiments. Barom, 29.616–29'666. Temp. 72’.

Air. Oxygen. Carbonic acid.
Gauge barometer in inches.
I. II. I. II. I. II.
Z/ Al Z/ Aſ J/ M/
28°5
26.5 237 236 || 262 262 196 197
24.5 239 || 239 266 266 199 202
23-5 129 129 141 141 107 106
From 28°5 to 23.5 inches 605 || 604 | 669 | 669 502 || 505
Mean Results.

Gauge barometer. - Air. Carbonic acid.
e . E . Time in seconds ...... 604'5 503.5
From 28°5 to 23-5 inches } Time of oxygen = 1 ... 0-9036 0-7526
The three results for carbonic acid by this capillary are therefore
0-7597, 0-7550, and 0.7526 ; of which the mean is 0.7558. The co-
efficient of capillary E for carbonic acid is therefore not so widely
different from 0.75 as it at first appeared.
With these large aspirator jars the rise of temperature within the
jar during the experiment becomes very small. In the six-pint jar it
did not amount to one-quarter of a degree Fahr., and in the nine-pint
jar it was altogether insensible.
I have now detailed the results of the transpiration of gases by all
the capillaries used except one,—a tube with which a few preliminary
experiments in the inquiry were made, not sufficiently precise to merit
being recorded. All of these tubes have given the same coefficient of
transpiration to each gas, or coefficients closely approximating, although
the tubes themselves have varied considerably in their respective dimen-
sions; namely, in diameter, from ºth to Tºwth of an inch; in length
from 2 inches to 22 feet; and from 12 to 70 seconds in the time of
transmission of one cubic inch of air into a vacuum. It can be said
that no selection of the tubes was made ; and their dimensions are in a
great measure accidental.
From the agreement in results obtained with tubes so different in
dimensions, I consider that a glass tube of any diameter whatever will
be found suitable for observations on transpiration, provided, a certain
length is given to it. If the tube is extremely short, a mere ring, then
we know that gases will be transmitted by it into a vacuum according
ON THE MOTION OF GASES. 139
to the law of effusion; oxygen, hydrogen, and carbonic acid in times
expressed by 1, 0:25, and 1:176 respectively. With the slightest elonga-
tion of the tube these ratios are disturbed; the number for hydrogen
soon increasing to 0.35 or 0:40, and that for carbonic acid falling to 1,
or 0.80, referring both to the time of oxygen always taken as unity.
The change with the increase of length is very great at first, but soon
falls off, and with a certain length of tube seems to cease altogether.
The coefficient of hydrogen is then found to have risen to some number
approaching closely to 0°4375 or 0:44, and the coefficient of carbonic
acid to approach closely to 0-75. The coefficient of nitrogen has fallen
at the same time from 0.9373 (its coefficient of effusion, that of oxygen
being 1) to nearly 0.875. -
With this length of the tube, the influence of effusion upon the
transpiration rate of the gas has ceased to be sensible.
The action of the tube attains a certain uniformity, at the same time,
in another respect. When the tube is deficient in length, the coefficient
of the gas varies greatly with the extent of the exhaustion of the vessel
into which the gas is flowing; the rate of transpiration inclining most to
the rate of effusion at a high degree of exhaustion of the aspirator jar.
But the amount of this variation progressively diminishes as the tube
becomes longer, till at last the coefficient of transpiration remains nearly
if not perfectly constant, whether the aspiratory jar be entirely vacuous,
or contains already gas of the tension of half an atmosphere, three-
fourths or even seven-eighths of an atmosphere.
The tube is now of the length most favourable for experiments of
transpiration. Farther addition to the tube appears to have no effect in
altering the coefficient of transpiration of air, provided the aspirator jar
into which the air passes is vacuous or nearly so; or the coefficient of
transpiration into a vacuum appears to remain constant for all greater
lengths of the tube. But the extent of the barometric range in the
aspirator jar to which the vacuum coefficient is found to apply is gradu-
ally limited. Instead of extending over seven-eighths of an atmosphere
it may be contracted to an eighth of an atmosphere or less, by greatly
lengthening the tube. -
The coefficients of transpiration which I have endeavoured to ascer-
tain are properly therefore the relative times of passage of the gases
into a vacuum, at the mean atmospheric temperature, or near that
temperature. * -
But even with the most favourable length of the tube, when the aspi-
ration is feeble, and does not exceed 2 or 3 inches of mercury, the rate of
transpiration is modified from an interference, which is connected with
the excessive resistance of the tube to the passage of the gas. I have
not been able to undertake an examination of the nature and extent of
140 ON TEIE MOTION OF GASES.
this interference, but suppose it to depend upon friction, while the rate
of transpiration seems again to depend upon a constitutional difference
in the gases themselves.
The theory of the transpirability of gases, which at present appears
to me most probable, is that it is a kind of elasticity depending upon
the absolute quantity of heat, latent as well as sensible, which different
gases contain under the same volume; and therefore that it will be con-
nected more immediately with the specific heat than any other property
of the gases.
The only other gases besides those already experimented upon,
which could be retained over water, and exposed to the metallic parts
of the apparatus without injury, are olefiant gas, nitric oxide and Sul-
phuretted hydrogen; and these were submitted to transpiration with
several of the tubes already used. I subjoin the results, although less
complete than is desirable, under the head of each gas.
7. Transpiration of Olefiant Gas.
TABLE XXXIII-Transpiration by Capillary H into a Six-Pint Jar.
Barom. 29.68. Temp. 59°. -

Air.
Gauge barometer in inches. Alr Olefiant gas.
I II. I II
A &A A A.
28.5 0 0
26°5 217 218 124 128
24°5 220 220 130 131
23.5 112 113 66 65
From 28-5 to 23-5 inches... 549 551 320 324
Transpiration by Capillary H into a One-Pint Jar.

| Air. Olefiant gas. Air.
Gauge barometer in inches. -
I. II. I. II, I.
28 Æ Aſ Z/ Af 4/
20 184 183 * 108 || 108 183
12 227 228 134 134 226
8 163 163 96 96 163
4 265 265 153 15] 265
2 260 264 149 149 260
From 28 to 2 inches......... 1099 1103 640 638 1097
ON THE MOTION OF GASES. 141

Air. Olefiant gas.
Time in seconds......... 550 322
From 28°5 to 23-5 inches & Time of air=1............ tº tº ſº. 0-5854
Time of oxygen = 1...... tº e gº 0°5268
Air. Olefiant gas.
Time in seconds....... 1099-7 639
From 28 to 2 inches ....... Time of air=1 .......... * - G 0-5810
Time of oxygen = 1.... • * * . 0-5229

TABLE XXXIV.-Transpiration by Capillary H (with cupped ends)
into a Six-Pint Jar. Barom. 302. Temp. 52°.

Air. "..." |olefiant gas. Air 90c,H,410CO. Air.
Gauge barometer yarog
in inches.
I. II. I. II. I. II. I. I. II. I. II.
Af Af AA zy f/ Af Aff A/ AA J/ Af
28'5 0 0 0 0 0 0 0 0 0 0 0
26'5 206 || 207 || 127 126 120 118 207 126 126 207 | 207
24°5 208 208 127 128 II9 121 208 I26 127 209 209
23.5 106 || 106 || 64 || 65 | 61 61 || 106 64 64 || 104 || 104
From 28°5 to 23'5 inches | 520 | 521 || 318 || 319 300 || 300 521 316 317 520 520
Mean Results.

Gauge barometer. Air. º oº: 90C, H,--10CO. Air.
... (Time in seconds .. 521.5 318 300 3.16-5
Fº: #: Time of air=1 ...... a gº tº 0, 61.18 0.5763 0-6080
* UTime of oxygen-1 ... 0°55'06 0. 5186 0.5472
The results for olefiant gas can be considered only as approximative
from the circumstance that the gas was always contaminated by a small
quantity of carbonic oxide, varying from 3 to 5 per cent, and a sensible
trace of the dense gas or vapour, to which allusion has already been
made. Both impurities would tend to raise the number for olefiant
gas; ten per cent. of carbonic oxide purposely added to that gas, raising
its number from 0-5186 to 0-5472. The calculated mean rate of the
last mixture is 0-5513, taking the rate of carbonic oxide at 0-8700, and
142 ON TEIE MOTION OF GASES.
that of olefiant gas at 0:5186. If the true coefficient for olefiant gas
should be a whole number, it may be expected to be 0.5, or exactly one-
half of the rate of oxygen.
8. Transpiration of Nitric Oxide.
TABLE XXXV.-Transpiration by Capillary E into a One-Pint Jar.
Barom. 30.45. Temp. 52°.

Gauge barometer Air. Nitric oxide. Oxygen. Air
in inches.
I. I. II. I. I.
º/ Z/ Æ ſ/ &A
28
20 135 135 131 149 135
12 167 162 I62 186 169
8 118 115 115 133 118
4 189 183 184 206 188
2 I92 184 188 219 195
From 28 to 4 in. 609 595 592 674 610
Mean Results.

Gauge barometer in inches. Air. Nitric oxide. Air.
o Time in seconds...... 609 593.5 610
From 28 to 4 in. {#. of oxygen = 1 0.9035 0-8805 0'9035
TABLE XXXVI.-Transpiration by Capillary E into a Two-Pint Jar.
Barom. 30.08. Temp. 60°.

Gauge barometer Nitrogen. Nitric oxide. Oxygen.
in inches.
I. II. III. I. II. I. II.
28 6 ô ô Af J/ Aſ M/
20 231 232 e tº º 237 235 | 266 267
12 286 287 286 288 || 287 327 328
8 200 | 200 | 202 | 203 || 206 || 227 227
4 320 || 317 | 320 || 313 || 312 || 363 || 364
2 314 || 320 316 || 311 || 315 361 361
From 28 to 2 inches...| 1351 || 1356 | ... 1352 1355 | 1544 1547
ON THE MOTION OF GASES.
T 43
Mean Results.
Gauge barometer. Nitrogen. Nitric oxide.
g Time in seconds ......... 517-83 523-5
From 28 to 12 inches Time of oxygen-1...... 0-87.17 0-8815
ſº Time in seconds ......... 519.7 517
From 12 to 4 inches {fi:. . .i. 0-8801 0-8755
tº Time in seconds ......... 316.7 313
From 4 to 2 inches Time of oxygen = 1...... 0.8772 0-8670
º } Time in seconds ......... 1354°2 I353-5
From 28 to 2 inches ; i. i. 0-8768 || 0-8764
The number for nitric oxide (NO2) approaches very closely to that of
nitrogen, if it does not actually coincide with that number; yet the
specific gravities of these two gases are different, that of nitric oxide
being 1-0405, air = 1; or 0.9375, oxygen = 1; the mean between the
densities of oxygen and nitrogen gases. It would appear from this
that the coefficients of transpiration of gases are less various than their
specific gravities. In conducting experiments with this gas, the surface
of the mercury in the gauge-tube is tarnished, which causes it to adhere
to the glass and descend irregularly, so that the observations want the
usual uniformity, as seen in both tables. When a few drops of water
were placed above the mercury in the gauge barometer, its descent
became more regular. This gas acted inconveniently in another way,
by forming a solid compound with the oil in the cylinders, and thus
clogging the action of the air-pump.
9. Transpiration of Sulphuretted Hydrogen.
TABLE XXXVII—Transpiration by Capillary H into a One-Pint Jar.
Barom. 29.89. Temp. 59°.
Air. Sulphuretted hydrogen. Air.
Gauge barometer in
inches.
ſ. II. I. II. III. I.
Aſ 47 A/ A/ wº £/
28 0 0 0
20 180 180 122 123 12I 178
12 226 224 156 153 153 225
8 155 158 108 109 110 156
4 | 262 257 177 174 173 258
2 253 256 175 173 173 255
From 28 to 2 inches ... 1076 || 1075 | 738 732 | 730 || 1072

144 ON THE MOTION OF GASES.
Mean Results.
Gauge barometer. Sulphuretted hydrogen.
Time in seconds......... 276
From 28 to 12 inches | Time of air - 1 , , , 0-6814
Time of oxygen = 1 ... 0.6132
Time in seconds......... 283-66
From 12 to 4 inches & Time of air = 1 ... 0.6738
Time of oxygen = 1 ... 0-6060
Time in seconds......... 173-66
From 4 to 2 inches | Time of air F 1 , , , 0-6825
Time of oxygen = 1 ... 0-6142
Time in seconds......... 733-3
From 28 to 2 inches & Time of air = 1 ... 0-6818
Time of oxygen = 1 ... 0-6136
TABLE XXXVIII.-Transpiration by Capillary H into a Six-Pint Jar.
Barom. 29.98. Temp. 59°.

Air. Sulphuretted hydrogen. Air.
Gauge barometer in inches.
I. II. I. II. III. IV. I. II. III. IV.
28.5
26°5 206 || 203 || 140 || 140 || 140 || 141 206 || 203 || 203 || 205
24°5 207 || 209 || 143 || 147 146 148 |216 214 217 | 215
23.5 107 || 109 || 77 || 75 77 || 75 | 108 || 109 || 109 || 111
From 28°5 to 23-5 inches ...] 520 | 521 360 362 || 363 || 364 530 526 529 531
Mean Results.
Gauge barometer. Su lphuretted hydrogen.
Time in seconds......... 362.25
From 28°5 to 23.5 inches & Time of air =1...... 0-6846
Time of oxygen = 1...... 0-6161

The experiments with this gas indicate a number above 0-60 for its
coefficient of transpiration; 0.625 is 5–8ths of oxygen, while the result
of Table XXXVIII., which is the more valuable of the two, is 0-6161.
But this gas is likely to vary sensibly in its coefficient with different
capillaries, like carbonic acid; and both its physical and chemical pro-
perties oppose difficulties to obtaining a correct result. The rate of
air following this gas is made very sensibly slower in the last table;
ON THE MOTION OF GASES. 145
indeed the rate of the capillary appears to be permanently altered,
possibly from the deposition of sulphur from the gas.
[I shall add, in an Appendix to this paper, a series of observations
on the transpiration of gaseous mixtures, which appear to warrant the
following conclusions:—
It appears from Tables XLII. and XLIII. that mixtures of oxygen
and nitrogen in all proportions maintain a rate which is sensibly the
arithmetical mean rate of the two gases.
From Tables XLIV. and XLV., that the rates of mixtures of oxygen
and carbonic oxide are also uniform, but that mixtures of carbonic
oxide and hydrogen deviate greatly from the mean, inclining always to
that of the heavier gas.
In Tables XLVI. and XLVII., that the mixtures of oxygen and
carbonic acid maintain the mean rate; and that mixtures of carbu-
retted hydrogen and hydrogen deviate greatly from the mean, always
inclining to the rate of the slower gas.
Tables from XLVIII. to LIII. inclusive exhibit the transpiration of
hydrogen mixed with various other gases, particularly nitrogen, oxygen,
carbonic acid, nitrous oxide, and nitric oxide; and Tables LIV. and LV.
contain the results of the transpiration of mixtures of carburetted
hydrogen with oxygen and with hydrogen. It appears that while all
the other gases tried appeared to maintain their usual rates of transpira-
tion in a state of mixture, those of carburetted hydrogen and hydrogen
are greatly altered; and when the proportion of the latter gas is not
more than from 5 to 15 per cent, its rate becomes as slow as the densest
gas with which it is mixed; the deviation from the mean in hydrogen
mixtures being relatively greatest when one of the gases is present in a
Small proportion. With an addition of so much as 25 per cent. of
hydrogen, carburetted hydrogen, carbonic acid, and nitrous oxide con–
tinue to be transpired in sensibly the same times as when pure and
unmixed. Hydrogen is then transpired of course as slowly as the other
gas with which it is mixed, although the time of hydrogen alone is 0:44,
while that of carburetted hydrogen is 0:55, and of carbonic acid and
nitrous oxide 0°75. Indeed, small additions of hydrogen, such as 5 or
10 per cent, made to carburetted hydrogen, appear to prolong the time
of transpiration; and what is very curious, raise the time of the mixture
to the empirical number of pure carburetted hydrogen, namely 0:5625
(Table XLVII.) A slight retardation of the same kind may also be
perceived in the similar carbonic acid mixtures. The transpiration-time
of equal volumes of hydrogen and carbonic acid is 0.7339, or very little
less than that of pure carbonic acid.
Carbonic oxide and nitric oxide, with equal admixtures of hydrogen,
K
146 ON THE MOTION OF GASES.
correspond as closely in their times as when pure, as will be seen on
comparing together the results of Tables XLV. and LIII. A similar
apparent rectification of the time of nitric oxide will be observed, in the
last of these tables, to be effected by the addition of 5 per cent. of hydro-
gen to that gas, as was remarked above of carburetted hydrogen; the
time of 100 NO, being 0-8661, that of 95 NO, + 5H is found 0.8788;
while the empirical coefficient for nitric oxide is the same as that of
nitrogen, namely, 0-8750, or 0.8785, adopting Regnault's density of the
latter gas.
It appears that the time of carburetted hydrogen is sensibly increased
by the addition of oxygen, at least when the proportion of the latter gas
amounts to or exceeds 25 per cent. of the mixture (Table LTW)
The times of transpiration of the hydrogen mixtures, which have
been most minutely observed, namely, those of hydrogen with oxygen,
with air, and with carbonic acid, are exhibited by the curves of Plate
XXXV. These curves start from a common point 44, the time of pure
hydrogen, and terminate respectively with the times of oxygen 100, of
air 90, and of carbonic acid 75.
It would be premature to enter at present upon any discussion of
these results; for the full elucidation of the transpiration of mixed gases,
must await, I believe, the further extension of our knowledge of the laws
of gaseous diffusion. Nov. 1846.]
TABLE XLII.—Transpiration by Capillary E into a One-Pint Jar.
APPENDIX.
Tables of the observed Transpiration of Gaseous Miatures.
Barom. 29.55. Temp. 53°.
Air. Oxygen. 97'5 O-H-2'5N. 95 O-H-5N. 90 O-H-10N. 75 O-H-25N. 66-6 O-H-33'8N. Oxygen.
Gauge barometer
in inches.
I. II. I. II. I. II. I. II. I. II. I. II. I. II. I.
28 ô ô ô // f/ f/ ô Ö ô AW ô f/ Ö f/ ô
20 142 143 158 158 • * * e e ºs 157 158 156 157 153 153 151 151 157
I2 176 175 196 195 353 353 194 194 192 I92 190 l89 187 187 195
8 123 123 137 138 137 137 137 136 136 136 133 134 131 132 137
4 197 197 222 220 220 219 220 219 218 216 214 214 211 211 220
2 199 197 221 222 222 223 220 221 219 22I 218 219 212 212 222
From 28 to 2 inches......... 837 835 934 933 932 932 928 928 921 922 908 909 892 893 931
Mean Results.
Gauge barometer. Air. 97.5 O-H-2'5N. 95 O-H-5N. 90 O-H-10N. 75 O-H-25N. 66'6 O-H-33'3N. Oxygen.
Time in seconds ... 836 932 928 921.5 908'5 892.5
From 28 to 2 inches {Time of oxygen = 1 0.8955 0°9984 0°994.1 0.9871 O'9734 0.9550
Calculated mean... tº & 0.9969 0-9938 0.9875 O'9688 0.9583
º


148
ON THE MOTION OF GASES,


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TABLE XLIV.-Transpiration by Capillary E into a One-Pint Jar.
Barom. 29.69. Temp. 54°.
oxygen. || “..." | 97 sco P250 | 95co-so 90CO-H-10 O. 75CO-H-25 O. Air. Oxygen.
Gauge barometer in inches.
I. I. I. I. I. I. I. I.
Af 4./ M/ 4 / # / 44 f/
28 0 O O O
20 157 137 139 138 140 142 143 158
12 195 169 169 170 172 176 175 196
8 137 118 120 120 120 124 123 138
4 219 192 191 192 194 198 197 221
2 221 190 192 193 202 202 199 221
From 28 to 4 inches ............ 708 616 619 620 626 640 638 713
Mean Results.
Gauge barometer. Carbonic oxide, | 97'5CO-H2'5 O. 95CO-H-5 O. 90CO+10 O. 75CO+25.0. Air. Oxygen.
Time in seconds...... 616 619 620 626 640 638
From 28 to 4 inches {Time of oxygen = 1 0.8701 0-8743 0.8757 0°8842 0-9040 0-9011
Calculated mean...... * † tº 0.8733 0.8765 0°8830 0-9026
:


TABLE XLV-Transpiration by Capillary E into a One-Pint Jar. Barom. 30:18. Temp. 52”.
tº Carbonic & * º e Oxy- * e º Hydro-
Gauge barometer Air. oxide. 66-7CO+33.8 O. 50CO+50 O. 66'7 O-H-83 3CO. 75 O-H-25CO. gen. 95CO+5H, 9000+10H. 75CO+25H, 92'5CO+7°5H. Air. gen.
in inches.
I. I. I. I. I. I. I. I. I. I. I. I. I.
28 Ö Ö 4/ Aff 6 ô Ö ô Ö Ö é Ö Ö
20 137 || 132 140 143 146 148 I52 133 132 128 132 137 78
12 169 | 164 172 177 181 183 || 189 164 163 159 163 170 | 84
8 119 || 116 122 125 128 130 133 115 | 116 113 115 121 59
4. I92 | 185 195 200 206 205. 215 184 185 181 185 193 95
2 193 | 188 201 205 209 204 219 190 191 E81 19]. 201 || 100
From 28 to 617 | 597 629 645 661 666 | 689 || 596 596 581 595 621 || 316
4 inches • |
Mean Results.
Gauge barometer. Air. *...* | 687c04-338 o. 50C04-500.|66704-338co. 750+25Co. oºco+5H. |90co-HOH. woºn. 92.5CO+7-5H. | Air. Hydrogen.
Frohl Time in seconds | 617 597 629 645 661 666 596 596 581 595. 621 316
2: ...", J Time of ox.<1 ... 0-8905 || 0:8664. Q9129 || 0:3361| 09593 || 0:9666|| 0:3650 || 0:3650. Q:8432| 0.335 | 0-9013| 0:4586
†ches ) Qale, mean, A. ... ...... tº e s is s a 0.9109 || 0-9332 || 0-9554 || 0-9666 || 0-8046 || 0-8256 || 0-7644 || 0-8358
Calc, mean, Bt...] ...... . ...... . ...... . ...... . ...... . ...... 0.8450 || 0-8237 0-7848 0.8344
* Mean with the number for hydrogen actually observed.
+ Mean with the number 0.44 as the coefficient of hydrogen. These last results are most to be depended upon, as the rate of the
hydrogen alone is often raised by a slight impurity, of which the effect would become much less sensible in the mixtures containing that gas.
g


ON THE MOTION OF GASES.
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TABLE XLVII-Transpiration by Capillary E into a One-Pint Jar. Barom. 29.61. Temp. 54°.
Carbu- Car-
retted t .er, Hydro- || Oxy- $yſ' '5CO.,.] bonic | 82°5CH2+17°5H.
Gauge barometer | *Xºro- 90CH,410H 95CH,45H. 97.5CH,+2.5H. . . . .900+10CO,750+25C0, 950+5C0, 97.50+2'5CO, º 2
in inches. gen.
I. I. I. I. I. I I. I. I. T. I. I.
A/ A/ A/ A/ A/ Aſ £f
28 £º Ö Ö Ö 0 O O 0 Ö O 0 O
20 87 89 89 87 71 158 154 149 155 156 119 88
I2 107 110 109 107 88 194 189 183 192 193 147 109
8 - e. e. 76 76 75 61 137 133 128 134 136 102 75
4 195 123 123 I 20 98 || 218 214 206 217 218 163 122
2 121 124 123 122 102 224 219 211 222 224 166 123
From 28 to 4 698 703 531 394
inches...... } 389 || 398 397 389 318 || 707 || 690 &
Mean Results.
Carburet- ". 5Co. Cºniº |82-5CH,+17.5H.
Gauge barometer. ted hydro-90CH2+10H. 950H2+5H. 97-5CH2+2.5H.|Hydrogen.900+10CO2. 75 O-H-25CO2. 95 O-H-5CO2. 97.5 O-H2 2" | acid. 2
gen.
3 : (Time in seconds | 389 398 397 389 3.18 690 666 698 703 531 394
º: ſ Time of ox. =I 0.5544 0. 5629 0.5615 0. 5502 0.4497 0.9759 0.9420 0.9872 0°9943 0.7510 §
ă. Uğ. mean, A* tº a º 0. 5439 0°5266 0. 5409 * † - 0.9750 0.9375 0'9875 0.9937 * * * 0-5343
#3 ( Calc, mean, B+ 0. 5429 0°5486 0°5515 gº tº e * * * © a e tº gº tº
* Mean with the number for hydrogen actually observed. f
t Mean with the number 0.44 as the coefficient of hydrogen. These last results are most to be depended upon, as the rate of the
hydrogen alone is often raised by a slight impurity, of which the effect would become much less sensible in the mixtures containing that gas.
§


ON THE MOTION OF GASES.
153


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TABLE XLIX—Transpiration by Capillary E into a One-Pint Jar. Barom. 29'57. Temp. 55°.
Gauge barometer Air. Hydrogen. |50H+50N |25H+75co, 10H+90co, 25H+75CH, °." | oxygen. |Nitrogen | Air
in inches.
I. I. I. I. I. I. I. I. I. I.
28 Z/ // ô Z/ 6 M/ 6 £/ 4/ Aſ/
20 143 71 127 120 120 90 88 158 138 142
12 175 87 156 146 ° 147 109 108 195 170 176
8 tº gº tº 62 105 103 103 76 75 136 120 122
4. 321 99 181 166 164 122 I2] 221 189 199
2 194 99 173 159 158 122 118 213 191 196
From 28 to 4 inches ......... © e º e º e 639 319 569 535 534 397 392 710 617 639
Mean Results.
Gauge barometer. Air Hydrogen. 50H-F50N |25H+75co, 10H+90co, 25H+75CH, i." | Nitrogen. Air
Time in seconds............ 639 319 569 535 534 397 392 617 639
From 28 to ) Time of oxygen = 1 ...... 0-9000 0°4493 0-8014 0-7535 0-7521 0.5591 0.5521 0-8690. 0-9000
4 inches Calculated mean, A ...... tº £ tº ſº tº 0-6590 0.6723 0.7172 0.5264
Calculated mean, B ...... tº e 0-6545 0-6702 0-7163 0.5240
:


ON THE MOTION OF GASES.
155

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Transpiration by Copper Capillary into a Three-Pint Jar. Barom. 30.19. Temp. 615.
Air. 50H-H 50 Air. 101BI-H 90 Air. 5PI-F95 Air.
Gauge barometer in inches.
I. II. I. I. I.
61°-5 61°-5 61°-5 61°-5 61°-5
28 07 0', 07 07 07
24 284 284. 258 280 282
20 302 302 274 298 300
12 727 728 662 721 724
8 514 515 471 510 514
62° 62° 62° 629 629
From 28 to 8 inches......... 1827 1829 1665 1809 1820
Mean Results.
Gauge barometer. Air. Hydrogen. 95H+5 Air. 90EI-H 10 Air. 75H+25 Air. 25H+75 Air.
• Time in seconds.................. 1803.5 902 1074.5 1196 1461 7987 Its. 97.67
* Time of air=1................... tº gº º 0.4927 O-5869 0-6534 0-79 g
From 25 to sinches #:...: tº º º 0°4434 0.5282 0.5880 0.7488 0-8790
Calculated mean.................. e e e ' 0°4630 0°4860 O-5500 0-7850
Air. 50H-H 50 Air, 10H-H90 Air. 5H+95 Air.
Time in seconds............ tº e º e g is 1828 1665 1809 1820
& Time of air=1 ................... tº gº tº 0°9108 0.9876 0.9956
From 28 to 8 inches Time of oxygen = 1............... tº e º 0.8197 0-8888 0-8960
Calculated mean.................. 0-6700 0.8540 0-8770
g



TABLE LI–Transpiration by Capillary E into a One-Pint Jar. Barom. 29.89. Temp. 54°.
97.5H4-25CO, 5H+500, ºn Hoco, 75H+25CO, 50H+50CO, Carbonic acid. Oxygen. - Hydrogen. Air.
Gauge barometer -
in inches. - —º-
I. I. *} I. I. I. I. I. I. I.
// . MM f/ A/ f/ 1 // M/ ſ/ 4/
28 - 0 O 0 0 0.
20 77 79 88 105 114 118 156 68 142
12 95 99 II.0 I 30 142 145 192 85 173
8 67 69 77 92 99 102 136 60 121
4 109 113 I25 148 160 162 217 97 195
2 : 111 115 127 150 16] 161 220 98 201
From 28 to 2 inches 459 475 527 625 676 688 92.1 398 832
Mean Results,
Gauge barometer. 97.5H+25CO, 95H+5CO, 90H+10CO, 75H+25CO, 50H+50CO, Carbonic acid. Hydrogen. Air.
From 28 to (Time in seconds || 459 475 527 625 676 688 398 832
8 inches Time of ox. = 1 0.4983 0.5157 0.5722 0.6786 0.7339 0.7470 0.4321 0'9033
Calculated mean 0°4402 0'4484 0°4648 0.5113 0-6455
§


158
ON THE MOTION OF GASES.
TABLE LII-Transpiration by Capillary E into a One-Pint Jar.
Barom. 30.39. Temp. 52°.
Air. Oxygen. Nitrous Oxide. 75NO+25.H. 90NO+10H. Air.
Gauge barometer in inches. -
I. I. I. I. I. I.
f/ M/ // A/ M/ ſ!,
28 O O 0
20 136 152 114 114 114 135
12 168 187 141 141 141 168
8 119 132 99 99 98 . 119
4 I89 212 157 159 158 190
2 198 222 159 162 159 196
From 28 to 4 inches...| 612 683 511 513 511 612
Mean Results.
Gauge barometer. Air. *...* |75No.425H.90No.410H. Air.
Time in seconds 612 511 513 511 612
º Time of oxy. = 1 0-8960 0-7481 || 0-7510 || 0-7481 || 0-8960
From 28 to 4 in. Calc, mean, A.... e tº ºr tº 0-6757 0.7292
Calc, mean, B.... -




TABLE LIII-Transpiration by Capillary E into a One-Pint Jar.
Barom. 30-62. Temp. 52°.
Air. Oxygen. Hydrogen. Nitric oxide. 95NO,4-5H.
Gauge barometer in inches.
I. I. I. I. II. I.
28 6 6 M/ M/ Ö ſ/
20 133 149 66 130 129 130
12 167 184 83 161 158 163
8 117 131 59 114 112 115
4. 189 212 95 183 184 186
2 192 214 97 183 181 184
From 28 to 4 inches ..., 606 676 303 588 583 594

ON THE MOTION OF GASES. 1.59
TABLE LIII.-Continued.
90NO +10H. 75NO,4-25H. 50No,+50H. 25No,+75H. Air.
Gauge barometer in inches.
I. I. I. I. I.
M/ ſ/ M/ A/ f/
28 0. ()
20 128 125 119 106 134
12 160 157 150 132 168
8 II3 I 12 117 95 120
4 181 180 170 151 192
2 181 185 179 153 193
From 28 to 4 inches ... 582 574 556 484 614
Mean Results.
Gauge barometer. Air. Hydrogen. Nitric oxide. 95NO2+5H.
- Time in seconds...... 606 303 585.5 594
From 28 to ) Time of oxygen = 1... 0-8964 0°4482 0-866] 0.8788
4 inches ) Calc, mean, A.......... tº º º tº º º tº ſe ºf 0-84.52
Calc, mean, B.......... 0-8447
90NO2+10H. 75NO2+25H. 50NO2+50H. 25NO 2+75.H.
Time in seconds ...... 582 574 556 484
From 28 to ) Time of oxygen – 1...] 0-8609 0-8491 0.8224 0.7159
4 inches ) Calc, mean, A.......... 0°8243 0-7616 || 0-6571 0-5527
Calc, mean, B.......... 0°8234 0-7596 0-6530 0.5465
Air.
From 28 to ( Time in seconds ...... 614
4 inches & Time of oxygen = 1...| 09082


TABLE LIV.-
TABLE LIV.—Transpiration by Capillary E into a One-Pint Jar.
Barom. 2971. Temp. 55°.
C* | 97.5CH,4-25 O. 95OH,4-5 o 90CH.4-10 o 75CH,4-25 O. 50CH,4-500. Air.
Gauge barometer Oxygen | “. 2 º 2+ 2+ 75CH2+ 2+
in inches,
I. I. I. I. I. I. I. I.
28 f/ A/ ô s Aſ/ Aſ/ 6 Aſ/ 6
20 157 91 91 92 94 109 127 141
12 195 109 112, 114 117 134 157 174
8 136 77 79 79 81 94 110 122
4. 219 122 126 127 13] 151 177 195
2 224 124 127 129 133 153 180 200
From 28 to 4 inches... 707 399 408 412 423 488 57.1 632
Mean Results.
Gauge barometer. º 97.5CH,4-25 O. 95CH,4-5 O. 90CH,4-100. |75CH,425 O. 50CH,+500. Air.
From 25 to 4 (Time in seconds. 399 408 412 423 488 571 632
inches Time of ox. = 1... 0.5629 0.5770 0-5827 0.5983 0-6902 0-8076 0-8939
Calc, mean........ tº e de 0-5734 0°5838 0-6062 0-6718 0-7814
3.


TABLE LV—Transpiration by Capillary E into a One-Pint Jar. Barom. 29°43. Temp. 55°.
Air |Hydrogen. 97.5H+25CH, 95H+5CH, 90H+10CH, 75H+25CH, 50H+50CH, °." | Hydrogen. Oxygen.
Gauge barometer g ydrogen.
in inches.
I. I. I. I. I. I. I. I. I. I.
ſ/ M/ A/ // M/ M/ A/ f/ A/ (/
28 O 0 0 O
20 144 73 75 77 79 84 88 88. 74 160
12 176 91 93 94 98 105 109 108 92 197
8 124 64 65 66 68 73 76 76 65 138
4 198 103 105 107 111 119 122 121 105 222
2 201 105 107 109 113 120 126 123 106 225
From 28 to 4 inches...| 642 33] 338 344 356 381 395 393 336 717
Mean Results,
Gauge barometer, Air. Hydrogen, 97.5H-H2'5CH2, 95H+5CH2. 90H+10CHA. 75H+25CH, 50H--50CH2. º Hydrogen.
Time in sec. ...[642 331 338 344 356 381 395 393 336
From 28 to W Time of ox. = 1 0.8955 || 0:4616 0-4714 0.4797 0°4965 0.5313 0.5596 0.5481 0.4686
4 inches Calc, mean, A tº tº º e - tº 0-4705 0.4725 0°4765 0°4884 0-5083
Calc, mean, B 0.4427 0°44'54 0'4508 0'4670 0.4940
3.


162 ON THE MOTION OF GASES.
XV.
ON THE MOTION OF GASES. PART II.”
From Phil. Trans. 1849, pp. 349-392.
ALL experiments on the velocity with which different gases rush
into a vacuum, or pass under pressure through an aperture in a thin
plate, are in strict accordance with the physical law that the times of
passage for equal volumes are proportional to the square roots of the
densities of the various gases. Besides being the law of “Effusion,”
this is also the law of the Diffusion of one gas into an atmosphere of
another gas. The result in both cases is simply and exclusively a con-
sequence of specific gravity.
The velocity with which gases of different nature pass through a
tube is necessarily much influenced by the law of their effusion, when
the tube is short and approaches in character to an aperture in a thin
plate. º if the length of the tube is progressively increased, its
diameter or the aperture remaining constant, then while the resistance
increases, and the passage for all gases becomes greatly slower, the
velocities of the different gases are found rapidly to diverge from those
of their effusion. The velocities of different gases appear at last how-
ever to attain a particular ratio with a certain length of tube and resist-
ance, and preserve the same relation to each other for greater lengths
and resistances. After attaining this constant ratio, the passage of all
the gases becomes slower, exactly in proportion to the increased length
of the tube, that is, in proportion to the resistance. The different gases
are now equally affected by the resistance, and their relative velocities
are therefore undisturbed and remain constant. The effect of the law
of effusion upon the velocities is no longer sensible, and appears to b
eliminated. | & -
As the rates of passage of different gases through a tube appear to
depend upon a new and peculiar property of gases, I have spoken of it.
as the Transpiration or Transpirability of gases. The rates of transpi–
ration appear not to be affected by the material of the tube, as they are
found the same for capillary tubes of glass and of copper and for a
porous mass of stucco. I may add, that such experiments exhibit a
constancy and possess a neatness and precision which is very extra-
ordinary. The experiments of M. Poiseuille indicate an equally remark–
able constancy and precision of result in the passage of Liquids through
capillary tubes, which has been fully confirmed by M. Regnault.”
1 Received June 21,–Read June 21, 1849.
2 Rapport sur un Mémoire de M. le Docteur Poiseuille, ayant pour titre, “Recherches
expérimentales sur le mouvement des liquides dans les tubes des très-petits diamétres.”
Annales de Chimie et de Physique, 3me série, t. vii. p. 50.
ON THE MOTION OF GASES. 1.63
The experiments of my former paper afford good grounds for assum-
ing the existence of a relation in the transpirability of different gases,
of an equally simple nature as that which is recognised among the
specific gravities of gases, or even as the still more simple ratios of their
combining volumes. Compared with solids and liquids, matter in the
form of gas is susceptible of Small variation in physical properties, and
exhibits only a few grand features. These differences of property, which
are preserved amidst the prevailing uniformity of gases, may well be
supposed to be among the most deep-seated and fundamental in their
nature with which matter is endowed. It was under such impressions
that I have devoted an amount of time and attention to the determina–
tion of this class of numerical constants, which might otherwise appear
disproportionate to their value and the importance of the subject. As
the results, too, were entirely novel, and wholly unprovided for in the
received view of the gaseous constitution, of which indeed they prove
the incompleteness, it was the more necessary to verify every fact with
the greatest care.
Perhaps the most general and simple result which I can offer is, that
the transpiration velocity of hydrogen is exactly double that of nitrogen.
These gases, it will be remembered, have a less simple relation in den—
sity, namely 1 to 14. This was the conclusion respecting the transpira-
tion of these gases in my former paper, and I have obtained since much
new evidence in its favour. The transpirability of carbonic oxide, like
the specific gravity of that gas, appears also to be identical with that of
nitrogen.
The result which I would place next in point of accuracy and im-
portance is, that the transpiration velocity of oxygen is related to that
of nitrogen in the inverse ratio of the densities of these gases, that is, as
14 to 16. In equal times it is not equal volumes but equal weights of
these two gases that are transpired; the more heavy gas being more
slowly transpired in proportion to its greater density. Mixtures of
Oxygen and nitrogen have the mean velocity of these two gases, and
hence the time of air is also found to be proportional to its density
when compared with the time of oxygen.
The relation between nitrogen and oxygen is, I believe, equally pre-
cise as that between nitrogen and hydrogen. The densities calculated
from the atomic weights of oxygen and nitrogen, namely, 16 and 14,
being 1 for oxygen, 0-9010 for air and 0.8750 for nitrogen; the observed
times of transpiration of equal volumes of the same gases are for oxygen
1, air 0.8970 to 0-9010, and for nitrogen from 0-8680 to 0-8708.
These slight deviations I look upon as of the same character as
those which accurate determinations of the densities of the same gases
indicate from their calculated or theoretical density; the observed den-
164 ON THE MOTION OF GASES.
sities of air and nitrogen being 0.9038 and 0.8785 referred to oxygen as
unity (Regnault), instead of 0-9010 and 0.8750; or the observed differ-
ence in density is sensibly less than it should be by theory. The de-
parture from the law in the transpiration of the same gases is certainly
somewhat wider, and it is in the opposite direction; the difference in
the observed times of transpiration being greater instead of less than
the calculated times.
The points respecting transpiration, which still most demand con-
sideration, are the following:—
1. Determination of the resistance and of the dimensions of the
capillary at which the transpiration of gases becomes normal; and the
properties of serviceable capillary tubes.
2. New determinations of the transpiration of various gases and
vapours.
3. Influence of change of density and elasticity, produced by change
of pressure, upon transpiration.
4. Influence of temperature upon transpiration.
I. CAPILLARY TUBES FOR TRANSPIRATION.
The transpiration of some gases appears to become sooner normal
than others, that is, in capillary tubes which are less elongated or less
contracted than is necessary for other gases. This was first observed
on breaking down and using portions of the glass capillary tube H of
my former paper, which was comparatively wide, being about 0.0222
inch, or #th of an inch in diameter, with the great original length of
22 feet; when it allowed 1 cubic inch of air to pass under the pressure
of one atmosphere into a vacuum in 15:64 seconds, or it discharged 3-84
cubic inches of air per minute.
The following table exhibits the times of transpiration of equal
volumes of several gases by this capillary reduced in length to a little
under 20 feet. The table contains two series of experiments. The first
is the transpiration time of a constant volume of the gases drawn from
a globular vessel standing over water, into a sustained vacuum. This
vessel was terminated above and below by glass tubes, forming hollow
axes to the globe. The measure transpired was the capacity of the
vessel between a mark on the lower and a mark on the upper tube, and
amounted to 56°5 cubic inches. The second series, which consists of
carbonic acid gas, with air for comparison, is the transpiration of these
gases into a nine-pint jar or receiver upon the plate of an air-pump,
beginning the experiment with an exhaustion of 28.5 inches by the
attached barometer, and terminating at 23-5 inches. It was necessary
to measure the volume of carbonic acid in this manner after transpira-
ON THE MOTION OF GASES. 165
tion and not before it, to avoid the error which the solution of a portion
of this gas in water might introduce. The gases all passed through a
drying tube containing asbestos moistened with oil of vitriol, before
reaching the capillary.
TABLE I.—Transpiration by Capillary H. 237°875 inches in length, and
# inch in diameter.

Gas transpired. ; .# Mean. Air=1. oxygen-1. Observations.
Oxygen .................. 1146 | 1.14% |1146.5] ... 1:0000 | Bar. 29,696. Temp. 67°Fahr.
Air ........................ 1032 | 1032 1032" | 1.0000 || 0-9001
Hydrogen ............... 509 510 || 509'5 | ... 0-4443
Protocarb. hyd. (CH2) 63] 630 || 630-5 tº sº º 0-5499
Carbonic oxide......... 994 995 994-5 0-8674
T . . . . . . . . . . . . . . . . . . . . . . . . 798 799 || 798.5 - tº - • * * Bar. 29.602. Temp. 69° Fahr.
Carbonic acid ......... 668 668 | 668" | 0-8366 0-7529
I produce these results principally to show how small the variation
is in carefully made experiments, not amounting to more than 1 Second
in times which exceed 1000 seconds for two of the gases, as well as to
afford standard numbers to compare with those obtained for reduced
lengths of the same tube.
TABLE II-Transpiration times of equal volumes by Capillary H of
different lengths.

Length of capillary. oxygen. Air Cººlººlºº." Hydrogen
237-875 inches=1:0000 I 0-9001 || 0-8674 0-7529 0.5499 0-4443
0-8539 I 0-8983 e tº º - - - © - © 0°4422
0-6521 I 0-9009 || 0-8681 0-7585 0°55'06 0.4434
0-4513 l 0-9013 || 0-8743 || 0-7900 0-5636 0.4424
0°3195 I 0.9131 || 0-8793 || 0:850l 0-5826 0.4041
0-2149 I 0.9149 || 0-8799 || 0-8849 0-6049 0.3842
- 0-1234 l 0-9131 || 0-8790 || 0-8802 0-5860 0-3924
18:125 inches=0.0762 l 0-9138 || 0 8879 || 1:03.95 0-5948 0.3879
The absolute times of transpiration varied with air from 1032
seconds for the greatest to 116 seconds for the shortest length of the
capillary.
It will be remarked that the transpiration times of air and hydrogen
are preserved with the greatest uniformity, while the length of the
capillary is reduced from 1 to 0-4513, air varying only from 09001 to
0-9013, and hydrogen from 0.4443 to 0.4424. The variation of the rate
166 ON TEIE MOTION OF GASES.
of carbonic oxide is more sensible although still Small, namely, from
0-8674 to 0-8743. Protocarburetted hydrogen, however, rises for the
same change in the tube from 0-5499 to 0-5636, and carbonic acid still
more considerably, namely, from 0-7529 to 0-7900. The resistance of
the tube is insufficient for shorter lengths, the influence of effusion
becoming manifest, and most conspicuously so in carbonic acid. The
times of effusion of equal volumes, to which the gases are now con-
verging, although with unequal degrees of rapidity, are, for oxygen 1,
air 0.9507, carbonic oxide 0.9356, carbonic acid 1:1760, protocarburetted
hydrogen 07071, and hydrogen 0.2502.
An important conclusion to be drawn from these results is, that the
transpiration of all gases does not become normal for the same length of
tube or amount of resistance, but that a greater length of the tube and
consequent resistance is more necessary for some than for others.
Carbonic acid in particular, of which the effusion rate differs so widely
from its transpiration rate, appears to require a considerably greater
resistance than the other gases transpired to bring it to a uniform rate.
Indeed the results respecting that gas suggest the inquiry whether the
resistance is sufficient with the present capillary in its greatest length,
and whether the true transpiration time for this gas may not be less
than 0.75, the number provisionally adopted. Let us therefore observe
the effect of greatly increased resistances upon the transpiration of this
and other gases.
A thermometer tube of the finest flat bore was selected, K, of which
52% inches contained only 13.5 grains of mercury. The bore was not
quite uniform, 0:6 grain of mercury occupying 2 inches of the cavity
at each end of the tube, and 2-3 inches near the middle. Under the
pressure of 1 atmosphere, 1 cubic inch of air passed into a vacuum by
this capillary in 1513 seconds, or the discharge of air was not more
than 0-4 cubic inch per minute. The resistance was therefore ten times
greater than in the capillary H when of its greatest length of 22 feet.
Air and other gases were transpired through K into a two-pint jar
placed upon the plate of an air-pump, or into a space amounting to
71-08 cubic inches, till the attached barometer of the air-pump fell from
28'5 to 25-5 inches.
(1.) The time required by air in three experiments was 1075, 1073,
and 1074 seconds; and for oxygen in two experiments 1192 and 1.192
seconds; the temperature being 56°Fahr., and the height of the baro-
meter 30-162 inches. This gives 09010 as the transpiration time of
air, referred as usual to the time of oxygen as 1, the result accidentally
coinciding with the theoretical number for air.
(2) The time required by hydrogen in two experiments was 552
and 550 seconds, the time of air being 1081, 1079, 1082, and 1080
ON THE MOTION OF GASES. 167
seconds; thermometer 57 degrees, and barometer 29,918 inches.
Dividing the mean number for hydrogen 551 by the mean number for
air 1080.5, we obtain 0.5099 as the time of hydrogen, that of air being 1.
To reduce the time of hydrogen to that of oxygen as 1, we have to
multiply 0.5099 by 09010, which gives 0.4593 as the transpiration time
of hydrogen. This is a considerable departure from the theoretical
number 0.4375; but it was found to be due to a small addition of air
to the gas, which it obtained from the water over which it stood in the
pneumatic trough, and necessarily much longer than usual, from the
slow manner in which it was removed by transpiration through the
present capillary. In a series of experiments made with hydrogen con-
taining 1, 2, 4, 25, 50, and 75 parts of oxygen in 100 of the mixture,
this capillary was found to give the transpiration times 0°4901, 0:5055,
0.5335, 0.7750, 0.9061, and 0-9718. Half a per cent of air would
therefore more than account for the increased time observed with the
first hydrogen. In experiments, also, made with other equally fine
capillaries, when the hydrogen was preserved in a state of great purity
by transmitting it by a bent tube from the generating retort to the
upper part of the pneumatic receiver, and in large volumes, so that the
gas never passed through water, and was retained only a very short
time in contact with the surface of that liquid, the transpiration time
then fell, as will afterwards appear, quite as low as the theoretical
number.
(3) The transpiration of carbonic oxide took place in 1051 and 1051
seconds, against 1090 and 1089 seconds for air; thermometer 58° Fahr.,
barometer 29.866. This gives for carbonic oxide the transpiration
times 0-9646, air = 1; and 0-8690, oxygen = 1. The transpiration time
of the same gas by the former capillary H was 0-8674; while the
number corresponding with the theoretical density of the gas is 0.8750.
The capillary K was now shortened to 39-375 inches, and the
following experiments were made with it.
(1) Carbonic acid was transpired in 661 and 659 seconds, thermo-
meter 58°, and barometer 30.024. The time of oxygen was 900 and
903 seconds. The means give 0.7321 as the transpiration time of car-
bonic acid, a number considerably less than 0.75, and confirming my
suspicion that the latter number was too high, and that the resistance
of H was not sufficiently great to eliminate the whole influence of effu-
sion in this gas. It may be remarked, in passing, that the new number
for carbonic acid approaches 0.7272, which is equal to #3, or is the
reciprocal of the density of carbonic acid gas. Such a relation suggests
the idea that carbonic acid possesses the time of oxygen (of which
gas, carbonic acid contains its own volume), diminished by the carbon
present, which gives an additional momentum corresponding to its
168 ON THE MOTION OF GASES.
weight to the compound gas, and acts thus entirely in increasing its
velocity. -
In another series of experiments the numbers were 659 and 659 for
carbonic acid, against 900 and 902 for oxygen; thermometer 58, and
barometer 30:052. This gives 0.7303 as the transpiration time of car-
bonic acid.
(2) Without entering into a detail of the experiments, I may add,
that the capillary K of its present length gave 0.9034 as the transpira-
tion time of air, and 0.4500 as the transpiration time of hydrogen; the
time of the latter gas being undoubtedly elevated by a minute impurity,
as in the former case.
The length of capillary K was now reduced to 26:25 inches, and in
order to increase the transpiration time, which fell to about 567 seconds
for air, the range of the attached barometer observed was increased from
3 to 5 inches, the observations being made at 28:5 and 235 inches of
the barometer attached to the air-pump.
(1) The times for air were 946 and 945 seconds; the time for
Oxygen 1053 seconds, giving 0-8979 as the transpiration time of air;
thermometer 57°, and barometer 30.096.
(2.) The times for carbonic acid were 773 and 773 seconds, the times
for air observed immediately before being 942 and 943 seconds; ther-
mometer 57°, and barometer 29.982. This gives 0.8202 as the transpi-
ration time for carbonic acid referred to air, and 0.7361 referred to
Oxygen.
The length of the capillary K being now reduced to 13125 inches,
air was found to enter so as to depress the attached barometer from
28°5 to 25-5 inches in 284 seconds, and from 28-5 to 23-5 inches in
472 seconds; thermometer 56°, and barometer 29:758 inches. To
obtain longer times, the two-pint jar, used as the aspirator-jar, was
replaced by the six-pint jar, which last gives an available vacuous
Space estimated at 201:78 cubic inches. The fall of the attached baro–
meter continued to be observed from 28°5 to 23-5 inches.
(1) The times of air were 1348 and 1353 seconds; the times of
oxygen 1498 and 1499 seconds; thermometer 58°, and barometer 29.628.
The means give 0-9013 as the transpiration time of air.
Observing only through the smaller range of the attached baro-
meter, namely, from 28°5 to 25-5 inches, the follówing results were
obtained —
(1) The time of air was 809, 809 seconds.
(2) The time of carbonic oxide was 780 and 779 seconds.
(3) The time of hydrogen was 399, 400, and 398 seconds.
(4.) The time of carbonic acid was 658 and 657 seconds.
ON THE MOTION OF GASEs. 169
The experiments were made successively in the order in which they
are stated, with the thermometer at 59°, and the barometer from 29:450
to 29°422. The results may be given as follows:—
TABLE III.-Transpiration Times.

Air=1. Oxygen-1.
Carbonic oxide ..................... 0.9635 0-8671
Hydrogen ........................... 0°4932 0°44.38
Carbonic acid........................ 0-8127 0°7314
The transpiration times of the second column are obtained by multi-
plying the times of the first column by 0-9, a number which represents
the time of air with sufficient accuracy, the time of oxygen being 1. It
will be observed that the number for carbonic oxide remains wonder-
fully constant for all lengths of K ; that the number for hydrogen,0.4438,
now approaches more nearly to 0-4375, probably as nearly as a slight
impurity of the gas, resulting from its short contact with water, would
admit ; and that the number for carbonic acid, 0.7314, is still low, and
does not differ much from 0.7272.
In a second series of experiments, which need not be detailed, num-
bers corresponding closely with the preceding were obtained; namely,
09003 for air, 0.8656 for carbonic oxide, and 0.7336 for carbonic acid.
The capillary K was reduced to 875 inches, or to one-sixth of its
original length, the six-pint jar being retained as the aspirator-jar, and
the fall of the attached barometer observed from 28-5 to 23-5 inches.
(1) The times of air were 933 and 933 seconds; of oxygen 1036,
1036, and 1037 seconds; of carbonic oxide 897, 897 seconds; thermo-
meter from 59° to 60°, and barometer from 29-1 to 29-134 inches.
These experiments give the following transpiration times:–
Oxygen, de & e l
Air, . * t & 0-9003
Carbonic oxide, ſº $º 0-8656
(2) The times of air were 920 and 920 seconds; of hydrogen 450
and 451 seconds; of carbonic acid 763, 762 seconds; thermometer 58°,
barometer 29.346. The resulting transpiration times for hydrogen and
carbonic acid are 0.4886 and 0.8288, the time of air being 1; or, multi-
plying by 0.9 so as to have oxygen 1–
- Hydrogen, . * e 0°4398
Carbonic acid, e & 0.7459
(3) Experiments on the same gases were repeated at a temperature
170 ON THE MOTION OF GASES.
lower by 10 Fahr. The times of air were 902 and 902 seconds; of
hydrogen 442 and 444 seconds, and of carbonic acid 742 and 742
seconds; thermometer 48° Fahr., barometer 29:334. These numbers
give the transpiration times 1, 0:4911, and 0-8226 for air, hydrogen, and
carbonic acid respectively; or, with oxygen as 1—
Hydrogen, . & e 0°4419
Carbonic acid, e º 0.7403
Another series of experiments gave for carbonic acid the transpira-
tion time 0-7432 at 43", and with barometer 29:620. It will be observed
that the time for carbonic acid now begins to rise, as if the capillary
were too short, and the resistance insufficient to neutralize entirely the
effect of effusion in that gas. The times however of air, hydrogen, and
carbonic oxide continue normal.
Experiments were made with the same capillary reduced to 6:4375
inches, or to one-eighth of its original length, which are still pretty
normal. The times for air were 670 and 670 seconds; for oxygen 746
and 745 seconds; for hydrogen 322 and 322 seconds; for carbonic acid
563 and 562 seconds, with thermometer from 61° to 62°, and barometer
from 29.832 to 29-826. These give the transpiration ratios,
Oxygen, e º * l
Air, e o º ſº 0.8987
Hydrogen, . t º 0°4319
Carbonic acid, º te 0-7545
For shorter lengths of the capillary K, the deviation from the tran-
spiration rates becomes very notable. I shall supply the results of such
experiments, as they illustrate the progress of the deviation from the
transpiration rates in a short and narrow capillary, while the results of
Table II., page 165, show the progress of this deviation in a long and
comparatively wide capillary.
TABLE IV—Transpiration times of equal volumes, by Capillary K of
reduced lengths.

Length of capillary. Oxygen. Air. Hydrogen. Carbonic acid.
4-3125 inches I 0-8985 0.4250 0.7770
3.25 l O'9035 0-4176 0-8059
2-1875 l 0-9121 0-3969 0-8446
1° 125 l 0.9199 || 0.3876. 0-9379
The absolute times for air, with the tubes of these four different
lengths, were 473, 370, 270, and 178 seconds; the temperature varying
from 61° to 63, and the barometer from 29'562 to 29-782 inches. These
ON THE MOTION OF GASES. 171
times, it will be observed, do not become shorter, exactly as the length
of the tube is diminished, but less rapidly in a very sensible degree.
This is owing to the interference of effusion.
When K was 4.3125 inches in length it allowed 1 cubic inch of air
to pass into a vacuum, under the pressure of 1 atmosphere, in 14 seconds;
or it discharged 43 cubic inches of air per minute. The discharge by
the capillary H of its greatest length, 237.875 inches, was 384 cubic
inches per minute. These two tubes therefore offer a nearly equal
resistance to the passage of air under pressure. On comparing the first
lines of Tables II. and IV., however, it will be perceived that the tran-
spiration rates of hydrogen and carbonic acid are sensibly more normal
for the long than for the short tube, although the difference is not great.
Still it appears that contracting the diameter of a tube does not produce
an equally available resistance as increasing its length. In other respects
the progress of the deviation from the normal transpiration rates of the
same gas, and of different gases compared together, in proportion as the
resistance diminishes, appears to follow the same law in the short as in
the long tube.
While discussing the properties of capillaries of different dimensions,
I may allude to results obtained by another capillary M, of the same
extreme length, 52-5 inches, and of nearly the same resistance as K, but
of which the bore was cylindrical and not flat like that of K. The bore
of M was not highly uniform, 0.75 grain of mercury occupying a length
of the cavity which varied from 3-3 inches at one end to 2-3 inches at
the other end of the tube. It was employed with the two-pint aspirator-
jar, and the fall of the attached barometer was observed through the
usual range from 28-5 to 23-5 inches.
(1) This capillary gave the transpiration time of air 0-8997, a highly
normal result.
(2.) The times for air in two experiments being 1133 and 1132
Seconds, the times of carbonic acid were 913 and 911 seconds; thermo-
meter 68°, and barometer 29.672.
Transpiration time of carbonic acid, {º § O'7247
In a second series of experiments made upon the same gases, the
times of air being 1104 and 1103 seconds, the times of carbonic acid
were 892 and 892 seconds; and of hydrogen 534 and 534 seconds;
thermometer 58°5, barometer 30-068. These observations give the
transpiration time 0,7275 for carbonic acid and 0.4355 for hydrogen.
(3) The times of air being 1109 and 1109 seconds, the times of
carbonic oxide were 1070 and 1070 seconds; thermometer 67°5, baro-
meter 29°808.
Transpiration time of carbonic oxide, § & 0-8683
172 ON THE MOTION OF GASES.
(4) The times of air being 1098 and 1099 seconds, the times of
nitrogen were 1064 and 1062 seconds; thermometer 64 to 65°, baro-
meter 29'904.
Transpiration time of nitrogen, e e º O'8708
(5) The times of air being 1084 and 1084 seconds, the times of hy-
drogen were 529 and 529 seconds; thermometer 69°, barometer 30'242
inches.
Transpiration time of hydrogen, . º * 0.4392
In the present experiments with hydrogen, the precautions formerly
referred to for excluding as much as possible the access of a sensible
trace of air from the water of the pneumatic trough were put in practice.
The times obtained for this and all the other gases, with the present
capillary, will be observed to be in the highest degree normal.
(6.) The times of air being 1095 and 1096 seconds, those of olefiant
gas were 641, 641, and 641 seconds; thermometer 69", barometer 30:102.
Transpiration time of olefiant gas, . G * 0°5265
The time formerly obtained for the same gas by the capillary H of
small resistance was 0.5186. This new capillary M was afterwards very
fully employed in determining the times of various other gases and
vapours, and in examining the influence of pressure and temperature.
It is therefore desirable to have the preceding results which this capil-
lary gives with the more familiar gases.
(7.) The times of air being 1120 and 1120 seconds, those of proto-
carburetted hydrogen (the gas of the acetates) were 684, 686, and 685
seconds; thermometer 61°5, barometer 29.844.
Transpiration time of protocarburetted hydrogen, . 0-5504
The time 0:5515 was formerly obtained for this gas by capillary E,
which was a long tube of small resistance, very like capillary H.
(8.) The times of air being 1110 and 1111 seconds, those of binoxide
of nitrogen (NO2) were 1070, 1070, and 1070 seconds; thermometer
60°-5, barometer 29.948 to 29-782 inches.
Transpiration time of binoxide of nitrogen, . 0-8672
This result is in accordance with the conclusion drawn from my
former experiments upon the same gas, made with capillary E, namely,
that the time of nitric oxide gas coincides with that of nitrogen and
carbonic oxide.
(9) Observations were made with the same capillary M a little
reduced in length, namely, to 50:5 inches, and with a smaller aspirator-
jar; the range observed of the attached barometer being still from 28.5
to 23-5 inches.
It now gave for the transpiration time of air 0-8984.
ON THE MOTION OF GASES. 173
The times for air being 460 and 459 seconds, those of carbonic acid
were 381 and 381 seconds, and those of protoxide of nitrogen (NO) 380
and 380 seconds; thermometer 56°, barometer 29.674.
Transpiration time of carbonic acid, º e 0-7448
Transpiration time of nitrous oxide, º º 0.7429
results which illustrate the identity in transpiration rate of these two
gases, which have also the same specific gravity, and appear to corre-
spond remarkably in several other physical properties.
The difference of resistance to the passage of a gas offered by the
various capillary tubes already used is certainly considerable; the
resistance for equal lengths of tube being in round numbers fifty times
greater in the new capillaries K and M, than in the old capillaries E
and H. But large as is this range, in which a remarkable uniformity
of transpiration rate of the gases has been observed, it may still be
much extended. The capillaries of extreme resistance to which I shall
now refer, have great advantages over the others already described, and
form the instruments which I would recommend for the further study of
the laws of transpiration.
A thermometer tube of the finest cylindrical bore being selected, a
portion of about 8 inches is taken, and being progressively heated and
softened at the lamp, is crushed up into a length of 1 inch or less,
which can be done without obliterating the cavity. The cylindrical
mass is then, while still soft, drawn out into a tube of ten or twelve
times its original length. A thin and extremely fine capillary tube is
thus obtained, which is much more regular in bore than might be
expected from the description of its preparation. It is convenient to
divide the rod, which is less in diameter than a fine straw, into lengths
of 4% inches, and to seal immediately the open extremities of each
piece. A transpiration capillary was formed of a bundle of thirty of
these little rods, which were placed together within a short glass tube,
as a case, of about 3% inches in length and half an inch in diameter; so
that the ends of the rods projected at both ends of the tube. The rods
were fixed within the tube by stucco, which was dried and afterwards,
while warm, soaked in melted bees'-wax. These arrangements being
entirely completed, and the bundle proved to be impervious to air, the
ends of the rods were now broken off, and the tubes thus opened. The
transpiration instrument P consisted of a bundle of thirty such capillary
tubes, each about 4 inches in length. Each end of the solid cylinder
was connected with a block-tin tube of the same diameter by means of
a thick vulcanized caoutchouc adopter. One of these tin tubes was con-
nected with the aspirator-jar, or left open to the air, and the other
connected with the receiver containing the gas to be transpired.
174 ON THE MOTION OF GASES.
The mode of conducting the experiment was further changed.
Instead of drawing the gas through the capillaries into an exhausted
receiver or vacuum, the gas was compressed in a stout metallic receiver
or condenser, provided with a mercurial pressure gauge, by which the
elasticity of the gas within could be observed." This gauge tube was a
barometer about 70 inches in length, with a vacuum above the mercury.
The gas was allowed to escape from the condenser through the capillaries
into the open atmosphere, or into a space containing air, of which the
tension was preserved uniform, and which formed an artificial constant
atmosphere, the time being noted which the mercury in the gauge tube
of the condenser took to fall through a fixed range of 2, 4, or 10 inches,
according to the degree of compression. The available capacity of the
condenser was about 72 cubic inches. -
The resistance of the fine capillary tube of the present bundle was
not less than 400 times greater than the resistance of the finest tubes
hitherto used, namely K and M, the comparison being made between
equal lengths of the different tubes.
Experiments with compound Capillary P.
(1) Dry oxygen was thrown by a syringe into the condenser till the
pressure indicated by the pressure gauge exceeded, by more than 20
inches, the pressure of the external atmosphere. The gas was then
allowed to escape from the condenser through the capillaries into the
atmosphere, and the times noted which the mercury of the pressure
gauge took to fall from 20 to 15, 10, 8, 6, 4, and 2 inches. •,
TABLE V.—Transpiration of Oxygen.

Pressure by gauge barometer. Experiment I. Experiment II, Experiment III.
Inches, Z/ &/ 4/
20 0 O 0
15 24] 240 24l
10 352 353 352
8 202 202 200
6 266 266 265
4 379 382 378
2 653 650 647
From 20 to 2 inches ...... 2093 2093 2083
(2) A similar series of experiments was made on the transpiration
of compressed air, of which the results are as follows:–
* Phil. Trans, 1846, Plate XXXIII, fig. 3 (see ante, p. 105).
'ON THE MOTION OF GASES. 175
TABLE VI—Transpiration of Air

Pressure by gauge barometer. Experiment I. Experiment II.
Inches. Aſ A
20 O
15 217 217
10 316 316
8 181 181
6 239 238
4 400 400
2 524 524
From 20 to 2 inches ...... 1877 1876
Both these last series and the series which follows on carbonic acid
were made with the thermometer at 66°, and barometer from 30:144 to
30-112 inches. Means were taken to preserve the temperature con-
stant during this and similar experiments, by immersing the condenser,
and also the capillary, in vessels of water of which the temperature was
watched by an assistant, and preserved uniform.
The average times of falling from a pressure of 20 to 10 inches are for
oxygen and air, 593 and 533 seconds respectively; numbers which are in
the proportion of 1 to 0-8988. The average times from 10 to 6 inches are
467 and 419-5 seconds; that is, as 1 to 0-8983 : from 6 to 2 inches, 1030
inches and 924 seconds; that is, as 1 to 0-8971. The average whole
time of escape, or during the fall from 20 to 2 inches, is 2088 seconds
for oxygen and 1876-5 seconds for air, numbers which are in the pro-
portion of 1 to 0.8987.
The transpiration time of air is therefore highly uniform under
different pressures, and approaches closely to its theoretical density or
time 0-9010.
(3) The parallel experiments on compressed carbonic acid gas escap-
ing into air are contained in the following Table:–
TABLE VII.-Transpiration of Carbonic Acid.

Pressure by gauge barometer. Experiment I. Experiment II.
º A/ Aſ
15 178 178
10 260 260
8 148 148
6 I95 195
4. 278 279
2 475 474
From 20 to 2 inches...... 1534 1534
176 ON THE MOTION OF GASES.
Comparing these times with the times of oxygen, we obtain the
following results:—
Transpiration times of Carbonic Acid.
From 20 to 10 inches pressure, º e 0.7384
From 10 to 6 inches pressure, tº - 0.7345
From 6 to 2 inches pressure, & º 0.7311
From 20 to 2 inches (average), . º 0'7346
The times for carbonic acid have not the nearly perfect uniformity
of those of air, for different pressures, but still their relation was close,
particularly in the lower part of the scale where times are long and can
be best observed. The time from 4 to 2 inches is 474-5 seconds with
carbonic acid and 650 seconds with oxygen, which give as the tran-
spiration time of carbonic acid 0.7300.
It will be observed how nearly the times for this gas approach
0.7272, the reciprocal of its density.
In a second series of experiments made upon carbonic acid, at the
same time as those which follow upon hydrogen, the transpiration times
which were obtained for the three portions of the scale already described
were 0.7344, 0-7388, and 0.7294, which approach the speculative number
for carbonic acid quite as closely as the experiments previously detailed.
(4) The hydrogen was prepared (as was always the case) from zinc
which contained no arsenic, and was passed through a wash bottle
containing oxide of lead dissolved in caustic soda, and dried by passing
over asbestos moistened with oil of vitriol. The thermometer was 67°
and the barometer 29'506 inches.
TABLE VIII-Transpiration of Air and Hydrogen.

Air. Hydrogen.
Pressure by gauge
barometer. -
Experiment I. Experiment II. Experiment I. Experiment II.
Inches. Aſ Z/ M/ Z/
20
15 221 22] 107 107
10 328 328 158 I59
8 188 185 92 91
6 251 251 I2] 121
4 422 423 176 178
2 579 580 310 308
From 20 to 2 inches... 1989 1988 964 964
ON THE MOTION OF GASES. 177
The results calculated from the means of these experiments are as
follows, the transpiration time of air being taken as 09:— -
Transpiration times of Hydrogen.
Air=1. Oxygen–l.
From 20 to 10 inches... 0°4845 0-4352
From 10 to 6 inches... 0°4866 0-4371
From 6 to 2 inches... 0-4859 0°4364
From 20 to 2 inches... 0°4867 0-4371
The experimental times for hydrogen vary only in the smallest
degree at different pressures, and almost coincide with the theoretical
time for this gas, 0-4375, which is one-half of the time of nitrogen and
7-16ths of that of oxygen. This result is so important that I shall
make no apology for presenting another series of experiments in which
hydrogen was compared directly with oxygen.
The temperature during the following experiments was 67”, and the
barometer 29°420 to 29°458 inches.
TABLE IX—Transpiration of Hydrogen and Oxygen.

i Hydrogen. Oxygen.
Pressure by gauge barometer.
Experiment I. Experiment II. Experiment I. Experiment II.
-------- Inches. | Al li il
20 0 0 O
15 107 107 242 246
l 10 158 158 263 260
8 9I 90 208 208
6 120 120 274 274
4 174 175 396 398
2 298 299 687 687
From 20 to 2 inches...... 948 949 2170 2173
By dividing the means of the hydrogen numbers by the means of
the oxygen numbers, as usual, we obtain the following results:—
Transpiration times of Hydrogen.
From 20 to 10 inches, 0°4380
From 10 to 6 inches, 0°4367
From 6 to 2 inches, 0°4363
From 20 to 2 inches, 0°4370
M
178 ON THE MOTION OF GASES.
These results are therefore in entire concordance with the pre-
ceding series, and with 0.4375 as the transpiration time of hydrogen
gaS.
(5) A series of experiments were made on the transpiration of
carbonic oxide in conjunction with those last related.
TABLE X.—Transpiration of Carbonic Oxide.

Prº{ flºº"eter Experiment I. Experiment II.
Inchès. li |
20 0
15 213 213
10 315 315
8 181 181
6 24l 241
4 346 346
From 20 to 4 inches...... 1296 1296
The experiments on this gas are only given from 20 to 4 inches, some
error of observation having occurred in taking the times at 2 inches.
Comparing them with the last experiments on oxygen, we obtain the
following results:—
Transpiration time of Carbonic Oxide.
Erom 20 to 10 inches, . G 0-8727
From 10 to 6 inches, . º 0-8755
From 6 to 4 inches, . º 0-8715
From 20 to 4 inches, . gº 0-8737
The transpiration time of carbonic oxide thus appears to be uniform
at different pressures, and to correspond very closely with its theoretical
density, 08750. The transpiration times of this gas and of nitrogen
no doubt correspond with each other as closely as their densities, and
are both double the time of hydrogen. - -
It thus appears that the results obtained by means of the sheaf of
capillaries of extreme resistance are the most uniform of all, and that
they afford a confirmation of the conclusions drawn from the results
of former capillaries of greatly less resistance, which it is difficult to
withstand. These conclusions are, that the times of passage through
capillary tubes, of equal volumes of different gases under the same
pressure, approximate to, and have their limit in, the following
numbers :—
ON THE MOTION OF GASES. - 179
Transpiration times.
Oxygen, e g & e 1.
Air, . & & • * 0-9010
Nitrogen and carbonic oxide, . 0-87.50
Hydrogen, . e e tº 0°4375
Carbonic acid, e e ſº 0.7272
The times of oxygen, nitrogen, carbonic oxide, and air, are directly
as their densities, or equal weights of these gases pass in equal times.
Hydrogen passes in half the time of nitrogen, or twice as rapidly for
equal volumes. The result for carbonic acid appears at first anomalous.
It is, that the transpiration time of this gas is inversely proportional to
its density, when compared with oxygen. It is to be remembered, how-
ever, that carbonic acid is a compound gas, containing an equal volume
of oxygen. The second constituent carbon which increases the weight
of the gas, appears to give additional velocity to the oxygen in the same
manner and to the same extent as increased density from pressure, or
from cold (as I believe I shall be able to show), increases the transpira-
tion velocity of pure oxygen itself. A result of this kind shows at once
the important chemical bearing of gaseous transpirability, and that it
emulates a place in science with the doctrines of gaseous densities and
combining volumes. *
The circumstance that the transpiration time of hydrogen is one-half
of that of nitrogen, indicates that the relations of transpirability are
even more simple in their expression than the relations of density
among gases. In support of the same assertion may be adduced the
additional fact, that binoxide of nitrogen, although differing in density,
appears to have the same transpiration time as nitrogen. Protoxide of
nitrogen and carbonic acid have one transpiration time, so have nitrogen
and carbonic oxide, as each pair has a common density.
II. TRANSPIRATION OF WARIOUS GASES AND WAPOURS.
1. Protocarburetted Hydrogen, CH3.
It is necessary to mention how this gas was prepared, as it is one,
like olefiant gas, of which we are never quite certain of the absolute
purity. Six hundred grains of dried acetate of soda, the same weight
of fused hydrate of potash, and nine hundred grains of unslaked quick-
lime, all in fine powder, were well mixed in a coated Florence flask used
as a retort, and the gas brought off by heat. The last portions of gas
were rejected. The hydrate of baryta never, in my hands, gave so pure
a gas, when substituted for the hydrate of potash, Free hydrogen, the
180 ON THE MOTION OF GASES.
usual impurity in this gas, I have formerly shown to have scarcely any
effect upon the rate of carburetted hydrogen, when present only to the
extent of a few per cent.
The old experiments with the long 20-feet capillaries E and H, of
small resistance, agreed remarkably in the transpiration time 0:5515 for
this gas. With capillary M., 52.5 inches in length, and transpiring into
a vacuum, I obtained 684, 686, 685 seconds as the time for this gas,
against 1120 and 1120 seconds for air; thermometer 62", and barometer
29.844 inches. This gives 0.5504 for carburetted hydrogen for a capil-
lary of great resistance. This gas, in a state of compression, Was tran-
spired by the same capillary into air as in the experiments to follow on
olefiant gas. The results, without details, were as follows: thermometer
64", barometer 30:050 to 30.074.
Transpiration of Protocarburetted Hydrogen (into air) by Capillary M,
52-5 inches in length.

Air = 1. Oxygen = 1.
From 20 to 10 inches ... 0-6304 0°5495
From 10 to 6 inches ... 0-6254 0.5490
From 6 to 4 inches ... 0-6269 0-5515
From 4 to 2 inches ... 0-6335 0.5525
From 2 to 1 inch...... 0-6349 0-5607
From 10 to 1 inch ...... 0-6321 0.5541
The transpiration of this gas appears highly uniform at different
pressures. Excluding the two observations at the extremes of the scale,
the mean result is— .
Transpiration time of protocarburetted hydrogen, 0:55 10
A repetition of the last experiments gave a slightly different series
of numbers, namely, 0-5583, 0.5497, 0.5541, 0:5523, 0:5549; showing
that the slight departure from uniformity among the results at different
pressures before observed is of an accidental nature, and does not follow
any fixed law. The mean of the three preferable new observations gives
0.5510, or precisely the same result as the former series.
This number for protocarburetted hydrogen closely approaches
0-5536, which is seven-elevenths, or # of 0-870, the time of nitrogen.
The numerical relation may be accidental, but the circumstances that 14,
which expresses the density and time of nitrogen, is double the time of
hydrogen 7, and that 22 expresses the density of carbonic acid, to which
carburetted hydrogen presents a certain chemical analogy in composi-
tion, appear to afford some physical basis for it. r
ON THE MOTION OF GASES. 181
The time of protocarburetted hydrogen may also be stated to be one-
fourth more than 0.44, the usually observed time of hydrogen itself.
2. Olefiant Gas.
The circumstance that olefiant gas has the same theoretical density
as nitrogen and carbonic oxide, and yet differs greatly from these gases
in transpirability, gives a peculiar interest to the transpiration time of
that gas. The olefiant gas used was always prepared in the following
manner:-Fifty-four volumes (water ounce measures) of oil of vitriol
were mixed with twenty-eight volumes of water and cooled, which gave
an acid of specific gravity 1-600. To this twenty-four volumes of
alcohol, generally of specific gravity 0.84, were added, and the mixture
allowed to stand over night. The gas was evolved by a heat of about
320 Fahr., and transmitted, for the purpose of purifying it, through five
wash-bottles, the first containing potash, the second water, the third oil
of vitriol, the fourth potash, and the fifth oil of vitriol. The process
yielded a good deal of ether, with a large product of gas.
My old experiments, with capillary H of great length but Small
resistance, gave 0-5186 as the transpiration time of this gas. I subse-
quently obtained the number 0.5241 with capillary K of 875 inches in
length, and also of small resistance. With capillary M of 52-5 inches
in length, and of considerable resistance, I also obtained the number
0-5265; the gas in all these cases passing into the nearly vacuous jar
under the pressure of the atmosphere. But the most complete series
of experiments was made upon this gas in a compressed state, in the
globular digester of 72 cubic inches in capacity, the gas escaping into
air. The capillary M was employed of 50:5 inches in length.
TABLE XI.--Transpiration of Olefiant Gas and Air (into air).
Air. Olefiant gas.
Height of gauge barometer
above 1 atmosphere. •
Experiment I. Experiment II. Experiment L | Experiment II.
* Af Af 6 fº
15 198 196 116 116
10 285 285 165 165
8 16] 161 * 93 93
6 213 213 120 12]
4 307 307 174 174
2 530 530 301 301
l 529 530 299 300

The fall from 20 to 10 inches requires 482 seconds in air and 281
182 ON THE MOTION OF GASES.
in olefiant gas, numbers which are as 1 to 0:5830. The ratios or tran-
spiration times appear in the following Table:– -
Transpiration times of Olefiant Gas.

Air=l. Oxygen–l.
From 20 to 10 inches ... 0°5830 0-5212
From 10 to 6 inches ... 0.5709 0.5103
From 6 to 4 inches ... 0.5667 0-5066
From 4 to 2 inches ... 0.5679 0-5085
From 2 to 1 inch...... 0.5656 0-508.1
In reducing these results from the scale of air to that of oxygen,
the following coefficients were used as the transpiration times of air.
They were obtained by experiment. From 20 to 10 inches air = 0.8941;
from 10 to 6 inches 0-8939; from 6 to 4 inches 0.8941; from 4 to 2
inches 0.8967; from 2 to 1 inch 0.8967; the air coefficients being all
sensibly lower than 0.9.
The transpiration time of this gas appears to vary at different parts
of the scale of pressure fully more than carbonic acid does. This may
arise, as with carbonic acid, from the extreme difference which exists
between the effusion and transpiration rate of the gas.
Hence an unusually great resistance, which is only met in the
lower part of the scale, is required to eliminate completely the influence
of effusion upon the transpiration rate. The smallest transpiration
time observed above for olefiant gas is 0.5066, which certainly does not
differ much from 0-5, or half the time of oxygen. But it would be
premature to adopt that relation definitively, as a number nearer to 0-51
would be the more legitimate expression of the whole results.
In a second series of experiments conducted precisely in the same
manner, with the thermometer at 67° and the barometer 30.020 to
30-034, the results were as follows:—
Transpiration time of Olefiant Gas (into air).

Air=1. Oxygen-1.
From 20 to 10 inches ... 0.5855 0°5234
From 8 to 6 inches ... 0.5745 0°5136
From 6 to 4 inches ... 0-5663 0-5062
From 4 to 2 inches ... 0.5642 0-5043
From 2 to 1 inch...... 0.5647 0°5048
From 20 to 1 inch...... 0.5669 0°5068
ON THE MOTION OF GASES. 183
The same remarks apply to the last as to the immediately preceding
series of experiments; the two series agreeing together most closely.
The mean of the three times observed in the range of pressure from 6
inches to 1 inch is 0.5051 ; and the least transpiration time observed
for olefiant gas (from 4 to 2 inches pressure) is 0:5043.
To contrast the two different methods of transpiration, that of con-
densed gas escaping into air, and of gas under the usual pressure of the
atmosphere only, or under a less pressure, passing into a vacuum, a third
series of experiments was made upon olefiant gas. The same globular
condenser being full of olefiant gas, of the tension of the atmosphere at
the time, which was 30'034 inches, the gas was allowed to escape
through the capillary M into the receiver of an air-pump kept vacuous
by constant exhaustion. It was thus transpired into a vacuum, but
with constantly diminishing force, for the force with which the gas was
sent out would diminish of course in proportion as the globular receiver
was emptied. The barometric gauge tube of this receiver, being closed
at top and vacuous, gave the necessary means of observing the pro-
gress of the escape of the gas as it was transpired into the vacuum.
In the following table of observations, the first column of the height of
the gauge barometer is its absolute height, and expresses the whole
tension or elasticity of the gas. Thermometer 67°.
TABLE XII-Transpiration of Olefiant Gas.

Olefiant gas. Air.
Height of gauge barometer.
Experiment I. Experiment II. Experiment I. Experiment II.
| |
Inches. AA f/ Aſ ſ/
30 ()
25 191 191 327 327
20 276 276 480 480
18 - 152 i52 267 267
16 187 | 187 316 315
14 242 242 432 430
12 3.18 319 558 55S
10 446 446 773 771
From 20 to 10 1347 1345 2346 2341
The results are sensibly different in one part of the scale from those
obtained by the other method of transpiration, as will be seen by com-
paring the following statement with the former results.
| 84 ON THE MOTION OF GASES.
Transpiration of Olefiant Gas (into a vacuum).

Air = 1. Oxygen = 1.
From 30 to 20 inches ... 0.5791 0.5212
From 20 to 16 inches ... 0'5476 0°49.28
From 16 to 14 inches ... 0°5615 0°5054
From 14 to 12 inches ... 0.5717 0-5.145
From 12 to 10 inches ... 0.5777 0.5199
From 30 to 10 inches ... 0.5743 0.5169
The time seems to increase as we descend in the scale, or with the
resistance, with the exception of the first observation, which probably
is made to deviate from the general progression by some accidental
cause. It would probably be more correct to take the first and second
times together, or the whole fall from 30 to 16 inches, which gives—

Air = 1. Oxygen = 1.
i
Transpiration time of olefiant gas ...... 0.5659 0.5093
The times from 30 to 14 inches, 0:5093 and 0.5054, will thus closely
approach to the average time obtained by the other method. But under
14 inches of pressure, where the transpiration becomes extremely slow
as the resistance is greatly increased, the times rise to 0.5145 and
0.5199. In the present state of our knowledge respecting transpiration,
it is difficult to decide upon the comparative value of these results, and
to say which represents best the true transpiration time of olefiant gas.
An unexplained variation of 1% per cent. in the transpiration time of
this gas must at present be admitted, which is a much greater latitude
in the results than was observed with nitrogen, hydrogen, protocar-
buretted hydrogen, or even with carbonic acid.
3. Ammonia.
This gas is supposed to have certain chemical relations to olefiant
gas, although differing very widely from the latter in its physical pro-
perties. The theoretical density of ammonia is 85, that of oxygen
being 16; or 539-6 to oxygen 1000. It is therefore considerably lighter
than olefiant gas; it is also liquefied by pressure, and highly soluble in
water, which the latter is not.
ON THE MOTION OF GASES. 185 -
This gas was always dried by passing over fragments of fused hydrate
of potash. The mode of operating with gases like ammonia, which
cannot be retained over water, found most convenient was to maintain
a continued and copious evolution of the gas during the whole period
of the transpiration experiments, conveying the gas into an empty
bottle in the first instance, of which the cork was perforated by three
tubes. By one of these tubes the gas entered this bottle, by another
the portion of gas required for transpiration was conducted to the capil-
lary, and the third, which was bent downwards and its extremity
allowed to dip a line or two into a little cup of water, formed a waste-
pipe or relief tube, by which the excess of gas evolved escaped into the
atmosphere. The same method was equally applicable to hydrogen,
carbonic acid, chlorine, etc., and does away with the necessity of
collecting these gases over water, and so exposing them to contami-
nation. -
(1) This gas was transpired by capillary K, 8.5 inches in length,
into the six-pint aspirator-jar upon the plate of the air-pump, through
the usual range of 28.5 to 23-5 inches on the gauge barometer; thermo-
meter 54°, barometer 29.772 inches. In two experiments with air the
times were 982 and 981 seconds; in three experiments with ammonia
546, 546, and 546 seconds. This gives 0-5563 for the time of ammonia
referred to air, or multiplying this number by 0-9 to reduce it to the
scale of oxygen = 1, we have, L
Transpiration time of ammonia, & tº * 0-5007
The conclusion suggested by this result, that the transpiration time
of ammonia is one-half that of oxygen, is not supported so strongly by
capillary tubes of great resistance.
(2) Experiments were made with capillary M., 52-5 inches in length;
thermometer 61°, barometer 29.900 to 29.908 inches. The time of air
being 1110, 1111, and 1111 seconds, that of ammonia was 632, 632, and
632 seconds; as 1 to 0-5688. Referred to oxygen, the result becomes—
Transpiration time of ammonia, e c © 0-51 19
A second series of experiments with the same capillary, thermo-
meter 61°5 and barometer 29.800 to 29-810, gave a very similar result,
namely, 1121 and 1123 seconds for air, and 640 and 640 seconds for
ammonia; numbers which are as 1 to 0-5704, and give,
Transpiration time of ammonia, e º º 0°5134
(3.) A third series of experiments was made upon this gas under
pressure in the globular digester, and escaping into air by the sheaf of
thirty capillary tubes P. The thermometer was at 60°, and the baro-
meter from 29.888 to 29.918 inches during the experiments.
186 ON THE MOTION OF GASES.
TABLE XIII–Transpiration of Ammonia (into air).

Air. Ammonia.
Height of gauge barometer
above 1 atmosphere. -
- Experiment I. Experiment II. Experiment I. Experiment II.
Inches. l! lſ il Il
20 -
15 218 217 124 124
10 319 321 182 182
8 186 186 107 106
6 243 243 138 139
4 354 355 201 201
2 621 621 350 357
l 635 645 352 350
From 20 inches to 1...... 2576 2588 1454 1459
The observation at 1 inch, or even at 2 inches, does not admit of the
same precision as in the higher parts of the scale, owing to the slowness
with which the mercury descends, leaving a doubtful period of 3 or 4
seconds which the mercury is in passing the mark. The experiments
at different parts of the scale, it will be seen, concur in giving nearly
the same result, except for the last inch, where this uncertainty appears
to have occasioned a sensible error.
Transpiration times of Ammonia at different pressures.

Air = 1. Oxygen = I.
From 20 to 10 inches...| 0:5698 0-5112
From 10 to 6 inches ... 0.5711 0.5128
From 6 to 2 inches ... 0.5684 0°5104
From 2 to 1 inch...... 0°5484 0.4936
The common multiplier by which the numbers of the oxygen scale
have been derived from the air scale is 0-898. Excluding the last
result we have, on the oxygen scale,_
The mean transpiration time of ammonia, 0°5115
This time for ammonia corresponds very closely with the results
previously obtained by the long single capillary M, namely, 0-5119 and
0.5134. The coincidence in the rates of M with those of the compound
capillary, for a liquefiable gas like ammonia, is a circumstance of con-
siderable importance, as a large proportion of the experiments which I
have to detail on gases of this class were made with the first-named only
of these capillaries. The number for ammonia certainly approaches to
0.5076 and 0.5093, the mean transpiration times of olefiant gas, but
ON THE MOTION OF GASES. 187
cannot be said to coincide with them, and is of course somewhat more
distant from 0'5.
4. Cyanogen.
This gas was prepared from well-crystallized and perfectly dry
cyanide of mercury. To secure its purity the gas was besides passed
over red oxide of mercury and chloride of calcium. The gas was con-
veyed to the capillary in the same manner as ammonia. The capillary
employed was the long tube M, of 52.5 inches, the gas under the pres-
sure of the atmosphere being drawn into the two-pint aspirator-jar,
exhausted as usual upon the plate of an air-pump. Thermometer 60°,
barometer from 29-910 to 29°864 inches.
The experiments were made in the following order:-air 1113,
1114 seconds; cyanogen, 626, 628, 627, and 627 seconds; air, 1117,
1117 seconds. The slight increase of the air-time in the last-made
experiments is undoubtedly owing to the fall of the barometer. The
ratio of the cyanogen to the first air-time is 0-5631, and to the second
air-time 0:5613; or 0:5068 and 0-5052, with oxygen = 1. The mean
of the two results gives—
Transpiration time of cyanogen, . * ſº 0.5060
The transpiration time of cyanogen may therefore be confounded
with that of olefiant gas, 0-5076, transpired in the same manner,
although the densities of these two gases differ so widely as 14 to 26
(oxygen = 16).
5. Hydrocyanic Acid.
A considerable quantity of the absolute acid was prepared by dis-
tilling 15 ounces of crystallized ferrocyanide of potassium with 9 ounces
of oil of vitriol diluted by an equal weight of water. The liquid acid
was afterwards dried by digesting it over pounded chloride of calcium.
As hydrocyanic acid is liquid at the usual temperature, air or
hydrogen saturated with the vapour of the acid was transpired instead
of the pure substance itself. The air or hydrogen was made to stream
through the liquid acid contained in a wash-bottle to a depth of 2
inches, and surrounded with water to which a slight heat was applied,
So as to maintain the water and wash-bottle at the fixed temperature of
the experiment, and to compensate for the cold of evaporation. The
tension of the hydrocyanic acid vapour at 59°, the temperature of the
experiments, was found to be 18-8 inches. The composition of the
mixed vapour operated upon was—
Volumes.
Air or hydrogen, t * 10’8 Or 36°48
Hydrocyanic acid, * {* 18.8 Or 63’52
29'6 I 00-00
188 ON THE MOTION OF GASES.
The vapour was transpired under the pressure of the atmosphere by
the capillary M., 52-5 inches in length, into the two-pint aspirator-jar,
through the usual range (28.5 to 235 inches) of the attached barometer.
Thermometer 59°, barometer 29'518 to 29-644 inches. -
The transpiration time of air was 1138 and 1138 seconds in two
experiments. The time of air impregnated with hydrocyanic acid was
807, 809, 808, 808 seconds, in four experiments; which gives to the
latter the ratio of 0.7100. Multiplying by 0-9 we obtain—
Transpiration time of air Saturated with hydrocyanic acid vapour
at 59°, 0.6390.
It is obvious therefore that hydrocyanic acid vapour is greatly more
transpirable than air. The theoretical density of hydrocyanic acid
vapour is 13:5, the density of oxygen being 16.
Hydrogen gas equally impregnated with hydrocyanic acid vapour
was transpired in the times 579 and 579 seconds, which gives the ratio
to air of 0:5088. Multiplying by 0-9 we obtain— -
Transpiration time of hydrogen Saturated with hydrocyanic acid
vapour at 59°, 0.4579.
Judging from our former results on mixtures of hydrogen with
denser gases, in which it appeared that the rate of the mixture never
deviated far from that of the dense gas in a state of purity, unless the
proportion of hydrogen exceeded 50 per cent, it may be inferred that
the transpiration time of pure hydrocyanic acid vapour is between
0.4375, the time of hydrogen, and 0.4579, the observed time, but much
nearer to the latter than to the former. For the transpiration of gaseous
mixtures of more nearly equal density, it is known, on the contrary,
that the transpiration time does not deviate far from the mean time of
the constituents when transpired separately. Taking the transpiration
time of air as 0-9, and that of hydrocyanic acid vapour as 0:46, then
36-48 volumes of the first and 63.52 volumes of the second would give
a mean time of 0-6205. - -
The time observed of a mixture in these proportions was 0.6390.
Hydrocyanic acid is composed of equal volumes of cyanogen and
hydrogen united without condensation. The transpiration time of the
compound gas is intermediate between the times of its constituents.
6. Hydrosulphuric Acid.
This gas was evolved by the action of hydrochloric acid upon the
sulphide of antimony; it was washed with water, and afterwards dried
by passing over chloride of calcium.
(1) Hydrosulphuric acid was first transpired by a short length of
ON THE MOTION OF GASES. 189
capillary M, of 875 inches, into the six-pint aspirator-jar, through the
usual range of 28.5 to 23.5 inches of the attached barometer: thermo-
meter 62°, barometer 29-674 to 29-652 inches. The following observa-
tions were made in the order in which they are related:—times of air,
999 and 1001 seconds; of hydrosulphuric acid, 692, 692 seconds; of
hydrosulphuric acid gas Saturated with the vapour of bisulphide of
carbon, 682, 680 seconds; and lastly, of hydrosulphuric acid again, 685,
685 seconds. -
The ratio of the first hydrosulphuric acid to air is 0.691, and of the
second 0.685; the ratio of the hydrosulphuric acid saturated with the
vapour of bisulphide of carbon is 0.681, or differs little from that of
hydrosulphuric acid itself; showing that these two sulphur compounds
nearly coincide in transpirability. Multiplying these results by 0-9, we
have— -
Transpiration time of hydrosulphuric acid (1), . 0-62.19
Transpiration time of hydrosulphuric acid (2), . 0-6165
Mean transpiration time, º º g 0.6192
This gas proved less uniform in its rate in different experiments
than I have generally observed for other gases, at least with the present
capillary.
In a repetition of the preceding experiments, thermometer 60°,
barometer 29.860 to 29.858, the times observed were for air, 982,983,
and 981 seconds; for hydrosulphuric acid saturated with bisulphide of
carbon, 659, 659, 659 seconds; and for hydrosulphuric acid alone, 663,
664 seconds; which give the ratios to air of 0-6711 and 0-6746. And
multiplying by 0-9, we have—
Transpiration time of hydrosulphuric acid, . o 0-607]
(2) Hydrosulphuric acid gas was also transpired by means of the
long capillary M., 52.5 inches in length, into the two-pint aspirator-jar.
It was then supplied from a wash-bottle with a relief tube as in the
experiments upon cyanogen and ammonia, without being retained over
water. Thermometer 59°5 Fahr., barometer 29'550 to 29:292.
The times of air were 1134, 1134 seconds; of hydrosulphuric acid,
782, 780 seconds; of hydrosulphuric acid carried through a column of
bisulphide of carbon 2% inches in depth and kept at the fixed tempe-
rature of 59°5, 773, 771, 772 seconds. These give the ratios to air, of
0-6887 for hydrosulphuric acid, and 0-6808 for hydrosulphuric acid
Saturated with the vapour of bisulphide of carbon at 59°-5. Also, mul—
tiplying by 09,-
Transpiration time of hydrosulphuric acid, . - 0-6198
190 ON THE MOTION OF GASES.
This last result almost coincides with the first determinations with
the short capillary M, namely 0.6192. The mean of the two results
is,
Transpiration time of hydrosulphuric acid, . . . 0-6195
The mercury in the gauge tube of the air-pump was soiled by these
experiments, and the tube required to be cleaned after them.
7. Bisulphide of Carbon.
At the temperature of 63°, the tension of the vapour of bisulphide
of carbon was observed to be 10:462 inches. Experiments were made
with air, oxygen, hydrogen, and carbonic acid gases, all Saturated with
the vapour of bisulphide of carbon at 63%, and with barometer from
29.874 to 29.850 inches. The short capillary K, 8.75 inches in length,
was made use of, and the gas was transpired into the six-pint aspirator
jar. The gases were impregnated by the vapour in passing through a
large U-shaped tube filled with cotton-wick which was moistened by
the liquid bisulphide of carbon.
Air alone was transpired in 982 and 981 seconds; air Saturated with
bisulphide of carbon vapour in 837 and 838 seconds; oxygen Saturated
with bisulphide of carbon vapour in 895 and 896 seconds; hydrogen
Saturated with bisulphide of carbon vapour in 662 and 661 seconds;
carbonic acid saturated with bisulphide of carbon vapour in 763 and 762
Seconds. The ratios appear in the following Table :-
Transpiration times of different Gases saturated with CS, at 63".

Air=l. Oxygen-l.
Oxygen...................... 0-9124 0.8212
Air ........................... 0-8533 0-76.79
Carbonic acid............... 0-7769 0.6992
Hydrogen................... 0.6739 0-6065
It may be safely concluded that the transpiration time of bisulphide
of carbon is not less than 0-6065, but probably sensibly greater. It
must, according to former observations, approach very closely to, if it
does not actually coincide with, 0.6195, the transpiration time of hydro-
sulphuric acid gas. -
8. Sulphurous Acid.
This gas was evolved by the action of copper upon sulphuric acid,
was washed with water, and conveyed in a continuous manner to a bottle
ON THE MOTION OF GASES.. " 191
#
with a relief tube from which the capillary was supplied, as in the
experiments with ammonia and cyanogen. The gas was dried by passing
over pumice soaked in oil of vitriol before reaching the capillary.
(1) With short capillary K, 875 inches in length, the six-pint
aspirator-jar, and usual range from 2-85 to 23-5 inches: thermometer
53°, barometer 29.964 to 29.942 inches.
The time of air was 970, 970 seconds; of sulphurous acid, 714 and
711 seconds; ratio of latter to air, 0.7345. Multiplying by 0-9, we
obtain—
Transpiration time of Sulphurous acid, . gº 0'6610
(2) With the long capillary M., 52.5 inches in length, this gas was
transpired into the two-pint jar: thermometer 60°5, barometer 29.880
to 29.878 inches. - -
The time of air was 1120, 1120, and 1120 seconds; the time of Sul-
phurous acid 814, 811, and 812 seconds. Using the two last observa-
tions only for sulphurous acid, we obtain the transpiration time 07245
for that gas, air being 1; or multiplying by 0-9,-
Transpiration time of sulphurous acid, e º 0.6520
In a second series of experiments with the same capillary, thermo-
meter 58° and barometer from 29.880 to 29°886, the following observa–
tions were made. Time of air, 1105, 1111, 1105, and 1111 seconds;
time of sulphurous acid, 798, 797, and 798 seconds, and ratio to air
0.7199. This gives—
Transpiration time of sulphurous acid, . g 0-64.79
The mean of the two results by this capillary gives—
Transpiration time of Sulphurous acid, . ſº 0-6500
9. Sulphuric Acid.
Both air and oxygen gas saturated with the vapour of anhydrous
sulphuric acid were transpired under the pressure of the atmosphere
into an air-pump vacuum, by the short capillary K, 8.75 inches in
length. Certain new arrangements of the apparatus, however, were
required in operating upon so highly corrosive a vapour as that of Sul-
phuric acid. Two ounces of the solid sulphuric acid were melted by
heat in a U-tube stuffed with asbestos, and having while liquid impreg-
nated the asbestos, were allowed to cool and become solid again before
the air or other gas to be saturated with sulphuric acid vapour was
conducted through the U-tube. For the tin conducting-tubes of the
former arrangements, glass tubes were substituted, and the air-pump
was employed to exhaust a stout globular glass globe of six pints in
capacity and provided with three openings, which was employed as the
192 ON THE MOTION OF GASES.
aspirator cavity. Two of the openings of the globular receiver were in
the sides, and one at the bottom of the receiver; by one of the former
openings the globular receiver was connected with the transpiring
capillary and by the other with the air-pump; a tube containing car-
bonate of potash being interposed between the receiver and the air-pump,
to arrest the acid vapours and prevent them from reaching the air-pump,
when the latter was used for exhausting the globular receiver. The
third and lower opening communicated with a gauge barometer, by
which the tension of the gas or vapour within the globular receiver was
observed. The mercury in this barometer was found to adhere slightly
to the glass, and not to descend with an entirely level surface in the
transpiration experiments, owing to a slight chemical action of the acid
vapour upon the mercury. This circumstance prevents the times being
observed with the same precision as in other gases.
With the thermometer from 72° to 74°, and barometer from 30:076
to 30.028 inches, the times of descent of the gauge barometer from 28-5
to 23-5 inches were, with air, 865 and 863 seconds; with air saturated.
with sulphuric acid vapour at 73° Fahr., 960, 961, and 958 seconds.
The ratio of the last times to air is 1*1106; and multiplying by 0.9, we
obtain,_
Transpiration time of air saturated with vapour of SOs at 73°, 0.9993
The tension of the vapour of anhydrous sulphuric acid at 73” was
observed to be 11:50 inches. -
The experiments on sulphuric acid vapour were repeated: thermo-
meter 67°5, barometer 29.914 to 29.908 inches; the range of the gauge
barometer now observed, however, being only from 28-5 to 24-5 inches.
The time for air was 695 and 694 seconds; for oxygen saturated with
the vapour of sulphuric acid at 67°5, 786 and 782 seconds; for oxygen
alone at 68°, 774 seconds; and for air alone again 692 seconds. The
result to be deduced is,
Transpiration time of oxygen Saturated with vapour of SOs at 67°5, 1-0130
The sensible equality of the times of air observed at the beginning
and end of the experiments proves that the working of the apparatus
was not deranged by the Sulphuric acid vapour. It is evident that the
time of pure Sulphuric acid vapour itself cannot deviate far from that of
oxygen gas. Sulphuric acid appears to be one of the very few gases,
the transpirability of which, if not really coincident with, is slightly
inferior to, or slower than, that of oxygen.
10. Chlorime.
The transpiration time of chlorine has a peculiar interest as that of
ON THE MOTION OF GASES. 193
an elementary substance. The same arrangements were had recourse to
with this corrosive gas as with sulphuric acid. It was found necessary,
in addition, to preserve a small column of water above the mercury in
the gauge barometer, to defend the metal from the action of the chlorine,
or at least to prevent the surface of the metal from becoming foul and
adhesive. This gas immediately reached the capillary, like ammonia,
from a bottle with a relief tube, to permit the escape of the redundant
supply. It was dried by means of chloride of calcium.
(1) The transpiration was made by capillary K, 8.75 inches in length,
into the six-pint globular receiver as aspirator, from 28-5 to 23-5 inches
by the gauge barometer attached to the latter: thermometer 70° to 71°,
barometer 30-222 to 30°208 inches.
The times of air in two experiments were 865 and 866 seconds; the
times of chlorine 670 and 672 seconds; giving the ratio to air of 0.7753.
Multiplying the latter number by 0.9, we have—
Transpiration time of chlorine, & e g 0.6978
(2) In a second series of experiments with the same capillary, the
following observations were made; the thermometer being 72° to 74°,
and barometer 30'248 to 30°218 inches.
The times of air were 858, 860, and 859 seconds; the times of car-
bonic acid 711 and 712 seconds; the times of chlorine 670, 670, 670,
and 670 seconds; the time of air again 866 and 867 seconds. A slight
increase in the air-time is observed, after the chlorine experiments, but
I would refer this increase more to the rise of two degrees in tempera-
ture between the first and last observations, than to any derangement
in the apparatus. Taking the last observed air as the standard of com—
parison for the chlorine, and the first observed air for the carbonic acid,
we find—

Air = 1. Oxygen = 1.
Transpiration time of chlorine, ......... 0-7732 0.6959
Transpiration time of carbonic acid, ... 0-8282 0.7454
But the true transpiration time of chlorine gas is probably less than
0.6959, for the true time of carbonic acid is certainly less than 0.7454,
the time obtained above for the latter gas. The present capillary, it has
been already remarked, is one of too small resistance to bring out the
true transpiration time of a gas whose effusion rate differs very widely
from its transpiration rate. The present experiment indeed is not
inconsistent with the true transpiration time of chlorine, being 2 or 3
N
194 ON THE MOTION OF GASES.
per cent. lower than that observed, or falling as low as 0.66, that is,
two-thirds of the time of oxygen. -
(3) The transpiration of chlorine was also observed by means of the
long capillary M., 52-5 inches in length, with the same six-pint glass
globular receiver as aspirator-jar. The fall observed by the gauge
barometer was only 3 inches, or from 28.5 to 25-5 inches. Thermometer
58", barometer 29.742 inches. - -
The time of air was 1907 and 1911 seconds; of chlorine 1432 and
1395 seconds. The difference of 37 seconds in the two observed times
of chlorine, which is so considerable, arose from the action of chlorine
upon the mercury; for notwithstanding that the latter was covered with
water, its surface became so uneven that the observations could not be
made with any great nicety. The first observation of chlorine gives the
time of that gas 0.7501 referred to air, and 0.6751 referred to oxygen;
the second observation gives the time of chlorine 07307 referred to air,
and 0.6576 referred to oxygen. Calculating from 1413.5 seconds, the
mean of the two observed times for chlorine, we obtain— s

Air = 1. Oxygen = 1.
Transpiration time of chlorine, ......... 0-7404 0.6664
The transpiration time of chlorine appears therefore to be about two-
thirds of the time of oxygen; or, chlorine passes through a tube with
13 time the velocity of oxygen.
11. Bromine and Hydrochloric Acid.
The only observations which I possess upon the transpiration of
these two substances were made by means of the short capillary K, of
875 inches in length, the six-pint globular receiver being the aspirator,
and the fall being as usual from 285 to 23.5 inches of the gauge baro-
meter. For both the bromine and hydrochloric acid the bottle and
relief tube were employed also as before, to regulate the supply of
gas to the capillary. Chloride of calcium was employed to dry the
gases. - - *
The time of air was 846, 848 seconds; of hydrochloric acid, 693,.693
seconds; of air saturated with the vapour of bromine at 75°, 889, 889,
and 889 seconds; of hydrogen Saturated with the vapour of bromine,
760, 760 seconds: thermometer from 73° to 75°, barometer 30-230 to
30-178 inches. In an observation which was made at the same time
upon the tension of bromine vapour, it was found that liquid bromine
placed in an air-pump vacuum depressed the mercurial gauge 9:19
ON THE MOTION OF GASES. 195
inches at 75", which may therefore be taken as the tension of the vapour
of bromine in the present experiments. The results are as follows:–

Air = 1. Oxygen = 1.
| Transpiration time of hydrochloric acid gas..................... 0.818] 0.7363
Transpiration time of 9-2 vol. bromine and 21-0 vol. air ... 1-0496 || 0-9446
Transpiration time of 9-2 vol. bromine and 21-0 vol. hydrogen 0.8973 0-8076
|
It appears that the transpiration time of hydrochloric acid observed,
0.7363, is greater than that of chlorine, 0.66, while that of hydrocyanic
acid was found less, on the contrary, than that of cyanogen.
Bromine vapour increases the transpiration time of air, and is there-
fore less transpirable. This vapour, however, does not appear to be
greatly more transpirable than Sulphuric acid vapour or oxygen gas.
12. Ether (Owide of Ethyl, C.H.O).
The ether employed was carefully washed with water, to deprive it
of alcohol, and afterwards dried by agitation with pounded chloride of
calcium. Dry hydrogen and other gases were impregnated with the
vapour of this substance in the same manner as with bromine.
(1) The first experiments were made with the short capillary K,
875 inches in length; the gas being transpired as usual under the
pressure of the atmosphere into the exhausted six-pint aspirator jar,
through the range from 28.5 to 23-5 inches of the gauge barometer of
the air-pump : thermometer 56°, barometer 29.670 to 29-708 inches.
. The tension of the ether vapour at 56° being found 12.85 inches, the
mixture transpired may be represented as composed of 1285 volumes
ether vapour and 16.85 volumes gas; or of 43:26 ether vapour and 56-74
gas in 100 volumes.
The time of air was 988, 988 seconds; of hydrogen 474, 473 seconds;
of hydrogen gas saturated with ether vapour at 56°, 498, 500 seconds;
of oxygen gas Saturated with ether vapour at the same temperature,
696 and 695 seconds. The transpiration times deducible from these
observations are, -

Air = 1. Oxygen = 1. .
Transpiration time of hydrogen.................................... 0.4792 0.4312
Transpiration time of ether vapour and hydrogen............. 0-5051 0°4546
Transpiration time of ether vapour and oxygen................ 0-7040 0-6336
196 ON THE MOTION OF GASES.
©
It thus appears that the transpiration time of hydrogen, 0.4312, is
only increased to 0-4546 by 43.26 per cent of ether vapour. As the
influence of hydrogen upon the rate of transpiration of the dense gases
and vapours is scarcely sensible, this may be held as proving that the
time of ether vapour does not sensibly exceed the time of the hydrogen
mixture, 0.4546. But as the experiment has been made with a capil-
lary of small resistance, it is not impossible that the normal time of
ether vapour may be still sensibly less. -
(2) The capillary M., 52.5 inches in length, with the two-pint
aspirator, was now used, the other arrangements remaining as before :
thermometer 68°5 to 69°, barometer 30.242 to 30.264 inches.
The time of air was 1084, 1084 seconds; of air saturated with ether
at 68°5 (59-5 ether vapour to 40-5 air), 675, 676 and 673 seconds; of
hydrogen saturated with ether vapour at 68°5 (59-5 ether vapour to
40.5 hydrogen), 533, 529 and 531 seconds; of oxygen saturated with
ether vapour at 68°5 (59-5 ether vapour to 40-5 oxygen), 728, 725 and
727 seconds; of hydrogen alone, 529, 529 seconds. The tension of ether
vapour was observed at the time to be 17-95 inches at 69°. The results
deduced from these experiments are as follows:—
Air = 1. Oxygen = 1.
Transpiration time of ether vapour and air..................‘.... 0-6224 0-5601
Transpiration time of 59.5 ether vapour and 40.5 hydrogen | 0:4898 0-4408
Transpiration time of 59.5 ether vapour and 40-5 oxygen... 0-6771 0-6039
Transpiration time of hydrogen.................................... 0'4880 0.4392
In this capillary of great resistance, the time of hydrogen is there-
fore not sensibly affected by nearly one and a half times its volume of
ether vapour, from which it may be inferred that the transpiration time
of ether vapour itself does not diverge sensibly from that of hydrogen.
The near if not perfect coincidence in transpirability in these two
substances is very remarkable, considering their great dissimilarity in
physical characters, particularly in weight, the densities of hydrogen and
ether vapour being as 1 to 37.
Although hydrogen and ether may have the same transpirability,
still the influence which each of these gases exerts upon the transpira-
tion of other gases with which it is mixed, is widely different. It will
be seen by the experiments above on ether and air, or ether and oxygen,
that the transpiration time inclines most to the ether rate, while in
hydrogen mixtures the time also deviates from the mean of the mixed
gases, but greatly in the direction of the rate of the other gas, and not
towards the hydrogen rate. The density of a gas is no doubt an impor-
tant element in this influence.
ON THE MOTION OF GASES. 197
In an experiment with the short capillary K, the time of olefiant
gas was reduced from 0.5246 to 0-4816, by Saturation with ether vapour
at 60°-5.
The rates of hydrogen and ether appear to diverge from each other
in experiments made at a high temperature. The water in the copper
trough in which the long capillary M was always placed, with the view
of commanding a constant temperature, was heated to 203’ (95° Centig),
and preserved at that temperature during the continuance of the follow-
ing experiments. Thermometer in air 60°5, barometer 29.956 to 29.982
inches.
Time of air 1634 and 1637 seconds; of hydrogen, 798 and 797
seconds; of hydrogen Saturated with ether vapour at 60°5, 863, 863
seconds. As the gas transpired was measured at 60°5 instead of 203°,
the temperature at which it passed through the capillary, these times
fall to be diminished in the proportion of the volume of air at 203 and
at 60°-5 respectively. We thus obtain as the three mean times in which
equal volumes were transpired at 203°,-air 1282°4 seconds, hydrogen
625.9 seconds, and hydrogen Saturated with ether vapour at 60°5, 677.3
Seconds.

Air = 1. Oxygen = 1.
Transpiration time at 203°Fahr. of hydrogen.................. 0°4880 0.4392
Transpiration time at 203° of hydrogen saturated at 60°-5
with ether vapour................................................ 0.5281 0-4753
While air and hydrogen preserve, at 203°, their usual ratio of tran-
spirability, ether vapour appears therefore to become sensibly less
transpirable at the high temperature.
13. Methylic Ether (Ocide of Methyl, C.H.O).
This vapour was evolved in a continuous manner in proportion as
required for transpiration, with the arrangements necessary for gases
soluble in water. The vapour was passed over both hydrate of potash
and chloride of calcium. The experiments were made with the short
capillary K, 8.75 inches in length, like the first experiments with com-
mon ether. Thermometer 56°, barometer 29.650.
Time of air 993 and 991 seconds; of methylic ether, 532 and 532
seconds; of methylic ether Saturated with the vapour of common ether
at 56°, 508, 506, and 507 seconds. -
198 ON THE MOTION OF GASES.
Transpiration times.

Air = 1. Oxygen = 1.
Methylic ether.…......…............................... 0.5363 || 0:4826
Methylic ether saturated with ether vapour at 56°............ 0.5ll 1 0.4600
The time of methylic ether, 0.4826, is decidedly longer than that of
common ether, 0.4546, as the latter was formerly observed by the same
capillary; and consequently an addition of ether vapour shortens the
methylic ether time, as appears in the second experiment, where the
transpiration time of such a mixture falls to 0-4600. -
14. Hydrochloric Ether (Chloride of Ethyl, C, H,Cl).
The experiments were made with the same short capillary K, 87 5
inches in length, and with the other arrangements as for the two preced-
ing ethers. Thermometer 56°, barometer from 29-794 to 29°758 inches.
The time of air was 980 and 981 seconds; of hydrochloric ether,
548, 544, and 543 seconds.

Air = 1. Oxygen = 1.
It would be unsafe to draw any conclusion from a single experiment
upon this ether and that experiment made with a capillary of inferior
resistance, but it may be remarked that the time of this ether approaches
to half the time of oxygen, while the density of the vapour is little more
than double that of this gas; the theoretical density of hydrochloric
ether vapour being 32°25 to hydrogen l and oxygen 16.
15. Hydrochloric Methylic Ether (Chloride of Methyl, C, H,Cl).
This ether, which like the two last is entirely vaporous at the tem-
perature of the experiments, was prepared by distilling together half a
pound of wood-spirit, one and a half pounds of oil of vitriol, and one
pound of common salt. The gas was exposed to a large quantity of
dilute caustic soda in two wash-bottles, and dried afterwards by chloride
of calcium. The same capillary and arrangements were employed as
in the immediately preceding experiments. Thermometer 54°, baro-
meter 29.862 to 29°856 inches.
ON THE MOTION OF GASEs. 199
The time of air was 973, 973 seconds; of chloride of methyl, 592,
587, and 582 seconds; of chloride of methyl again, after changing the
solution of caustic soda in the wash-bottles, 592, and 592 seconds.
Calculating from the last observed time of chloride of methyl, we
have—

Air = 1. Oxygen = 1.
Transpiration time of chloride of methyl ...... 0-6084 0-5475
It thus appears that the chloride of methyl has a longer time, or is
more slowly transpired than the corresponding chloride of ethyl ; as the
oxide of methyl was also found to be less transpirable than the oxide of
ethyl, Indeed the difference between the two oxides and between the
two chlorides appears to be the same, or about 0.045 in both cases. This
is in accordance with the general observation, that transpiration is pro-
moted by increase of density. The theoretical density of chloride of
methyl is 25-25 to hydrogen 1 and oxygen 16. -
16. Water.
Although great care was always taken to dry air when transpired, as
well as other gases, in all experiments, still it does not appear that the
rate of air is much affected by the presence of aqueous vapour unless
the latter is present in considerable proportion.
The times observed by capillary K, 875 inches in length, into a
vacuum, were for air dried by chloride of calcium 1008 seconds, and for
air drawn afterwards directly from the atmosphere, of which the tem-
perature was 60°, and the dew-point 32", 1006 and 1006 seconds. So
Small a difference may be due to accidental causes.
With dry air at 60°, the times with the same capillary were, upon
another occasion, 1021 and 1021 seconds; and with air of 60° tempera-
ture, but containing aqueous vapour with the dew-point at 38°, 1018
and 1017 seconds. -
In other experiments, the presence of aqueous vapour appeared to
occasion a sensible retardation in the time of air. The transpiration
was made into a vacuum by the capillary M., 52-5 inches in length; the
temperature of the capillary being maintained at 58°5, and the baro-
meter varying from 29-798 to 29.832 inches. The air was charged with
vapour by passing through a tube filled with cotton wick, which had been
previously moistened with dilute sulphuric acid of different strengths.
The time of dry air was 1115, 1115 seconds; of air carried over the
fourth hydrate of sulphuric acid (HO. SOs 4-3HO), 1117, 1117 seconds;
200 ON THE MOTION OF GASEs.
of air passed over the eighth hydrate (HO. SO, +7HO), 1120 and 1121
seconds; of air passed over the eighteenth hydrate (HO. SOs + 17HO),
1122, 1122, and 1121 seconds. Here we observe in the dampest air a
slight but sensible increase of the air time, not exceeding 7 seconds.
But on repeating the experiment immediately afterwards with dry air,
the time was 1120 and 1119 seconds, or within two seconds of the im-
mediately preceding observations with moist air. Indeed the transpira-
tion of moist air appears to produce a slight but sensible retardation of
a persistent character, probably from the condensation of a film of mois-
ture on the inner surface of the capillary, which is not immediately
removed by the subsequent passage of dry air.
With the same capillary, thermometer 57° and barometer 30:136 to
30,078 inches, dry air was transpired in 1089, 1089 seconds; dry hydro-
gen in 532 and 532 seconds; air saturated with aqueous vapour at 57°5
in 1098, 1098 seconds; hydrogen Saturated with aqueous vapour at the
same temperature, in 548 and 548 seconds; and lastly, dry air, first in
1 106 seconds, and afterwards in 1084 and 1085 seconds. Here the
damp air is less transpirable, volume for volume, than dry air by 9
Seconds. Also, dry air immediately following the damp air does not
recover its usual transpirability in the first experiment.
These experiments upon damp and dry air seem to indicate that the
transpiration time of aqueous vapour does not differ greatly from that of
air itself. The influence of aqueous vapour upon the time of hydrogen,
however, is considerably less than that of air upon the same gas, and
therefore suggests a more rapid transpiration,
17. Alcohol.
Air was impregnated with the vapour of alcohol of specific gravity
0.835 at 60°, barometer 29.358. The tension of the vapour of alcohol
of specific gravity 0.813 at 60° is estimated at 1:23 inch. The capillary
K, 8.75 inches in length, was made use of, with an air-pump vacuum,
as in all these experiments. - -
The time of dry air was 1013 and 1014 seconds; of air containing
alcohol vapour, 1011 and 1012 seconds. The rate of air is scarcely
affected, and consequently the time of alcohol vapour must approximate
to that of air.
18. Naphtha and Coal-Gas.
In experiments made with air Saturated with the vapour of coal-tar
naphtha at 62°, the capillary K being employed, the times obtained for
air alone were 978 and 979 seconds; for air saturated with naphtha
vapour, 949 and 949 seconds. The transpiration time of air is diminished
ON THE MOTION OF GASES. 20 I
30 seconds, showing that the volatile hydrocarbons of naphtha are
highly transpirable, like ether vapour. The time of coal-gas, taken
from the service-pipes of a London company, and observed in the same
circumstances, was 621 and 622 Seconds; of the same coal-gas impreg-
nated with naphtha vapour, 621 and 621 seconds, or the naphtha vapour
produced no sensible change in the transpirability of the gas; showing
a near coincidence in their transpirabilities. The transpiration time of
the coal-gas, reduced to the oxygen scale, is 0.5716, or a little more than
protocarburetted hydrogen, 0:5510.
That a considerable quantity of naphtha vapour was taken up by the
coal-gas, notwithstanding that its transpiration was unaffected, appears
in certain experiments which were made with a particular object upon
the effusion of the same gases. The capillary was removed and replaced
by a plate of platinum foil, G of former paper, having an extremely
minute aperture, the other arrangements remaining the same. The
gases were all moistened with water. For the passage of equal volumes
into an air-pump vacuum (the six-pirit aspirator-jar, through the usual
range from 28-5 to 23-5 inches of the attached barometer), the times
were, at 61°, for air, 434 and 434 seconds; for hydrogen, 139 and 139
seconds; for coal-gas, 314 and 314 seconds; for coal-gas Saturated with
naphtha vapour at 61°, 331 and 331 seconds; for hydrogen and naphtha
vapour, 194 and 193 seconds; and for air with naphtha vapour, 503
and 503 seconds. It is to be remembered that the densities of the
gases effused are in the proportion of the squares of these times, and
may be deduced from the latter. The time of coal-gas is increased by
the addition of naphtha vapour, but to a much less extent, than hydro-
gen and air are, no doubt from the former being from the first partially
saturated with naphtha vapour.
A good deal of light could be obtained, I believe, upon the composi-
tion and value of coal-gas by a combination of effusion and transpira-
tion experiments. Great density, which would be indicated by slow
effusion, is always valuable, unless when occasioned by air, carbonic
oxide or carbonic acid, which gases exclusively make the transpiration
slow; so that slow effusion with rapid transpiration would mark the
coal-gas of Superior quality.
III, TRANSPIRATION OF AIR OF DIFFERENT DENSITIES OR ELASTICITIES.
A series of observations on air varying in density from 0-5 to 2
atmospheres, made with the long 20-feet capillary E in my former
paper, appeared to establish the conclusion that “for equal volumes of
air of different densities, the times of transpiration are inversely as the
202 ON THE MOTION OF GASES.
densities.” The law of Effusion, or flow of air into a vacuum by an
aperture in a plate, is entirely different; equal volumes of air of all
densities passing in equal times.
With the short capillary K, 875 inches in length, the result was.
now found to be materially different. Air in three different states of
rarefaction was drawn into a sustained vacuum from a globular receiver
of which the capacity was 56-5 cubic inches, standing over water. To
command the desired density of the air in the globular receiver, the
little system of the latter and the basin of water in which it stood was
retained within a large air-pump receiver, the atmosphere of which was
adjusted to the requisite pressure. Thermometer 62", external barometer
from 29'984 to 29.936 inches. -
Transpiration of equal volumes of Air.

Time in seconds.
Density or Elasticity.
Experiment I. Experiment II.
1 atmosphere........................ 2172 2173
0-75 atmosphere........................ 2948 2.946
0-5 atmosphere........................ 5292 5288
It will be observed that the time 5292 seconds for air of 0.5 density
is considerably more than double 2172 seconds, the time for air of 1
density.
With compressed air, varying in density from 1 to 2-5 atmospheres,
the deviation from the law was equally conspicuous; the times of tran-
spiration of equal volumes at 1, 1:25, 15, 175, 2, and 2-5 atmospheres,
being in the ratio of 1, 0-8625, 0-7553, 0-6834, and 0.5519, instead of
1, 0:8, 0.6666, 0.5714, 0'5, and 0.4. - -
On operating, however, with the long capillary M., 52-5 inches in
length, and of great resistance, results were again obtained in strict
accordance with the law. The air was drawn from a metallic digester
provided with a gauge barometer, in which it was preserved of a con-
stant elasticity; this digester itself being supplied from a second similar
digester, in which the air was in a state of still higher compression.
The air was transpired into the two-pint aspirator-jar (capacity about
72 cubic inches) upon the plate of the air-pump, for the usual range
of the gauge barometer from 28°5 to 23-5 inches. Thermometer 66°,
external barometer 30: 122 to 30.086 inches.
ON THE MOTION OF GASES. 203
Transpiration of equal volumes of Air.
Time in seconds. -
Density or elasticity. *...* |a.º.º.
Experiment I. Experiment II.
l atmosphere ...... 1095 1096 1095-5 1095-5
1.25 atmosphere ...... 707 707 883 - 1 884-8
l'5 atmosphere ...... 493 493 739-5 737-3
1-75 atmosphere ...... 359 359 628-25 632
2 atmospheres...... 277 276 553 553
2.25 atmospheres...... 218 217 489.4 491-5
2-5 atmospheres...... 176 176 440 442
The column of “Time in seconds,” contains the times of the fall of
the air-pump barometer from 28°5 to 23-5 inches actually observed, and
which are produced by the admission to the aspirator-jar of an equal
volume of air of constant density. These times must therefore be
multiplied by the density in atmospheres of the air transpired, to obtain
the reduced times of the following column. It will be observed that
these reduced times are in perfect harmony with the “Calculated
times” of the last column. Indeed nothing could illustrate more
strongly the great precision of which transpiration experiments are
susceptible, than these results.
The conclusion to be drawn from the present observations with the
capillary M, and the old observations with E, as compared with the
observations made with the short capillary K, is that to bring out the
normal effect of densities on transpiration, a greater resistance and length
of tube are necessary than are required for the observations of the
normal relations in the transpiration times of such gases as oxygen,
nitrogen, and hydrogen; for the short capillary K, which fails so much
in the law of densities, exhibits the other relations nearly with as much
accuracy as the long capillary M. The marked superiority also of the
20-feet tube E over the 8-inch tube K, although the power of resistance
of these two capillaries is nearly equal, suggests again the idea that
resistance produced by elongation of the capillary acts differently from
an equal resistance produced by contracting the diameter of the
capillary, and more advantageously in transpiration experiments,
IV. TRANSPIRATION OF AIR AND OTHER GASES AT DIFFERENT
TEMPERATURES.
The experiments which I have made upon the transpiration of air
and also of other gases at different temperatures are very numerous, but
204 ON THE MOTION OF GASES.
not altogether satisfactory. Looking upon the experiments as only
preliminary, I shall confine myself at present to a statement of results
without detail, and endeavour to return to the subject at Some future
opportunity.
The transpiration of equal volumes becomes slower as the tempera-
ture rises. The experiments which follow upon air, carbonic acid, and
hydrogen, were made upon different days with slightly different baro-
metric pressures, so that the absolute times of one gas cannot be com—
pared with another; but this is unnecessary for our present purpose.
The capillary employed was M., 52-5 inches in length, and of great
resistance.
TABLE XIV.-Transpiration of equal volumes at different temperatures.

Time in seconds.
Temperature.
Air. Carbonic acid. Hydrogen,
32 Fahr. 1054-1 857-9 545°4
59 1092-8 897.4 557-8
86 1133-4 931°5 577.7
I 13 1175-7 969°4 598.8
140 1211 993'9 615-9
The difference of time of transpiration at the two extreme tempera-
tures, 32° and 140°, is 157-9 seconds for air, 136 seconds for carbonic
acid, and 70.5 seconds for hydrogen. The differences, calculated in the
proportion of the transpiration times of the same gases at the tempera-
tures usually observed (56° to 74°), namely air 09, carbonic acid 0.73,
and hydrogen 0.44, are for carbonic acid 128:1 seconds instead of 136,
and for hydrogen 732 seconds instead of 70°5. It would be unsafe to
conclude from these small deviations that the transpiration of the three
gases in question is unequally affected by heat in the range of tempera-
ture from 32” to 140”; for at temperatures distant from the temperature
of the atmosphere, the unavoidable errors of observation increase in
magnitude. The increment upon the time of air was 1562 seconds,
and upon hydrogen 62.8 seconds, at 140°, in a repetition of the same
experiments.
My most unexceptionable experiments all concur in showing that no
sensible change takes place in the transpiration ratios of hydrogen,
nitrogen, and carbonic oxide, at temperatures so high as 347° Fahr.
Thus the observed transpiration times of a mixture of equal volumes of
hydrogen and carbonic oxide at 60° and 347", were 0.8870 and 0.8853;
ON THE MOTION OF GASES. 205
the transpiration times of air observed at the same temperatures being
taken as unity. The transpiration times of a mixture of equal volumes
of hydrogen and nitrogen, referred to the times of air in the same
manner, were at 65°, 0.8939; at 347°, 0.8924; again, at 64°5, 0.8930;
and at 347°, 0.8872. The transpiration ratios are thus as nearly as
possible constant at these widely distant temperatures.
The transpiration times of air and hydrogen alone, at 203", were
found on two different occasions as 1 to 0°4841, and 1 to 0°4880.
Multiplying these hydrogen times by 0-9 to bring them to the scale of
oxygen, we have for the transpiration times of hydrogen at 203', 0.4357
and 0.4392, numbers which might have been obtained at atmospheric
temperatures.
Carbonic acid, however, appears to present a sensible deviation from
this uniformity of rate. In a series of observations made upon this gas
at 60°, 203", 299", and 347", its transpiration time referred to air at the
same temperatures was 0.8291, 0:8551, 0-8777, and 0.8907; and referred
to oxygen, 0.7448, 0-7541, 0.7741, and 0.7855. The transpiration time
of carbonic acid at 347 varied in other experiments from 0.7729 to
0.7905, the time of oxygen being 1. The protoxide of nitrogen gave
the number 0.7969 at the same high temperature.
The time of oxygen appears also to become relatively slower at high
temperatures, although much less considerably than carbonic acid. It
gave the numbers 0.8877 and 0-8860 for air at 347°, instead of 0-8984,
the number at low temperatures. As we may assume from its uniform
relation to hydrogen that the nitrogen remains constant, it follows that
the oxygen has become relatively slower in transpiration at the high
temperature.
If oxygen deviates from a supposed normal rate at high temperatures,
it cannot necessarily coincide with that rate at any lower temperature,
which is accidental, such as that of the atmosphere. But this influence
of heat upon the transpiration time of oxygen is, I believe, still sensible
at the low temperature in question.
By increasing the time of oxygen, this influence of heat may be the
cause of that slight deviation, so uniform in its amount, of the observed
times of air and nitrogen from their theoretical times, which was always
remarked. I am disposed then to look upon the slight inconstancy of
transpiration rate observed in some gases at different temperatures, as a
fact of the same class as the deviations from their theoretical specific
gravities observed in a greater or less degree in the same substances,
and to those other points in which all the gaseous bodies we have to
operate upon depart in some measure from the mechanical idea of a
perfect gas.
The normal effect of temperature upon transpiration, as observed in
206 ON THE MOTION OF GASES.
air, varies I find with the resistance of the capillary in a much higher
degree than any other property of transpiration; the retardation from
the same change of temperature being much greater in a capillary of
great than small resistance. The resistance of a capillary such as M,
which exhibits so exactly the law of densities, is insufficient to bring
out the full effect of temperature. With the fine tubes of the compound
capillary, on the other hand, the limit to the retarding influence of
heat seems to be reached. The retardation then appears to be simply
in proportion to the expansion; and rarefaction by heat, therefore, to
have the same effect upon transpiration as expansion from diminished
pressure.
In illustration of this inequality of action upon heated air, I may
refer to results obtained by two capillary tubes of small and of inter-
mediate resistance, before stating the normal results of capillaries of
extreme resistance.
With the copper capillary tube described in my former paper, and
which admitted 1 cubic inch of air into a vacuum in 22 seconds, the
time of passage of a constant volume of air into a vacuum was 853
seconds at 60°, 899 seconds at 116°, and 924-5 seconds at 152°. The
theoretical times, or those corresponding to the rarefaction by heat at
these temperatures, are 853, 945, and 1004 seconds. Here the observed
times at 116° and 152*, are 46 and 79.5 seconds shorter respectively than
the times obtained by calculation; and the difference in transpirability
observed at the high and low temperatures only amounts to about one-
half of what it should be. 4-
With capillary M, of which the resistance is seven times greater
than the last capillary, the observed times of air at 59° (15° Centig),
and at 203’ (95° Centig.), were 1106.5 and 1286.4 seconds. The time
at the higher temperature is 1400 seconds by calculation, and the
observed time is therefore 113-6 seconds deficient. The difference at
the high and low temperatures amounts to nearly two-thirds of the
difference which theory requires. The deviation is therefore less than
with the preceding capillary.
Air compressed in the globular digester with pressure gauge, of
which the capacity was reduced to about 10 cubic inches by the intro-
duction of mercury, was transpired by a small capillary V, 3 inches in
length, into the atmosphere, from a pressure beginning at 17 inches
above that of the barometer. Thermometer 50°, barometer 29.546 to
29'590. - - -
The resistance of this capillary is excessive. Under a pressure of
17 inches of mercury, 1 cubic inch of air is transpired in 2329 seconds,
or the volume transpired is 0.0258 cubic inch per minute.
ON THE MOTION OF GASEs. 207
TABLE XV-Transpiration of Air under pressure (into air) at different
- temperatures. *
Time in seconds.
Ratio at 203°,
Pressure by gauge barometer.
Time at 50° = 1.
Thermometer 50° Fahr. | Thermometer 203° Fahr. -
Inches. Aſ Z/
17
16 1370 2329 1-7000
15 1445 2442 1.6900
14 1541 260] 1-6880
From 17 to 14 inches...... 4356 7372 1.6924
, Now the volume of air at 32° being = 1, at 50° it is 10366, and at
203°, 13480. But it must be remembered that the volume actually
transpired in the experiment was greater at 203 than that at 50°, in
proportion as the volume of air is expanded at the higher of these two
temperatures, that is as 13480 to 10366 (volume at 32° = 1). It is
therefore necessary to reduce the observed times of the table at 203 in
that proportion. The time from 17 inches to 16 is thus reduced from
2329 to 1792-5 seconds, which last is the true time of the passage of the
same volume at 203 as passed at 50°. The law requires that the times
of equal volumes should be inversely as the densities of air at these
temperatures, or as 1.0366 to 13480. Thus calculated from 1370
seconds, the time at 50°, the time at 203° is 1780.9 seconds; the time
actually observed was 1792-5 or 11-6 seconds more, a close approxima-
tion considering the difficulties of the experiment.
But the resistance does not require to be so excessive as in capillary
V to bring out the law of temperature. It appeared equally distinct in
a capillary tube, having only one-ninth of the resistance of V for equal
lengths. This tube however was used in lengths of 4% inches (instead
of 3 inches), so that its resistance is properly stated at one-sixth of V.
A sheaf was put together of thirty lengths of the new tube, forming the
compound capillary Q. The digester was employed of its full capacity,
of 72 cubic inches, to contain the compressed air, which was allowed to
escape by the channels of Q into the atmosphere. The range of pressure
was from 20 inches to 8. The observed times at 49° and 203 without
reduction were 802, 799, and 798 seconds at the low temperature, and
1350 and 1347 seconds at the high temperature. Taking the means
800 and 1349 seconds, and reducing as in the experiments with W, we
have 1036-1 seconds for the high temperature. Now the calculated
time for that temperature is 1041:6 seconds, or only 5.5 seconds above
208 ON THE MOTION OF GASEs.
the observed time. The barometer during these experiments marked
from 30:044 to 30.058 inches.
In another series of experiments, the time observed at 49° being 797
Seconds, the times observed after reduction, at certain intermediate
temperatures, were as follows:— f
TABLE XVI—Times of transpiration of Air (into air) in seconds.

Temperature. Observed time. Calculated time. Error of observation.
49 Fahr. 797 797
96 879.3 870-4 + 8-9
14] 950-1 - 935.8 + 14:3
203 1020-8 1032-1 – 11'3
The deviations of the observed from the calculated times, from 8.9
to 14:3 seconds, are small considering the difficulty of maintaining the
temperature constant in the experiments. Nor are they always in the
same direction. This appears in a third series of experiments, conducted
in the same manner as the last, of which I subjoin the results.
TABLE XVII-Times of transpiration of Air (into air) in seconds.

Temperature. Observed time. Calculated time. Error of observation.
49 Fahr. 797 797
96 897.3 870-4 + 8-9
141 932-3 940-8 – 8°5
These observations leave little doubt that the transpiration of air at
different temperatures takes place according to the law by which the
times above have been calculated. In one experiment which was
made upon oxygen at 49° and 203", the increase upon the time at the
higher temperature corresponded within 0.7 per cent. of the increase upon
the time of air, and evidently followed the same ratio. I may add that
the transpiration times of air and oxygen, as determined by a single
observation in each case, were 0.9058 to 1 for the compound capillary
Q, and 0.9020 to 1 for the single capillary V of extreme resistance.
In conclusion I may sum up the general results hitherto obtained in
this inquiry. -
1. The velocities with which different gases pass through capillary
tubes bear a constant relation to each other, and appear to constitute
a peculiar and fundamental property of the gaseous form of matter,
which I have termed transpirability. The constancy of these relations,
ON THE MOTION OF GASEs. 209
or of the transpiration times, has been observed for several of the gases
for tube resistances varying in amount from 1 to 1000. These relations,
there is reason to believe, are more simple in their expression than
the densities of the gases. The following relations are particularly
'remarkable :—
The velocity of hydrogen is exactly double that of nitrogen and
carbonic oxide.
The velocities of nitrogen and oxygen are inversely as the specific
gravities of these gases. -
The velocity of binoxide of nitrogen is the same as that of nitrogen
and carbonic oxide. - -
The velocities of carbonic acid and protoxide of nitrogen are equal,
and directly proportional to their specific gravities, when compared with
Oxygen. -
The velocity of protocarburetted hydrogen is 0:8, that of hydrogen
being 1. -
The velocity of chlorine appears to be 1; that of oxygen; of bromine
vapour and sulphuric acid vapour the same as that of oxygen.
Ether vapour appears to have the same velocity as hydrogen gas.
Olefiant gas, ammonia, and cyanogen to have equal or nearly equal
velocities, which approach closely to double the velocity of oxygen.
Hydrosulphuric acid gas and bisulphide of carbon vapour appear to
have equal or nearly equal velocities.
The compounds of methyl appear to have a less velocity than the
corresponding compounds of ethyl, but to be connected by a certain
constant relation.
2. The resistance of a capillary tube of uniform bore to the passage
of any gas is directly proportional to the length of the tube.
3. The velocity of passage of equal volumes of air of the same
temperature but of different densities or elasticities, is directly propor-
tional to the density.
4. Rarefaction by heat has a similar and precisely equal effect in
diminishing the velocity of the transpiration of equal volumes of air, as
the loss of density and elasticity by diminished pressure has.
5. A greater resistance in the capillary is required to bring out the
third result, or the law of densities, than appears necessary for the first
and second results; and a resistance still further increased, and the
highest of all, to bring out the fourth result or the law of temperatures.
6. Finally, it will be remarked throughout, that transpiration is pro-
moted by density, and equally whether the increased density is due to
compression, to cold, or to the addition of an element in combination, as
the velocity of oxygen is increased, by combining it with carbon without
change of volume, in carbonic acid gas.
O
210 ON THE MOLECULAR MOBILITY OF GASES.
It was no part of my plan to investigate the passage of gases
through tubes of great diameter, and to solve pneumatic problems of
actual occurrence, such as those offered in the distribution of coal-gas
by pipes. But I may state that the results must be similar, with truly
elastic gases such as air and carburetted hydrogen, whether the tubes
are capillary or many inches in diameter, provided the length of the
tube is not less than 4000 times its diameter, as in the long glass
capillaries of my early experiments. The small propulsive pressure
applied to coal-gas is also favourable to transpiration, as well as the
great length of the mains; and I should therefore expect the distribution
of coal-gas in cities to exemplify approximately the laws of gaseous
transpiration. The velocity of coal-gas should be 1:575, that of air
being 1, under the same pressure (p. 201). And with a constant pro-
pulsive pressure in the gasometer, the flow of gas should increase in
volume with a rise of the barometer or with a fall in temperature, directly
in proportion to the increase of its density from either of these causes.
XVI.
ON THE MOLECULAR MOBILITY OF GASES."
From Phil. Trans. 1863, pp. 385-405. [Chemical News, viii. 1863, pp. 79-81; Paris
Comptes Rendus, lvii. 1863, pp. 181-192; Pharmaceut. Journ., v. 1864, pp.
166-171; Poggendorf, Annal. cxx. 1863, pp. 415-425.] -
THE molecular mobility of gases will be considered at present chiefly
in reference to the passage of gases, under pressure, through a thin
porous plate or Septum, and to the partial separation of mixed gases
which can be effected, as will be shown, by such means. The investi-
gation arose out of a renewed and somewhat protracted inquiry regard—
ing the diffusion of gases (which depends upon the same molecular
mobility), and has afforded certain new results which may prove to be
of interest in a theoretical as well as in a practical point of view.
In the Diffusiometer, as first constructed, a plain cylindrical glass
tube, about 10 inches in length and rather less than an inch in diameter,
was simply closed at one end by a porous plate of plaster of Paris, about
one-third of an inch in thickness, and was thus converted into a gas-
receiver.” A superior material for the porous plate has since been
found in the artificially compressed graphite of Mr. Brockedon, of the
1 Received (i.e. by the Royal Society) May 7,-Read June 18, 1863.
* “On the Law of the Diffusion of Gases,” ante, pp. 44-70 (Trans, of the Royal Society
of Edinburgh, vol. xii. p. 222; or Phil. Mag. 1834, vol. ii. pp. 175, 269, 351).
W
ON THE MOLECULAR MOBILITY OF GASES. 2 || 1
quality used for making writing-pencils. This material is sold in
London in small cubic masses about 2 inches square. A cube may
easily be cut into slices of a millimetre or two in thickness by means of
a saw of steel spring. By rubbing the surface FIG. I. FIG. 2.
of the slice without wetting it upon a flat
sand-stone, the thickness may be further
reduced to about one-half of a millimetre. A
circular disc of this graphite, which is like a
wafer in thickness but possesses considerable
tenacity, is attached by resinous cement to one
end of the glass tube above described, so as to
close it and form a diffusiometer (fig. 1). The
tube is filled with hydrogen gas over a mercu-
rial trough, the porosity of the graphite plate
being counteracted for the time by covering it
tightly with a thin sheet of gutta percha (fig. 2).
On afterwards removing the latter, gaseous dif-
fusion immediately takes place through the
pores of the graphite. The whole hydrogen
will leave the tube in forty minutes or an hour,
and is replaced by a much smaller proportion
of atmospheric air (about one-fourth), as is to
be expected from the law of the diffusion of
gases. During the process, the mercury will
rise in the tube, if allowed, forming a column
of several inches in height—a fact which illustrates strikingly the
intensity of the force with which the interpenetration of different gases
is effected. Native graphite is of a lamellar structure, and appears to
have little or no porosity. It cannot be substituted for the artificial
graphite as a diffusion-septum. Unglazed earthenware comes next in
value to graphite for that purpose. -
The pores of artificial graphite appear to be really so minute, that a
gas in mass cannot penetrate the plate at all. It seems that molecules
only can pass; and they may be supposed to pass wholly unimpeded
by friction, for the smallest pores that can be imagined to exist in the
graphite must be tunnels in magnitude to the ultimate atoms of a
gaseous body. The sole motive agency appears to be that intestine
movement of molecules which is now generally recognised as an essen-
tial property of the gaseous condition of matter.
According to the physical hypothesis now generally received," a gas
1 D. Bernoulli, J. Herapath, Joule, Krönig, Clausius, Clerk Maxwell, and Cazin.
The merit of reviving this hypothesis in recent times, and first applying it to the facts
of gaseous diffusion, is fairly due to Mr. Herapath. See Mathematical Physics, in two
volumes, by John Herapath, Esq. (1847).

212 ON THE MOLECULAR MOBILITY OF GASES.
is represented as consisting of solid and perfectly elastic spherical par-
ticles or atoms, which move in all directions, and are animated with
different degrees of velocity in different gases. Confined in a vessel, the
moving particles are constantly impinging against its sides and occa-
sionally against each other, and this contact takes place without any
loss of motion, owing to the perfect elasticity of the particles. If the
containing vessel be porous, like a diffusiometer, then gas is projected
through the open channels, by the atomic motion described, and escapes.
Simultaneously the external air is carried inwards in the same manner,
and takes the place of the gas which leaves the vessel. To this atomic
or molecular movement is due the elastic force, with the power to resist
compression, possessed by gases. The molecular movement is accelerated
by heat and retarded by cold, the tension of the gas being increased in
the first instance and diminished in the second. Even when the same
gas is present both within and without the vessel, or is in contact with
both sides of our porous plate, the movement is sustained without abate-
ment—molecules continuing to enter and to leave the vessel in equal
number, although nothing of the kind is indicated by change of volume
or otherwise. If the gases in communication be different but possess
sensibly the same specific gravity and molecular velocity, as nitrogen
and carbonic oxide do, an interchange of molecules also takes place
without any change in volume. With gases opposed of unequal density
and molecular velocity, the permeation ceases of course to be equal in
both directions. .
These observations are preliminary to the consideration of the passage
through a graphite plate, in one direction only, of gas under pressure,
or under the influence of its own elastic force. We are to suppose a
vacuum to be maintained on one side of the porous septum, and air or
any other gas, under a constant pressure, to be in contact with the other
side. Now a gas may pass into a vacuum in three different modes, or
in two other modes besides that immediately before us.
1. The gas may enter the vacuum by passing through a minute
aperture in a thin plate, such as a puncture in platinum foil made by a
fine steel point. The rate of passage of different gases is then regu-
lated by their specific gravities, according to a pneumatic law which
was deduced by Professor John Robison from Torricelli's well-known
theorem of the velocity of efflux of fluids. A gas rushes into a vacuum
with the velocity which a heavy body would acquire by falling from
the height of an atmosphere composed of the gas in question, and sup-
posed to be of uniform density throughout. The height of the uniform
atmosphere would be inversely as the density of the gas, the atmosphere
of hydrogen, for instance, sixteen times higher than that of oxygen.
But as the velocity acquired by a heavy body in falling is not directly
ON THE MOLECULAR MOBILITY OF GASES. 213
as the height, but as the square root of the height, the rate of flow of
different gases into a vacuum will be inversely as the square root of
their respective densities. The velocity of oxygen being 1, that of
hydrogen will be 4, the square root of 16. This law has been experi-
mentally verified.” The relative times of the effusion of gases, as I
have spoken of it, are similar to those of molecular diffusion; but it is
important to observe that the phenomena of effusion and diffusion are
distinct and essentially different in their nature. The effusion move-
ment affects masses of gas, the diffusion movement affects molecules;
and a gas is usually carried by the former kind of impulse with a velocity
many thousand times as great as is demonstrable by the latter.
2. If the aperture of efflux be in a plate of increased thickness, and
so becomes a tube, the effusion-rates are disturbed. The rates of flow
of different gases, however, assume again a constant ratio to each other
when the capillary tube is considerably elongated, when the length
exceeds the diameter by at least 4000 times. These new proportions
of efflux are the rates of the “Capillary Transpiration” of gases.” The
rates are found to be the same in a capillary tube composed of copper
as they are in glass, and appear to be independent of the material of the
capillary. A film of gas no doubt adheres to the surface of the tube,
and the friction is really that of gas upon gas, and is consequently
unaffected by the tube-substance. The rates of transpiration are not
governed by specific gravity, and are indeed singularly unlike the rates
of effusion.
The transpiration-velocity of oxygen being 1, that of chlorine is 1-5,
that of hydrogen 2:26, of ether vapour the same or nearly the same as
that of hydrogen, of nitrogen and carbonic oxide half that of hydrogen,
of olefiant gas, ammonia, and cyanogen 2 (double or nearly double that
of oxygen), of carbonic acid 1376, and of the gas of marshes 1815. In
the same gas the velocity of transpiration increases with increased
density, whether occasioned by cold or pressure.
The transpiration-ratios of gases appear to be in direct relation with
no other known property of the same gases, and they form a class of
phenomena remarkably isolated from all else at present known of gases.
There is one property of transpiration immediately bearing upon
permeation of the graphite plate by gases. The capillary offers to the
passage of gas a resistance analogous to that of friction, proportional to
the surface, and consequently increasing as the tube or tubes are multi-
plied in number and diminished in diameter, with the area of discharge
preserved constant. The resistance to the passage of liquid through a
capillary was observed by Poiseuille to be nearly as the fourth power of
1 “On the Motion of Gases,” ante, p. 88 (Phil. Trans. 1846, p. 573).
* Ante, p. 108; also p. 162 (Phil. Trans. 1849, p. 349).
214 ON THE MOLECULAR MOBILITY OF GASES.
the diameter of the tube. In gases the resistance also rapidly increases;
but in what ratio, has not been observed. The consequence, however,
is certain, that as the diameter of the capillaries may be diminished
beyond any assignable limit, so the flow may be retarded indefinitely,
and caused at last to become too small to be sensible. We may then
have a mass of capillaries of which the passages form a large aggregate,
but are individually too small to allow a sensible flow of gas under
pressure. A porous solid mass may possess the same reduced perme-
ability as the congeries of capillary tubes. Indeed, the state of porosity
described appears to be more or less closely approached by all loosely
aggregated mineral masses, such as lime-plaster, stucco, chalk, baked
clay, non-crystalline earthy powders like hydrate of lime or magnesia
compacted by pressure, and in the highest degree perhaps by artificial
graphite.
3. A plate of artificial graphite, although it appears to be practically
impermeable to gas by either of the two modes of passage previously
described, is readily penetrated by the agency of the molecular or diffu-
sive movement of gases. This appears on comparing the time required
for the passage through the plate of equal volumes of different gases
under a constant pressure. Of the three gases, oxygen, hydrogen, and
carbonic acid, the time required for the passage of an equal volume of
each through a capillary glass tube, in similar circumstances as to
pressure and temperature, was formerly observed to be as follows:–
Time of capillary transpiration
of equal Volumes.
Oxygen, © º º e * I
Hydrogen, © & -> º e 0°44
Carbonic acid, . e e º º 0.72
Now through a plate of graphite, half a millimetre in thickness, the
same gases were observed to pass, under a constant pressure of a column
of mercury of 100 millimetres in height, in times which are as follows:—
Time of molecular passage. Square root of density (oxygen I).
Oxygen, & 1 1
Hydrogen, . O'24.72 0-2502
Carbonic acid, 1’ 1886 1:1760
It appears that the times of passage through the graphite plate have
no relation to the capillary transpiration-times of the same gases as first
quoted. The new times in question, however, show a close relation to
the square roots of the densities of the respective gases, as is seen in the
last Table; and they so far agree with theoretical times of diffusion
usually ascribed to the same gases.
These results were obtained by means of the graphite diffusiometer,
ON THE MOLECULAR MOBILITY OF GASES. 215
already referred to, which was a plain glass tube about 22 millimetres
in diameter, closed at one end by the graphite plate. In order to
conduct gas to the upper surface of the graphite plate, a little chamber
was formed above the plate, to which the gas was conveyed in a mode-
rate stream by the entrance-tube e (fig. 3); while the gas brought in
excess was constantly FIG. 3.
escaping into the air by
the open issue-tube i. 22.
The chamber was formed *
of a short piece of glass
tube, about two inches
in length, cemented over
the upper end of the dif-
fusiometer. The upper
opening of this short
tube was closed by a
cork perforated for the
entrance and exit tubes.
It will be observed that
by this arrangement the
upper surface of the
graphite plate was con-
stantly swept by a stream
of gas, which was under
no additional pressure
beyond that of the at-
mosphere, a free escape
being allowed by the
exit-tube. The gas also
was always dried before
reaching the chamber.
The diffusiometer stood
over mercury, and was
raised or lowered by the
lever movement introduced by Professor Bunsen in his very exact experi-
ments upon gaseous diffusion." To obtain the pressure of 100 millime-
tres of mercury, the diffusiometer was first entirely filled with mercury
and then raised in the trough. Gas gradually entered till the column of
mercury in the tube fell to 100 millimetres. The mercury was then
maintained at this height, but gradually raising the tube in proportion
as gas continued to enter and the mercury to fall, so as to maintain a con-
stant difference of level of 100 millimetres, as observed by the graduation
1 Bunsen's Gasometry, by Roscoe,

216 ON THE MOLECULAR MOBILITY OF GASES.
inscribed upon the tube itself, between the level of the mercury in the
tube and trough. The experiment consisted in observing the time in
seconds which the mercury took to fall 10 millimetre divisions with each
gas. The constant volume of gas which entered was 2.2 cubic centimetres
(0.1342 cubic inch). Two experiments were made with each gas.
Oxygen entered in 898 and 894 seconds; mean 896 seconds.
Hydrogen in 222 and 221 seconds; mean 221-5 seconds.
Carbonic acid in 1070 and 1060 seconds; mean 1065 seconds.
In such experiments the same gas exists on both sides, and also
occupies the pores of the diaphragm. But the molecular movement
within the pores in a downward direction is not fully balanced by the
molecular movement in an upward direction, owing to the less tension,
by 100 millimetres, of the gas below the diaphragm and within the tube
FIG. 4. FIG. 6.
than the gas above and without. The influx of gas indicates the differ-
ence of molecular movement in opposite directions. Taking the full
tension of the gas above the diaphragm at 760 millimetres, that below
would be 660 millimetres, and the movement downwards and that
upwards are represented by these numbers respectively.
To increase the inequality of tension and favour the passage of gas
through the graphite plate, a diffusion-tube was now used, 48 inches in
length, or of the dimensions of a barometer-tube, by which a Torricellian
vacuum could be commanded. The pneumatic trough in which this
gas-tube was suspended consisted of a pipe of gutta percha of equal
length, closed at the bottom by a cork, and widening into a funnel-form
at the top. In one modification of the instrument it was found con-
venient to cement a capillary glass tube to the side of the glass diffusio-

ON THE MOLECULAR MOBILITY OF GASES. 217
meter, within about 15 millimetres of the upper end of the tube. An
opening into the upper part of the glass tube was thus obtained, by
means of which the gas contained in FIG. 7.
the diffusiometer could escape when
the latter was depressed in the mer-
curial trough. A flexible tube with
clip was attached to the capillary
tube referred to, so that the latter
could be closed. From the same
opening a specimen of the gas con-
tained in the diffusiometer could be
drawn when required for exami-
nation. -
In another and more serviceable
modification of this barometrical dif-
fusiometer a large space was ob-
tained above the mercurial column
by surmounting the long glass tube,
unprovided with a graphite plate by
a glass jar about half a litre in capa-
city. This jar was more correctly
a small bell jar (fig. 4) open at top.
It was fitted in an inverted position,
as in fig. 5, to the open end of the
long glass tube d, by means of a cork
and cement. The large upper open-
ing was closed by a circular plate of
gutta percha (fig. 5), about 10 milli-
metres, or nearly half an inch, in
thickness. This disc of gutta percha
had two perforations at f and g (fig.
6), the former of which was fitted
above with a wide glass tube. The
tube f was closed below by the plate
of graphite, and above with a per-
forated cork carrying a quill tube, e.
This quill tube was the entrance-
tube for gas, and was accompanied by
the usual issue-tube, i. The other
aperture in the gutta percha cover
was fitted with a plain quill tube,
h, which did not descend below the
level of the gutta percha, and formed


218 ON THE MOLECULAR MOBILITY OF GASES.
a tube of exit. No difficulty was found in making all these junctions
air-tight, by applying the heated blade of a knife to fuse the gutta
perchain contact with the glass. Gutta percha is indeed of no ordinary
value in the construction of pneumatic apparatus. The graphite plate
itself required to be not less than 1 millimetre in thickness, in order
to support the pressure of a whole atmosphere, to which it is exposed
in the present apparatus. This barometrical diffusiometer is supported
from above by a cord passing over a pulley, and is duly counterpoised
by a hanging weight. -
In operating, the first point is to expel the air from the barometer-tube
and upper chamber. The instrument (fig. 7, p. 217) is sunk completely
in the mercurial trough previously described, till the whole is filled,
and mercury enters the quill tube of exit, h. The caoutchouc extension
of this tube is then closed by a pinch. The diffusiometer is now ele-
vated 30 or 40 inches, when the mercury sinks in the glass tube till
it comes to stand at the barometric height for the time, leaving the
upper chamber entirely vacuous. The gas to be tried has in the mean-
time been made to stream over the upper surface of the graphite plate,
exactly as in the experiment with the former diffusiometer. The graphite
is permeated by the gas, and the mercury in the diffusiometer-tube begins
to fall, but it now falls slowly, owing to the considerable vacuous space
to be filled. It is allowed to fall about half an inch, and the exact time
is then noted, by a watch, when the mercury passes a certain point in
the graduation of the tube, and again when the mercury descends to
another fixed point an inch or two below the former. The time of
permeation of a certain volume of gas is thus ascertained in seconds.
The experiment is immediately repeated with two or more gases in
succession, in similar circumstances as to pressure, and with great care
taken to insure uniformity of temperature during the whole period.
In a series of four experiments made with hydrogen, the mercury
fell from 758 to 685 millims. (29.9 inches to 27 inches) in 252,256,254,
and 256 seconds; mean 254-5 seconds. -
In three experiments with oxygen the mercury fell through the same
space in 1019, 1025, and 1024 seconds; mean 10227 seconds:–
1022.7
25.4°5
= 4°018.
The times of these gases appear therefore to be as 1 to 4:018, while
the times calculated as being inversely as the square root of the den-
sities of the same gases are as 1 to 4.
On another day, with a different height of the barometer, four
gases were passed through the graphite plate in succession through a
ON THE MOLECULAR MOBILITY OF GASES. 219
somewhat shorter range, namely, from 754 to 685 millims, (297 to 27
inches). I
- The time of permeation of air was 884 and 885 seconds; mean
884.5 seconds.
The time of carbonic acid was 1100 and 1106 seconds; mean 1103
seconds. -
The time of oxygen was 936, 924, and 930 seconds; mean 930
seconds.
The time of hydrogen was 229, 235, and 335 seconds; mean 233
Seconds.
These times of permeation are in the following proportion:—
Times of the permeation of equal volumes
of gas through graphite.
Oxygen, . º e o o l
Air, . . . . . . 0-9501
Carbonic acid, e e e o 1:1860
Hydrogen, . * º wº cº 0°2505
These numbers approach so closely to the square roots of the den-
sity, or the theoretical diffusion-times of the same gases, namely, oxygen
1, air 0.9507, carbonic acid 1:176, and hydrogen 0.2502, that they may
be held to indicate the prevalence of a common law. They exclude
the idea of capillary transpiration, which gives to the same gases entirely
different numbers.
The movement of gases through the graphite plate appears to be
solely due to their own proper molecular motion, quite unaided by
transpiration. It seems to be the simplest possible exhibition of the
molecular or diffusive movement of gases. This pure result is to be
ascribed to the wonderfully fine (minute) porosity of the graphite. The
interstitial spaces appear to be sufficiently small to extinguish capillary
transpiration entirely. The graphite plate is a pneumatic sieve which
stops all gaseous matter in mass, and permits molecules only to pass.
It is worth observing what result a plate of more open structure,
such as stucco, will give in comparison with graphite. For the graphite
plate, a cylinder of stucco, 12 millims, in thickness, was accordingly
substituted, and gas allowed to percolate at both low and high pressures,
as in the former experiments with graphite.
1. Under a constant pressure of 100 millims. of mercury, gas was
allowed to enter through 100 millim. divisions of the diffusiometer.
With air, the time in two experiments was 515, and again 515
seconds. -
With hydrogen 178 seconds, and again 178 seconds:
− = 2*894,
178 894
515
220 ON THE MOLECULAR MOBILITY OF GASES.
2. Under a pressure beginning with 710 millims. (28 inches) and
ending with 660 millims. (26 inches), the time with air was 374 and
375 seconds; mean 374-5 seconds. The time with hydrogen was 129
and 130 seconds; mean 129°5 seconds: .
374-5. .
I29-5 T 2°891.
The stucco cylinder of the preceding experiments had been dried
over sulphuric acid, without the application of heat. It was further
desiccated at 60° C. for twenty-four hours, in order to find whether the
porosity would be altered. The ratio of the time of hydrogen to that
of air now became 1 to 2788 at the lower degree of pressure, and 1 to
2.744 at the higher degree of pressure.
It will be observed that the theoretical diffusion-ratio of hydrogen
to air, which is 1 to 3-80, is greatly departed from in these experiments
with stucco. The ratio appears to be tending to the proportion of the
transpiration-times of the same gases, namely, I to 2:04. In an experi-
ment recorded by Bunsen, the ratio observed between the times of
hydrogen and oxygen in passing, under a small degree of pressure,
through stucco dried by heat, was so low as 1 to 2-73, the stucco being
probably less dense than in the experiments before us.
With stucco the permeation of gases under pressure appears to be a
mixed phenomenon—to some extent molecular diffusion into a vacuum,
such as holds with the plate of graphite, but principally capillary
transpiration of gas in mass. -
The diffusiometer was now closed by a plate of white biscuitware,
2.2 millims. in thickness. The time of fall at the constant pressure of
100 millims, through a range of forty divisions of the diffusiometer,
was, for air 1210 seconds, for hydrogen 321 seconds.
* º'-3769
Hydrogen, tº 321 T. o
The time, again, from 736 to 685 millims. (29 to 27 inches) was, for
air 685 and 684 seconds; mean 684-5 seconds; and for hydrogen 183,
183, and 184 seconds; mean 1833 seconds. -
Air, . . 684.5
Hydrogen, . Isai – 3754.
The stoneware was evidently of a much closer texture than stucco,
and the ratio appears again less influenced by capillary transpiration.
In fact the molecular ratio of 1 to 3-80 is approached within 1 per cent.
Biscuitware therefore appears to be but little inferior to graphite for
such experiments, a circumstance which is important, as the latter is
ON THE MOLECULAR MOBILITY OF GASES. 221
not easily procured, and cannot be converted into tubes and other con-
venient forms like plastic clay. -
Further, the rate of passage of gas through the plate of graphite
appears to be closely proportional to the pressure. The resistance was
increased by augmenting the thickness of the plate to 2 millims. ; and
with air and hydrogen at a pressure maintained constant at 50 and 100
millims, the time was observed that the gas took to enter 10 linear
millimetre divisions of the tube. -
Seconds. Ratio.
Air under pressure of 100 millims, . 1925 I
Air under pressure of 50 millims., . 3880 2°015
Hydrogen under pressure of 100 millims, 497 1
Hydrogen under pressure of 50 millims, 1022 2:056
By halving the pressure the time of passage is doubled or increased
somewhat more. Greater pressures might probably give a rate of
passage corresponding more exactly with the pressure.
The ratio between the comparative times of the two gases in the last
experiments may also be noticed, the observations having been made in
similar circumstances as to pressure and temperature.
Barom. 760 millims. ; At pressure of 50 millims.
Therm. 12°-9 C. * =
Air, ſº ſº *=3.79%
— E 5* { *
Hydrogen, te 1022
Baronn. 760 millims. ; At pressure of 100 millims.
Therm. 12° 9 C.
Air, gº & 1925 3-873
Hydrogen, & 497 - -
The observation was repeated at the pressure of 100 millims. with
barometer at 754 millims, and thermometer at 10°C.
* *-3ss;
Hydrogen, * 498 T tº
The velocity of hydrogen appears, as usual, to be nearly 3-8 times
1
Jogºs-37994. -
An experiment was made at the same time as the former series upon
a mixture of 95 hydrogen and 5 air, which gave an unlooked-for result
that led to a great deal of inquiry. It is known that such a mixture is
effused through an aperture in a fine plate in a time which is as the square
root of the density of the mixture, and therefore nearly the arithmetical
mean of the two gases effused separately. But in transpiration by a
capillary, a mixture of 95 hydrogen and 5 air requires a considerably
longer time than the gases transpired separately. In fact 5 per cent of
that of air;
222 ON THE MOLECULAR MOBILITY OF GASES.
air retards the transpiration of hydrogen nearly as much as 20 per cent.
of air would retard the effusion of hydrogen." Now the mixture in
question permeates the graphite plate in 527-5 seconds, while the cal-
culated mean of the times of the two gases is 562-1 seconds.
The mixture has therefore passed neither in the effusion time, nor
in a longer time, as it would do by capillary transpiration, but, singular
to say, in a time considerably shorter than either. The gas that came
through was found by analysis to be altered in composition. It Con-
tained more hydrogen and less air than the original mixture. Hence
it passed through with increased rapidity. On consideration it
appeared that such a separation of the mixed gases must follow as a
consequence of the movement being molecular. Each gas is impelled
by its own peculiar molecular force, which, as has been seen, is capable
of causing hydrogen to permeate the graphite plate about 3-8 times as
rapidly as air. -
Each gas may permeate a graphite plate into a vacuum with the
same relative velocity as it diffuses into another gaseous atmosphere,
but it remains a question whether the velocities of permeation and
diffusion are absolutely as well as relatively the same. To illustrate
this point, hydrogen and air were first allowed to permeate into a
vacuum, and then to diffuse into each other, through the same graphite
plate, which was 1 millim. in thickness. The plate was a circular disc
of 22 millims, in diameter.
The mercurial column in the barometrical diffusiometer fell from
762 to 685 millims. (30 inches to 27) with air in 878 seconds, and with
hydrogen in 233 seconds.
Air, gº g 878
— = 3-768.
Hydrogen, . º 233
The volume of gas which produced this effect was found by the calibra-
tion of the tube to be 8.85 cub. centims. Hence 1:22 cub. centim. of
the hydrogen entered the diffusiometer in 60 seconds, or one minute.
But the pressure under which the hydrogen gas entered was the mean
of 762 to 685 millims, or 723.5 millims.; while a whole atmosphere (the
height of the barometer at the time) was 765 millims. The volume of
the gas has therefore to be increased as 723.5 to 765 to give the full
action of a vacuum. The volume becomes 1289 cub. centim, in one
minute.
When the diffusiometer was filled with hydrogen and the gas allowed
to diffuse into air, the rise of the mercury was pretty uniform for the
first five minutes, being 15.5 millim. divisions in the first two minutes,
7 in the third minute, 7-5 in the fourth minute, and 7 in the fifth
* Ante, pp. 155, 156: Table L. (Philosophical Transactions, 1846, p. 628).
ON THE MOLECULAR MOBILITY OF GASES. 223
minute, making 37 divisions in five minutes. But as in diffusion 1 air
may be supposed to enter the tube for 38 hydrogen which escape, the
hydrogen which diffused was more than 37 divisions, by is that is, by
about 10 divisions. Hence 47 divisions of hydrogen have diffused into
air in five minutes. These divisions measured, by the calibration of the
tube, 6'215 cub. centims. One-fifth of this amount, that is, 1243 cub.
centim, diffused in one minute. The result of the whole is that in one
minute there passed of hydrogen through the graphite plate,
1289 cub. centim. by permeation into a vacuum,
1243 cub. centim. by diffusion into air.
The numbers indicate a close approach to equality in the velocities
of permeation into a vacuum and of diffusion into another gas, through
the same porous diaphragm. The diffusion appears the slower of the
two by a small amount; but this is as it should be, our estimate of the
diffusion-velocity being certainly underrated; for the initial-diffusion,
or even the diffusion in the first minute, must obviously be somewhat
greater than the average of the first five minutes, which we have taken
to represent it—the hydrogen necessarily diffusing out in a diminishing
progression, or more slowly in proportion as air has entered the diffusio-
meter. It is strictly the initial velocity of diffusion (that of the first
second if it could be obtained) that ought to be compared with the per-
colation into a vacuum. -
In fine, there can be little doubt left on the mind that the permea-
tion through the graphite plate into a vacuum and the diffusion into
a gaseous atmosphere, through the same plate, are due to the same
inherent mobility of the gaseous molecule. They are the exhibition of
this movement in different circumstances. In interdiffusion we have
two gases moved simultaneously through the passages in opposite direc-
tions, each gas under the influence of its own inherent force; while with
gas on one side of the plate and a vacuum on the other side, we have a
single gas moving in one direction only. The latter case may be assimi-
lated to the former if the vacuum be supposed to represent an infinitely
light gas. It will not involve any error, therefore, to speak of both
movements as gaseous diffusion,-the diffusion of gas into gas (double
diffusion) in one case, and the diffusion of gas into a vacuum (single
diffusion) in the other. The inherent molecular mobility may also be
justly spoken of as the diffusibility or diffusive force of gases.
The diffusive mobility of the gaseous molecule is a property of
matter fundamental in its nature, and the source of many others. The
rate of diffusibility of any gas has been said to be regulated by its specific
gravity, the velocity of diffusion having been observed to vary inversely
as the square root of the density of the gas. This is true, but not in the
224 ON THE MOLECULAR MOBILITY OF GASES.
sense of the diffusibility being determined or caused by specific gravity.
The physical basis is the molecular mobility. The degree of motion
which the molecule possesses regulates the volume which the gas
assumes, and is obviously one, if not the only, determining cause of the
peculiar specific gravity which the gas enjoys. If it were possible to
increase in a permanent manner the molecular motion of a gas, its
specific gravity would be altered, and it would become a lighter gas.
With the density is also associated the equivalent weight of a gaseous
element, according to the doctrine of equal combining volumes.
Diffusion of mixed gases into a vacuum, with partial separation
—Atmolysis.
Oaygen and hydrogen.—A diffusiometer of the same construction as
that described (fig. 3, p. 215), with a graphite plate of 1 millim. in thick-
ness, was now employed. The upper surface of the plate was swept by
a current of the mixed gas proceeding from a gas-holder, the excess of
gas being allowed to escape into the atmosphere, as usual, by an open
exit-tube. The gas was drawn through the graphite by elevating the
diffusiometer containing a column of mercury, from its well, so as to
command a partial vacuum in the upper part of the tube. Care is taken
that any gas left in the upper part of the diffusiometer-tube before the
experiment begins, should be of the same composition as the gas to be
allowed afterwards to enter, so that, on starting, the gas may be uniform
in composition on both sides of the graphite plate. The height of the
mercurial column, which measures the aspirating force of the diffusio-
meter, is preserved uniform by gradually raising the tube in the mer-
curial trough in proportion as gas enters and the mercury falls. The
diffusiometer is suspended from the roof of the apartment by a cord
passing over a pulley and properly weighted, as in former experiments.
The mixture to be diffused consisted of nearly equal volumes of
oxygen and hydrogen. The effect of different degrees of pressure on
the amount of separation produced was first observed. It will be seen
that as the pressure or aspirating force is increased the amount of sepa-
ration becomes greater. Barom. 0-759 millim.; therm. 18°3 C.
Diffusion into a partial vacuum.
Oxygen. Hydrogen.
Composition of original mixture in 100 parts, . © 49°3 50-7
Diffused by pressure of 100 millims., . º & e 47.0 53-0
Diffused by pressure of 400 millims., . & tº ſº 37.5 62.5
Diffused by pressure of 673 millims. (mean of 635-710), 26-4 73-6
Diffused by pressure of 747 millims. (mean of 736-759), 22.8 77.2
In the last observation, or that with the greatest pressure (747
millims), the oxygen is reduced to 22.8 per cent. and the hydrogen
ON TEIE MOLECULAR MOBILITY OF GASES. 225
increased to 77.2 per cent of the diffused mixture, showing a consider-
able separation. The mixed gases appear to make their way through
the graphite plate independently, each following its own peculiar rate
of diffusion.
But it is only under the aspiration of a complete vacuum that the
separation can attain its maximum, and reach the full difference that
may exist between the special diffusibilities of the two gases. The
reason is that while we have the original mixture on both sides of the
plate, and of equal tension, the gases are not at rest, but diffusion is pro-
ceeding as actively through the plate in opposite directions, as if the gases
were different or the tension unequal on the two sides. This is a con-
dition of the molecular mobility of gases (p. 212). The tension therefore
being supposed to differ by 100 millims, only, as when the gas above
the plate was of 759 millims. tension, and below of 659 millims. (in the
first experiment of the last series), then 100 volumes only out of 759 of
the mixture are subject to separation. But while these 100 volumes
press through they are accompanied by 659 volumes of unchanged
mixture. The latter 659 volumes are replaced by an equal bulk of
unchanged mixture diffused from below, so that the volumes are not
disturbed by this portion of the molecular interchange.
The amount of separation, then, attainable by transmitting a mixed
gas through a porous diaphragm by pressure will be in proportion to the
pressure—that is, to the inequality of tension on different sides of the
diaphragm.
Oxygen and Nitrogen.—The separation of the gases of the atmosphere
by transmission through the graphite plate has a peculiar interest.
In an experiment resembling those last described, atmospheric air
was swept over the upper surface of a graphite plate having a thickness
of 2 millims. The gas that penetrated into the vacuum contained, as
was to be expected, the lighter and more diffusible constituent in excess.
It gave by the pyrogallic acid and potash process of Liebig,
Oxygen, . & * ſº e 20
Nitrogen, . o e & ge 80
This was an increase in the nitrogen of quite 1 per cent. ; for air, ana–
lysed for comparison at the same time and in the same manner, gave
oxygen 21:03 and nitrogen 78-97.
It may be legitimately inferred from the last experiment, that if
pure hydrogen in a diffusiometer were allowed to diffuse into the atmo-
sphere through a porous plate, the portion of air which then enters the
diffusiometer should also have its composition disturbed. A diffusion
of hydrogen through a graphite plate was interrupted before completion.
The air which had entered was found to consist of
P
226 ON THE MOLECULAR MOBILITY OF GASES,
, Oxygen, ſº wº * & 1977
Nitrogen, tº e * * 80-23
100'00
The increase of nitrogen is 1:23 per cent.
While the nitrogen is increased and the oxygen diminished in the
air which makes its way under pressure through the graphite, the con-
verse effect must be produced on the air left behind. But the latter
result of atmolysis cannot be made apparent without a change in the
mode of experimenting.
With the view of effecting an increase in the proportion of oxygen,
a volume of air, confined in a jar suspended over mercury, was allowed
to communicate through a graphite plate of 2 millims. in thickness,
with a vacuum sustained by means of an air-pump, the gauge being
about 1 inch only below the height of the barometer during the whole
time of experimenting.
The jar containing the air to be atmolysed was formed of a plain
glass cylinder, open at both ends, and about 400 millims, in height
(1575 inches). The upper end was closed by a thick plate of gutta
percha cemented on. This plate was itself penetrated by a wide glass
tube, descending about an inch into the jar. The last tube carried the
graphite disc, which was 27 millims. (1:04 inch) in diameter, sufficient
to close the lower end of the tube upon which it was cemented. The
other or upper end of the same tube was fitted with a cork and quill
tube, and was put into communication with a large bell jar upon the
plate of the air-pump.
The permeation was slow, owing to the unusual thickness of the
graphite plate, occupying three hours to drain away one-half of the
original volume of air in the jar. The air remaining behind in the jar
was examined in a series of experiments, in which the original volume
was reduced to one-half, one-fourth, one-eighth, and one-sixteenth.
The residual air, reduced to one-half, gave in two experiments 21:4
and 21:57 per cent of oxygen, the air of the atmosphere being by the
same analytical process 21 per cent.
Reduced to one-fourth of its volume, the residual air gave, in two
experiments, 21.95 and 22:01 per cent of oxygen.
Reduced to one-eighth of its volume, the air gave 22:54 per cent of
oxygen. -
Reduced to one-sixteenth of its volume, the air gave 23:02 per cent.
of oxygen. The proportion of oxygen had therefore increased about
one-tenth in the last experiment, where the effect is greatest.
When the numbers are compared, it appears that by a reduction to
half its volume the air gains about one-half per cent of oxygen; when
ON THE MOLECULAR MOBILITY OF GASES. 227
this last air is reduced to one-half again, another half per cent of oxygen
is gained, and so on—the gain in the proportion of oxygen increasing
in an arithmetical ratio, while the volume of air is diminished in a
geometrical ratio, or as the powers of the number 2.

Reduction of 1 volume of air. o: º
To 1 volume..................... 2] O
To 0-5 volume..................... 21'48 0-48
To 0-25 volume..................... 21-98 O'98
To 0-125 volume..................... 22°54 1'54
To 0.0625 volume..................... 23:02 2.02
The densities of oxygen and nitrogen approach too nearly to admit
of any considerable separation being effected by this method. The
density of oxygen being taken as 1, that of nitrogen is 0.8785. The
Square roots of these numbers are 1 and 0.9373, which are inversely
as the diffusive velocity of the two gases.
Diffusive velocity.
Oxygen, * * º º 1
Nitrogen, . tº e tº 1-0669
The velocity of nitrogen therefore exceeds that of oxygen by about
6.7 per cent. Hence by a simple diffusion of a whole volume of air the
oxygen could only be increased 67 per cent., according to theory. In
experiments such as the preceding only one-half of the volume of the
air is diffused, and consequently only one-half of the stated amount
of concentration of oxygen could possibly be produced at each step.
About three-fourths of the theoretical separation is actually obtained,
although the apparatus works at an obvious disadvantage from the air
within the jar being at rest.
This diffusive method of separation recalls the original observation
of Döbereiner on the escape of hydrogen gas from a fissured jar standing
over water, which will always hold its place in scientific history as the
starting-point of the experimental study of gaseous diffusion. That
observation proved to be an instance of double diffusion, air entering
the jar by the fissure at the same time that hydrogen escaped by it—
although, as Döbereiner looked upon the phenomenon, it was more akin
to single diffusion or the passage of gas in one direction only."
The atmolytic power of other diffusing plates was tested, besides the
artificial graphite. *
The barometrical diffusiometer already described was closed by a
1 Annales de Chimie, 1825.
228 ON TEIE MOLECULAR MOBILITY OF GASEs.
plate of red unglazed earthenware 4 millims, in thickness, which was
attached to the glass by resinous cement.
Dry air was swept over the upper surface, as in operating with the
graphite plate. With a mercurial column of 340 millims, falling to
200 millims, the air which entered was found to contain 79-45 per cent,
of nitrogen, instead of 79. With a column of mercury, maintained at
508 millims, in the tube, the air entering contained 79-72 nitrogen, and
with a column beginning at 761 millims, the full barometrical height,
and falling to 679 millims, in seven minutes, the air entering contained
80-21 nitrogen. This is a full degree of separation, exceeding 1 per
cent, while the time was greatly shorter than with graphite. Thermo-
meter 19°5 C. e
With a diffusing plate of gypsum (stucco) 10 millims. in thickness,
the proportion of nitrogen was also increased, although less considerably
than with biscuitware. The standard proportion of nitrogen observed
in atmospheric air being 78.99 per cent, the air drawn into the diffusio-
meter was as follows:—
Proportion of nitrogen per cent.
In air entering over column of 330—200 millims, mercury, . 79.26
In air entering over column 508 millims., {º tº e g 79-32
ſn air entering over column 761–685 millims., . º & 79-53
In air entering over column 761–685 millims., . ge * 79.69
The separation is sufficiently decided, and is certainly remarkable
considering the comparatively loose texture of the stucco plate. The gas
entered in the two last experiments in about one minute, which appears
too rapid a passage, and not to be attended with increased separation,
compared with the immediately preceding experiment, in which the
pressure was less and the passage of the gas proportionally slower. In
all such highly porous plates, we have always to apprehend the passage
of a large proportion of the gas in the manner of Capillary transpiration,
where no separation takes place. .
It may be concluded that all porous masses, however loose their
texture, will have some effect in separating mixed gases moving through
them under pressure. The air entering a room by percolating through
a wall of brick or a coat of plaster will thus become richer in nitrogen,
in a certain Small measure, than the external atmosphere.
The Tube Atmolyser.
In the application of diffusion through a porous septum to separate
mixed gases, as a practical analytical method, it is desirable that the
process should be more rapid than it can be made with the use of
graphite and other diffusing-plates of Small size, and also that the
process should if possible be a continuous one. Both objects are
ON THE MOLECULAR MOBILITY OF GASEs. 229
"-
e
>
:
==
attained in a considerable degree by adapting a tube of porous earthen-
ware to the purpose. Nothing has been found to answer better than
the long stalk of a Dutch tobacco-pipe used as the porous tube. A tube
of this description, about two feet long and having an internal diameter
of 2.5 millims, is fixed by means of perforated corks within a glass or
metallic tube, a few inches less in length and about 1% inch in diameter
(e, i fig. 8), as in the construction of a Liebig condenser. A second
Quill tube (v) is inserted in one of the end corks, and affords the means
of communication between the annular space and the vacuum of an air-
pump. The external surface of the corks, and of those portions of the
pipe-stalk which project beyond the enclosing tube, should be coated
with a resinous varnish, to render them impermeable to air. Now, a
good vacuum being obtained within the outer tube, and sustained by
the action of an air-pump, the mixed gas is made to enter and traverse
the clay tube. More or less of gas is drained off through the porous
walls and pumped away, while a portion courses on and escapes by the
FIG. 8.
s=
Eº:
s
==
-:E---
*º-
zº=
/*Eºſ:~-
E-
5-
#:
-----------
— —-==-
E
F
==
A. - - -- g|W
other extremity of the clay tube, where it may be collected. The stream
of gas diminishes as it proceeds, like a river flowing over a pervious bed.
The lighter and more diffusive constituent of the mixed gases is drawn
most largely into the vacuum, leaving the denser constituent, in a more
concentrated condition, to escape by the exit end of the clay tube. The
more slowly the mixed gas is moved through that tube, the larger the
proportion of light gas that is drained off into the vacuum, and the
more concentrated does the heavy gas become. The rate of flow of
the mixed gas can be commanded by either discharging it from a gas-
holder, or drawing it into a gas-receiver, in either case by a regulated
pressure. -
To observe the effect of a more or less rapid passage through the
tube atmolyser, the impelling pressure was varied so as to allow a con-
stant volume of half a litre of atmospheric air to pass through and be
collected in different periods of time. The clay tube used in these
particular experiments was not a tobacco-pipe, but a wide unglazed
tube about 431 millims. (17 inches) long and 19 millims. (0.75 inch) in




230 ON THE MOLECULAR MOBILITY OF GASES.
internal diameter. It was required to place so wide a tube in a
vertical position, and to admit the air by the upper and draw it off by
the lower extremity of the tube. The proportion of oxygen in the half-
litre of air collected was as follows:—

Oxygen per cent
Lxperiment 1, Experiment 2. - Mean.
When collected in 1 minute ... 21:00 & º º tº e ſº
When collected in 13 minutes... 22:33 22-25 22:29
When collected in 75 minutes... 22-77 23:02 22.89
When collected in 120 minutes... 23-25 23-22 23:23
When collected in 304 minutes... 23'54 23:51 23-53
The proportion of oxygen in the air circulated appears thus to increase
with the slowness of its passage through the tube atmolyser. The pro-
portion of air drawn into the air-pump vacuum must be very large
when the time is protracted; but the additional concentration of
Oxygen appears Small. -
The preceding observations being made by means of a porous tube
which may be considered wide and of considerable capacity with refer-
ence to its internal surface, the experiment was varied by substituting
a porous tube about eight times as long, very narrow, and therefore of
small internal capacity. This second atmolyser was composed of
twelve ordinary tobacco-pipe stems, each about 10 inches in length and
of 1.9 millim. internal diameter, connected together by vulcanized
caoutchouc adapters so as to form a single tube. Having flexible
joints, the tube was folded up and placed within a glass cylinder that
could be exhausted. Air was then circulated through this atmolyser
by the pressure of several inches of water. The instrument appeared
to work with most advantage when the air delivered at the exit-tube
amounted to about one-fourth of a litre per hour. A volume of 268
cubic centimetres, which had circulated in one hour, was found to con-
tain 24:37 per cent. of oxygen. The current was then made slower, so
that only 108 cub. centims. of gas passed and were collected in one
hour, but with little further concentration of the oxygen. The result,
however, is interesting as being the highest concentration of oxygen yet
obtained by an instrument of this kind. The air collected was com-
posed of -
Oxygen, e p º 24°52
Nitrogen, e o to 75°48
100'00
ON THE MOLECULAR MOBILITY OF GASES. 231
The increase of oxygen is 3.5 per cent. ; that is an increase of 16-7 upon
100 oxygen originally present in the air.
With the single pipe-stalk, 24 inches long, first described, the
oxygen of atmospheric air was concentrated about 2 per cent. when one
litre was transmitted in one hour. Of 450 cub. centims. of air collected
in that time, the composition proved to be
Oxygen, º e e 23:12
Nitrogen, º º tº 76-88
100'00
About 9 litres were drawn into the vacuum at the same time.
The separation of the gases of atmospheric air is a severe trial of the
powers of the atmolyser, owing to the small difference in the specific
gravities of these gases. But where a great disparity in density exists,
the extent of the separation may become very considerable.
Several experiments were made upon a mixture of equal volumes of
oxygen and hydrogen carried through the single tube atmolyser, 24
inches in length.
1. Of the mixture described, 7.5 litres entered the tube and 0°45
litre was collected in one experiment. The mixture was composed as
follows:
Oxygen. Hydrogen.
Before traversing the atmolyser, 50 + 50
After traversing the atmolyser, 92.78 + 7:22
2. In another similar experiment, 14 litres of the mixed gas entered
the tube and 0:45 litre was delivered in a period of two hours. The
result was—
Oxygen. Hydrogen.
Before traversing the atmolyser, 50 + 50
After traversing the atmolyser, 95 + 5
Here the proportion of hydrogen is reduced from 50 to 5 per cent.
3. Of the explosive mixture, consisting of 1 volume oxygen and 2
volumes hydrogen, 9 litres were transmitted and 0:45 litre collected in
one hour. The change effected was found to be as follows:—
oxygen. Hydrogen.
Before traversing the atmolyser, 33-33 + 66'66
After traversing the atmolyser, 90.7 -H 9.3
The result in such experiments is striking, as the gas ceases to be
explosive after traversing the porous tube, and a lighted taper burns in
it as in pure oxygen. A mixture of oxygen and hydrogen is not explo-
sive till the hydrogen rises to 11 per cent.
To illustrate the analogy of diffusion into a vacuum with diffusion
232 ON THE MOLECULAR MOBILITY OF GASES.
into air, the outer glass tube of the diffuser was now withdrawn, and
the porous tube of the instrument was exposed directly to the air of the
atmosphere. A mixture of equal volumes of oxygen and hydrogen was
again transmitted at the same rate of velocity as in experiment 1.
The gas atmolysed and collected was found to consist of
Oxygen, tº * © o 51°75
Hydrogen, . © * ſº 5-47
Nitrogen, • & © g 42.78
100'00
And may be represented as containing
Oxygen, & & º tº 40°38
Hydrogen, . * © © 5'47
Air, . . . . . 54°15
100'00
A nearly similar concentration of the oxygen of the mixed gas is here
observed as appeared in experiment 1; but the gas collected is now
diluted with air which has entered by diffusion. The external air
manifestly discharges the same function in the latter experiment which
the air-pump vacuum discharged in the former experiment. .
Interdiffusion of Gases—double diffusion.
The diffusiometer was much improved in construction by Professor
Bunsen, from the application of a lever arrangement to raise and depress
the tube in the mercurial trough ; but the mass of stucco forming the
porous plate in his instrument appears too voluminous, and, from being
dried by heat, is liable to detach itself from the walls of the glass tube.
The result obtained of 3-4 for hydrogen, which diverges so far from
the theoretical number, is, however, no longer insisted upon by that
illustrious physicist. It is indeed curious that my old experiments
generally rather exceeded than fell short of the theoretical number for
hydrogen; W0-06926= 37994. With stucco as the material, the cavi-
ties existing in the porous plate form about one-fourth of its whole
bulk, and affect sensibly the ratio in question according as they are or
are not included in the capacity of the instrument. Beginning the
diffusion always with these cavities, as well as the tube, filled with
hydrogen, the numbers now obtained with a stucco plate of 12 millims.
in thickness and dried without heat, were 3783, 3:8, and 3.739 when the
volume of the cavities of the stucco is added to both the air and hydro-
gen volumes diffused; and 3.931, 3-949, and 3883.when such addition
is not made to these volumes. The graphite plate, on the other hand,
ON THE MOLECULAR MOBILITY OF GASES. 233
being very thin, and the volume of its pores too minute to require to be
taken into account, its action is not attended with the same uncertainty.
With a graphite plate of 2 millims. in thickness, the number for hydro-
gen into air was 3.876, instead of 38; and for hydrogen into oxygen
4:124, instead of 4. With a graphite plate of 1 millim. in thickness,
hydrogen gave 3.993 to air 1. With a plate of the same material 0:5
millim. in thickness, the proportional number for hydrogen to air rose
to 3.984, 4,068, and 4'067. An equally considerable departure from
the theoretical number was observed when hydrogen was diffused into
oxygen or into carbonic acid, instead of air. All these experiments were
made with dry gases and over mercury. It appears that the numbers
are most in accordance with theory when the graphite plate is thick,
and the diffusion slow in consequence. If the diffusion be very rapid,
as it is with the thin plates, something like a current is possibly formed
within the channels of the graphite, taking the direction of the hydrogen
and carrying back in masses a little air, or the slower gas, whatever it
may be. I cannot account otherwise for the slight predominance which
the lighter and faster gas appears always to acquire in diffusing through
the porous septum.
Interdiffusion of Gases without an intervening septum.
The relative velocity with which different gases diffuse is shown by
the diffusiometer, but the absolute velocity of the molecular movement
cannot be ascertained by the same instrument. For that purpose it
appears requisite that a gas should be allowed to diffuse into air through
a wide opening.
In certain recent experiments, a heavy gas, such as carbonic acid,
was allowed to rise by diffusion into a cylindrical column of air, pretty
much as the saline solution is allowed to rise into a column of water in
my late experiments upon the diffusion of liquids. This method of
gaseous diffusion appears to admit of considerable precision, and deserves
to be pursued further. A glass cylinder of 0.57 metre (22:44 inches) in
height had the lower tenth part of its volume occupied with carbonic
acid, and the upper nine-tenths with air, in a succession of experiments:
thermometer 16° Cent. After the lapse of a certain number of minutes,
the upper tenth part of the volume was drawn off from the top of the
jar and examined for carbonic acid. Before the carbonic acid appeared
above, it had ascended, that is, it had diffused a distance of 0.513 metre,
or rather more than half a metre. After the lapse of five minutes, the
carbonic acid so found in two experiments amounted to 0-4 and 0.32
per cent. respectively. In seven minutes, the carbonic acid observed
was 1.02 and 0.90 per cent.; mean 0.96 per cent. The effect of diffu-
234 ON THE MOLECULAR MOBILITY OF GASES.
sion is now quite sensible, and it may be said that about 1 per cent.
of carbonic acid has diffused to a distance of half a metre in seven
minutes. -:
A portion of carbonic acid has therefore travelled by diffusion at an
average rate of 73 millims, per minute. It may be added that hydrogen
was found to diffuse downwards, in air contained in the same cylindrical
jar, at the rate of 350 millims. per minute, or about five times as rapidly
as the carbonic acid ascended. In these experiments the glass cylinder
was loosely packed with cotton wool, to impede the action of currents
in the column of air; but this precaution was found to be unnecessary,
as similar results were afterwards obtained in the absence of the cotton.
To illustrate the regularity of the results, I may complete this statement
by exhibiting the proportion of carbonic acid found in the upper stratum
already referred to, after the lapse of different periods of time.
Carbonic acid per cent.
Experiment 1. Experiment 2. Mean.
After 5 minutes ...... 0.4 0.32 0.36
After 7 minutes ...... 1.02 0-90 0.96
After 10 minutes ...... l'47 l'56 1.51
After 15 minutes ...... l'70 I '68 I-69
After 20 minutes ...... 2-4.1 2-69 2-55
After 40 minutes ...... 5-60 5-15 5-37
After 80 minutes ....., 8°68 8-82 8.75

—w-
In eighty minutes the proportion of carbonic acid had risen to 875
per cent., 10 per cent. being the proportion which would indicate the
completion of the process of diffusion.
The same intestine movement must always prevail in the air of the
atmosphere, and with even greater velocity, in the proportion of 1 to
1°176, the relative diffusion-ratios of carbonic acid and air. It is cer–
tainly remarkable that in perfectly still air its molecules should spon-
taneously alter their position, and move to a distance of half a metre,
in any direction, in the course of five or six minutes. The molecules of .
hydrogen gas disperse themselves to the distance of a third of a metre
in a single minute. Such a molecular movement may become an
agency of considerable power in distributing heat through a volume of
gas. It appears to account for the high convective power observed in
hydrogen, the most diffusive of gases.
ON THE ABSORPTION OF GASES BY COLLOID SEPTA. 235
XVII.
ON THE ABSORPTION AND DIALYTIC SEPARATION OF
GASES BY COLLOID SEPTA."
From Phil. Trans. 1866, pp. 399-439.
PART I.—ACTION OF A SEPTUM OF CAOUTCHOUC.”
[MIXED gases must differ considerably in diffusibility and specific
gravity, in order to separate from one another to any great extent in
their molecular passage into a vacuum through a porous septum, such
as the plate of graphite or the walls of an unglazed earthenware tube.
The agency of atmolysis is therefore very limited in parting the oxygen
and nitrogen of atmospheric air—gases which differ so little in density
from each other.
Substances existing in the liquid condition often admit of being
separated much more fully than gases, by the proper use of dialytic
septa in addition to the agency of liquid diffusion.]
Evidently there cannot be anything like the dialysis of gases; for
dialysis involves the passage of a substance through a septum composed
of soft colloid matter, such as must be wholly destitute of open channels,
and therefore be impermeable to gas as such. Still liquid dialysis may
be imported into the treatment of gases, in consequence of the general
assumption of liquidity by gases when absorbed by actual liquids or by
soft colloids. Water when charged with air holds liquid oxygen and
nitrogen in solution; and the latter substances then become amenable
to liquid diffusion and dialysis, and so penetrate animal membrane in
the act of respiration.
[A considerable time ago Dr. Mitchell of Philadelphia discovered a
power in gases to penetrate india-rubber in a thin sheet, or in the form
of the little transparent balloons which Dr. Mitchell was the first to
prepare from that substance. He remarked in particular that such bal-
loons collapse sooner when inflated with hydrogen than with atmo-
spheric air, and still sooner when filled with carbonic acid; and he
connected the latter fact with the observation that a solid piece of
india-rubber is capable of absorbing its own volume of carbonic acid
1 Received by the Royal Society June 20,-Read June 21, 1866.
* Several paragraphs have been crossed in pencil on the author's copy, but no
sufficient authority was found for differing from the original version in the Philos.
Trans., a few words inserted, it is believed by the author, to explain the meaning being
excepted. The paragraphs crossed are placed within brackets. º
236 ON THE ABSORPTION AND
when left long enough in the pure gas. By means of a proper arrange-
ment, Dr. Mitchell found that various gases passed spontaneously
through the caoutchouc membrane, when there was air on the other side,
with different degrees of velocity. “Ammonia transmitted in 1 minute
as much as sulphuretted hydrogen in 23 minutes, cyanogen in 3%
minutes, carbonic acid in 5% minutes, nitrous oxide in 63 minutes,
arsenietted hydrogen in 27# minutes, olefiant gas in 28 minutes,
hydrogen in 37% minutes, oxygen in 1 hour and 53 minutes, carbonic
oxide in 2 hours and 40 minutes.” The rate of penetration of nitrogen
appeared to be even slower than that of carbonic oxide."
It will be observed that those gases penetrate most readily which
are easily liquefied by pressure, and which are also “generally highly
soluble in water or other liquids.” The memoir of Dr. Mitchell was
ably commented upon, shortly after its publication, by Dr. Draper of
New York, who also added many new observations on the passage of
both gases and liquids through membranous septa. These early Speeu-
lations, however, lose much of their fitness from not taking into account
the two considerations already alluded to, which appear to be essential
to the full comprehension of the phenomena—namely, that gases undergo
liquefaction when absorbed by liquids and such colloid substances as
india-rubber, and that their transmission through liquid and colloid
septa is then effected by the agency of liquid and not gaseous diffu-
sion. Indeed, the complete suspension of the gaseous function during
the transit through colloid membrane cannot be kept too much in
view.
Dr. Mitchell was led to infer, from a single casual observation, that
rubber expands in volume when carbonic acid is absorbed—a result to
be expected from the porosity of the solid mass, then assumed in expla–
nation of the penetrativeness of gaseous fluids. But on placing 50
grms. of thin sheet rubber, 0.6 millim. in thickness, in carbonic acid
over mercury, it was seen that the rubber gradually absorbed 0-78
volume of gas in twenty-four hours at 15°, of which 0.7 yolume was taken
up in the first hour. The mass of rubber was previously measured
with care by the displacement of mercury in a specific-gravity bottle,
and again when the rubber was charged with carbonic acid; it gave
the same displacement of mercury within a hundredth of a gramme.
No measurable change in the bulk of the rubber, therefore, had occurred.
It may be added that the absorbent power of vulcanized rubber for
* “On the Penetrativeness of Fluids,” by J. K. Mitchell, M.D., Philadelphia Journal
of Medical Sciences, vol. xiii. p. 36; or Journal of the Royal Institution, vol. ii. pp. 101
and 307; London, 1831.
See also Treatise on the Forces which produce the Organization of Plants, with an
Appendix containing several Memoirs on Capillary Attraction, Electričity, and the
Chemical Action of Light, by John William Draper, M.D.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 237
-carbonic acid appears to be less than that of rubber in its natural state,
being found only 0.57 volume in a comparative experiment.]
The penetration of rubber by gases may be illustrated by their
passage into a vacuum, as well as into an atmosphere of another gas, in
the old experiments of Dr. Mitchell. The diffusiometer, consisting of
a plain glass tube of about 22 millims, in diameter and nearly a whole
metre in length, closed at the upper end by a thin plate of stucco, and
open below, is taken advantage of in such experiments. A thin film of
rubber from a small balloon is stretched over the upper end of the tube,
where it is supported by the stucco plate, bound with copper wire, and
cemented at the edges in contact with the glass with gutta percha
softened by heat. If the tube be now filled with mercury and inverted,
a Torricellian vacuum is obtained above, into which the air of the
atmosphere gradually penetrates, passing through the film of rubber
and depressing the mercurial column in the tube. In order to compare
the penetration of different gases, a hood of thick vulcanized rubber,
provided with a small entrance and exit tube for gas (such as is often
used in gas experiments), is placed over the upper end of the diffusio-
meter described, and cemented to it by means of fused gutta percha.
The gas to be operated upon can thus be conveyed from the apparatus
in which it is generated, or from a gasometer in which the gas is stored,
into the hood or upper chamber of the diffusiometer, and the excess of
gas supplied be allowed to escape into the atmosphere by the exit-tube
of the hood. The stucco plate used as a support to the film of rubber
is so highly porous as not to add sensibly to the resistance experienced
by the gases in passing through the rubber, and, having no absorbent
power of its own, may be left entirely out of consideration.
A comparison was made of the passage through the rubber film, on
the same day, of carbonic acid, hydrogen, oxygen, and nitrogen; barom.
77.3 millims, therm. 23° to 23°5 C. The time during which the mer-
curial column fell 25 millims in the diffusiometer, namely, from 748 to
723 millims, was noted in seconds, and also from 723 to 698 millims.
The gases were all carefully dried.
TABLE I.—Passage of Carbonic Acid in seconds.

Height of mercurial
co., iii.er. Experiment I. Experiment 2. Experiment 3.
millims.
748 Z/ Z/ Z
723 107 102 102
698 143 138 138
250 240 240
238
ON THE ABSORPTION AND
The passage of carbonic acid thus exhibited will be found to be
considerably more rapid than those of hydrogen and the two other gases
which follow :-
TABLE II.

Height
of mercurial
Column in
diffusiometer.
Passage in seconds,
of Hydrogen.
of Oxygen.
of Nitrogen.
Experiment 1.
Experiment 2.
Experiment l.
Experiment 2.
Experiment 1.
Experiment 2.
millims.
748
723
698
// // // M/
277 270 545 554
316 323 727 722
593 593 1272 1276
1413 1428
1832 1850
3245 3278
A single experiment, made at the same time on the passage of
atmospheric air, gave times of 1318" and 1524" for the two stages, or
2842" for the whole fall. The time of penetration of air is therefore
intermediate between that of oxygen and nitrogen entering singly.
Although such numbers do not possess the close uniformity which
appears in diffusion and transpiration experiments, for reasons which
will immediately appear, yet they give a comparative estimate of the
penetrativeness of the different gases through rubber, which may be
available for some practical purposes.
Upon another occasion carbonic oxide and marsh-gas (CHA) were
introduced into the comparison, the same film of rubber remaining upon
the diffusiometer; barom, 768 millims, therm. 19°5 C.
TABLE III.
Passage in Seconds,
Height
of mercurial
column in of Carb, oxide. of Hydrogen. of Carbonic acid. of Marsh-gas (CH4).
diffusiometer.
Expt. 1. Expt. 2. Expt. 1. Expt. 2. Expt. 1. Expt. 2 | Expt. 3. Expt. 1. Expt. 2.
millims.
748 £/ Æ // MM AV M/ M/ Z/ f/
723 1620 | 1631 || 435 434 125 119 117 803 821
698 1920 | 1924 505 511 170 169 172 1009 1045
3540 || 3555 | 940 945 295 288 289 1812 1866

The results may be summed up by deducing the times in which a
constant volume of the various gases is transmitted by the rubber, the
time of passage of carbonic acid, which is the shortest, being taken as
unity for the sake of comparison.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 239
Penetration of rubber by equal volumes of Gas.
* Time.
Carbonic acid, ſº o e º e I
Hydrogen, . • tº tº º º 2'470
Oxygen, º º º e º e 5°316
Marsh-gas (CHA), . & wº -> º 6'325
Atmospheric air, . º ſº © . 11'850
Carbonic oxide, º º e º º 12:203
Nitrogen, º © e º e 13:585
Or, with the times taken equal, the volume of each gas which passes
then expresses the velocity of penetration.
Penetration of rubber in equal times.
Velocity.
Nitrogen, . - * º º ſº 1
Carbonic oxide, º º de º tº 1 : 113
Atmospheric air, . ſº * º e 1 149
Marsh-gas (CH4), . e & - • 2-148
Oxygen, º A g & -> * 2°556
Hydrogen, . º * ë º * 5-500
Carbonic acid, º e º º e 13'585
Considering the circumstances in which the gases pass through the
sheet of rubber into a vacuum, it is not to be expected that any relation
will be found among the preceding numbers, as between the coefficients
of diffusion in gases. The first absorption of the gas by rubber must
depend upon a kind of chemical affinity subsisting between the material
of the gas and substance of rubber, analogous to that attraction which
is admitted to exist between a soluble body and its solvent, conducing
to solution. Carbonic acid being Soluble in ether and volatile oils, it
is not wonderful that it is also dissolved by the hydrocarbons of rubber.
The rubber being wetted through by the liquefied gas, the latter comes
to evaporate into the vacuum, and reappears as gas on the other side of
the membrane. Now it is known that such evaporation is the same
into a vacuum and into another gas, being equally gas-diffusion in both
circumstances. It is not indispensable, therefore, to have a vacuum on
one side of the rubber membrane as in the experiments detailed above.
A foreign gas will answer for the vacuum, as in the experiments of
Dr. Mitchell.
The numbers for the velocity of passage of the different gases in the
last Table may be taken also as representing not remotely the relative ab-
sorption and liquefaction of the various gases by the substance of rubber.
The passage of gases through rubber is also illustrated by the rapid
collapse of the little balloon when filled with carbonic acid gas, or even
with hydrogen, or with marsh-gas, as compared with atmospheric air.
The converse fact is observed when the inflating gas is pure nitrogen :
240 ON THE ABSORPTION AND
then the balloon is found to become further distended after a few hours,
in consequence of more oxygen entering from the atmosphere without,
than of nitrogen escaping from the balloon during the same time; while
the composition is being equalized on both sides of the membrane, and
the gas within the balloon is finally of the same composition as the
external air. A rubber balloon filled with nitrogen was found, when
roughly gauged, to increase in diameter from 132 to 136 millims. in the
course of twenty-four hours. On the other hand, a balloon filled with
pure oxygen fell in the same time from 150 to 113 millims, in diameter.
[Inforty-eight hours a balloon filled with hydrogen 154 millims, in
diameter contracted to 87 millims., and then contained 250 cub. centims.
gas, of which 53 cub. centims, were absorbed by pyrogallic acid and
potash, showing the presence of 21.2 per cent. of oxygen, or sensibly
the same proportion as in the external atmosphere.
If the upper end of a diffusiometer be closed by a thin sheet of
rubber, and the instrument standing over mercury be filled with
hydrogen gas, a contraction is observed to take place slowly, but to a
greater extent ultimately than could be due to the diffusion of hydrogen
as a gas. Beginning with 249 volume divisions of gas in the tube, the
rise of the mercurial column, or reduction of volume, was 1-5 division
in the first hour, 1.5 division in the second hour, 2-0 in the third hour,
3 in the fourth hour, and 51 divisions in the first twenty-four hours
taken together. Then the rise in the following successive days was
42, 59, 37, 29, 13, 5, 1, 0:5, 0.5 (in two days), and 0:0, the original
volume of 249 volumes of hydrogen being finally replaced by 53 volumes
of atmospheric air; barom, 747 millims, therm. 21°-1. The ultimate
replacing volumes are here as 1 to 4-7. In gas diffusion they are as
1 to 3-8.]
A balloon filled with air subsided in forty-eight hours from 150 to
147 millims. in diameter, from the mechanical effect alone of the
elasticity of the membrane in compressing the enclosed gas. These
little balloons vary from 0.75 to 1 grim. in weight. Supposing the
form to be truly spherical, a balloon of 150 millims. in diameter would
have a surface of 0-0706 Square metre (5'905 inches in diameter and
0.08454 Square yard of surface). Supposing the balloon to be 1 grim, in
weight, the thickness of the membrane will be # of a millim, with a
specific gravity = 1, or # of a millim, with a specific gravity = 0.93,
the admitted density of pure rubber. This last is a thickness of wºrs
of an inch, or it would require nearly 2000 such films, laid upon each
other, to form the thickness of a single inch. Yet such a film of rubber
appears to have no porosity, and to resemble a film of liquid in its
relation to gases—differing entirely in this respect from a thin sheet of
paper, graphite, earthenware, or even gutta percha, as will appear here-
DLALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 241
after. These last enumerated bodies appear all to be pervaded by open
channels or pores, sufficiently wide to allow gases to be projected through
by their own proper molecular movement of diffusion. But liquids and
colloids have an unbroken texture, and afford no opportunity for gaseous
diffusion. They form even in the thinnest film an impervious barrier
to gas.
The penetration of rubber is much affected by temperature, and
apparently in two different ways at the same time. An increase of
temperature no doubt renders all gases less easily liquefied by pressure,
and consequently less considerably absorbed by any liquid or colloid.
But such an influence of heat appears to be counteracted in rubber by
the tendency of that colloid to become more soft when heated, and to
acquire more of liquid and less of solid properties. Certainly the rubber
film becomes more and more permeable to gases as the temperature is
elevated, within a moderate range. This was distinctly observed in
operating with silk cloth varnished on one side with rubber, such as is
sold as a waterproof material. Without anticipating a detail of the
experiments, it may be stated in general terms that the same specimen
of silk varnished with rubber was penetrated by air from the atmo-
sphere passing into a vacuum, at the following rates per Square metre
of surface:–
At 4°C., by 0-56 cub. centim, of air in 1 minute.
At 14° C., by 2:25 3) 35
At 60° C., by 6:63 25 3}
The volumes of gas are all reduced to barom. 760 millims. and
therm. 20° C.
Such numbers are probably not strictly constant; for it appears
that the effect of temperature upon rubber is much influenced by the
length of time that the temperature is continued, the change in degree
of softness with change of temperature requiring hours, or even days,
fully to complete it. The rigidity of rubber under cold and its softening
under warmth are well known to take place in a slow and gradual
Iſla,Illelſ.
With the softening of rubber by heat, the retentive power of that
substance for gases appears to be modified. Soft rubber, first charged
with carbonic acid at 20°, and then made rigid by cold, appeared to lose
its carbonic acid, when afterwards freely exposed to air, less rapidly than
the same rubber equally charged but exposed from the first in its soft
condition. The quantity of carbonic acid retained in the former case
was 10-76 per cent, and in the latter 7:08 per cent. of the volume of the
rubber, after a similar exposure of forty-eight hours. This point,
although not sufficiently examined, is alluded to here on account of the
Q
242 ON THE ABSORPTION AND
analogy which appears to hold between rubber and the malleable metals
in a power to absorb a gas when they are softened by heat, and to
retain the same gas with great tenacity when they are afterwards made
rigid by cold. .
The condensation of oxygen gas by masses of solid rubber punched
out of a block was made the subject of observation, by placing 50 grms.
of that substance within a jar of oxygen standing over mercury during a
period of several days. From the rubber afterwards there was extracted,
by the action of a vacuum continued for twenty-one hours, 621 cub.
centims, of gas; of which 3-67 cub. centims. were oxygen, 0.14 carbonic
acid, and the remainder chiefly nitrogen. Taking the bulk of the rubber
at 53.8 cub. centims, the oxygen absorbed amounts to 682 per cent, of
the volume of the rubber. Oxygen then may be regarded as fully twice
as soluble in rubber as the same gas is in water at the Ordinary tem-
perature. No experiment was made at a higher temperature; but as the
penetrativeness of rubber is much increased by heat, the presumption is
that the solubility of gases in rubber is increased in the same degree.
More than one attempt was made to identify the presence of free
hydrogen in the substance of rubber after being kept in that gas for
some time before a positive result was obtained. The absorbed hydrogen
appears to be rapidly dissipated, owing to its extreme diffusibility as a gas.
Dialytic separation of Oaxygen from Atmospheric Air, (1) by means of
- other gases, (2) by means of a vacuum.
1. A balloon of rubber filled with hydrogen and exposed to the
atmosphere, gradually loses the form of gas, which is finally replaced
by a considerably smaller volume of air, presenting a deceptive resem-
blance to the diffusion of hydrogen gas into air. When the progress of
the entrance of air was observed at different stages of the exchange, it
appeared that after three hours, when the balloon had fallen from 150
to 128 millims. in diameter, the composition of its contents was —
Oxygen, • • 8'98 41-6
Nitrogen, . e 12'60 58'4
Hydrogen, . ſº 78'42
100:00 100.0
Setting aside therefore the hydrogen still remaining, the balloon
now contained a portion of a mixture of oxygen and nitrogen in the
proportion of 41.6 volumes of the former to 58.4 volumes of the latter.
This was the largest proportion of oxygen to the nitrogen observed; for
the former gas has a tendency to flow back again to the external atmo-
sphere when the hydrogen becomes Small in volume; and the proportion
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 243
of oxygen becomes eventually no higher than 21 per cent of the whole
gases remaining in the balloon, including the hydrogen. Thus after six
hours the proportion of oxygen was 33°63 to nitrogen 66°37 volumes,
and after twenty-four hours oxygen 2648 to nitrogen 73°52 volumes,
the hydrogen constantly diminishing at the same time.
The entrance by infiltration of atmospheric air into a balloon of
rubber inflated with carbonic acid gas brings us still nearer to a practical
dialytic separation, as the carbonic acid can be withdrawn entirely by
means of caustic alkali, after a certain time has elapsed, and the infiltered
air enriched with oxygen be dealt with by itself. A balloon containing
carbonic acid, when placed in the atmosphere, was reduced in four hours
from 160 to 90 millims. in diameter, and it had now acquired 199 cub.
centims. of gas not dissolved by alkali. This gas was capable of reviving
the combustion of wood burning without flame, and was found to consist of
Oxygen, . e - º 37-1 vols.
Nitrogen, . º * - 62.9 ,
100'0
To produce this concentration of oxygen, it is quite necessary that
the operation be interrupted at an early stage, as was done in the last
experiment; otherwise the oxygen diminishes again in proportion to the
nitrogen, falling at last to the normal proportion of 21 per cent. as in
the external air. [Thus a balloon inflated by carbonic acid to 150
millims. in diameter was found to lose nearly all its carbonic acid in
the course of twenty-four hours. It gave 150 cub. centims. of gas after
treatment with caustic potash. This was air of the composition,
Oxygen, . º º & º 22-6
Nitrogen, * tº o & 77°4
100'0
and exhibited therefore no material augmentation in the proportion of
oxygen.]
It may be inferred, from the familiar fact that air dissolved in water
contains So high a proportion as 30 per cent. of oxygen, that if carbonic
acid gas were divided from atmospheric air by a film of water, the
former gas would come to be charged through the film with air bearing
the same high proportion of 30 per cent. of oxygen. But it is not easy
to imitate this experiment unless the dividing film is supported by a
membrane of some sort. The air from the atmosphere, which entered a
fresh ox-bladder preserved humid and inflated with carbonic acid, was
found to possess 24-65 per cent. of oxygen to 75:35 of nitrogen, which
is but a small increase in the proportion of oxygen. But the thickness
of the membrane here was too great, and other circumstances of the
experiment were unfavourable.
244 ON THE ABSORPTION AND
A balloon of rubber inflated to 150 millims. in diameter with Carbonic
acid was submerged in water, at 22°C., for forty-eight hours. Only a
small portion of carbonic acid remained in the residual gas, which, after
being washed with potash, consisted of
Oxygen, e e & * 25-77
Nitrogen, º e © sº 74°23
100'00
2. With the colloid septum properly supported over a vacuous space,
as by a stucco plate in the diffusiometer covered by a film of rubber
(p. 237), a considerable separation of mixed gases can be effected. The
constituents of atmospheric air appear to be carried through a film of
rubber into a vacuum, nearly in the same relative proportion as the
same gases penetrate singly (p. 239). The velocities of nitrogen and
oxygen passing separately were observed to be as 1 to 2:556, and hence
by calculation,
Oxygen, 21 x 2.556 = 53.676 . . 40'46
Nitrogen, 79 x 1 = 79 e º 59'54
100-00
Hence air dialysed by the rubber septum should consist of 40°46
oxygen and 59:54 nitrogen in 100 volumes. Now air from the atmo-
sphere was found to enter the vacuum of the 48-inch diffusiometer-tube,
through a disk of rubber 22 millims, in diameter, to the amount of 3.48
cub. centims. in twenty-one hours, under the pressure of the atmosphere;
therm. 23° to 24°C. Of the 3:48 cub. centims, of gas so collected, 2 cub.
centims. were absorbed by pyrogallic acid and potash, representing 42:53
per cent. of oxygen in the dialysed air. Here the gas was transferred
from the diffusiometer for examination by depressing the diffusiometer
in mercury, and using a very narrow tube of rubber as a gas-siphon
communicating between the gas in the diffusiometer and a jar inverted
in the mercurial trough. The elastic tube is first filled with mercury,
and, being of considerable length, a portion of it is drawn repeatedly
through the fingers so as to throw the mercury and aspirated gas into
the collecting receiver. The transference of gases in such circumstances
may also be effected with much advantage by means of the vacuum-
tube invented by Dr. Hermann Sprengel, as will immediately be shown.
The process of dialytic separation by means of a rubber septum may
be varied in three points, (1) in the condition of the rubber septum,
which may be a film of rubber formed from caoutchouc varnish as well
as from distended sheet rubber; (2) in the nature of the support given
to the septum, which may be a backing of cotton cloth or of silk (com—
mon waterproof cloth prepared by means of caoutchouc varnish, in
short), as well as a plate of stucco, earthenware, or wood; and (3) in
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 245
the means had recourse to for sustaining a vacuum, or at least a con-
siderable degree of exhaustion, on one side of the dialytic septum, while
atmospheric air, or any other gaseous mixture to be dialysed, has access
to the other side of the same septum. Or the air to be dialysed may be
compressed on one side of the septum, and left of the usual tension on
the other side, inequality of tension on the two sides of the septum
being all that is required to induce penetration.
The pneumatic instrument of Dr. Sprengel (fig. 1) is peculiarly
applicable to researches of the present kind. Indeed, without the use
of his invention some parts of FIG. I.
this inquiry would have been
practically impossible.” The in-
strument was originally offered
by the inventor as the means of
producing a vacuum, or as an
air-pump. But by bending the
lower end of the straight fall-
tube, the instrument may be
further made to deliver gas into
a receiver, and be used with ad-
vantage as the means of trans-
ferring small volumes of gas from
One vessel to another.
While the mercury in the
funnel A is allowed to flow down-
ward into the barometer-tube CB,
of 2% millims, in diameter, by
relaxing the clamp upon the
adapter tube of rubber at C, a
connexion is also made with the
close receiver to be exhausted,
Such as an air-tight bag E, by
means of the branch tube a. The
air in E, gaining access to the
Torricellian vacuum, is swept on
by the falling mercury, and deli-
vered below into the small gas-
receiver R, previously filled with mercury and inverted over mercury in
the mortar B below. The principal difficulty in obtaining a good vacuum
in E by means of this apparatus arises from the necessity of joining the
glass tubes in more than one place by means of adapter tubes of rubber.
* Researches on the Vacuum, by Hermann Sprengel, Ph.D., Chemical Society's Journal,
ser. 2, vol. iii. p. 9 (January 1865).

246 ON THE ABSORPTION AND
The directions given by Dr. Sprengel on this point require to be closely
followed:—“The connexions between the glass tubes are made of well-
fitting black vulcanized caoutchouc tubing, sold under the name of French
tubing. This is free from metallic oxides, which render the tubing porous.
Besides this all these joints are bound with coils of copper wire, which is
easily accomplished with a pair of pliers.” The joints should also be
coated with gutta percha liquefied by heat, or with fused rubber. An
exhausting-syringe, or air-pump, may often be used with advantage to
begin the exhaustion, and to withdraw the greater bulk of the air, if the
receiver is large, the Sprengel tube being reserved to complete the
exhaustion. The vacuum appears to be as perfect as can be formed
in a barometer-tube filled with unboiled mercury, and to come within
1 millim. of the barometric gauge.
The following modifications of the experiment exhibit the dialytic
action of Caoutchouc in its various forms.
1. India-rubber between dowble cottom cloth vulcanized.
This was a common elastic carriage-bag 18 inches by 15. The
surface of both sides amounted to 0.3482 square metre. The bag was
pressed flat by the hands, and still further exhausted by means of
Sprengel's tube. After all the contents of the bag were extracted and
the collapse complete, the Sprengel tube began again to throw out air in
a slow but exceedingly regular manner. A small portion of Sawdust,
or of sand, introduced beforehand into the bag, appeared to be useful in
preventing the sides coming together too closely, but was not essential.
The air thus extracted from the bag in one hour amounted to 15-65
cub. centims, or sensibly 1 cubic inch; therm. 23° to 24° C. Such
dialysed air, from three successive experiments of one hour each, con-
tained 38, 40.3, and 41.2 per cent. of oxygen, the inferior proportion of
oxygen in the earlier experiments being no doubt due to a small residue
of undialysed air remaining in the bag before exhaustion. This dialysed
air rekindled glowing wood, so as to illustrate the direct separation of
oxygen gas from atmospheric air. For the purposes of combustion, it
may be viewed as air from which one-half of the inert nitrogen has been
withdrawn.
It will be convenient to express the permeability of the colloid sep-
tum with uniform reference to a square metre of area, and to an hour,
or to a single minute of time. Here, for a square metre of cloth, the
passage of air amounted to 44-95 cub. centims. (3 cubic inches nearly)
per hour, or to 0-749 cub. centim. per minute.
The view which the observation suggests of the nature of such an
air-tight fabric is, that it may be truly impenetrable to air when the
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 247
composition and tension of the air are the same on both sides of the
cloth; but it is penetrable when a vacuum or a reduced state of tension
is maintained on one side of the cloth and not on the other. The com-
pression of the air confined in a bag would no doubt have a similar
effect, and then the flow would be in an outward direction. But there
is no evidence of a porous structure in the varnished cloth. The gases
of atmospheric air would pass through actual openings according to the
law of gaseous diffusion, which favours the nitrogen or lighter gas, while
it is the oxygen which is found to pass through the material most
readily in these experiments. The imbibition of the liquefied gas by
the substance of the rubber, with the subsequent evaporation of this
liquid into the vacuum on the other side, is all the explanation required.
2. Vulcanized india-rubber tubing.
A stout caoutchouc tube with an external diameter of 13 millims.
(half an inch), an internal diameter of 9 millims, thickness of 2 millims,
and length of 3-658 metres (4 yards) was exhausted, one end being
closed and the other end connected with the Sprengel pump. The gas
collected in thirteen hours amounted to 11:25 cub. centims. ; therm. 20°
to 23° C. This gas contained 37.8 per cent. of oxygen. The gaseous
penetration is not great in so thick a tube, and there is reason to fear
the influence of gaseous diffusion to a small extent. The admission of
air would be equally sensible if the tube were occupied by coal-gas, or
any other foreign gas, instead of being vacuous. As the inner surface
of the tube amounted to 0-1034 Square metre and the passage of air to
0-8653 cub. centim. per hour, the passage for a square metre would be
8-37 cub. centims. per hour, or 0-14 cub. centim. per minute. The rate
of penetration through the tube-walls appears to be one-fifth of what
was found for the rubber cloth.
3. Sheet rubber, 1 millim. in thickness.
Although an increased thickness was no doubt attended by slow-
ness of passage, it was of interest to observe whether the proportion of
oxygen per cent might not at the same time be varied. The sheet used
was still, however, as thin as the manufacturer could succeed in cutting
from a solid cylinder of wrought rubber by the usual method. The
rubber was not vulcanized. The sheet of rubber was made into a bag
having 0-149 square metre (231 square inches) of surface, a double
thickness of felted carpet being placed within the folds of rubber. A
glass quill tube, cemented to the bag, communicated with the interior
of the cavity, and was connected at the other end with Sprengel's tube.
After the first exhaustion of the gaseous contents of the bag, for which
248 ON THE ABSORPTION AND
the aid of an exhausting syringe or air-pump is useful, air continued to
infiltrate through the sheet rubber, but very slowly. Of the dialysed
air 11:45 cub. centims, were collected in four hours. This air contained
41:48 per cent of oxygen, with a sensible trace of carbonic acid. The
penetration for a square metre amounts to 19.2 cub. centims, of air per
hour, or 0.32 cub. centim. per minute.
The same bag, left exhausted for eighteen hours, was found after-
wards to yield at once 4.1-6 cub. centims. of air, containing 40.3 per
cent. of oxygen, which had accumulated in the cavity of the bag; therm.
about 20° C. - *
From a larger bag of similar thin sheet rubber, having a surface of
640 square inches, distended by ten or twelve ounces of sawdust, 21:35
cub, centims. of dialysed air were obtained in one hour; barom. 761
millims, therm. 19°5 C. This dialysed air appeared to consist of
Oxygen, © . º. & tº 41-80
Carbonic acid, & gº tº 0°94.
Nitrogen, ſº e e tº 57.26
100'00
It does not appear, then, that the increased thickness of the rubber
septum tends to increase the proportion of oxygen in the dialysed air,
while this thickness causes the passage to be proportionally slower.
The oxygen appears to attain, but never to exceed, at 20° C., the pro-
portion of 4.1-6 to 58°4 nitrogen.
The thick rubber brings notably into view the carbonic aid of the
air. The small proportion of this gas in air is probably increased in all
experiments with the rubber septum, however thin. . It was observed to
rise so high in a small crowded room, as to negative the inflaming action
of the oxygen on Smouldering wood. But rubber appears to have a
power to charge itself gradually from atmospheric air with about half
per cent. of its volume of carbonic acid. This carbonic acid, accumu-
lated in thick sheet rubber, appears again to be carried on by the other
gases imbibed in a dialytic experiment. -
4. Thin Balloons of india-rubber.
These little balloons were made available for the dialytic passage of
air into a vacuum by filling them with sifted sawdust through a funnel,
an operation which requires some address. The balloon collapsed upon
the sawdust, which formed an interior ball, the sides of rubber still
retaining a thickness of about one-fiftieth of a millimetre. The rubber is
not vulcanized. Such a ball, of which the original rubber weighed 0.76
grm, still remained 95 millims, in diameter after the air was exhausted.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 249
It was found, when exhausted, to admit 19.6 cub. centims, of dialysed
air in forty-one minutes; barom. 579 millims, and therm. 19°C. The
same air possessed 41.32 per cent of oxygen. The ball had a surface of
0.0283 square metre, and it dialysed 0:48 cub. centim. of air in one
minute. For a square metre of surface this is a passage of 169 cub.
centims. per minute. The passage therefore is about fifty times faster
than through a sheet of rubber of 1 millim. in thickness, while the high
proportion of oxygen is sensibly the same. Such a ball was found to
dialyse air in the same manner for more than a month, if protected
from mechanical injury.
[Three such balls, each containing twenty-three ounces of sifted
sawdust, were made to act together, by connecting them with three
dependent branches from the same horizontal glass tube. The horizontal
tube was connected at one end with an ordinary air-pump, which pro-
duced a good vacuum by thirty or forty strokes of the piston. The
other end of the horizontal glass tube was attached to a good Sprengel
apparatus of the largest admissible size, constructed by Messrs. Elliot of
the Strand. It was found, however, that the dialysed air entered rather
more rapidly than it could be extracted by a single Sprengel apparatus.
This was at the rate of 5 cub. centims. in one minute ; therm. about
20° C. The dialysed air contained 40.5 per cent. of oxygen.]
The greatest amount of ačrial dialysis per square metre was obtained
by means of a rubber bag, larger than usual, and weighing 1-55 grim.
When filled with the sawdust and exhausted, this bag still remained of
143 millims, in diameter, and with a surface therefore of 0-0642 square
metre. The air which passed through amounted to 17:05 cubic centims.
in ten minutes; therm. about 20°. This air gave 407 per cent. of
oxygen. For a square metre of surface, this is the passage of 26-5 cub.
centims. per minute, the highest which has yet been observed.
[In the thin transparent envelope of the little balloon of rubber we
have a colloid substance in the most favourable form yet applied to the
dialysis of mixed gases. But there is still much room for improvement
in the mode of using the thin Septum in question. The balls are apt
to contract considerably, owing to their elasticity, in the operation
referred to, of filling them with sawdust; their walls become at the
same time thicker and less quickly pervious. A mode of destroying
the elasticity of the membrane when in its most attenuated condition,
so that the balloon might be cut open and the membrane spread out
without shrinking, would be very useful. Instead of depending upon
the interior support of sawdust, the membrane could then be stretched
over a more convenient frame to support it, of thin porous deal, of
unglazed earthenware, and even of a felted fabric, or several thicknesses
of unsized paper supported by a slight frame, so as to form a hollow
250 ON THE ABSORPTION AND
cavity that admitted of being exhausted of air. The attention of manu-
facturers of rubber might be advantageously directed to the preparation
and proper support of the thinnest possible septa of that material]
The varnish of rubber which appeared to offer the best septum on
drying, was a thin solution of rubber in 200 times its weight of chloro-
form. Four or five coats of this varnish required to be applied to a
surface of wood, or of unglazed earthenware, to form an air-tight en-
velope. The film appeared to exceed in thickness the rubber balloons,
and it dialysed air less rapidly. But a better result may be expected
at the hands of experienced manufacturers.
[The thin rubber membrane of the balloons was stretched over the
ends of glass tubes already closed with a plate of porous stucco–and
also over the mouths of small glass bulbs or osmometers, closed with a
disk of porous wood or of unglazed earthenware, and which presented a
surface of one-hundredth of a square metre. The membrane of the
balloon could only be applied while double; but after the covering was
securely bound to the glass and cemented with fused gutta percha at
the edges, the outer coating was torn off, so as to leave only a single
thickness of rubber as the dialytic septum. A bulb of the kind
described, when exhausted by a Sprengel pump, gave afterwards 16:36
cub. centims, of dialysed air in two hours, containing by analysis 41.3 per
cent of oxygen, therm. 23° C.; in the following two hours, 17:35 cub.
centims. of air, containing 42.6 per cent of oxygen. This last is at the
high rate, for a square metre of surface, of 14:46 cub. centims. per minute.]
5. Silk cloth varnished with rubber on one side, slightly vulcanized.
This is a thin but close silk fabric, much used for waterproof gar-
ments. It appears also to be employed, when dyed of a fancy colour,
in the preparation of artificial flowers and for other purposes. The silk
cloth is of a single thickness; and the coating of rubber, which is of a
black colour, appears on one side only. It is a much superior material
to the ordinary cotton fabrics, which are double, with the two varnished
sides pressed together, and is much more to be depended upon for being
sound and free from Spores than the “waterproof” cotton cloth. The
silk cloth, however, should always be tested by examining air dialysed
by means of it. If the proportion of oxygen falls below 40 per cent.
the silk is unsound at one or more spots. These spots may generally
be discovered by wetting one side of the silk with a sponge and observing
where the passage of water is indicated by a visible stain on the other
side. The defective spot may be covered by a small disk of sheet rubber
applied warm to the surface. Such varnished silk, although not the
most rapid in its dialytic action, was more convenient in use than any
other septum hitherto tried.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 251
The varnished silk stretched over a disk of porous earthenware (for
support) closing the mouth of the small glass bell-jar or osmometer,
which has an opening of one hundredth part of a square metre, gave 10
cub. centims. of dialysed air in one hour, containing 42.2 per cent. of
oxygen; barom. 767 millims, therm. 23°5. For a square metre of surface
this is a passage of 277 cub. centims. of air per minute.
A small bag, useful for experimental purposes, was constructed of a
portion of the same varnished silk, 0.53 metre in length by 0:27 metre
in width, which had therefore a surface of 0-143 square metre. The
varnished side was turned inwards. Between the folds of the silk was
placed a double thickness of common felt carpet or a piece of wadding,
so as to occupy the interior of the bag. A glass quill tube also entered
the bag to the depth of a few inches, and projected as much outside, so
as to admit of being connected, by means of a sound adapter tube of
French rubber, with a Sprengel pump, as shown in fig. 1 (page 245).
The edges of the silk cloth were cemented round by caoutchouc varnish,
to a depth of 10 millims., so as to close the bag; and care was taken
also to cement the glass tube well to the edges of the bag. When the
silk bag is exhausted of air, it remains nearly flat, and feels hard like a
piece of cardboard. Such an air-dialyser is further improved by inter-
posing a strong glass flask or bottle, of one or two litres in capacity,
between the bag and the pump, so that both are exhausted of air at the
same time. The flask must be strong enough to bear the full pressure
of the atmosphere without breaking. An auxiliary air-pump, to produce
the first exhaustion, cannot well be dispensed with where the space
to be made vacuous is so considerable; the Sprengel tube is brought
into action afterwards. The advantage gained by the vacuous flask,
and even by the thick wadding placed within the bag, is that they form
a magazine in which the dialysed air can be allowed to accumulate for
several hours or a whole day, and from which the air may afterwards
be drawn quickly by the Sprengel tube for the purpose of experiment.
A narrow glass receiver tube, which can be closed by the thumb, may
be used to take 5 or 6 cub. centims, for an observation on the inflam-
mation of a chip of wood in the highly oxygenated air. When the
proportion of oxygen is under 33 per cent, the wood is not rekindled;
but in the ordinary action of this dialyser the oxygen is seldom found
under 40 per cent. The best result is obtained when the exhaustion
is within half an inch of the barometric vacuum. When the pressure
was allowed to fall to one-half or one-third of an atmosphere, the
proportion of oxygen was lessened by 2 or 3 per cent.
The action of heat and cold on the penetrability of rubber is con-
siderable, as has already been stated. Operating with the dialysing-bag
described, without any intermediate flask, the volume of air collected
252 ON THE ABSORPTION AND
in twenty minutes was 635 and 6:57 cub. centims, in two consecutive
experiments; barom. 760 millims, therm. 20°. For a square metre
the rate is 2:22 and 2:29, average 2:25 cub. centims. per minute. The
proportion of oxygen was, in the first experiment 42°5, and in the
second 41-66 per cent. -
When the same dialysing-bag was kept at a temperature of 60°C.,
the volume of air collected in seven minutes was 6:22 and 7:06 Cub.
centims. For the square metre this amounts to 621 and 7:05, mean
6-65 cub. centims. per minute. The passage of air through rubber is
therefore almost exactly three times as quick at 60° as at 20° C.
Again, the dialysing-bag was kept at 4°C. by being surrounded by
ice and salt. The air now collected in seventy-two minutes was 5'78
and 577 cub. centims. in volume—for a square metre 0.56 cub. centim.
per minute. The passage of air through rubber thus appears to be four
times as slow at 4°C. as it is at 20°. The proportion of oxygen in the
dialysed air increased at the same time. In the two portions of air
collected at 4” the oxygen was 46.75 and 47.43 per cent. The increase
of oxygen at a low temperature was confirmed in other experiments;
but it appeared at the same time that the rubber was liable to acquire
a true porosity to a slight extent when retained for some hours about
0° C. The rubber then allowed air to pass through it containing no
more than 28 or even 23 per cent of oxygen, and in volume still very
small. The rubber has become rigid by the cold, and is now acting
feebly as a porous substance, allowing a little gas-diffusion to take place
through its substance. Such a condition, which is accidental to caout-
chouc at a low temperature, appears to be constant with gutta percha,
a harder material, at 20°C., and even higher temperatures.
A large bag of varnished silk with a surface of 1-672 square metre
(two square yards) was found still more convenient. It was, however,
rather beyond the exhausting-power of the largest Sprengel pump. It
yielded in eight minutes, without any collecting flask, 22, 21:55, and
21-5, mean 21-68 cub. centims. This was a supply of 271 cub. centims.
per minute, and was at the rate, for a square metre, of 1-62 cub. centim.
per minute. The supply would have been about a half more if the dia-
lysed air had not gained upon the pump. The air of the first and last
observations contained respectively 41.89 and 41.85 per cent. of oxygen.
The usual proportion of oxygen in air dialysed by rubber appears to
be about 41.6 per cent.; and it may be described as atmospheric air
deprived of one-half of its usual proportion of nitrogen. A single
dialysis of air therefore carries the experimenter already half-way from
air to pure oxygen as the final result. But the gain by a second
dialysis could not be so great, as it would only withdraw one-half of the
nitrogen that remained after the first operation, a third dialysis one-
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 253
half of the nitrogen remaining after the second operation, and so on—
each step of the concentration of the oxygen being obtained at a greater
cost than the last, and the best conceivable result being only a good
approximation. The practical problem which is suggested by the air-
dialyser is to attain the means on a large scale of reducing to one-half,
or so, the proportion of nitrogen in atmospheric air, to be applied to
certain useful purposes.
6. Percolation of air through gutta percha and other septa.
Thin transparent sheets of a certain material represented as air and
Water tight are in common use. It is often spoken of as consisting of
Caoutchouc, but appears to have a body of gutta percha, softened pro-
bably by a drying-oil. From its softness and thinness, this sheet of
gutta percha appeared at first highly promising. But it appears not to
be free from small apertures for any considerable surface. When a
Small sound portion was operated upon, air was found to percolate
through it very slowly. In a tube diffusiometer of 1.3 metre in length
and 20 millims. in diameter, closed at the top with this septum sup-
ported by stucco, the mercurial column fell from 28-7 to 22:625 inches
in 18% hours. The gas which had entered above the mercury measured
13:54 cub. centims, and was found to contain 2012 oxygen to 79.8
nitrogen—a proof that the air had entered by gas diffusion. The mate-
rial is in fact of sufficient porosity to permit the molecular passage of
gases in a slow manner.
Warnishes of gelatine and of drying-oil have been tried as dialytic
septa, but hitherto without marked results.
PART II.—ACTION OF METALLIC SEPTA AT A RED HEAT.
Platinum.
The surprising passage of gases through the homogeneous substance
of a plate of fused platinum or of iron, at a red heat, discovered by
MM. H. Ste.-Claire Deville and Troost, may possibly prove to be analo-
gous in its mode of occurrence to the passage of gases through the
rubber septum. At the same time it must be admitted that such an
hypothesis as that of liquefaction can only be applied in a general and
somewhat vague manner to bodies so elastic and volatile at an elevated
temperature as the gases generally must be, and hydrogen in particular.
Still some degree of absorbing and liquefying power can scarcely be
denied to a soft or liquid substance, in whatever circumstances it may
be found, with such a patent fact before us as the retention by fused
silver of 18 or 20 volumes of oxygen at a red heat. It may safely be
254 . ON THE ABSORPTION AND
assumed that the tendency of gases to liquefaction, however much
abated by temperature, is too essential a property of matter to be ever
entirely obliterated.
A little consideration also shows that the absorption of gas by a
liquid or by a colloid substance is not a purely physical effect. The
absorption appears to require some relation in composition—as where
both the gas and the liquid are hydrocarbons, and the affinity or attraC-
tion of solution can come into play. May a similar analogy be looked
for, of hydrogen to liquid or colloid bodies of the metallic class?
With reference to the mechanical pores of a solid mass, liquids are
probably more penetrating than gases. The former show often a power
of adhesion to solids, while gases appear to be essentially repulsive. A
degree of minute porosity is conceivable, which will admit a liquid, but
may be impassable to a gas, even under its molecular movement of
diffusion.
Finally, there is presented to us a bold and original conjecture by
M. Deville, in explanation of his own observations. It is clearly
expressed in the following quotation taken from the last publication of
M. Deville on this subject —
“La perméabilité de la matière est d’une nature toute différente
dans les corps homogenes, comme le fer et le platine, et dams des pâtes
plus Ou moins discontinues, resserrées par la cuisson ou la pression,
comme la terre à creuset, la plombagine, dont M. Graham s'est Servi
dans Ses mémorables expériences. Dans les métaux, la porosité résulte
de la dilatation que la chaleur fait éprouver aux espaces intermolé-
culaires; elle est en relation avec la forme des molécules que l’on peut
toujours supposer régulières, et avec leur alignement que détermine le
clivage ou les plans de facile fracture des masses cristallisées. C'est
cet intervalle intermoléculaire que le phénomène de la porosité des
métaux purs et fondus accuse avec une évidence éclatante, c'est aussi
par ce phénomène qu'on peut espérer de calculer la distance des
molécules solides aux températures élevées of les gaz peuvent s'y
introduire.”
A new kind of porosity in metals is imagined, of a greater degree of
minuteness than the porosity of graphite and earthenware. This is an
intermolecular porosity due entirely to dilatation. The intermolecular
porosity of platinum and iron is not sufficient to admit any passage
of gas at low temperatures, but is supposed by M. Deville to be
developed by the expansive agency of heat upon the metals, and to
become sensible at the temperature of ignition. Such a species of
porosity, if it exists, may well be expected to throw light on the
distances of solid molecules at elevated temperatures, when gases intro-
duce themselves. The ready passage through platinum of some gases,
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 255
particularly of hydrogen, and the difficult passage of others, render such
molecular views the more remarkable.
The passage of hydrogen through the substance of heated platinum
appears in its most simple aspect when the gas is allowed to make its
way through the metal into a vacuous space. The experiment of M.
Deville, where a tube of platinum charged with nitrogen is placed
within a large porcelain tube charged with hydrogen,' was modified by
placing the platinum tube, closed at one end, in communication by the
other (open) extremity with the Sprengel pump, so that a vacuum was
substituted for the nitrogen. It was then easy to observe that a
vacuum in the platinum tube was preserved for hours when the exter-
nal gas admitted into the annular space between the porcelain and
platinum tubes was either atmospheric air or hydrogen at the natural
temperature. The tubes being placed across an empty furnace, the
latter was now lighted; and it was seen that, with air circulating out-
side the platinum, the vacuum remained undisturbed, even when the
temperature of the tubes rose to a bright red heat. But when dry
hydrogen was driven through the same annular space, the platinum,
while continuing impermeable at all temperatures below a dull red heat,
began to admit hydrogen to the vacuum as soon as the external porce-
lain tube became visibly red-hot. In seven minutes the Sprengel
pump now delivered 15:47 cub. centims. of gas, of which 1527 cub.
centims, appeared, by explosion with oxygen, to be hydrogen.
In a repetition of the last experiment, hydrogen dried by Sulphuric
acid was again allowed to circulate in excess outside the platinum.
After a vacuum was once obtained within the platinum tube, the gas
delivered by the Sprengel pump, in the cold, during a period of forty
minutes, amounted to no more than a bubble of the size of a pin-head,
showing the tightness of the apparatus. The Sprengel pump being
constantly kept in action, the tubes were now heated to redness, and
then gradually to a temperature approaching a white heat. The gas
delivered each five minutes was found to be 13, 15-5, 17°4, 16:9, 18-6
cub. centims. as the temperature rose. These volumes are referred to a
temperature of 20° and barometer of 760 millims. The last observation
gives a passage of 372 cub. centims. Of hydrogen per minute. The
platinum tube employed here was joined without solder, having been
drawn from a mass of platinum which had been aggregated by fusion.
It was similar in this respect to the tube employed by M. Deville. The
tube was 0-812 metre in length (32 inches) and 1:1 millim. in thickness,
with an internal diameter of 12 millims. But only a portion of about
200 millims. (8 inches) of the tube were heated to redness in the furnace
experiment. The inner surface of the heated portion has therefore
* Comptes Rendus, vol. lvii. p. 965.
.
:
:
*
i
:
".
s
i
256 ON THE ABSORPTION AND
an area of 0.0076 square metre. Hence one square metre of heated
platinum delivers 489:2 cub. centims, of hydrogen per minute. This
result admits of comparison with the passage of gases through a septum
of rubber. In the most favourable circumstances, when the thin mem-
brane of a rubber balloon was employed, the passage of air into a
Vacuum was at the rate of 26-5 cub. centims. per square metre in one
minute. The passage of hydrogen may be taken as 4-8 times as rapid
as that of atmospheric air, or at 1272 cub. centims. per minute. But
while the thickness of the platinum septum was 1:1 millim., that of the
rubber film was only one-seventieth part of a millimetre. Hence we
have the ultimate comparison – g
Passage of hydrogen gas in one minute through a septum of 1
Square metre :—
Through rubber 0:01.4 millim. in thickness, 127:2 cub. centims. at
20° C.;
Through platinum 1:1 millim. in thickness, 489:2 cub. centims, at
bright red heat.
If the permeation of hydrogen is due to the same agency in both
Septa, can the vast Superiority of the platinum septum be connected
with its greatly higher temperature ?
It was interesting now to turn from hydrogen to the passage of
other gases through heated platinum. The experiments were all made
in the same way, and at a full red heat. The temperature, it will be
observed, was short of that at which the elements of water and car-
bonic acid are partially dissociated. 4.
Oaxygen and Nitrogen.—Atmospheric air, which may be taken to
represent both of these gases, was now allowed to flow through the
annular space between the tubes, the interior platinum tube being
kept vacuous as usual. In one hour the gas collected by the constant
action of a Sprengel pump amounted only to 0-3 cub. centim. Hydrogen
in the same time would have given 211 cub. centims. It is very
doubtful, too, whether the trifling fraction of a centimetre of gas col-
lected had all passed through the platinum; a part (or the whole of it)
may have entered by the joints of the apparatus. Platinum, then,
cannot be said to be sensibly permeable to either oxygen or nitrogen,
even at a full red heat.
Carbonic acid—This gas was supplied from a bottle containing
marble, by the action of pure hydrochloric acid, the gas being after-
wards washed with water and dried by sulphuric acid in its way to the
exterior porcelain tube. In one hour the interior platinum tube yielded
only three-tenths of a cubic centimetre of gas, of which, again, only an
indeterminate small portion was condensed by baryta water and ap-
peared to be carbonic acid. The passage of carbonic acid is therefore
incalculably small at a full red heat.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 257
Chlorine.—This gas, evolved slowly from a glass flask containing
peroxide of manganese and hydrochloric acid, was washed by water,
dried by sulphuric acid, and thrown as usual into the porcelain tube
so as to occupy the annular space between the two tubes. A small
tube containing slaked lime was interposed between the end of the
platinum tube and the Sprengel pump, so as to absorb the chlorine, if
any came through the substance of the platinum. After the tube had
been heated for an hour, the lime was examined for chlorine, but did
not contain a trace of that substance. A minute quantity of gas,
probably air, amounting to 0-15 cub. centim., was collected during
the time. Platinum, then, is not sensibly penetrated by chlorine at
a red heat.
Hydrochloric acid, dried over sulphuric acid, was passed for one
hour through the porcelain tube. About 0.5 cub. centim. of gas was
collected from the platinum tube, which contained no hydrochloric acid
and no free hydrogen. The ignited platinum, then, is not penetrated
by hydrochloric acid ; nor does it appear to dissociate the elements of
that gas at the temperature of the experiment.
Wapour of water.—A stream of steam was carried for one hour
through the porcelain tube. During that time half a cub. centim. of
gas appeared to be drawn from the platinum tube, which gas contained
no hydrogen. There is no evidence of the passage through the platinum
of the vapour of water, nor of its decomposition.
Ammonia.-This gas appeared to be decomposed to a considerable
extent in passing through the heated annular space, hydrogen passing
freely at the same time through the ignited platinum. No trace of
undecomposed ammonia, although the gas was transmitted in consider-
able excess, was discovered accompanying the free hydrogen found in
the platinum tube. When the ammonia was evolved slowly, the
quantity of hydrogen entering the platinum tube amounted to 16:4 cub.
centims, in five minutes, or was sensibly the same as when pure
hydrogen was carried through the annular space. Ammonia, then,
appears to be incapable of penetrating the ignited platinum.
Coal-gas.—When coal-gas was carried through the porcelain tube,
the following quantities of hydrogen came through the platinum in
successive periods of twenty minutes each, 13-3 cub. centims., 52, and
88. The first portion, when exploded with oxygen, did not disturb
baryta-water after condensation ; 133 cub. centims. contained 13:16
cub. centims. of hydrogen. It appears, then, that the permeating gas
was free hydrogen only, and that no compound of carbon present in
coal-gas was capable of passing through the platinum. This may be
held as excluding the passage of carbonic oaside, marsh-gas, and olefiant
gas, all represented in the coal-gas.
R
258 ON TEIE ABSORPTION AND
Hydrosulphuric acid—This gas, prepared from sulphide of anti-
mony and hydrochloric acid, washed, and dried over chloride of
calcium, was then circulated through the outer porcelain tube. The
hydrosulphuric acid was nearly all decomposed into sulphur and
hydrogen, the latter coming through the platinum at the rate of 9 cub.
centims, in five minutes. A trace of hydrosulphuric acid may also
have passed through, as the mercury of Sprengel's tube was slightly
soiled; but no indication of this gas could be perceived in the hydrogen
collected. It appears, then, that hydrosulphuric acid is to be classed
among the non-penetrating gases. The result appears to be —
I. Gas capable of passing through a septum of platinum 1:1 millim. in
thickness at a full red heat.
Hydrogen (211 cub. centims, per hour).
II. Gases incapable of passing through a septum of fused platinum
1.1 millim. in thickness at a full red heat.
Oxygen, . . . . (not to the extent of 0.2 cub. centim, per hour)
Nitrogen, . . . . 33 35
Chlorine, . . . . - 55 25
Hydrochloric acid, . 33 32
Vapour of water, . jj 25
Carbonic acid, . . 23 25
Carbonic oxide, . . 2 y 22
Marsh gas (CHA), . 53 32
Olefiant gas, . tº
Hydrosulphuric acid, 22 25
Ammonia, . . . 5 * 35
It remains to be discovered whether a sensible passage of any of
these gases could be effected through a platinum Septum much reduced
in thickness, or through the same septum under the influence of a
considerably higher temperature. A fallacious appearance of permea-
tion is sometimes occasioned by the escape from the platinum itself of
a small quantity of gas, particularly of carbonic oxide and hydrogen, as
will immediately appear. The permeation is in consequence never un-
equivocal for the first hour or two that the platinum septum is heated.
[One of the curious experiments of M. Deville was repeated, in which
hydrogen appears to escape from the platinum tube pretty much as the
same gas would escape from a graphite diffusiometer—the platinum
tube being full of hydrogen, while the annular space between the
platinum and outer porcelain tube was occupied by atmospheric air.
At the maximum temperature the supply of hydrogen to the platinum
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 259
tube was shut off, as that gas entered at one end of the tube, while the
other end of the platinum tube was left in connexion with a barometer-
tube dipping into a cistern of mercury. Immediately the mercury
began to rise in the gauge tube from the passage of hydrogen outwards
through the walls of the platinum tube; and the latter in the end
became nearly vacuous from the complete escape of the hydrogen.
Heated platinum tube containing hydrogen; air outside.
Time. Rise of mercury in gauge barometer.
0 minute. 0 millim.
10 minutes. 115 millims.
20 35 245 52
30 53 400 52
40 25 535 5 2.
50 25 645 25
60 25 710 25
the actual height of the atmospheric barometer being 750 millims. at
the same time. The tension of the residual gas was therefore no more
than 40 millims. of mercury. The ratio between the volume of gas at
the beginning and end of the hour is here as 1875 to 1; whereas in a
diffusion experiment of hydrogen into air, the ratio would be as 3-8 to 1.
Further, the residual gas in the platinum tube still retained a small
portion of hydrogen. Withdrawn by means of the Sprengel pump and
examined, the residual gas in the platinum tube amounted to 3-56 cub.
centims., and consisted of
Nitrogen, ſº wº 3:22 cub. centims.
Hydrogen, e º 0°34. 52
3-56 33
The available capacity of the platinum tube was 113-1 cub. centims.;
and when the tube was heated, the gas driven out by dilatation measured
in the cold 39-5 cub. centims., leaving in the hot platinum tube 73-6
cub. centims. of gas estimated at 20° C. and barom. 760 millims.]
It was found necessary in these experiments to stuff that portion of
the platinum tube that was placed across the furnace and strongly
heated, with asbestos, to give support to the tube when softened by the
heat of ignition, and to prevent the tube from collapsing.
[It is difficult to say where the small volume of nitrogen found in
the platinum tube, amounting to 3:22 cub. centims, actually came from.
It appears too great in amount to have formed an impurity in the
original hydrogen gas, or to have gained access to the vacuum through
defective joinings in the apparatus. Its presence suggests the inquiry,
admitting that nitrogen cannot pass alone through platinum into a
vacuum, whether the same gas may not be enabled to pass, in some
260 ON THE ABSORPTION AND
this paper.
and liquefying hydrogen gas 2
small proportion, while hydrogen is simultaneously travelling through
the platinum in the opposite direction. The liquid or the gaseous
hydrogen occupying the platinum septum would thus form 8, vehicle OT
channel, by the help of which another analogous body. like nitrogen
might be conceived capable of passing through the platinum in Small
quantity, by a process of liquid or gaseous diffusion.]
Absorption and detention of Hydrogen by Platinum.—The passage of
a gas through a colloid septum is preceded by the condensation of the
FIG. 2.
A.
§ 7/2
Eğ
º:
=s
y-
Sº
|S -
jº
gas in the substance of the septum, according to the views taken in
Is a plate of ignited platinum capable, then, of condensing
The subject could scarcely admit of
experimental investigation without the application of the same useful


DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 261
air-exhauster that was employed with the non-metallic colloids. The
metal was always treated in the same manner; so that a description of
the details of one experiment will apply to all."
Platinum wire or plate being provided, the surface of the metal was
first divested of all adhering oily matter, by boiling in caustic alkali
and afterwards in distilled water.
The platinum, generally in the form of wire, was then introduced
into a porcelain tube M, N (fig. 2), glazed both outside and inside,
0.55 metre in length and 23 millims. in internal diameter. This tube
could be heated either by means of the combustion-furnace used for
organic analysis, or by placing the tube across the chamber of a small
cylindrical furnace. The porcelain tube was fitted at both ends with
perforated corks, well cemented with fused gutta percha, and provided
each with a small quill tube. Such may be described as the distilla-
tory apparatus employed. It was connected at the end N with the
Sprengel pump A B, to be used as an exhauster and transferrer of gas,
by means of good caoutchouc adapters (not vulcanized), and at the other
end M, with the apparatus for supplying dry hydrogen, atmospheric air,
or any other gas. By a screw clamp upon the adapter at M, the tube
could be closed, and the gas-producing apparatus then detached, leaving
the porcelain tube shut at one end. A tube of the hard glass used in
combustion analysis may be substituted for the porcelain tube in many
such experiments. A less degree of heat suffices than was at first
Supposed. -
The porcelain tube is exhausted by continuing the action of the
Sprengel for ten or fifteen minutes, till Small bubbles of gas cease to be
delivered by the tube A B in the mercurial trough below. The suffi-
ciency of the joints is thus first ascertained. Heat being then applied
to the porcelain tube, its impermeability at a red heat will also be
tested. -
The platinum, when introduced, was confined to about two-thirds of
the central portion of the porcelain tube, which could be conveniently
heated. The apparatus obviously affords the means both of heating
the platinum in a vacuum and also in an atmosphere of hydrogen or
any other gas admitted into the interior of the porcelain tube at M.
Fused platinum.—Articles of manufactured platinum appear now to
be prepared exclusively from the fused metal.
1. A quantity of clean platinum wire from fused metal, measuring
0-695 metre in length, 4.1 millims, in diameter, and 201 grims, in weight,
was bent and introduced into the porcelain tube, which was then ex-
* Platinum in the peculiar condition of platinum-black absorbs 745 times its
volume of hydrogen gas-Traité de Chimie Générale, par MM. Pelouze et Frémy,
t. iii. p. 398.
262 ON THE ABSORPTION AND
hausted. The platinum was first heated alone for an hour to drive off
any natural gaseous product, and then dry hydrogen gas was admitted
to the porcelain tube, the gas being evolved from pure sulphuric acid
and pure zinc. The hydrogen was conveyed in excess into the porce-
lain tube, at a cherry-red heat, and the temperature was them allowed
to fall in a gradual manner—a procedure which was found to promote
the absorption of the gas. The platinum was thus retained for about
twenty minutes in an atmosphere of hydrogen, at a temperature partly
above and partly below dull redness, terminating with the lower tem-
perature. After the fire was withdrawn and the tube allowed to cool,
air or nitrogen was driven through it, and all free hydrogen thus ex-
pelled from the apparatus. -
The closed tube was now exhausted in the cold, but no hydrogen
came off. The platinum being still retained in a good vacuum, heat
was again very gradually applied, and the action of the Sprengel pump
maintained. Simultaneously with the first appearance of visible igni-
tion, gas began to be evolved. In one hour, the porcelain tube being
heated to redness, 2:12 cub. centims, of gas were collected, of which
about one-third was collected in the first ten minutes. It was found,
by explosion with oxygen, to consist of
Hydrogen, © © l'93 cub. centim.
Nitrogen, © • 0.19 33
Now, taking the specific gravity of the platinum wire at 21:5, the
volume of 201 grims. of metal will be 9:34 cub. centims. Hence one
volume of platinum held, the gas being measured cold,
0.207 vol. hydrogen.
The platinum did not appear sensibly altered in lustre, or in any
other way, by its relation to the hydrogen.
2. The same piece of platinum wire was drawn out into four times its
first length, and the experiment of charging with hydrogen was repeated.
The platinum gave up at a red heat, maintained for one hour, 1:8 cub.
centim. of gas, of which 1-6 cub. centim. was hydrogen. Here one
volume of platinum appears to have held
0.171 vol. hydrogen.
The absorption of hydrogen has not been increased by increasing the
surface of the metal.
In two further experiments upon the same platinum wire, the volume
of hydrogen retained by one volume of platinum was— -
3. 0.173 cub. centim, hydrogen.
4. 0-128 ,
22
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 263
There is an evident tendency of the hydrogen taken up to diminish
in quantity. These experiments have the advantage for comparison with
the earlier observations on the penetration of a platinum Septum by
hydrogen gas, that both wire and tube had been drawn out from the same
mass of fused metal. No iridium had been added to this platinum, as
is sometimes done to increase the elasticity of the metal. The absorption
of hydrogen is small, amounting, according to the mean of the four
observations, to 17 per cent. of the volume of the platinum. At the
temperature of a low red heat, when the absorption took place, the gas
would be considerably dilated, to the extent of at least three times its
volume stated above, or to about 51 per cent., half the volume of the
platinum. It is to be considered whether an absorption of half a volume
of gas would be sufficient to account for the observed penetration of
a septum of metal 1:1 millim. in thickness. The data appear to favour
an affirmative conclusion ; but their value cannot be very decidedly
estimated.
It appears necessary to recognise in platinum a new property, a
power to absorb hydrogen at a red heat, and to retain that gas at a
temperature under redness for an indefinite time. It may be allowable
to speak of this as a power to occlude (to shut up) hydrogen, and the
result as the occlusion of hydrogen by platinum.
The observation was extended to platinum in other conditions of
form, but where, it is to be observed, the metal had not been fused, but
only welded, and was not of recent manufacture.
5. Of the grey pulverulent spongy platinum, prepared from the
ammonio-chloride, 22.2 grns, were heated by the combustion-furnace,
and for half an hour allowed to cool gradually in dry hydrogen gas as in
the preceding experiments. The volume of the platinum is 1.032 cub.
centim. by calculation. In the first experiment it yielded to heat and
the action of the Sprengel pump 2.2 cub. centims. of a gas which burned
like hydrogen. In a second experiment the platinum yielded in one
hour (when it appeared to be exhausted) 17 cub. centim. of gas, found
by explosion to consist of hydrogen 1:52 cub. centim., and nitrogen 0.18
Cub. centim. Here one volume of spongy platinum appears capable
of occluding
1:48 vol. hydrogen.
6. Wrought platinum, in the form of plate from an old crucible cut
up, after washing and ignition, was charged with hydrogen three times
in succession. The weight of the platinum was 24.1 grims, and its
volume 1-12 cub. centim. It yielded in seventy-five minutes 4:19 cub.
centims, of gas, and in thirty minutes further I-5 cub. centim. more,
making together 5-69 cub. centims., of which 494 cub. centims, proved
264 ON THE ABSORPTION AND
to be hydrogen; therm. 14°2, barom. 760 millims. Not a trace of
carbonic acid was found in the gas before or after explosion. Again,
after a second charge, 5'12 cub. centims, of gas were given up in an
hour, of which 44 were hydrogen; and lastly, 376 cub. centims. in an
hour, of which 342 were hydrogen. Hence, occluded by 1 vol. Wrought
platinum–
5-53 vols. hydrogen.
4'93 , 35
3-83 , 22
The volume of occluded hydrogen is much larger than in the fused
platinum, or even in the spongy platinum. It exhibits a tendency to
fall off on repeating the experiment. But the declension in absorbing
power may possibly be connected with the reduced duration of the
exposure to hydrogen of the metal while cooling.
7. Wrought platinum, which had been formed many years ago into
a small tube, weighing 64.8 grms, 0.322 metre in length and 5 millims.
in diameter, was cut into three equal lengths for convenience in placing
the metal within the porcelain tube, to be heated and charged with
dry hydrogen. By an hour's exhaustion afterwards the platinum yielded
9.2 cub. centims. gas, of which 8-9 were hydrogen. The volume of the
platinum itself was 39 cub. centims. ; and one volume of metal had
therefore occluded 228 vols. hydrogen, measured at about 20°C. In
all such experiments, besides blowing out the free hydrogen by air, the
apparatus was also thoroughly exhausted by the Sprengel pump in the
cold, before the occluded hydrogen was extracted.
The lustre and appearance of the metallic platinum was not altered
by the ingress of the hydrogen; but after the escape of the gas the
platinum appeared whiter in colour.
Repeating the experiment, the gas collected by an hour's exhaustion
was 87 cub. centims, of which 8:46 cub. centims, were hydrogen. Here
the metal occluded 28 vols. of hydrogen. •
The same platinum was a third time charged with hydrogen; but
on this occasion the platinum was placed in a tube of hard glass, and
the tube connected with the air-exhauster. The glass tube was heated
by an oil-bath, and the platinum kept in vacuo at a temperature of
220° C. for an hour. Not a bubble of gas was evolved. The glass tube
was afterwards heated by a Small Bunsen burner, which was calculated
to give a degree of heat little short of visible redness, still no hydrogen
came off. The tube was now heated sufficiently to soften glass (500°).
Gas began to come off, of which 18 cub, centim, containing 1:72 hydro-
gen, were collected in ten minutes. The glass tube having cracked, the
whole apparatus was allowed to cool, and the platinum transferred to a
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 265
porcelain tube. Further heated by a combustion-furnace for one hour,
the platinum gave off 8-6 cub. centims. gas, of which 82 were hydrogen.
The platinum therefore appears to have occluded altogether 379 vols.
of hydrogen.
The preceding experiment appeared to show a complete sealing up
of the occluded hydrogen at low temperatures, seeing that, although
nearly four volumes of gas were present, none escaped below a red heat.
But to test the effect of time at the temperature of the atmosphere, the
platinum, again charged with hydrogen, was sealed up hermetically in
a glass tube, which it nearly filled, and not opened for two months.
The air in the tube was then transferred and examined. It did not
exhibit any reduction of volume under the electric spark or a pellet of
spongy platinum. The air therefore appeared to contain no hydrogen;
the latter had not diffused out, but, it is to be presumed, was retained
by the platinum without loss. These experiments, although related
last, were the first performed in this inquiry. The included hydrogen
was never entirely extracted in an hour, and is probably understated.
The gas always came off gradually, more than one-half of the whole in
the first twenty or thirty minutes. The last results may be stated as
follows:—
1 vol. hammered platinum occluded 228 vols. hydrogen.
32 2.80 25
3.79 25
25 }}
22 25 32
The high absorbing power of the hammered platinum, or rather the
low absorbing power of the fused metal, was ascribed to a mechanical
difference between the two—to a more open texture in the former, per-
mitting more free access of hydrogen, liquefied as it may be, to the
interior of the metal.
8. The extrication of occluded hydrogen from platinum had always
required a degree of temperature verging upon a red heat, even when
aided by a vacuum ; and this remains true of hydrogen originally
absorbed at or near a red heat. But the fact appears to be compatible
with the absorption of the gas, under the pressure of the atmosphere, at
a considerably lower temperature. Thin platinum-foil was first deprived
of a little natural gas by ignition in vacuo in the porcelain tube. The
foil was afterwards placed in a glass tube and heated again in a stream
of hydrogen, to a temperature not exceeding 230°C., for three hours, by
means of an oil-bath, and further allowed to cool slowly in an atmosphere
of the same gas for several hours. A second glass tube receiver, to which
the platinum-foil was transferred, was exhausted, as usual, at 20°C. with-
out any sensible evolution of gas. With a red heat superadded, gas
came off in twenty minutes (but nearly all in the first seven minutes)
266 ON THE ABSORPTION AND
to the extent of 0.75 cub. centim, of which 0-56 cub, centim, proved to
be hydrogen. The volume of 83 grms of platinum is 0.385 cub, centim.
Hence one volume of platinum-foil appears to take up, in three hours,
1:45 vol. hydrogen at 230° C.
9. The same portion of platinum-foil was again charged with hydro-
gen at a still lower temperature, namely between 97” and 100°, for
three hours. Submitted to exhaustion at red heat, the platinum now
gave off 0.5 cub. centim. of gas in thirty-five minutes, of which about
03 cub. centim. were hydrogen. One volume of platinum-foil has
taken up
076 vol. hydrogen at 100°.
By this property platinum is connected with palladium, which of
all metals appears to possess the power of absorbing hydrogen in the
highest degree.
Palladium.
Of late years palladium has become comparatively uncommon; and
some difficulty was experienced at first in procuring more than a
gramme or two of the metal, in the form of thin foil. The palladium-
foil first employed weighed 1:58 grm., and measured 0-133 cub. centim.,
taking the specific gravity of the metal at 11-86, and had a surface of
0:00902 square metre. It gave off, when heated in vacuo for one hour,
1:50 cub. centim. of natural gas, containing no compound of carbon, but
consisting of hydrogen and air.
1. As it appeared from preliminary experiments that the occlusion
of hydrogen by palladium was likely to be a phenomenon exhibited at
a comparatively low range of temperature, the metal was heated in
hydrogen no higher than 245° C., by an oil-bath, and allowed to cool
very slowly, so as to pass through still lower ranges of temperature
which might be favourable to the absorption of hydrogen. The metal,
when afterwards transferred to the distillatory glass tube, appeared to
give out nothing to a vacuum at 17°8 C. and barom. 759 millims. But
the moment the combustion-furnace was lighted under the tube, gas
came off most freely. Of the first portion collected, 1177 cub, centims.
contained 1174 cub. centims. hydrogen. The gas ceased to be evolved
in fifteen minutes, when 6992 cub. centims. were collected, of which
the greater part came over in the first ten minutes. Hence palladium
has taken up a large Volume of gas when the temperature of the metal
never exceeded 245° C.
1 vol. palladium held 526 vols. hydrogen.
2. In a similar experiment the temperature of absorption was still
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 267
further lowered with good effect. The palladium was exposed to
hydrogen between 90° and 97° C. for three hours, and then allowed to
cool in the gas for one hour and a half. Now placed in a glass tube,
exhausted, and heated by a gas-flame, the palladium gave off gas in a
continuous stream for twelve minutes, when it ceased. The gas
amounted to 85.56 cub. centims, of which 96.8 per cent. was hydrogen;
therm. 17°5, barom. 764 millims.
1 vol. palladium held 643.3 vols. hydrogen.
By the care of my zealous assistant, Mr. W. C. Roberts, the hydrogen
employed in these experiments was purified to the highest degree by
passing it in succession through alcohol, water, caustic potash, and
tubes of 0.7 metre each, filled with broken glass impregnated with
nitrate of lead, sulphate of silver, and oil of vitriol. The gas was
inodorous, and burned with a barely visible flame.
No alteration was sensible in the metallic appearance of the palla-
dium-foil when charged with hydrogen, or when discharged. The foil
was much crumpled and rather friable after repeated use; but this may
have arisen from frequent handling.
3. Palladium appears to absorb hydrogen largely, even at natural
temperatures, provided that the metal has been recently ignited in vacuo.
The foil, without such preparation, was placed in a bottle of pure
hydrogen for several hours, but yielded nothing when afterwards
ignited in the Sprengel vacuum. The foil, however, being immediately
returned after cooling to a stoppered bottle containing hydrogen, and
left in the gas for a night, absorption now took place—air rushing in,
on opening the stopper, as into a partial vacuum ; therm. 19°. When
the palladium-foil was afterwards transferred to a glass tube and con-
nected with the Sprengel pump, it was found difficult to obtain a
vacuum for some time, owing to hydrogen coming off at the tempera-
ture of the atmosphere. But after a fair vacuum was produced 6.96
cub. centims. were collected, of which 678 proved to be hydrogen.
Heat was then applied, and 42 cub. centims. came over in five minutes,
making altogether more than 50 cub. centims, or 376 volumes of gas.
The absorption of hydrogen appears, then, to be suspended at a low
temperature, unless the condition of the metal be favourable. The
action of a plate of clean platinum in determining the combustion of
explosive gas is equally critical at a low temperature.
4. A different specimen of palladium-foil, weighing 5-76 grms, and
having a volume of 0.485 cub. centim, was charged with hydrogen, and
discharged, more than once. In the Second experiment, the foil was
heated in hydrogen at 100° for three hours. Distilled afterwards in a
268 ON THE ABSORPTION AND
porcelain tube at a low red heat in the usual way, the palladium was
found to have absorbed, at 100°,
3477 vols. of hydrogen measured at 18°2 C, and barom, 756 millims.
5. So large an absorption of hydrogen should increase the weight of
the palladium sensibly, notwithstanding the lightness of the gas. One
litre, or 1000 cub. centims, of hydrogen at 0° C. and 760 millims.
weighs 0.0896 grm. Of new palladium-foil, believed to be from fused
metal, 5'9516 grms, increased to 5'9542, or by 0.0026 grim., when the
metal was charged with hydrogen at 100° for four hours. This amounts
to only 29:01 cub. centims. of hydrogen at 0° C. and 760 millims.
barom. The gas actually extracted afterwards from the palladium did
not exceed 34.2 cub. centims. at 19°C., and barom. 758 millims, equi-
valent to 31-84 cub. centims. at 0°C. and 760 millims. barom. The
whole gas extricated (68 vols.) seems unusually small, but it corre-
sponds closely enough with the volume calculated from the increase of
the palladium in weight. An inferior absorbing power for hydrogen
appears to be connected in both platinum and palladium with the
fusion of the metal.
6. A portion of similar palladium-foil, charged with hydrogen, was
found to have its gas reduced from 20-7 to 162 cub. centims. after
exposure to the air for forty-two hours. The liquid hydrogen, whether
held by the substance or in the pores of the metal, appears therefore
to evaporate slowly at the temperature of the atmosphere, therm, 19°,
barom. 752 millims.
7. Spongy palladium, from the ignition of the cyanide, being heated
in hydrogen at 200, and allowed to cool slowly in the same gas for
four hours, the metal was found to have taken up 686 vols. of
hydrogen.
Treated in a similar manner with air, spongy palladium exhibited
no absorbing power for oxygen or nitrogen. ~
Hydrogen, condensed either in the palladium sponge or foil, was
observed to have its chemical affinities enhanced. The palladium being
placed in dilute solutions of the following substances for twenty-four
hours in the dark at the ordinary temperature, the action of the
hydrogen became manifest.
Persalt of iron became protosalt.
Perricyanide of potassium became ferrocyanide.
Chlorine water became hydrochloric acid.
Iodine-water became hydriodic acid."
* The power of platinum-black charged with hydrogen to communicate the latter
element to organic compounds has lately been observed by M. P. de Wilde, following
Dr. Debus.—Bulletin de la Société Chimique, Mars 1866. -
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 269
Apart from hydrogen, the palladium sponge exhibits a power of
selection and absorption of alcohol in preference to water. 30 grims.
of the sponge were left in contact with 9-5 cub. centims. of dilute
alcohol of specific gravity 0-893, for fifty-one hours, sealed in a tube.
The supernatant liquid now drawn off to the extent of 3.9 cub. centims.
was of specific gravity 0901, while the portion retained by the palla-
dium was found when distilled to be of specific gravity 0.885, or it was
sensibly concentrated. This chemical action of palladium sponge was
more than once verified. Platinum sponge, on the other hand, exhibited
no indication of a similar separating power; nor did the sponge of iron
reduced by hydrogen from the oxide.
8. Connected, it may be, with this chemico-molecular action of
palladium is the variable absorptive power for different liquids ex-
hibited by palladium-foil. Immersed in various liquids for an hour,
and afterwards dried by pressure for a few seconds between folds of
blotting-paper, a quantity of palladium-foil represented by 1000 was
found to retain in its pores—
Of Water, e g y g 1:18 part.
Of Alcohol (0-802), . e & 5.5 parts.
Of Ether, e º * g 17 part.
Of Acetone (0-794), . & g 0'54 ,
Of Glycerine, . t e * 4-5 parts.
Of Benzol, * * & * 3.5 32
Of Oil of sweet almonds, . tº 18-1 25
Of Castor-oil, g g * 10-2 }}
The superior penetrativeness of alcohol over water is well marked;
capillary action appears to merge into a chemical affinity. Liquid
hydrogen would also appear as highly absorbable by palladium-foil. It
would appear also to be separable from other gases (or liquids), as
alcohol is from water, by the palladium-pores.
Alloy of 5 palladium and 4 silver.—The power to absorb hydrogen
appears to extend to this alloy of palladium. A plate of the alloy,
about 180 millims, in length, 31 millims. in width, and weighing 743
grms., was bent, so as to be able to enter a wide porcelain tube that
could be exhausted of air when required. The volume of the palladium
alloy was 621 cub. centims. The plate of metal being placed in the
porcelain tube, had hydrogen gas passed over it at a low red heat for
one hour, and was then allowed to cool slowly in the same gas. Taken
out and examined, the metal was not visibly altered. For the extrica-
tion of gas the metal was distilled in the porcelain tube heated by jets
of gas, and connected with the Sprengel pump, as usual. In seven
minutes after the gas furnace was lit, 24 cub, centims, of gas came off;
270 ON THE ABSORPTION AND
in ten minutes more, 80-71 cub. centims.; and in seventy-five minutes
more, 36.75 cub, centims, making altogether 141:46 cub, centims. Of
this gas 127:74 cub. centims, proved to be hydrogen, the remainder
being nitrogen, derived, no doubt, from the large imperfectly exhausted
porcelain tube. The palladium alloy, in the form of a thick plate,
appears therefore to have held
20:5 vols. hydrogen, measured at 18°2 and barom, 756 millims.
This alloy of palladium becomes crystalline by heating, and appears
to lose much of its absorbent power at the same time.
The conclusion, then, is that welded palladium, in the condition of
thin foil, readily absorbs hydrogen, to the extent of upwards of 600
times the volume of the metal at a temperature under the boiling-point
of water, upwards of 500 volumes at 245°, and less at higher tempera-
tures, the metal being always surrounded by hydrogen under atmo-
spheric pressure. Hydrogen is also largely absorbed, although less
constantly, at ordinary temperatures. On the other hand, palladium
already fully charged with hydrogen at or under 100°, and under the
pressure of the atmosphere, begins to give out gas when exposed either
to atmospheric air or to a vacuum at the original temperature of absorp-
tion; and the gas is freely discharged at 200° C.
It is probable that hydrogen enters palladium in the physical condi-
tion of liquid, whether the phenomenon proves to be analogous to the
imbibition of ether, chloroform, and such solvents by the colloid india-
rubber, or whether a certain porosity of structure in the palladium is
required. The porosity of the metal is supposed to be of that high
degree which will admit liquid but not gaseous molecules. Now the
numerous liquid compounds of carbon and hydrogen have all a nearly
similar density, generally a little under that of water. There is no rea-
son to suppose that the density of liquid hydrogen would differ greatly
from the hydrocarbon class; but then the surprising lightness of hydro-
gen gas must cause liquid hydrogen to yield a volume of vapour dispro-
portionately large when compared with the former class of substances,
or, indeed, with any other substance whatever. The absorption of
hydrogen by palladium will appear, then, less extravagantly great when
viewed as the absorption of a highly volatile liquid capable of yielding
an exceedingly light vapour, rather than that of a gas.
An excellent opportunity of observing the penetration by hydrogen
of a compact plate of palladium, 1 millim. in thickness, was afforded by
a tube of that metal constructed by Mr. Matthey. This tube was said
to have been welded from palladium near the point of fusion of the
metal. The length of the tube was 115 millims, its internal diameter
12 millims, thickness 1 millim, and external surface 0.0053 of a square
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 271
metre. It was closed by thick plates of platinum soldered at both ends,
one of the plates being perforated by a long Small tube of platinum, by
which the cavity of the palladium tube could be exhausted of air.
Now the closed palladium tube remained air-tight, when exhausted
by the Sprengel tube, at the ordinary temperature, at 260°, and at a
temperature verging on low redness, the gas without being atmospheric
air. Hydrogen being then substituted as the external gas, the walls of
the palladium tube still remained impermeable at a low temperature.
No hydrogen gained the interior in three hours at 100°. But the tem-
perature being gradually raised by means of an oil-bath to 240°, hydro-
gen then began to come through, and at a gradually increasing rate to
265°. The hydrogen then entered steadily at the rate of 8-67 cub.
centims. in five minutes. This gives a rate of 327 cub. centims. for a
square metre of surface per minute. Heated to a temperature just short
of redness, the passage of hydrogen was increased to 11.2 cub. centims.
in five minutes, or 423 cub. centims. for a square metre per minute.
With coal-gas as the external atmosphere the penetration of the
palladium began about the same temperature, and was continued at 270°
at the rate of 57 cub. centims. for a square metre of surface per minute.
The penetrating gas had no odour of coal-gas, contained no trace of
carbon, and appeared to be absolutely pure hydrogen. The exact isola-
tion of the latter gas by septa of both platinum and palladium appears
most extraordinary. -
A quantitative determination of the hydrogen in a gaseous mixture
could probably be effected by means of the hollow cylinder of pal–
ladium.
Is the power to penetrate the metals in question confined to hydro-
gen’ It has been lately concluded by Dr. C. Wetherill that the tur-
gescence of the ammonium amalgam depends entirely upon the retention
of hydrogen gas-bubbles;" hydrogen, then, appears to exhibit an attrac-
tion of a peculiar kind for mercury. The ready liquefaction of the same
gas by the platinum metals evinces also a powerful mutual attraction.
The only other volatile body which has been observed to pass, like
hydrogen, through a plate of palladium is common ether—and that at
the atmospheric temperature, while a passage was denied to hydrogen
at the same time. The palladium was in the form of foil. Although
thin foil of this metal is generably visibly porous and allows air to pass
through like a sieve, a tube diffusiometer, covered with a disk of the
selected palladium foil, and standing over mercury, retained a volume of
40.5 millims, of air over a vertical column of 155 millims, of mercury
for twenty-four hours without depression of the mercury. The air was
dried by sticks of potash, but still it did not penetrate the palladium.
* American Journal of Science, vol. xlii. No. 124.
272 ON THE ABSORPTION AND
Dry hydrogen was then conducted to the upper surface of the palladium
disk, but still without any penetration by that gas after several hours.
Cotton-wool moistened with ether was now placed upon the disk, when,
after eight minutes, the confined air within the tube began to expand;
and in the course of an hour longer, the 40-5 volumes of confined air
increased to 90.4 (thermometer 18°5, barometer 758), when the expan-
sion ceased. The increase of volume appeared to be due entirely to
ether-vapour, absorbable by a pellet charged with sulphuric acid. Why
hydrogen proved to be incapable of penetrating the palladium in such
circumstances it is difficult to say. It can only be imagined that the
palladium foil may have previously condensed on its surface a minute
film of foreign matter, which rendered the palladium inactive to hydro-
gen, but not to ether-vapour.
On the other hand, the penetrating power of hydrogen, here referred
to the liquefaction of that gas, appears not to be solely confined to metallic
Septa. There is reason to suspect that in diffusing through a plate of
graphite hydrogen passes in a small proportion as a liquid, without any
counterdiffusion of air. Hence the constant excess observed of the
diffusive coefficient of hydrogen, which came out 3.876, 3.993, and
4,067," instead of the theoretical number 3:8, corresponding to the
density of the gas referred to air. Such phenomena of gaseous pene-
tration suggest a progression in the degree of porosity. There appear to
be (1) pores through which gases pass under pressure or by capillary
transpiration, as in dry wood and many minerals, (2) pores through
which gases do not pass under pressure, but pass by their proper mole-
cular movement of diffusion, as in artificial graphite, and (3) pores
through which gases pass neither by capillary transpiration nor by their
proper diffusive movement, but only after liquefaction, such as the pores
of wrought metals and the finest pores of graphite.
Osmium-iridium.
A portion of Small grains of osmium-iridium, amounting to 2:528
grms, was exposed to hydrogen through all descending temperatures
from a red heat, as the preceding metals had been treated. The osmium-
iridium was then heated again to redness in the Sprengel vacuum, to
extricate any hydrogen that might have been absorbed. But only a
bubble or two of gas, too minute to be measured, passed over in fifteen
minutes, at a red heat. Osmium-iridium, then, exhibits no absorbent
power for hydrogen—a result which is consistent with the crystalline
character of the substance.
* Philosophical Transactions, 1863, p. 404.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 273
Copper.
The power to occlude gases appears not to be confined to palladium
and platinum among the metals. The exact experiments of M. Dumas,
by which the atomic weights of the leading elements were definitely
settled, afford an indication of the absorption of hydrogen gas by spongy
metallic copper reduced from the oxide, Šufficient to affect the weight
of the metal to the extent of about 3 parts in 100,000."
1. With the view of applying the method of extracting gas followed
in the treatment of the preceding metals, so much oxide of copper was
reduced by hydrogen as was calculated to yield 50 grims. of metallic
copper. The reduced metal was again heated to redness and slowly
cooled in a stream of dry hydrogen. After free exposure to the air for
a few minutes, the metal was now submitted, at a red heat, to the action
of the Sprengel pump. It then gave off in one hour 3-35 cub. centims.
of gas, measured cold, which appeared to be pure hydrogen (the explo-
Sion with oxygen indicated 3-4 hydrogen). Taking the specific gravity
of copper at 8:85, 50 grms. of that metal would be 5-65 cub. centims. in
volume, and the result is that
1 vol. reduced copper sponge occludes 0-6 vol. hydrogen.
Hydrogen being about 12,000 times as light as copper (at 15°), 1 part
of gas by weight has been taken up by 20,000 parts of metal.
2. The same weight and volume of fine copper, in the form of wire,
thoroughly cleaned, was exposed to hydrogen at a red heat, and then
submitted to exhaustion for one hour. It gave 2-6 cub. centims. gas, of
which 2 cub. centims. were hydrogen, and the remaining 0-6 principally
carbonic oxide. It may be represented that
1 vol. wrought copper occludes 0.306 vol. hydrogen.
Where a metal, such as wrought copper, may contain small quantities
of carbon and oxygen, an obvious cause will exist for the production and
evolution of carbonic oxide under the influence of heat. Gas so gene-
rated appears to be added to the occluded hydrogen when extricated, in
the last experiment.
Gold.
1. A quantity of gold was precipitated from the assay cornettes used
below by means of oxalic acid. The gold weighed 93.3 grims, with a
1 Annales de Chimie et de Physique, 3 sér. t. wiii. p. 205. The observations of M.
Melsens show that 240 grms of copper may fix about 0.007 grm. of hydrogen, most
being fixed when the oxide of copper is reduced by hydrogen at a low temperature. In
the subsequent oxidation of the copper the gas does not come out suddenly, but in a
gradual manner. .
S
274 ON THE ABSORPTION AND
volume of 4.83 cub. centims, taking the specific gravity of the metal as
19:31. Exhausted at a red heat without any further treatment, the
reduced gold yielded 34 cub. centims, of gas, which may therefore be
supposed to be gas usually present in gold reduced in the manner
described. This is 0.704 vol. of the gold. The occluded gas in preci-
pitated gold gave to analysis
0-05 cub. centim. Oxygen.
1:50 , ,, Carbonic acid.
1°85 , , Carbonic oxide, etc.
3°40
2. Of the original cornettes of fine gold, from gold assays conducted
several months before, 93.3 grims, having a volume of 4.83 cub. centims,
were submitted without any further treatment to aspiration at a red
heat. The gold gave up in the first half hour 9:45 cub. centims of gas,
and in the second half hour 0-8 cub. centim., making together 10:25
cub. centims. Hence 1 volume of the gold cornettes appears to hold
2-12 volumes of gas. This gas consisted of -
6'70 cub. centims. Carbonic oxide.
1'50 , 25 Carbonic acid.
1.58 , 25 Hydrogen.
0°44 , 3 y Nitrogen.
0.03 , 3) loss.
10-25
The cornettes do not appear ever to assume again so much gas as
they first acquired in the assay muffle. It follows that the weight of a
gold cornette is increased about 2 parts in 10,000 by the weight of
occluded gas. As the gold also retains 7 or 8 parts of silver in 10,000,
it follows that the absolute quantity of gold in a cornette is less than
the weight of the cornette as indicated by the balance, by 1 part in
1000. This does not disprove the accuracy of the usual gold assay,
which is always made in comparison with gold of known composition
as a check, and is therefore relatively true.
3. The same volume of gold cornettes, amounting to 4.83 cub.
centims, heated again in carbonic oxide gas, gave up afterwards 1-6
cub. centim. of occluded gas, composed of -
14 cub. centim. Carbonic oxide.
0-2 , ,, Carbonic acid.
1-6
4. The same mass of gold cornettes heated in hydrogen gas, gave
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 275
up afterwards in one hour 2:7 cub. centims. of gas, which appeared to
consist of
2:34 cub. centims. Hydrogen.
0.36 , 25 Nitrogen, etc.
*=s*
2-70
The power of this metal to occlude hydrogen gas is very sensible.
The metal here appears to hold 0:48 volume of hydrogen gas. The
same gold, when dissolved and precipitated, was also found capable of
holding 0-44 volume of hydrogen.
5. The same mass of cornettes, heated in carbonic acid gas, gave up
afterwards in one hour 1-05 cub. centim, gas, in which baryta-water
showed the presence of
0.78 cub, centim. Carbonic acid.
The charged cornettes were always freely exposed to air for some
time before occluded gas was extracted from them and measured, so as
to allow the escape of any loosely attached gas.
6. The same cornettes were heated and cooled in a stream of dry
air, in like manner as they had been treated with other gases. The
occluded air given out in one hour amounted in two different experi-
ments to 1:15 and 0.95 cub. centim. respectively. The gas of the
second experiment gave -
0-82 cub. centim. Nitrogen = S6-3
0.08 , ,, Carbonic acid = 8.4
0-05 , , Oxygen – 5-3
0.95 * 100-0
The whole occluded air amounts to 0-2 volume of the gold, and is
principally nitrogen. The indifference of gold to oxygen is remarkable,
and contrasts with the power of silver to occlude the same gas.
Silver.
1. Fine silver, in the form of wire, 2 millims. in diameter, with its
surface duly purified, was first heated alone in the porcelain tube, and
then exhausted of gas by the Sprengel tube in the usual way. The
natural gas derived from this metal was small in quantity, and it ap-
peared to come off almost entirely in one hour. The silver wire
weighed 1088 grms, and had a volume of 10:37 cub. centims, taking
the specific gravity of pure silver as 10°49. The gas extracted
amounted to
276 ON THE ABSORPTION AND
2.2 cub. centims. in thirty minutes.
0-8 , 32 ,
*
3-0 , 33 in one hour.
The gas consisted of
2.4 cub. centims. Carbonic acid.
0-6 , 23 Carbonic oxide.
3.0
Silver wire therefore appeared to hold occluded 0.289 volume of
gas, principally carbonic acid. There is reason, however, to suppose
that the occluded gas may really be oxygen, and that the latter was
converted into carbonic acid at the temperature of extrication, by a
trace of carbon existing in the fine silver.
2. The same quantity of silver wire was now charged with hydrogen,
by being heated to redness and afterwards cooled slowly in that gas.
The gas extricated amounted to -
2:3 cub. centims. in forty-five minutes.
0:2 , 23 in fifteen minutes.
2°5 , 22 in one hour.
The gas consisted of
2.2 cub. centims. Hydrogen.
0-3 , 22 Nitrogen, etc.
2.5
The fine silver had therefore occluded 0.211 volume of hydrogen.
The metal acquired a beautiful frosted appearance on the surface; and
by repeated heating it became highly crystalline and brittle. *
3. The same portion of silver was now charged with oxygen. The
Occluded gas given off amounted to
7-5 cub. centims. in thirty minutes.
O'3 35 y 5 > y
7-8 , , in one hour.
The gas consisted of
7-6 cub. centims. Oxygen.
0-2 , 55 Nitrogen, etc.
7-8
The silver therefore held occluded 0.745 volume of oxygen. This
gas, like the hydrogen in platinum, was permanently fixed in the metal
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 277
at all temperatures below an incipient red heat. It did not tarnish the
bright metallic surface of the silver, or produce any appearance Sugges–
tive of the oxidation of a metal.
4. The same portion of silver, after being dissolved in acid, precipi-
tated as chloride, and reduced again, was exposed to atmospheric air at
a red heat, and afterwards exhausted. The gas given off amounted to
5-56 cub. centims. in fifteen minutes.
0.30 , 25
5-86
Of this gas 5'56 cub. centims, or nearly the whole, proved to be
oxygen gas; or the silver held occluded 0-545 volume of oxygen. This
silver had been purified from the chloride, and it contained no trace of
Copper. -
When silver, of British Standard (that is, containing 7.5 per cent. of
copper), is exposed to air or oxygen at a low red heat, the silver becomes
almost black on the surface from oxidation of the copper. Silver wire
in this blackened state gave off several volumes of oxygen under the
action of heat and a vacuum. Much of the Superficial oxide disappeared
at the same time. It appeared as if the operation tended to the reduc-
tion of the Superficial oxide of copper, oxygen being liberated, and the
copper absorbed by the mass of silver.
5. A specimen of silver reduced from the oxide, in the form of
sponge, which was considered pure, but was not analysed, occluded 6:15,
8:05, and 7:47 volumes of oxygen, in successive experiments, without
any visible tarnish of the surface. Can the attraction or affinity of
silver for oxygen, which enables the pure metal to occlude that gas, be
enhanced by the presence of a mere trace of some positive metal like
copper ? -
6. The same specimen of fritted silver was found to occlude, in suc-
cessive experiments,
0.907 vol. Hydrogen.
0.938 , 53
0.486 , Carbonic acid.
0-545 , 33 25
0-156 , Carbonic oxide.
Hydrogen and carbonic acid, as well as Oxygen, appear to be taken
up in larger proportion by this silver than by the former specimen of
the same metal.
7. Of pure silver highly laminated, 500 leaves, weighing 12.5 grms,
were exposed to air at a red heat, and thereafter exhausted at the same
temperature. The silver (1 vol.) gave up 137 volume of oxygen, 0.20
volume of nitrogen, and 0.04 volume of carbonic acid.
2 3
278 ON THE ABSORPTION AND
It appears that silver has a relation to oxygen similar to that exhi-.
bited by platinum, palladium, and iron to hydrogen. The power of
silver and of litharge in a state of fusion to absorb oxygen, and to allow
that gas to escape on solidification, may be connected with the observed
capacity of the colloid metal, softened by heat, to absorb the same gas,
although to a less extent.
Iron.
The penetration of iron by hydrogen is demonstrated as clearly by
MM. Deville and Troost as that of platinum. A thin tube of cast steel,
3 or 4 millims. in thickness, already enclosing hydrogen gas in its
cavity, was surrounded by air or by nitrogen gas circulating in an
annular space between the steel tube mentioned and a wider external
porcelain tube. In the absence of any visible pores in the steel, hydro-
gen made its way through the substance of the metal, and escaped into
the annular space as soon as the system of tubes was exposed to a red
heat. A nearly if not entirely complete vacuum was formed within the
iron tube." In another modification of the experiment, carbonic oxide
from an uncertain source appeared within the iron tube, particularly
when the temperature was most elevated.”
Wrought iron, in the form of thin wire (No. 23), about 0.4 millim.
in diameter, first carefully cleaned with caustic alkali and water, was
heated alone in the porcelain tube exhausted of air, for the purpose of
eliminating any natural gases.
1. Of the iron wire referred to, 46 grms, with a volume of 5.9 cub.
centims, the specific gravity of the metal being taken at 7-8, were
heated by the open combustion-furnace. Gas came off freely at a red
heat,
(1) In fifteen minutes, 15-6 cub. centims, containing 3-5 cub. cen–
tims. carbonic acid, or 22.4 per cent.
(2) In fifteen minutes, 7-17 cub. centims, containing 0-52 cub. cen-
tim, or 7.2 per cent. of carbonic acid. The gas of this and the following
stages of observation now burnt with a blue flame, and was principally
carbonic oxide.
(3) In thirty minutes, 10.4 cub. centims, of which 6:86 cub. centims.
were carbonic oxide.
(4) In thirty minutes, 816 cub. centims, of which 0:12, or 1.4 per
cent. was carbonic acid.
(5) In thirty minutes, 5:52 cub. centims, of which 0.03 was carbonic
acid—that is, 0.5 per cent. -
Hence 46 grims, of wrought iron have in two hours given off 46.85
* Comptes Rendus, t. lvii. p. 965 (1863). * Ibid. t. ix. p. 102 (1864).
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 279
cub. centims of gas, measured at about 15° C.; or 1 volume of iron has
discharged 794 volumes of gas, of which about two-thirds was carbonic
oxide; and the metal does not appear to be yet quite exhausted. Iron
is a metal not unlikely to contain small quantities of carbon and oxygen,
both in chemical union with iron; and the gas extricated may partly
be due to a reaction of these elements upon each other at a red heat.
2. In another similar experiment upon 32 grims. of clean iron wire
(No. 21), measuring 4-1 cub. centims, the iron was heated in a small
glass tube, to exclude the idea of the conceivable permeability of the
porcelain tube. The iron gave off gas at a pretty uniform rate, which
amounted in an hour to 29-8 cub. centims, of which 4:44 cub. centims.
were carbonic acid, and the remainder principally carbonic oxide, with
hydrogen and a trace of a hydro-carburet. Here the iron wire gave off
7-27 volumes of gas.
3. In a third experiment on thin iron wire (No. 23), the extrication
of the natural gases at a red heat was pushed to a greater degree of
exhaustion. The weight of the iron was 39 grims., and its volume 5 cub.
centims. In the first and second hour the gas collected was 45 cub.
centims. ; in the third hour 10-85 cub. centims. ; in the fourth and fifth
hours 5-65 cub. centims. ; in the sixth hour 0-9 cub. centim., and in the
seventh hour 0-7 cub. centim. The iron appears to be now nearly
exhausted, after the extrication of 63:1 cub. centims, or 12:55 volumes
of gas.
It is evident that iron cannot be safely dealt with in experiments
upon the permeation or upon the absorption of gases, till these gases,
whether self-produced or pre-existing, are first extricated from the
metal. The carbonic oxide observed in the tube experiments of M.
Deville may have been derived from the same source.”
4. To observe the absorption of hydrogen, the mass of exhausted
iron wire remaining after the last experiment was heated to redness,
and cooled gradually in the same gas. The metal was afterwards freely
exposed to air (as usual) to get rid of any loosely attached hydrogen.
Now exhausted again by the Sprengel pump at a low red heat, the iron
gave 2.5 cub. centims, of gas in one hour, but the greater portion in the
first ten minutes, consisting of
2:3 cub. centims. Hydrogen.
0-2 , yy Carbonic oxide, etc.
2.5
The iron appears therefore to be capable of holding 0:46 volume of
1 The gases which escape from cast iron in a state of fusion have been examined by
M. L. Cailletet. They appear to contain from 49 to 58 per cent. of carbonic oxide, 34.
to 39 of hydrogen, and 8 to 12 of nitrogen.—Comptes Rendus, t. Ixi. p. 850 (1865).
2SO oN THE ABSORPTION AND
. Yo
hydrogen. The wire became white, like galvanized iron. This was
confirmed in a second observation, a thicker wire holding 0.42 vol.
hydrogen.
5. The same specimen of iron was now charged with carbonic oxide
gas, in the manner it had previously been charged with hydrogen. It
was also freely exposed to air. The iron wire remained soft, was not
capable of becoming hard when heated red-hot and suddenly cooled,
and was not altered in aspect or in solubility in acids. The gas extri-
cated by the air-exhauster amounted to
9:45 cub. centims. in 13 minutes.
2'43 , }} 5 33
8:05 , 3 y 42 2 3
3:15 , 39 60 ,
23:08 , 22 in two hours.
Of this gas 2076 cub. centims. proved to be carbonic oxide. Pure
dron, then, is capable of taking up at a low red heat, and holding when
cold, 4-15 volumes of carbonic oxide gas. This fact was confirmed in
various other experiments. It explains partly, if not entirely, the
abundance of carbonic oxide observed among the natural gases of iron
in experiments 1, 2, and 3. In the course of its preparation wrought
iron may be supposed to occlude six or eight times its volume of car-
bonic oxide gas, which is carried about ever after. How the qualities
of iron are affected by the presence of such a substance, no way metallic
in its characters, locked up in so strange a way, but capable of reappear-
ing, under the influence of heat, at any time, with the elastic tension of
a gas, is a subject which metallurgists may find worthy of investigation.
The relations of the metal iron to carbonic oxide gas appear to be
altogether peculiar. They cannot fail to have a bearing upon the im-
portant process of acieration. The intervention of carbonic oxide in the
usual process of the cementation of iron with charcoal, long recognised
by accurate observers, may be said now to be placed beyond all doubt
by the recent beautiful research of M. Margueritte." Hitherto the
decomposing action of the iron upon carbonic oxide has been supposed
to be exercised only at the external surface of the metal. A surface-
particle of the iron has been supposed to assume one half of the carbon
belonging to an equivalent of carbonic oxide (C.O.), while the remain-
ing elements diffused away into the air as carbonic acid (CO), to
reacquire carbon from the charcoal placed near, and to become capable
of repeating the original action. It is now seen that such a process
need not be confined to the surface of the iron bar, but may occur
throughout the substance of the metal, in consequence of the prior
* Annales de Chimie, etc., 4 sér. t. vi., 1865.
DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 281
penetration of the metal by carbonic oxide. The direct contact and
action of carbon (in the form either of diamond or charcoal) upon iron
is allowed to produce cast iron and not steel. It appears that the &
diffused action of carbonic oxide is the proper means of distributing the
carbon throughout the mass of iron. The blistering of the bar appears
to testify to the necessary production and evolution of carbonic acid,
owing to the decomposition of the carbonic oxide in the interior of the
bar. &
The inquiry suggests itself whether acieration would not be promoted
by alternation of temperature frequently repeated. The lowest red
heat, or a temperature even lower, appears to be most favourable to the
absorption of carbonic oxide by iron, or for impregnating the metal with
that gas; while a much higher temperature appears to be required to
enable the metal to decompose carbonic oxide, to appropriate the carbon,
and become steel. The action of a high temperature is made very clear
by M. Margueritte. The process of acieration, it seems then, should be
divided into two distinct stages, conducted at very different tempera-
tures,--the first to introduce carbonic oxide into the iron, and the second
to decompose the carbonic oxide so introduced. The carbonic oxide
once safely occluded by the iron, the metal might even be cooled and
preserved in the air, the second heating being postponed for any length
of time. Such alternations of temperature are not unlikely to occur by
accident during the usual long process of cementation; but they might
be properly regulated with advantage, and the process may admit of
being abridged in point of time.
Antimony, as a highly crystallizable metal, was exposed to hydrogen
gas both above and below the point of fusion of the metal, and after-
wards submitted to exhaustion in the usual manner. No hydrogen was
extricated.
XVIII.
ON THE OCCLUSION OF HYDROGEN GAS BY METEORIC
IRON.
From Proceedings of the Royal Society, vol. xv. p. 502, May 16, 1867. [Comptes Rendus,
May 27, 1867, vol. lxiv, p. 1067; Poggendorff’s Annal. vol. cxxxi. (1867), p. 151].
SOME light may possibly be thrown upon the history of such metals
found in nature as are of a soft colloid description, particularly native
iron, platinum, and gold, by an investigation of the gases which they
282 ON OCCLUSION OF HYDROGEN GAS BY METEORIC IRON.
hold occluded, such gases being borrowed from the atmosphere in which
the metallic mass last found itself in a state of ignition. The meteoric
iron of Lenarto appeared to be well adapted for a trial. This well-known
iron is free from any stony admixture, and is remarkably pure and mal-
leable. It was found by Wehrle to be of specific gravity 7-79, and to
consist of
Iron, . wº • e 90°883
Nickel, ę & e 8’450
Cobalt, ſº e wº 0.665
Copper, ſº & tº 0-002
From a larger mass a strip of the Lenarto iron 50 millimetres by 13 .
and 10 millimetres, was cut by a clean chisel. It weighed 45.2 grammes,
and had the bulk of 578 cubic centimetres. The strip was well washed
by hot solution of potassa, and then repeatedly by hot distilled water, and
dried. Such treatment of iron, it had been previously found, conduces
in no way to the evolution of hydrogen gas when the metal is subse-
quently heated. The Lenarto iron was enclosed in a new porcelain tube,
and the latter being attached to a Sprengel aspirator, a good vacuum
was obtained in the cold. The tube being placed in a trough combus-
tion furnace, was heated to redness by ignited charcoal. Gas came off
rather freely, namely—
In 35 minutes, tº ſº e 5:38 cub. centims.
In 100 minutes, . ſº § 9°52 25
In 20 minutes, o * * 1:63 22
In 2 hours 35 minutes, . . 1653 22
The first portion of gas collected had a slight odour, but much less
than that of the natural gases occluded by ordinary malleable iron.
The gas burned like hydrogen. It did not contain a trace of carbonic
acid, nor any hydrocarbon vapour absorbable by fuming sulphuric acid.
The Second portion of gas collected, consisting of 9:52 cub. centims,
gave by analysis—
Hydrogen, . . . 826 cub. centims. . . 85.68
Carbonic oxide, . * 0°43 25 º e 4'46
Nitrogen, . º te 0.95 X5 * * 98.6
9-64 . , * . 100'00
The Lenarto iron appears, therefore, to yield 2:85 times its volume
of gas, of which 86 per cent. nearly is hydrogen. The proportion of
carbonic oxide is so low as 4% per cent.
The gas occluded by iron, from a carbonaceous fire, is very different,
the prevailing gas then being carbonic oxide. For comparison a quan-
ON THE OCCLUSION OF HYDROGEN GAS BY METALS. 283
tity of clean horse-shoe nails was submitted to a similar distillation.
The gas collected from 235 grammes of metal (3:01 cub, centims.) was—
In 150 minutes, . gº 5:40 cub. centims.
In 120 minutes, . we 2:58 32
In 4 hours 30 minutes, . 7-98 22
The metal has given 2-66 times its volume of gas. The first portion
collected appeared to contain, of hydrogen 35 per cent., of carbonic oxide
503, of carbonic acid 7-7, and of nitrogen 7 per cent. The latter portion
collected gave more carbonic oxide (58 per cent.) with less hydrogen
(21 per cent), no carbonic acid, the remainder nitrogen. The predo-
minance of carbonic oxide in its occluded gases appears to attest the
telluric origin of iron. - -
Hydrogen has been recognised in the spectrum-analysis of the light
of the fixed stars, by Messrs. Huggins and Miller. The same gas consti-
tutes, according to the wide researches of Father Secchi, the principal
element of a numerous class of stars, of which a Lyrae is the type. The
iron of Lenarto has no doubt come from such an atmosphere, in which
hydrogen greatly prevailed. This meteorite may be looked upon as
holding imprisoned within it, and bearing to us, hydrogen of the stars.
It has been found difficult, on trial, to impregnate malleable iron
with more than an equal volume of hydrogen, under the pressure of our
atmosphere. Now the meteoric iron gave up about three times that
amount, without being fully exhausted. The inference is that the
meteorite has been extruded from a dense atmosphere of hydrogen gas,
for which we must look beyond the light cometary matter floating about
within the limits of the solar system.
XIX.
ON THE OCCLUSION OF HYDROGEN GAS BY METALS.
From Proceedings of the Royal Society, June 11, 1868, vol. xvi. p. 422. [Comptes Rendus,
May 25, 1868, vol. lxvi. p. 1014; Archives des Sciences, June 1868, vol. xxxii.
p. 148; Annales de Chimie et de Physique [4] vol. xiv. p. 315; Poggendorff's
Annal. vol. cxxxiv. 1868, p. 321 ; Philosophical Magazine [4], vol. xxxvi. p. 63.]
IN my experiments, already published, on the occlusion of hydrogen
by the metals palladium, platinum, and iron, the absorption of the gas
was observed to be of uncertain occurrence at low temperatures, but
was insured by heating the metal, whether in the form of sponge or
284 ON THE OCCLUSION OF HYDROGEN GAS BY METALS.
aggregated by hammering, and allowing it to cool slowly and completely
in a hydrogen atmosphere. This fact was referred to the condition of
absolute purity of the metallic surface being essential to the first ab-
sorbing action, as it is to the action of platinum-foil or wire in deter-
mining the combustion of the gaseous mixture of oxygen and hydrogen,
as observed by Faraday. A new method of charging the metals with
hydrogen at low temperatures has lately presented itself, which is not
without interest.
When a plate of zinc is placed in dilute sulphuric acid, hydrogen
is freely evolved from the surface of the metal, but no hydrogen is
occluded and retained at the same time. A negative result was indeed
to be expected from the crystalline structure of zinc. But a thin plate
of palladium immersed in the same acid, and brought into metallic Con-
tact with the zinc, soon becomes largely charged with the hydrogen, which
is then transferred to its surface. The charge taken up in an hour by a
palladium plate, rather thick, at 12° amounted to 173 times its volume.
The absorption of hydrogen was still more obvious when the palla-
dium plate was constituted the negative electrode in acidulated water
to a Bunsen battery of six cells. The evolution of oxygen gas at the
positive electrode continuing copious, the effervescence at the negative
electrode was entirely suspended for the first twenty Seconds, in con-
sequence of the hydrogen being occluded by the palladium. The final
absorption amounted to 2004 volumes, and was greater in amount than
the volume of hydrogen occluded by the same plate heated and cooled
in an atmosphere of the gas, which did not exceed 90 volumes.
It is worthy of remark that, although the hydrogen enters the pal-
ladium, and no doubt pervades the whole mass of the metal in such
circumstances, the gas exhibits no disposition to leave the metal and
escape into a vacuum, at the temperature of its absorption. Thus a
thin plate of palladium, charged with hydrogen in the manner de-
scribed, was washed, dried by a cloth, and then sealed up in an ex-
hausted glass tube. On breaking the tube under mercury after two
months, the vacuum was found perfect. No hydrogen had vaporized
in the cold (about 12"); but on the application afterwards of a heat of
100° and upwards, 333 volumes of gas were evolved from the metal.
A similar result was obtained on making a hollow palladium
cylinder, of which the length was 115 millimetres, diameter 12 milli-
metres, and thickness 1 millimetre, the negative electrode in an acid
fluid, while the closed cavity of the cylinder was kept exhausted by
means of a Sprengel aspirator. No hydrogen whatever passed through
into the vacuous cavity in several hours, although the gas was no doubt
abundantly absorbed by the outer surface of the cylinder, and pervaded
the metal throughout.
on THE occLUSION OF HYDROGEN GAs By METALs. 285
It appears, then, that when hydrogen is absorbed by palladium, the
volatility of the gas may be entirely suppressed; and hydrogen may be
largely present in metals without exhibiting any sensible tension at low
temperatures. Occluded hydrogen is certainly no longer a gas, what-
ever may be thought of its physical condition. The same conclusion
was indicated by another series of experiments, in which it was found
that, to be occluded by palladium, and even by iron, hydrogen does not
require to be applied under much pressure, but, on the contrary, when
highly rarefied is still freely absorbed by these metals.
The occluded hydrogen is readily extracted from palladium by
reversing the position of the latter in the decomposing cell of the
battery, so as to cause oxygen to be evolved on the surface of the
metal. The hydrogen is then drawn out as rapidly as it had previously
entered the palladium, and the metal is exhausted in a complete
manner by such treatment. When palladium charged with hydrogen
, is left exposed to the atmosphere, the metal is apt to become suddenly
hot, and to lose its gas entirely by spontaneous oxidation.
Platinum may be charged with hydrogen by voltaic action, as well
as palladium, but with the usual inferior proportion of gas. The charge
of hydrogen taken up in a decomposing voltaic cell by old platinum in
the form of a tube, of the thickness of a small crucible, was 2-19
volumes. This absorbed gas was also readily withdrawn from the
platinum, and oxidized on reversing the place of the metal in the de-
composing cell. The platinum acquired its well-known polarizing
power in virtue of the occluded hydrogen. This power was retained
by the metal after being washed with pure water and wiped with a
cloth, and was brought into action on placing the metal in dilute acid.
The temperature required to expel the hydrogen so absorbed by pla–
tinum was found to be little short of a red heat, although the gas had
entered the metal at a low temperature.
Soft iron, left some time in a dilute acid, occluded 0-57 volume of
hydrogen. This charge of gas was also retained at low temperatures,
and did not escape into a vacuum till the temperature was raised nearly
to redness. This proves that, like platinum, iron is not penetrated
through in the cold by hydrogen, the temperature of emission being
elevated considerably."
While hydrogen was absorbed freely by palladium and platinum as
negative plates, no oxygen whatever was absorbed by plates of the same
metals in the position of positive electrodes. Oxygen gas was dis-
1 In M. Cailletet's experiment of exposing a thin sheet of iron to an acid, the metal
is no doubt penetrated through by hydrogen in the cold, but apparently from the pene-
trating agency of the acid which is insinuating itself into the metal at the same time.—
Comptes Rendus, 4 Mai 1868.
286 ON THE OCCLUSION OF HYDROGEN GAS BY METALS.
engaged freely on the surface of the latter without being condensed. A
platinum plate which had acted for several hours as a positive elec-
trode gave afterwards, when submitted to heat with exhaustion, a
Small trace of carbonic acid, but no oxygen.
The familiar igniting power of platinum sponge (or clean plate) upon
a jet of hydrogen in the air seems to depend solely upon the influence
of the metal upon its occluded hydrogen. The hydrogen appears to be
polarized, and to have its attraction for oxygen greatly heightened. I
beg to offer the following representation of this phenomenon, with an
apology for the purely speculative character of the explanation. The
gaseous molecule of hydrogen being assumed to be an association of two
atoms, a hydride of hydrogen, it would follow that it is the attraction
of platinum for the negative or “chlorylous” atom of the hydrogen
molecule which attaches the latter to the metal. The tendency, im–
perfectly satisfied, is to the formation of a hydride of platinum. The
hydrogen molecule is accordingly polarized, oriente, with its positive or
“basylous” side turned outwards, and having its affinity for oxygen
greatly enlivened. It is true that the two atoms of a molecule of
hydrogen are considered to be inseparable ; but this may not be incon-
sistent with the replacement of such hydrogen atoms as are withdrawn,
on combining with oxygen, by other hydrogen atoms from the adjoin-
ing molecules. It is only necessary to suppose that a pair of con-
tiguous hydrogen molecules act together upon a single molecule of the
external oxygen. They would form water, and still leave a pair of
atoms, or a single molecule of hydrogen, attached to the platinum.
The oxidation of alcohol, ether, and similar hydrocarbons, through
the agency of platinum, likewise appears to be always an immediate
consequence of a similar polarization of the hydrogen of those sub-
stances, or of some other oxidable constituent.
As has already been remarked, it does not follow that, because a gas
is occluded by a metal, under the pressure of the atmosphere, at a low
temperature, the gas will also escape from the metal into a vacuum at
the same temperature, a much higher temperature being often required
for the expulsion of the gas than for its first absorption. This is parti-
cularly true of carbonic oxide occluded by iron. Cast iron is much too
porous for such experiments, and allows carbonic oxide, equally with
other gases, to pass through abundantly by the agency of gaseous dif-
fusion. Even with malleable iron there is a difficulty in observing,
owing to the long time during which that metal continues to discharge
carbonic oxide from its own store of that gas. But a malleable iron
tube, first thoroughly deprived of its natural gas, was found to allow
carbonic oxide to pass through it into a vacuum very slowly compared
with hydrogen, although the volume of carbonic oxide which the metal
ON THE OCCLUSION OF HYDROGEN GAS BY METALS. 287
is capable of absorbing is very sensible, amounting to 4 volumes, and
more considerable than the volume of hydrogen which the same metal
can occlude. Carbonic oxide did not sensibly pass through iron of 1.7
millimetre in thickness till the temperature was greatly elevated; and
then the passage of gas was, in a minute—
Of carbonic oxide, at a full red heat, 0.284 cub. centims. per
square metre of surface.
Of hydrogen oxide, at a full red heat, 76.5 cub. centims. per
square metre of surface.
The condition of hydrogen as occluded by a colloidal metal may be
studied with most advantage in its union with palladium, where the
proportion of gas held is considerable. In the pulverulent spongy
state, palladium took up 655 volumes of hydrogen; and so charged it
gave off no gas in vacuo at the ordinary temperature, nor till its tem-
perature was raised to nearly 100°. Hammered palladium foil has been
observed to take up quite as much gas. But the condition in which
palladium appears to be most absorptive is when precipitated from a
Solution of about 1.6 per cent of the chloride, by the action of a voltaic
battery, in the form of a compact metal. Palladium is not one of the
metals readily thus precipitated; but it may be thrown down upon a
thin platinum wire, in brilliant laminae, by the action of a large single
cell. The palladium after a time detaches itself from the wire, exhibit-
ing a bright white metallic surface where it had been in contact with
the platinum, and a dull surface, suggesting metallic arsenic, on the side
exposed to the acid. As so prepared, it does not contain any occluded
hydrogen. But the metallic films, when heated to 100° in hydrogen,
and allowed to cool slowly for an hour in the same gas, were found
to occlude 982-14 volumes of gas, measured with thermometer at 11°,
and barometer at 756 millimetres. This is the largest absorption of
hydrogen observed. From the palladium so charged there was a slight
indication of the escape of hydrogen into a vacuum, with extreme slow-
ness in the cold. This charged palladium is represented by weight as
Palladium 1:0020 grn., tº * . 99.277
Hydrogen 0:0073 grm., g º . . .723
100'000
It is in the proportion of one equivalent of palladium to 0-772 equi-
valent of hydrogen," or there is an approximation to single equivalents
Pd H. But the idea of definite chemical combination is opposed by
various considerations. No visible change is occasioned to the metallic
palladium by its association with the hydrogen, Hydrides of certain
º: 1 H=1, Pd = 106.5.
288 ON THE OCCLUSION OF HYDROGEN GAS BY METALS.
metals are known, as the hydride of copper (Wurtz) and the hydride of
iron (Wanklyn); but they are brown pulverulent substances with no
metallic characters. Indeed, a hydride of palladium itself can be
formed, but not preserved, on account of its great instability. Follow-
ing the process of M. Wurtz for the hydride of copper, nitrate of palla-
dium was boiled with sulphuric acid, and the sulphate of palladium
(a red crystalline salt) prepared. A solution of this salt, with an excess
of sulphuric acid, was precipitated by the hypophosphite of Soda ; a
black powder fell, which speedily underwent decomposition at 0°, evolv-
ing copious volumes of hydrogen gas. The final residue appeared to be
pure palladium, of its usual black amorphous appearance, and with no
trace of crystallization. It is singular that this palladium precipitate
contained no occluded hydrogen; and even when heated, and after-
wards exposed to an atmosphere of hydrogen in the usual manner, the
palladium black So prepared condensed no sensible quantity of that gas.
I am inclined to conclude that the passage of hydrogen through a
plate of metal is always preceded by the condensation or occlusion of
the gas. But it must be admitted that the rapidity of penetration is
not in proportion to the volume of gas occluded; otherwise palladium
would be much more permeable at a low than at a high temperature.
A plate of that metal was sensibly exhausted of hydrogen gas at 267”,
but continued permeable, and in fact increased greatly in permeability,
at still higher temperatures, and without becoming permeable to other
gases at the same time. In a striking experiment, a mixture of equal
volumes of hydrogen and carbonic acid was carried through a small
palladium tube, of which the internal diameter was 3 millimetres, and
the thickness of the wall 0.3 millimetre. From the outer surface of this
tube gas escaped into a vacuum, at a red heat, with the enormous velo-
city of 1017-54 cub. centims. per minute for a square metre of surface.
This gas did not disturb baryta-water. It was pure hydrogen.
A still more rapid passage of hydrogen was observed through the
| Substance of a hollow cylinder of palladium 1 millimetre in thickness,
at a higher temperature, approaching the melting-point of gold. The
palladium cylinder being enclosed in a porcelain tube charged with
pure hydrogen, was exhausted as usual, and gave 105.8 cub. centims. of
gas in five minutes, measured with bar. 753 millims., therm. 10°. As
the external surface of the palladium tube amounted to 0.0053 square
metre, the passage of gas was
3992'22 cub. centims, from a square metre of surface per minute.
The rate of penetration of hydrogen through the same palladium
tube, at the lower temperature of 265°C., was previously observed to be
327 cub, centims, from a square metre of surface per minute,
ON THE OCCLUSION OF HYDROGEN GAS BY METALS. 289
The velocity of penetration thus appears to increase in a rapid ratio
with the temperature.
When carbonic acid was substituted for hydrogen, at the same high
temperature, a very minute penetration was perceived, amounting to
186 cub. centim. from a square metre of surface per minute.
This gives for carbonic acid one twenty-thousandth part of the rate
of hydrogen. Whether it is a penetration of the same sort, although
greatly less in degree, or rather the consequence of a sensible porosity
in the palladium (of which it would become the measure), remains
uncertain. :-
The quantity of hydrogen held by the metal at these high tempera-
tures may become too small to be appreciated ; but I presume it is still
present, and travels through the metal by a kind of rapid cementation.
This extreme mobility is a singular property of hydrogen, which was
involved in the fundamental discovery, by MM. H. Sainte-Claire Deville
and Troost, of the passage of that gas through plates of iron and
platinum at high temperatures.
The marked rapidity of the passage of the same gas through a thin
sheet of Caoutchouc appears to be more capable of explanation on
known principles. Caoutchouc of less than 0.1 millimetre in thick-
ness, if impregnated with hydrogen, loses its gas entirely by the most
momentary exposure to the air. A tube of 2 millimetres in thickness,
through which hydrogen and carbonic acid were singly passed, each for
an hour, was found to retain—
Of hydrogen, sº g e 0.0113 volume.
Of carbonic acid, tº º g 0.2200 ,
The absorption, then, is in the proportion of 1 hydrogen to 20 carbonic
acid; but the comparative rate of penetration of the two gases through
a sheet of caoutchouc is as 1 hydrogen to 2% carbonic acid; or the
hydrogen moves eight times as rapidly as the density of its solution
would indicate. But these gases differ in diffusibility as carbonic acid
1 to hydrogen 4-7. The rapid passage of hydrogen through caoutchouc
is thus partly explained by the rapid manner in which that gas is
brought to one surface of the sheet and conveyed away from the other
by gaseous diffusion. Again, both substances travel through the sub-
stance of the caoutchouc by their diffusibility as liquids. Suppose
hydrogen in that form to be nearly as much more diffusive than the
other substance as it is when both are gaseous, then the observed rapid
passage of hydrogen through Caoutchouc would appear to be fully
accounted for. -
Liquid diffusion has also a bearing upon the rapid dissemination of
T
290 ON THE RELATION OF
hydrogen through a soft colloid metal, like palladium or platinum, at a
high temperature. The liquid diffusion of salts in water is known to be
six times as rapid at 100° as at 0°. If the diffusion of liquid hydrogen
increases with temperature in an equal ratio, it must become a Very
rapid movement at a red heat. Although the quantity absorbed may
be reduced (or the channel narrowed), the flow of liquid may thus be
increased in velocity, The whole phenomena appear to be consistent
with the solution of liquid hydrogen in the colloid metal. The “solu-
tion affinity” of metals appears to be nearly confined to hydrogen and
carbonic oxide, so that metals are not sensibly penetrated by other gases
than these. t
XX.
ON THE RELATION OF HYDROGEN TO PALLADIUM, AND
ON HYDROGENIUM.
From Proceedings of the Royal Society, vol. xvii. pp. 212, 500, Jan. 14, 1869. [Comptes
Rendus, Jan. 18, and June 28, 1869, vol. lxviii. pp. 101, 1511; Annals de Chimie
et de Physique [4], vol. xvi. p. 188; Chemical News, vol. xix. p. 478; Rerichte der
deutschen chemischen Gesellschaft, No. 2, 1869; Annalen der Chemie, vol. clii. p.
168 ; Philosophical Magazine, December 1869; Poggendorff’s Annalen der Physik,
vol. cxxxviii. (1869), p. 49.]
IT has often been maintained on chemical grounds that hydrogen
gas is the vapour of a highly volatile metal. The idea forces itself upon
the mind that palladium with its occluded hydrogen is simply an alloy
of this volatile metal, in which the volatility of the one element is
restrained by its union with the other, and which owes its metallic aspect
equally to both constituents. How far such a view is borne out by the
properties of the compound substance in question will appear by the
following examination of the properties of what, assuming its metallic
character, would have to be named Hydrogenium.
1. Density.—The density of palladium when charged with eight or
nine hundred times its volume of hydrogen gas is perceptibly lowered;
but the change cannot be measured accurately by the ordinary method
of immersion in water, owing to a continuous evolution of minute hydro-
gen bubbles which appears to be determined by contact with the liquid.
However, the linear dimensions of the charged palladium are altered
HYDROGEN TO PALLADIUM. 29 I
so considerably that the difference admits of easy measurement, and
furnishes the required density by calculation. Palladium in the form
of wire is readily charged with hydrogen by evolving that gas upon the
surface of the metal in a galvanometer containing dilute sulphuric acid
as usual." The length of the wire before and after a charge is found by
stretching it on both occasions by the same moderate weight, such as will
not produce permanent distension, over the surface of a flat graduated
measure. The measure was graduated to hundredths of an inch, and by
means of a vernier, the divisions could be read to thousandths. The
distance between two fine cross lines marked upon the surface of the
wire near each of its extremities was observed.
Expt. 1–The wire had been drawn from welded palladium, and
was hard and elastic. The diameter of the wire was 0.462 millimetre;
its specific gravity was 12:38, as determined with care. The wire was
twisted into a loop at each end and the mark made near each loop. The
loops were varnished so as to limit absorption of gas by the wire to the
measured length between the two marks. To straighten the wire, one
loop was fixed, and the other connected with a string passing over a
pulley and loaded with 1.5 kilogramme, a weight sufficient to straighten
the wire without occasioning any undue strain. The wire was charged
with hydrogen by making it the negative electrode of a small Bunsen's
battery consisting of two cells, each of half a litre in capacity. The
positive electrode was a thick platinum wire placed side by side with
the palladium wire, and extending the whole length of the latter within
a tall jar filled with dilute sulphuric acid. The palladium wire had, in
consequence, hydrogen carried to its surface, for a period of 13 hour. A
longer exposure was found not to add sensibly to the charge of hydrogen
acquired by the wire. The wire was again measured and the increase
in length noted. Finally the wire, being dried with a cloth, was divided
at the marks, and the charged portion heated in a long narrow glass tube
kept vacuous by a Sprengel aspirator. The whole occluded hydrogen
was thus collected and measured; its volume is reduced by calculation
to bar. 760 millims, and therm. 0°C.
The original length of the palladium wire exposed was 609-144
millims. (23.982 inches), and its weight 16832 grm. The wire received
a charge of hydrogen amounting to 936 times its volume, measuring
128 cubic centims, and therefore weighing 0.01147 grim. When the gas
was ultimately expelled, the loss as ascertained by direct weighing was
0.01164 grim. The charged wire measured 618-923 millims, showing an
increase in length of 9.779 millims. (0.385 inch). The increase in linear
dimensions is from 100 to 101-605, and in cubic capacity, assuming the
expansion to be equal in all directions, from 100 to 104,908. Supposing
1 Proceedings of the Royal Society, p. 422, 1868.
292 ON THE RELATION OF
the two metals united without any change of volume, the alloy may
therefore be said to be composed of
By volume.
Palladium, . * 100 Or 95°32
Hydrogenium, gº 4'908 Or 4°68
I 04'908 100
The expansion which the palladium undergoes appears enormous if
viewed as a change of bulk in the metal only, due to any conceivable
physical force, amounting as it does to sixteen times the dilatation of
palladium when heated from 0 to 100° C. The density of the charged
wire is reduced, by calculation, from 12:3 to 11-79. Again, as 100 is to
4.91, so the volume of the palladium, 0-1358 cubic centim, is to the
volume of the hydrogenium, 0:0067.14 cubic centim. Finally, dividing
the weight of the hydrogenium, 0.01147 grim., by its volume in the alloy,
0-0067.14 cubic centim., we find
Density of hydrogenium, . * * 1-708
The density of hydrogenium, then, appears to approach that of mag-
nesium, 1743, by this first experiment.
Further, the expulsion of hydrogen from the wire, however caused,
is attended with an extraordinary contraction of the latter. On expel-
ling the hydrogen by a moderate heat, the wire not only receded to its
original length, but fell as much below that zero as it had previously.
risen above it. The palladium wire first measuring 609-144 millims,
and which increased 9.77 millims., was ultimately reduced to 599:444
millims, and contracted 9.7 millims. The wire is permanently shortened.
The density of the palladium did not increase, but fell slightly at the
same time, namely, from 12:38 to 12:12, proving that this contraction
of the wire is in length only. The result is the converse of extension
by wire-drawing. The retraction of the wire is possibly due to an effect
of wire-drawing in leaving the particles of metal in a state of unequal
tension, a tension which is excessive in the direction of the length of
the wire. The metallic particles would seem to become mobile, and to
right themselves in proportion as the hydrogen escapes; and the wire
contracts in length, expanding, as appears by its final density, in other
directions at the same time.
A wire so charged with hydrogen, if rubbed with the powder of
magnesia (to make the flame luminous), burns like a waxed thread
when ignited in the flame of a lamp.
Expt. 2–Another portion of the same palladium wire was charged
with hydrogen in a similar manner. The results observed were as
follows:–
HYDROGEN TO PALLADIUM. 293
Length of palladium wire, º º 488.976 millims.
The same with 867-15 volumes of occluded gas, 495.656 ,
Linear elongation, . • & e 6'68 22
Linear elongation on 100, . e • 13663 ,
Cubic expansion on 100, . s - 4°154 25
Weight of palladium wire, º * 1.0667 grm.
Volume of palladium wire, - º 0-08072 cub. cent.
Volume of occluded hydrogen gas, º 75°2 25
Weight of same, e º º 0.00684 grm.
Volume of hydrogenium, . . º 0.003601 cub. cent.
From these results is calculated
Density of hydrogenium, . - tº " I '898.
Expt. 3–The palladium wire was new, and on this occasion was well
annealed before being charged with hydrogen. The wire was exposed
at the negative pole for two hours, when it had ceased to elongate.
Length of palladium wire, . e 556°185 millims.
Same with 888:303 volumes hydrogen, 563-652 2 >
Linear elongation, º º º 7'467 32
Linear elongation on 100, . s 1°324 2 3
Cubic expansion on 100, o º 4'025 52
Weight of palladium wire, . º 1-1675 grm.
Volume of palladium wire, . e 0.0949 cub. centim.
Volume of occluded hydrogen gas, . 84-3 cub. centims.
Weight of same, e º º 0.007553 grim.
Volume of hydrogenium, º e 0-003820 cub. centim.
These results give by calculation
Density of hydrogenium, e e I '977.
It was necessary to assume in this discussion that the two metals do
not contract nor expand, but remain of their proper volume on uniting.
Dr. Matthiessen has shown that in the formation of alloys generally the
metals retain approximately their original densities."
In the first experiment already described, probably the maximum
absorption of gas by wire, amounting to 935-67 volumes, is attained.
The palladium may be charged with any smaller proportion of hydrogen
by shortening the time of exposure to the gas (329 volumes of hydrogen
were taken up in twenty minutes), and an opportunity be gained of
observing if the density of the hydrogenium remains constant, or if it
varies with the proportion in which hydrogen enters the alloy. In
the following statement, which includes the three experiments already
reported, the essential points only are produced.
1 Philosophical Transactions, 1860, p. 177.
29.4 ON THE RELATION OF
TABLE.
Volumes Linear expansion in millimetres. Domsity
of Hydrogen of . |
occluded. Hydrogenium.
From To
329 496-189 498°552 2:055
462 493-040 496-520 1-930
487 370-358 373-126 1.927
745 305-538 51.1°303 1917
867 488.976 495'656 13898
888 556-185 563-652 1977
936 609-144 618-923 1-708

If the first and last experiments only are compared, it would appear
that the hydrogenium becomes sensibly denser when the proportion of it
is small, ranging from 1708 to 2:055. But the last experiment of the
Table is perhaps exceptional; and all the others indicate considerable
uniformity of density. The mean density of hydrogenium, according to
the whole experiments, excluding that last referred to, is 1951, or nearly
2. This uniformity is in favour of the method followed for estimating
the density of hydrogenium. -
On charging and discharging portions of the same palladium wire
repeatedly, the curious retraction was found to continue, and seemed to
be interminable. The following expansions, caused by variable charges
of hydrogen, were followed on expelling the hydrogen by the retractions
mentioned.
Elongation. Retraction.
1st Experiment 9.77 millims, 9-70 millims.
2d 35 5'765 .. . . . 6'20 ,
3d 2 3 2'36 32 . . . 3'14 ,
4th 3 ) 3'482 35 . . . 495 ,,
23.99
The palladium wire, which originally measured 609-144 millims,
has suffered, by four successive discharges of hydrogen from it, a per-
manent contraction of 23.99 millims. ; that is, a reduction of 3.9 per
cent. On its original length. The contractions will be observed to exceed
in amount the preceding elongations produced by the hydrogen, parti-
cularly when the charge of the latter is less considerable. With another
portion of wire the contraction was carried to 15 per cent of its length
by the effect of repeated discharges. The specific gravity of the con-
tracted wire was 12:12, no general condensation of the metal having
taken place. The wire shrinks in length only.
In the preceding experiments the hydrogen was expelled by exposing
EHYDROGEN TO PALLADIUM. 295
the palladium placed within a glass tube to a moderate heat short of
redness, and exhausting by means of a Sprengel tube; but the gas was
also withdrawn in another way, namely, by making the wire the positive
electrode, and thereby evolving oxygen upon its surface. In such cir-
cumstances a slight film of oxide of palladium is formed on the wire,
but it appears not to interfere with the extraction and oxidation of the
hydrogen. The wire measured,
Difference.
Before charge, . . . 443.25 millims.
With hydrogen, . . . 44990 , + 6-65 millims.
After discharge, . . . 437:31 , — 5'94 ,
The retraction of the wire therefore does not require the concur-
rence of a high temperature. This experiment further proved that a
large charge of hydrogen may be removed in a complete manner by
exposure to the positive pole (for four hours in this case); for the wire
in its ultimate state gave no hydrogen on being heated in vacuo.
That particular wire, which had been repeatedly charged with
hydrogen, was once more exposed to a maximum charge, for the pur-
pose of ascertaining whether or not its elongation under hydrogen
might now be facilitated and become greater in consequence of the
previous large retraction. No such extra elongation, however, was
observed on charging the retracted wire more than once; and the
expansion continued to be in the usual proportion to the hydrogen
absorbed. The final density of the wire was 12:18.
The wire retracted by heat is found to be altered in another way,
which appears to indicate a molecular change. When the gas has been
expelled by heat, the metal gradually loses much of its power to take
up hydrogen. The last wire, after it had already been operated upon six
times, was again charged with hydrogen for two hours, and was found
to occlude only 320 volumes of gas, and in a repetition of the experi-
ment, 330-5 volumes. The absorbent power of the palladium had there-
fore been reduced to about one-third of its maximum.
The condition of the retracted wire appeared, however, to be im-
proved by raising its temperature to full redness by sending through it
an electrical current from a battery. The absorption rose thereafter
to 425 volumes of hydrogen, and in a second experiment to 422:5
volumes.
The wire becomes fissured longitudinally, acquires a thready struc-
ture, and is much disintegrated on repeatedly losing hydrogen, particu-
larly when the hydrogen has been extracted by electrolysis in an acid
fluid. The palladium in the last case is dissolved by the acid to some
extent. The metal appeared, however, to recover its full power to
absorb hydrogen, now condensing upwards of 900 volumes of gas.
296 . ON THE RELATION OF
The effect upon its length of simply annealing the palladium wire
by exposure in a porcelain tube to a full red heat, was observed. The
wire measured 556-075 millims, before, and 555.875 millims. after heat-
ing ; or a minute retraction of 0.2 millim, was indicated. In a second
annealing experiment, with an equal length of new wire, no sensible
change whatever of length could be discovered. There is no reason,
then, to ascribe the retraction after hydrogen, in any degree, to the heat
applied when the gas is expelled. Palladium wire is very slightly
affected in physical properties by such annealing, retaining much of its
first hardness and elasticity. r
2. Tenacity.—A new palladium wire, similar to the last, of which
100 millims. weighed 0-1987 grm, was broken, in experiments made on
two different portions of it, by a load of 10 and of 10:17 kilogrammes.
Two other portions of the same wire, fully charged with hydrogen, were
broken by 8:18 and by 827 kilogrammes. Hence we have—
Tenacity of palladium wire, . º e 100
Tenacity of palladium and hydrogen, & 81:29
The tenacity of the palladium is reduced by the addition of hydrogen,
but not to any great extent. It is a question whether the degree of
tenacity that still remains is reconcileable with any other view than
that the Second element present possesses of itself a degree of tenacity
such as is only found in metals.
3. Electrical conductivity.—Mr. Becker, who is familiar with the
practice of testing the capacity of wires for conducting electricity, sub-
mitted a palladium wire, before and after being charged with hydrogen,
to trial, in comparison with a wire of German silver of equal diameter
and length, at 10°5. The conducting power of the several wires was
found as follows, being referred to pure copper as 100 :—
Pure copper, . te • º º ... 100
Palladium, . º º e º º 8:10
Alloy of 80 copper +20 nickel, . ſº e 6.63
Palladium + hydrogen, . º º º 5'99
A reduced conducting-power is generally observed in alloys, and the
charged palladium wire falls 25 per cent. But the conducting-power
remains still considerable, and the result may be construed to favour
the metallic character of the second constituent of the wire. Dr.
Matthiessen confirms these results.
4. Magnetism.—It is given by Faraday as the result of all his ex-
periments, that palladium is “feebly but truly magnetic; ” and this
element he placed at the head of what are now called the paramagnetic
metals, But the feeble magnetism of palladium did not extend to its
HYDROGEN TO PALLADIUM. 297
salts. In repeating such experiments, a horse-shoe electro-magnet of soft
iron, about 15 centims. (6 inches) in height, was made use of. It was
capable of supporting 60 kilogs, when excited by four large Bunsen cells.
This is an induced magnet of very moderate power. The instrument
was placed with its poles directed upwards; and each of these was
provided with a small square block of soft iron terminating laterally
in a point, like a small anvil. The palladium under examination was
suspended between these points in a stirrup of paper attached to three
fibres of cocoon silk, 3 decimetres in length, and the whole was covered
by a bell glass. A filament of glass was attached to the paper, and
moved as an index on a circle of paper on the glass shade divided into
degrees. The metal, which was an oblong fragment of electro-deposited
palladium, about 8 millims. in length and 3 millims. in width, being at
rest in an equatorial position (that is, with its ends averted from the
poles of the electro-magnet), the magnet was then charged by connecting
it with the electrical battery. The palladium was deflected slightly
from the equatorial line by 10° only, the magnetism acting against the
torsion of the silk suspending thread. The same palladium charged with
604-6 volumes of hydrogen was deflected by the electro-magnet through
48°, when it set itself at rest. The gas being afterwards extracted, and
the palladium again placed equatorially between the poles, it was not
deflected in the least perceptible degree. The addition of hydrogen
adds manifestly, therefore, to the small natural magnetism of the palla-
dium. To have some terms of comparison, the same little mass of
electro-deposited palladium was steeped in a solution of nickel, of sp.
gr. 1082, which is known to be magnetic. The deflection under the
magnet was now 35°, or less than with hydrogen. The same palladium
being afterwards washed and impregnated with a solution of protosul—
phate of iron of sp. gr. 1048, of which the metallic mass held 2:3 per
cent of its weight, the palladium gave a deflection of 50°, or nearly the
same as with hydrogen. With a stronger Solution of the same salt, of
sp. gr. 1:17, the deflection was 90°, and the palladium pointed axially.
Palladium in the form of wire or foil gave no deflection when placed
in the same apparatus, of which the moderate sensitiveness was rather
an advantage in present circumstances; but when afterwards charged
with hydrogen, the palladium uniformly gave a sensible deflection of
about 20°. A previous washing of the wire or foil with hydrochloric
acid, to remove any possible traces of iron, did not modify this result.
Palladium reduced from the cyanide and also precipitated by hypophos-
phorous acid, when placed in a small glass tube, was found to be not
sensibly magnetic by our test ; but it always acquired a sensible mag-
netism when charged with hydrogen.
It appears to follow that hydrogenium is magnetic, a property which
298 ON THE RELATION OF HYDROGEN TO PALLADIUM.
is confined to metals and their compounds. This magnetism is not
perceptible in hydrogen gas, which was placed both by Faraday and
by M. E. Becquerel at the bottom of the list of diamagnetic substances.
This gas is allowed to be upon the turning-point between the paramag-
netic and diamagnetic classes. But magnetism is so liable to extinction
under the influence of heat, that the magnetism of a metal may very
possibly disappear entirely when it is fused or vaporised, as appears to
be the case with hydrogen in the form of gas. As palladium stands
high in the series of the paramagnetic metals, hydrogenium must be
allowed to rise out of that class, and to take place in the strictly mag-
netic group, with iron, nickel, cobalt, chromium, and manganese.
5. Palladium with Hydrogen at a high Temperature.—The ready
permeability of heated palladium by hydrogen gas would imply the
retention of the latter element by the metal even at a bright red heat.
The hydrogenium must in fact travel through the palladium by cemen-
tation, a molecular process which requires time. The first attempts to
arrest hydrogen in its passage through the red-hot metal were made by
transmitting hydrogen gas through a metal tube of palladium with a
vacuum outside, rapidly followed by a stream of carbonic acid, in which
the metal was allowed to cool. When the metal was afterwards
examined in the usual way, no hydrogen could be found in it. The
short period of exposure to the carbonic acid seems to have been suffi-
cient to dissipate the gas. But on heating palladium foil red-hot in a
flame of hydrogen gas, and suddenly cooling the metal in water, a small
portion of hydrogen was found locked up in the metal. A volume of
metal amounting to 0.062 cubic centim. gave 0-080 cubic centim. of
hydrogen; or, the gas, measured cold, was 1.306 times the bulk of the
metal. This measure of gas would amount to three or four times the
volume of the metal at a red heat. Platinum treated in the same way
appeared also to yield hydrogen, although the quantity was too small
to be much relied upon, amounting only to 0-06 volume of the metal.
The permeation of these metals by hydrogen appears therefore to
depend on absorption, and not to require the assumption of anything
like porosity in their structure. . *
The highest velocity of permeation observed was in the experiment
where four litres of hydrogen (3992 cub. centims.) per minute passed
through a plate of palladium 1 millim. in thickness, and calculated for
a square metre in surface, at a bright red heat a little short of the
melting-point of gold. This is a travelling movement of hydrogen
through the substance of the metal with the velocity of 4 millimetres
per minute. -
6. Chemical Properties.—The chemical properties of hydrogenium
also distinguish it from ordinary hydrogen. The palladium alloy pre-
IDEAS RESPECTING THE CONSTITUTION OF MATTER. 299
A-
cipitates mercury and calomel from a solution of the chloride of mercury
without any disengagement of hydrogen; that is, hydrogenium decom-
poses chloride of mercury, while hydrogen does not. This explains
why M. Stanislas Meunier failed in discovering the occluded hydrogen
of meteoric iron, by dissolving the latter in a solution of chloride of
mercury; for the hydrogen would be consumed, like the iron itself, in
precipitating mercury. Hydrogen (associated with palladium) unites
with chlorine and iodine in the dark, reduces a persalt of iron to the
state of protosalt, converts red prussiate of potash into yellow prussiate,
and has considerable deoxidizing powers. It appears to be the active
form of hydrogen, as ozone is of oxygen.
The general conclusions which appear to flow from this inquiry are,
that in palladium fully charged with hydrogen, as in the portion of
palladium wire now submitted to the Royal Society, there exists a com-
pound of palladium and hydrogen in a proportion which may approach
to equal equivalents." That both substances are solid, metallic, and of
a white aspect. That the alloy contains about 20 volumes of palladium
united with a volume of hydrogenium; and that the density of the latter
is about 2, a little higher than magnesium, to which hydrogenium may
be supposed to bear some analogy. That hydrogenium has a certain
amount of tenacity, and possesses the electrical conductivity of a metal.
And finally, that hydrogenium takes its place among magnetic metals.
The latter fact may have its bearing upon the appearance of hydro-
genium in meteoric iron, in association with certain other magnetic .
elements.
I cannot close this paper without taking the opportunity to return
my best thanks to Mr. W. C. Roberts for his valuable co-operation
throughout the investigation.
XXI.
SPECULATIVE IIDEAS RESPECTING THE CONSTITUTION
OF MATTER,” *
From the Philosophical Magazine for February 1864.
IT is conceivable that the various kinds of matter, now recognised
as different elementary substances, may possess one and the same ulti-
mate or atomic molecule existing in different conditions of movement.
The essential unity of matter is an hypothesis in harmony with the
1. Proceedings of the Royal Society, 1868, p. 425. * Ibid. 1863, p. 620.
300 SPECULATIVE IDEAS RESPECTING
equal action of gravity upon all bodies. We know the anxiety with
which this point was investigated by Newton, and the care he took to
ascertain that every kind of substance, “metals, stones, woods, grain,
Salts, animal substances, etc.,” are similarly accelerated in falling, and
are therefore equally heavy.
In the condition of gas, matter is deprived of numerous and varying
properties with which it appears invested when in the form of a liquid
or Solid. The gas exhibits only a few grand and simple features. These
again may all be dependent upon atomic and molecular mobility. Let
us imagine one kind of substance only to exist, ponderable matter; and
further, that matter is divisible into ultimate atoms, uniform in size and
Weight. We shall have one substance and a common atom. With the
atom at rest the uniformity of matter would be perfect. But the atom
possesses always more or less motion, due, it must be assumed, to a
primordial impulse. This motion gives rise to volume. The more rapid
the movement the greater the space occupied by the atom, somewhat as
the orbit of a planet widens with the degree of projectile velocity.
Matter is thus made to differ only in being lighter or denser matter.
The specific motion of an atom being inalienable, light matter is no
longer convertible into heavy matter. In short, matter of different
density forms different substances—different inconvertible elements as
they have been considered.
What has already been said is not meant to apply to the gaseous
volumes which we have occasion to measure and practically deal with,
but to a lower order of molecules or atoms. The combining atoms
hitherto spoken of are not therefore the molecules of which the move—
ment is sensibly affected by heat with gaseous expansion as the result.
The gaseous molecule must itself be viewed as composed of a group or
system of the preceding inferior atoms, following as a unit laws similar
to those which regulate its constituent atoms. We have indeed carried
one step backward, and applied to the lower order of atoms, ideas sug-
gested by the gaseous molecule, as views derived from the solar system
are extended to the subordinate system of a planet and its satellites.
The advance of science may further require an indefinite repetition of
such steps of molecular division. The gaseous molecule is then a repro-
duction of the inferior atom on a higher scale. The molecule or system
is reached which is affected by heat, the diffusive molecule, of which the
movement is the subject of observation and measurement. The diffu-
sive molecules are also to be supposed uniform in weight, but to vary
in velocity of movement, in correspondence with their constituent
atoms. Accordingly the molecular volumes of different elementary
substances have the same relation to each other as the subordinate
atomic volumes of the same substances.
THE CONSTITUTION OF MATTER. 301
But further, these more and less mobile or light and heavy forms of
matter have a singular relation connected with equality of volume.
Equal volumes of two of them can coalesce together, unite their move-
ment, and form a new atomic group, retaining the whole, the half, or
some simple proportion of the original movement and consequent
volume. This is chemical combination. It is directly an affair of
volume, and only indirectly connected with weight. Combining weights
are different, because the densities, atomic and molecular, are different.
The volume of combination is uniform, but the fluids measured vary
in density. This fixed combining measure—the metron of simple sub-
stances—weighs 1 for hydrogen, 16 for oxygen, and so on with the
other “elements.”
To the preceding statements respecting atomic and molecular mobi-
lity, it remains to be added that the hypothesis admits of another
expression. As in the theory of light we have the alternative hypotheses
of emission and undulation, so in molecular mobility the motion may
be assumed to reside either in separate atoms and molecules, or in a
fluid medium caused to undulate. A special rate of vibration or pulsa-
tion originally imparted to a portion of the fluid medium enlivens that
portion of matter with an individual existence, and constitutes it a dis-
tinct substance or element.
With respect to the different states of gas, liquid and solid, it may
be observed that there is no real incompatibility with each other in these
physical conditions. They are often found together in the same sub-
stance. The liquid and the solid conditions supervene upon the gaseous
condition rather than supersede it. Gay-Lussac made the remarkable
observation that the vapours emitted by ice and water, both at 0°C., are
of exactly equal tension. The passage from the liquid to the solid state
is not made apparent in the volatility of water. The liquid and solid
conditions do not appear as the extinction or suppression of the gaseous
condition, but something superadded to that condition. The three con-
ditions (or constitutions) probably always coexist in every liquid or
solid substance, but one predominates over the others. In the general
properties of matter we have, indeed, to include still further (1) the
remarkable loss of elasticity in vapours under great pressure, which is
distinguished by Mr. Faraday as the Caignard Latour-state, after the
name of its discoverer, and is now undergoing an investigation by Dr.
Andrews, which may be expected to throw much light upon its nature;
(2) the colloidal condition or constitution, which intervenes between the
liquid and crystalline states, extending into both and affecting probably
all kinds of solid and liquid matter in a greater or less degree. The
predominance of a certain physical state in a substance appears to be a
distinction of a kind with those distinctions recognised in natural history
302 IDEAS RESPECTING THE CONSTITUTION OF MATTER.
as being produced by unequal development. Liquefaction or Solidifica-
tion may not therefore involve the suppression of either the atomic or
the molecular movement, but only the restriction of its range. The
hypothesis of atomic movement has been elsewhere assumed, irrespective
of the gaseous condition, and is applied by Dr. Williamson to the eluci-
dation of a remarkable class of chemical reactions which have their seat
in a mixed liquid.
Lastly, molecular or diffusive mobility has an obvious bearing upon
the communication of heat to gases by contact with liquid or Solid Sur-
faces. The impact of the gaseous molecule, upon a surface possessing
a different temperature, appears to be the condition for the transference
of heat, or the heat movement, from one to the other. The more rapid
the molecular movement of the gas the more frequent the contact with
consequent communication of heat. Hence, probably, the great cooling
power of hydrogen gas as compared with air or oxygen. The gases
named have the same specific heat for equal volumes, but a hot object
placed in hydrogen is really touched 3-8 times more frequently than it
would be if placed in air, and 4 times more frequently than it would be
if placed in an atmosphere of oxygen gas. Dalton had already ascribed
this peculiarity of hydrogen to the high “mobility” of that gas. The
same molecular property of hydrogen recommends the application of
that gas in the air-engine, where the object is to alternately heat and
cool a confined volume of gas with rapidity.
S A. L T S.
*º-º-º-mºmºm-
I.
ON EXCEPTIONS TO THE LAW THAT SALTS ARE MORE
SOLUBLE IN HOT THAN IN COLD WATER ; WITH A
NEW INSTANCE.
From Philosophical Magazine and Annals of Philosophy, ii. 1827, pp. 20-26.
THE bodies which have been observed to possess this anomalous solu-
bility are the hydrate of lime and the sulphate of soda ; its detection in
the first case we owe to Mr. Dalton, and in the latter to M. Gay-Lussac.
The phosphate of magnesia, a body like the hydrate of lime of sparing
solubility, appears from our experiments to belong to the same class.
To form phosphate of magnesia, phosphate of soda and sulphate of
magnesia in crystals were separately dissolved in water, in the propor-
tion of 21 parts of the former to 15.375 parts of the latter, or of an
integrant particle of each. These solutions were mixed and set aside.
Within twenty-four hours the phosphate of magnesia had precipitated,
generally in tufts of short acicular crystals, while sulphate of soda
remained in solution. According to Dr. Thomson this salt is composed of
One atom phosphoric acid, º 3.5
One atom magnesia, * * 2'5
Seven atoms water, & e 7.875
13-875
It is efflorescent, rapidly losing its water of crystallization when exposed
to the air, and falling down in a white powder.
The crystals were drained, purified with great care by repeated
agitation with water, and finally thrown upon a filter with more water,
and allowed to dry. Solutions were obtained by occasionally agitating
the salt with pure water during three or four days, in the proportion of
2 ounces phosphate of magnesia to 1 pint of water. The solutions were
then decanted off and filtered. Although the water drained from the
304 ON EXCEPTIONS TO THE LAW THAT SALTS ARE
crystals upon the filter was nearly tasteless, yet the solutions thus
obtained were of a sweetish taste, which was sufficiently perceptible.
A quantity of the solution, in the preparation of which distilled
water only had been employed, was gradually heated by immersion in
the water-bath. Before the bath had arrived at 120°, the solution
became turbid, and it assumed more and more of a milky appearance as
the heat increased, till the temperature settled at 212°, when a cloudy
precipitate slowly subsided, and the supernatant liquid became nearly
transparent. The precipitate was found not to differ in its sensible
properties from phosphate of magnesia deprived of its water of crystal-
lization.
To determine the solubility of this salt at different temperatures, a
solution was prepared by repeated agitation with water, for more than a
week, of a quantity of the salt from which already three solutions had
been derived. The temperature was about 45°.
8000 grains of this solution, carefully filtered, were evaporated to
dryness on the sand-bath. The residue was found to be 10-75 grains
anhydrous phosphate of magnesia. Hence 744 grains water dissolve 1
grain of the anhydrous salt. -
8000 grains of the same solution, in a glass-stoppered phial, were
heated to 212° in the water-bath and retained for some time at that
temperature. When the precipitate had subsided, a large portion of the
transparent liquid was decanted off, and the remainder with the precipi-
tate thrown upon a filter while still hot. It weighed when accurately
dried 3-8 grains. Hence 8000 grains water at 212" retain in solution
1075–38 = 6.95 grains; or 1151 grains water retain in solution 1 grain
of anhydrous phosphate of magnesia. Hence 1 part water dissolves of
anhydrous phosphate of magnesia, .
at 45° * g * 7 TT :
at 212° te tº te TT5 T.
Of the hydrate, or phosphate of magnesia in the state of crystals, 1 part
water will therefore dissolve
;
at 45° & & e ##3;
at 212° g * #s.
The precipitate by heat was exceedingly bulky and not crystallized.
It did not amount in general to so much as 38 grains from 8000 grains
of the solution. Indeed, the mean of seven experiments made upon
different solutions was 2.5 grains of precipitate. But it was found that
the amount of the precipitate depended much upon the time and agita-
tion employed in effecting the solution, as it is difficult to saturate water
with this salt. It is evident, therefore, that not the mean but the
greatest result will approach nearest to the truth.
MORE SOLUBLE IN HOT THAN IN COLD WATER. 305
Phosphate of magnesia boiled in water for several hours, afterwards
yielded solutions possessing this property. By the heat, the crystals
assumed the appearance in the water of having effloresced.
Phosphate of soda and sulphate of magnesia were added separately
to solutions of phosphate of magnesia, in the proportion of 10 grains to
1000 grains solution, without influencing in the slightest degree the
amount or appearance of the precipitate.
Phosphate of magnesia appears to be much more soluble in the acids
than in water; at least it was observed to dissolve with facility in the
following acids, even when in a very dilute state—acetic, oxalic, phos-
phoric, muriatic, nitric, and sulphuric. The addition of the smallest
quantity of any of these acids to the aqueous solution prevents the
appearance of the usual precipitate by heat, by increasing the solvent
power of the menstruum."
In prosecuting this subject I had occasion to make several observa–
tions. º
Mere continuance of the heat had no effect in increasing the amount
of the precipitate, in the solutions of hydrate of lime or of phosphate of
magnesia, provided no part of the solution was at any time converted
into vapour. When filtered solutions of lime and phosphate of mag-
nesia, which had formerly been heated, were again subjected to a tem-
perature of 212° by complete immersion in the water-bath in close
vessels, and retained at that temperature for several hours, no additional
precipitate appeared. But when heat of greater intensity was applied
to elevate the temperature of the solution to 212°, this was seldom the
case. When such a solution was heated by the flame of a spirit-lamp,
even in a close vessel, a slight precipitate generally appeared. When
the vessel, although close, was only occupied in part by the solution,
the precipitate was greater; and when the space occupied by the solu-
tion bore so small a proportion to the whole capacity of the vessel, that
the solution might be made to boil, and be condensed in the upper part
of the vessel and returned without loss, the precipitate might be
increased ad libiţum, particularly in the case of lime-water. The cause
of the precipitate appears to be the same in all these cases. The moment
a drop of the solution is converted into vapour, it deposits the quantity
of lime or salt that it held in solution; and in the case of bodies which
dissolve so sparingly and with so much difficulty, as the hydrate of lime
and phosphate of magnesia, although the water be returned again to the
solution, it is incapable of re-dissolving what it has deposited. We
know that it would be a hopeless task to form a Saturated solution of
1 The experiment of the partial precipitation of phosphate of magnesia in solution,
by heat, has been repeated successfully by my friend Mr. A. Steel, in the laboratory of
Dr. Thomson, with great care and very pure materials.
U
306 ON EXCEPTIONS TO THE LAW THAT SALTS ARE
lime, by agitating with the water no more than the few grains which it
is capable of dissolving; and in the case before us, when the lime is once
deposited the same difficulty should be experienced in taking it up.
These observations show the advantage of employing the water-bath
in heating the solutions,—a procedure which was always followed by
the author, and by which he regularly obtained precipitates of hydrate
of lime as well as of phosphate of magnesia. They also account for a
phenomenon in the solubility of lime observed by Mr. Richard Phillips,
which otherwise appears anomalous." -
Mr. Phillips heated a quantity of lime-water in a flask, the neck of
which was elongated by a tube, to prevent the access of carbonic acid
gas from the atmosphere, and made to boil till 1-13th part was dissi-
pated in vapour. From the deposition which mere elevation of tem-
perature would occasion without any evaporation, the quantity of lime
in solution would be reduced to Tºroth part, but it was found to amount
to no more than Hºrs. But much more of the solution would be con-
verted into vapour during the boiling, than what actually escaped, the cool
sides of the long tube being singularly adapted to condense the rising
vapour and return it to the Solution, supposing that the tube had any
elevation; while the hydrate of lime, which had been deposited in hard
crystals, would not admit of being re-dissolved in an appreciable degree.
It is evident that this effect of cohobation will take place not only in
lime-water and the Solution of phosphate of magnesia, but to a certain
extent in all bodies of difficult solubility. I have observed it to a con-
siderable extent in the solution of sulphate of lime, even when greatly
diluted, and believe that the deposit from slight boiling observed in
many mineral waters, and generally attributed to the dissipation of
carbonic acid gas, depends in some instances upon this cause. However
weak the solution may be, it is evident that a portion of the salt may
be deposited in this way.
It had occurred to us as a method of determining the relative solubility
at different temperatures of bodies of this class, to form a saturated solution
at the lowest temperature, and dilute it with water till it ceased to deposit
at the high temperature. But this method was found inconvenient from
the difficulty of incorporating the solution with the water added.
4000 grains lime-water were diluted with 2000 grains water, agitated
and set aside for two hours. Upon being then heated in the water-bath
to 212°, a precipitate appeared, which being received upon a filter and
dried was found to amount to nearly 2 grains hydrate of lime. Phos-
phate of magnesia similarly treated gave 12 grains of precipitate.
4000 grains lime-water diluted with an equal quantity of pure water,
and occasionally agitated for three days in a stoppered phial, became
* Annals of Philosophy, N. S., vol. i. p. 109.
MORE SOLUBLE IN HOT THAN IN COLD WATER. 307
slightly turbid upon being carefully heated in the water-bath, and
deposited a small quantity of hydrate of lime, of which 0.15 grain was
recovered. The solution of phosphate of magnesia in the same circum-
stances yielded a precipitate, which although it rendered the solution
much more turbid, did not amount to so much.
It was found, as might be expected from the previous experiments,
that the deposit by heat from lime-water was not diminished sensibly
by being allowed to remain in the solution till it became cool, or was
not re-dissolved upon cooling. Hence it is unnecessary to filter the
solution while hot. The phosphate of magnesia, however, appeared to be
re-dissolved in a more sensible degree, probably from the state of extreme
division in which it is deposited. At least 2-3 grains of precipitated
phosphate of magnesia were obtained by filtering at 212°, while an equal
quantity of the same solution, allowed to cool with occasional agitation
before filtration, gave a precipitate which did not exceed 2 grains. In
appearance, the precipitate had suffered a very great reduction.
The rapidity with which phosphate of magnesia effloresces when
exposed to the atmosphere led us, from theoretical considerations, to
look for this anomaly in its solubility. Efflorescence in the hydrates of
the salts certainly indicates a weak affinity for water at the atmospheric
temperature—an attraction or affinity, too, which is much diminished
by slight elevation in temperature. If the attraction subsisting between
the salt and water, when in solution, be of the same nature as that
between the base and water when in the state of a solid hydrate, we
might expect the striking power of heat in weakening the affinity or
attraction, to affect the solubility of the salt at different temperatures.
Even supposing that the solvent power of water increased to a certain
extent with rise in temperature, yet this rapid diminution of the attrac-
tion of the salt for water as the temperature rose, might counteract and
eventually overcome the increasing power of the solvent, in salts so
efflorescent as phosphate of magnesia or sulphate of soda. Hence the
solubility of such salts might begin to lessen, when the temperature was
raised beyond a certain point.
As the hydrates of all the salts, whether they may be efflorescent at
the temperature of the atmosphere or not, are decomposed by heat, the
cause assigned, as counteracting the increase of the solvent power of
water with temperature, if it exists, must be general, and influence to a
greater or less extent the solubility at different temperatures of all salts
whatever. In fact, the consequence necessarily follows from it, that for
every salt there is a point in the scale of temperature above which it
ceases to become more soluble in water, and diminishes in solubility.
In the case of the efflorescent Salts, whose affinity for water, when in the
state of hydrate, is much impaired by slight elevation of temperature,
308 ON EXCEPTIONS TO THE LAW TEIAT SALTS ARE
this point of temperature appears to be low—in some cases under 212”;
in the case of hydrates which retain their water with more force it will
be higher, and in hydrates which require a considerable heat to decom-
pose them, the maximum point of solubility will be proportionally high,
and such as would require the retention of the solvent in the liquid state
by vast pressure, in order to be exhibited.
In that extensive class of salts which do not form solid combinations
with water, we do not possess such a clew to their solubility at different
temperatures. They may, therefore, be subject in some cases to this
anomaly in solubility as well as the efflorescent salts. Indeed the theory
is not applicable even to all the hydrates without distinction. There is
a class of hydrates, in which the combination between the base and
water appears to differ essentially from that of the ordinary hydrates of
the salts. This class comprehends the hydrates of the alkalies, the
earths and metallic oxides, and these appear not to be subject to the law.
Many salts, oxides and earths of this class are known to be deprived
of solubility by exposure to a considerable heat. This arises from the
loss of the water with which they were previously combined, and not, as
it is often supposed, from the action of heat in hardening and increasing
the cohesion of the particles of such bodies. For if we examine the
Solubility of these bodies, we shall find it necessary to suppose, that at
no time is the simple substance itself dissolved, but always an Original
and intimate compound of the substance with water. These compounds
are of a higher order than the common hydrates, and frequently require
peculiar circumstances for their formation. Silica is a good instance.
Dried and destitute of water it is altogether insoluble, and cannot be
made again to form a solid combination with water, but in a state of
previous and intimate combination with water it is soluble. It is evident
then that the solution should be viewed not as a solution of silica, but as
a solution of hydrate of silica. The alkalies are in the same situation;
and the fact strikingly illustrates our position, that when the alkalies
dissolve in alcohol they are still in the state of hydrates. The combina-
tion between water and lime in slaked lime is of this superior kind, so
that lime-water may be considered not as a solution of lime, but as a
solution of hydrate of lime. The water appears to be in more close
union with the lime, than the water of crystallization of salts to which
efflorescence is confined. It is therefore no objection to the theory that
hydrate of lime is more soluble in cold than in hot water, and yet does
not effloresce. Were the hydrate of lime to form a loose compound
with an additional quantity of water, like the water of crystallization of
ordinary salts, then if that hydrate did not effloresce, the circumstance
would be inimical to the theory. -
The coincidence of efflorescence with diminished solubility at high
MORE SOLUBLE IN HOT THAN IN COLD WATER. 309
temperatures, in the case of sulphate of soda, is favourable to the view
taken of the connection between these properties. If the solubility of
the efflorescent salts were examined particularly, more of them probably
would give indications of the same property.
Carbonate of magnesia in crystals is very efflorescent, and according
to Butini” it is more soluble in cold than in hot water impregnated with
carbonic acid.
II.
AN ACCOUNT OF THE FORMATION OF ALCOATES,
DEFINITE COMPOUNDS OF SALTS AND ALCOHOL
- ANALOGOUS TO THE HYDRATES.”
From Edinb. Roy. Soc. Trans. xi. 1831, pp. 175-193. [Phil. Mag. iv. 1828, pp. 265-
272, 331-336; Journ. de Pharm. xv. 1829, pp. 105-124; Poggend. Annal. xv.
1829, pp. 150-153; Quart. Journ. of Science, ii. 1828, pp. 442, 443; Schweigger,
Journ. lvi. (=Jahrb. xxvi.) 1829, pp. 180-203.] -
IN determining the solubility of salts and other bodies in alcohol, it
is desirable to operate with a spirit wholly free from water. But anhy-
drous or absolute alcohol is formed with difficulty, even by the most
improved process—that of Richter. In rectifying alcohol from chloride
of calcium, as recommended by Richter, I have never obtained it under
the specific gravity 0.798 at the temperature of 60°, by a single distilla-
tion; but upon rectifying this product again from new chloride of cal-
cium, I generally succeeded in reducing it to 0.796, which is the specific
gravity of the standard alcohol of that chemist. The following experi-
ment illustrates this process. &
Four measures of alcohol of the specific gravity 0.826 were poured
into a retort, and a quantity of well-dried chloride of calcium, amount-
ing to three-fourths of the weight of the alcohol, gradually added with
occasional agitation. Much of the salt was dissolved with the evolution
of heat; and the combination was promoted by boiling the whole for a
few minutes, the vapour being condensed in the neck of the retort, and
returned to the solution. A receiver was then adjusted to the mouth of
the retort, and the distillation conducted so slowly that the alcohol was
condensed entirely in the neck of the retort, and fell drop by drop into
the receiver, nearly two seconds elapsing between the fall of each drop.
The first measure of alcohol which came over was of the specific gravity
1 “Sur le Magnésie.” Wide Thomson's System, under Salts of Magnesia.
* Read 17th December 1827.
310 AN ACCOUNT OF THE FORMATION OF ALCOATES.
0-800, at 60°; the second measure, 0.798; and the third measure, 0.801 :
the distillation was then discontinued. These three measures were mixed
together, and subjected to a second distillation, which was conducted in
the same manner; and two measures of alcohol obtained of the specific
gravity 0.796. It was found that further rectification did not reduce the
specific weight of the alcohol below 0.796. From the analysis of alcohol
by Saussure, and the determination of the specific weight of its vapour
by Gay Lussac, there can be little doubt that the alcohol thus obtained is
perfectly anhydrous. It is true that such alcohol still contains oxygen
and hydrogen to the amount of an atomic proportion of water; but this
proportion of oxygen and hydrogen is essential to the constitution of
alcohol, the partial abstraction of it converting alcohol into ether, and
its total abstraction converting alcohol into olefiant gas; while the Sup-
position that the oxygen and hydrogen exist in the state of water is
altogether gratuitous.
The process of Richter is exceedingly tedious, from the necessity of
conducting it so slowly, and the waste of alcohol is considerable. I
tried newly burnt quicklime instead of chloride of calcium, and distilled
by the heat of a saline water-bath. If it is merely our object to obtain
alcohol perfectly free from water, no process could be more effectual.
The product was of the specific gravity 0-794; but it contained a trace
of ether, to which the extraordinary lowness of its specific gravity is
attributable ; and had an empyreumatic odour, notwithstanding the
moderate temperature at which the distillation was conducted. This
likewise is a very slow process.
The process which I preferred is founded on the principle of Mr.
Leslie's frigorific apparatus. The alcohol is concentrated by being placed
under the receiver of an air-pump, with quicklime. A large shallow
basin is covered to a small depth with recently burnt lime in coarse
powder, and a smaller basin containing three or four ounces of commer-
cial alcohol is made to rest upon the lime: the whole is placed upon
the plate of an air-pump, and covered over by a low receiver. Exhaus-
tion is continued till the alcohol evinces signs of ebullition, but no
further. Of the mingled vapours of alcohol and water which now fill
the receiver, the quicklime is capable of combining with the aqueous
vapour only, which is therefore quickly withdrawn, while the alcohol
vapour is unaffected. But as water, unless it has an atmosphere of its
own vapour above it, cannot remain in the alcohol, more aqueous vapour
rises. This vapour is likewise absorbed, and the process goes on till
the whole water in the alcohol is withdrawn. Several days are always
required for this purpose, and in winter a longer time than in summer.
The following cases exhibit the rate, according to which the water is
withdrawn. The first experiment was made in summer. Four ounces
AN ACCOUNT OF THE FORMATION OF ALCOATES. 3.11
of alcohol of the specific gravity 0.827 were concentrated. The specific
gravity was taken every twenty-four hours, and the following series of
results obtained :— ...r
0-827
0.817
0-808
O'802
O'798
O'796
In this case the whole water was withdrawn in five days, but occasion-
ally a period somewhat longer is required, although it rarely exceeds a
week. In winter the alcohol generally requires to be exposed to the
lime for a day or two longer than in summer. . The following rate of
concentration was observed in one case in winter, the quantity of
alcohol and other circumstances being the same as in the former experi-
ment :—
0.825
0.817
0.809
0.804
0-799
0.797
0.796
Quicklime, as a porous substance, appears to be capable of condens-
ing a small portion of alcohol vapour. It is therefore improper to use
it in great excess. In one case, in which three pounds of quicklime
were employed with four ounces of alcohol, about one-sixth of the
alcohol was lost from this absorption. The quicklime should never
exceed three times the weight of the alcohol, otherwise the quantity of
alcohol absorbed becomes sensible. It should be spread over as great
a surface within the receiver as possible.
In Richter's process it is improper to operate upon more than a few
ounces of alcohol at a time; as when a large quantity of materials is
introduced into the retort, the heat necessary to disengage the alcohol
in the centre of the mass inevitably expels the water left in the chloride
of lime, at the points where it is more exposed to the heat. In the air-
pump also, only a few ounces can in general be concentrated at a time.
But in a tall receiver, two or three shallow basins of quicklime can be
supported at a little height above each other, each of them containing a
small basin of alcohol resting in it. Or the process might be conducted
with facility on the large scale, by means of a tight box of any size,
furnished with numerous shelves, which might be covered with quick-
lime in powder, and support a large number of basins of alcohol. The
312 AN ACCOUNT OF THE FORMATION OF ALCOATES.
box might be sufficiently exhausted of air by means of a Syringe, for it
is not necessary that the exhaustion be nearly complete; and indeed
more inconvenience is to be apprehended from a complete than from
an imperfect exhaustion. After producing the exhaustion, no further
attention would be necessary; and upon opening the box at the expira-
tion of a week or ten days, the alcohol would be found anhydrous. It
is evident that absolute alcohol, procured by this process, could be sold
at a price but little exceeding its original cost. It would moreover be
of much greater value for the purposes for which it is employed in the
arts and medicine. I believe, however, that, by the excise laws as they
at present exist, no rectifier of spirits is permitted to concentrate
alcohol beyond a certain strength. Licensed apothecaries alone are
allowed to prepare and sell absolute alcohol."
Alcohol may be concentrated in a close vessel with quicklime, with-
out exhausting; but the process goes on much more slowly, at least at
the temperature of the air. The experiment was tried at a high tem-
perature, by heating in a water-bath a large bottle with a very wide
mouth, containing a quantity of alcohol at the bottom, and quicklime
suspended over it in a linen bag. When the water-bath attained the
temperature of 150°, the bottle was corked, and the bath prevented
from becoming hotter. Much of the lime was very quickly converted
into hydrate, and the alcohol considerably concentrated. But the pro-
cess is troublesome, and much inferior to that in which the air-pump is
employed. - *
In the place of quicklime, sulphuric acid cannot be substituted in
the foregoing process as an absorbing liquid, from a remarkable property
which it possesses. It is capable of absorbing the vapour of absolute
alcohol, in the same manner as it absorbs the vapour of water. I was
led to make this observation from a consideration of the phenomena
which attend the mixing of alcohol and sulphuric acid. Nearly as
much heat is evolved as if water had been added to the acid, even
although absolute alcohol be employed. Alcohol is also retained by
the acid when heated to 500° or 600°, or at a temperature when the
alcohol would be decidedly in the state of vapour, which indicates the
possibility of the same relation between sulphuric acid and alcohol
vapour that subsists between water and those gases which it detains in
the liquid state, such as ammoniacal gas, when they would naturally
* Care should be taken that the temperature be nearly equable during the experi-
ment; otherwise, when the atmosphere becomes cold, a condensation of alcohol vapour
takes place upon the cooled bell-glass, which runs down upon the plate of the pump.
The experiment, therefore, should not be performed in a room with a fire, or near a
window, but in a dark closet or press. From the manner in which I performed the
experiment, this condensation had never been experienced by myself; but Dr. Duncan,
junior, observed it, on repeating the process.
AN ACCOUNT OF THE FORMATION OF ALCOATES. 3.13
assume the elastic form. But besides merely detaining such gases,
water can condense and absorb them. Sulphuric acid, besides merely
detaining alcohol vapour, might therefore condense and absorb it.
As alcohol, like water, occasions cold by its evaporation, it may be
substituted for water in Mr. Leslie's frigorific apparatus, sulphuric acid
being retained as the absorbing liquid. In circumstances precisely
similar, it was found that the thermometer, the bulb of which was
covered with cotton, fell to 7 when moistened with water, but when
moistened with absolute alcohol its temperature fell to —24”. Con-
tinuance of the pumping during the experiment, as is done in the case
of ether, had a prejudicial effect. But alcohol diluted with a third of
water was found to have as great a cooling power as absolute alcohol.
The advantage to be derived from the great volatility of alcohol appears
to be counterbalanced in part by the small latent heat of its vapour.
Probably a mixture of alcohol and water, in certain proportions, would
produce the greatest degree of cold attainable by this process. Sulphuric
acid loses its power to absorb alcohol vapour by being diluted with
water. When impregnated with alcohol vapour, the acid becomes of a
pink colour; but no appreciable quantity of gas is emitted at the tem-
perature of the atmosphere, even in the vacuum of an air-pump.
Erom one experiment, water appears to have the power to induce
the evaporation of alcohol by absorbing its vapour, as sulphuric acid
does, but much more feebly. Two cups, one containing alcohol and the
other pure water, were enclosed together in a tin canister which was
nearly air-tight, and set aside in a quiet place for six weeks. The cups
were not in contact, but a little apart from each other. At the expira–
tion of that period it was found, on opening the canister, that the cup
which originally contained pure water, now contained a mixture of
water and alcohol, while the alcohol remaining in the other cup was of
diminished strength. Professor Leslie informs me, that he performed a
similar experiment a considerable time ago, although no account of it was
published. But the absorption of alcohol vapour by water is so feeble
as not to occasion a sensible reduction of temperature in the alcohol.
Chloride of calcium is disqualified as an absorbent of aqueous vapour
in the purification of alcohol, for the same reason as sulphuric acid. I
find that chloride of calcium absorbs the vapour of absolute alcohol, and
runs into a liquid, or it deliqueSces in alcohol vapour. A small quantity
of this substance was suspended in a little capsule, at the height of two
inches above a quantity of absolute alcohol, in a close vessel. In the
course of twenty-four hours it was entirely resolved into a liquid, just
as if it had been suspended over water. The liquid proved to be a
solution of chloride of calcium in absolute alcohol. The experiment
was frequently repeated. As Salts which deliquesce from the absorption
314 AN ACCOUNT OF THE FORMATION OF ALCOATES.
of aqueous vapour are always capable of forming hydrates, I was led
from the observation of this fact to attempt the formation of analogous
compounds of alcohol and salts, to which I now proceed.
These solid compounds of salts and alcohol, which are definite and
imperfectly crystallizable, may be denominated Alco-ates, a designation
which is not unexceptionable, but appeared to me preferable to the name
Vinate, as there is a sulpho-vinous acid, or to any other name that might
have been imposed upon them.
The alcoates which I succeeded in forming are not numerous. They
were formed simply by dissolving the salts previously rendered anhy-
drous, in absolute alcohol, with the assistance of heat. On cooling, the
alcoates were deposited in the solid state. The crystallization was
generally confused, but in some cases crystalline forms appeared of a
singular description. The crystals are transparent, decidedly soft, and
easily fusible by heat in their alcohol of crystallization, which is gene-
rally considerable, amounting in one instance to nearly three-fourths of
the weight of the crystals.
1. Alcoate of Chloride of Calcium.
Pure muriate of lime was dried as much as possible on a sand-bath
of the temperature of 600° or 700°, and then slowly heated to redness,
and retained for some time at that temperature. The dry chloride of
calcium thus obtained dissolves in absolute alcohol at 60° with great
facility, and with the production of much heat, sometimes occasioning
the boiling of the solution. The quantity of chloride taken up increases
with the temperature; and at 173*, the boiling point of alcohol, 10 parts
alcohol dissolve 7 parts chloride of calcium. This solution is thick and
viscid, but perfectly transparent, provided the chloride be pure. It
boils at 195°, alcoholic as well as aqueous solutions boiling at higher
temperatures than the pure liquids. The viscidity of the solution of
chloride of calcium increases greatly as it cools. Bright crystalline
stars soon appear on the surface and on the sides of the vessel, which
have been moistened by the solution. The solution, however strong,
never crystallizes instantaneously, but gradually, in thin transparent
and colourless plates, the forms of which cannot be made out, except
on the surface of the Solution and sides of the vessel.—To obtain the
alcoate in a state of absolute purity, it is necessary to form a solution
so weak, that, while hot, it will pass through thin filtering paper; and
afterwards to concentrate the filtered solution by heat. A solution of
one part chloride of calcium in five parts alcohol passes through the
filter. It is remarkable that the most distinct crystalline forms are not
obtained from the slow crystallization of comparatively weak solutions;
AN ACCOUNT OF THE FORMATION OF ALCOATES. 315
4
but in solutions which have been fully Saturated, or nearly so, at the
boiling temperature. In the former case, the crystalline plates are
large, but confused, and nothing but angles can be made out; while in
the latter, the forms, under which the plates appear on the surface of
the solution, and to the greater advantage, on the sides of the vessel,
are generally distinct. These plates are always small, often beautiful,
and delicately striated; and they always present the form of isosceles
triangles. In general, four of these triangular figures are grouped with
their apices together; and if similar, they form a Square. But, as more
frequently happens, the opposite pairs of triangles only are similar;
and the figure presented is a rectangular parallelogram, divided by two
diagonal lines into four triangles. The resolution of the rectangle into
triangular figures is rendered perceptible by the discontinuance of the
striae, and the formation of clear diagonal lines, which have a beautiful
effect. These crystals cannot be removed from the phial in which they
are formed without injury, from their softness. Exposed to the air,
they speedily deliquesce from the absorption of hygrometric moisture.
The heat of the hand is sufficient to melt them. The whole of the
alcohol is expelled by a heat amounting to 250°, and pure chloride of
calcium remains, which emits nothing else upon being heated to
redness.
A quantity of this alcoate was dried, first by strong pressure between
many folds of linen, and then by pressure between folds of blotting
paper. The alcoate, carefully dried in this way, had a white appearance
much resembling bleached wax, and was soft, but without tenacity.
Ten grains were heated in a glass capsule, till the whole alcohol was
driven off. There remained 41 grains chloride of calcium. The atomic
weight of chloride of calcium is 7, and that of alcohol. 2:875. In the
alcoate, 41 grains chloride of calcium were combined with 5-9 grains
alcohol.
4.1 : 5.9 : : 7 : 10-0731.
In a second analysis, in which 20 grains of alcoate were employed,
the result was precisely similar, as 82 grains chloride of calcium
remained, which is just double what was obtained in the previous case
from half the quantity of alcoate. If this alcoate should be considered
a compound of one equivalent proportion of chloride of calcium, and
three and a half proportions alcohol, the alcohol would amount to
10.0625, which approaches very nearly to the experimental results.
But it would be better to express the composition of the alcoate thus:–
Two atoms chloride of calcium, 14"
Seven atoms alcohol, e © 20-125
34° 125
316 AN ACCOUNT OF THE FORMATION OF ALCOATES.
In the solution of chloride of calcium, no crystallization takes place
at the temperature of 50°, when the alcohol exceeds the proportion of
10 parts to 4 parts of the dry salt. But the solution crystallizes readily
when further concentrated. A solution saturated at 170°, and which
consisted of 10 parts alcohol and 7 parts chloride of calcium, or nearly
the atomic proportions of the alcoate, crystallized slowly upon cooling,
forming crystals upon the surface of the liquid and sides of the phial,
of great regularity and beauty. The whole crystallized during a cold
night, leaving no mother liquor whatever.
The injurious effect of the presence of water, in the formation of this
alcoate, was evident in alcohol of the specific gravity 0.798, in which
the contaminating water did not amount to 1 per cent. A solution of
chloride of calcium in alcohol of this strength did not crystallize readily,
and the crystals eventually deposited were small and ill formed.
Chloride of calcium does not crystallize at all in alcohol of the specific
gravity 0.827. The same inconvenience arises from employing chloride
of calcium containing a little water.
Although the alcoate of chloride of calcium in a state of purity is
entirely decomposed at a temperature not exceeding 250°, yet, when
water is present, alcohol can be retained by the chloride of calcium at a
much higher temperature. Thus I repeatedly found, that chloride of
calcium, from which alcohol had been rectified, and which afterwards
had been washed out the retort by water, gave indications of the pre-
sence of alcohol, after being exposed on the sand-bath to a heat of 400°
or 500° for several hours. Transferred in a crucible to the fire, after it
ceased to lose weight on the sand-bath, alcohol-vapour was emitted,
which took fire and burned. -
2. Alcoate of Nitrate of Magnesia.
It is difficult to expel the whole of the water with which nitrate of
magnesia is combined, without driving off a portion of the acid, and
decomposing the salt. For this salt may be wholly reduced in a glass
tube by the heat of a spirit-lamp, and yet a sand-bath heat of 600° or
700° is not sufficient to drive off all its water of crystallization. But a
partial decomposition of this salt is of no great consequence, as alcohol
dissolves the undecomposed portion of the salt, while the magnesia
resulting from the decomposition precipitates, and may be separated by
decanting the Solution, or by filtering.
Four parts alcohol at 60° dissolve one part nitrate of magnesia, and
boiling alcohol dissolves more than half its weight of this salt. From
the great difference between the solubility of this salt at high and low
temperatures, the alcoate is obtained with facility. A hot solution,
AN ACCOUNT OF THE FORMATION OF ALCOATES. 317
containing a greater proportion of nitrate than one part to three parts
alcohol, became, upon cooling, an irregular dry mass, which could be
indented by the point of a glass-rod, but was much harder than the
alcoate of chloride of calcium. In Solutions considerably weaker
crystals were deposited on cooling, which sometimes resembled the
crystals of the former alcoate, but were much smaller, and less distinct;
but more frequently the crystals were exceedingly minute, and detached,
without any regular form which could be discerned. But the great
mass of crystalline matter precipitated in scales of a pearly lustre and
whiteness, but apparently made up of the small crystals.
Dried by pressure, in blotting-paper, this alcoate much resembled
the alcoate of chloride of calcium in external characters. It sank in
water, but floated on the surface of a saline solution of the specific
gravity 1-1. Heated, it melted readily; boiled, and much alcohol was
given off. When boiled violently, red fumes rise with the alcohol-
vapour; but when dried slowly, no loss of acid takes place.
Upon cautiously heating 13.4 grains alcoate of nitrate of magnesia
to dryness, there remained 3-56 grains nitrate of magnesia. This gives
9-84 alcohol to 3-56 nitrate of magnesia. But the atomic weight of
anhydrous nitrate of magnesia is 9:25. Now,
3°56 : 9'84 : : 9°25 : 25°57.
In another case, 16 grains alcoate were reduced to 42 grains. This
gives 11-8 grains alcohol to 42 grains nitrate of magnesia.
4'2 : 11-8 ; ; 9:25 : 25°99.
On the supposition that this alcoate consists of one atom nitrate of
magnesia united with nine atoms alcohol, the alcohol should amount to
25875, a number intermediate between the two results. This alcoate
will be thus represented:—
One atom nitrate of magnesia, . 9:25
Nine atoms alcohol, . sº . 25'875
35' 125
3. Alcoate of the Nitrate of Lime.
Nitrate of lime may be obtained anhydrous with much greater
facility than nitrate of magnesia, as, after being dried on the sand-bath,
it may be heated in a glass capsule by the spirit-lamp without decom-
position, although it partially fuses. Boiling alcohol saturated with
this salt formed a solution, which became very viscid on cooling, and
remained without crystallizing for a whole day. But during a frosty
night it was resolved into an amorphous Solid, slightly moist, but with-
3.18 AN ACCOUNT OF THE FORMATION OF ALCOATES.
out any appearance of crystallization. This substance was carefully
dried in the usual way.
148 grains were reduced by heat to 88 grains. This gives 6 grains
alcohol to 88 grains nitrate of lime. The atomic weight of anhydrous
nitrate of lime is 10:25. Now, -
8°8 : 6 : : 10°25 : 6'98.
In another case, 15-6 grains were reduced to 9:2, which gives 6'4
alcohol to 9:2 nitrate of lime. But,
9.2 : 64 : : 10:25 : 713.
This approaches 7-1875, or two and a half equivalent proportions of
alcohol. The composition of the alcoate of nitrate of lime would be
represented on this view, by
Two atoms nitrate of lime, e 20:5
Five atoms alcohol, o © 14-375
34'875
In another strong alcoholic solution of nitrate of lime, a few irregular
crystals were deposited, but the quantity was not sufficient to admit
of examination, although they proved that this alcoate is capable of
Crystallizing.
4. Alcoate of Protochloride of Manganese.
The protochloride of manganese, dried in a glass tube, at a red heat,
was light, friable, and of a reddish colour. Alcohol dissolved a very
large quantity of it. When the solution was made at a high tempera-
ture, the alcoate crystallized readily upon cooling in plates with ragged
edges. 14.6 grains of this alcoate, carefully dried by pressure in blotting-
paper, were reduced by heat to 7 grains. The alcoate, therefore, con-
sisted of 7 grains protochloride of manganese, and 7.6 grains alcohol.
The atomic weight of protochloride of manganese is 8. Now,
7 : 7.6 : : 8 : 8°686.
This slightly exceeds three atoms alcohol = 8.625, but the approxima-
tion to the theoretical number is as close as could be expected. The
composition of this alcoate may therefore be expressed by
One atom protochloride of manganese, . 8.
Three atoms alcohol, . tº e ſº 8°625
16*625
AN ACCOUNT OF THE FORMATION OF ALCOATES. 3.19
!
5. Alcoate of Chloride of Zinc.
Alcohol dissolves chloride of zinc with great facility, and the solu-
tion when filtered is of a light amber colour. This solution may be
concentrated to a very great extent without injury, and becomes so
viscid when cold, that it may be inverted without flowing perceptibly.
It is not till so concentrated that it begins to deposit crystals, which are
small and independent, but apparently of no regular shape. A viscid
solution, in which crystals formed, was found to be composed of 20 parts
chloride of zinc, and 7 parts alcohol. The small proportion of alcohol
is astonishing; yet no more alcohol was given out when the chloride
was heated nearly to redness, and began to volatilize; nor did a portion
of the chloride thus heated take fire when exposed directly to the flame
of a candle.
The crystalline matter was dried with difficulty by pressure in
blotting-paper. When dry, it possessed the usual waxy softness of the
alcoates, and was of a yellowish colour. Heated, it entered into a state
of semifusion, and gave off its alcohol. Nine grains alcoate were
reduced by the application of sufficient heat to 7.65 grains. Hence the
alcoate consisted of 7-65 chloride of zinc, and 1:35 alcohol. But the
atomic weight of chloride of zinc is 8-75.
7-65 : 1:35 : : 875 : 1'544.
1:544 slightly exceeds 1:4375, or half an atomic proportion of alcohol.
It is probable that the excess was owing to the difficulty of freeing the
alcoate completely from the viscid solution. According to this view,
the alcoate of zinc consists of
Two atoms chloride of zinc, e 17.5
One atom alcohol, . e e 2.875
20-375
Besides these alcoates, similar compounds of chloride of magnesium
and of protochloride of iron and alcohol were formed, although in quan-
tities too minute to enable me to ascertain their proportions. Alcohol
is retained with great force by chloride of iron, and is partially decom—
posed when heated, as is the case with many metallic chlorides.
As I had it only in my power to present the fixed alkalies to abso-
lute alcohol in the state of hydrates, no alcoate appeared to be formed.
The same was the case with the vegetable acids soluble in alcohol.
It is probable that many more alcoates of salts may be formed, parti-
cularly of the metallic chlorides. The great obstacle to their formation
is the difficulty, and frequently the impossibility, of rendering the salts
perfectly anhydrous, before their solution in alcohol is attempted.
320 AN ACCOUNT OF THE FORMATION OF ALCOATES.
I am not aware of any other compounds in the Solid form of the
same class as the hydrates and alcoates. But there is an oxide, classed
by Dr. Thomson, in his System of Chemistry, with water and other neutral
and unsalifiable oxides, the habitudes of which with certain Salts are
exceedingly remarkable, and have been looked upon as anomalous, but
on which the established properties of hydrates and alcoates appear to
me to throw some light. I refer to the deutoxide of azote or nitrous
gas. 100 volumes pure water are capable of absorbing only 5 volumes
of this gas, according to the experiments of Dr. Henry. But Dr.
Priestley and Sir H. Davy ascertained that certain metallic salts, parti-
cularly the protoSalts of iron, are capable of absorbing this gas in large
quantities; and again emit the greater part of it unaltered, on being
heated. That the absorption of deutoxide of azote by these salts is not
dependent upon the oxygen of their bases, or the water which they
contain, I have proved in two ways, in the case of protomuriate of iron.
By heating this salt to redness in a glass tube, it is reduced to the state
of protochloride of iron. Now, I find that this chloride in the dry state
absorbs deutoxide of azote, although in a comparatively small propor-
tion. And the alcoholic solution of the chloride, where neither oxygen
nor water interferes, appears to exceed the aqueous solution of the
protomuriate in its capacity for deutoxide of azote.
Deutoxide of azote, formed by the action of dilute nitric acid on
copper, was conducted into a globular receiver surrounded by cold
water, and thence through a glass tube of two feet in length, filled with
small fragments of chloride of calcium. Thus dried, the deutoxide of
azote was passed slowly over carefully prepared protochloride of iron
in the state of powder, and contained in a glass tube of Small diameter.
The protochloride immediately became darker in colour; and upon
being withdrawn, after exposure to the current of gas for some time,
was found to retain the smell of nitrous gas, and to have increased in
weight. In one case, 30 grains chloride had increased to 31°l grains;
and in another case, 25 grains chloride to 25-5 grains. On being gently
heated, the deutoxide of azote was evolved, and the chloride restored to
its former colour.
The solution of protochloride of iron in absolute alcohol absorbed a
much greater quantity of deutoxide of azote, and became nearly black.
A solution Saturated with gas began to boil at 100°, evolving gas in great
abundance, which, being collected in the pneumatic trough, proved to
be pure deutoxide of azote. The greater part of the gas was expelled
before the alcohol rose to its boiling point, and after the solution was
in the state of ebullition for a few seconds gas ceased to rise, and the
alcoholic solution recovered its original colour, which was generally a
chocolate-brown, from the presence of a little bichloride of iron. The
AN ACCOUNT OF THE FORMATION OF ALCOATES. 321
quantity of gas evolved from a solution of one part protochloride of iron in
five parts absolute alcohol, amounted to 23 times the volume of the alcohol.
I think it probable that the absorption of deutoxide of azote by
protochloride of iron, is analogous to the absorption of alcoholic and
aqueous vapours by the same body. For I find that protochloride of
iron absorbs alcohol-vapour as well as the vapour of water. The absorp-
tion of deutoxide of azote may depend upon a tendency of chloride of
iron to deliquesce in like manner, in an atmosphere of that neutral oxide.
At a very low temperature, which it is perhaps out of our power to
reach, protochloride of iron would probably absorb this gas in sufficient
quantity to exhibit the appearance of deliquescence, and might form
with it a neutral compound similar to its alcoate or hydrate.
A reason can also be given for the Superiority of the aqueous and
alcoholic solutions of this chloride over the dry chloride itself, in
absorbing deutoxide of azote. We formerly saw that the alcohol of the
alcoate of chloride of calcium was completely expelled by a heat of 250°,
when no water was present; but that, when a considerable quantity of
water was present, alcohol was retained by that chloride at the tempera-
ture of 400° or 500°. Now chloride of iron might be enabled to retain
deutoxide of azote more powerfully, by the assistance of alcohol or water,
in the same manner. But the retaining power we have formerly found
in a similar case to be an index of the absorbing power. Hence solutions
of protochloride of iron might absorb deutoxide of azote more powerfully
than the chloride itself.
III.
RESEARCHES ON THE ARSENIATES, PHOSPHATES, AND
MODIFICATIONS OF PHOSPHORIC ACID.
CoMMUNICATED BY EDWARD TURNER, M.D., F.R.S., &c."
From Philosophical Transactions, 1833, pp. 253-284.
I. OF THE SUBSALTS.
No classes of salts have more liberally rewarded investigation than
the arseniates and the phosphates. Witness the discovery of the
extraordinary phosphates of lime by Berzelius; the observation of the
identity of form of the corresponding arseniates and phosphates by
Mitscherlich, and the doctrine of isomorphism to which that observation
1 Received January 29,-Read June 19, 1833.
X
322 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
led; the discovery by the same chemist of two biphosphates of soda,
agreeing in composition but differing in form; and lastly, the discovery
of the pyrophosphates by my friend and townsman Mr. Clark. Much,
however, still remains to be done to complete the history of these
interesting salts.
1. Subarseniate and Subphosphate of Soda.
The extraordinary disposition of arsenic and phosphoric acids to
form subsesquisalts—such as the brown arseniate and the yellow phos-
phate of silver, the common subarseniates of lime, lead, etc.—is well
known. Corresponding alkaline salts exist, which merit the considera-
tion of chemists.
- To a strong solution of arseniate or phosphate of soda add a solution
of caustic soda till the liquor feels soapy between the fingers. At least
half as much soda as already in the salt must be added, but an excess
of alkali is not injurious. Concentrate the liquor till a pellicle forms
on its surface, and then allow the solution to cool. At the temperature
of 150°, tufts of slender prismatic crystals appear in it; these rapidly
increase in quantity, and finally fill the vessel. The crystals must be
drained as well as possible, and the mother-liquor may be thrown away,
as it contains little else than the excess of caustic soda and the soluble
impurities of the salts. It is necessary, without loss of time, to redis-
solve the crystals in twice their weight of hot water, to filter the solu-
tion through paper, and to recrystallize.
Both salts crystallize readily, as their solutions cool, in the form of
six-sided prisms, which are generally slender. The prism is often termi-
mated by a flat surface, which appears to be a right section. The angles
of the crystals were not measured, but two of them are much more
obtuse than the remaining four. The subarseniate may be procured in
crystals of larger size than the subphosphate, but of the same form.
These salts in the crystalline form are not altered by exposure to the
air, but in solution they absorb carbonic acid; and when again crystal-
lized, a portion of carbonate is found to adhere pertinaciously to the
crystals. It is easy, however, to produce fine crystals by the process
described, free from carbonic acid, and apparently pure.
A solution of the subarseniate is precipitated exactly neutral, by an
excess of fused nitrate of silver, the brown subarseniate of silver falling
down, which proves the alkaline Subarseniate to be in the same state
of neutrality as the metallic subarseniate, and consequently of a similar
constitution. The subphosphate gives, with the same reagent, the
yellow subphosphate of silver, and leaves a liquid either neutral or very
faintly alkaline by the most sensible cudbear paper. The alkalinity, how-
AND MODIFICATIONS OF PHOSPHORIC ACID. 323
ever, must be accidental, as it disappears on the addition of the smallest
quantity of acetic acid. These salts, therefore, rank as subsesquisalts,
containing one proportion and a half of base to one of acid.” They are
interesting as the only known soluble salts of that constitution. The
subphosphate had been previously crystallized by Dr. Dalton and
recommended as a reagent;” but it was supposed to contain twice as
much soda as the common phosphate. Mitscherlich also infers the
existence of a subsesquiphosphate of Soda, from the quantity of carbonic
acid expelled, when phosphate of Soda is calcined with carbonate of
soda.” The same salt appears likewise to have fallen into the hands of
Dr. Thomson, as an accidental product, but is described as a carbono-
phosphate of soda, being probably impure.”
In regard to the properties of these salts. They are strongly alkaline
to the taste, and act upon chlorine and iodine like free alkalies. Indeed,
the excess of their alkali is separated by the weakest acids, even by
carbonic acid, and the common rhomboidal phosphate or arseniate after-
wards appears on crystallizing. When the pure crystals are thrown
into neutral nitrate of ammonia, the volatile alkali is disengaged. At
60° Fahr. 100 parts water dissolve 28 crystallized subarseniate of soda ;
and the crystals by themselves melt at 186°.
At 60°, 100 parts water dissolve 19.6 crystallized subphosphate of
soda, and the crystals melt at 170°. Hence, although more fusible, they
are less soluble than the crystals of Subarseniate.
It is a fact of extraordinary interest, that the acid of this subphos-
phate is not convertible into pyrophosphoric acid by the action of heat
upon the salt, like the acid of the common phosphate of soda. Indeed,
when the pyrophosphate of soda itself is calcined with an excess of
carbonate of soda, carbonic acid is expelled, and the former salt passes
entirely into subphosphate of soda, which crystallizes in the usual form,
and contains not pyrophosphoric but phosphoric acid. This change
takes place equally well although both the carbonate and pyrophos-
phate be made anhydrous before being calcined ; and we can obtain
consequently an anhydrous subphosphate of Soda. A Solution of pyro-
phosphate of soda, to which sufficient caustic soda or carbonate of soda
has been added, cannot be evaporated to dryness without becoming
subphosphate. But pyrophosphate of Soda may be boiled with caustic
soda for hours without sensible alteration, provided the solution is not
evaporated to dryness; and it crystallizes afterwards in its original form,
exhibiting no disposition whatever to form a subpyrophosphate.
* Three atoms oxygen in the base for five atoms oxygen in the acid.
? Manchester Memoirs, N.S., vol. iii. p. 12.
3 Annales de Chimie et de Physique, tom. xix. p. 363.
* First Principles, etc., vol. ii. p. 451.
324 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
I may premise thus early, that the preceding facts, and many others
to be afterwards enumerated, appear to be most easily explained on the
hypothesis that phosphoric acid, in contradistinction to pyrophosphoric,
is characterized by a disposition to unite with three atoms of base;—
that common phosphate of soda, for instance, is a phosphate of soda
and of water, and that its symbol is Na’HP. Now for this basic water
an atom of any of the usual bases may be substituted; an atom of soda,
for instance, as in our subphosphate, of which the symbol is Na"P; an
atom of oxide of silver, as in the yellow subphosphate of silver; and so
in the other subphosphates. ‘We have here a clew also to the disposition
of phosphoric acid to form such subsesquisalts; for the common phos-
phate of Soda which we use as a precipitant exchanges its basic water
for a fixed base. Hence, although a phosphate of neutral composition,
such as the common phosphate of soda, cannot be made anhydrous with-
out becoming pyrophosphate, the subphosphates, having an excess of
fixed base, may be anhydrous, as was observed by Stromeyer; and indeed
they are not convertible into pyrosalts.
The pyrophosphoric acid of Clark, which exists in the pyrophosphate
of soda, appears to unite with only two atoms of base.
Phosphoric acid, produced in white flakes on burning phosphorus in
air or oxygen gas, or the acid heated to redness by itself, constitutes,
we shall afterwards find, a third modification of phosphoric acid. This
third variety is characterized by alone coagulating albumen; by pro-
ducing precipitates, even when free, in muriate of barytes, lime, etc.
Much time and attention were devoted to the determination of the
water of combination of the foregoing subsalts. Both salts, when dried
by heat, act upon glass with as much violence as the caustic alkalies,
absorb carbonic acid with avidity, and retain a small but notable quan-
tity of water under the most intense heat. The problem is therefore
environed by difficulties. -
(1) Excellent hard crystals of subarseniate of soda lost nothing
when reduced to powder and exposed to a dry atmosphere. Dried
most cautiously in a platinum flask, on a sand bath, -
Water.
In Exp. 1. 42.42 grs, crystallized salt lost 21:13 . . . 49.81 per cent.
,, 2. 26'04 25 12-94 . . . . 49-69 25
,, 3. 41' 9 3 20-40 . . . 49-76 22
Mean . . 49.75
These results exhibit the entire quantity of water which the salt
abandons by the action of heat alone; for an adopter being applied to
the flask and made tight by luting, the Salt was in each case sub-
sequently heated for a few minutes to full redness, without any further
AND MODIFICATIONS OF PHOSPHORIC ACID. 3.25
loss of weight. No sensible absorption of carbonic acid occurred when
the experiment was conducted in this manner. The salt was not fused;
indeed, it is not fused by a strong white heat.
But the calcined salt still contains water, as may be shown by fusing
it with any body capable of combining with the excess of alkali. A
quantity of bichromate of potash in a glass tube may easily be kept in
a state of fusion by the flame of a lamp. On throwing the calcined
subarseniate into that fused and anhydrous salt, a notable quantity of
water was given off, which condensed in the upper part of the tube.
Exp. 1. About 50 grains of the fused bichromate of potash, as it
falls to pieces in the progress of cooling, but still warm, were introduced
into the platinum flask containing 13.1 grains of calcined salt of Expe-
riment, 2d above, and the whole maintained in a state of fusion for a
considerable time at a low red heat, by means of a spirit-lamp. The
Salt lost 0:16 grain additional, and no green oxide of chromium was
formed. This is an additional loss of 0.62 per cent on the crystallized
salt, and makes the entire water amount to 50.31 per cent.
EXP. 2. 25'57 grains of crystallized subarseniate were introduced,
with a little water, into a crucible containing already 20 grains of pure
anhydrous arsenic acid, calcined immediately before by a spirit-lamp
heat which does not decompose it. The whole was cautiously dried,
and finally fused by a red heat. The loss amounted to 12:8 grains, or
50.06 per cent.
EXP. 3. To 25°11 grains of binarseniate of soda previously fused in
a crucible, 45.5 grains of subarseniate of soda were added, with water
sufficient to dissolve the whole. Cautiously evaporated to dryness in a
crucible partially covered by a watch-glass, as usual, and finally heated
to redness, the subarseniate lost 22.88 grains, or 50:29 per cent. This
last is certainly the preferable mode of determining the problem.
The mean of the three experiments detailed gives the entire water
in the subarseniate of soda 50:22 per cent., while the proportion expelled
by heat alone amounts to 49.75 per cent. Hence the quantity retained
amounts to 0-47 per cent.
When the calcined salt retaining this small quantity of water is
reduced to an impalpable powder, and heated afresh on the sand-bath,
the whole water is expelled, with the exeeption of a mere trace.
Although small, the quantity of water retained in the caleined salt
could not be passed over without investigation, as it may afford indication
of some internal change which the subarseniate undergoes. Calcined in
the open fire, this salt absorbs carbonic acid gas, and afterwards effervesces
briskly with an acid. The salt becomes at the same time anhydrous. This
may arise from the hydrate of soda becoming carbonate of soda.
A portion of subarseniate of Soda, dried by the spirit-lamp, was
326 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
reduced to powder, and calcined anew with a mass of carbonate of
ammonia in the same crucible, so that the maximum absorption of
carbonic acid (as it was imagined), might take place. The Salt was
kept uncovered for some time, at a low red heat, after all the volatile
carbonate had escaped. It was found that the quantity of carbonic acid
absorbed, might be determined most exactly by disengaging the gas over
mercury by means of a small quantity of muriatic acid slightly diluted.
Eleven grains of calcined salt afforded 0-49 cubic inch of carbonic
acid gas, at 60°; of which the weight is 0.23 grain, and which is equi-
valent to 0-56 grain of carbonate of soda. Hence, by calculation, 100
parts of the calcined salt contain 2:1 carbonic acid, or 5:1 carbonate of
soda; 21 carbonic acid are equivalent to 0-9 water; but 50 calcined
salt, it was previously shown, retain 0-47 water, and therefore 100
calcined salt retain 0-94. It would thus appear that the carbonic acid
is just in quantity sufficient to occupy the place of the water. The
carbonic acid is not expelled by an intense white heat.
The supposition is quite inadmissible that our salt contains the
notable quantity of soda which becomes carbonate, as a casual impurity,
and not essential to its composition; for the salt employed in all these
experiments was in large, clear and perfect crystals. Such a supposition
is also opposed by the analytic determination of the soda.
The quantity of water in the salt, namely, 50:22 per cent, is not
easily reconciled with our best data for atomic weights. Adopting
the atomic weight of arsenic acid, given by Berzelius, which I had an
opportunity of verifying, a salt of
*24 atomic proportions of water correspond with 50.82 per cent.
23% 55 53 50'29 ,
23 5, 33 49.75 ,
Our experimental result agrees closely with the middle number, and
is perhaps compatible with either 23 or 24 atoms of water. Chemists
will probably agree with me that the last supposition is the most likely.
If so, it is curious that the Subarseniate differs only from the neutral
arseniate, by the substitution of an atom of Soda for an atom of water,
for the last salt contains 25 atoms of water.
It is well known that the analytic determination of the acid in the
arseniates and phosphates is attended with considerable difficulty,
chiefly from unsteadiness in the proportions of the precipitates.
41-87 grains of crystallized subarseniate of soda, precipitated by an
excess of pure acetate of lead, gave a neutral mother-liquor, and a
* We are obliged to adopt the double atom of arsenic acid here (As- 1440. 1); and
consider these subsalts as consisting of one proportion of arsenic acid (containing five
proportions oxygen) and three proportions of base (containing three of oxygen).
AND MODIFICATIONS OF PHOSPHORIC ACID. 327
quantity of subarseniate of lead, which successfully washed by decan-
tation, without the use of a filter, and heated to redness, weighed 46-41
grains; 35.17 grains of this subarseniate of lead, freshly calcined, were
dissolved entirely in water, acidulated with nitric acid; and, precipitated
by sulphate of soda, gave 35'86 grains of sulphate of lead, which con-
tain 26:38 oxide of lead. In such calculations the atomic numbers of
Berzelius are adopted in this paper. Hence the portion of Subarseniate
of lead analysed contains 8-79 arsenic acid; and the whole 46.41 grains
subarseniate of lead contain 11-62 arsenic acid, which is therefore the
quantity of arsenic acid in the portion of subarseniate of soda submitted
to analysis. Hence crystallized subarseniate of soda contains 27.76 per
cent. arsenic acid.
The soda of the salt was determined in the usual way. The arsenic
acid being precipitated by acetate of lead, and received on a filter, the
excess of lead was removed by carbonate of ammonia added to the hot
liquor. The solution of acetate of soda resulting, was then filtered,
concentrated, and transferred into a platinum crucible, in which it was
evaporated on the sand-bath to dryness with the greatest caution ;
partially covered by a watch-glass; and eventually decomposed by a
full red heatgradually applied to the crucible still covered by the watch-
glass, as from the effervescence during the decomposition of the acetates,
small particles are thrown up with considerable force, and would other-
wise be lost. The solution of carbonate was then filtered, evaporated
to dryness in a crucible, and raised to a strong red heat. The following
results were obtained after a knowledge of all the necessary precautions
had been acquired. -
ExP. l. 39.98 grains of crystallized subarseniate of soda yielded
15 61 carbonate of soda, equivalent to 9-14 soda ; or the Salt contains
22.87 per cent. soda. Now 22:87 soda contain 585 oxygen, and 50°22
water contain 45-74 oxygen; or the oxygen in the water is 7-819 times
that in the base. But as there are three atoms of oxygen in the base,
there are 7:819 × 3, or 23:457 atomic proportions of oxygen in the
Water.
ExP. 2. 40.3 grains of crystallized subarseniate of soda yielded 1573
carbonate of soda, equivalent to 9:21 Soda ; or the Salt contains 22.85
per cent. Soda. -
ExP. 3. 21-62 grains of crystallized salt gave 8:41 carbonate of soda,
equivalent to 4-93 soda ; or 100 grains of crystallized Salt contain 22:8
soda.
These experiments agree very closely among themselves; but I am
doubtful whether this method gives the alkali with perfect precision in
the case of the arseniates, but somewhat in excess. The general result
of the analysis may be stated as follows:–
328 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
Subarseniate of soda.
Experiment, Theory of 23 atoms water.
Arsenic acid, . * . 27.76 . , 27°69 .
Soda, e e s ſº 22.85 . . 22°55
Water, . te * . 50'22 . . 49.75
100'83 . . 100°
(2.) The crystals of subphosphate of soda submitted to analysis
were smaller than the crystals of subarseniate, but well formed and
remarkably pure, containing not a trace of sulphuric, muriatic, or car-
bonic acid.
EXP. 1. A quantity of the salt had been reduced to powder and
exposed to a dry atmosphere, in which it lost a little weight; of the salt
so dried, 29-12 grains lost by red heat in a platinum retort, as described
in the case of the Subarseniate, 16-07 grains; which is 55-19 per cent.
Water. -
EXP. 2. 21.83 grains of crystallized salt heated in the platinum
retort on the sand-bath lost 12:05 grains, or 55.2 per cent. Being heated
thereafter to redness by the lamp, the loss appeared to be only 12:01
grains; but the calcined Salt had acquired a little carbonic acid, not-
withstanding the precautions, and now effervesced with acids. These
two experiments give, therefore, the same result.
The Salt still retained a little water, about twice as much as the
subarseniate in the same circumstances. But when the calcined sub-
phosphate was reduced to an impalpable powder, and heated anew, the
greater portion of the water which had been retained was readily
expelled.
EXP. 3. Fused with recently ignited protoxide of lead, 1936 grains
of crystallized salt lost 10:84 grains, or 55.99 per cent, which is the
entire water in the salt.
EXP. 4. To 17 grains of biphosphate of soda recently fused in a
crucible, 35-54 grains of crystallized subphosphate of soda were added,
with a quantity of water, in which the salts were dissolved together by
digestion. Evaporated to dryness, and calcined by a red heat without
fusing, the salts sustained a loss of 1992 grains. Hence 100 crystallized
salt have abandoned 56.05 water.
Calcined with access of carbonic acid, the subphosphate, like the sub-
arseniate, absorbs that gas, becoming at the same time anhydrous; but
redissolved in water and evaporated, it affords crystals of the Original
form and composition, which retain a trace of carbonic acid.
A quantity of the subphosphate ignited in an open crucible was
found to consist of
AND MODIFICATIONS OF PHOSPHORIC ACID. 329
Subphosphate of soda, . gº * 100
Carbonic acid, & & tº tº 2-3
Another portion, calcined with a mass of dry carbonate of ammonia
in the same crucible, consisted of
Subphosphate of soda, . º . 100
Carbonic acid, & ſº e tº 2.25
A quantity of subphosphate of soda dissolved in a solution of car-
bonate of ammonia, was thereby purposely contaminated by a large
quantity of carbonic acid, and calcined three times in succession with
alternate pulverization. It finally consisted of
Subphosphate of soda, . ſº wº 100
Carbonic acid, te e * > C 1.7
Or of
Subphosphate of soda, . g ſº I 00
Carbonate of soda, . * & ſº 4’3
It seemed to follow from the last experiment, that, by pulverizing the
Salt and recalcining it, the quantity of carbonic acid may be diminished,
as in the case of water in the hydrate of the same salt.
The calcined salt did not fuse at a strong white heat, but acquired
a beautiful blue tint where in contact with platinum. .
By the mean of two experiments detailed above, 100 crystallized
subphosphate of Soda contain 56°03 water. Twenty-three atoms would
be 55-61 per cent, only, and twenty-four atoms water would be 56-66
per cent."
The soda of the subphosphate was determined directly, in the same
manner as the soda of the subarseniate.
EXP. 1. 41'23 grains of crystallized salt gave 17-27 carbonate of
Soda, equivalent to 10-12 soda. Hence 100 of crystallized salt contain
24°54 soda.
EXP. 2. 40 grains of the crystallized Salt gave 16-97 carbonate of
soda, equivalent to 7:03 soda, or 24.87 per cent. soda.
It was also attempted to determine the phosphoric acid directly, by
precipitating with nitrate of silver, which leaves a mother-liquor either
exactly neutral or feebly alkaline. The result was 18.6 per cent, phos-
phoric acid, which certainly approaches the truth. But the subphosphate
of silver was discovered to carry down with it a portion of nitrate of
silver, which comes away gradually, but which no continuance of Washing
is sufficient entirely to remove. The Subarseniate of silver has the same
1 Assuming the double atom of phosphoric acid (P)=8923.
330 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
property. Thus to precipitate 27.5 grains of crystallized subphosphate
of soda, 381 grains of fused nitrate of silver were found necessary, which
is more than one grain above the theoretical quantity: 25 grains of
crystallized subarseniate of soda required 31.08 grains of nitrate of
silver for complete precipitation, which is an equally excessive propor-
tion of the precipitant. From these precipitates fumes of nitrous acid
were evolved, on the application of heat. When nitrate of ammonia,
exactly neutral, was first mixed with the solution of subarseniate of Soda,
a less quantity of nitrate of silver sufficed; 30.05 grains of nitrate of
silver left still an excess of arsenic acid, when added to 25 grains of
subarseniate of soda; but on introducing 0.06 grain of nitrate of silver
additional, the liquid contained an excess of silver: but the nitrate of
ammonia retains in solution a trace of subarseniate of silver. It is
curious that the pure subarseniate of silver, precipitated in the way last
mentioned, withdraws nothing from a solution of nitrate of silver. This
shows that the subarseniate of silver carries down the soluble nitrate
only at the moment of precipitation, and by the agency of some chemical
affinity very different from the attraction of animal charcoal for many
bodies in solution.
The addition of a little acetic acid to a solution of subarseniate of
soda, occasioned a notable deficiency in the amount of the precipitate
by nitrate of silver. -
It may be safely concluded from the quantity of soda which it con-
tains, that the salt under examination is a subsesquiphosphate. The
crystals consist of
Subsesquiphosphate of soda, . te 43'97
Water, tº tº e de ºr 56°03
100°
2. Subphosphates and Subarseniate of Potash.
The corresponding salts of potash were formed, but I did not succeed
in obtaining them in a state of purity.
When caustic potash is added in excess to phosphoric acid, the
solution becomes muddy although dilute, and a precipitate partly flaky
and partly in a gritty powder shows itself. This precipitate in both
conditions is a diphosphate of potash according to Dr. Thomson, who
examined it." When arsenic acid was treated in the same way, with
excess of caustic potash, no insoluble salt fell; but on concentrating
the solution it crystallized almost entirely in the form of minute needles.
These crystals I could not free from carbonate; and either of themselves,
or rather from the presence of free potash, they were deliquescent in the
* Inorganic Chemistry, vol. ii.
AND MODIFICATIONS OF PHOSPHORIC ACID. 331
extreme. There is every reason to believe that they constitute a subsalt
corresponding with the subsalt of soda.
A crystallized subphosphate of potash, however, may be formed by
fusing together phosphoric acid and an excess of carbonate of potash
(bicarbonate was employed). A strong solution crystallizes in small
needles, like the preceding subsalts. These crystals were exceedingly
soluble, and retained a little carbonate of potash, but were not at all
deliquescent. They precipitated the yellow subphosphate from nitrate
of silver in excess, and left a neutral or slightly alkaline mother-liquor.
The soluble subarseniate and subphosphate of soda present a favour-
able opportunity of forming the corresponding insoluble earthy and
metallic subsalts. Salts of this formula, it is well known, generally pre-
sent themselves, even when the alkaline salts of arsenic and phosphoric
acid, which are neutral in composition, are employed as precipitants.
But the consequent and unavoidable acidity of the mother-liquor is apt
to prevent complete precipitation, the phosphates, with few exceptions,
being soluble in an excess of acid.
3. Subarseniate and Subphosphate of Barytes.
To a solution of subarseniate of soda, chloride of barium was gradu-
ally added till in slight excess. The precipitate first appeared gelatinous,
consisting of little pellucid masses; but on the application of heat to the
liquor, the precipitate immediately became small-flaky and heavy, and
subsided. The mother-liquor proved strongly alkaline, and the preci-
pitate, it was found, had taken down with it a quantity of Subarseniate
of soda, of which protracted washing did not entirely divest it. Berzelius
has remarked that barytes is most disposed to combine with phosphoric
acid in the proportion of a neutral salt, which is true also of arsenic acid,
and accounts for the above derangement of precipitation, a little of the
neutral salt being probably formed. The process was reversed, and into
a large quantity of neutral solution of chloride of barium, a solution of
50 grains of subarseniate of soda was gradually poured with stirring. A
pulverulent heavy precipitate fell easily. The filtered mother-liquor did
not fully restore the blue colour of reddened litmus paper in some hours,
but acted at once as an alkali on cudbear paper, although in a feeble
manner. The precipitate, however, was easily washed. While still
wet on the filter, it had acquired a sensible trace of carbonic acid;
and when heated, it displayed, like the corresponding alkaline salts,
considerable avidity for carbonic acid. 22.33 grains of this salt,
heated to redness by the spirit-lamp, were found by one analysis to be
composed of
332 RESEARCHES ON THE ARSENIATES. PHOSPHATES,
Carbonic acid, . • e 0.18
Arsenic acid, . e * 7:10 . . . 32°06
Barytes, . º • * * 15:05 . . . 67.94
22°33 100°
If we may trust a single analysis, the salt contains an excess of
barytes; for by theory a subsesquiarseniate of barytes should be com-
posed of -
Arsenic acid, . º . 1440.1 . . . 33°4
Barytes, . e e . 2870.6 . . . . 66'6
4310-7 T007
When a solution of subphosphate of soda is added to chloride of
barium, a corresponding subphosphate of barytes subsides as a heavy,
small-flaky precipitate, leaving a mother-liquor neutral or nearly so.
4. Subarseniate and Subphosphate of Lime.
The subarseniate of lime, formed by pouring chloride of calcium into
subarseniate of soda, is a bulky gelatinous body, and continues so
although heated. It carries down subphosphate of soda, but to a less
extent than the subarseniate of barytes prepared in the same way.
Prepared by the converse process, the Subarseniate precipitates in little
gelatinous masses, as before; although the general aspect is flaky, par-
ticularly after the liquor has been heated. The mother-liquor from 50
grains of Subarseniate of soda precipitated in this way, required several
minutes to affect reddened litmus paper unequivocally, being slightly
alkaline. The precipitate appears, therefore, to correspond closely with
the subarseniate of soda. The properties of the subphosphate appeared
to be similar. Such a phosphate occurs native, but hitherto had not
been formed artificially.
Berzelius proves the existence of another subphosphate of lime,
which has acquired the name of the Subphosphate of lime of bones,
a gelatinous body, formed when muriate of lime is poured into an
excess of phosphate of soda ; or when phosphate of lime, dissolved in
muriatic acid, is precipitated by ammonia. The composition of this
phosphate is singular and without parallel, consisting, on the simplest
view which can be taken of it, of three proportions of phosphoric acid
and four of lime. It is designated by Gay-Lussac the # phosphate,
while the preceding compound is called the # phosphate. The anomaly
may in some measure be removed by viewing this salt as a compound
of one proportion of the neutral phosphate of lime and two proportions
of the subseSquiphosphate. Its formula would be as follows:
Caº + 2(Čaº).
AND MODIFICATIONS OF PHOSPEIORIC ACID. 333
Berzelius finds the calcined bones of the ox to be composed of such
a phosphate of lime with a small quantity of carbonate of lime. His
analysis may be stated thus:
Phosphate of lime, { Fº acid, . º : º
Li 3 * w e gº ...] 51.86
Carbonate of lime ime, . . ; º tº
’ Carbonic acid, º * 1.69
100°
The only doubt we can entertain of this view arises from the circum-
stance, that the presence of carbonic acid in the calcined phosphate of
the bones is no proof of the existence of carbonic acid in the same body
previous to calcination. We know that the subphosphate of soda absorbs
a variable quantity of carbonic acid when calcined. The quantity of
carbonic acid which the earth of bones contains is variable. A speci-
men which had been calcined more than a year before, contained 12
per cent. As this was below the determination of Berzelius, I reduced
a portion to fine powder, and kept it for some minutes in an atmosphere
of carbonate of ammonia, at a heat scarcely amounting to redness. The
earth, however, by this treatment, had lost carbonic acid, and now con-
tained only 0.5 per cent. Another portion reduced to powder, and gently
heated in the same way, but without the carbonate, retained 0.57 per
cent. carbonic acid.
The earth of bones, although calcined at a high temperature, con-
tains phosphoric acid and not pyrophosphoric acid, the excess of base
preventing the transition. But eight ounces of earth of bones being
mixed with two ounces of sulphuric acid, and calcined again, were found
thereafter to contain a large proportion of an acid which precipitated
silver white, -
5. Subarseniate and Subphosphate of Lead.
When the subarseniate or subphosphate is poured into a solution of
acetate of lead in excess, the salt which falls was found to contain an
excess of base. I therefore had recourse to the converse process. To
50 grains of subarseniate of soda in solution, 50 grains of acetate of lead
in solution were gradually added with stirring, which left an excess of
the first in solution. The subarseniate of lead was washed by decanta-
tion, till the water digested upon it ceased to acquire an alkaline reaction.
Heated to low redness, this substance acquired a yellow tint, but became
white again on cooling; it was found somewhat aggregated together by
the heat, but not fused. 15:25 grains were dissolved in dilute nitric
acid, and precipitated by sulphate of soda added in excess. The sulphate
334 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
of lead amounted to 15:41 grains, equivalent to 11:336 oxide of lead.
The washings became of a brown tint on the addition of sulphuretted
hydrogen, but the quantity of lead which they contained was too small
to be appreciated. This analysis affords a striking confirmation of the
atomic weight of arsenic acid, deduced by Berzelius from his analysis of
arsenious acid by sulphur. I place together the results of my analysis,
and the composition of the same salt calculated by that accomplished
analyst from his own data.
Analysis. Theory of Berzelius.
Arsenic acid, * te e 25-67 25-61
Oxide of lead, . º º 74°33 74’39
In another analysis, the quantity of lead which escaped precipita-
tion by the sulphate of soda was even more notable, from the presence
of too much nitric acid. The result was 74.18 per cent. oxide of lead.
This salt I believe to be most suitable of all the arseniates for deter-
mining directly the combining proportion of arsenic acid.
II. OF THE NEUTRAL PHOSPHATES AND PYROPHOSPHATEs.
It is well known that the phosphate of soda is a highly alkaline
salt, although generally viewed as neutral in composition. Mitscher-
lich found that a solution of this salt required the addition of half as
much acid as it already possesses, to deprive it of an alkaline reaction.
This result I had an opportunity of confirming in a general way,
although I could not ascertain the exact point of Saturation, from the
test-paper proving doubtful in its indications for a considerable distance
on either side of the supposed point of neutrality.
Although Mr. Clark's experiments afford strong evidence that the
phosphate of Soda of the usual form contains twenty-five atoms water,
yet it was thought proper to settle the point by a careful experiment.
Pure crystals were employed, which had been formed about six months
before and were dry, but possessed bright surfaces. A portion for
analysis was reduced to powder in a damp day, and pressed for twenty
hours between folds of dry blotting-paper. A crystal exposed to the air
at the same time, beside the paper, remained perfectly bright. Care-
fully dried and heated to redness, 35:44 grains of the salt lost 22:29 grains
of water. Hence the crystallized salt consists of
Phosphate of soda, . & e e e 37.1
Water, . º º º e e º 62.9
*s-s
100°
AND MODIFICATIONS OF PHOSPHORIC ACID. 335
Our result gives 25:22 atoms water, and therefore confirms the previous
determination.
Mr. Clark has the entire merit of discovering the change which takes
place upon phosphate of soda by the action of heat, and his original
description of the pyrophosphate of soda is very complete." He like-
wise remarked the connexion between the transition into pyrophosphate
and the loss of the last atom of water of the phosphate of soda, which
atom requires a much higher temperature to expel it than the other
twenty-four; but he did not entertain the idea, broached in this paper,
of the basic function of that atom of water in the constitution of
the salt. sº
The phosphate of Soda contains three atoms base; namely, two
atoms soda and one atom water; and when added to the earthy or
metallic salts, gives precipitates which uniformly contain three atoms
base, namely, three atoms of the foreign oxide, as in the case of the
subphosphate of silver, or one atom water and two atoms of the other
oxide, as in the phosphate of barytes. These precipitations afford the
strongest proof of the basic function of that atom of water which is
essential to the phosphate of Soda, as they can be accounted for, on the
usual laws of double decomposition, on no other supposition. The pyro-
phosphate of soda, on the other hand, contains only two atoms soda as
base, and gives, accordingly, bibasic precipitates.
In his Traité de Chimie, Dumas speaks in an incidental manner of a
third phosphate of soda, differing from the two preceding, obtained by
keeping for a long time a solution of the common phosphate at the
boiling temperature; but I have been able to discover no description nor
any other notice of this new salt. To investigate the point, I boiled for
several hours each day during three weeks, an ounce of phosphate and
the same quantity of pyrophosphate of Soda, in separate flasks, with
several ounces of water. A considerable heavy, flaky precipitate soon
appeared in both, but was most abundant in the pyrophosphate. The
flasks, on removing the liquors from them, were found strongly cor-
roded. The solution of pyrophosphate, on being filtered and concen–
trated, yielded crystals of our subphosphate of soda to the last drop.
It had evidently derived alkali from the glass, while a portion of its
acid had also united with the oxide of lead of the glass, and formed a
precipitate insoluble both in water and in acids. But the solution of
the boiled phosphate of soda filtered, concentrated, and set aside in a
cool place, became gradually filled with crystalline plates, which were
the finest films and had a beautiful silky lustre. The mother-liquor
being poured off, yielded a second, third, and fourth crop of crystals of the
same singular appearance. The last drops of the liquor were still alka-
1 Edinburgh Journal of Science, vol. vii. p. 298.
336 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
line, but I thought not so strongly so as the phosphate of soda. The
crystallization in these cases was gradual, and not hurried and confused.
To look at these silky films, nobody would have guessed them to be phos-
phate of soda. But on examining them minutely, complete rhomboidal
plates of the common form of phosphate of soda were distinguished; and
the water of crystallization of the salt was found to be exactly the same
as that of the rhomboidal phosphate. In a dry atmosphere, too, a
portion of the silky plates, and an equal quantity of pounded crystals
of the common phosphate lost their water pari passw. It is evident,
therefore, that we have nearly obtained the phosphate of soda of an
unusual appearance. I shall have occasion, in the sequel of the paper, to
notice other circumstances in which the phosphate presents itself of
this appearance. On dissolving and recrystallizing the silky plates, the
usual solid rhomboids presented themselves. It was also determined by
experiment, that neither the phosphate nor pyrophosphate of Soda is
altered by being boiled for a week in water contained in a silver capsule,
in which no decomposition can take place. There can be no doubt,
therefore, that these salts undergo no change at the boiling tempera-
ture, unless they react upon the material of the containing vessel. Even
at the usual temperature a solution of these alkaline salts corrodes a
glass phial and becomes turbid in the course of months.
III. OF THE SUPERPHOSPHATES.
1. Of the Biphosphate of Soda.
This Salt admits, as I shall immediately show, of so many changes in
its constitution and properties, as to entitle it to be considered one of
the most interesting of chemical substances. The facts which I have to
communicate on this subject are certainly the most extraordinary of the
paper, and were determined with care and considerable difficulty.
I had an opportunity of noticing the dimorphism of this salt, and
confirmed the observation of Mitscherlich, that both forms of crystals
possess the same chemical properties and the same proportion of water.
Of the four atoms of water which the crystals contain, they lose, I find,
two atoms at the temperature of 212°, and not a particle more till heated
up to about 375°. -
1st. Thus 496 grains of the crystals reduced to powder, when dried
on the water-bath for several days, retained only 0.76 water, or con- .
sisted of
Biphosphate of soda, . e tº e 100
Water, o º tº e º & 18:09
118:09
AND MODIFICATIONS OF PHOSPHORIC ACID. 337
This is as nearly as possible one-half of the entire water in the crystals,
which by the mean of Mitscherlich's experiments consist of
Diphosphate of soda, . g e 100
Water, tº e ſº º º 35.57
135°57
2d. 10.01 grains of the salt dried on the water-bath retained 1-53
water, which is 18:04 water to 100 dry salt, or the same result as in 19.
3d, 50 grains of the crystals lost 6'52 grains on the water-bath; their
entire water being by theory 12.77.
There is every reason to believe that the two atoms of water retained
are essential to the constitution of the biphosphate of soda, and that its
composition is expressed by the following formula,
NaH2P.
It contains three atoms base, namely, one atom soda and two atoms
water, united to a double atom of phosphoric acid. The salt cannot
sustain the loss of any portion of this water without assuming a new
train of properties. There are accordingly three atoms oxygen in the
base (two in the water, and one in the base), and five in the acid.
When crystallized the salt contains, besides, two atoms water of crystal-
lization.
The crystals of biphosphate of potash contain only the two essential
atoms of water, and the lustre of their surfaces is not affected by a
water-bath heat, nor by any degree of heat under 400 Fahr.
A solution of either of these alkaline biphosphates, when added to
nitrate of silver, occasions a copious precipitation of the yellow sub-
phosphate of silver; and if ammonia be cautiously added, so as merely
to make up the excess of nitric acid disengaged, the whole phosphoric
acid falls in that state. It is to be here remarked, that the three atoms
base of the alkaline biphosphate are replaced in this precipitation by
three atoms of oxide of silver.
2. Second variety of Biphosphate of Soda, or Bipyrophosphate of Soda.
When a quantity of the biphosphate of soda, previously dried on the
water-bath, is afterwards gradually heated on a solder-bath, it begins to
lose water at about 375°, and before it is raised to 400° it has lost exactly
half the water which it possessed, or one atom. The dried salt may
thereafter be heated up to 450°, and maintained for an hour or more at
that temperature, without sustaining any further loss. When rapidly
heated in a glass tube, the Salt undergoes semifusion at Some point near
400°, and the same quantity of water comes off in a state of ebullition.
Y
338 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
Af
1st. Thus 2-62 grains of the salt dried on the water-bath, when
heated in a thin glass tube, lost at once 0:2 grain water on attaining
400", which is one-half of the water which it possessed, namely, 0-396
grain; while it was exposed again for four hours to a temperature
between 450° and 470°, without losing 0.01 grain additional.
2d. In one experiment, 1845 grains of the crystallized biphosphate
lost 3.68 grains by 400° Fahr. on the solder-bath. This is 27:04 of the
35-57 parts water, which are united to 100 dry salt in the crystals. The
salt has lost 3:04 atoms of water. -
3d. A quantity of the salt, previously deprived of its two atoms
water of crystallization, was kept for three hours at a temperature rang-
ing between 400° and 460°, 11:19 grains of the salt so dried contained
0-9 water, or consisted of
Biphosphate of soda, tº * 100
Water, & ge tº & 8-72
108-72
The water retained amounts to 0-981 atom, which is a close approxima-
tion to 1 atom.
4th. A quantity of the salt which had been heated to 400° was dis-
solved in water, evaporated to dryness, and exposed again for some days
on a solder-bath at a temperature not exceeding 400°, 13.94 grains of
the salt so dried still retained 1:06 grain water, as was found by fusing.
the salt at a red heat; or it consisted of
Biphosphate of Soda, tº tº 100
Water, tº e * & 8'23
108'23
This is less than one atomic proportion, which is 8.89 parts; but the
temperature at which the Salt loses its entire water is elevated no great
number of degrees above that in which it loses the atom under con-
sideration; and a protracted exposure to the air at 400° occasions the
partial dissipation of the last atomic proportion of water, as in this
experiment.
The heated Salt which retains one atom water, is still very soluble
and possesses an acid reaction, but it is altered essentially in properties.
Added to nitrate of silver, it produces a sparing chalky white, pulveru-
lent precipitate, and a very acid liquor. By the cautious addition of
ammonia so as merely to take up the excess of nitric acid, the entire
phosphoric acid is precipitated in the same state. The precipitate
proved, on analysis, to be the pyrophosphate of silver, containing two
atoms oxide of silver to one double atom phosphoric acid.
AND MODIFICATIONS OF PHOSPHORIC ACID. 339
Of this precipitate, heated to redness but not fused, 1875 grains
dissolved in nitric acid and precipitated by muriatic acid, afforded 17.82
grains chloride of silver, equivalent to 14:41 oxide of silver. The com—
position of this phosphate and of the pyrophosphate of silver, with which
it appears to correspond, is as follows:—
Experiment. Theory.
Oxide of silver, g 76'85 76°49
Phosphoric acid, we 23:15 23:51
100 100
Added to acetate of lead, this altered biphosphate likewise threw
down the pyrophosphate of lead. The acid of this last salt was separated
by sulphuretted hydrogen, and when afterwards neutralized by carbonate
of soda, it afforded crystals of pyrophosphate of soda.
Now this variety of the biphosphate of soda, which may be called the
bipyrophosphate, contains one atom of basic water, and its formula is,
NaHP;
or it contains two atoms base like the salt of silver which it precipitates.
This salt when treated with caustic soda affords the neutral pyrophos-
phate. It also occasions a precipitate in muriate of barytes, in which
respect it differs from the proper biphosphate. I failed in all my
attempts to obtain the bipyrophosphate of Soda in a crystalline form.
It uniformly dried up into the state of a friable white crust.
3. Third variety of the Biphosphate of Soda.
When the salt last described was exposed on the solder-bath for
several days at a temperature between 400° and 470°, it lost weight;
only 3:48 parts out of the entire 35-57 water were retained in one expe-
riment, and 2.81 parts water in another. The whole water was expelled,
with the exception of 0.38 to 100 dry salt, in other experiments in
which the salt was heated on the sand-bath, probably at a temperature
not much under 600°. The salt became in fact very nearly anhydrous.
Now on pouring water upon the salt so dried, the greater part of it dis-
solved at once, but an inconstant quantity remained undissolved, vary-
ing from 6:57 to 18 parts in 100 salt, but increasing with the intensity
of the heat to which the salt had been exposed. This insoluble matter
is a fourth variety of the biphosphate, which shall immediately be
noticed. As this insoluble Salt may be proved to be of the same com-
position as the biphosphate, it follows that the soluble portion is un-
altered in composition.
The insoluble portion appears a heavy dense powder; yet as a part
340 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
of it remains in suspension in the liquid for a long time, it is necessary
to filter to obtain the soluble salt in a state of purity.
The preceding two varieties of biphosphate of soda have a distinct
acid reaction, but the solution of this salt is exactly neutral, as was
determined by very careful experiments. This property is the best
distinctive character of this variety that I can mention. When a solu-
tion of the salt is concentrated, it does not deposit any of the insoluble
variety, but allows rings of dry salt to form round the margin of the
fluid, which are soluble. I have not succeeded in crystallizing it in the
vacuum of an air-pump, or by other means which were employed. The
salt always dried up into a friable white crust, which on one occasion,
when dried at 212°, contained 11:56 parts water to 100 anhydrous salt.
This salt occasions a precipitate in muriate of barytes like the preceding.
With nitrate of silver it gives a considerable white pulverulent precipi-
tate, and the liquid becomes strongly acid. 8:38 grains of this precipi-
tate dried and heated to redness without fusing, were found to consist
of 6:58 oxide of silver and 1.8 phosphoric acid, or 77.32 oxide of silver
and 22.68 phosphoric acid=100; while the neutral pyrophosphate of
silver, containing two atoms oxide of silver, consists of 76°49 oxide of
silver, and 23:51 phosphoric acid. The correspondence is sufficiently
close to prove that our silver precipitate is the same neutral phosphate
which presents itself when the second variety of biphosphate of soda is
precipitated in the same manner. Like that variety, also, this form of
the biphosphate afforded crystals of the pyrophosphate of soda when
treated with caustic soda. &
In regard to the exact constitution of this variety I entertain con-
siderable doubt. We are warranted to presume that the biphosphate of
soda can exist in an anhydrous condition soluble in water, and neutral
in its reaction on litmus. The formula of the salt may be,
NaP.
It must, however, be allowed that no confirmation of this view of the
constitution of the Salt can be drawn from the composition of the silver
precipitate. But the precipitate that should fall by theory, is the
biphosphate of silver. Now no such salt exists, the biphosphate of
silver described by Berzelius containing the new modification of phos-
phoric acid.
4. Fourth or insoluble variety of Biphosphate of Soda.
When any of the preceding varieties of the biphosphate of soda is
heated for a few minutes at a temperature approaching but not amounting
to low redness, it becomes anhydrous, if not so before, and the whole of
AND MODIFICATIONS OF PHOSPHORIC ACID. 341
it becomes insoluble in water. We are apt to overheat the salt in a
crucible if a lamp be employed. I found it the most convenient process
to introduce a quantity of the crystallized biphosphate into a platinum
crucible, to place this in sand contained in a Hessian crucible, and to
place the whole in a situation in an open fire where it would not be
heated with rapidity. The time was watched when the sand was red
hot to within a small space of the platinum crucible, and the whole then
withdrawn from the fire. The appearance of the heated Salt depends
entirely upon circumstances. If the heat be applied rapidly, the salt
undergoes fusion on losing its two essential atoms of water, and is
found of a slaggy appearance and hard. But if the heat be applied in
a gradual manner, the water escapes without any fusion, the powder
merely shrinks and aggregates slightly together. In both states the
resulting salt is the same. It may be reduced with ease to the most
impalpable powder, and in this condition is very slowly acted upon by
continued digestion in a large quantity of boiling water. When it does
dissolve, it appears to pass into the preceding variety. But it may be
inferred analogically, that if a more intense heat could be applied to
the salt under consideration without inducing another change (to be
described) the salt would be rendered perfectly insoluble. The biphos-
phate of potash affords this analogy.
This last salt contains only the two essential atoms of water. When
heated above 400°, it begins to undergo a semifusion, although the heat
has been applied in a gradual manner; and becomes partially insoluble,
without exhibiting the changes which precede this in the biphosphate
of soda. A still higher temperature, approaching a red heat, renders the
biphosphate of potash as insoluble as the biphosphate of Soda. But the
biphosphate of potash may be fused in a platinum crucible and heated
to whiteness without undergoing any further change of state; and after
being thus strongly heated, it may be reduced to powder and digested
in boiling water for hours without dissolving to such an extent as
to afford a solution capable of affecting nitrate of silver in a sensible
manner. It may be inferred, therefore, that if the biphosphate of soda
could be sufficiently heated, water would be wholly incapable of acting
upon it. Dilute acids have no action upon this insoluble variety of
biphosphate of soda; but alkalies by long digestion withdraw a portion
of the phosphoric acid. So far as we can judge, the acid appears not to
be in a modified or altered condition.
5. Fifth variety of Biphosphate of Soda, or Metaphosphate of Soda.
When the preceding insoluble variety, or the biphosphate in any
condition, is heated in a platinum crucible to low redness, it undergoes
342 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
fusion, and on cooling presents itself as a transparent glass, which deli-
quesces in a damp atmosphere and is highly soluble in water. But the
fused salt has undergone a most extraordinary and permanent change
of properties. The solution has a very feeble acid reaction when
compared with crystallized biphosphate. Indeed, the addition of 43
anhydrous carbonate of soda to one hundred fused biphosphate of soda
imparted to the latter a distinct alkaline reaction. When this salt is
added to nitrate of silver, the phosphoric acid is nearly entirely thrown
down in gelatinous flakes, which aggregate together as a soft Solid when
heated near 212°, and correspond in composition with the Soda salt.
This silver precipitate loses acid when washed. It agrees in properties
with the biphosphate of silver described by Berzelius, which, when
washed, appeared to pass into a sesquiphosphate. He formed it by
adding phosphoric acid to nitrate of silver, but the phosphoric acid
employed by him must have been the glacial acid recently dissolved."
When the fused biphosphate of soda is added to muriate of barytes,
nearly the whole of the phosphoric acid precipitates with the barytes as
a flaky gelatinous precipitate, which contains only one atom barytes to
the double atom phosphoric acid, like the soda salt. But all the new
properties of this salt depend upon the acid having undergone an essen-
tial change in constitution. The acid may be separated in the usual
way, namely, precipitating by acetate of lead, Washing the phosphate
of lead and decomposing it by a stream of sulphuretted hydrogen gas.
After exposure for some hours to allow the escape of the Sulphuretted
hydrogen, the acid liquid, without being neutralized, uniformly pro-
duced an opal-white flaky precipitate in muriate of barytes, which
appeared immediately, unless the liquors were very dilute. This is also
a character, I find, of phosphoric acid recently ignited per se. The acid
of our salt possesses also the property of coagulating albumen. In fact,
this acid appears to be the glacial phosphoric acid, which had been
hastily assumed by recent writers upon this subject to be the pyrophos-
phoric acid, but is totally different. I shall take the liberty to designate
provisionally the acid of the fused biphosphate of soda, the Metaphos-
phoric acid, from an hypothesis of its constitution to be immediately
explained; and the fused salt itself, the Metaphosphate of soda.
The metaphosphate of soda is insoluble in alcohol. Its solution in
water is not altered by time; at least no change could be perceived in
a solution which had been kept for several months. When exposed to
a temperature not exceeding 100 Fahr, the solution becomes viscid as
it concentrates, and finally dries into a transparent brittle pellicle like
gum, . All my attempts to crystallize this salt by slow evaporation in
the atmosphere, or by means of the air-pump, have failed. It never
* Annales de Chimie et de Physique, tom. xlvi. p. 143.
AND MODIFICATIONS OF PEIOSPEIORIC ACID. 343
presented the slightest trace of crystallization. But many of the inso-
luble metaphosphates fall down in the state of hydrates, which have the
fluid form; which may also be the form that the soda salt is disposed
to assume.
The hydrated metaphosphate of soda dried over sulphuric acid in
the vacuum of an air-pump, at the ordinary temperature of the atmo-
sphere, was found to consist of
Metaphosphate of soda, . © tº 100
Water, * & º § g 10-86,
by an experiment in which 11:64 grains of the hydrated salt lost 1:14
by fusion at a red heat. This is 1:22 atomic proportion of water.
When heated to 400°, the hydrated salt appears to retain 1 atom of
water, and to pass into the bipyrophosphate of soda. 13.94 grains dried
on the solder-bath at 400° for several days, retained 1:06 water; or the
Salt consisted of
Biphosphate of soda, g tº ſº 100
Water, ſº tº e & © 8'23
108.23
This is less than one proportion of water (8-89); but the additional loss
of water which the salt sustained is accounted for by the length of time
that it was exposed to the heat, which had the effect of converting a
Small portion of it into the insoluble and anhydrous variety. The dried
salt when dissolved in water gave with nitrate of silver a chalky, white,
heavy precipitate, which evidently was not the usual metaphosphate of
silver. A portion of the salt was therefore precipitated by acetate of
lead, and the acid liberated in the usual manner. The acid did not
disturb albumen, nor precipitate muriate of barytes; but when neutra-
lized with caustic soda it gave excellent crystals of the pyrophosphate
of soda. There can be no doubt, therefore, that the metaphosphoric acid
has returned to the condition of pyrophosphoric acid. The question
arises, Is this transition the consequence of merely exposing the meta-
phosphate of soda to a particular temperature (400), or does the water
interfere and the transition arise from the affinity of phosphoric acid for
water, as a base, with soda. ? Now, upon trial, the anhydrous fused
metaphosphate of soda, as it is first formed, was found to undergo no
alteration when kept for several days between 400° and 600°. The
change is therefore peculiar to the hydrated salt, and effected by the
interference of the water. -
A solution of the metaphosphate of Soda may be treated with caustic
soda, and even boiled with it, without any change in the nature of the
344 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
acid; at least, the saline solution still precipitates silver white, and the
acid when separated coagulates albumen. The solution may even be
evaporated gently to dryness, without a change of acid; but if dried by
a sharp sand-bath heat, and if the alkali be present in sufficient quantity,
the common subphosphate of soda is formed.
The metaphosphate of soda forms a series of insoluble metaphos-
phates when added to solutions of the earthy and metallic Salts.
Metaphosphate of Barytes.
The metaphosphate of barytes has already been alluded to. As this
Salt is soluble in an excess of the metaphosphate of soda, it is best pre-
pared by adding that Salt to muriate of barytes in excess. There is an
abundant, white, flaky precipitate, and the mother-liquor remains acid.
This precipitate washed and dried at 600°Fahr, formed brittle masses;
these masses heated to redness give off water and undergo an imperfect
fusion. 1186 grains of the ignited salt were dissolved with considerable
difficulty by pure nitric acid, and then precipitated by sulphate of soda.
The sulphate of barytes amounted to 9-69 grains, which is equivalent to
6:36 grains barytes. The composition of this metaphosphate, and of a
biphosphate of barytes, is as follows:
Metaphosphate of Barytes. Biphosphate of Barytes.
Barytes, . & g 53-62 . . . . . 51-75
Phosphoric acid, . © 46'38 . . . . . 48.25
100° 100°
Our salt is therefore 187 per cent. deficient in phosphoric acid. I
thought that muriate of barytes had perhaps been carried down by the
precipitate, but on examining a portion I found it free of muriatic acid.
But another quantity of the metaphosphate of barytes was prepared,
with the precaution of having a more decided excess of muriate of
barytes, and the liquors less dilute. 6.61 grains of the ignited salt
yielded 5.24 grains sulphate of barytes, which is equivalent to 3:44
grains barytes. This specimen therefore consisted of
Barytes, g § ſº g 52'04
Metaphosphoric acid, & ſº 47-96
100°
which will be found on comparison to correspond very closely with the
biphosphate of barytes.
The metaphosphates in general precipitate with considerable diffi-
culty from very dilute solutions, although when once precipitated they
AND MODIFICATIONS OF PHOSPHORIC ACID. 345
are highly insoluble. The last washings of the metaphosphate of barytes,
hot water being employed, contained no sensible trace of barytes, for
they had no effect upon a sulphate. Hence the metaphosphate of
barytes is an insoluble salt.
The metaphosphate of barytes may be boiled in water for two hours
without sensible change; but it then begins to dissolve, and the solution
proceeds at an accelerated rate, till eventually the whole disappears.
The resulting solution is strongly acid, and certainly contains biphos-
phate of barytes, for it precipitates silver yellow. We have here, there-
fore, an instance of an insoluble metaphosphate passing into a soluble
phosphate.
Metaphosphate of Lime.
On adding metaphosphate of soda to muriate of lime in excess, a
precipitate appears like what occurs on throwing into water a solution
of an essential oil in alcohol. A transparent semi-fluid body of the
consistency of pitch collects at the bottom, which is a hydrate of the
metaphosphate of lime in the liquid form, but insoluble in water. This
salt appears to have occurred to Berzelius, and is described in his paper
on the phosphates." He formed it by precipitating muriate of lime by
metaphosphoric acid, but did not observe the circumstances necessary
to insure the success of the process.
IV. OF THE MODIFICATIONS OF PHOSPHORIC ACID.
The distinctive character of phosphoric acid which exists in common
phosphate of soda, as compared with the other modifications, is a dispo-
sition to form salts which contain three atoms of base to the double atom
of acid. Of these salts the most remarkable is the yellow subphosphate
of silver, which the soluble phosphates precipitate when added to nitrate
of silver. This acid does not affect albumen; and the other modifi-
cations pass directly into the condition of this acid on keeping their
aqueous solutions for some days, and more rapidly on boiling these
solutions; or upon fusing the other modifications or their salts with at
least three proportions of fixed base.
Pyrophosphoric acid, or the acid which exists in the fused phosphate
of soda, is remarkably disposed to form salts having two atoms base,
which is the constitution of the white pyrophosphate of silver, formed
on testing the pyrophosphate of soda with a salt of silver. Such salts of
the preceding acid as contain no more than two atoms of fixed base,
pass into pyrophosphates when heated to redness. The acid under con-
* Annales de Chimie et de Physique, tom. ii. p. 172,
346 RESEARCHES ON THE ARSENIATES, PHOSPHATES,
sideration, when free, does not disturb albumen, nor produce a precipitate
in muriate of barytes.
The metaphosphoric acid is disposed to form salts which contain one
atom of base to the double atom of acid. The other modifications pass
into metaphosphoric acid when heated to redness per se, or when heated
to redness in contact with no more than one atomic proportion of certain
fixed bases, such as soda. This acid, when free, occasions precipitates
in solutions of the salts of barytes and of most of the other earths and
metallic oxides, and forms an insoluble compound with albumen. The
glacial or metaphosphoric acid appears to be capable of dissolving in
general only about four-fifths of the quantity of carbonate of soda which
it can decompose when converted into phosphoric acid. But a large
quantity of the meta-acid passes into phosphoric acid on uniting with
the alkali, and the solution deposits phosphate of soda in tufts composed
of fine crystalline plates of a silky lustre. The salt presented itself of
this appearance, it will be remembered, in the case of a solution of
phosphate of soda which had been boiled for a long time in a glass vessel.
The liquid about the crystals, in the present case, still contained meta-
phosphoric acid.
Now it is a matter of certainty that if we take one combining propor-
tion of any modification of phosphoric acid, and fuse it with soda or its
carbonate, we shall form a metaphosphate, a pyrophosphate, or a phos-
phate, according as we employ one, two, or three proportions of base.
The acid when separated from the base will possess, and retain for some
time, the characters of its peculiar modification. It would appear, there-
fore, that the acid is impressed with a disposition to form different classes
of salts by the proportion of base to which it has been united, and that
it retains this disposition even when liberated from the original com—
pound. But I suspect that the modifications of phosphoric acid, when
in what we would call a free state, are still in combination with their
usual proportion of base, and that that base is water. Thus the three
modifications of phosphoric acid may be composed as follows:
Phosphoric acid, . . . HºP
Pyrophosphoric acid, . e º Hºf
Metaphosphoric acid . º . Hiſ ;
or they are respectively a terphosphate, a biphosphate, and phosphate
of water. Now, when one of these compounds is treated with a strong
base, the whole or a part of the water is supplanted, but the amount of base
in combination with the acid remains unaltered. There are thus three
sets of phosphates, in which the oxygen in the acid being five, the
AND MODIFICATIONS OF PHOSPHORIC ACID. 347
oxygen in the base is three, two, and one. The constitution of the acids
and of the salts of soda which they form, is exhibited in the following
Table :
Oxygen in
Soda. Water. Acid.
Phosphoric acid,
O 3 5
g Biphosphate of soda, I 2 5
First Class. i. of soda, 2 1 5
Subphosphate of soda, 3 0 5
Pyrophosphoric acid, () 2 5
Second Class. & Bipyrophosphate of Soda, . 1 1 5
Pyrophosphate of soda, 2 O 5
/n7, ” Metaphosphoric acid, 0 1 5
Third Class. jº of soda, 1 0 5
The hypothetic composition of the acid hydrates may also be stated
as follows:
Acid. Water.
Phosphoric acid, . . . 100 37.81 = 3 atoms.
Pyrophosphoric acid, . . 100 25-21 = 2 ,
Metaphosphoric acid, . . 100 12°61 = 1 atom.
By a heat of 300° a dilute solution of phosphoric acid in a platinum
crucible concentrates readily till the water is reduced to the proportion
of three atoms, at which stage the acid assumes a dark colour, and is of
the consistence of treacle when cold, but much more fluid when hot.
In this condition the acid gives an unmixed yellow precipitate with
silver, and is entirely phosphoric acid. By exposure for seven days over
sulphuric acid in the vacuum of an air-pump, the water was reduced to
435 parts, and almost the whole of the acid had crystallized in thin
plates, which were deliquescent in the extreme, and which there is every
reason to believe were the terhydrate. By a protracted exposure to 300°
or 320°, the acid continues to lose water, but much more slowly. At
460° the water was quickly reduced to 344 parts, or little more that 23
atoms, in an experiment conducted in an open crucible, and the acid now
precipitated silver white with a trace of yellow; but when neutralized
by carbonate of soda, it afforded crystalline plates of phosphate of soda,
among which no crystals of pyrophosphate existed. But it may be
deemed possible from this result that a hydrate of phosphoric acid exists,
containing 23 atoms water to 1 atom acid, which is 8 atoms base to 3
atoms acid, the proportion of base to acid in the salt termed by Berzelius,
the phosphate of lime of bones. In another case in which the evapora-
tion was conducted much more slowly in a platinum flask, the above
compound was certainly not formed; but the evaporation at 415°, after
348 RESEARCHES ON THE ARSENIATES, PHOSPHATES, ETC.
advancing for several days, seemed to cease entirely when the water was
reduced to 29.9 parts, which is very nearly 2% atoms of water. Acid at
this degree of concentration, neutralized as usual by ammonia, gave,
with silver, a chalky white precipitate without a shade of yellow, which
suggests the idea that an acid hydrate of 24 water may exist, having a
corresponding silver salt. Acid, so far concentrated, when neutralized
by carbonate of soda, afforded a mixture of crystals of phosphate and
pyrophosphate of soda, in which the latter predominated. For the pro-
duction of metaphosphoric acid, the concentration of a much higher
temperature was requisite; but this acid was observed to appear before
the proportion of water had fallen under 2 atoms, namely, when it
amounted to 28.05 per cent. in one experiment. By the greatest heat
of the sand-bath, which was considerably above the melting point of
lead, the proportion of water was reduced a little under 2 atoms, namely,
to 22.99 parts; and the acid then contained abundance of metaphosphoric
acid, as evinced by its power to coagulate albumen. In the glacial phos-
phoric acid, Dulong found 100 acid united with 20.6 water, and Rose
100 acid with only 10:42 water. The latter determination falls short of
1 atom water, and would indicate that phosphoric acid may be rendered
partially anhydrous by heat. I do not enter upon the details of my
experiments on the hydrates of phosphoric acid, as the subject is diffi-
cult, and requires a much more minute investigation than I have as yet
had it in my power to give it.
Although of opinion that there is only one phosphoric acid, and that
the modifications are entirely due to the quantity of water combined
with the acid, I have still retained the names which have come into use,
and even proposed a third, metaphosphoric acid, implying merely that
the acid to which this name is applied is phosphoric acid with Some–
thing else, namely, with an atom of water. As the classes of Salts
which the acid hydrates form are quite distinct, these trivial names are
practically convenient, and may be adopted provisionally till chemists
are prepared, by an extended knowledge of the Salts, to innovate upon
their nomenclature with more advantage than can be done at present.
I may be allowed to state, before concluding, that the binarseniate of
soda does not appear to undergo the same remarkable changes as the
biphosphate; at least, after being exposed to heat of various degrees of
intensity, it continued to give the usual brown subarseniate, with nitrate
of silver. But arsenic acid exhibits a weaker affinity for water than
phosphoric acid, and is readily made anhydrous by heat,
ON HYDRATED SALTS AND METALLIC PEROXIDES. 349
IV.
ON HYDRATED SALTS AND METALLIC PEROXIDES; WITH
OBSERVATIONS ON THE DOCTRINE OF ISOMERISM.
From Brit. Assoc. Report, 1834, pp. 579–582. [Liebig, Annal. xii. 1834, pp. 1-12;
Poggend. Annal. xxxii. 1834, pp. 33-75.]
VARIOUS classes of salts, besides the arseniates and phosphates, con-
tain water, which is essential to their constitution: of this the sulphates
of magnesia, and the protoxides of zinc, manganese, iron, nickel, copper,
and cobalt, are examples.
These salts crystallize from their aqueous solutions, either with seven
or five atoms of water, one of which is in a state of much more intimate
union than the other six or four. Thus, crystallized sulphate of zinc
loses six atoms of water, at a temperature not exceeding 65°, when
placed over sulphuric acid in vacuo, but retains one atom of water at 410°
and all inferior temperatures. This salt may be viewed as a sulphate
of oxide of zinc and water, with six atoms of water of crystallization; a
constitution which may be expressed as follows, HZnS + 6H. This
sulphate may be made anhydrous, but when moistened always regains
one atom of water, slaking with the evolution of heat. This last atom
of water appears to discharge a basic function in the constitution of the
salt, and affords a clew to the disposition of this sulphate to form double
sulphates. Sulphate of zinc combines with sulphate of potash, and forms
a well-known double salt, in which the basic water of the sulphate of
zinc is replaced by sulphate of potash, without any further change. The
formula of the double sulphate is (KS)ZnS + 6H. In the double salt,
the whole six atoms of water are retained with somewhat greater force
than in the simple sulphate; but even the double sulphate becomes
anhydrous below 212° in vacuo.
The sulphates of the other metallic oxides mentioned are quite
analogous to sulphate of zinc in their habitudes with water, although
the particular temperature at which they part with their water of crys-
tallization is different in each. The analogy holds also in the double
sulphates of those oxides.
Of hydrous sulphate of lime, or gypsum, the two atoms of water
which it contains appear to be essential, and are retained at 212°. At
a temperature not exceeding 270°, this salt becomes anhydrous, but
retains the power of recombining with two atoms of water, or setting.
The salt is then in a peculiar condition. It is the débris of the hydrate,
350 ON HYDRATED SALTS AND METALLIC PEROXIDES.
and not a neat chemical compound. Heated above 300° the salt becomes
properly sulphate of lime, and has lost the disposition to combine with
Water.
The protochlorides, and corresponding cyanides of zinc, manganese,
iron, etc., are disposed to combine with two atoms of water. Hence the
cyanide of iron combines with two atoms of cyanide of potassium, to form
the double cyanide of iron and potassium, commonly called the ferro-
prussiate of potash. -
Berzelius found the peroxide of tin formed by the action of nitric
acid on metallic tin, to differ in certain properties from the same com-
pound precipitated from a persalt of tin by an alkali, and distinguished
the first under the name of the nitric acid peroxide of tin. Both per-
oxides combine with muriatic acid, but the muriate of the nitric acid
peroxide is peculiar in being insoluble in water strongly acidulated with
muriatic acid. But the precipitated peroxide of tin assumes, I find,
all the properties of the other modification, when kept for some time
exposed to the heat of boiling water, or even when strongly dried over
sulphuric acid in vacuo, at the ordinary temperature of the atmosphere.
The two modifications are merely different hydrates of the peroxide of
tin, but it is difficult to ascertain what proportion of water is essential
to each. The hydrates combine with acids, and form two sets of com-
pounds; but absolute peroxide of tin itself (which is obtained by heat-
ing the hydrated peroxide to redness), has no disposition to combine
with acids. The same is true of many other metallic peroxides; they
combine as hydrates only with acids. There are at least two hydrates
of peroxide of iron; the muriate of that which contains least water is
red in solution, and the muriate of the other, yellow; but these muriates
pass readily into each other. Mr. R. Phillips observed of the red
muriate, that it is precipitated by an access of acid, which, it may be
remarked, establishes an analogy between it and the muriate of the
nitric acid peroxide of tin, which possesses the same property.
Metallic peroxides can in general be obtained by the application of
a moderate heat to their hydrates, in a state in which they are the
débris of hydrates, and not neat chemical compounds. Upon heating
peroxides in this condition to redness, they generally glow or become
spontaneously incandescent at a particular temperature (a phaenomenon
to which the attention of chemists has been particularly directed by
Berzelius), and lose their solubility in acids at the same time. Till they
have undergone this change, they are not absolute or proper peroxides.
Various salts, such as phosphates, antimoniates, etc., exhibit the same
phaenomenon when heated; but they all had possessed water, which is
essential to their first constitution, but not to their second.
The doctrine of isomerism, or that two bodies may exist of the same
ON HYDRATED SALTS AND METALLIC PEROXIDES. 351
composition, but differing in properties, has been proposed by Berzelius
as a sequence from such facts as the preceding. But the propriety of
the inference may be doubted. Most, if not all, cases of apparent
isomerism may be explained by reference to one or other of the following
facts:— *.
1. Water is essential to the constitution of many bodies. Thus,
what have been called metaphosphoric acid, pyrophosphoric acid, and,
common phosphoric acid, are three different phosphates of water, or
compounds of one absolute phosphoric acid with three different propor-
tions of water.
2. A particular condition of bodies must be recognised, in which they
are the débris of some compound, and not proper chemical compounds
of their constituents. Thus, on heating a certain borate of water and
magnesia to redness, water only is expelled; but what remains is not a
simple borate of magnesia, but a mixture of boracic acid and magnesia,
from which the former may be dissolved out by water. Stucco in a
state for setting is in this particular condition. But this is a depart-
ment of corpuscular philosophy which stands much in want of further
development.
3. The proximate constitution of many bodies may be widely dif-
ferent, of which the ultimate composition is the same. Thus the cyanic
acid of Wöhler is undoubtedly an oxide of cyanogen, but we have no
evidence that cyanogen exists in fulminic acid, which consists of the
same proportions of carbon, nitrogen, and oxygen as cyanic acid. It is
wrong, therefore, to speak of the fulminic as a second cyanic acid, and
useless to couple them together as isomeric bodies. Tartaric and
racemic acids are of the same ultimate composition, but they certainly
contain different radicals, and probably have as little natural relation to
each other as any two vegetable acids which could be named. Why,
then, associate them as isomeric bodies, and call them the tartaric and
paratartaric acids 2
4. A minute trace of adventitious matter may sometimes affect the
properties of a chemical body to a surprising degree.
Professor Rose, of Berlin, has shown that the two kinds of phos-
phuretted hydrogen, one of which is spontaneously inflammable in air,
and the other not so, are of the same composition and specific gravity.
To account for their possessing different properties, recourse is had to
the doctrine of isomerism. But my observations indicate the existence
of a peculiar principle in the spontaneously inflammable species, which
principle may be withdrawn, and leaves the gas not spontaneously
inflammable. Phosphuretted hydrogen gas, which is not spontaneously
inflammable in air, may be made So, by the addition to it of one ten-
thousandth part of its volume of nitrous acid vapour. There are grounds
352 ON WATER AS A CONSTITUENT OF SALTS.
for supposing that the peculiar principle of the ordinary gas is a volatile
oxide of phosphorus analogous to nitrous acid, and that it is present in
a minute, almost infinitesimal, proportion. Subsequently to the meet-
ing of the Association, an account of the author's researches on phos-
phuretted hydrogen has been published in the number for December
1834, of the London and Edinburgh Journal of Science.
V.
ON WATER AS A CONSTITUENT OF SALTS.
From Edin. Roy. Soc. Trans. xiii. 1836, pp. 297-314. [Phil. Mag. vi. 1835, pp.
327-334, 417-424; Annal. de Chimie, lxiii. 1836, pp. 45-64; Edrm. Journ. Prak.
Chem. v. 1835, pp. 90-109; xv. 1838, pp. 437-439; Liebig, Annal. xx. 1836,
pp. 141-149 ; Poggend. Annal. xxxviii. 1836, pp. 123-142.]
IT may be useful to distinguish some of the functions which water
is already admitted to discharge in the constitution of hydrated salts.
Every amphigene ammoniacal Salt contains an atom of water, and
cannot exist without it. The state of combination of the water is
peculiar, and has been represented by supposing that the elements of
ammonia unite with the hydrogen of the water, and form a new com-
pound radicle, to which the name Ammonium is given, while the
oxygen of the water unites with this radicle, and produces oxide of
ammonium. Hence nitrate of ammonia, in which there exist the
elements of one atom of nitric acid, of ammonia, and of water, is viewed
as anhydrous nitrate of the oxide of ammonium, and corresponds with
nitre or the nitrate of the oxide of potassium. But it is not the
object of this paper to discuss particularly the state of water in the
ammoniacal Salts.
We have it often in the crystals of salts, united by a feeble affinity,
and known under the name of water of crystallization. The number
of atoms of water with which some salts unite, in crystallizing from a
state of solution, is affected by temperature, and other slight causes.
This water is commonly viewed as a constituent of salts which is not
essential, owing to the facility with which it may in general be expelled
by heat, and also to the circumstance that many salts usually hydrated
are likewise capable of existing in a crystalline state without water.
In the hydrates of the caustic alkalies and of the earths, water is
retained by a strong affinity, and is generally supposed to be united,
like an acid, to the alkali or earth. In such hydrates, water discharges
an acid function.
ON WATER AS A CONSTITUENT OF SALTS. 353
In the case of hydrates of the acids, the portion of water which is
found to be inseparable by heat, or to be very strongly retained, has
generally been presumed to be in the place of a base to the acid,
although little attention has been paid to the subject. The most highly
concentrated sulphuric acid retains one atom of water, and is supposed
to be a sulphate of water. In the case, too, of such a superSalt as
bisulphate of potash or bitartrate of potash, the single atom of water
which is known to be persistently attached to the salt, has been viewed
of late, by our most enlightened chemical theorists, as essential to its
constitution, and the possibility admitted that such salts may really be
double salts; the bisulphate of potash, a sulphate of potash combined
with sulphate of water, and the bitartrate of potash, a tartrate of potash
combined with tartrate of water.
In a late publication, I have developed this view of water acting as
a base in the case of phosphoric acid. That acid is capable of combining
with water in three different proportions; and the number of atoms of
water with which the acid combines at any time depends upon circum-
stances which are understood. That the water is basic in these dif-
ferent hydrates, follows from the fact that, on treating them with an
alkali, the water is constantly replaced by a quantity of alkali chemi-
cally equivalent to the water. By nitrate of silver, the same precipi-
tate is thrown down from any phosphate of soda and from the corre-
sponding phosphate of water; the composition of the precipitate being
determined in both cases by the same double decomposition. The peculi-
arity of phosphoric acid is, that it is capable of uniting with water as a
base, in several proportions, while all other acids combine with water as
a base in one proportion only, so far as is yet known. By these dis-
coveries in regard to phosphoric acid and its salts, the ordinary concep-
tions entertained of the constitution of salts were completely deranged.
The salts called biphosphate of soda, phosphate of soda, and subphos-
phate of Soda, are all tribasic salts. The common idea of a SuperSalt is
inapplicable to any of them.
I have subsequently found water to exist in a different state in
certain Salts, not possessed of a true basic function, being replaceable
by a salt, and not by an alkaline base. To illustrate this new function
of water as a constituent of salts is my principal object in the present
communication.
The tendency of phosphate of soda to unite with an additional dose
of soda, and form a subsalt, I had traced to the existence of basic water
in the former. The inquiry suggested itself, is there any analogous pro-
vision in the constitution of such salts as have a tendency to combine
with other salts, and to form double salts 2 The salts which combine
together most readily are the sulphates, and to these I therefore turned.
Z
3.54 ON WATER AS A CONSTITUENT OF SALTS.
The result was, that in that well-known class of sulphates, consisting
of sulphates of magnesia, zinc, iron, manganese, copper, nickel, and
cobalt, all of which crystallize with either five or seven atoms of water,
one atom proved to be much more strongly united to the salt than the
other four or six, which last generally may be expelled by a heat under
the boiling point of water, while the remaining atom uniformly requires
a heat above 400° Fahrenheit for its expulsion, and seems to be in a
manner essential to the salt. The constitution of crystallized sulphate
of zinc, for instance, may be expressed thus:
ZnSH + H%. -
We here divide the seven atoms of water into one atom, which is
essential to the constitution of the salt as we know it, and six atoms
which are not so ; and to this last quantity we may restrict the appli-
cation of the name “water of crystallization.” Now, in the double
sulphate of zinc and potash, the single atom of water in question per-
taining to the sulphate of zinc is replaced by an atom of sulphate of
potash, and the six atoms of water of crystallization remain. Sulphate
of magnesia combines with sulphate of potash after the same manner,
and so do all the other salts of the class. The constitution of the
crystallized sulphate of zinc and potash, which may be taken as the
type of this family of double salts, is therefore represented by the fol-
lowing formula,
ZnS(KS)+H";
which differs only from the previous formula in having the sign of sul-
phate of potash (KS) substituted for the sign (H) of the essential atom
of water.
From a contemporaneous examination of the Supersulphates, the
conclusion proved to be inevitable, that they also are double salts;
that the bisulphate of potash, for instance, is a sulphate of water and
potash, and that its formula is as follows,
HS(KS),
with or without water of crystallization in addition. There is likewise
a provision in the constitution of hydrated sulphuric acid for the pro-
duction of such a double salt, as in the case of the sulphate of zinc.
Hydrated Sulphuric acid of specific gravity 1-78 contains two atoms of
water, and is capable of crystallizing at a temperature so high as 40°
Fahrenheit. It is the only known crystallizable hydrate of sulphuric
acid. It may be representated by the formula,
HSH,
ZnSH,
ON WATER AS A CONSTITUENT OF SALTS. 355
which may be compared with that of sulphate of zinc placed below it.
This second atom of water present in hydrated sulphuric acid is re-
placeable by sulphate of potash, a salt; and the bisulphate of potash
results from the substitution. But the first atom of water in the acid
hydrate can be replaced only by an alkali or true base. The function
of the first atom is basic, but a new term is required to distinguish the
function of the second atom of water, or of the essential atom of water
in the sulphate of zinc. The application of the epithet Saline to that
atom of water, may, perhaps, be permitted, to indicate that it stands in
the place of a salt. The hydrate of sulphuric acid in question contains,
therefore, an atom of basic, and an atom of Saline water. It is “a sul-
phate of water with Saline water,” as the hydrous sulphate of zinc is
“a sulphate of zinc with saline water.” The bisulphate of potash also
is “a sulphate of water with sulphate of potash,” and corresponds with
the Sulphate of zinc and potash; which last is “a sulphate of zinc with
sulphate of potash.”
A reason could now be given why there exist no supersulphates (or
indeed any superSalts) of magnesia, zinc, etc. A bisulphate of mag-
nesia would be a compound of sulphate of water with sulphate of mag-
nesia, on our view of SuperSulphates. Now sulphate of magnesia, and
Sulphate of water, are bodies of analogous constitution, or of the same
Category, and should have as little disposition to combine together, as
sulphate of zinc and sulphate of magnesia have.
1. Sulphate of Water with Saline Water: HŠH.
Sulphuric Acid of sp. gr. 1:78.
It appears, then, that in an exposition of the relations of the sul-
phates, we may set out from this body as our primary Sulphate. Of the
two atoms of water which it contains, that atom which is basic cannot
be separated from the acid, unless by the agency of a stronger base.
The second, or saline atom of water, may be separated by heat, but not
by any degree of heat, under 400 Fahrenheit, and is re-absorbed with
great avidity.
A diluted sulphuric acid may, I find, be concentrated at a tempera-
ture not exceeding 380°, without the loss of a particle of acid; and the
quantity of water retained is reduced to two atoms most precisely.
This in fact is an exact method of obtaining the definite sulphate of
water with saline water; which may be kept at 380° or 390°, without
sustaining any further loss. I have observed a close approximation to
the same proportion of water, even in the case of a dilute acid concen-
trated at a temperature not exceeding 300°. But at 400° or 410°, this
356 ON WATER AS A CONSTITUENT OF SALTS.
hydrate begins to be decomposed, and a portion of it is apt to distil
over with the water expelled. When, however, this hydrate is distilled
ºn vacuo, at the last-mentioned temperature, it loses nothing but water
for some time.
In one experiment, a small quantity of dilute sulphuric acid was
found to concentrate down to three atoms of water, at a temperature
not exceeding 212°, at which it was sustained in vacuo for not less than
forty hours. It consisted of 100 parts dry acid united with 68.07 water,
while three atomic proportions of water are 67.32 parts.
The concentrated acid of commerce, which is a definite sulphate of
water, without the saline atom, does not freeze at a temperature so low
as –36°, according to Dr. Thomson. To sulphuric acid of sp. gr. 178,
I added water in the proportion of two, four, and six atoms; but all
these hydrates remained fluid, when kept for a short time at 0°Fahren-
heit. Anhydrous sulphate of magnesia or zinc never dissolves, as such,
in water; or exhibits any determinate chemical character. It must
always combine with its saline atom of water in the first instance, or
with something equivalent, and it is the compound which is soluble,
etc. So it is with the sulphate of water, or concentrated sulphuric acid
(HS). In chemical character it is an incomplete body. There is a hiatus
in its constitution, which must be filled up. When it dissolves in any
menstruum, we may be sure that it has first acquired its second or Saline
atom of water, or something in its place. Hence a set of reactions of
sulphuric acid, which are peculiar to its concentrated condition, upon
alcohol and many organic bodies. But to this peculiar state of bodies
I shall again have occasion to allude under sulphate of lime, a body
which illustrates it more strikingly than the sulphate of water.
Sulphate of Water with Sulphate of Potash : HŠ(KS),
Bisulphate of Potash.
Of all the Sulphates, the acid sulphates or bisulphates of potash and
soda deviate least from the primary sulphate of water. We have, in
the one case, merely sulphate of potash; and, in the other, sulphate of
soda, substituted for the saline atom of water of the sulphate of water.
In none of the Specimens of these salts which I had occasion to examine,
was there any water of crystallization, and the evidence which is given
of its occasional presence is of a very doubtful description. The crystals
could be heated to 300°, without impairing their transparency; and
they fused at a temperature not under 600°, without the loss of any-
thing, except a trace of water, which had been mechanically retained.
Upon heating a bisulphate nearly to redness, a portion of sulphate of
ON WATER AS A CONSTITUENT OF SALTS. 357
water is expelled, I greatly doubt whether water ever comes off in
such a case unaccompanied by Sulphuric acid, although Berzelius appears
to be of a different opinion. It is well known that the sulphate of water
is not entirely expelled from these salts by heat alone, even the most
intense. Sulphate of water, however, leaves the sulphate of soda with
greater facility than it leaves the sulphate of potash.
These sulphates should be crystallized from concentrated solutions
at a high temperature; for their solutions are very apt to undergo
decomposition at low temperatures, the neutral Sulphate crystallizing,
and leaving “the sulphate of water with saline water” in solution. I
have often observed this decomposition to occur, even in solutions con-
taining a great excess of sulphuric acid. At low temperatures, there-
fore, the affinity of sulphate of water for “saline water,” prevails over
its affinity for sulphate of potash. Crystals of bisulphate of Soda,
pounded and put under pressure in blotting-paper, are apt to undergo
the same decomposition, if the air is damp, and frequently impart a
large quantity of their sulphate of water to the paper in the course of
twenty-four hours. This circumstance must be kept in view in prepar-
ing bisulphates for analysis. The facility with which these salts are
decomposed by water, accords well with their relation to sulphate of
water with saline water, which we have supposed to exist. Sulphate
of zinc, sulphate of magnesia, etc., are capable of separating the sulphate
of water from these salts, at a temperature approaching to redness, and
take its place.
I have observed that the bisulphate of soda is more prone to decom-
position, when dissolved in water, than the bisulphate of potash. The
double salts of sulphate of soda with sulphate of magnesia, etc., are also
much less stable than the corresponding double salts containing Sulphate
of potash. Indeed, I believe that the former are uniformly decomposed
when dissolved in water. - -
Sulphate of Potash, Sulphate of Soda. KS, NS.
These salts differ from other sulphates in having no saline water.
Of the ten atoms water with which sulphate of Soda crystallizes, none
is essential to its constitution. The whole were lost, even at a tempera-
ture not exceeding 47° Fahrenheit, when the crystals of the salt were
exposed over sulphuric acid in vacuo for five days. From the regular
progress of the desiccation of the salt, which was observed by occasion-
ally weighing it, it was evident that no portion of the water was more
strongly retained than the rest. It is well known that sulphate of soda
crystallizes in an anhydrous condition from a hot solution,
358 ON WATER AS A CONSTITUENT OF SALTS.
Sulphate of Zinc with Saline Water: ZnSH + H'.
Sulphate of Zinc.
In the sulphate of zinc, we have the basic atom of water contained
in sulphate of water displaced by oxide of zinc, while the Saline atom
remains; and to this compound six atoms of water are attached in the
common crystals. These crystals, placed over sulphuric acid in vacuo,
thermometer 68°, were found to lose six atoms water, retaining only
one. Exposed to the air at 212°, the crystals likewise readily effloresced
down to one atom; and the sulphate of zinc is known to be deposited
from a boiling solution, in crystalline grains, containing one atom of
water. On the other hand, the sulphate of zinc was found to retain
this single atom of water at the high temperature of 410°Fahrenheit,
but to lose it, and become anhydrous, at a temperature not exceeding
460°. In all such cases, the hydrated salt was heated in a tube receiver,
by means of an oil or solder-bath, of which the temperature was ob-
served by a thermometer. However strongly it has been heated, with-
out being decomposed, the sulphate of zinc always regains this atom of
water when moistened, slaking with the evolution of heat. Common
sulphate of zinc is therefore “sulphate of zinc with saline water;” and
the true or absolute sulphate of zinc is unknown to us in the crystalline
form, or in a soluble state. But we may continue to designate the salt
we possess as Sulphate of zinc, as the name is attended with no dubiety.
Sulphate of Zinc with Sulphate of Potash : Žns(KS) +H".
Sulphate of Zinc and Potash.
In this well-known double salt, we have sulphate of potash substi-
tuted for the saline water of Sulphate of zinc, and the six atoms of water
of crystallization remain. It is readily formed, on mixing together
solutions of sulphate of zinc and sulphate of potash, in atomic propor-
tions. It is formed likewise, and separates by crystallization, when the
sulphate of zinc is added to the bisulphate of potash; and, in that case,
an interesting double decomposition occurs. -
Sulphate of water with sulphate of ash.
Sulphate of zinc with saline water, | Sulphate of zinc with sulphate of pot-
yield
potash, Sulphate of water with saline water.
In the sulphate of zinc and potash, the whole six atoms of water are
retained with considerably greater force than in the sulphate of zinc
itself; but even the double Salt becomes anhydrous at 250°, and, indeed,
the water retained falls below a single atomic proportion, when the salt
is dried in vacuo over Sulphuric acid, at a temperature not exceeding
ON WATER AS A CONSTITUENT OF SALTS. 359
78° Fahrenheit. The sulphate of potash in the double salt has not the
effect of neutralizing the acid reaction of sulphate of zinc, according to
my observations; nor has it that effect in the case of any other double
salt.
I subjoin a table of observations, made on the quantity of water
retained by this double salt, in different circumstances. In the first two
columns, the composition of the quantities actually examined is stated
in grains.

Anºus Water. Angºus Water.
Dried in vacuo over sulphuric acid for ten - g -
days, temp. from 68° to 78°, | 17.2 0-68 100 3.95
Nine hours, at 238°, o e ſº º 19-03 1°33 100 6'99
Two hours at 250°, and one hour at 270°, . 7.79 0. 100 0.
Four hours, at 250°, e e g 6'55 0. 100 0.
Composition of sulphate of zinc and potash | 100 5-37
with one atom water (by theory), .
Sulphate of Zinc with Sulphate of Soda ; ZnS(NŠ) + H+.
Sulphate of Zinc and Soda.
This salt, I believe, has not hitherto been described. I failed in
attempting to form it, by dissolving together sulphate of zinc and sul-
phate of soda in atomic proportions: the salts uniformly crystallized
apart, either in cold or in warm weather. Each of the salts was also
added in excess to the other, but with no better effect. It appears,
then, that sulphate of soda does not displace the saline water of sulphate
of zinc, so easily as sulphate of potash does. But the desired salt was
obtained by a process of double decomposition, suggested from consi–
deration of the relations of the sulphates. Solutions of bisulphate of
Soda, and of sulphate of zinc, were mixed together in atomic propor-
tions, from which the sulphate of zinc and soda separated in a gradual
manner in the course of a day or two, leaving sulphuric acid in solu-
tion.
Sulphate of zinc with saline water, ield Sulphate of zinc with sulphate of soda.
Sulphate of water with sulphate of *} yie §. of water with saline water.
This salt is deposited in distinct tabular crystals, of a peculiar form,
which are often associated in tufts, and is best obtained by evaporating
the mixed solutions over Sulphuric acid without heat. It cannot be
redissolved in pure water, without undergoing decomposition, which
accounts for the impossibility of forming it by the direct process. The
360 ON WATER As A CONSTITUENT OF SALTS.
crystals contain four atoms of water, and are about as deliquescent as
nitrate of soda, in a damp atmosphere. The anhydrous Salt undergoes
fusion, like all the other double sulphates, at an incipient red heat,
without the evolution of acid fumes. The fused salt solidifies, on cool-
ing, into a white and opaque mass. -
Sulphate of Copper with Saline water: ČušH+ H+.
Sulphate of Copper.
The common blue rhomboidal crystals of sulphate of copper contain
five atoms of water, four of which are readily expelled by drying the
salt in air at 212°; by which treatment the salt loses its blue colour,
and becomes white, with a dirty shade of green. The sulphate of
copper with one atom of water was also obtained in a crystallized state
by Dr. Thomson, and called by him green sulphate of copper. Dried
over sulphuric acid in vacuo for seven days, when it had ceased to lose,
at a temperature between 65° and 74°, the common hydrated salt re-
tained 21.67 parts water to 100 anhydrous salt, which is somewhat
under two atomic proportions of water, namely 22:57 parts. At a tem-
perature between 430° and 470°, the sulphate of copper loses its fifth,
or saline, atom of water, and is found in the state of a powder, which is
white without any shade of colour. When a few drops of water are
thrown upon anhydrous Sulphate of copper, it slakes and becomes blue,
and so much heat is evolved as to occasion the ebullition of the water.
In one case the temperature was observed to rise to 276°. This arises
from the resumption of saline water by the salt.
Sulphate of Copper with Sulphate of Potash: Čuš(KS) +H".
Sulphate of Copper and Potash.
This salt may be formed by mixing sulphate of copper with either
sulphate or bisulphate of potash, in atomic proportions. Dried in the
open air, it loses six atoms water, and becomes quite anhydrous at a
temperature not exceeding 270° Fr. The following Table of the com-
position of this hydrated Salt in different circumstances illustrates three
facts, that the Salt has a disposition to retain two atoms of water
when dried at 212° in open air, that a greater portion of water
of crystallization is withdrawn from the salt by drying it over sul-
phuric acid in vacuo, without artificial heat, than by drying it at 212°
under the atmospheric pressure, and that the mechanical water re-
tained by the crystals of this salt may exceed 3 per cent. of their
weight.
ON WATER AS A CONSTITUENT OF SALTS. 361

Anhydrous Anhydrous
Salt - Water. §.alt. Water.
Dried on water-bath at 212°, for three days, & º *
or till it ceased to lose weight, & 19:6 2.21 100 11:27
Dried on nitre-bath at 238°, for three days, 22-06 2-37 100 10'74
Dried in vacuo over sulphuric acid for seven
days, or till it ceased to lose weight ;
therm. from 65° to 74°, © sº º
Crystals pounded, and slightly dried at 80°,
so as not to injure the lustre of an entire
crystal, ve e g º to &
Same crystals not deprived of mechanical
water by the above treatment, . º
ſ 22-97 1-61 100 7-09
l
ſ
Composition of sulphate of copper º
\
ſ
13-94 3-4 100 32-25
23.79 8-64 100 36-22
potash with two atoms of water (by 100 10-77
theory), © & e º º º
Composition of do. with six atoms of water 100 32-33
(by theory), e e e © º
I have confirmed the observation of Berzelius, that a concentrated
solution of this salt, when boiled, deposits an insoluble subsalt, con-
taining sulphate of potash, but which is decomposed by washing, and
cannot be had in a proper state for analysis. But the crystals of the
double salt are quite soluble after being heated to 212°, so that they
do not undergo the same change as their solution does at that tem-
perature. - - -
This double salt retains its blue colour after being fused at a red
heat and cooled, and does not become white like the sulphate of copper.
Indeed, it appears that, to be coloured, the salts of the oxide of copper
require the addition of some other constituent, such as saline water,
sulphate of potash, or ammonia. Hence, if the absolute sulphate of
copper could be obtained in a crystallized state, it would be a colourless
salt.
Sulphate of Copper with Sulphate of Soda ; Cuš(N Š) +H".
Sulphate of Copper and Soda.
Like the other double salts of sulphate of soda, this salt cannot be
formed directly, being decomposed by water. Even when it is attempted
to form it by double decomposition from the bisulphate of soda, in
general a large quantity of sulphate of soda and of sulphate of copper
are separately deposited before the double salt appears. It is then
deposited in a crust, consisting of Small but distinct crystals, which are
slightly deliquescent, and appear to contain two proportions of water.
This salt is easily made anhydrous, and thereafter fuses at an incipient
red heat without loss of acid, and remains of a blue colour when cool.
The fused salt does not split into thin scales in the progress of cooling,
as the corresponding Sulphate of copper and potash does.
36.2 ON water. As A CONSTITUENT OF SALTs.
Sulphate of Manganese with Saline Water: MnSH + H+.
Sulphate of Manganese.
The water in this salt was found to be reduced from five atomic
proportions to little more than one, by drying the crystals in open air
at 238°, while one entire atomic proportion was retained at 410°.
Flesh-coloured crystals, dried in vacuo in warm summer weather,
without artificial heat, lost somewhat more than three proportions of
Water.

Angiºus Water. Anºus Water.
|Flesh-coloured crystals of salt, e
Do. dried at 238°, º e e º
A portion of last, afterwards dried for one
hour between 380° and 410°, º
28:42 17-07 100 60'06
21:53 2-92 100 13.05
9-54 1-12 100 ll 74
A portion of same, dried for one hour -
between 415° and 468°, . gº o
! 10-90 0-56 100 5'14
Crystals dried for nine days in vacuo : - -
sulphuric acid, thermometer 64° to 72°, 8-62 11 100 20-88
but had lost nothing the last two days, -
Composition of sulphate of manganese with -
one atom of water (by theory), . © tº 8 tº 100 11.88
Composition of do. with five atoms of water, • * * * - © 100 59°4
A crystalline crust of sulphate of manganese, deposited from a warm
solution, was found to contain three atoms of water. It is likewise
known to be deposited from a boiling solution with only one atom of
water, namely, the saline atom. We have, therefore, sulphates of this
class with no water of crystallization, and with two, four, and six
atoms.
The sulphate of manganese and potash did not crystallize on mixing
the solutions of its constituents. The sulphate of manganese and soda
was obtained in analogous circumstances with the sulphate of copper
and soda, but was not examined. -
Sulphate of Iron with Saline Water: fesH+H". Sulphate of Iron.
Of the seven atomic proportions of water which the crystals contain,
5:48 proportions were lost in vacuo over sulphuric acid; and six pro-
portions at 238°, and probably at lower temperatures. The saline atom
of water is retained by this salt at so high a temperature as 535°. But
the salt can be made perfectly anhydrous, with proper caution, without
appreciable loss of acid.
ON water. As A CONSTITUENT OF SALTs. 363
Sulphate of Iron with Sulphate of Potash: feš(KS) +H".
Sulphate of Iron and Potash.
A specimen of this salt was made anhydrous by a sandbath heat,
which was found not to affect the saline atom of water of the preceding
compound. -
Sulphate of nickel was found to correspond closely with sulphate of
iron in the temperatures at which it lost its water of crystallization,
and also its saline water. And in the case of both of the compounds of
these salts with sulphate of potash, a considerably higher temperature
was required to render them perfectly anhydrous, than in the case of the
corresponding double salt of zinc.
Sulphate of Magnesia with Saline Water: MgSH +H".
Sulphate of Magnesia.
One atom of water is retained by sulphate of magnesia at 460°, but
the other six are not entirely expelled under 270° in open air. In-
deed, this sulphate is remarkable for a disposition to retain two atoms
of water, in which respect it resembles the sulphate of lime. Dried at
212° in open air, the crystals of sulphate of magnesia were found in
several experiments to retain somewhat more than two atomic propor-
tions of water. When dried at the same temperature in vacuo over
sulphuric acid, the water was reduced to two proportions. Crystals
placed over sulphuric acid in vacuo, without heat, were found to retain
only two and a quarter atomic proportions of water.

Anhydrous Anhydrous
Salt. Water. Salt. Water.
Crystallized salt, dried in vacuo at 70° for tº & a .4 c |
six days, or till it ceased to lose, . } 12-34 4°13 100 33°46
| Do. in vacuo at 212°, e © ſº te 21-8 6-24 100 28.62
Do. heated between 410° and 460° for one * * tº
hour, being previously dried at 238°, . 4-9 0-74 100 15-1
Relative composition of the anhydrous salt 100 14-81
with one atom of water (by theory), . is tº e tº º tº
The sulphate of magnesia and ammonia lost its six atoms of water
of crystallization and became anhydrous, when exposed to a temperature
not exceeding 270°, for one hour, having previously been dried at 212°.
It retained of course the atom of water which is essential to the ammo-
niacal salts. A somewhat higher temperature was required to deprive
the sulphate of magnesia and potash of its whole water of crystal-
lization.
364 ON WATER AS A CONSTITUENT OF SAILTS,
Hydrated Sulphate of Lime: CašH+ H.
The only crystalline hydrate of sulphate of lime, which is known,
contains two atoms of water. It occurs native in gypsum and selenite.
Pounded selenite loses little or nothing in the open air at 212°. Water
begins to escape at a temperature not much higher, but is not completely
expelled by any degree of heat under 270°. That hydrated sulphate of
lime may contain an atom of saline water, is indicated by the existence
of a double salt of sulphate of lime with sulphate of soda, constituting
the mineral Glauberite. I succeeded in obtaining a definite compound
of sulphate of lime with one atom of water, by drying pounded selenite,
at 212°, in vacuo over sulphuric acid.” The salt which had been so
dried at 212° did not form a coherent mass, like stucco, when made into
a paste with water. The affinity of sulphate of lime for the saline atom
of water appears to be feeble, as the salt can be made quite anhydrous
under 300°; and consequently the sulphate of lime has much less dis-
position to form double salts than the sulphates of magnesia, zinc, etc.

Anhydrous Anhydrous
Salt. Water. Salt. Water.
sº dried for ten days in open air at 17-07 4:27 100 25:01
Do, dried in vacuo at 212, 17.61 | 3:04 || 100 14.72
Sulphate of lime with one atom of water s
(by theory), . . . . . . º, º º º e e 100 13-13
Do. with two atoms of water (by theory), . tº º º tº e de 100 26-26
In drying gypsum, to make plaster of Paris, a third or a fourth of the
water of the Salt is allowed to remain, by which it sets more strongly.
But the salt may be made quite anhydrous, I find, and yet retain the
power of recombining with two atoms of water, if dried at a temperature
not exceeding 270° F.; although the hydrate which results on slaking
in the last case is rather pulverulent. When gypsum has been dried at
a higher temperature, as at 300° or 400°F., it refuses entirely to com-
bine with water, and is technically called burnt stucco. The anhydrous
sulphate of lime which occurs in nature exhibits the same indifference to
water. In Anhydrite we have, I believe, the true or absolute sulphate
of lime in a crystallized state. The body which results from exposing
hydrated sulphate of lime to 270°, although composed of nothing but
sulphuric acid and lime, should be viewed as the débris of the hydrated
sulphate of lime, and not confounded with the absolute sulphate of lime,
which last has no disposition to combine with water. The first, which
* It has subsequently been observed, that the water is reduced under one atomic
proportion, by a protracted exposure to the same temperature.
ON THE WATER OF CRYSTALLIZATION OF SODA-ALUM. 365
We may call “anhydrous gypsum,” is an imperfect body. We know
sulphate of lime in four states, which may be expressed symbolically
as follows:
Gypsum, e tº & is & ČašH+ H
Gypsum dried at 212", . wº . ČašH
Anhydrous gypsum (dried at 270°), . Čas—
Anhydrite, . º º e o Čaš.
Here we distinguish the imperfect body, anhydrous gypsum, from anhy-
drite, by placing the minus sign after the former. In the same manner,
concentrated sulphuric acid, or oil of vitriol, may be represented by
HŠ–; anhydrous sulphate of magnesia, Sulphate of zinc, etc., by
Mgs—, Žns—, etc.; the absolute sulphates of water, magnesia, zinc,
etc., HS, MgS, ZnS, etc., being unknown to us.
The view which is given in this paper of the constitution of the
sulphates, must not be hastily generalized and applied to other classes
of salts. From investigations not yet completed, I am satisfied that
each class of Salts has its peculiarities, which must be studied before the
law of the class can be laid down.
WI.
- ON THE WATER OF CRYSTALLIZATION OF SODA-ALUM."
From Phil. Mag. ix. 1836, pp. 26-32. [Liebig, Annal. xxiii. 1837, pp. 269, 270 ;
Poggend. Annal. xxxix. 1836, pp. 582-585.]
THE double sulphate of alumina and soda crystallizes in the form of
the regular octohedron, like the Sulphate of alumina and potash, while
the former salt is supposed to contain twenty-six atoms of water, and
the latter contains only twenty-four. The coincidence in form of these
two salts is most interesting, for in no other corresponding salts of potash
and soda has such a relation been observed from which any inference in
respect to isomorphism could properly be drawn. Yet if the soda-salt
contains two atoms more of water than the potash-salt, the conclusion
which follows is, not that soda and potash are isomorphous bodies, but
that soda plus two atoms water is isomorphous with potash, as ammonia
plus one atom of water is isomorphous with the same body. But the last
analogy is superficial and likely to prove illusory.
1 Communicated by the Author.
366 º
ON THE WATER OF CRYSTALLIZATION OF SODA-ALUM.
The exact determination of the water of crystallization of a Salt is
often a problem of no inconsiderable difficulty, as many precautions must
be taken which are by no means obvious. To have alumina free from
potash or ammonia, it was precipitated from pure potash-alum by means
of carbonate of soda. A solution of sulphate of alumina was formed by
dissolving the precipitated alumina in the proper quantity of Sulphuric
acid, and the requisite proportion of sulphate of soda was added. A
considerable crop of crystals of soda-alum were obtained from the above
solution allowed to evaporate spontaneously in air.
Like most very soluble salts the crystals of soda-alum, when newly
prepared, retain hygrometrically a notable quantity of the Saline liquor
in which they have been formed. But the crystals of this salt cannot
be dried easily, as after they lose their hygrometric water they are nearly
as efflorescent as sulphate of soda itself. Before being submitted to
analysis the crystals had been kept for five months of cold weather in
a large phial stopt by a cork. Their surfaces remained perfectly bright,
and not in the slightest degree effloresced; but the crystals had lost, from
the escape of their hygrometric water, that extreme and watery clearness
which we have in the crystal newly removed from its mother-liquor.
IFrom my experience in respect to such salts, I had reason to believe
that the crystals of soda-alum were now in a most suitable condition for
analysis.
Upon a very damp day the crystals were reduced to powder and
pressed in blotting-paper. A large crystal exposed to the air at the same
time lost nothing. 20:35 grs. of the Salt so prepared were exposed on a
sand-bath to a heat, which was gradually raised so as to effloresce the
salt without melting it or causing vesicular swelling. In eight hours the
salt had been heated above the melting point of tin, and had lost 8.98
grains. It was thereafter heated, in a gradual and cautious manner, to
low redness by the spirit-lamp, and the loss became 9'65 grains. By a
continued exposure to the same heat for half an hour more, the Salt lost
only one hundredth of a grain additional. Supposing it now to have lost
all its water, the salt will consist of
Theory of 24
atoms of Water.
Sulphate of alumina and soda, 10-69 100° 100°
Water, º e & tº 9'66 90°37 88-9
*
20'35 190°37 1889
The calcined salt dissolved slowly but completely in boiling water.
By precipitation with muriate of barytes it afforded 21:22 grains sulphate
of barytes, equivalent to 737 grains sulphuric acid. Or the crystal-
lized salt contains 34.73 per cent. of sulphuric acid, while the theory of
ON. THE CONSTITUTION OF OXALATES, NITRATES, ETC. 367
twenty-four atoms of water supposes it to contain 34.93 per cent. Sul-
phuric acid. sº
It follows from this analysis that Soda-alum contains twenty-four
atoms of water and not twenty-six. -
There is no reason to question the perfect accuracy of the analysis
of potash-alum by Berzelius, which gives to it likewise twenty-four
atoms of water. Dried in the manner described for Soda-alum, I found
it to consist of
Theory of 24
atoms of water.
Sulphate of alumina and potash, . 100' 100°
Water, • , , º º tº 84-8 83°4.
184'8 183°4
In such analysis there is imminent danger of the water carrying off
a little acid with it, unless it is expelled in the most slow and cautious
manner. It is probably from this cause that the water has come to be
over-estimated in the case of the alums. But they stand a low red heat
without decomposition, if first made quite anhydrous.
VII.
INQUIRIES RESPECTING THE CONSTITUTION OF SALTS,
OF OXALATES, NITRATES, PHOSPHATES, SULPHATES,
AND CHLORIDES.”
From Phil. Trans, 1837, pp. 47-74. [Liebig, Annal. xxix. 1839, pp. 1-35.]
FROM the results obtained in a former paper upon water as a con-
stituent of sulphates, it seemed likely that a close analogy would gene-
rally be found to exist between any hydrated acid and the magnesian
salt of that acid. The sulphate of water is constituted like the sulphate
of magnesia; and so do I now find the oxalate of water to resemble the
oxalate of magnesia, and the nitrate of water to resemble the nitrate of
magnesia. Indeed, it appears probable that the correspondence between
water and the magnesian class of oxides (as we may call the metallic
oxides isomorphous with magnesia) extends beyond their character as
bases, that in certain subsalts of the magnesian class of oxides we have
the metallic oxide replacing the water of crystallization of the neutral
salt, or discharging a function which was thought peculiar to water.
* Received June 23,-Read November 24, 1836.
3.68 ON THE CONSTITUTION OF OxALATES, NITRATES,
In the formation of a double sulphate a certain kind of substitution
or displacement was observed, such as the displacement of an atom of
water pertaining to the Sulphate of magnesia, by an atom of sulphate of
potash, to form the double sulphate of magnesia and potash. The same
kind of displacement appears to occur likewise in the construction of
double oxalates; and the tracing of it enables us to form an idea of the
constitution both of the double and of the superoxalates, and to explain
their derivation, as in the case of the Sulphates.
I. OF THE OXALATES.
The oxalates promised ample scope for investigation from their
number and variety. For we have not only neutral oxalates, double
oxalates, and binoxalates, but likewise an unparalleled combination, the
quadroxalate of potash, of which the true constitution or proximate com—
position is a most interesting subject of inquiry. .
1. Oaxalate of Water, or Hydrated Oaxalic Acid.
HCCH*.
The recent and accurate experiments of Berzelius, Gay-Lussac, and
Turner, leave no doubt that the crystals of Oxalic acid contain three
atoms of water. I find the acid to crystallize with this proportion of
water in a variety of circumstances, and believe that it is never deposited
from its aqueous solution in any other state. Of these three atoms of
water one atom is basic, which is expressed in the formula by placing its
symbol before that of the acid; while the other two atoms of water are
attached to this oxalate of water, and may be termed the constitutional
water of the oxalate of water. These two atoms of water are found in
the oxalate of magnesia, the oxalate of zinc, and the other oxalates of the
magnesian class, as well as in the oxalate of water. :-
It is well known that Oxalic acid can likewise exist in combination
with no more than one atom of water (its basic water), and is obtained
in that state by drying it at a temperature a little above 212° Fahr., or
on subliming the hydrated acid by a higher temperature. I have made
many experiments in order to discover whether, in the case of the other
two atoms of water, one is retained more strongly than the other, or
whether an oxalate of water with one additional atom of water, instead
of two, could be obtained. The common crystals were dried at various
temperatures, both in air and in vacuo, but either none of the water was
lost, or the entire two atomic proportions. There is certainly no inter-
mediate hydrate.
PHOSPHATES, SULPHATES, AND CHLORIDES. 369
2. Oxalate of Zinc.
ZnCCH*.
In the oxalate of water we observe a contracted solubility, and all
the oxalates of the magnesian class of oxides are very sparingly soluble
in water. They may be obtained by precipitation, on mixing a solution
of oxalate of potash with sulphate of zinc, etc. Cold solutions of the
salts were always made use of in our experiments; and the precipitates,
which were always granular and more or less distinctly crystalline, were
washed with cold water, and dried by exposure to the air for a week or
two, without the application of artificial heat.
The oxalate of zinc is admitted to possess two atoms of water, and
these I find are retained pretty strongly, as in the case of oxalate of
water. It was observed that 24-95 grains of the salt lost only 0.44 grain
by three days’ exposure to 212° Fahr. ; but by a few hours at 315° Fahr.
the salt lost in all 4'87 grains of water, and appears to have become
anhydrous. -
3. Oacalate of Magnesia.
MgCCH*.
The oxalate of magnesia retains its two atoms of constitutional water
very strongly, and it is doubtful whether they can be expelled without
decomposing the salt; 1374 grains of the salt lost only 0°32 grain by
an exposure to 212°, protracted for several days; and by two days at 300°
Fahr. the whole loss amounted only to 0-47 grain. 22:36 grains of the
same salt, ignited, left 5'94 grains of caustic magnesia, or one part of the
salt contains 0.2656 magnesia. A salt constituted with two atoms of
water should contain 0-2759 magnesia, of which the specimen analysed
falls a little short, probably from containing some hygrometric moisture.
The oa'alate of manganese lost nothing at 212°, and was found by
analysis to contain 0.2416 water, which approaches very closely the
quantity equivalent to two atoms, namely, 0.2474 water in one hydrated
oxalate of manganese.
In regard to several other oxalates of this class, namely, the oxalate
of the protoxide of iron, of oxide of nickel, of oxide of cobalt, and of
oxide of copper, I believe it is impossible to obtain them in a state of
sufficient purity for analysis. They appear to carry down with them
portions of the precipitating salts; and they alter manifestly in appear-
ance and composition during the progress of the washing, to which they
must be submitted for the purpose of purification. In the case of oxalate
of copper, which was examined most particularly, the results were so
anomalous that no inference whatever could be drawn from them.
- 2 A
370 ON THE CONSTITUTION OF OXALATES, NITRATES,
It will appear, however, that a neutral oxalate of copper with two
atoms of water can exist but in combination with oxalate of potash, or .
With oxalate of ammonia, as a double salt.
None of the oxalates of the magnesian class of oxides is more soluble
in oxalic acid than in water, and none of them combines with that acid
to form a binoxalate. The crystals, which are obtained on mixing
together solutions of binoxalate of potash and sulphate of magnesia, and
which have been supposed to be a binoxalate of magnesia, are really a
mixture of oxalate of magnesia and of quadroxalate of potash. Hence
there is no combination of oxalate of magnesia with oxalate of water;
which illustrates the fact that bodies of the same class, such as these
two oxalates are, have no disposition to enter into union and form a
new compound.
4. Oaxalate of Lime.
CaCOH4.
The oxalate of lime contains two atoms of water, like the oxalate of
magnesia, but parts with its water more freely than that salt. Thus
12:06 grains of the hydrated oxalate of lime were found to lose 1:6 grain
of water at 212° Fahr. in the course of two days, 1.68 grain in three
days, 184 grain in six days, and nothing more in nine days. The salt
originally consisted of 100 oxalate of lime united to 27-85 water, of
which last it has lost 19:53 parts, and retained 832 at 212°. It is pro-
bable therefore that the constitution of hydrated oxalate of lime is the
same as that of hydrated oxalate of magnesia, that oxalate of lime forms
only one definite hydrate, containing two atoms of water, but that it
parts with the whole of its constitutional water at a moderate tempera-
ture.
5. Oaxalate of Barytes.
facCH.
This oxalate differs from all the preceding, and contains only one
atom of water. It was formed by digesting an excess of oxalic acid
upon carbonate of barytes, and afterwards washing the resulting oxalate
with cold water. 20-60 grains of the oxalate, calcined by a low red heat,
left 16:45 grains carbonate of barytes, equivalent to 1277 barytes.
Hence it follows that the oxalate consisted of
- Composition of BacdH.
Barytes, º 100 100
Wolatile matter, 61:32 59'08
161°32 159:08
PHOSPHATES, SULPHATES, AND CHLORIDES. 3.71
Before being washed this oxalate had a sour taste, and the volatile
portion of it amounted to 67.01 parts instead of 61:32; but it was evi-
dently the neutral oxalate with a little free oxalic acid. It was not a
binoxalate; nor did such a salt present itself on digesting the neutral
oxalate in oxalic acid, so that I am constrained to deny the existence of
a binoxalate of barytes. Indeed, it is scarcely a matter of doubt that no
SuperSalt whatever exists of barytes, strontian, lime, or of the magnesian
class of oxides. -
6. Oaxalate of Potash.
ECCH.
Oxalate of potash is known to crystallize from solution with one
atom of water, and with no other proportion. The crystals speedily
become white and opake at 212° Fahr., from the loss of water, but can-
not, I believe, be made quite anhydrous at that temperature; at least a
portion of the salt, which had been exposed to 212° for four days, still
retained water, consisting of 100 oxalate of potash and 3-4 water, which
is rather less than a third of the water which the salt originally con-
tained (10.8 parts). The oxalate of potash becomes quite anhydrous
when dried at 300°. Of salts so dried 100 parts reabsorbed 10-63 water
in a damp atmosphere with the greatest avidity. The oxalate of potash
has therefore a certain attraction for a single atom of water, and this is
an important feature of the salt.
7. Binoa'alate of Potash.
RCC+HCCH*.
This salt has hitherto been supposed to contain only two, but it cer–
tainly contains three atoms of water.
21:37 grains of the salt, calcined by a full red heat, which is neces-
sary for complete decomposition, left 10:14 grains of carbonate of potash.
Allowing the potash an equivalent proportion of Oxalic acid, the salt
must consist by this experiment of
Potash, & * º tº 32°23
Oxalic acid, . g * ę 49°38
Water, * * & tº 18-39
100°
The water almost coincides with three atoms, which would amount to
18:42 per cent. of the salt.
In the formation of the binoxalate of potash, the constitutional
atom of water of the neutral oxalate of potash appears to be displaced
37.2 ON THE CONSTITUTION OF OXALATES, NITRATES,
by an atom of hydrated oxalic acid; so that the formula of binoxalate
of potash represents anhydrous oxalate of potash, followed by oxalate of
water with two atoms of water, as given above. The same principle
of derivation applies most happily to that anomalous Salt, the qua-
droxalate of potash.
8. Quadroaialate of Potash.
Analitic formula, º K(ČC)*H'.
Rational formula, * K(CC) + Höö + 2(HööH')
The formula of the preceding salt is terminated by two atoms of
water: let us replace them by two atoms of hydrated oxalic acid, and
we have the quadroxalate of potash. We thus derive the quadroxalate
from the binoxalate, in the same way that the binoxalate itself is
derived from the oxalate.
There can be no doubt, from the accurate analysis of Berzelius, that this
salt contains Seven atoms of water. He found 100 parts of the quadroxa-
late of potash to yield by ignition 27-225 carbonate of potash. In an ex-
periment in which 17.3 grains of the salt were ignited by us, there resulted
4.7 carbonate of potash; which is 27:11 carbonate of potash from 100 qua-
droxalate. Berzelius determined the water directly by igniting the Salt
with oxide of copper, and found it to amount to 24.8 per cent. of the salt.
Calculated from our experiment, the water comes out 25:05 per cent,
while the theory of seven atoms of water in the salt requires 24-72 per cent.
10.87 grains of this salt, dried by a mitre-bath, of which the tempe-
rature was 240°, lost eventually 146 grains; or 100 salt lost 13:43.
Four atoms of water amount to 14.12 per cent. of the salt, to which the
experimental result approximates sufficiently to prove that this salt
parts readily with four of its seven atoms of water. These four atoms
of water are evidently the constitutional water of the two atoms of
hydrated oxalic acid, which the quadroxalate contains. When the salt
is still more strongly heated, oxalic acid itself goes off, partly as a sub-
limate and partly in a decomposed state.
9. Oa'alates of Ammonia.
The oxalate and the binoxalate of ammonia agree exactly in com-
position with the corresponding salts of potash, the hypothetic oxide of
ammonium being substituted for potash. It has been supposed that no
quadroxalate of ammonia exists; but this is a mistake. Such a salt is
formed, on dissolving together equal weights of binoxalate of ammonia
and hydrated Oxalic acid, and is analogous in form and composition to
the quadroxalate of potash.
PHOSPHATES, SULPHATES, AND CHLORIDES. 373
10. Owalate of Soda.
NaCC.
This salt is perhaps the least soluble of the salts of soda, and pre-
sents itself as a granular precipitate on Saturating carbonate of soda
with oxalic acid. Of the oxalate of soda dried in air without the appli-
cation of heat, 23.44 grains left 18:52 carbonate of soda when strongly
ignited, or 100 oxalate yield 79.01 carbonate of soda. Now 100 anhy-
drous oxalate of soda should yield 79.09 carbonate of soda. Hence the
oxalate of soda is correctly stated to be anhydrous. It nevertheless
combines with hydrated Oxalic acid, and forms a binoxalate. In this
compound we have simply the attachment of an atom of the oxalate
of water, to the atom of oxalate of Soda, without the displacement of
an atom of water, as in the formation of the binoxalate of potash.
Probably the absence of the atom of water in the oxalate of soda indi-
cates an indifference on the part of this salt to enter into further com-
bination. There is certainly a binoxalate of soda ; but this binoxalate
cannot support the further attachment to it of two atoms of hydrated
oxalic acid, and there is no quadroxalate of Soda.
11. Binozalate of Soda.
NaCC + HCCH*.
This salt I find to resemble the binoxalate of potash, in containing
three atoms of water. 22-11 grains, strongly ignited, left 8:05 grains
fused carbonate of soda ; or 100 binoxalate leave 40-67 carbonate of
soda, equivalent to 23-84 soda ; while a binoxalate with three atoms
of water should yield 23.95 per cent. soda, or almost exactly the
experimental result. The binoxalate of Soda lost little more than
1 per cent of its weight when kept at 212° Fahr. over sulphuric acid in
vacuo. But by a heat approaching 300 Fahr. the salt lost 14.64 per
cent. of water, which is a little more than two atomic proportions,
namely, 13.78 per cent. Hence this salt retains the whole of its con-
stitutional water at 212°, but loses two atoms of it at a higher tem-
perature, retaining strongly the third atom of water, which is basic.
Double Oaxalates.
The number of double oxalates is not so great as is generally Sup-
posed. On mixing a solution of binoxalate of potash either with the
muriate or the Sulphate of magnesia, zinc, etc., the oxalate of magnesia
374 ON THE CONSTITUTION OF OXALATES, NITRATES,
or of zinc precipitates, while the quadroxalate of potash is formed, and
remains in solution or crystallizes, being very sparingly soluble, accord-
ing to circumstances. When binoxalate of potash is digested upon
magnesia or upon oxide of zinc, a portion of the oxide is dissolved, but
is quickly deposited again as an insoluble oxalate, and no double salt
formed. But one member at least of the magnesian class of oxides,
namely, oxide of copper, is dissolved by the binoxalates of the alkalies,
and forms double salts, which were discovered and carefully examined
by M. Vogel of Bayreuth.
12, Oxalate of Copper and Potash.
RCC+ CuCCH*;
and also
RCC + CuCCH* + H+.
The binoxalate of potash, when considerably diluted, and digested
with heat upon the oxide of copper, dissolves it easily, and a double Salt
of sparing solubility crystallizes, presenting itself generally in two forms,
one of which contains two and the other four atoms of water, according
to the analyses of M. Vogel, which I have repeated and confirmed so
far as the water is concerned. The crystals containing four atoms of
water soon become opake by exposure to the air, and lose two atoms of
water by efflorescence.
Binoxalate of ammonia likewise dissolves oxide of copper, and does
so still more readily than the binoxalate of potash, which may depend
upon the circumstance that the resulting double Salt of ammonia is
considerably more soluble in water than the double salt of potash. The
oxalate of copper and ammonia crystallized in plates of a blue colour,
and seemed to affect one form only. Of these plates, 9:38 grains were
readily decomposed by heat, and left 2:37 grains black oxide of copper,
or 25.27 per cent, which is almost exactly the proportion of that of the
oxide of copper, which a salt of two atoms water should contain, namely,
25:37 per cent. This salt loses water readily at 212° Fahr.; and of the
11:52 per cent, which it is supposed to have on the theory of its con-
taining two atoms of water, 11:46 per cent. escaped by the exposure of
the Salt to that temperature. M. Vogel describes two other double
oxalates of copper and ammonia; but it is evident that they contain
ammonia and not oxide of ammonium; so that they do not come under
our consideration at present.
It is to be remarked that the oxalate of copper and potash is repre-
sented above by a formula quite analogous to that of binoxalate of
potash, oxide of copper being simply substituted for basic water. We
PHOSPHATES, SULPHATES, AND CHLORIDEs. 375
have oxalate of potash in both cases, to which there is attached oxalate
of copper with two atoms of water in the one formula, and oxalate of
water with two atoms of water in the other. It is to be remembered
that in the case of the sulphates, the double sulphate of copper and
potash was shown to have a similar analogy in constitution to the
bisulphate of potash.
Owalate of Chromium and Potash, of Perozide of Iron and Potash, of
- Peroſcide of Iron and Soda, etc.
tº £ tº ſº e ºs
This group of salts has not hitherto been submitted to analysis,
although they occupy the same important position among the oxalates
which the alums do among the Sulphates.
13. Owalate of Chromium and Potash.
This remarkable salt was first described by Dr. Gregory, and its
optical properties have been made the subject of a memoir by Sir David
Brewster." It is easily prepared by the following process, which is Dr.
Gregory's, with the proportions slightly altered, from a knowledge of the
composition of the salt. One part of bichromate of potash, two parts
binoxalate of potash, and two parts hydrated Oxalic acid, are dissolved
together in hot water. There is a copious evolution of carbonic acid
gas, arising from the deoxidation of the chromic acid, and nothing fixed
remains except the salt in question; of which a pretty concentrated solu-
tion crystallizes upon cooling in prismatic crystals, which are black by
reflected light, but of a splendid blue colour by transmitted light, when
sufficiently thin to be translucent. -
This salt, strongly dried without decomposition, was found to lose 11-67
per cent. of water. -
The oxide of chromium cannot be precipitated from it completely by
means of an alkaline carbonate, and it is very remarkable that only a
small portion of the oxalic acid is thrown down from this salt by .
chloride of calcium. --
To determine the proportion of Oxalic acid, the Salt was heated in
strong sulphuric acid, and the gases allowed to escape through a tube
containing chloride of calcium. 15:19 grains of the crystals lost 6-71
1 Philosophical Transactions, 1835.
376 ON THE CONSTITUTION OF OXALATES, NITRATES,
grains by this treatment, which loss is the weight of the oxalic acid.
Hence this salt contains 44:17 per cent. of oxalic acid.
When this double oxalate is ignited, carbonic oxide escapes, and the
residuary salt is a mixture of chromate and carbonate of potash, which is
entirely soluble in water, and contains no oxide of chromium. In four
experiments the fused residuary salt amounted to 0-5458,05411, 0:5454,
and 0.5425 of the weight of the crystals operated upon, while it should
be 0.5433, provided this residuary salt is a mixture of two atoms
chromate and one atom carbonate of potash, and that the composition
of the crystals is as follows:
One atom oxide of chromium, CrCr, . 1003.6 16:28
Three atoms potash, 3K, e . . . 1769-7 28-70
Six atoms oxalic acid, 6CC, e e {º 2717 '4 44'07
Six atoms water, 6H, * e Q e 67.5° 10-95
6.165-7 100'
The results in regard to the water and oxalic acid narrated above,
agree completely with this view, and so does the determination of the
oxide of chromium. 26.01 grains of the crystals left, when ignited,
14:08 grains of the mixed chromate and carbonate of potash, which
were dissolved in water, and being acidulated with acetic acid, the
chromic acid was precipitated by acetate of lead, and gave 17:45 grains
chromate of lead, equivalent to 4.28 grains oxide of chromium. Hence
by this experiment the crystals contain 16:46 per cent. of oxide of
chromium, which approaches very nearly to the theoretical result. The
fused residuary chromate and carbonate of potash amounted to 0-5425
of the weight of the crystals, which is so near the theoretical result,
namely, 0.5433, that we may safely conclude that the quantity of potash
in the salt agrees with our theoretical estimate.
This salt is clearly, therefore, a compound of one atom oxalate of
chromium, containing three atoms oxygen in the oxide and nine atoms
oxygen in the acid, with three atoms oxalate of potash; and the Salt
has six atoms of water of crystallization. The oxygen in the oxide of
chromium being 1, that in the potash is also 1, that in the water 2, and
that in the Oxalic acid 6.
I made several attempts to crystallize the oxalate of chromium
itself, but without success, so that I had no opportunity of studying its
constitution in relation to the constitution of the preceding double
salt. -
PHOSPHATES, SULPHATES, AND CHLORIDES. 377
14. Owalate of Perovide of Iron and Potash.
This salt, which has not hitherto been described, is formed by dis-
Solving the hydrated peroxide of iron to Saturation in binoxalate of
potash. There is no effervescence, but a sap-green solution results,
which, when concentrated, deposits the Salt in question in tabular
crystals, of which the form has no resemblance to that of the corre-
sponding oxalate of chromium and potash, and which are of a beautiful
grass-green colour. These crystals are permanent in the air, unless it
is very dry, when they lose water by efflorescence and become brown
and opake. The solution of the salt is decomposed by ammonia, and
the peroxide of iron completely thrown down. The salt, when ignited,
leaves peroxide of iron and carbonate of potash. It loses 10:56 per
cent. of water at a temperature not exceeding 230° Fahr., but is par-
tially decomposed at 300°. Below, the theoretical composition of this
Salt is placed in juxtaposition with the results of an analysis.
Theory. Experiment.
One atom peroxide of iron, e 15.93 16:13
Three atoms potash, e e 28-82 29-07
Six atoms oxalic acid, º e 44'25 43°74
Six atoms water, . º e 11:00 10-56
100° 99°50
Hence its composition is the same as that of the preceding salt, iron
being substituted for chromium. -
15. Oaxalate of Peroxide of Iron and Soda.
This salt is formed by dissolving the hydrated peroxide of iron in
binoxalate of soda. It crystallizes in solid green crystals. It is com-
posed as follows, the water being calculated from the loss on the
analysis:
- Theory. Experiment.
One atom peroxide of iron, e 16-32 16-56
Three atoms soda, . e e 19:57 19°66
Six atoms oxalic acid, º & 45°34 45°51
Ten atoms water, . . e 1877 18-27
100. I 00-
Of the ten atoms water which this salt contains it readily loses six
at 212° Fahr., and retains four atoms water at that temperature. It
differs, therefore, in composition, and it does so also in form, from either
of the preceding double oxalates.
378 ON THE CONSTITUTION OF OXALATES, NITRATES,
A corresponding oxalate of chromium and soda was produced by a
similar process, and crystallized with some difficulty in solid dark
crystals, which appeared to have the same form as the preceding Soda-
Salt, and were found, like it, to contain ten atoms of water.
There is also a double oxalate of alumina and potash, which may be
made by dissolving hydrated alumina in binoxalate of potash, and
crystallizes in white tables of a pearly lustre, which have the same
form as the oxalate of iron and potash.
II. OF NITRATES.
I. Hydrated Nitric Acid, the Nitrate of Water.
HNH3.
Nitric acid combines with one atom of water as base, and with three
atoms more by a less powerful affinity. The well-defined character of
the combination containing four atoms water, which is the acid of specific
gravity 1:42, is evinced in its high boiling point and in an appearance
of saturation which it exhibits. The true and complete nitrate of
water has therefore three atoms of constitutional water attached to it.
And in the case of the nitrates of those metallic oxides which corre-
spond with water in their basic character, we find the water of crystalli-
zation likewise to be three atoms, or a multiple of three, and no other
number.
2. Nitrate of Copper.
CuMH*;
and also
•,•
CuINH* + 3H.
There are two nitrates of copper, one of which crystallizes in prisms,
and the other in rhomboidal plates of a lighter blue colour than the
prisms; the first of which I find to contain three and the other six
atoms of water. Both are deliquescent to a certain degree, the salt which
contains the large proportion of water being more so than the other.
(1.) Of the dark blue prisms, 28:12 grains carefully calcined left
8.98 grains black oxide, or 31.94 per cent. In a second experiment,
22.9 grains left 7:34 grains oxide, or 32.05 per cent. The salt being
neutral in composition, the quantity of nitric acid may be inferred from
the oxide of copper, and the difference between their sum and the weight
of the salt operated upon is the water. By the first analysis the water
PHOSPHATES, SULPHATES, AND CHLORIDES. 379
amounts to 3:38, and by the second to 3:28 atomic proportions. The
excess above three atoms is probably hygrometric moisture, to remove
which from this salt we cannot employ the ordinary means. In a third
experiment upon a portion of the same salt, which has been dried over
sulphuric acid till it began to effloresce, 33:19 grains of nitrate left 11:04
grains oxide, which gives 2.83 atomic proportions of water to the salt,
or the result is a little below the three atoms. Hence this nitrate may
safely be supposed to possess three atoms of water.
(2) Of the lighter coloured crystals in plates, 10.60 grains left 278
grains oxide of copper when ignited, or 27.36 per cent. Hence the Salt
is composed of
With six atoms water.
Nitrate of copper, . . 6-57 100° 100'
Water, . º e © 4'03 61°33 57-54
10:6 161.33 157°54
The experimental determination is a little above the theoretical esti-
mate, as might be expected from the deliquescent nature of the salt.
The crystals speedily became opake over sulphuric acid in vacuo,
and 10:6 grains lost 2:18 grains water in a night, retaining 1.85 water;
which is 28°16 water retained to 100 anhydrous salt, or almost exactly
three atoms of water. Hence this salt parts easily with half its water.
The other three atoms of water are retained more strongly; for by a
second day's exposure over sulphuric acid there was an additional loss
of only 0:15 grain water; or the water retained was reduced to 25'87
parts united to 100 anhydrous salt.
3. Submitrate of Copper.
- HNCu°.
It is well known that when the nitrate of copper is heated to the
temperature of 400° or 500 Fahr. it is decomposed, nitric acid and water
being expelled, and a submitrate remaining, which consists of one atom
of nitric acid, one atom of water, and three atoms of oxide of copper.
This decomposition I find to take place and be completed at a very
moderate temperature, not exceeding 150°Fahr. ; and it appears, besides,
that none of the three constitutional atoms of water of the nitrate of
copper can be expelled without a certain corresponding loss of acid : that
on heating the salt in question, nitric acid and water go off together, in
the form of nitrate of water with its three atoms water. Thus, three atoms
of crystallized nitrate of copper, containing three atoms acid, three atoms
oxide, and nine atoms of water, are resolved into two atoms nitrate of
water, each containing one atom acid and four water; and one atom of
380 ON THE CONSTITUTION OF OxALATES, NITRATES,
subnitrate of copper, which contains one atom acid, one water, and three
oxide of copper. - -
Eageriment.—In a stove of which the temperature never exceeded
150°Fahr., 27-54 grains crystallized nitrate of copper, containing three
atoms of water, exposed on a capsule, suffered the following gradual
reduction of weight: a loss of 2:59 grains in one day, of 9-62 in six days,
of 11:1 in seven days, of 13:35 in eleven days, of 13:47 in twelve days,
of 13:58 in sixteen days, of 13.60 in eighteen days, and nothing more
afterwards by a heat of 300° Fahr., continued for several hours. Of the
crystallized nitrate, 27-54 grains have left 13.94 grains subnitrate; or
we have 0:5062 submitrate from 1 nitrate. By calculation the residuary
subnitrate should be 0.5026, with which the experimental result closely
corresponds. * -
Another portion of the same nitrate of copper, dried exactly in the
same way, lost 1 per cent of its weight when afterwards heated to 400°
Fahr. ; and thereafter, being ignited, was found to consist of
Experiment. Theory.
Oxide of copper, . g 100° 100'
Wolatile matter, e iº 53-19 53-1
153-19 153-1
I am satisfied that no other submitrate except the preceding, which
contains three atoms of oxide of copper, can be obtained by the decom-
position of the neutral nitrate by means of heat. For a quantity of the
submitrate of copper of the first experiment narrated above being gradu-
ally exposed in a platinum crucible to a heat above the melting point of
lead, by means of a sand-bath, so as actually to reduce a portion of the
subsalt in contact with the bottom of the crucible to the state of black
oxide, yet the major portion of the subsalt, which still retained its green
colour, was found to be little altered in composition. After this extreme
heating the subsalt consisted of
Oxide of copper, . ſº d 100'
Wolatile matter, w tº tº 50-6
I 50-6
Or the proportion of volatile matter in the subsalt has suffered only a
small reduction, namely, from 53°1 to 50-6 parts. This last submitrate
afforded drops of nitric acid with fumes of nitrous acid when heated in a
tube, so that the submitrate of copper retains water even at a tempera-
ture above the melting point of lead.
The submitrate of copper merits a careful consideration; for
the subsalts of the magnesian class of oxides, which can be had
PHOSPHATES, SULPHATES, AND CHLORIDES. 381
of a definite composition, are really much fewer in number than is
generally supposed. What constitution ought to be assigned to this
salt It will be observed that I have represented it by the singular
formula • . . .
- HNCu”;
implying that the single atom of water which it contains is really the
base of the salt, and that the three atoms of oxide of copper are in the
place of the constitutional water of this nitrate of water. This opens a
new view of the constitution of subsalts. The excess of metallic oxide
which they contain may not be basic at all in certain cases like the
present, but discharge a function in the constitution of the Salt which
has hitherto been recognised only as executed by water. For if we find
water and oxide of copper strongly resembling each other as bases, why
may not the analogy between them extend further, and oxide of copper
be capable of discharging the function of constitutional water or water
of crystallization in the composition of a salt 2 Indeed, the speculation
that all salts whatever are neutral in composition is highly probable.
Where the metallic oxide is in excess, as in what are called subsalts, we
can attribute another function than that of base to the whole or a por-
tion of the metallic oxide, and thus preserve the salt neutral in com—
position, or according to its formula. To this subject I shall again
TěCUIT.
The following observation is particularly favourable to the view
which we are taking of the constitution of submitrate of copper. When
the black oxide of copper is drenched with the strongest nitric acid, it is a
submitrate of copper which is formed, although the nitric acid may be in
great excess. The black oxide is converted into a green powder, from
which the excess of nitric acid should be drained off as well as possible,
and the powder will be found to be in great part insoluble in water. The
explanation seems to be, that the concentrated nitric acid employed
does not contain the constitutional water which the neutral nitrate of
copper requires, and accordingly that salt is not formed; but the nitrate
of water supplies itself with oxide of copper in the place of its deficient
constitutional water ; so that the result is a nitrate of water with three
atoms of oxide of copper attached. But when nitric acid of a specific
gravity not exceeding 1:42 is digested upon the same black oxide of
copper, the neutral nitrate of copper only is formed, and no submitrate.
This view seems likewise to be necessary to account for the great
force with which the single atom of water is retained by the sub-
nitrate of copper. The water cannot be expelled without decom-
posing the salt, notwithstanding the great excess of oxide of copper
present.
38.2 ON THE CONSTITUTION OF OXALATES, NITRATES,
4. Nitrate and Submitrate of Bismuth.
BiNH3
- HNBiº,
The neutral nitrate is admitted to contain three atoms of water, like
the nitrate of copper, and its constitution appears to be similar.
No portion of the constitutional water of this salt can be expelled
without decomposing the salt. Indeed, this salt loses acid by exposure
to dry air at a temperature not exceeding 80° Fahr. The crystals of
the Salt are resolved by a heat of 212° into a solid and fluid portion, the
first of which is probably the submitrate, while the last is hydrated
nitric acid, containing much nitrate of bismuth in solution, and not a
Supernitrate of bismuth. But the fluid portion fixes so readily upon
cooling that the solid product cannot be obtained in a definite state.
Eageriment.—28-61 grains of nitrate of bismuth in good crystals,
being exposed to a gradual ignition, left 14:16 grains of fused oxide of
bismuth. This result accords with the view which is taken above of
the composition of this salt :
Experiment. - Theory.
Oxide of bismuth, º 14°16 100° 100°
Nitric acid and water, 14°45 102'04 102.72
28-61 202'04 202'72
It appears likewise that three atoms of the hydrated nitrate of bis-
muth are resolved, when dried at a high temperature, into two atoms
hydrated nitrate of water and one atom subnitrate of bismuth, which
last is of the same constitution as the submitrate of copper.
Eageriment 1.—Dried on the sand-bath at a temperature above the
melting point of tin, 28-61 grains of nitrate of bismuth lost 9:29 grains,
and retained 5'16 grains of volatile matter, or consisted of
Experiment. Submitrate by theory.
Oxide of bismuth, e 14°16 100° 100°
Volatile matter, º 5'16 36'44 34'24
19:32 136'44 134'24.
Eageriment 2.-A portion of nitrate dried in a stove at a temperature
not exceeding 180° Fahr., till it ceased to lose weight, was thereafter
found to consist of
Oxide of bismuth, º © © 21:24 100°
Wolatile matter, º tº tº 7:57 35-64
28°81 135°64
PHOSPELATES, SULPHATES, AND CHLORIDES. 383
It appears from the second of these experiments that the submitrate
of bismuth may be produced at a temperature so low as 180° Fahr., and
from the first experiment that the submitrate may be exposed to a tem-
perature of 500°Fahr, without decomposition.
Several experiments were made to produce another definite sub-
nitrate, containing a greater proportion of oxide of bismuth, by the
action of heat upon this subnitrate, but without success. The salt was
partially decomposed at various temperatures under redness, but no defi-
nite compound resulted. Hence the submitrate described is probably
the only definite submitrate of bismuth that can exist. The small pearly
crystals obtained on throwing the neutral nitrate of bismuth into a
moderate quantity of water, are of the same composition as the submitrate
obtained by heat.
5. Nitrate of Zinc.
Žns H% + 3H.
This salt is easily obtained by dissolving zinc in nitric acid. It is
very soluble in water, and moderately deliquescent.
Eageriment.—29.17 grains of the crystals ignited, left 7-86 grains
oxide of zinc. In this experiment we have 0-2694 oxide from one salt,
which is very near 0:2713 oxide, the proportion which should be left,
supposing the salt to contain six atoms of water. By efflorescence at
212° one part of this salt loses 0-18 water, which is one-half of the whole
water which the salt is assumed to contain, namely, 0.3639 water. It
loses no acid at 212°. Hence this salt is of the same constitution as the
nitrate of copper, but is not decomposed at So low a temperature. The
proportion of water, however, cannot be reduced below three atoms
without a loss of acid, and there appears to be a submitrate of zinc
resembling the submitrate of copper.
6. Nitrate of Magnesia.
MgSH-4-3H.
Ea'periment.—27-12 grains of crystals of nitrate of magnesia, when
çalcined, left 43 grains caustic magnesia; a result which indicates 6:17
atomic proportions of water in the salt, or the salt contains six atoms of
water.
The nitrate of magnesia stands exposure to a heat which would melt
lead without losing acid. At that high temperature the proportion of
water is reduced to one atom, which cannot be expelled without loss of
38.4 ON THE CONSTITUTION OF OxALATES, NITRATES,
acid. The salt remains in a fused state and transparent, and dissolves
afterwards completely in water.
Baperiment.—18:40 grains of the crystals, containing 7.71 grains
water, lost 6-60 grains by a strong sand-bath heat continued till the salt
ceased to lose weight. This is a loss of exactly five-sixths of the water
contained in the salt.
Ea:periment.—1976 grains, containing 828 water, by similar treat-
ment lost 6-77, which approaches very closely to 6.90 grains, the num-
ber representing five atomic proportions of water.
This single atom of water retained by the nitrate of magnesia, is not
displaced and expelled upon heating the salt, together with an atomic
proportion of nitrate of potash to 600° or 700°Fahr., so that the reten-
tion of an atom of water does not indicate a disposition, upon the part
of nitrate of magnesia, to form a double salt. It is probable that this
peculiar and intimate combination of nitrate of magnesia with one atom
water does not exist in the crystals or ordinary hydrate of nitrate of
magnesia, but is the result of a new arrangement of the constituents of
the salt at a high temperature. There are indications of the existence
of a similar nitrate of water. -
There does not appear to be a submitrate of magnesia like the sub-
nitrate of copper.
Supposed Double Nitrates and Supernitrates.
As double nitrates are said to exist, I have repeatedly attempted to
form them ; but when nitrate of magnesia, nitrate of zinc, or nitrate of
copper was mixed with nitrate of potash or with nitrate of ammonia, the
salts uniformly separated again in crystallizing. There is no proof of
the existence of a single Supernitrate.
Most of the nitrates of oxides not belonging to the magnesian class
are anhydrous salts, such as the nitrates of potash, soda, barytes, stron-
tian, lead, etc., and do not suggest any new subject-matter of inquiry.
III. OF PHOSPHATEs.
In the present state of our knowledge phosphoric acid is quite pecu-
liar in being capable of combining with bases in three different propor-
tions, forming, besides the usual class of salts' containing one atom of
acid to one atom of protoxide as base, two other anormal classes of salts,
in which two or three atoms of base are united to one atom of acid,
namely, the pyrophosphates and the common phosphates. Arsenic acid
forms only one class of salts, but that class is anormal, every member of
it containing three atoms of base to one atom of acid, like the common
PHOSPHATES, SULPHATES, AND CHLORIDES. 385
phosphates. These anormal classes of phosphates and arseniates, with
perhaps the phosphites, are, I believe, the only known salts to which
the ordinary idea of a subsalt is truly applicable; or in the formulae of
these salts only, ought more than one atom of any protoxide to appear
in a basic relation to one atom of acid. All other reputed subsalts are
probably neutral in composition, as I have endeavoured to show in the
case of the submitrate of copper; for to this salt they all bear an analogy
in their small solubility and other properties, while they exhibit little
resemblance to those classes of phosphates and arseniates which really
possess more than one atom of base. The following Table contains the
formulae of the most important phosphates, with a new nomenclature of
these salts, which I offer for consideration.
First Class.
Monobasic phosphate of water (metaphosphate
of water), . e tº e gº wº HF.
Monobasic phosphate of soda (metaphosphate . .
of soda), tº e * & . NaP.
Second Class.
Bibasic phosphate of water (pyrophosphate of . .
water), e ſº tº to e . H*P.
Bibasic phosphate of Soda and water (bipyro- . . .
NaFIP.
phosphate of soda), º tº e
Bibasic phosphate of soda (pyrophosphate of . . *
Soda), tº . . & . Na”P + 10H.
Third Class.
Tribasic phosphate of water (common phos- . .
phate of water), . * : e & . H3P.
Tribasic phosphate of water and soda (biphos- . . . &
phate of soda), . * º gº . NaH"P+ 2H.
Tribasic phosphate of soda and water (phos- . . . *
phate of Soda), . e ſº © . Na”HP+ 24H.
Tribasic phosphate of soda (subphosphate of . . -
Soda), tº * e Q. . Na"P+ 24H.
Tribasic phosphate of soda, ammonia, and . . . . .
water (microcosmic salt), © tº . NaNH4HP + 8H.
Tribasic phosphate of magnesia and water . . . . * *
(phosphate of magnesia), . . º . Mg”HP+ 2H + 12H.
Tribasic phosphate of magnesia and ammonia . . . * *
(ammoniaco-magnesian phosphate), . . Mg”NH*P+ 2H + 10H,
2 B
386 ON THE CONSTITUTION OF OXALATES, NITRATES,
It is my object to get rid of the trivial names pyrophosphates, meta-
phosphates, and common phosphates, which have tended to keep up an
erroneous impression that the phosphoric acid is of a different nature in
these classes of salts, or is modified in some way unknown. This notion
has arisen from the pertinacity with which phosphoric acid continues
combined with a constant number of atoms of base, whether it be
one, two, or three, although the base itself be repeatedly changed by
decomposing the original combination. But this is an occurrence quite
analogous to the formation of different sets of sulphurets or of chlorides,
when we decompose two or more different oxides of the same metal, such
as the oxide and suboxide of mercury, by sulphuretted hydrogen or
by muriatic acid. The metal continues in the same relative state of
Saturation throughout a series of such decompositions; and so does the
phosphoric acid, because in both cases the decomposition is effected by
an equivalent substitution. - -
A difficulty occurs in naming two members of the tribasic class, so
as to distinguish them from each other, namely, the biphosphate of soda
and phosphate of soda, both of which contain soda and water as base.
But this difficulty is obviated by placing first in the name that base of
which two atoms are present. Thus the biphosphate of soda is “the
phosphate of water and soda,” and the phosphate of soda is the phos-
phate of soda and water, both being at the same time characterized as
“tribasic.” - e . . . -- - a'
What I have to add at present in regard to the phosphates relates
chiefly to the last three salts, of which formulae are given in the pre-
ceding Table, which belong to classes of tribasic phosphates that were
not examined in my former paper upon the phosphates." But I may
premise a few observations, which are more strictly supplementary to
the results of that paper.
1. The bibasic phosphate of water (pyrophosphate of water) is pos-
sessed of very considerable stability. Both weak and concentrated
solutions of this salt have been kept for five or six months without any
sensible change or production of the tribasic phosphate of water.
2. It appears to be impossible to crystallize any bibasic phosphate
(pyrophosphate) of potash. Such salts can exist in solution, but not in
the dry state. The same observation applies to the bibasic phosphates of
ammonia, or we have no pyrophosphates of ammonia except in solution.
Indeed, the solution of the bibásic phosphate of water and ammonia
assumes another atom of basic water when the evaporation is carried
far, and crystallizes as the tribasic phosphate of water and ammonia
(biphosphate of ammonia). *. . -
3. In the case of tribasic phosphates containing potash, I have suc-
* Philosophical Transactions, 1833.
PHOSPHATES, SULPHATES, AND CHLORIDEs. 387
ceeded in crystallizing the tribasic phosphate of potash, and the tribasic
phosphate of water and potash, but not the tribasic phosphate of potash
and water, or what would be considered on the old view as the neutral
phosphate of potash.
4. Both the bibasic and tribasic phosphates of water may be treated
with an excess of caustic potash in solution without the formation of
any precipitate or sparingly soluble combination. It is only in the
monobasic phosphate of water that a sparingly soluble combination is
formed by potash, such as that which is described by Dr. Thomson
under the name of diphosphate of potash.
1. Tribasic Phosphate of Soda, Ammonia, and Water.
(Phosphate of Soda and Ammonia : Microcosmic Salt.)
* ~ * NaNH’HP+ 8H.
I have repeated more than once the analysis of this salt, and obtained
the same result as M. Mitscherlich. It appeared to contain 0.5094 of
volatile matter: and there may be derived from an atom of this salt one
atom of phosphoric acid, of soda and of ammonia respectively, and ten
atoms-of water. It has hitherto been viewed as a double phosphate or
combination of phosphate of soda with phosphate of ammonia; but
no reason can be assigned why these particular salts should combine
together, and combinations of salts of Soda and ammonia are exceed-
ingly unusual. The view expressed above in the formula is much more
likely to be true, namely, that this salt is simply a tribasic phosphate, of
which the three atoms of base are all different : they are soda, oxide of
ammonium, and water; and the salt possesses eight atoms of water of
crystallization. By a graduated heat it is possible to expel the water
of crystallization of this salt, and likewise the ammonia of its oxide of
ammonium ; and the water of the last remaining as base, the salt
NaH"P is produced. -
M. Mitscherlich now admits that there is no tribasic phosphate cor-
responding with this, but containing potash instead of oxide of ammo-
nium, a conclusion of which I have ascertained the accuracy.
I endeavoured to form a tribasic phosphate to contain two atoms
soda and one atom of oxide of ammonium, but such a salt appears to
have no existence. For when ammoniacal gas was passed into a strong
and hot solution of the common phosphate of soda, a slight deposition
of the tribasic phosphate of soda took place, followed by the rhomboidal
crystals of the common phosphate unchanged. -
It likewise appears that when the bibasic phosphate of soda and the
388 ON THE CONSTITUTION OF OXALATES, NITRATES,
bibasic phosphate of potash (pyrophosphates) are mixed together, no new
salt is produced; but the former may be crystallized out, and the latter
remains uncrystallizable.
2. Tribasic Phosphates containing Owides of the Magnesian Class.
(1) Tribasic Phosphate of Zinc and Water. (Phosphate of Zinc)
Żnºhi’ + 2#.
This salt, which is nearly insoluble, is obtained in minute silvery
plates, by mixing three ounces of sulphate of magnesia with four ounces
of phosphate of soda, each dissolved in two pounds of cold water. These
crystalline plates consist of
Theory of Żnif H2.É.
Anhydrous salt, . 100' 100°
Water, e • 19-63 17-77
119:63 117.77
Dried above the melting point of tin the crystals still retained a
glistening appearance, but had lost two-thirds of their water; for they
now consisted of
Theory of Žnář.
Anhydrous salt, . 100° 100.
Water, º e 6'08 5°92
106-08 105'92
The two atoms of water which are expelled in the above experi-
ment are, notwithstanding, pretty strongly attached to the salt, being
retained at the boiling point of water. Indeed, these two atoms of
water are highly constitutional, and are found in all the phosphates
of this class. - -
This phosphate fuses at a red heat, after it becomes anhydrous, but
it continues soluble in dilute acids.
(2) Tribasic Arseniate of Magnesia and Water. (Arseniate of Magnesia.)
MgHAs +2H+12H.
This salt precipitated on mixing dilute solutions of 500 grains of
arseniate of soda and 300 grains of sulphate of magnesia. It consisted of
PHOSPHATES, SULPHATES, AND CHLORIDES. 389
Theory of Mºñ&# 14H.
Anhydrous Salt, . 100' 100'
Water, * ſº 86'58 86°25
- 186°58 186°25
This salt contains in all fifteen atoms of water, of which three are
retained and twelve expelled at the boiling point of water. Dried at
212° it consisted of
Theory of Mg-Håstºi.
Anhydrous salt, . 100° 100'
Water, tº e 17.17 17-25
117:17 117:25
It therefore retains pretty strongly two atoms of water besides its basic
atom, resembling the preceding salt in this respect.
This arseniate and the corresponding phosphate are rendered insolu-
ble in dilute acids by the effect of a strong red heat.
(3) Tribasic Phosphate of Magnesia and Water. (Phosphate of Magnesia.)
MgHP+2H + 12H.
This salt appears in distinct prismatic crystals in the course of
twenty-four hours, upon mixing two ounces of sulphate of magnesia with
three ounces phosphate of soda, each dissolved in two pounds of water.
Cold water is capable of dissolving about one thousandth part of its
weight of these crystals. They have been stated erroneously to be much
more soluble. The proportion of water which they contain has hitherto
been stated at fourteen atoms instead of fifteen, which is the truth. By
analysis the crystals were found to consist of -
Theory of MgºńP+14H.
Anhydrous salt, . 100' 100°
Water, ge * 121-7 1 19-76
221-7 21976
I find that the proportion of water retained by this salt is readily
reduced at 212°, from fifteen atoms to seven, by the escape of eight
atoms of water. Of the seven atoms retained one is basic, and there-
fore expelled with difficulty; but from a variety of experiments which I
have performed it appears probable (although I have never attained
very precise results) that the other six atoms go off in pairs at different
temperatures between 212° and 350° Fahr. But even at 410° the
quantity of water retained by this salt was sensibly above one atomic
39 () ON THE CONSTITUTION OF OXALATES, NITRATES,
proportion. We may with considerable probability represent the con-
secutive combinations of this salt with water by such a formula as the
following:
Mg"HP+2H+2H +2H +8H.
Besides the preceding salt there is a tribasic phosphate of magnesia,
which is obtained as an insoluble precipitate on mixing tribasic phos-
phate of soda with sulphate of magnesia. Of this salt the whole three
atoms of base are magnesia, as its name implies. Dried at 212 it retains
five atoms of water. At a red heat it glows, but it continues soluble in
acids even after exposure to a white heat. , But I did not succeed in
forming the other tribasic salt, containing two atoms of water and one
atom of magnesia as bases, which is wanted to complete the series.
Such a salt does not appear to exist. . . . . .
It may be mentioned here in reference to the monobasic phosphate
of magnesia (metaphosphate of magnesia), that although this salt does
not present itself on mixing the monobasic phosphate of soda with the
sulphate of magnesia, yet it is readily precipitated in the form of a soft
viscid body, on using the acetate of magnesia instead of the sulphate. ,
(4.) Tribasic Phosphate of Magnesia and Ammonia. (Ammoniaco-
w ... * magnesian Phosphate.) . . . .
Mg'NH-P4-2H +10H.
This salt is the well-known granular precipitate formed on adding a
salt of magnesia to any soluble tribasic phosphate with which ammonia
or a salt of ammonia has been mixed. I was much interested in ascer-
taining the true constitution of this salt, and have carefully analysed
seven or eight different specimens of it, prepared with and without free
ammonia in the liquors. The result is that only one tribasic salt of
these constituents exists, although two have often been admitted; while
in this compound there exists only one atom of ammonia instead of two,
as M. Riffault has supposed. I subjoin the preparation and analysis of
one specimen of this salt. 350 grains of crystallized phosphate of soda,
100 grains of chloride of ammonium, and 200 grains of aqua ammoniae
were dissolved together in four pounds of cold water, and 200 grains of
crystallized sulphate of magnesia were added to that mixture. The
precipitation was gradual, and the liquor remained alkaline. The pre-
cipitate was slightly washed with cold water, and afterwards dried in
the air for ten days, the thermometer being 65° Fahr, without artificial
heat. The true proportions of water, which this and many other pre-
cipitates affect, have often been mistaken, and definite hydrates not
PHOSPHATES, SULPHATES, AND CHLORIDES. 391.
obtained, from using hot solutions in their preparation. Of this preci-
pitate 26-8 grains lost by ignition 145 grains, or one part of the preci-
pitate contains 0.541 volatile matter. For the ammonia, the volatile
matter from 9'65 grains of the precipitate was sent over quicklime con-
tained in a tube, so as to arrest the water. The loss, or the ammonia,
amounted to 0.67 grain, or to 0-0695 of the precipitate. Hence this
precipitate consists of
t - Theory of *NH3+2H+loń.
Anhydrous salt, . 45'90 45'85
Ammonia, . . . 6'95, 6'98
Water, • * 47: 15 47.17
100. 100'
From the manner in which this specimen of the Salt was prepared,
it should contain the maximum proportion of ammonia of which the
salt admits, and yet that proportion is one atom only, and not two, as it
was estimated by Riffault. A salt of the same composition was obtained
from the same materials, omitting the caustic ammonia. In that case
the product was not so abundant, and the mother liquor remained acid
from the production of tribasic phosphate of water and soda, which has
an acid reaction. When this salt, contained in a little retort, is heated
in a very gradual manner to 212° by means of a water-bath, it is possible
to distil over ten atomic proportions of the water without any ammonia
whatever. Of the three atoms of water which remain (the whole quan-
tity originally present in the salt being thirteen atoms), one appears to
be combined with the ammonia in the formation of oxide of ammonium,
while the other two are the constitutional water of the tribasic phos-
phate of magnesia and water.
It appears, then, that this salt is not a double phosphate, or combi-
nation of two phosphates, but that it is formed from the tribasic phos-
phate of magnesia and water, by the substitution of oxide of ammonium
for the basic water of that salt; and it is a tribasic phosphate of mag-
nesia and oxide of ammonium. The oxygen in the magnesia is double
that in the oxide of ammonium. - -
This Salt is the type of a class of tribasic phosphates, in which the
magnesia is replaced by the other oxides, which are isomorphous with
that base. Two of these salts were discovered and carefully examined
by Dr. Otto of Brunswick."
Dr. Otto's analysis of what we may call the tribasic arseniate of
manganese and ammonia corresponds exactly with the analysis given
above of the magnesian salt, except that he derives only twelve instead
of thirteen atoms of water from his salt. The deficiency in the propor-
1 Journal für Praktische Chemie, von Erdman und Schweigger-Seidel, 1834, p. 409.
392 ON THE CONSTITUTION OF OXALATES, NITRATES,
tion of water found by him, I attribute to the use which he made of hot
water in washing his salt.
His analysis of the tribasic phosphate of the protoxide of iron and
ammonia is particularly interesting, as it proves that this salt is preci-
pitated, containing no more than three atoms of water, or exactly of the
composition of the magnesian salt dried at 212°, as we have described.
The constitution of this salt of iron I would therefore represent by the
formula
Fe’NH4F +2H.
In the same paper Dr. Otto describes another extraordinary phos-
phate, under the name of paraphosphate of soda, ammonia, and oxide of
manganese, which does not belong to any class of phosphates that I
have examined, but may possibly be a combination of two bibasic phos-
phates. Its constituents are 2.É. 2Mn, NH' and 6H. It is prepared
from bibasic phosphates, and would be said in the old language to con-
tain pyrophosphoric acid.
IV. OF SULPHATES.
In a former paper upon water as a constituent of sulphates.' I
examined particularly the constitution of hydrated sulphuric acid and
of the Sulphates of the magnesian class of oxides. All these salts contain
one atom of constitutional water, which is displaced in the formation of
the double Sulphates by an atom of an alkaline sulphate. This view is
illustrated by the following formulae:
Sulphate of water (acid of sp. gr. 1-78), . . HSH
Sulphate of magnesia, . * & te MgSH +6H
Sulphate of magnesia and potash, . tº MgSOKs) +6H
Sulphate of water and potash (bisulphate of . . . .
potash), . * e & & . HS(KS).
It will be found upon experiment that the salts Sulphate of mag-
nesia and sulphate of zinc become anhydrous at much lower temperatures
when mixed with Sulphate of potash than by themselves, the sulphate
of potash displacing the constitutional water of the other salt at a very
moderate heat, although the salts are mixed in the state of dry powders.
* Edinburgh Transactions, vol. xiii. p. 297; or London and Edinburgh Philosophical
Magazine, 3d series, vol. vi. pp. 327, 417.
PHOSPHATES, SULPHATES, AND CHLORIDES. 393
In that paper the opinion was supported, originally suggested I
believe by M. Mitscherlich, that the bisulphate of potash is a double
sulphate of water and potash, and therefore really neutral in composi-
tion. The only difficulty which stood in the way of generalizing this
result, and maintaining that all the salts usually considered as bisalts
are really neutral in composition, was the composition of the bichromate
or red chromate of potash, a salt which unquestionably is anhydrous.
Here, it might be said, is a true bisalt. But M. H. Rose has lately
published some observations in regard to anhydrous sulphuric acid,
which, I think, afford a clew to the discovery of the true constitution of
the red chromate of potash. It appears that the vapour of anhydrous
sulphuric acid is absorbed by sulphate of potash and by chloride of
potassium, without decomposition, and definite compounds formed;
which, however, are destroyed by solution in water. Here we appear
to have a class of combinations of sulphuric acid with salts. Chromic
acid, which is isomorphous with sulphuric, forms combinations which I
consider as analogous to these. With the neutral or yellow chromate
of potash it forms the red chromate of potash, and with chloride of
potassium it forms M. Peligot's salt; which differ only from M. Rose's
corresponding combinations of sulphuric acid, in being more permanent.
The Superior stability of these chromic acid combinations unquestion-
ably depends upon the little affinity for water which their acid possesses,
while the affinity of sulphuric acid for water is very great. Hence we
may suppose that the red chromate of potash is not a direct combination
of two atoms of chromic acid with one atom of potash, but a combination
of one atom of chromic acid with one atom of yellow chromate of potash;
and it may be represented as follows:
(KCr)Cr.
The red chromate of potash will thus belong to a new order of com-
binations, differing essentially from proper salts, which contain an oxide
as base. This salt, therefore, cannot be adduced as militating against
the law that “all salts are neutral in composition;” the only known
exceptions to which law are, I believe, afforded by the anormal classes
of phosphates, phosphites, and arseniates.
I have devoted much time to the examination of subsulphates of the
magnesian class of oxides, particularly of the subsulphate of zinc and the
subsulphate of copper. These salts were generally formed by the partial
precipitation of sulphate of zinc or sulphate of copper by means of caustic
potash. They have both a disposition to carry down sulphate of potash,
which is never entirely removed from them by washing; while one of
them, the subsulphate of zinc, is itself decomposed by washing. When
most successfully prepared, they were found to contain four atoms of
304 ON THE CONSTITUTION OF OXALATES, NITRATES,
metallic oxide to one atom of acid (instead of three atoms oxide, as M.
Berzelius supposed), together with four atoms of water. I have not
hitherto been able to form a distinct idea of their constitution, or to
decide between different views which may be taken of it. But the force.
with which water is retained in these subsalts is very remarkable. The
subsulphate of copper loses no portion of its four atoms of water at.
212°, and I have not been able to reduce the quantity of water retained
by this salt so low as one atomic proportion, even at the melting point
of lead. -
The constitution of the subsulphate of copper appears to be changed
when it is made anhydrous by heat. In the progress of the desiccation
of the salt, its colour passes from a dull blue to an olive green, and it.
finally becomes of a chocolate brown, and is then anhydrous. Water
poured upon the brown matter comes off of a blue colour, dissolving out
a considerable portion of the soluble sulphate of copper. It appears,
therefore, that the water originally present in the subsulphate must
discharge some important function in its constitution, the subsalt being
obviously decomposed when made anhydrous.
The Alums form a most important class of the sulphates, but I have
never had it in my power to compare their constitution with that of the
sulphate of alumina itself, which is not easily obtained in a crystallized
state. The salt, however, is described as containing eighteen atoms of
water, while the alums have twenty-four. At present I would merely
throw out the conjecture, that in the alums we may have simply an
alkaline sulphate with the sulphate of alumina attached, that salt carrying
along with it its whole water of crystallization, and acquiring six atoms
more. The quantity of water in potash alum may be reduced by efflor-
escence to six atoms in a stove of the temperature of 150°Fahr. Hence
potash alum may perhaps be represented as follows:
KS--(AIAIS 4-6H +18H).
I have shown by an analysis conducted in very favourable circum-
stances, that soda-alum contains, like potash-alum, twenty-four, and not
twenty-six atoms of water. s
V. OF CHLORIDES.
The affinity which the hydracids exhibit for water is weak. Of the
lower hydrates of muriatic acid we know nothing, the volatility of the
acid putting it out of our power to form and examine such hydrates; but
it is likely that they will correspond with the hydrates of the chloride of
magnesium, etc., which can be examined.
PHOSPHATES, SULPHATES, AND CHLORIDES. 395
The law in the case of the chlorides of the magnesian class of metals
appears to be, that they have two atoms of water pretty strongly attached
to them, and which we may consider as constitutional. Thus chloride
of copper crystallizes with two atoms of water, and with no lower pro-
portion; but several chlorides of this class have two or four atoms more,
the proportion of water advancing by a multiple of two atoms.
1. Chloride of Copper.
CuCIH’.
The blue prismatic crystals of chloride of copper become brown and
lose the greater proportion of their water at a temperature not exceeding
the boiling point of water. Fifteen grains of the crystals, exposed to a
much higher temperature, lost 3:23 grains of water, leaving 1177 grains
of chloride of copper; and when this quantity of chloride of copper was
exposed to the atmosphere, it quickly recovered 3:16 grains of water,
and resumed the blue colour of the crystallized salt. I believe this
method of reabsorption; in the case of constitutional water, often to give
hydrates of which the composition is even more exact than if they had
been obtained from solution, owing to the absence of that water, which
is often mechanically interposed between the plates of crystals. The
hydrated chloride of copper obtained in this way consisted of 4.
- - Theory of CuClàº.
Chloride of copper, . 11-77, 100' 100'
Water, . º e 3'16 26'85 26'84
1493 12685 126.84
2. Chloride of Manganese.
MnOIH’ + 2H.
Eageriment.—Of the flesh-coloured crystals, 15:53 grains, precipitated
by nitrate of silver, gave 22:57 grains of chloride of silver, equivalent to
5-56 chlorine, or to 9-92 chloride of manganese, which leaves 5-61 grains
water in the salt, or 36'12 per cent. of water. Now a chloride of man-
ganese with four atoms of water would contain 36:33 per cent. of water.
This salt readily lost half its water when dried at 212° in open air,
or when dried over Sulphuric acid in the vacuum of an air-pump at the
ordinary temperature. But when the exposure of the salt in such cir-
cumstances was long protracted, a little of the constitutional water also
was lost. -
396 ON THE CONSTITUTION OF OXALATES, NITRATES,
3. Protochloride of Iron.
FeCIH” + 2#.
In three experiments made upon different specimens of crystallized
protochloride of iron, all newly and very carefully prepared, 1369 grains
chloride of silver were precipitated from 9:72 salt, 17:20 chloride of
silver from 12:44 salt, and 15.75 chloride of silver from 11:21 salt.
These experiments almost coincide in their results, which are, that 1
part of the salt contains 0.3466, 0.3463, and 0.3461 of chlorine. But
such proportions of chlorine are decidedly under the proportion which a
neutral salt with four atoms of water should contain, namely, 0.3593
chlorine. Indeed, the quantity of water in the salt is indicated by
these experiments to be four and a half atomic proportions almost
exactly. By crystallizing from an acid solution Bonsdorff has lately
obtained this Salt in a state of purity, and containing four atoms of
Water.
4. Chloride of Magnesium.
MgClfiº 4-4H.
Of the crystals of this salt, which are decidedly deliquescent, 12.65
grains were found to contain 429 chlorine; or the salt contains 33-91
per cent of chlorine, which approaches sufficiently near to the theoreti-
cal proportion 34-69 per cent, Supposing the salt to contain six atoms
of water.
5. Chloride of Calcium.
CaCIHº + 4H.
The crystals of this deliquescent salt, dried in vacuo till they began
to effloresce, were found to contain six atoms of water, the proportion
usually allotted to them; but it is remarkable, that, continued in vacuo
over sulphuric acid for ten days during the heat of summer, the crystals
became opake and of a talky lustre, without being disintegrated, and
their proportion of water was reduced to two atoms.
6. Double Chloride of Copper and Ammonium.
NHC14-CuCIH’.
Hydrated chloride of copper dissolved with chloride of ammonium,
in the proportion of eleven of the first to seven of the last, readily affords
PHOSPHATES, SULPHATES, AND CHLORIDES. 397
a double salt, in which we appear to have an atom of chloride of ammo-
nium with an atom of the hydrated chloride of copper attached. This
double Salt is less soluble than the chloride of copper itself, and retains
more strongly the two constitutional atoms of water of that salt; illus-
trating in both of these points what appear to be two very general occur-
rences: namely, 1st, the reduced solubility of double salts; and, 2d, the
closer attachment which constitutional water exhibits for a salt when
that Salt itself enters into combination.
Analysis. Theory of NH4C1+CuCIHº.
Chlorine, . s e 51*03 51*08
Copper, . te wº 23:35 22-83
Ammonium (NH4), . 13:20 13:10
Water, . º g 12-09 12-99
100 67 100'
The water cannot be entirely expelled without risking the sublimation
of chloride of ammonium, and hence the quantity of water obtained is
under the truth. The copper is above the truth, from having been
precipitated by caustic potash in the state of oxide, which last when so
obtained always retains a little potash.
There is a corresponding chloride of copper and potassium, but I
did not succeed in forming analogous double salts with chloride of
magnesium or with any other chloride of the class in the place of the
chloride of copper.
The chlorides have probably their analogues in the cyanides, but
with the single cyanides of iron, copper, etc., we are less acquainted.
It is worthy of remark, however, that the disposition of the protocyanide
of iron and of the cyanide of copper to combine with two atoms of
cyanide of potassium may depend upon the cyanides of iron and of
copper possessing two atoms of constitutional water (like the corre-
sponding chlorides), which are displaced by two atoms of the alkaline
cyanide in the formation of the double cyanides. In “ferrocyanic acid.”
we have the protocyanide of iron combined with two atoms of hydro-
cyanic acid, in the place of the same two atoms of water.
39S ON THE THEORY OF THE VOLTAIC CIRCLE.
VIII.
ON THE THEORY OF THE VOLTAIC CIRCLE.
From Brit. Assoc. Report, 1839 (Pt. ii.), pp. 29-31.
PROFESSOR GRAHAM explained the views now received of the propa-
gation of electrical induction through the fluid and solid elements of the
voltaic circle, by the formation of chains of polar molecules, each of
which has a positive and negative side, and in which no circulation of
the electricities is supposed, but merely their displacement and separa-
tion from each other in each polar molecule. These electricities in the
polar molecule of hydrochloric acid, for instance, are displaced, when
the acid acts as an exciting fluid, and the positive electricity is located
in the chlorine atom, and the negative electricity in the hydrogen atom.
The electricities are, at the same time, made the depositories of the
chemical affinities of the chlorine and hydrogen respectively. Mr.
Graham proposed to modify this hypothesis so far as to abandon the
idea of electricities being actually possessed by these bodies, and to refer
the phenomena at once to the proper chemical affinities of the bodies.
He assigned similarly polar molecules to the exciting fluid and metals;
and taking hydrochloric acid as a type of exciting fluids, he gave to
each molecule a pole, having an affinity resembling that of chlorine, or
chlorous affinity, instead of negative electricity, and another pole, having
an affinity resembling that of zinc or hydrogen, or zincous affinity, instead
of positive electricity. When zinc and acid are in contact, the polar
state of a single chain of molecules might be represented as in the figure.
#G)@@@@@@@@@@@)
The particle of acid B, next the zinc, has its chlorine atom in contact
with the metal and its hydrogen atom distant from it, marked respec-
tively cl and 2 in the figure. Part of the affinity of cl being engaged by
the zinc, the hydrogen is so far received from that affinity, and thus
attracts the cl of C. Thus, by a sort of induction, the 2 of B causes the
cl of C to be chlorous, or the molecule of acid C to become polar, and
that again the molecule D. In the zinc (the molecule being supposed
to contain two chemical atoms), while the external atom of A becomes
zincous, from its contact with the acid, the other atom becomes chlorous;
so that these atoms of this molecule may be marked cl and 2, and so also
the molecules E and I of the zinc, which become polar by induction.
ON THE THEORY OF THE VOLTAIC CIRCLE. 399
In another diagram Professor Graham showed how this chemico-
polar condition is propagated round a voltaic circle. The molecules of
the zinc and acid being polar by contact, which is sufficient to develop
their affinities, an induction one way through the zinc, and in the opposite
direction through the acid, conspire to produce the same polar condition
in the molecules. The result is, that the molecule 2 of A is zincous both
primarily and by induction, and its affinity for the atom cl of B greatly
increased; and, consequently, combination can take place between these
atoms when the circuit is completed, but not otherwise.
! If the connecting wire be broken, and a decomposable liquid, such
as hydriodic acid, be interposed between the extremities, a chain of polar
molecules comes also to be established in that liquid, the iodine (which
is the analogue of chlorine) being the seat of the chlorous affinity, and
the hydrogen the seat of the zincous affinity. The extremity of the
wire connected with the copper plate is zincous, or has zincous affinity,
and consequently attracts the iodine which appears there, when decom-
position occurs. The extremity of the wire connected with the copper
plate is chlorous, or has the affinity of chlorine; and consequently, the
hydrogen of the hydriodic acid is eliminated there when decomposition
occurs. These poles in the decomposing cell of the voltaic circle have,
from their importance, always received peculiar appellations, which,
with two other terms, Mr. Graham changes as follows:—
Chlorous = Negative.
Zincous = Positive.
Chloroid =The negative pole, the cathode, the platinode.
Zincoid = The positive pole, the anode, the zincode.
Mr. Graham afterwards endeavoured to show, that electrolytes were
bodies which, like hydrochloric acid, possessed a salt radical and basyle
element, which might be the seat of the chlorous and zincous affinities,
and which might, indeed, be called the chlorous and zincous elements
of the electrolyte; so that the same view was applicable to electrolytes
in general."
* Mr. Graham has since developed his views more fully in the Third Part of his
Elements of Chemistry, pp. 197-241.
400 ON THE CONSTITUTION OF SULPHATES AS II.LUSTRATED
IX.
ON THE CONSTITUTION OF THE SULPHATES AS ILLUS-
TRATED BY LATE THERMOMETRICAL RESEARCHES.”
From Chem. Soc. Mem. i. 1841-43, pp. 82-84. [Phil. Mag. xx. 1842, pp. 539-541.]
PROF. HESS and Dr. Andrews both apply the results of their late
inquiries respecting the heat evolved in combination” to test the
accuracy of a view of the constitution of double and acid salts which
was published by myself, and arrive, it is remarkable, at opposite
conclusions.
The view in question, I may first state, taking the example of double
and acid sulphates. Crystallized sulphate of magnesia, and the double
sulphate of magnesia and potash, I have represented thus:–
MgO, SO,(HO) + 6 HO,
MgO, SO,(KO, SO)+ 6 HO:
considering the latter salt to be derived from the former, by the substi-
tution of sulphate of potash for that single atom of water, which is found.
to be much more strongly attached to the sulphate of magnesia than the
other six. This atom of water, which is not basic water, was formerly
named Saline water, to indicate that it is replaceable by a salt; its
presence being considered a provision in sulphate of magnesia for the
formation of double salts. The water and sulphate of potash are there-
fore looked upon as equivalent in the construction of the two salts; and
the substitution of the salt for the water might therefore be reasonably
expected to occur without the evolution of heat.
In accordance with that statement, Dr. Andrews finds that no heat
is evolved on mixing Solutions of sulphates of magnesia and potash, nor
in the formation of any other double salt. On repeating the experi-
ment I found also no heat nor change of temperature on mixing the
solutions, although a change of goth of a degree Fahr. would have been
distinctly indicated by my thermometer.
Possibly, however, the double salt may not immediately be formed,
and hence no change of temperature at the moment of mixing the two
solutions, nor for Some time afterwards. To meet this objection, solu-
tions of sulphate of magnesia and of sulphate of ammonia (the last, from
its greater solubility, being preferred to sulphate of potash) were made
of such a strength that they might be mixed without the precipitation
1 Read January 18, 1842. * Phil. Mag. Jan. 1842.
BY LATE THERMOMETRICAL RESEARCHES. 401
of the double salt immediately occurring, but strong enough to allow
a large quantity of the double salt to fall upon stirring the liquid
strongly. The solutions were 154688 grains of cr. sulphate of mag-
nesia dissolved in so much water as to form 8000 water grain measures,
and 613.5 grains oil of vitriol, neutralized with ammonia and made up
to 4000 water grain measures. On mixing one ounce measure of the
first with half an ounce measure of the second, both exactly at 50°, not
the Smallest change of temperature could be observed; but as soon as
the double salt began to deposit, the temperature rose, and on stirring
strongly much salt was deposited, and the temperature rose 5’-40 Fahr.
On re-dissolving this salt, however, by substituting for the mother-liquor
an equal bulk of water, the temperature instantly fell 5°85. Hence
the heat which first appeared was produced by the solidification of the
double salt, and disappears upon its liquefaction. There is no heat
referable to combination of the two salts. The cold on dissolving was
always somewhat greater than the heat on precipitating the double salt,
in repetitions of this experiment, chiefly, I believe, from the slowness of
the precipitation, which requires a minute or two, so that a portion of
the heat is lost from contact with the atmosphere, and the whole not
observed, while the subsequent solution of the salt being almost instan-
taneous, the whole fall of temperature is observed. The same experiment
was made with a solution of sulphate of zinc, of the same strength as the
Sulphate of magnesia, and with similar results, only that the fall of
temperature, on solution, was somewhat less than that on solidification,
namely, as 9°22 to 9°67, difference 0°45 Fahr. This was principally
owing to the time required in re-dissolving this double salt being greater
than that occupied in precipitating it, three applications of water being
required to re-dissolve the double salt completely, owing to its sparing
solubility.
M. Hess's objection is made to the analogous constitution which I
have assigned to the bisulphate of potash :-
Sulphuric acid of specific gravity, 178, . HO, SO,(HO).
Bisulphate of potash, . tº tº tº HO, SO,(KO, SO).
He maintains that heat is evolved in the formation of a bisulphate, and
therefore that the combination is not effected by the equivalent substi-
tution supposed. He mixed sulphate of potash with HO, SO3 + HO,
and found heat evolved, but allows that the result here is fallacious, a
portion only of the sulphuric acid being converted into bisulphate, while
the other portion is diluted by the displaced water of the first portion,
and thus heat evolved.
On performing the direct experiment, which M. Hess appears to
have neglected, using a saturated solution of sulphate of ammonia, and
2 C
402 EXPERIMENTS ON THE HEAT
sulphuric acid of specific gravity 1.256, I obtained, on mixing 5*4 of cold
instead of any heat. But on diluting the sulphate of ammonia with a
volume of water equal to that of the dilute acid, a fall of 1*12 occurred.
Deducting this from the former, there remains a fall of 3°88 due to the
combination of the two salts, sulphate of water with sulphate of ammonia.
But this may be explained. The bisulphate of ammonia formed is an
anhydrous salt, unlike the double sulphate of magnesia and ammonia,
which carries along with it all the water of crystallization of the sul-
phate of magnesia. But the sulphate of water itself, as it exists in
diluted sulphuric acid, is a largely hydrated salt, like sulphate of magnesia.
The water of the former, on being set free in the last experiment, absorbs
heat, because heat was evolved originally in the combining of this Water
with the sulphuric acid.
Although certain small corrections on these experiments for changes
in capacity for heat of the liquids have been neglected, yet they are
sufficient to demonstrate that no heat is evolved in the formation of
double sulphates, and also, as appears by the last experiment, that these
compounds are formed at once on mixing the solutions of their consti-
tuent salts, whether precipitation occurs or not. Sulphate of potash and
water are therefore equivalent in the constitution of such salts, or equi-
calorous, if a term may be coined to express this relation.
X.
EXPERIMENTS ON THE HEAT DISENGAGED IN
COMBINATIONS."
From Chem. Soc. Mem. i. 1841-43, pp. 106-126; ii. 1843-45, pp. 51-70. [Annal. de
Chemie, viii. 1843, pp. 151-180; xiii. 1845, pp. 188-216; Erdm. Journ. Prak.
Chem. xxx. 1843, pp. 152-183; Phil. Mag. xxii. 1843, pp. 329-352; xxiv. 1844,
pp. 401-420.]
PART I.
THE observations, of which an account shall be given in the present
paper, are exclusively confined to the heat disengaged in combinations
formed in the humid way. The heat disengaged in such combinations
is in general easily collected and measured, as it is immediately com-
municated to a mass of fluid, of which the temperature may be observed
with accuracy. The elevation of temperature in an experiment may
* Read November 1, 1842.
DISENGAGED IN COMBINATIONS. 403
often, however, be greatly affected by incidental circumstances; such as
the liquefaction of the product of the combination, arising from its solu-
tion in the water, or other menstruum employed; or the hydration of
the compound formed, which so generally occurs with a salt formed by
uniting an acid and base; and can rarely, therefore, be taken as the
expression of the heat disengaged from the combination without con-
siderable correction.
Thus in a few preliminary experiments to ascertain whether, as has
been anticipated, different bases of the same class evolve equal quantities
of heat on combining with the same acid, it was found that equivalents
of oxides of copper and zinc, and the equivalent of magnesia on dissolv-
ing in highly diluted sulphuric acid, evolved respectively 4”20, 5*18,
and 11°70. But the sulphates formed are all hydrated salts, and a large
portion of the heat was found to be due to the combination of this water,
namely 3°49 in the sulphate of copper, 3°-90 in the sulphate of zinc,
and 4*12 in the sulphate of magnesia. Again, the salts are obtained
in solution; now the liquefaction or solution of salts is attended with
the absorption of a certain quantity of heat or fall of temperature, namely
by a fall of 0°-66 in the hydrated sulphate of copper, 0°-93 in the hydrated
sulphate of zinc, and 0°83 in the hydrated sulphate of magnesia. The
last quantities being added to the heat first observed in the solution of
the oxides, and the preceding quantities being subtracted from the same
heat first observed, we obtain as the corrected determinations of the heat
evolved from the combination with sulphuric acid of the oxides enume-
rated (or rather from the substitution of these metallic oxides for the
basic water of the sulphate of water), by oxide of copper 1°37, by oxide
of zinc 2°21, by magnesia 8°41; quantities which, so far from being
equal, are nearly in the ratio of the numbers 2, 3, and 12. It is obvious,
therefore, that experiments to determine both the heat absorbed in the
Solution of salts, and that evolved in their hydration, must precede
inquiries respecting the heat disengaged in the formation of the salts
themselves by the combination of their essential constituents, when the
salts are formed in the humid way.
The apparatus employed consisted of a delicate thermometer of small
bulb, namely, that used in the wet-bulb hygrometer, as prepared by
Greiner of Berlin. Every degree was divided into five parts, each part
again was divisible by the eye into five parts, so that observations were
made to ºth of a degree. The degree is that of Réaumur's scale. After
trying glass jars and various other vessels, it was found that nothing
answered better than a large platinum crucible, which weighed 1201.9
grains, and was capable of containing 5 ounces of water. The thermo-
meter and crucible, with a hollow cylinder of palladium, weighing 207:6
grains, employed as a stirrer, were all the apparatus necessary. Of the
404 EXPERIMENTS ON THE HEAT
Salt or other substance experimented upon, a quantity corresponding
with its atomic weight, and representing a single equivalent, was always
used; and the quantity of water was constant, namely 1000 grains, and
relatively large, so as to render the change of the specific heat of the
fluid insensible.
The water, crucible, stirrer, and thermometer, being the same in all
the experiments, the results are strictly comparable. The numbers
express the relative quantities of heat disengaged from atomic equiva-
lents of the bodies,
I. HYDRATION OF OIL OF WITRIOL.
1. HO, SOs. The protohydrate of sulphuric acid employed was pure,
and of density 1848. The quantity used of this and other substances
was always one-twentieth of the number expressing the equivalent taken
in grains; that is 30.68 grains of oil of vitriol, the equivalent of the
protohydrate being 613:5. It was weighed in an exceedingly thin and
light glass spherule, which was afterwards broken in the water, and the
acid diffused through the latter. The greater portion of the heat is
disengaged in the first two or three seconds after mixture, or its evolu-
tion is almost instantaneous. To avoid the loss of heat by communication
to the air, during the short time that must elapse before the thermo-
meter in the liquid becomes stationary, the crucible, water, and stirrer
were previously cooled down so far below the temperature of the air, as
the liquid was expected, from a preliminary experiment, to rise on the
addition of the acid. The crucible was also placed within a glass jar
containing tow, to impede the passage of heat by conduction. I am
indebted for several valuable hints on the mode of conducting such
experiments, to the papers of Dr. Andrews and Professor Hess, who
have preceded me in similar investigations.
The rise of temperature in a preliminary experiment, in which the
water and crucible were not previously cooled, was 3°78 R. In two
other experiments in which the crucible and water were previously
cooled before the addition of the acid, the rise was 3°88 and 3°-85. The
mean of the last results, or 3°86, may therefore be taken as the heat
disengaged in the hydration of an equivalent of the protohydrate of
sulphuric acid. No perceptible change of temperature occurred on
diluting further with water the products of these experiments.
2. HO, SO3 + HO. This is the crystallizable hydrate of sulphuric
acid, of density 1-78. 36.3 grains, the equivalent quantity, were mixed
with 1000 grains of water, as in the preceding case. The rise of tem-
perature in three experiments was 2°40, 2’-36 and 2°40; of which the
mean is 2°39.
DISENGAGED IN COMEINATIONS. 405
The dilution of this hydrate gives occasion to the disengagement of
1°47 less heat than the preceding hydrate. It appears, therefore, that
in the dilution of the first hydrate or of sulphate of water, 1°47 is due
to the combination of the first atom of water, with which it forms the
crystallizable hydrate, and 2°39 to combination with all the rest, making
togther 3°-86.
3. HO, SO3 + 2 HO. This is the hydrate of sulphuric acid in the
formation of which the greatest contraction is observed to occur. With
41.93 grains, or one equivalent, the rise of temperature on dilution was
in three experiments conducted as before, 1°88, 1°86, and 1°85, of which
the mean is 1°86. The difference between the heat evolved by the
present and the immediately preceding hydrate is 0°-53, which is there-
fore the heat evolved by the addition of the second atom of water to the
sulphate of water. It is scarcely one-third of 1°47, the quantity evolved
by the first atom.
4. HO, SO3 + 3 HO. With 47-55 grains, or one equivalent of this
hydrate, the rise by dilution was in three experiments 1°31, 1°31, and
1°27, of which the mean is 1°30. The difference between the heat
evolved by this and the preceding hydrate is 0°-56, which is therefore
the heat evolved by the addition of the third atom of water to the
sulphate of water. Now the second atom evolved 0°-53, so that the
second and the third atoms of water appear to evolve sensibly the same
Quantity of heat. This curious result favours the conclusion that the
Second and third atoms of water go together; or that the hydration of
the Sulphate of water here advances by two atoms at a time, and that
no intermediate hydrate exists, in a state of solution at least, between
HO, SO3 + HO and HO, SO3 + 3HO. The last may be represented as
HO, SOA, HO + 2 HO.
5. HO, SO3 + 4 HO. With 53.18 grains, or one equivalent of this
hydrate, the rise of temperature on dilution was 1*05, 1°07, and 1°05;
mean 1°06. The difference between this and the preceding hydrate,
namely, 0°24, is therefore the heat evolved by the combination of the
fourth atom of water with sulphate of water.
6. HO, SO3 + 5 HO. With 58.8 grains, or one equivalent of this
hydrate, the rise of temperature on dilution was 0°-88, 0°-88, and 0°-85;
mean 0°87. The heat from the combination of the fifth atom of water
is 0°19. It is not impossible that the heat evolved from the fifth is the
same in quantity as that evolved from the fourth atom of water, and that
these two atoms go together like the second and third. The present
hydrate of sulphate of water corresponds with crystallized sulphate of
Copper.
7. HO, SO3 + 7 HO. With 70.05 grains, or one equivalent, the rise
was 0°-68, 0°71, and 0°-65; mean 0°-68. The difference between the
406 EXPERIMENTS ON THE HEAT
effect of this and the preceding hydrate is 0°-19, which is therefore the
heat evolved by the combination of the last two atoms of water, namely
the sixth and seventh atoms. This hydrate of sulphate of water corre-
sponds with crystallized sulphate of magnesia.
By the continued hydration of the sulphate of water, the quantities
of heat evolved are therefore as follows:–
Heat evolved. Hydrate formed.
By first atom of water, e . 1°47...HO, SOs–H HO.
By second and third atoms together, 1°09...HO, SO3 + 3 H.O.
By fourth and fifth atoms together, . 0°43...HO, SOA-5 HO.
By sixth and seventh atoms together, 0°-19...HO, SO3 +7 HO.
By an additional excess of water, . 0°-68...HO, SO3 + 7 HO + æHO.
It will be observed that the heat evolved by the first atom is sensibly
the same as that evolved by the four following atoms, the quantities
being 1°47 and 1°52; the difference between these numbers being
within the limits of errors of observation. The same conclusion is
drawn from his experiments on the hydration of oil of vitriol by Pro-
fessor Hess. Supposing the whole heat disengaged in the hydration of
sulphate of water to be divided into 23 parts, 9 are evolved by the first
atom of water, 9 by the next four atoms, 1 by the following two atoms,
and 4 by the remaining excess.
Although the experiments detailed above agree with those of M.
Hess in bringing out one curious result, they yet differ from them to an
extent which it is difficult to account for in other respects. Thus re-
ducing my results to the same scale as those of M. Hess, the comparison,
is as follows. In the hydration of the sulphate of water,
Hess. Graham.
Heat from the first atom of water, 2 2.
35 second atom of water, I 0.72
55 next three atoms of water, . l 1:35
55 additional excess of water, I 1:18
5 5’25
8. HO, SOA, HO + 10 HO. An equivalent quantity of this hydrate,
or 92.55 grains, was mixed with 969.3 grains of water, the quantity of
the latter being diminished so as to make up 1000 grains with the
water already in the acid hydrate. The rise of temperature in two
experiments was 0°37 and 0°41, of which the mean is 0°-39. This
hydrate contains four atoms more of water than the last operated upon,
and disengages 0°29 less heat. The heat, therefore, due to the combi-
nation of the additional four atoms of water is 0°:29.
9. HO, SOA, HO + 14 HO. Of this hydrate the equivalent, or 115.05
DISENGAGED IN COMBINATIONS. 407
grains, was mixed with 915-6 grains of water, and occasioned a rise of
temperature in two experiments of 0°:23 and 0°:20, of which the last
was believed to be the most trustworthy result. Hence the four atoms
of water last added evolve 0°-09, or about one-third of the quantity
evolved by the preceding four atoms of water.
10. HO, SOA, HO + 24 HO. The equivalent of this hydrate, or 1713
grains, was mixed with 859'4 grains of water, and produced in one ex-
periment a rise of 0°-15. The hydrate was kept for three days before
it was diluted in the experiment; for immediately after its preparation
the heat which this hydrate yielded on dilution was considerably less
than the quantity assigned above to it; indeed, not more than 0°06 in
One experiment.
11. HO, SOA, HO + 36 HO. The equivalent quantity of this diluted
acid, or 238-8 grains, was mixed within an hour of its preparation with
792 grains of water; the rise of temperature was 0°-11.
12. HO, SOA, HO + 48 HO. The equivalent quantity, or 3063
grains, was mixed about three hours after its preparation with 724.4
grains of water; a rise occurred of 0°-08. The dilution of the same
hydrate twenty-four hours after its preparation was attended with a rise
of 0°-13.
The last hydrate is oil of vitriol diluted with nine times its weight
of water, yet it was still capable of evolving a sensible quantity of heat
by further dilution. The term at which the mixture of acid and water
ceases to disengage heat on a further addition of water was not observed,
but the effect was insensible in a mixture formed of one part of the
concentrated acid and thirty parts of water.
II. HYDRATION OF OTHER MAGNESIAN SULPHATES.
The heat produced in the hydration of different anhydrous sulphates,
compared with oil of vitriol, appears in the following results; equiva-
lent quantities of the anhydrous salts in the solid state being thrown
into the same quantity of water, and the rise of temperature observed
after the hydration and complete solution of the salts.
Protosulphate of manganese, . 3°-22
Sulphate of copper, 3°-73
Sulphate of water, . e e 3°-86
Sulphate of zinc, . g e 4°-17
Sulphate of magnesia, . * 4°-33
The most material difference in the circumferences of the experiments
is, that while the oil of vitriol was liquid, the salts with which it is
compared were necessarily applied in the solid form. The liquefaction
408 - EXPERIMENTS ON THE HEAT
of the latter during the experiment would therefore occasion an absorp-
tion of heat of unknown amount, which does not occur in the latter.
1. Sulphate of Magnesia.-The same mode of experimenting was
followed and apparatus used as in the preceding experiments with oil
of vitriol. On dissolving the equivalent quantity, 77°35 grains (one-
twentieth of 1547.02), of the crystallized salts in 960-6 grains of water,
a fall occurred in three experiments of 0°-96, 0°-90, and 0°-89, of which
the mean is 0°-92. In these experiments, the water contained in the
crystals, which amounts to 39.4 grains, was deducted from the 1000
grains of water usually employed to dissolve the salt; but if this quan-
tity of water is supposed to be added, the mean result would become
0°-88.
The salt was made certainly anhydrous by exposure to an incipient
red heat for a considerable time, and the equivalent quantity, 37-98
grains, in the state of a fine powder, was thrown into 1000 grains of
water. It did not cake, and was dissolved completely by stirring in
about one minute and a half. The rise of temperature in two experi-
ments was 4°30 and 4°36, of which the mean is 4°33. To this must
be added the heat lost by the liquefaction and solution of the hydrate
formed. -
Rise on solution of MgO, SOs, & e 4°-33
Fall from solution of MgO, SO3 + 7 HO, . 0°-92
Whole heat disengaged by MgO, SOs, e 5°-25
MgO, SOA, HO. It is not easy to obtain the sulphate of magnesia
with exactly one atom of water. The salt first operated upon retained,
after being dried by an oil-bath, at 400° to 100 sulphate of magnesia
only 14:14 water, instead of 14.81, the single equivalent. The hydrate
was therefore # HO. The heat evolved by the solution of 43.35 grains,
an equivalent quantity of this hydrate in two experiments, was 3’-06
and 3°-9, of which 3°08 may be taken as the mean.
Another portion of the same sulphate, less strongly dried, retained to
100 sulphate of magnesia 15-75 water, which is 11'ſ HO. The results
from the solution of 43.93 grains, the equivalent of this hydrate, were
3°03, 2’-98, and 2’-93, of which the mean is 2°-98. The mean of the
two sets of experiments, or 3°03, probably does not differ far from the
truth. •
Bise on solution of MgO, SOA, HO, . e 3°:03
Fall on solution of MgO, SOs, 4-7 HO, & 0°-92
Whole heat disengaged by MgO, SOA, HO, . 3°-95
The anhydrous salt disengaged 5°25, while the protohydrate disengages
3°-95; the difference, or 1°30, is therefore the heat disengaged by the
DISENGAGED IN COMBINATIONS. - 409
combination of the first atom of water with Sulphate of magnesia. It
thus appears that of the whole heat evolved in the complete hydration
of sulphate of magnesia, as nearly as possible one-fourth is due to the
combination of the first atom of water, one-fourth of 5°25 being 1°31.
2. Sulphate of Zinc.—The equivalent quantity of the crystallized
salt, 89'59 grains, contains 39:38 water, and was therefore dissolved in
960-6 water. The fall of temperature in two experiments was 1°01
and 0.98, of which the mean is 1°00. This sensibly exceeds the cold
produced by the solution of crystallized sulphate of magnesia, which is
0°-92. The difference has a real foundation, and is not the consequence
of errors in experiment; for in two other sets of observations on the
same salts made in glass, and which may be compared with each other,
although not with the preceding experiments, the results were for sul-
phate of magnesia 0°-85, 0°-80, and 0°-83, of which the mean is 0°83; for
sulphate of zinc 0°-97, 0°-91, 0°-92, of which the mean is 0°-93: greater
cold occasioned by the solution of sulphate of zinc than of sulphate of
magnesia, by the first experiments 0°-08, by the last experiments 0°-10.
Of sulphate of zinc, carefully dried and made perfectly anhydrous, the
equivalent quantity, 50'22 grains, was dissolved in 1000 grains of water,
with the exception of a mere trace of flaky matter. The rise in one expe-
riment was 4°:20; in another 4*15; mean 4°17. The results then are,
Rise on solution of ZnO, SOs, . {} 4°-17
Fall on solution of ZnO, SO3 + 7 HO, . 1°:00
Whole heat disengaged by ZnO, SOs, . 5°-17
There is the same difficulty in obtaining the protohydrate of sulphate of
zinc exactly definite, as the corresponding hydrate of Sulphate of mag-
nesia. The hydrate operated upon contained to 100 sulphate of zinc
11-99 water, instead of 11.207, which is a single equivalent. The equi-
valent quantity, 56.21 grains, was dissolved in 1000 grains of water, and
occasioned a rise of temperature in two experiments of 2°34 and 2°33.
As the rise for the anhydrous salt was 4*17, the deficiency from the
hydrate, 4:17 – 2:34 – 1°83, is due to the quantity of water already
combined in the salt of the experiment. But this deficiency cannot be
entirely ascribed to a single atom of water, as the combined water
exceeded that proportion as 11-99 to 11:21. It is difficult to find proper
elements for the necessary correction, but we may probably reduce the
amount of deficient heat to 1*71, that is, as 1199 to 11:21, without any
considerable error. Hence -
Rise on solution of ZnO, SOA, HO, . & 2°45
Fall on solution of ZnO, SOs + 7 HO, e 1.00
Whole heat disengaged by ZnO, SOs, HO, . 3°45
410 EXPERIMENTS ON THE HEAT
The difference between the heat disengaged by the protohydrate and the
anhydrous salt, or the heat due to the combination of the first atom of
water, namely 1°-71, is almost exactly one-third of the whole heat dis-
engaged in the hydration of sulphate of zinc.; one-third of 5°17 being
1°72. The quantities of heat disengaged by sulphate of zinc in the two
conditions specified, are therefore as 4 to 6.
3. Sulphate of Copper—The equivalent quantity of the ordinary
crystallized salt, containing 5 HO, namely 77.97 grains, was dissolved
in 1000 grains of water, with a fall of temperature in three experi-
ments of 0°-67, 0°-65, and 0°-68, of which the mean is 0°67. This
and other more sparingly soluble salts were pounded fine and sifted;
the solution took place with stirring within one minute.
Of the anhydrous salt, 49.84 grains, the equivalent quantity, Were
dissolved in 1000 grains of water, with a rise in two experiments of
3°72 and 3°74. Hence the results for the anhydrous salt are, L-
Bise on solution of CuO, SOs, . * . 3°.73
Fall on solution of CuO, SO3 + 5 HO, . * 0°-67
Whole heat disengaged by CuO, SOs, . e 4°40
The protohydrate was prepared by drying the crystallized salt by a nitre-
bath; it retained to 100 sulphate of copper 11.83 water, instead of 11:29
water, the single equivalent. The equivalent quantity, 55.72 grains,
was dissolved in 1000 grains of water, with a rise in two experiments
of 2°-15 and 2°-13. The result is 373 — 2:14 = 1°59 for the combined
water. This hydrate contained 13's HO. -
After being dried still further on an oil-bath at 370°, it consisted of
100 sulphate of copper and 11:44 water, or was lº's HO ; the salt was
now almost white, the green tint being barely perceptible. The equi-
valent quantity of the last salt, 55-54 grains, was dissolved in 1000
grains of water, but somewhat more slowly, and with greater difficulty
than the preceding salt. The heat evolved in two experiments was 2°09
and 2’-07, which instead of exceeding falls short of the preceding results.
The deficiency of heat in the last experiments is remarkable, and is in
some measure, but I believe not fully, accounted for by the slowness of
the solution. Giving a preference to the first results, and deducting
gººd part for the excess of water above one atom already combined with
the salt, there remains 1°47 for the heat due to the combination of the
first atom of water. The result for the protohydrate is,
Rise on solution of CuO, SOA, HO, . dº 2°:26
Fall on solution of CuO, SO3 + 5 HO, * 0°-67
Whole heat disengaged by CuO, SOA, HO, . 2°-93
One-third of 4°40, the whole heat evolved in the hydration of sulphate
DISENGAGED IN COMBINATIONS. 411
of copper, is 1°466, which is as nearly as possible the result obtained
above for the first atom of water. The ratio is the same as in the sul-
phate of zinc, while in the hydration of the sulphate of magnesia the
heat evolved by the first atom of water was one-fourth of that evolved
by the whole. It may be inferred from the experiments on oil of vitriol,
that it approaches more closely to the former salts than to sulphate of
magnesia in this character, although a rigid comparison cannot be made,
as we are unacquainted with the fully hydrated sulphate of water in a
crystalline form, and cannot therefore estimate its heat of liquefaction.
4. Protosulphate of Iron.—Of the crystallized salt containing seven
atoms of water, the equivalent quantity, 86°39 grains, dissolved in 1000
grains of water in two experiments with a fall of 1° and 1°04. Allow-
ing for the 39:38 grains of water introduced by the salt in addition to
the thousand grains employed, these results become 1°04 and 1°08, of
which the mean is 1°06.
Fall on the solution of Fe0, SO3 + 7 HO, . 1°-06
The protohydrate of sulphate of iron, formed by drying the crystallized
Salt in air at a temperature approaching 400°, was found to be nearly
insoluble in cold water. The anhydrous sulphate was more soluble,
but not sufficiently so for the determination of its thermal relations.
5. Protosulphate of Manganese.—The crystallized salt employed con-
tained five atoms of water. The equivalent quantity, 75.47 grains, of
the crystallized salt was dissolved in 972 grains of water at 59° Fahr.,
with a fall of temperature in two experiments of 0°11 and 0°13 R., of
which the mean is 0°12.
Of the same salt made anhydrous by heat, the equivalent quantity,
47-35 grains, was dissolved in 1000 grains of water at 60° Fahr., with a
rise in two experiments of 3°20 and 3°24 R.; mean rise 3°22.
Rise on solution of MnO, SOs, e e 3°-22
Pall on solution of MnO, SO3 + 5 HO, • 0°-12
Whole heat disengaged by MnO, SOs, . * 3°34
The crystallized salt being well dried at a temperature not exceeding
400 Fahr, was found to retain a quantity of water in combination,
which slightly exceeded a single equivalent, namely in the proportion
of 5-82 grains to 5.62 grains, in 52.97 grains of the hydrated salt. The
heat evolved in the solution of the equivalent quantity, 52.97 grains,
of this protohydrate by 1000 grains of water was in two experiments
1°80 and 1°78, of which the mean is 1°79.
Rise on solution of MnO, SOs, HO, . tº 1°-79
Fall on solution of MnO, SO3 + 5 HO, tºr O°-12
412 EXPERIMENTS ON THE HEAT
It follows that the heat evolved by the combination of the first atom of
water with sulphate of manganese is 3°34–1°91 = 1°43. This result
approaches to 1°47, the heat evolved by the combination of the first
atom of water with sulphate of copper. The small depression of
temperature produced by the solution of crystallized protosulphate of
manganese is remarkable, and distinguishes this salt from the other
magnesian sulphates. This salt alone of the class forms a thick solu-
tion, when highly concentrated, and crystallizes with difficulty. It was
also observed that the protohydrate of sulphate of manganese does not
dissolve easily in cold water; the quantity of the protohydrate employed
in the experiments narrated above requiring to be agitated with the
water for two and a half minutes, before the liquid ceased to be turbid
and the salt was entirely dissolved. The anhydrous sulphate of man-
ganese was dissolved quickly and with ease.
III. SULPHATES AND CHROMATES OF THE POTASH FAMILY.
1. Sulphate of Potash.-Good crystals of this salt were reduced to
powder and sifted. The solution of the equivalent quantity, 54-55
grains, in 1000 grains of water, which took place in thirty seconds, was
attended by a fall of temperature in two experiments of 1°50 and 1°52,
of which the mean is 1°51.
Fall on solution of KO, SOs, . º º 1°-51
The same quantity of sulphate of potash was dissolved in a mixture
of 300 water-grain measures of dilute sulphuric acid of density 1-1
mixed with 700 grains of water. The dry acid in the mixture amounted
to 36 grains; a single equivalent is represented by 25 grains. The
solution was quite as rapid, or more so, than in pure water; the fall of
temperature 2°04; the difference of 0°53 is probably connected with
the formation of bisulphate of potash.
2. Chromate of Potash.-The solution of the equivalent quantity,
62:09 grains, of this salt in 1000 grains of water, was attended with a
fall of 1*18 in water.
Fall on solution of KO, CrO3, . . o 1°-18
When dissolved in an equal quantity of the same dilute sulphuric acid
as was used with sulphate of potash, the solution became red from the
formation of bichromate, and only a very slight change of temperature
occurred, namely a fall of 0°08.
3. Bichromate of Potash.-The fused salt was used, as it is easily
reduced to a fine powder, and half the equivalent quantity used, as the
whole equivalent is not dissolved by 1000 grains of water at 57°Fahr.,
IDISENGAGED IN COMBINATIONS. 413
the temperature of the experiments. The solution of 47.34 grains, half
the equivalent quantity, was attended with the same fall of I*98 in
two experiments. No sensible change of temperature occurred on dilut-
ing this solution. In the dilute sulphuric acid used with the two pre-
ceding salts, the fall on the solution of half an equivalent of bichromate
of potash was 2°00, or sensibly the same as in pure water. The fall of
temperature for a whole equivalent of bichromate of potash will there-
fore be 3°96.
Fall on solution of Ko, 2 Cro, . . .3°-96
The heat of liquefaction of bichromate of potash is therefore very
considerable. It appears to be the same in quantity as that of nitrate
of potash. The equivalent quantity of the latter salt, 63.25 grains, was
dissolved in 1000 grains of water, with a fall of 3°86. The temperature
of this solution was further reduced 0°10, by dilution with another 1000
grains of water; so that by the solution of an equivalent quantity of this
salt in the same proportion of water as was employed for the solution
of an equivalent of bichromate of potash, a fall of temperature of 3°-96
is produced. In a second experiment the whole fall of temperature on
the solution of an equivalent of nitrate of potash was 3°95.
Fall on solution of KO, NOs, . e wº 3°-96
It is possible that this coincidence is not accidental, but depends on
a thermal equivalency of NO, and Cr,0s, the acids united with potash
in these two salts. If the single equivalent of nitrogen in nitric acid
be divided by three, or considered three atoms instead of one, as has
been inferred on other grounds, then the acid constituents of both salts
will contain the same number of atoms, namely eight; and the bichro-
mate of potash, which has hitherto appeared so anomalous among salts,
be assimilated to the nitrate of potash.
4. Terchromate of Potash.-Of this salt 63-63 grains, or one-half of
the equivalent quantity, were dissolved easily and entirely by 1000
grains of water, with a fall of 1*63. But the terchromate of potash
changes colour when thrown into water from decomposition, being
resolved in a great measure into bichromate of potash and chromic
acid, both of which are soon dissolved, the last more rapidly than the
first.
Half an equivalent of this salt was dissolved, with a fall of 1°28,
in 1000 water grain measures of dilute nitric acid, of specific gravity
11453. But in this menstruum also, the terchromate appeared to be
decomposed with separation of chromic acid, although to a much less
extent than in the preceding experiment. In a liquid, however, already
charged with the salt, like the last, an additional quantity may be dis-
414 EXPERIMENTS ON THE HEAT
solved without further decomposition. Half an equivalent of the salt
was dissolved in that liquid with a fall of 1°14, which is a fall of 2°28
for a whole equivalent of the salt. The capacity for heat of the solu-
tion in question does not (I believe) differ materially from that of 1000
grains of water.
Fall from solution of KO, 3 CrO3, . & 2°:28
Half an equivalent of the crystallized biphosphate of potash, or 42.68
grains, was dissolved in 1000 grains of water, with a fall of 1*12, which
gives 2°24 for the whole equivalent.
Fall from solution of 2 HO. KO, POs, • 2°:24
A corresponding proportion of the crystallized binarseniate of potash,
or 56.38 grains, were dissolved by 1000 grains of water, with a fall in
one experiment of 1°13, and in another of 1*18. In a third experi-
ment the solution of a whole equivalent of this salt, or 112-75 grains,
was attended by a fall of temperature of 2°-15. A greater discrepancy
is observable in the results obtained from this than from most other
salts, which appeared to arise from the full depression of temperature
not occurring at the moment of solution, but a small portion of it being
produced in a gradual manner for three or four minutes after the solu-
tion. The mean of the three observations gives 2°26 for the equivalent
quantity of the salt.
Fall from solution of 2 HO. KO, AsO3, . 2°:26
The thermal properties of these two salts are interesting in relation
to the terchromate of potash. The latter salt contains 14 atoms, which
is also the number of atoms in both biphosphate and binarseniate of
potash, if the equivalents of phosphorus and arsenic be supposed, like
that of nitrogen, to represent three atoms.
Potash being common to the terchromate and biphosphate of potash,
there remain, on subtracting that constituent from both salts, three
equivalents of chromic acid equivalent in some sense to one equivalent
of phosphoric acid together with two equivalents of water. This state-
ment respecting phosphoric acid, recalls the view which has lately been
proposed by M. Wurtz of the constitution of the hypophosphites, in
which the two atoms of water which they all contain are supposed not
to be basic, but to form part of the acid; a neutral hypophosphite
being represented by RO + PO, H,02, or rather by RO + PO.H. For
we are here representing biphosphate of potash as KO + PO.H., cor-
responding with the terchromate of potash KO + Cr,0, in which P is
equivalent to Crs, and Oz + H2 to Oa. The two atoms of water, how-
ever, may be replaced by a strong base in a biphosphate, but not in a
hypophosphite. The relations of these salts show a progressive and
DISENGAGED IN COMBINATIONS. 415
imperceptible passage of the basic elements of a salt into constituents of
its acid, and the existence of intermediate conditions of the elements in
question, which we may well conceive although our chemical formulae
fail to enable us to denote them ; these formulae being adapted only for
the expression of the extreme conditions.
Of anhydrous chromic acid an equivalent, 32°59 grains, was dissolved
by 1000 grains of water with a rise of 0°51. A second equivalent,
dissolved in the previous solution, produced a rise of only 0°38. The
relations of this acid to water are therefore very different from those of
sulphuric acid. -
5. Sulphate of Soda.-In removing the hygrometric water which the
crystals of this salt generally contain in large quantity, by pressure in
blotting-paper, the salt is apt to lose a little of its combined water. The
crystallized salt contained as determined by analysis, to 100 Sulphate of
soda, 121-5 water, instead of 126-1 water, which are ten equivalents.
The equivalent quantity of the fully hydrated salt is 100-85 grains, but
of the salt under examination only 98-79 grains. The last quantity,
which contains 54.2 grains of water, was dissolved in 946 grains of
water in half a minute, with a fall of 4°43. The fall is almost entirely
due, as will immediately appear, to the liquefaction of the combined
water of the salt, of which the quantity liquefied in the experiment was
54.2 grains instead of 562, the ten equivalents. The fall of 4°43
increased in the proportion of 542 to 562, becomes 4°59.
Fall on solution of NaO, SO3 + 10 HO, & 4°-59
The same quantity of the salt was dissolved in the diluted Sulphuric
acid of the experiments with the previous salts, with a fall of 5°00 ;
which, corrected in the same manner as the last result, gives a fall of
5*19 for the equivalent of the salt. Hence the fall on the solution of
the sulphate of soda in dilute sulphuric acid is 0°-60 greater than in
pure water; a circumstance connected probably with the formation of
bisulphate of soda.
Sulphate of soda was made anhydrous by a strong heat, without
being fused. The solution of the anhydrous salt is difficult, owing to
the instantaneous formation of a hard coherent mass when the salt is
thrown into the water, which it requires two or three minutes to break
up and dissolve. Very little change of temperature occurs. A rise
took place in one experiment of 0°-10. In another experiment, in
which the Salt was added in a gradual manner with constant stirring,
there was less caking, and the solution more rapid, although it still
required two minutes. A rise occurred of 0°18. The last experiment
is most to be depended upon. The results for the sulphate of Soda will
therefore be, - -
416 EXPERIMENTS ON THE HEAT
Rise on solution of NaO, SOs, . & e 0°-18
Fall on solution of NaO, SO, +10 HO, e 4°-59
Whole heat disengaged by NaO, SOs, . & 4°-77
The last number represents the heat evolved in the formation of a solid
hydrate of sulphate of soda containing ten atoms of water; it is remark-
able how little it exceeds the heat disengaged in the crystallization of
the same salt, or the fall observed on the solution of the crystallized
salt. It appears as if water abandoned little more than its heat of
fluidity on combining with dry sulphate of soda to form a solid
hydrate.
Sulphate of soda, which had been allowed to effloresce in dry air
between 50° and 55° Fahr. for a week, consisted of dry salt 100 and
water 0.46. The equivalent quantity of this salt, which is so nearly
anhydrous, or 44.81 grains, was dissolved in 1000 grains of water with
a very slight change of temperature, namely a rise of 0°05.
6. Sulphate of Ammonia.-Of the hydrated salt crystallized by
spontaneous evaporation in air, which contains one atom of water of
crystallization, the equivalent quantity, 47:03 grains, was dissolved in
1000 grains of water with a fall of temperature in three experiments of
0°65, 0°64, and 0°61, of which the mean is 0°63.
Fall on solution of NH,0, SO, +HO, . . 0°-63
The salt was obtained anhydrous by drying at 248° Fahr. ; it was
granular and crystalline, and neutral to test paper. The equivalent
quantity, 41°41, produced a fall in three experiments of 0°51, 0°53, and
0°49; of which the mean is 0°51.
Fall on solution of NH, O, SOs, * º 0°-51.
A sensible but very small reduction of temperature, not exceeding
0°02, occurred on mixing the solution of sulphate of ammonia with an
equal bulk of water at the same temperature.
Dissolved in the diluted acid, consisting of a mixture of 300 water-
grain measures of sulphuric acid of density 1-1 and 700 grains of water,
the equivalent, 41°41 grains, of the anhydrous salt produced a fall of
temperature in two experiments of 1°17 and 1°14; of which the mean
is 1*16. Hence the fall is greater on the solution of the sulphate of
ammonia in dilute sulphuric acid than in water, by 0°-65. The fall of
sulphate of Soda was also greater by nearly the same amount, 0°-60, and
of sulphate of potash by 0°53, when these salts were dissolved in the
same dilute acid instead of water.
DISENGAGED IN COMBINATIONS. 417
IV. DOUBLE SULPHATES.
1. Bisulphate of Potash.-Of the usual double sulphate of water and
potash crystallized in rhombohedral crystals, an equivalent quantity,
85.23 grains, was dissolved in 1000 grains of water, with a fall in two
experiments of 1°96 and 1°95. The same salt was fused by heat and
pounded; it dissolved afterwards with a fall of 1°94 and 1.90 in two
experiments. The cold upon solution of this salt appears to be the
same before and after fusion. The result is, -
Fall on solution of HO, SO3 + KO, SOs, . . 1°95
I was anxious to compare with this salt the anhydrous bisulphate of
potash of M. Jacquelin, which is described as being capable of dissolving
in water without decomposition. One equivalent of sulphate of potash
was accordingly dissolved in two equivalents of oil of vitriol, with the
aid of heat, and an abundant crop was obtained on cooling of a Salt in
small silky crystals. As these appeared to be the Salt in question, an
equivalent quantity, or 79-60 grains, was dissolved, and a fall observed
of 1°-90. The result not differing from that of the former salt, the pre-
paration of the anhydrous salt was repeated. The Spongy mass of thin
prismatic crystals obtained in a second experiment was pressed, dissolved
again in water, crystallized and pressed again. The Salt was still in
minute prisms. The solution of 39.8 grains, half the equivalent quan-
tity, was attended with a fall in two experiments of 0°91 and 0°95; or,
for a whole equivalent, 1°86. Of the same salt, before the second solu-
tion, half an equivalent produced a fall of temperature of 0°96; or, for
the whole equivalent, 1°-92. These results are identical with those
formerly obtained with the hydrated bisulphate, if allowance be made
for the smaller quantity of the salt employed, a circumstance which
excited a doubt as to the composition of the prismatic salt. The product
of the second crystallization was accordingly analysed; 19:30 grains of it
gave 32°34 grains of sulphate of barytes, equivalent to 11-12 sulphuric
acid, or 57-59 per cent. ; 22:53 grains of the crystals lost no weight at
150°, but lost 0:24 water, or 1:02 per cent, by cautious fusion. The pro-
portion of acid in the salt is greatly under that of an anhydrous bisul-
phate, namely 62.98 per cent, while it approaches sufficiently near that
of the hydrated bisulphate, 58.74 per cent. The process of M. Jacquelin
has not therefore given an anhydrous bisulphate of potash in my hands,
and none of my experiments favours the existence of such a salt; the
silky prismatic crystals which I obtained being nothing more than an
unusual form of the sulphate of water and potash.
2. Bisulphate of Soda.-An equivalent quantity, 75.27 grains, of one
and the same specimen of this salt, dissolved in three experiments with
2 D
4.18 EXPERIMENTS ON THE HEAT
a fall of 0°40, 0°28, and 0°17. It did not dissolve so easily as the
bisulphate of potash, possibly from partial decomposition and formation
of a portion of neutral sulphate of soda. The same supposition will
explain the want of agreement among the results. Taking the mean of
the results,
Fall on solution of HO, SO3 + NaO, SOs, . . 0°28
The fall of temperature observed on dissolving bisulphate of potash
in water approaches that observed on dissolving the neutral sulphate of
potash in dilute sulphuric acid, the first being 1°95 and the second 2°04.
But it is doubtful if the fall in the second case can be ascribed simply
to the immediate formation and solution of bisulphate of potash, when
the sulphate of potash and dilute sulphuric acid are mixed and dissolved
together. In the formation of bisulphate of potash we have both the
substitution of Sulphate of potash for the second atom of water of the
sulphate of water, and the throwing off of all the remaining water com-
bined with the sulphate of water in hydrated sulphuric acid, bisulphate
of potash containing no water of crystallization. Now as a great deal
of heat was disengaged by this additional water on originally combining
with the Sulphate of water, we should expect heat again to be assumed
by that water on becoming free, or cold to be produced.
3. Sulphate of Magnesia and Potash.--An equivalent quantity of the
crystallized salt, namely 126-28 grains, containing 33.75 grains of water
of crystallization, was dissolved in 976-2 grains of water at 52°Fahr.,
with nearly two minutes' stirring; a fall of temperature was observed
of 2°30 R. The experiment was repeated with the same result. But
a slow rise of temperature was afterwards observed to occur in the solu-
tion, independent of any external influence, which in the course of four
minutes amounted to 0°20 R. This is not the only salt in which the
fall of temperature on solution is immediately followed by a slight but
sensible rise.
This Salt was made anhydrous by a low red heat to which it was
exposed for upwards of two hours, but was not fused. When the salt
was thrown into water after this ignition, it gave a liquor which remained
white and milky for two or three minutes, but the salt finally dissolved
without residue. The rise of temperature on the solution of a whole
equivalent of the anhydrous Salt, or 92-53 grains, was 1°57; on solution
of one-half of an equivalent, or 46.2 grains, 0°80; which gives 1°60 for
the whole equivalent. -
Rise on solution of MgO, SO3 + KO, SOs, . º 1°-60
Fall on solution of MgO, SO3 + KO, SO,--6 HO, 2°30
Whole heat disengaged by MgO, SO, + KO, SOs, . 3°-90
DISENGAGED IN COMBINATIONS. 419
The crystallized sulphate of magnesia and potash, dried by a nitre-
bath, was found to retain 1832 water to 100 anhydrous salt. Now 18:24
water represents 3 HO ; the crystallized salt has consequently lost one-
half of its water, retaining only three atoms. Of this salt, an equivalent
quantity, or 109'4 grains, were dissolved in 1000 grains of water with a
fall in three experiments of 1°35, 1°30, and 1°35, of which the mean
is 1°33.
Fall on solution of MgO, SO3 + KO, SO3 + 3 HO, . 1°-33
The fall on the solution of this hydrate is less than on the solution
of the former, by the heat disengaged in the combination of the salt with
the deficient three atoms of water. The heat disengaged by the union
of the salt with the first three atoms. of water comes therefore to be
2”93, and with the second three atoms of water 0°-97, making together
3°-90. Hence as nearly as possible three times as much heat are dis-
engaged by the first three atoms of water as by the last three atoms.
4. Sulphate of Magnesia and Ammonia.-The solution of an equi-
valent quantity, 113-13 grains, of the crystallized salt in 1000 grains of
water was attended by a fall of temperature, in two experiments, of
2°20 and 2’-15, of which the mean is 2°17. If dissolved in 9762
grains of water, like the potash salt, the fall would have been about
gºth more, or 2°24.
Fall on solution of MgO, SO3 + NH, O, SOs + 6 HO, 2°-24
The fall on the Solution of the corresponding potash salt was 2°30.
5. Protosulphate of Iron and Ammonia.-The solution of 122:17
grains, the equivalent quantity of the crystallized salt in 1000 grains
of water, was attended with the same fall of 2°20 in two experiments.
But this determination should be increased by goth, like the last ; the
fall then becomes 2°27. -
Fall on solution of Fe0, SO, + KO, SO, + 6 HO, . . 2°27
6. Sulphate of Manganese and Ammonia.—In two experiments 61:20
grains of the crystallized salt, being one-half of the equivalent quantity,
were dissolved in 983 grains of water with a fall of 1*11 and 1°-13; or
2°24 for a whole equivalent.
Fall on solution of MnO, SOs + NH, O, SO3 + 6 HO, 2°:24
It thus appears that the heat of liquefaction of the four crystallized
double Salts, sulphate of magnesia and potash, Sulphate of magnesia and
ammonia, Sulphate of iron and potash, and sulphate of manganese and
ammonia, is sensibly the same,
7. Sulphate of Zinc and Potash.--The fall on the solution of half an
420 EXPERIMENTS ON THE HEAT
equivalent, 69.26 grains, of the crystallized salt in 1000 grains of water,
was in three experiments 1°33, 1°27, and 1°30, of which the mean is
1°30. The fall for a whole equivalent, 138.52 grains, is therefore 2°60.
This salt was made anhydrous by a heat little short of redness,
without being fused. Half an equivalent, 52.39 grains, was dissolved in
1000 grains of water with a rise of temperature of 0°83 and 0°87 in two
experiments, of which the mean is 0°85. The rise for a whole equivalent,
104-77 grains of the salt, is therefore 1*70.
Rise on solution of ZnO, SO3 + KO, SOs, . tº 1°-70
O
Fall on solution of ZnO, SO3 + KO, SO3 + 6 HO, . 2°-60
Whole heat disengaged in the hydration of ZnO,
SOs + KO, SOs, . * * • e
4°30
8. Sulphate of Copper and Ammonia.-Of the crystallized salt, 62:45
grains, or one half of the equivalent quantity, were dissolved in 983
grains of water with a fall of temperature of 1°33 and 1°28 in two
experiments; giving 2°63 for the whole equivalent.
Fall on solution of Cu0, SO3 + NH, O, SO3 + 6 HO, . 2°63
The fall on the solution of the two immediately preceding salts is
therefore sensibly the same.
9. Protosulphate of Iron and Potash.-Of this salt in small but
well-defined crystals, 67-66 grains, one half of the equivalent quantity,
were dissolved in 983 grains of water with a fall, in two experiments, of
1°25 and 1°22; or for the whole equivalent 2°47.
Eall on solution of MnO, SO3 + KO, SO3 + 6 HO, . . . 2°47
10. Sulphate of Zinc and Ammonia.-Of the crystallized salt half an
equivalent, 62-64 grains, was dissolved in 983 grains of water with a
fall of 1°37 and 1°36.
Fall on solution of ZnO, SO3 + KO, SO3 + 6 HO, . . 2°73
11. Sulphate of Copper and Potash.-The solution of half an equi-
valent of the crystallized salt, 69-07 grains, in 1000 grains of water, was
attended with a fall in two experiments of 1°54 and 1°50; or for the
whole equivalent of the salt, 138-14 grains; the fall is 3°08 and 3°00,
of which the mean is 3°04. -
The crystallized salt was made anhydrous by a heat short of redness,
which had the effect of causing it to frit but did not fuse it. The
solution of 52.2 grains, half an equivalent, in 1000 grains of water, was
attended by a fall in two experiments of 1°01 and 0°96; or for a whole
equivalent, 2°02 and 1°92, of which the mean is 1°97.
DISENGAGED IN COMBINATIONs. 421
Rise on solution of CuO, SO3 + KO, SO3, . e & 1°-97
Fall on solution of CuO, SO3 + KO, SO3 + 6 HO, . g 3 - 04.
Whole heat disengaged in hydration of CuO, SO3 + KO, SOs, 5°01
The fall on the solution of the preceding crystallized double salt is
3°04, while the fall on the solution of its constituents dissolved sepa-
rately is 1°51 for the sulphate of potash, and 0°67 for the hydrated
sulphate of copper, making together 2°18, which is less by 0°86 than
the former. The fall on the solution of the crystallized double sulphate
of zinc and potash approaches more closely to the united falls of its
constituents dissolved separately, the former being 2*60 and the latter
1* + 1°51=2°51. The fall on the solution of the crystallized double
sulphate of magnesia and potash is 2°30; the united falls of its consti-
tuent salts 0°92 + 1°51 = 2*43. No perceptible change of temperature
was observed when the solutions of a pair of these salts are mixed to
form the double salt; which is in accordance with the conclusion of
Dr. Andrews, that no heat is evolved in the combination of salts.
I have not, however, succeeded in obtaining any direct proof of the
formation of the double sulphates on mixture. To a solution of 77.97
grains, or one equivalent, of crystallized sulphate of copper in 1000
grains of water, 41°41 grains, one equivalent, of sulphate of ammonia
dried at 234° were added and dissolved. The fall on the solution of the
last salt was 0°56, or the same as when the salt is dissolved in pure
water. No change took place in the colour of the solution of the
copper salt. The last salt was selected for this experiment, because
it appears more disposed to form double salts than even the sulphate of
potash.
In certain cases, a double salt is formed on using a bisulphate, while
it is not with the neutral sulphate; as in the formation of sulphate of
zinc and Soda, from sulphate of zinc and bisulphate of soda, but not
from Sulphate of zinc and neutral sulphate of soda. To a solution of
85'23 grains, or the equivalent, of crystallized bisulphate of potash in
1000 grains of water, 89'59 grains, or the equivalent, of crystallized sul-
phate of zinc were added and dissolved, with a fall of 1°00, or the same
as in pure water. To a similar solution of bisulphate of potash, 77°35.
grains, or one equivalent, of crystallized sulphate of magnesia were added
and dissolved, with a fall of 0°86; the same fall also as on the solution
of the latter Salt in pure water. Yet the double salts crystallized out
readily from both of these solutions.
I have formerly represented the anhydrous sulphate of magnesia
and potash as corresponding with the protohydrated sulphate of mag-
nesia. Now both these salts assume six atoms of water, and the heat
then disengaged by the two salts is nearly the same —
422 EXPERIMIENTS ON THE HEAT
& Heat of hydration.
MgO, SO, +KO, SO, . . . . .3°-90
MgO, SO3 + HO, . g tº {} e 3°-95
When the corresponding salts of zinc are compared, the same equality
is not observed, but other relations appear.
Heat of hydration.
ZnO, SO3 + KO, SOs, . . . . 4°30
ZnO, SO3 + HO, . q tº § u 3°45
ZnO, SOs, . * © e • & B°. 17
These quantities of heat and the quantity disengaged by the anhy-
drous Sulphate of zinc, have a remarkable relation among themselves;
if they be all divided by 0°86, we have
Ratios of heat of hydration.
ZnO, SO3 + HO, . . . . . 4.01
ZnO, SO3 + KO, SOs, . . . . 5
ZnO, SOs, . . . . . . 6:01
The quantity of heat disengaged by the first atom of water on uniting
with sulphate of zinc is 1°71. If it had been only half that quantity,
or 0.86, and had the deficient 0°86 been evolved by the combination of
the six following atoms, in addition to the heat they actually evolve,
then the heat disengaged by the six atoms of water which unite with
protohydrated sulphate of zinc, and by the double sulphate of zinc and
potash, would be the same in both salts, as it is the same in the two
corresponding salts of magnesia.
The heat evolved by the corresponding copper salts with their ratios,
is as follows:—
Heat of hydration. Ratios.
CuO, SO3 + HO, . te te 2°-93 4°
CuO, SOs, . tº tº s º 4°40 6°
CuO, SO3 + KO, SOs, . te 5°.01 6°-86
It is to be observed, however, that while the protohydrate of sul-
phate of copper combines with only four atoms of water, the sulphate
of copper and potash combines with six atoms; the usual comparison
cannot therefore be made between these two salts.
The principal numerical results of the paper are exhibited in the
following tables:–
1. Heat absorbed by equivalent quantities of crystallized salts on
dissolving in water.
Sulphate of magnesia, . s . 7 HO 0°-92
Sulphate of zinc, º * tº º º e 1°00
Protosulphate of iron, . $º * gº º gº 1°06
Sulphate of copper, wº o . 5 HO 0°-67
DISENGAGED IN COMBINATIONS. 423
Sulphate of manganese, . * º gº º º 0°-12
Sulphate of magnesia and potash, . 6 HO 2°30
Sulphate of magnesia and ammonia, . 2°-24
Sulphate of manganese and ammonia, 2°:24
Sulphate of iron and ammonia, 2°-27
Sulphate of iron and potash, tº & © tº 2°-47
Sulphate of zinc and potash, . . 6 HO 2°-60
Sulphate of copper and ammonia, 2°.63
Sulphate of zinc and ammonia, 2°.73
Sulphate of copper and potash, tº º & 3° 04
Sulphate of soda, & & . 10 HO 4°59
Sulphate of potash, o & . anhydrous 1°51
Sulphate of ammonia, * tº º º 0°-51
Chromate of potash, 1°-18
Bichromate of potash, 3°-96
Nitrate of potash, 3°-96
Terchromate of potash, . & ge gº tº ſº. 2°:28
Biphosphate of potash, . & 2 HO 2°-24
Binarseniate of potash, . * sº ſº e º 2°-26
Sulphate of water and potash, . anhydrous 1°95
2. Heat disengaged in the complete hydration of anhydrous Salts.
Sulphate of magnesia, e º º 5°-25
Sulphate of zinc, . $ e ſº 5°-17
Sulphate of copper, & e & 4°40
Sulphate of manganese, . * * 3°34
Sulphate of magnesia and potash, ū 3°-90
Sulphate of zinc and potash, . e 4°30
Sulphate of copper and potash, . * 5°.01
3. Heat disengaged by the combination of the first atom of water in
the magnesian sulphates.
Sulphate of water, . & © & 1°47
Sulphate of copper, . te * * 1°47
Sulphate of manganese, . te e 1°43
Sulphate of magnesia, ſº sº & I°-30
Sulphate of zinc, . . . & º 1°.71
Simple relations are observed between the quantities of heat dis-
engaged by the sulphates of magnesia and zinc, which appear to belong
to one class, while the Sulphates of water, copper, and manganese belong
to another class.
424 EXPERIMENTS ON THE HEAT
XI.
EXPERIMIENTS ON THE HEAT DISENGAGED IN
COMBINATIONS.
PART II.
NEUTRALIZATION OF WARIOUS ACIDs By HYDRATE OF POTASH.
THE arrangements adopted for observing the heat evolved on neutra-
lizing acids by potash were similar to those described in the former
paper. The same platinum crucible, weighing 1201.9 grains, and hollow
cylinder of palladium, weighing 207:6 grains, were employed as the con-
taining vessel and stirrer; but the constant quantity of water employed
as a vehicle for the acid and alkali was increased from 1000 grains to
1544 grains, or 100 grammes, while the equivalent quantities of the
substances used were the same as before. The Solution of the Saline
body formed in an experiment was consequently one-half more dilute,
and the small but sensible effect of further dilution of the solution in
producing cold, observable in some of the former experiments, was thus
entirely avoided, while the increase of the mass of fluid reduced the
influence of external causes on its temperature. A mercurial thermo-
meter of greater delicacy was employed, of which the bulb was a cylinder
of 1:25 inch in length and 0-3 inch in diameter; the scale was graduated
into degrees Fahrenheit, ranging from 40° to 70°, each degree being 0:42
inch in length (0-74 inch for one degree centigrade), divided into tenths
of a degree, each of which could again be subdivided into fifths by the
eye, so that the observation was made to one-fiftieth of a degree Fahren-
heit. The eye was directed to the scale through a straight cylindrical
tube of small diameter, supported in a horizontal position. The mercury
in the bulb of the thermometer was equivalent in capacity for heat to
11-5 grains of water, and the containing vessel and stirrer to 49 grains,
making together 60.5 grains of water; the capacity of the salt dissolved
or formed rarely exceeded that of 12 grains of water.
I. NEUTRALIZATION OF HYDRATE OF POTASH BY NITRIC AND
HYDROCHLORIC ACIDS.
The equivalent proportion of this acid adopted in these experiments
is 33.85 grains, that is one-twentieth of 677, the usual equivalent of
nitric acid on the oxygen Scale. Nearly one-half the quantity mentioned
was used in an experiment, namely 0:455 equivalent, diluted in the
crucible with about four-fifths of the water, while the remaining portion
of the 1544 grains of water, in a small and thin glass flask, contained
DISENGAGED IN COMBINATIONS. 425
hydrate of potash in quantity sufficient to saturate the acid, and leave
a slight excess of alkali. The two liquids were afterwards brought to
exactly the same temperature, which was observed by two thermometers,
the corresponding points of which were accurately determined, and the
potash solution then emptied into the nitric acid. The following are
the results of three observations of the temperature of the liquids before
mixture, and the temperature after mixture:—
Before mixture, . . 61°91 62°13 62°-13
After mixture, . . . 66°70 66°-91 66°-89
Rise of temperature, . 4°79 4°-78 4°-76
Increasing 4°78 the mean of the experiments, in the proportion of
0:455 to 1, we have 10°50 as the rise of temperature on saturating a
whole equivalent of potash by nitric acid.
The heat evolved upon combination is sensibly affected by a con-
siderable difference in the temperatures at which the acid and alkali are
mixed; being less at the lower temperature. This appears by the fol-
lowing experiments, in which 0-5 equivalent of nitric acid was neutra-
lized at a temperature twenty-two degrees lower than in the former
experiments.
Before mixture, . . 40°25 40°-60
After mixture, . . 45°43 45°-80
Rise of temperature, . 5*18 5°:20 Mean 5°-19
Hence we have the heat from the neutralization of the nitric acid by
hydrate of potash—
10°-50, at 62°F.
10°38, at 40° F.
Half an equivalent of hydrochloric acid, 11:38 grains, was neutra-
lized with hydrate of potash in slight excess, exactly as the nitric acid
was treated in the preceding experiment.
Before mixture, . . . 60°20 60°:00 59°-95
After mixture, . . . 65°30 65°-15 65°-10
Rise of temperature, . 5*10 5°-15 5°-15
Mean rise 5°13 for 0°5' equivalent of hydrochloric acid, or 10°:26
for 1 equivalent of that acid. The neutralization of hydrate of potash,
therefore, in very dilute solutions with these two different acids produces
nearly the same disengagement of heat, the result with nitric acid being
10°-50. -
The heat of combination appears also to be sensibly affected in
amount by the temperature of the experiment:-
426 EXPERIMENTS ON THE HEAT
Before mixture, . . . .40°:00 40° 25
After mixture, . . . 45°02 45°-30
Rise of temperature, . 5°02 5°.05 Mean 5°03
From which it follows that the heat from the neutralization of hydro-
chloric acid by hydrate of potash is—
10°26, at 60° F.
10°06, at 40° F.
It is remarkable how large a proportion the cold produced on dis-
Solving in water crystallized nitrate of potash and chloride of potassium,
the Salts produced in these experiments, bears to the heat observed in
the formation of the same salts. {
One equivalent of crystallized nitrate of potash (63.25 grs) well dried,
pounded and sifted, was dissolved in the usual quantity of water—
Before solution, . . 61°80 62°20 61°88
After solution, . . 56°-10 56°45 56°-18
Fall of temperature, 5°70 5°75 5°70 Mean 5°72
Before solution, . . 56°45 57°70 55°45
After solution, . . 50°80 52°00 49°75
Fall of temperature, 5°65 5°70 5°70 Mean 5°68
The cold on dissolving this Salt is not quite constant, but increases
sensibly at low temperatures, a law which appears to prevail in a class
of salts:— - -
Before solution, . . 47°00 46°40 45°-95
After solution, . . 41*05 40°47 40°:00
Fall of temperature, 5°95 5°93 5°95 Mean 5°-94
It appears, on comparing the last set of experiments with that
immediately preceding it, that a difference of ten degrees at this part of
the scale makes a difference of 0°26, or ºd part, in the fall of tem-
perature consequent upon the Solution of an equivalent of nitrate of
potash. It is this increased absorption of heat at the low temperature
probably which occasions the observed heat of combination of the salt
to diminish at the same part of the scale.
On the other hand, the cold, on dissolving several equivalents of
nitrate of potash successively at a constant temperature, in the same
quantity of water diminishes considerably with the number of equiva-
lents of Salt dissolved. The capacity for heat of the crystallized Salt is
0.239 (Regnault).
DISENGAGED IN COMBINATIONS. 427
Dissolved in 1544 grains of water,
First equivalent of nitrate of potash :-
62°34. 63°68
56°-68 57°-90
Eall, 5*66 5°78 Mean 5°72
Second equivalent of nitrate of potash —
63°47 63°-12
58°17. 57°86 -
Fall, 5°30 5°26 Mean 5°28
Third equivalent of nitrate of potash :-
63°40 63°-56
58°47 58°-61
Fall, 4°-93 4°-95 Mean 4°-94
Fourth equivalent of nitrate of potash :-
63°-57 63°35
58°-95 58°-76
Fall, 4°-62 4°-59
Fifth equivalent of nitrate of potash —
63°40 63°-34
59°-08 59°-10
Fall, 4°32 4°24 Mean 4°28
Sixth equivalent of nitrate of potash :-
63°45
69°-63
|Fall, 3°.82
In consequence of this diminished absorption of heat in the solution
of the latter equivalents of nitrate of potash, the addition of water to the
strong solution finally obtained occasions a further absorption of heat;
or dilution produces cold.
The last prepared solution, which consisted of 379.5 grains of nitrate
of potash dissolved in 1544 grains of water, and is a solution nearly
saturated for the temperature, was mixed with another 1544 grains of
water in a pint silver crucible with silver spatula, weighing 1650 grains,
both liquids being at the same temperature —
428
EXPERIMENTS ON THE HEAT
Before mixture,
After mixture, *
Fall of temperature,
63°-19
61°-91
e 1°:28
{º.
A second portion of 1544 grains of water being added to the above
solution, occasioned a further fall of temperature —
Before mixture,
After mixture,
|Fall, . * > º
63°-57
63°-19
O
O 38
*
tº.
tº tº
It appears from these experiments on the solution of successive
equivalents of nitrate of potash in the same quantity of water, that much
of the cold on dissolving that salt is properly referable to the dilution of
the Solution, and not to the simple liquefaction or solution of the crys–
talline salt.
But this is more obvious in dissolving a salt of great
solubility, such as nitrate of ammonia, of which many more equivalents
may be dissolved in succession.
Dissolved in 1544 grains of water,
100.4 grains, or 2 equivalents of nitrate of ammonia:-
66°-25
57°-91
Tall, 8°34
Third and fourth equivalents:— Ninth and tenth equivalents:–
66°43 • 66°26
58°-91 60°41
Fall, 7°-52 Fall, 5°.85
Fifth and sixth equivalents:— º and twelfth equiva-
gºl 66°-53
- 59°36 6 I°:0 6
Fall, 6°-85 Tall, 5°47
Seventh and eighth equiva-
lents:—
66°-10
59°-82
Fall, 6°28
Thirteenth and fourteenth equi-
valents:—
66°45
61°29
5°-16
Fall,
DISENGAGED IN COMBINATIONS.
429
Fifteenth and sixteenth equi-
valents:–
66°47
61°-55
Fall, 4°92
Seventeenth and eighteenth
equivalents:–
66°-61
61°-99
Fall, 4°62
Nineteenth and twentieth equi-
valents:–
66°:26
61°-91
Fall, 4° 35
Twenty-first and twenty-second
equivalents:—
66°-58
62°45
Fall, 4°13
Twenty-third and twenty-fourth
equivalents:—
66°-66
62°.63
Fall, 4°03
Twenty-fifth and twenty-sixth
equivalents:—
66°-83
63°16
Fall, 3°-67
Twenty-seventh and twenty-
eighth equivalents:–
66°-53
62°-97
Fall, 3’-56
Twenty-ninth and thirtieth equi-
valents:—
66°-57
63°:24
3°-33
Fall,
Thirty-first and thirty-second
equivalents:—
Thirty-fifth and thirty-sixth equivalents:—
Eall,
66°-80
63°-57
Eall, 3°23
Thirty-third and thirty-fourth
equivalents:–
66°37
63°-24
Fall, 3°-13
66°45
63°-50
2°-95
Here we find that while the fall on the solution of the first two
equivalents of nitrate of ammonia is 8°34, that of the last two dissolved
is only 2°-95, or little more than a third of the former.
The liquid,
however, finally consisted of 1544 grains of water and 1807-2 grains of
salt, and would therefore have a considerably greater capacity for heat
than the water alone ; but the proper correction for this increase of
capacity cannot at present be made, as the specific heat of nitrate of
ammonia has not been ascertained.
430 EXPERIMIENTS ON THE HEAT
The last solution of nitrate of ammonia, which was nearly saturated
for the temperature, was of density 1°247. Three portions of 100
grammes of water were added to it in succession, to discover the cold
produced on dilution.
First 100 grammes of water:-
Before mixture, 66°.83
After mixture, 60°-27
Fall, 6°-56
Second 100 grammes of water:—
Before mixture, 67°06
After mixture, 64°40
Tall, 2°-66
Third 100 grammes of water :-
Before mixture, 67°-06
After mixture, 65°-61
Fall, 1°45
The high solubility of the nitrate of soda adapts it for similar
experiments. It will be observed that a difference of 13 degrees of
temperature does not materially affect the amount of heat absorbed on
dissolving a single equivalent of this salt. The capacity for heat of the
crystallized salt is 0.278 (Regnault).
One equivalent of nitrate of soda, 53:40 grains, dissolved in 100
grammes of water —
Before solution, 65°.07 51°78 51°.63
After solution, 61°-56 48°.25 48°.08
Tall, 3°-51 3°-53 3°-55
Ten equivalents of this salt being dissolved successively in the same
100 grammes of water, the following changes of temperature were
observed :-
I. II. III. TV. W.
65°-07 65°.01 64°-63 64°-80 64°-84
61°56 61°70 61°65 63°14 62°.29
Fall, 3°51 3°31 2°-98 2°-66 2°-55
WI. VII. VIII. IX. X.
64°77 64°63 64°89 64°77 64°-64
62°38 62°34 62°·74 62°.79 62°.76
Fall, 2°39 2°:29 2°15 1°-98 1°-88
DISENGAGED IN COMBINATIONS. 431
The solution of the tenth equivalent of this salt produces therefore
Only one-half the cold due to the first equivalent.
The solution of chloride of potassium in water is attended with a
fall of temperature, which is considerable, although not so great as with
nitrate of potash.
One equivalent of chloride of potassium (46-62 grains) dissolved in
100 grammes of water:-
Before solution, . 62°·05 61°80 61°70
After solution, . . 59°10 58°88 58°75
Fall of temperature, 2°95 2°-92 2°-95 Mean 2°-94
At a lower temperature:–
Before solution, . 45°55 45°04 45°-53
After solution, . . 42°55 42°02 42°50
Fall of temperature, 3°00 3°-02 3°03 Mean 3°02
II. NEUTRALIZATION OF HYDRATE OF POTASH BY SULPHURIC ACID.
Half an equivalent of sulphuric acid, 12:53 grains, was Saturated
with a slight excess of hydrate of potash, the united liquids containing
100 grammes of water, as in the preceding experiments with nitric and
hydrochloric acids:—
Before mixture, . . 61°31 61°45 61°-53
After mixture, . . 67°01 67°-13 67°:21
Tise, . . . . . 5°-70 5°-68 5°-68 Mean 5°-69
The rise of temperature on saturating a whole equivalent of hydrate
of potash with sulphuric acid will therefore be 11°38.
The saturation of sulphate of water, already in combination with
sulphate of potash in the bisulphate of that base, is attended with the
disengagement of a still greater quantity of heat. Half an equiva-
lent of fused bisulphate of potash, dissolved in water like the acid of
the former experiments, was neutralized by potash, with the usual
conditions:—
Before mixture, . . 62°·74 62°-92 63°05
After mixture, . . 68°-95 69°12 69°-22
Rise, . . . . . 6°21 6°-20 6°17 Mean 6°-19
The saturation of the whole equivalent of Sulphate of water in a
4.32 EXPERIMENTS ON THE HEAT
solution of the bisulphate of potash therefore occasions the disengage-
ment of 12°38; free sulphate of water only 11°38; the excess in the
former case being 1°00. -
Now, in Saturating two equivalents of sulphuric acid, the heat evolved
is twice 11°38, or 22°-76; but as 12°38 is evolved in Saturating the
second equivalent of sulphuric acid, it follows that 10°38 only are evolved
in Saturating the first equivalent of acid. Hence we have—
Heat disengaged in the formation of bisulphate of potash, 10°38
25 » . Saturating acid of , , 23. 12°38
22°-76
The cold, on dissolving an equivalent of crystallized sulphate of
potash, 54-55 grains, in 100 grammes of water, was also observed:—
Before solution, , 66°69 66°01, 66°27
After solution, . . 64°38 63°75 63°-96
Fall, . . . . . 2°31 2°:26 2°31 Mean 2°:29
On mixing solutions of sulphate of potash and sulphate of water
(dilute sulphuric acid), to form bisulphate of potash, cold is produced,
as was formerly observed; and from this cause sulphate of potash, when
dissolved in water acidulated with Sulphuric acid, produces more cold
than in pure water, by about one-third of the quantity from the latter.
This excess of heat absorbed I was disposed to connect with the com-
bination of sulphate of water with sulphate of potash, and formation of
a double salt. But it is remarkable that the magnesian sulphates, which
we do not certainly know to combine with hydrated acids, as Sulphate
of potash does, likewise produce greater cold on dissolving in acidulated
than in pure water.
Thus an equivalent of crystallized sulphate of magnesia, which dis-
solves in 1000 grains of water with a fall of 0.88 R. (Chemical Memoirs,
vol. i. p. 111), dissolved in the same quantity of water already contain-
ing an equivalent of sulphuric acid with a fall of 1*12, 1°17, 1°18 R. in
three experiments; of which the mean is 1*16, being 0°28 more than
in pure water. A second equivalent of Crystallized sulphate of magnesia,
when dissolved in the same liquor, produced a fall, in three experiments,
of 0°-96, 0°-92, 0°95 R., of which the mean is 0°94, or only 0°.06 more
than in pure water. -
In an equivalent of nitric or of hydrochloric acid, the fall from the
solution of an equivalent of crystallized sulphate of magnesia was nearly
double what it is in pure water.
The fall in water containing 1 equivalent of nitric acid was 1”70,
1°68, 1°64, of which the mean is 1°67. -
DISENGAGED IN COMBINATIONS. 433
The fall in water containing 1 equivalent of hydrochloric acid was
1°70, 1°70, 1°68; mean 1°69 R.
The fall on the solution of 1 equivalent of sulphate of magnesia
in # equivalent of hydrochloric acid was 1°37, 1°37, 1°38; mean 1°37 R.
The excess of cold produced by the half equivalent of this acid, over
water alone, was therefore 0°-50; the excess by the whole equivalent of
acid 0°82; so that fully more than one-half of the effect is produced by
the first half equivalent of acid.
An excess above 1 equivalent of acid to 1 equivalent of a salt of this
class increases the depression of temperature still further, but in a less
degree than the direct proportion of its quantity. Thus the cold on
dissolving 1 equivalent of sulphate of zinc in water being 1°02 R.-
In 1% equivalent of sulphuric acid, 1°22, 1*19, 1°25; mean 1":22.
In 1 equivalent of nitric acid, 1°56, 1°55, 1°54; mean 1°55.
In § equivalent of hydrochloric acid, 1°50, 1°50, 1°47; mean 1°49.
In 1 equivalent of hydrochloric acid, 1°82, 1°83, 1°86; mean 1":83.
In 2 equivalents of hydrochloric acid, 2°26, 2°26, 2°24; mean 2°25.
The Solution of an equivalent of crystallized sulphate of iron was
attended with a fall of temperature,
In water of 1°06 R.
In 1 equivalent of sulphuric acid, of 1°28, 1°20, 1°26, 1°25; mean 1":25.
In 1 equivalent of hydrochloric acid, of 1°69, 1°68, 1°73; mean I*70.
The Solution of an equivalent of crystallized sulphate of copper was
attended with a fall of temperature,
In water of 0°-63 R.
In 1 equivalent of sulphuric acid, of 0°94, 0°-96, 1°02; mean 0°-97 R.
The mixture of an equivalent of sulphate of water, 30-68 grains, in
300 grains of water, with another 700 grains of water, occasioned a rise
of 0°09 R.; with 700 grains of water containing 1 equivalent of hydro-
chloric acid a rise of 0°16, and with 700 grains of water containing 1
equivalent of nitric acid, 0°00.
The magnesian sulphates generally resemble sulphate of water in
producing heat and not cold on dilution of their strong solutions. The
Solutions of the three following salts were Saturated in the cold:—
Sulphate of zinc (density 1:395), with equal bulk of water, + 0°-60.
Sulphate of magnesia (density 1294), with equal bulk of water,
+ 0°-60.
Protosulphate of iron (density 1-227), with equal bulk of water,
+ 0°04.
The experiments on the solution of salts in acids leave it doubtful,
whether the additional depression of temperature is due in every case
and entirely to a combination of the Salt with the acid, as it may be
supposed to be when sulphate of potash is dissolved in dilute sulphuric
2 E
434 EXPERIMENTS ON THE HEAT
acid, bisulphate of potash being then formed, or whether it is a conse-
quence of a partial decomposition of the salt by the free acid to which
it is exposed. The small portion of acid, generally a single equivalent,
which produces the greatest proportional effect, seems to indicate that
combination or decomposition is the cause, rather than any alteration in
the solvent power of the liquid. The action of hydrochloric acid and of
nitric acid is often the same, and is greater than that of Sulphuric acid.
This appears even in the solution of a magnesian chloride in water and
in these acids.
Thus 42:29 grains, 1 equivalent, of the fused anhydrous chloride of
zinc were dissolved in 1000 grains of water with a rise in two experi-
ments of 3°42, 3°45 R., of which the mean is 3°44 R. In 1000 grains
of water containing I equivalent of sulphuric acid, with a rise of 3°43,
3°42, 3°42 R., in three experiments; which is nearly the same result as
in pure water. In the same quantity of water containing 1 equivalent
of hydrochloric acid, with a rise of 2°86, 2°88, 2°86; of which the mean
is 2°87 R., being 0°57 less heat than in water alone. The presence of
the hydrochloric acid has therefore occasioned a fall of 0°57 in the solu-
tion of chloride of zinc, while the action of sulphuric acid is insensible.
An alkaline chloride was little affected by the presence of an equi-
valent of these acids in the water in which it was dissolved. Thus
chloride of sodium was dissolved with a fall—
In 1000 grs. water, of 0°57, 0°-60, Mean 0°.59 R.
25 , -ī- HCl, of 0°-60, 0°-60, 0°-60, , 0°-60 R.
33 , + NOs, of 0°-50, 0°-50, 0°52, , 0°-51 R.
33 , +SOs, of 0°50, 0°50, 0°43, , 0°48 R.
To obtain light upon this influence of acids on the thermal pheno–
mena of the solution of salts, experiments were made upon two other
salts. Sulphate of ammonia without any water of crystallization
(1 equivalent, or 41°41 grains) was observed to dissolve in 1000 grains
of water with a fall of 0°51 R. In water containing $ HCl, with a fall
of 1°12, 1°10, and 1°12 R. ; mean 1°11. In water containing HCl,
with a fall of 1°30, 1°22, 1°28; mean 1":27 R. In water containing
NO, with a fall of 1°28, 1°30, 1°30; mean 1°29 R. In water con-
taining SOs, with a fall of 0°92, 0°-92, 0°-90; mean 0°-92 R. The addi-
tion of a second equivalent of highly diluted sulphuric acid to the last
solution produced a change of temperature in three experiments of
0°02, 0°00, 0°00. The addition of a second equivalent of sulphate of
ammonia to the preceding Solutions of the bisulphate of ammonia, occa-
sioned a fall of 0°58, 0°55, 0°-60 R.; mean 0°58, or very little more
than in pure water (0°51). In 1544 grains of water containing I equi-
valent of acetic acid (32:15 grains), with a fall of 0°84, 0°78, 0°81 F.,
DISENGAGED IN COMBINATIONS. 435
of which the mean is 0°81 F., the experiment being made at 67° F.
In 1 equivalent of oxalic acid (22.64 grains), with a fall of 1°20, 1°21,
and 1°22 F, the experiment being made at 65° F. To render the last
two experiments comparable with the former, they must be reduced in
the proportion of 19 to 13, that is, the effect of the acetic acid to 0°-55 R.,
of the oxalic acid to 0°83 R.; so that the influence of the acetic acid is
almost nothing, of the oxalic acid much less than that of the mineral acids.
While 1 equivalent of nitrate of potash was dissolved in 1000 grains
of water at 63 F., with a fall of 3°76, 3°72 and 3°80 R., of which the
mean is 3°76; it was dissolved in the same quantity of water contain-
ing 1 equivalent of nitric acid at 67° F., with a fall of 3°64, 3°54, 3°64
R., of which the mean is 3°57; in the same quantity of water contain-
ing I equivalent of sulphuric acid at 58° F., with a fall of 3°53, 3’-50,
3°50 R., of which the mean is 3’-51.
The mere mixing of solutions of such neutral salts as are understood
to combine together and form a double salt, is not attended with such
changes of temperature. No sensible change of temperature was per-
ceived on mixing dilute solutions of a magnesian and potash Sulphate ;
and one of these salts was dissolved in a solution of the other with the
same fall of temperature as in pure water. Although I think it all but
certain that these salts combine at once on mixing, I could not discover
a single circumstance which was decisive of the fact. The density of
such a mixture of salts was not altered by boiling it alone or with
spongy platinum, and was exactly the same as that of the liquid formed
on dissolving in water a corresponding quantity of the crystallized
double sulphate. The addition of an equivalent of sulphuric acid
already highly diluted to each of the solutions thus compared, produced
exactly the same fall of temperature. On the other hand, this fall of
temperature was as nearly as possible the same as that obtained on
dividing the acid into two equal portions, and mixing separately a solu-
tion of each of the constituent salts with each portion. The solution of
a double Salt appears therefore to be as nearly as possible equivalent to
the constituent salts dissolved apart. Even in the formation of alum
no certain change of temperature was observable; one-fourth of an
equivalent of sulphate of potash (13.63 grains), when dissolved in 1000
grains of water, producing a fall of 0°32 R., while when dissolved in
1000 grains of water containing one-fourth of Als Os + 3 SOs, the fall
was 0°35, 0°32, 0°35 R., of which the mean is 0°34; the experiments
being made at 57 F.
But these double sulphates being all less soluble than their consti-
tuent sulphates, it was desirable to make the experiment upon the for-
mation of a double salt, which is more soluble than its constituents;
such as the double chloride of mercury and ammonium. One-half of
436 EXPERIMENTS ON THE HEAT
an equivalent of chloride of mercury, 42.70 grains, was dissolved in 1544
grains of water at 64° F., with a fall of 0°:29, 0°30, 0°30 F., of which
the mean is 0°30 F. The same quantity of chloride of mercury was
dissolved in 1544 grains of water, containing half an equivalent, 1674
grains, of chloride of ammonium, at 63°F, with a fall of 0°13, 0°12,
0°12 F., of which the mean is 0°12 F. Doubling these results, we have
the fall from a whole equivalent of chloride of mercury in water equal
to 0°-60; from chloride of mercury in chloride of ammonium 0°24; the
difference, or 0°36, being due to heat evolved in the formation of the
double salt. The latter, however, or sal-alembroth, assumes an atom of
water of crystallization in its formation, which may perhaps occasion
Some change of temperature.
When I equivalent of chloride of mercury was dissolved in half an
equivalent of chloride of ammonium at 63%, the fall was 0°45, 0°45,
0°47 F., of which the mean is 0°46 F. The disengagement of heat in the
formation of this second double salt is therefore 0°60–0°46= 0°14 F.
It is doubtful whether the heat here can be ascribed to hydration; as
the resulting double Salt has been crystallized at the usual temperature
by Dr. Kane, both anhydrous and with one atom of water. The circum-
stance however of the chloride of mercury being dissolved by a solution
of Sal-ammoniac in much larger quantity than by pure water, affords a
proof of the immediate formation of a double Salt on the solution of its
constituents together, which cannot be obtained in the magnesian or
aluminous double Sulphates.
I may be allowed to place under the present head of Sulphuric acid,
the results of experiments on the solution in water of two double sul-
phates, namely, Sulphate of zinc and Soda, and Sulphate of manganese
and soda, no experiment on a double salt of the Soda division of this
class being recorded in the former paper. The Sulphate of zinc and Soda,
formed by Mr. Arrott, was in excellent crystals, containing four atoms
of water; of which the composition is expressed by the formula ZnO,
SOs + NaO, SO3 + 4 HO. One-half of an equivalent, 58-61 grains of
the salt, containing 11.25 grains of water of crystallization, was dissolved
in 9888 grains of water at 62°F., with a fall in three experiments of
0°-02 R., 0°-04, 0°-02; mean 0°-03 R.
Of the same Salt made anhydrous by heat and fused, half an equiva-
lent, or 47.41 grains, was dissolved in 1000 grains of water at 62°F.,
with a rise in three experiments of 1°86, 1°87, 1°84; mean 1°86 R.
Doubling the results of the experiments in both cases, to obtain the
changes for a whole equivalent, we find—
Cold on solution of ZnO, SO3 + NaO, SO, + 4 HO 0°06 R.
Heat on solution of ZnO, SO3 + NaO, SOs 3°72 R.
As the two Sulphates, in all the double sulphates of this class contain-
DISENGAGED IN COMBINATIONS. 437
ing Sulphate of soda, crystallize apart when the salt is dissolved in water
at 62°, the double salt is probably decomposed in these experiments;
and the circumstances of its solution may therefore be very different from
those of a magnesian double sulphate containing sulphate of potash.
The Sulphate of manganese and soda, for which I am also indebted to
Mr. Arrott, was in good crystals containing two atoms of water; the
formula of this salt being MnO, SO3 + NaO, SO3 + 2 HO. 1 equivalent
of the crystallized salt, 103.2 grains, containing 11:25 grains of water of
crystallization, was dissolved in 988.8 grains of water, with a rise of
temperature in three experiments of 0°77, 0°70, and 0°70; of which the
mean is 0°-72 R.
Of the same salt, fused by heat and anhydrous, 1 equivalent, 91-95
grains, was dissolved in 1000 grains of water, with a rise in two experi-
ments of 3°02 and 2’-99; of which the mean is 3°00 R. The results
therefore, for this double salt, are—
Heat on solution of MnO, SO3 + 2 HO, e O”72
MnO, SOs, . tº g 3°:00
37 22
III, NEUTRALIZATION OF BICHROMATE OF POTASH BY HYDRATE OF
|POTASH.
Half an equivalent of bichromate of potash, 47:34 grains, and a little
more than half an equivalent of hydrate of potash contained separately
in different portions of the usual quantity 1544 grains or 100 grammes
of water, were brought to the same temperatures exactly, and mixed in
two experiments:—
Before mixture, . e e 63°:23 63°-50
After mixture, , e de 6.7°.71 67°-97
Rise of temperature, . e 4°48 4°47
Doubling 4°48, the mean result, we have 8°-96 F. as the heat evolved
on neutralizing the second equivalent of chromic acid in bichromate of
potash.
Of the neutral or yellow chromate of potash, which is the product
of this neutralization, 1 equivalent, 62.08 grains, was dissolved by 1544
grains of water at 65° F., with a fall in three experiments of 1°82, 1°81
and 1°87, of which the mean is 1°83.
IV. NEUTRALIZATION OF ACETIC ACID BY HYDRATE OF POTASH.
Half an equivalent of acetic acid, 16:08 grains, was neutralized by
potash in very slight excess, as in the other experiments:—
4.38 EXPERIMENTS ON THE EIEAT
Before mixture, . . 63°52 63°-81 63°-94
After mixture, . . 68°68 68°-98 69°-12
Rise of temperature, 5°16 5°-17 5°-18
The mean result of these experiments 5°17 being doubled, we have
10°34 F. as the heat evolved on the saturation of acetic acid by hydrate
of potash.
Of acetate of potash fused without becoming black, l equivalent,
61-65 grains, was dissolved in 1544 grains of water at 65° F., with a rise
of temperature in three experiments of 2°45, 2°47, 2°44; of which the
mean is 2°45 F.
W. NEUTRALIZATION OF OXALIC ACID BY HYDRATE OF POTASH.
Half an equivalent of oxalic acid was neutralized by potash under
the usual circumstances:—
Before mixture, . . 64°-60 64°-66 64°69
After mixture, . . 69°-84 69°-89 69°-95
Rise of temperature, 5°24 5°:23 5°-26
Doubling 5°24, the mean result, we have 10°48 F. as the heat evolved
on the saturation of a whole equivalent of Oxalic acid by hydrate of
potash.
One equivalent of crystallized ovalic acid, 39-50 grains, containing
12.5 grains of water of crystallization, was dissolved in 1533 grains of
water at 67° F., with a fall of 3°04, 3°06, 3°04; of which the mean is
3°05.
One equivalent of oacalate of water deprived of its water of crystal-
lization, 28.26 grains, was dissolved in 1544 grains of water at 67° F.,
with a fall of 0°-99, 0°-99, 1°01; of which 1°00 is the mean, The dif-
ference between the falls on solution of the hydrated and anhydrous
oxalate, is occasioned by the hydration of the latter on solution. The
heat disengaged when oxalate of water combines with its two atoms of
constitutional water is therefore 3°05— 1 00 = 2*05 F.
Neutral oxalate of potash crystallizes with a single atom of water,
which requires a heat of 212° to expel it. 1 equivalent of the crystallized
salt, 57-76 grains, containing 6'25 grains of water, was dissolved in 1538
grains of water at 67° F., with a fall of 2°65, 2°66 and 2°-67; of which
the mean is 2°66 F.
Of the same salt made anhydrous by heat, one-half of an equivalent,
25-75 grains, was dissolved in 1544 grains of water, with a fall of 0°76,
DISENGAGED IN COMBINATIONS, 439
0°71, 0°74; of which the mean is 0°74. A whole equivalent of the salt
would therefore have dissolved with a fall of 1°58, which is 1°08 less
than the fall from the hydrated Salt. The last quantity represents the
heat of combination of oxalate of potash with one atom of water of crys-
tallization. It approaches nearly to one-half of the heat disengaged by
oxalate of water, in combining with two atoms of water, one-half of 2*05
being 1°025; the difference is within the errors of observation.
When hydrated oxalate of potash is dissolved in water containing
oxalic acid, the change of temperature is very much the same as in pure
water, although in the former case a superoxalate will be formed. One-
fourth of an equivalent of oxalate of potash, 14°44 grains, was dissolved
in 1544 grains of water containing in solution one-fourth of an equi-
valent of hydrated oxalic acid, at 67° F., with a fall of 0°70, 0°68, 0°68;
mean 0°68 F. If it were therefore possible to dissolve a whole equiva-
lent of the salt in a whole equivalent of the acid contained in the quantity
of water to which we are restricted, the fall would be four times greater,
or 2°72 F., which is nearly the same as the cold on dissolving crystal-
lized oxalate of potash in water, namely, 2°66. Here again little or
no heat is observed in forming a double salt, for the binoxalate of potash
must be regarded as such.
Binoacalate of Potash. KO, C,0s + HO, C,0s, 2EIO.—As with bisul-
phate of potash, the saturation of the excess of acid in this Salt causes
the disengagement of more heat than the saturation of the same quantity
of free acid. One-fourth of an equivalent of the crystallized binoxalate,
22.91 grains, was neutralized by hydrate of potash at 67°:—
Before mixture, . . 66°-80 66°85 66°-96
After mixture, . . 69°91 69°96 70°04
Rise of temperature, 3°1] 3°-11 3°08 Mean 3°10
The mean quantity, multiplied by four, gives 12°40 F., as the heat
evolved on neutralizing by potash the second equivalent of Oxalic acid
in binoxalate of potash. Now distributing the heat from the saturation
of two equivalents of oxalic acid, 20°68 (= 10°34 × 2), as was done in
sulphuric acid, we have—
Heat disengaged in the formation of binoxalate of pot. 8°28
25 32 in Saturating acid of binoxalate of pot. 12°40
20°.68
One-fourth of an equivalent of binoxalate of potash, 22.91 grains,
containing 6'25 grains of water of crystallization, was dissolved in
1538 grains of water at 64° F., with a fall of 1°65, 1°66, 1°65; mean
1°65 F. The mean result multiplied by four, gives 6*60 F. as the fall
440 EXPERIMENTS ON THE EIEAT
on dissolving a whole equivalent of binoxalate of potash in water. This
is 0°89 more than the sum of the falls on dissolving the constituent
salts separately, 2°66 +3°05 being equal to 5’71 only.
Quadroaialate of Potash. KO, C, Os -- HO, C, Os–H 2 (HO, C, Os
+ 2 HO).-Four-sixths of an equivalent of hydrated oxalic acid, 26-22
grains, were mixed with one-sixth of an equivalent of potash exactly to
form this salt —
Before mixture, . e 64°-25 64°23 64°-25
After mixture, . º 66°-01 66°-01 65°-99
Bise of temperature, . 1°.76 1°78 1°-74
The mean result 1°76 multiplied by six, gives 10°56, as the heat
evolved in the formation of quadroxalate of potash; that is, in the
saturation of 1 equivalent of potash by 1 of Oxalic acid, and the further
combination of that oxalate of potash with 3 equivalents of oxalate of
water. This rise of temperature is nearly the same as that in the for-
mation of neutral oxalate of potash, namely 10°48.
To observe the heat disengaged on neutralizing quadroxalate of
potash by hydrate of potash, one-sixth of an equivalent of that acid salt
in solution was mixed with three-sixths of an equivalent, or rather
more, of the alkali, so as to form neutral oxalate:—
Before mixture, . º 64°-19 64°:20 64°-51
After mixture, . e 69°38 69°42 69°-71
Rise of temperature, . 5°-19 5°-22 5°:20
Doubling 5°20, the mean result, we have 10°40 F as the heat dis-
engaged on Saturating 1 equivalent of potash by each of the 3 atoms of
oxalate of water in the quadroxalate of potash.
0.192 equivalent (30.70 grains) of quadroxalate of potash was dis-
solved in 1540 grains of water at 63, with a fall of 2°02, 2°13, 2°14;
of which the mean is 2°10 F. This gives by calculation a fall of 10°-93
for the solution of a whole equivalent of quadroxalate of potash, which
is 0°88 less than the fall of its constituent salts dissolved separately,
2°-66 with three times 3’-05 amounting to 11°81.
The different oxalates enumerated appear to absorb quantities of
heat, on dissolving, which have a simple relation to each other. Thus,
dividing the different falls of temperature by 0°88, a number which
has more than once presented itself in the discussion of these experi-
ments, we obtain a set of ratios given in the Second column; and which,
being multipled by two in the third column, approach nearly to round
numbers:–
DISENGAGED IN COMBINATIONS. 441
I. II. III.
Cold on solution. Ratios. Ratios.
O
Cr. oxalate of potash, { } 2°-66 3'02 6:04 6.
Cr. Oxalic acid, G tº 3°-05 3:47 6-94 7.
Cr. binoxalate of potash, . 6°-60 7:50 15:00 15.
Cr. quadroxalate of potash, 10°-93 12'42 24'84. 25.
VI. NEUTRALIZATION OF BICARBONATE OF POTASH WITH HYDRATE OF
POTASH.
Half an equivalent of the crystallized salt, 31.38 grains, dissolved in
Water, was neutralized with hydrate of potash :-
Before mixture, . º 67°-28 67°-93 6.7°.68
After mixture, . º 70°-66 71°:24 71°-03
Rise of temperature, . 3°38 3°31 3°35
Doubling 3°35, the mean result, there is obtained 6°70 as the heat
disengaged on Saturating the second proportion of carbonic acid in the
bicarbonate of potash.
One equivalent, 62-76 grains, of the crystallized bicarbonate was
dissolved in 100 grammes of water at 67°, with a fall in three experi-
ments of 3°68, 3°-69 and 3°74 ; mean 3°70.
One equivalent of anhydrous carbonate of potash was dissolved in
100 grammes of water at 67, with a rise in three experiments of 2°48,
2°43 and 2’-47; mean 2°46. The heat evolved on dissolving anhy-
drous acetate of potash is nearly the same, being 2°45.
VII. NEUTRALIZATION OF ARSENIC AND PHOSPHORIC ACIDS By
HYDRATE OF POTASH.
Half an equivalent of arsenic acid, 36°00 grains, in solution as
usual, was mixed with exactly half an equivalent of hydrate of potash,
to form the binarseniate of potash (2HO, KO, AsO.):—
Eefore mixture, . & 63° 04 63°-19 63°29
After mixture, . e 68°-14 68°-30 68°38
Rise of temperature, . 5°-10 5°-11 5°-09
Doubling 5*10, the mean result, we obtain 10°20 F. as the heat
disengaged by neutralizing 1 equivalent of potash in the formation of
binarseniate of potash.
4 42 EXPERIMENTS ON THE HEAT
One-fourth of an equivalent of arsenic acid, 18:00 grains, was mixed
with exactly half an equivalent of potash, to form arseniate of potash
(H0, 2KO, AsO.):—
Before mixture, . . 63°27 63°33 63°42
After mixture, . . 67°87 67°94 68°05
Rise of temperature, 4°60 4°-61 4°63 Mean 4°61
Twice 4°61, or 9°22 F, is therefore the heat disengaged on neutral-
izing 1 equivalent of hydrate of potash in the formation of the neutral
arseniate of potash.
The same salt was formed by mixing together solutions of half an
equivalent of binarseniate of potash, 56.37 grains, and exactly half an
equivalent of potash :-
Before mixture, . . . 64°28 64°-27 64°:20
After mixture, . . . 68°31 68°-33 68°26
Rise of temperature, . 4°03 4°-06 4”-06
Taking 4°05 as the mean, we have twice that quantity, or 8*10 F.,
as the heat disengaged on neutralizing 1 equivalent of potash with the
acid in binarseniate of potash.
On forming the subarseniate of potash (3KO, AsO.), by mixing
together solutions of one-sixth of an equivalent of arsenic acid and
exactly half an equivalent of potash —
Before mixture, . . . 63°41 63°-50 63°-50
After mixture, . . . 67°40 67°-52 67°49
Rise of temperature, . 4°09 4”-02 3°-99
Doubling 4°03, the mean result, we have 8°06 F. as the heat dis–
engaged in the formation of one-third of an equivalent of subarseniate
of potash, or in the neutralization of each of 3 equivalents of potash by
a single equivalent of arsenic acid.
Hence the successive addition of 3 equivalents of potash to 1 of
arsenic occasions the following disengagements of heat:-
By first KO 10°20; formation of binarseniate of potash.
, second KO 8*10; formation of arseniate of potash.
, third KO 5°88; formation of subarseniate of potash.
24°18 – 8:06 x 3.
Of hydrated phosphoric acid, which had been boiled in water for a
considerable time to render it fully tribasic, half an equivalent was
DISENGAGED IN COMBINATIONs. 443
mixed with half an equivalent of potash, to form biphosphate of potash
(2HO, KO, PO):—
Before mixture, . . . 64°00 64°:00 64”-03
After mixture, . . . 69°01 68°-99 69°02
Rise of temperature, . 5°01 4°-99 4°-99
Taking 5°00 as the mean, we have 10°00 F as the heat disengaged
on saturating 1 equivalent of potash with 1 equivalent of phosphoric
acid in the formation of biphosphate of potash, containing KO + 2.HO
as bases.
By mixing one-fourth of an equivalent of phosphoric acid with half
an equivalent of potash, phosphate of potash (HO, 2KO, PO):—
Before mixture, . . . 64°00 63°-61 63°-63
After mixture, . . . 68°49 68°08 68°-18
Rise of temperature, . 4°49 4°47 4°-55
Doubling the mean result, 4°50, we have 9°00 F. as the heat dis–
engaged in forming half an equivalent of neutral phosphate of potash,
or in Saturating each of 2 equivalents of potash by 1 equivalent of phos-
phoric acid, in the formation of phosphate of potash.
The same phosphate of potash was formed by mixing solutions of
half an equivalent of biphosphate of potash with half an equivalent of
potash :-
Before mixture, . . . 64°06 64°14 64°15
After mixture, . . . 68°09 68°-15 68°16
Rise of temperature, . 4°03 4”-01 4°01
Doubling 4°02, the mean result, we have 8°04 F. as the heat dis-
engaged on Saturating an equivalent of potash with the acid of biphos-
phate of potash.
To form the subphosphate of potash (3RO, PO.), one-sixth of an
equivalent of phosphoric acid, 7:43 grains, was mixed with half an
equivalent of potash :-
Before mixture, . . . 63°61 63°.67 63°-69
After mixture, . . . 67°87 67°-93 6.7°.99
Rise of temperature, . 4°26 4°-26 4°30
Twice the mean result, 4°27, is 8°54 F., which is the heat disengaged
on neutralizing each of three equivalents of potash by a single equiva-
lent of phosphoric acid.
The heat therefore disengaged in the gradual saturation of phos-
phoric acid by 3 equivalents of potash may be thus distributed:—
444 ON THE DIFFUSION OF LIQUIDS.
By first equivalent of potash, . . 10°00
, Second 2) 35 8°-08
, third 25 3) 7°-54
25°-62 = 8.54 × 3.
XII.
ON THE DIFFUSION OF LIQUIDS."
THE BAKERIAN EECTURE.
From Phil. Trans. 1850, pp. 1-46, 805-836; 1851, pp. 483-494. [Annal. de Chemic
xxix. 1850, pp. 197-229; Brit. Assoc. Rep. 1851 (Pt. 2), p. 47; Chem. Soc. Journ.
iii. 1851, pp. 60-67; Jour. de Pharm. xix. 1851, pp. 394-401; Liebig, Annal.
lxxvii. 1851, pp. 56-89, 129-160; Phil. Mag. xxxvii. 1850, pp. 181-198, 254-281,
341-349.] w
ANY saline or other soluble substance, once liquefied and in a state
of solution, is evidently spread or diffused uniformly through the mass
of the solvent by a spontaneous process.
It has often been asked whether this process is of the nature of the
diffusion of gases, but no satisfactory answer to the question appears to
be obtained, owing, I believe, to the subject having been studied chiefly
in the operations of endosmose, where the action of diffusion is compli-
cated and obscured by the imbibing power of the membrane, which is
peculiar for each soluble substance, but no way connected with the
diffusibility of the substance in water. Hence also it was not the dif-
fusion of the salt, but rather the diffusion of the solution, which was
generally regarded. A diffusibility like that of gases, if it exists in
liquids, should afford means for the separation and decomposition even
of unequally diffusible substances, and being of a purely physical char-
acter, the necessary consequence and index of density, should present a
scale of densities for substances in the state of solution, analogous to
vapour densities, which would be new to molecular theory.
M. Gay-Lussac proceeds upon the assumed analogy of liquid to
gaseous diffusion in the remarkable explanation which he suggests of
the cold produced on diluting certain Saline solutions, namely, that the
molecules of the salt expand into the water like a compressed gas
admitted into additional space.
* Received November 16,-Read December 20, 1849.
ON THE DIFFUSION OF LIQUIDS. 445
The phenomena of solubility are at the same time considered by that
acute philosopher as radically different from those of chemical affinity,
and as the result of an attraction which is of a physical or mechanical
kind. The characters indeed of these two attractions are strongly con-
trasted. Chemical combination is uniformly attended with the evolu-
tion of heat, while solution is marked with equal constancy by the
production of cold. The substances which combine chemically are the
dissimilar, while the soluble substance and its solvent are the like or
analogous in composition and properties.
In the consideration of solubility, attention is generally engrossed en-
tirely by the quantity of Salt dissolved. But it is necessary to apprehend
clearly another character of solution, namely, the degree of force with
which the salt is held in solution, or the intensity of the solvent attrac-
tion, quite irrespective of quantity dissolved. In the two solid crystal-
line hydrates, pyrophosphate of Soda and Sulphate of soda, we see the
same ten equivalents of water associated with both salts, but obviously
united with unequal degrees of force, the one hydrate being persistent
in dry air and the other highly efflorescent. So also in the solutions of
two salts which are equally soluble in point of quantity, the intensity
of the attraction between the salt and the water may be very different,
as exemplified in the large but feeble solubility in water of such bodies
as the iodide of starch or the sulphindylate of potash, compared with
the solubility of hydrochloric acid or of the acetate of potash, which last
two substances are capable of precipitating the two former, by displacing
them in solution. Witness also the unequal action of animal charcoal
in withdrawing different salts from Solution, although the salts are
are equally soluble; and the unequal effect upon the boiling-point of
water produced by dissolving in it the same weight of various salts.
Besides being said to be small or great, the Solubility of a substance has
also therefore to be described as weak or strong.
The gradations of intensity observed in the solvent force are parti-
cularly referred to, because the inquiry may arise how far these grada-
tions are dependent upon unequal diffusibility; whether indeed rapidity
of diffusion is not a measure of the force in question.
I have only further to premise, that two views may be taken of the
physical agency by which gaseous diffusion itself is effected, which are
equally tenable, being both entirely sufficient to explain the pheno-
I0.62E18. -
On one theory, that of Dr. Dalton, the diffusibility of a gas is referred
immediately to its elasticity. The same spring or self-repulsion of its
particles which sends a gas into a vacuum, is supposed to propel it
through and among the particles of a different gas.
The existence of an attraction of the particles of one gas for the
446 ON THE DIFFUSION OF LIQUIDS.
particles of all other gases is assumed in the other theory. This attrac-
tion does not occasion any diminution of volume of gases on mixing,
because it is an attraction residing on the surfaces only of the gaseous
molecules. It is of the same intensity for all gases, hence its effect in
bringing about intermixture is dependent upon the weight of the mole-
cules of the gases to be moved by it; and the velocity of diffusion of a
gas comes to have the same relation to its density on this hypothesis as
upon the other."
The surface attraction of molecules assumed will recall the surface
attraction of liquids, which is found necessary to account for the eleva-
tion of liquids in tubes and other phenomena of capillary attraction.
(1) An early preliminary experiment was made upon the liquid
diffusion of a body, with whose diffusion as a gas we are already well
acquainted, namely, carbonic acid dissolved in water.
Two half-pound stoppered glass bottles were selected, of which the
mouths were 1-2 inch in diameter, and the lips were ground flat so as
to close tight when applied together (fig. 1.)
One of them, placed firmly in an upright
position, was filled to the base of the neck
with carbonic acid water. Over this distilled
water was poured, care being taken to disturb
the liquid below as little as possible, in filling
* up the neck. The second bottle, filled with
distilled water and inverted upon a glass plate,
FIG. 1.

was slipped over the first at the water-trough.
The solution of carbonic acid in the lower
bottle was thus placed in free communication
by an aperture of 1:2 inch, with an equal vo-
lume of pure water in the upper bottle. It was
expected that the carbonic acid would be found,
in time, equally diffused through both bottles.
After forty-eight hours, the upper inverted bottle was again slipped
off from the lower one, upon a glass plate, and the ratio of the gas
found in the upper to that in the lower bottle determined by the weight
of carbonate of baryta which the liquids of the two bottles afforded re-
spectively. It was as 1:18 to 1280 (about 1 to 11), instead of the ratio
of equality, which would undoubtedly be the ultimate result of diffusion,
were sufficient time allowed.
1 Both of the molecular theories of the diffusion of gases were first publicly explained,
and at the same time ably discussed, with the reference to the law of diffusion which
had been drawn from observation, by my late friend Mr. T. S. Thomson of Clitheroe.
A decided preference was given by Mr. Thomson, and also by the late Mr. Ivory, to
the last, or the attraction theory of diffusion, over that of gases being vacua to each
other. See Phil. Mag., 3d series, vol. xxv, pp. 51, 282.
ON THE DIFFUSION OF LIQUIDS. 447
After five days, in a second experiment with a weaker solution of
Carbonic acid, the gas was found to be distributed—
In upper bottle, ſº * o 1:63
In lower bottle, e tº & 8’44
or in the proportion of 1 to 5 nearly.
In other experiments where the liquid in the upper bottle was a
solution in water of nitrous oxide gas, instead of pure water, the car-
bonic acid of the lower bottle was also observed to diffuse into the
liquid above it, as freely as it did into pure water in a comparative
experiment; the ultimate ratios being 1 to 0-12 in the nitrous oxide
liquid, and 1 to 0-10 in the water experiment.
With the necks of the pair of bottles occupied by sponge charged
with distilled water, the diffusion of the carbonic acid of the lower
bottle proceeded with little change in its rapidity, or in the result when
nitrous oxide was placed above it. The carbonic acid found in the
upper bottle, and which had diffused into it from the lower, was 0.231
when the upper bottle contained water alone, and 0.229 when it was
water charged with three-fourths of its volume of nitrous oxide gas, to
1 carbonic acid remaining undiffused in the lower bottle in both cases.
It appeared, then, that the liquid diffusion of carbonic acid was a
slow process compared with its gaseous diffusion, quite as much as days
are to minutes.
That this diffusion of the liquid carbonic acid takes places with
undiminished vigour into water already saturated with nitrous oxide,
the substance of all others most resembling carbonic acid in solubility
and the whole range of its physical qualities. The diffusion of the
liquid carbonic acid appears no more repressed by the liquid nitrous
oxide, than the diffusion of gaseous carbonic acid is by gaseous nitrous
oxide.
But the chief interest of these observations was the practical solu-
tion which they give to the question, whether, in conducting experi-
ments on liquid diffusion, accidental causes of disturbance and inter-
mixture of two liquids, communicating freely with each other, can be
avoided. It was made evident that little is to be feared from accidental
dispersion when ordinary precautions are taken.
An excess of density in the lower liquid of not more than Tºro part
is found adequate to prevent any considerable change of place of the
latter, from expansion by heat, accidental tremors and such disturbing
causes, which must exist,-for days together.
(2) Another early inquiry was, how far is the diffusion of various
salts governed or modified by the density of their solutions.
Solutions of eight hydrated acids and salts were prepared, having
4.48 ON THE DIFFUSION OF LIQUIDS.
the common density of 1:200, and were set to diffuse into water in the
following manner :—
Eighteen or twenty six-ounce phials were made use of to contain
the solutions, and to form what I shall call the Solution phials or cells.
They were of the same make and selected from a large stock, of the
common aperture of 1.175 inch. Both the mouths and bottoms of these
phials were ground flat. The mode of making an experiment was first
to fill the phial to the base of the neck, or rather to a constant distance
of 0-6 inch below the ground surface of the lip. A little disc of Cork,
provided with a slight upright peg of wood, was then floated upon the
solution in the neck, after having been first dipt in water. The neck
itself was now filled up with pure water by means of a pointed Sponge,
the drop suspended from the sponge being made to touch the peg of
the float, and water caused to flow in the gentlest manner, by slightly
pressing the sponge. The only other part of the apparatus, the Water-
jar, was a plain cylindrical glass jar, of which the inner surface of the
bottom was flat or slightly concave, to give a firm support to the phial.
The phial, with its solution only, was first placed in this jar partly
filled with distilled water, and the neck of the former was then filled
up with distilled water in this position, as before described, to avoid
any subsequent movement. The phial was ultimately entirely covered
to the depth of an inch with water, which required about 30 ounces of
FIG. 2. the latter, fig. 2. The saline solution in the diffu-
<= sion cell or phial thus communicated freely with
gº. -- about 5 times its volume of pure water, the liquid
s=r atmosphere which invites diffusion. Another modi-
s fication of this procedure was the substitution of
phials cast in a mould, of the capacity of 4 ounces, or
more nearly 2080 grs., which were ground down to
a uniform height of 3-8 inches. The neck was 1:25
- inch in diameter and 0-5 inch in depth ; and the
S-E- phial was filled up with the solution to be diffused
to that point. The solution cell or phial and the water-jar form together
a Diffusion cell. - -
The diffusion was stopped, after twenty-seven days in the present
experiments, by closing the mouth of the phial with a plate of glass,
and then raising it out of the water-jar. The quantity of salt or of
acid which had found its way into the water-jar-the diffusion product
as it may be called,—was then determined by evaporating to dryness
for the salts, and by neutralizing the same liquid with a normal alkaline
solution for the acids. The quantities of the acids diffused are esti-
mated at present as protohydrates for the Sake of comparison with the
salts. - -

ON THE DIFFUSION OF LIQUIDS. 449
TABLE I—Diffusion of Solutions of Density 1200. Temp. 66°Fahr.

Placed in solution cell. Found in water-jar.
Proportion of Diffusion product.
anhydrous salt, or of |Boiling-
acid protohydrate, point.
to 100 of water. In grains. Ratio.
«» O
Chloride of sodium........................ 34-21 225.5 269-80 || 100
Nitric acid................................. 37.93 227 581-20 215:42
Sulphuric acid............................. 29-03 223 455-10 | 168-68
Chloride of potassium (density 1-178) 34.86 22I 320-30 || 118-71
Bisulphate of potash..................... 31-85 216 319-00 || 118-23
Nitrate of soda............................ 32°42 220 260°20 96-44.
Sulphate of magnesia..................... 22:38 214 95.87 35-53
Sulphate of copper.............. .......... 21.56 213% 77.47 28-71
It appears that the diffusion from solutions of the same density is
not equal but highly variable, ranging from 1 to 0-1333.
The results also favour the existence of a relation between large or
rapid diffusibility and a high boiling-point. The latter property may
be taken to indicate of itself a high degree of attraction between the
salt and water. -
I. CHARACTERS OF LIQUID DIFFUSION.
1. Diffusion of Chloride of Sodium.
The characters of liquid diffusion were first examined in detail in the
case of this salt. * -
(1) Do different proportions of chloride of sodium in solution give
corresponding amounts of diffusion ?
Solutions were prepared of chloride of sodium in the proportion of
100 water with 1, 2, 3, and 4 parts of the salt.
The diffusion of all the solutions was continued for the same time,
eight days, at the mean temperature of 52°5 Fahr.

Diffusion product.
Proportion of salt to 100 water.
In grains. Ratio.
l 2.78 1.
2 5-54 I '99
3 8-37 3-01
4 11 *ll 4'00
2 F
450 ON THE DIFFUSION OF LIQUIDS.
The quantities diffused appear therefore to be closely in proportion
(for this salt) to the quantity of salt in the diffusing solution. The
density of the solutions containing 1, 2, 3, and 4 parts of chloride
of sodium, was at 60°, 1:0067, 1:01.42, 1-0213, 10285. The increase
of density corresponds very nearly with the proportion of chloride of
Sodium in solution. A close approach to this direct relation is indeed
observable in most salts, when dissolved in proportions not exceeding
4 or 5 per cent.
The relation which appears in these results is also favourable to the
accuracy of the method of experimenting pursued. The variation from
the speculative result does not in any observation exceed 1 per cent.
(2) Is the quantity of salt diffused affected by temperature ?
The diffusion of similar solutions of chloride of sodium was repeated
at two new temperatures, 39°-6 and 67”, the one being above and the
other below the preceding temperature. It was necessary to use artifi-
cial means to obtain the low temperature owing to the period of the
season. A close box of double walls, namely, the ice-safe of the Wen-
ham Ice Company, was employed, masses of ice being laid on the floor
of the box, and the water-jars supported on a shelf above. The water
and solution were first cooled separately for twenty-four hours in the
ice-box, before the diffusion was commenced. It was found that the
temperature could be maintained within a range of 2° or 3° for eight
days. It was doubtful however whether the temperature was constantly
the same to a degree or two in all the jars; and the results obtained at
an artificial temperature were always less concordant and sensibly
inferior in precision to observations made at the atmospheric tempera-
ture.
I)iffusion of Chloride of Sodium.
Diffusion product.
Proportion of salt to 100 water.
In grains. Ratio.
1 At 39°-6 2.63 1.
2 At 39°-6 5.27 2:00
3 At 39°-6 7-69 2-92
4 At 39°-6 10:00 3.80
I At 67° 3.50 1-
2 At 67° 6'89 1.97
3 At 67° 9-90 2.83
4. At 67° 13-60 3-89

The proportionality in the diffusion is still well preserved at the
different temperatures. The deviations are indeed little, if at all, greater
ON THE DIFFUSION OF LIQUIDS. 451
than might be occasioned by errors of observation. The ratio of diffu-
sion, for instance, from the solutions containing 4 parts of salt, is 3.80
and 3.89 for the two temperatures, which numbers fall little short of 4.
The diffusion manifestly increases with the temperature, and as far
as can be determined by three observations, in direct proportion to the
temperature. The diffusion-product from the 4 per cent. Solution in-
creases from 10 grs. to 1360, with a rise of temperature of 27°4, or
rather more than one-third. Supposing the same progression continued,
the diffusibility of chloride of sodium would be doubled by a rise of 84
or 85 degrees.
(3) The progress of the diffusion of chloride of sodium in such ex-
periments as have been narrated was further studied by intercepting
the operation after it had proceeded for different periods of 2, 4, 6, and
8 days. The solution exployed was that containing 4 parts of salt to
100 water. Two of the six-ounce phials were diffused at the same time
for each period. The temperature given is the mean of the tempera-
tures of a water-jar observed each each day of the period. The daily
fluctuation was not more than two or three-tenths of a degree Fahr.
In 2 days, temperature 63°7; the salt diffused was 4:04 and 3.86
grs. ; mean 395 grs.
In 4 days, temperature 63°7; the salt diffused was 678 and 7-12
grs. ; mean 6'95 grs.
In 6 days, temperature 63°8; the salt diffused was 10:02 and 9.70
grs. ; mean 9:86 grs.
In 8 days, temperature 64°; the salt diffused was 13:00 and 13:25
grs. ; mean 13 12 grs.
The proportion diffused in the first period of two drys is given
directly in the first experiments. The proper diffusion for each of the
three latter periods of two days is obtained by deducting from the result
of each period the result of the period which precedes it :—
Diffused in 1st two days, . & 3.95 grs.
Diffused in 26 two days, e. º 3:00 grs.
Diffused in 3d two days, e o 2.91 grs.
Diffused in 4th two days, . e 3.26 grs.
The diffusion appears to proceed pretty uniformly, if the amount
diffused in the first period of two days be excepted. Each of the phials
contained at first about 108 grs. of salt, of which the maximum quantity
diffused is 13:12 grs. in eight days, or sºn of the whole salt. Still the
diffusion must necessarily follow a diminishing progression, which
would be brought out by continuing the process for longer time, and
appear at the earliest period in the salt of most rapid diffusion.
All the experiments which follow being made like the preceding on
452 ON THE DIFFUSION OF LIQUIDS.
comparatively large volumes of solution in the phial, and for equally
short periods of seven or eight days, may be looked upon as exhibiting
pretty accurately the initial diffusion of such solutions, the influence of
the diminishing progression being still small. The volume of water in
the water-jar is also relatively so large, that the experiment approaches
to the condition of diffusion into an Unlimited Atmosphere.
2. Diffusion of various Salts and other Substances.
With these notions regarding the influence of temperature and pro-
portion of salt on the amount of diffusion, an examination was next
undertaken of the relative diffusibility of a variety of salts and other
substances. The results of this first survey I shall state as shortly as
possible, as I consider these, as well as the experiments which preceded,
as of a preliminary character. The experiments were all made by
means of the diffusion phials already described, namely, the six-ounce
phials, and with similar manipulations.
In the following experiments, the diffusion took place at a tempera-
ture ranging from 62° to 59°, mean 60°-5, and was continued for a period
of eight days; the proportion of salt in solution to be diffused being
always 20 salt to 100 water, or 1 to 5. I add as usual the density of
the Solutions.
TABLE II.-Diffusion of solutions of 20 salt to 100 water, at 60°5,
for eight days. -
Anhydrous salt diffused.
Name of Salt. S gº.
In grains. Means.
Chloride of sodium ..................... 1.1265 58'5
Chloride of sodium..................... I 1265 58.87 58.68
Sulphate of magnesia.................. 1-185 27:42 27:42
Nitrate of soda ........................ 1 - 120 52. I
Nitrate of soda ........................ l'120 51*02 51-56
Sulphate of water ..................... I 108 68-79
Sulphate of water ..................... I 108 69'86 69-32
Crystallized cane-sugar ............... 1-070 26-74 26-74
Fused cane-sugar ..................... 1-066 26-21 26.21
Starch-sugar (glucose)..............., e 1.061 26-94 26'94
Treacle of cane-sugar .................. 1-069 32°55 32°55
Gum-arabic .............................. 1-060 13:24 13:24
Albumen ................................. 1-053 3:08 3:08

The following additional ratios of diffusion were obtained from
similar solutions at a somewhat lower temperature, namely 48°;—
chloride of sodium 100, hydrate of potash 151.93 (ammonia from a 10
ON THE DIFFUSION OF LIQUIDS. 453
per cent. solution, saturated with chloride of sodium to increase its
density, 70), alcohol saturated with chloride of sodium 75-74, chloride of
calcium 71°23, acetate of lead 45°46.
Where two experiments upon the same Salt are recorded in the table
they are seen to correspond to within 1 part in 40, which may be con-
sidered as the limit of error in the present observations. It will be
remarked that the diffusion of cane- and starch-sugar is sensibly equal,
and double that of gum-arabic. On the other hand, the sugars have less
than half the diffusibility of chloride of sodium. It is remarkable that
the specifically lightest and densest solutions, those of the sugars and of
sulphate of magnesia, approach each other closely in diffusibility. On
comparing together, however, two Substances of similar constitution,
such as the two salts, chloride of sodium and Sulphate of magnesia, that
salt appears to be least diffusive of which the solution is densest.
But the most remarkable result is the diffusion of albumen, which is
low out of all proportion when compared with saline bodies. The solu-
tion employed was the albumen of the egg, without dilution, but strained
through calico and deprived of all vesicular matter. As this liquid,
with a density of 1:04.1, contained only 14.69 parts of dry matter to 100
of water, the proportion diffused is increased in the table to that for 20
parts, to correspond with the other substances. In its natural alkaline
state the albumen is least diffusive, but when neutralized by acetic acid,
a slight precipitation takes place and the liquid filters more easily.
The albumen is now sensibly more diffusive than before. Chloride of
sodium appears 20 times more diffusible than albumen in the table,
but the disparity is really greater; for nearly one-half of the matter
which is diffused consisted of inorganic salts. Indeed, the experiment
appears to promise a delicate method of proximate analysis peculiarly
adapted for animal fluids. The value of this low diffusibility in retain-
ing the serous fluids within the blood-vessels at once suggests itself.
Similar results were obtained with egg albumen diluted and well
beaten with 1 and 2 volumes of water. The solution diluted with an
equal bulk of water, and made slightly acid with acetic acid, contained
7% dry matter to 100 water. Diffused from two four-ounce bottles of
1.25 inch aperture, for seven days, at a mean temperature of 43°5 Fahr.,
it gave products of 1.73 and 1:48 gr., from the evaporation of two
water-jars, in which cubic crystals of common salt were abundant. The
whole matter thus diffused in two cells was found to consist of
Coagulable albumen, . º 0.94 gr.
Soluble salts, tº e tº 227 grs.
..3-21 grs.
The diffusion product of the same solution of albumen left alkaline,
454 ON THE DIFFUSION of LIQUIDS.
or without the addition of acetic acid, in the same circumstances, was
1:41 and 120 grs. in two cells, and consisted of—
Coagulable albumen, . º 0.63 gr.
Soluble salts, e tº e 1.98 gr.
2.61 grs.
The diffusion product of a solution of 74 parts of chloride of sodium
to 100 water, from similar cells and for the same time and temperature,
would amount to about 30 grs. of salt. It is to be remarked also that
5:53 grs. of the ignited salt diffused from albumen contained 1:32 gr. of
potash or 23.9 per cent, which is a high proportion, and indicates that
Salts of potash diffuse out more freely from albumen than salts of soda.
Nor does albumen impair the diffusion of salts dissolved together
with it in the same solution, although the liquid retains its viscosity.
Three other substances, added separately in the proportion 5 parts to
100 of the undiluted solution of egg albumen, were found to diffuse out
quite as freely from that liquid as they did from an equal volume of
pure water: these were chloride of sodium, urea, and sugar. Urea proved
to be a highly diffusible substance. It nearly coincided in rate with
chloride of sodium.
A second series of salts were diffused containing 1 part of salt to 10
of water; a smaller proportion of salt which admits of the comparison of
a greater variety of salts. The temperature during the period of eight
days was remarkably uniform, 60°–59°.
TABLE III–Diffusion of solutions of 10 salt to 100 water at 59°5.

Anhydrous salt diffused.
Name of Salt. sº
In grains. Means.
Chloride of sodium .................. 1-0668 32.3
Chloride of sodium ............... .. 1-0668 32.2 32-25
Nitrate of soda ........................ 1.0622 30-7 30-7
Chloride of potassium ............... 1*0596 40° 15 40° 15
Chloride of ammonium ............... 1:0280 40-20 40:20
Nitrate of potash ..................... 1-0589 35"] .
Nitrate of potash ..................... 1-0589 36-0 35-55
Nitrate of ammonia. .................. 1-0382 35-3 35-3
Iodide of potassium .................. I'0673 37:0 37:0
Chloride of barium..................... 1'0858 27-0 27.0
Sulphate of water ..................... 1.0576 37:18
Sulphate of water ..................... 1.0576 36-53 36'85
Sulphate of magnesia.................. 1-0965 15-3
Sulphate of magnesia.................. 1-0965 15-6 15:45
Sulphate of zinc........................ 1°0984 15-6
Sulphate of zinc........................ 1'0984 16:0 15-80
ON THE DIFFUSION OF LIQUIDS. 455
Before adverting to the relations in diffusibility which appear to
exist between certain salts in the preceding table, I may state the results
of the diffusion of the same solutions at a lower temperature.
TABLE IV.--Diffusion of solutions of 10 salt to 100 water at 37°5.
Anhydrous salt diffused.
Name of Salt.
In grains. Means.
Chloride of sodium ................................. 22-21
Chloride of sodium ................................. 22-74 22:47
Nitrate of soda....................................... 22-53
Nitrate of soda................................. ..... 23:05 22-79
Chloride of ammonium ........................... 31'14 3] : 14
Nitrate of potash................................ • * g tº 28:84
Nitrate of potash.................................... 28'56 28-70
Nitrate of ammonia................................. 29' 19 29' 19
Iodide of potassium................................. 28-10 28-10
Chloride of barium ................................. 21:42 21:42
Sulphate of water ................................. 31-11
Sulphate of water ................................. 28-60 29-85
Sulphate of magnesia .............................. 13:03
Sulphate of magnesia.............................. 13-11 13-07
Sulphate of zinc .................................... 11-87
Sulphate of zinc .................................... 13-33 12-60
The near equality of the quantities diffused of certain isomorphous
salts is striking at both temperatures. Chloride of potassium and
chloride of ammonium give 40:15 and 40:20 grs. respectively in the first
table. Nitrate of potash and nitrate of ammonia 35-55 (mean) and 35.3
grs. respectively in the first table, and 28.70 and 29:19 grs, in the second
table. Sulphate of magnesia and sulphate of zinc 15:45 and 15.8 grs.
(means) in the first table, with 13:07 and 12-60 grs. in the second. The
relation observed is the more remarkable, that it is that of equal weights
of the salts diffused, and not of atomically equivalent weights. In the
salts of ammonia and potash, this equality of diffusion is exhibited also,
notwithstanding considerable differences in density between their solu-
tions; the density of the solution of chloride of ammonium, for instance,
being 1:0280 and that of chloride of potassium 1:0596. It may have
some relation however, but not a simple one, to the density of the
solutions; sulphate of magnesia, of which the solution is most dense,
being most slowly diffusive; and salts of soda being slower, as they are
denser in solution, than the corresponding salts of potash. Nor does it
depend upon equal solubility, for in none of the pairs is there any
approach to equality in that respect.
A comparison was now made of the diffusibility of several acids.
456 ON THE DIFFUSION OF LIQUIDS.
They were diffused from the same six-ounce phials, and for eight days.
Solutions were prepared in the proportion of 4 parts of the anhydrous
acid to 100 parts of water. The quantity of acid which diffused into
the water-jar was estimated by the proportion of carbonate of soda
which it neutralized.
TABLE V-Diffusion of acid solutions (4 acid to 100 water) at 59°3.
Anhydrous acid diffused.
Name of Acid. S ºw.
In grains. Means.
Nitric acid....................................... 1-0243 29-2I
28-19 28-7
Hydrochloric acid ..................... * * * * * * 1-0225 34-22
33-99 34°l
Sulphuric acid ................................. 1-0317 1871
18-26 18°48
Acetic acid .................................... 1-0094 19:13
17-19 18-16
Oxalic acid .................................... 1-0235 12-38
- 12:38 12.38
Arsenic acid .................................... 1.0320 12-16
12°16 12-16
Tartaric acid.................................... l’0194 9-90
9-69 9.79
Phosphoric acid .............................. I'0284. 9.09
9-09 9.09
Chloride of sodium ........................... 1-0285 12-32 12-32
Considerable latitude thus appears to exist in the diffusibility of the
different acids. [To make the result for nitric acid fairly comparable
with that for hydrochloric acid, the former should be increased in the
proportion of 54 to 63, that is estimated as nitrate of water. This cal-
culation gives 33.5 grs. of nitrate of water diffused, which approaches
closely to 34.1 grs, the quantity for chloride of hydrogen or hydrochloric
acid.] The quantity of soda neutralized by the sulphuric and hydro-
chloric acids diffused was as 14:32 to 28.97, or nearly as 1 to 2. Sul-
phuric and acetic acids, on the other hand, appear to be equally
diffusible. Phosphoric acid is the least diffusible acid in the series,
presenting only about half the diffusion product of the two last-men-
tioned acids. The Solution of phosphoric acid had been boiled for half
an hour before diffusion, and was therefore in the tribasic state. The
same precaution was not thought of for arsenic acid, although it is
possibly required by this acid also. These two acids do not exhibit the
equality of diffusion anticipated from their recognised isomorphism, but
it is to be stated that the acidimetrical method of analysis followed is
not so properly applicable to these two acids as it is to all the others.
ON THE DIFFUSION OF LIQUIDS. 457
3. Diffusion of Ammoniated Salts of Copper.
. It was interesting to compare together such related salts as sulphate
of copper, the ammoniated Sulphate of copper of Soluble compound of
sulphate of copper with 2 equivalents of ammonia and the sulphate of
ammonia. It is well known that metallic oxides, or subsalts of metallic
oxides, when dissolved in ammonia and the fixed alkalies, are easily
taken down by animal charcoal. This does not happen with the ordi-
nary neutral salts of the same acids, which are held in solution by a
strong attraction. Supposing the existence of a scale of the solvent
attraction of water, the preponderance of the charcoal attraction will
mark a term in that scale. And if the solvent force is nothing more
than the diffusive tendency, it will follow that salts which can be taken
down by charcoal must be less diffusible than those which cannot.
Of sulphate of ammonia and sulphate of copper, solutions were pre-
pared, consisting of 4 anhydrous salt to 100 water, the sulphate of
ammonia being of course taken as NH4O. SOs. The solution of the
copper Salt was divided into two portions, one of which had caustic
ammonia added to it in slight excess, so as to produce the azure blue
Solution of ammonio-Sulphate of copper.
The solutions were diffused for eight days, at a mean temperature of
64°9 for the sulphates and nitrates, and 67°7 for the chlorides.
TABLE WI.-Diffusion of solutions, 4 salt to 100 water.

Density of solution Anhydrous salt
Name of Salt. at sº Of diffused in grains.
Sulphate of ammonia..................... 1-0235 12-13
Sulphate of ammonia..................... 1-0235 I 1.96
Sulphate of copper ..................... 1-0369 6-19
Sulphate of copper ..................... 1.0369 6:51
Ammonio-sulphate of copper ......... 1*0308 1:45
Ammonio-Sulphate of copper ......... 1*0308 | 43
Nitrate of ammonia .................... 1-0136 16- 15
Nitrate of ammonia ..................... 1-0136 : 15:44
Nitrate of copper ........................ 1.0323 9-77
Nitrate of copper ........................ 1.0323 9-77
Ammonio-nitrate of copper ............ 1-0228 1-77
Ammonio-nitrate of copper ............ 1-0228 1-36
Chloride of ammonium.................. 1-0 100 16-18
Chloride of ammonium.................. 1-0 100 17:00
Chloride of copper........................ 1-0328 10-83
Chloride of copper........................ 1-0328 10°48
Ammonio-chloride of copper...... * - e º tº e 1-0209 4'54
Ammonio-chloride of copper............ 1-0209 3-94
458 ON THE DIFFUSION OF LIQUIDS.
It is to be observed, that in preparing the ammoniated salts, the
solutions of the neutral salts of copper were slightly diluted by the
water of the solution of ammonia added to them, so that the proportion
of Salt of copper which they possessed was sensibly reduced below 4 per
cent. On the other hand, the copper salt which diffused out is estimated,
not as ammoniated, but as neutral salt. It will be observed that the
quantity of sulphate of copper diffused out in the experiments falls from
6:35 in the neutral salt to 1:44 gr. in the ammoniated salt; of nitrate of
copper from 977 to 1:56, and of chloride of copper from 10:65 to 4'24.
These numbers are to be taken only as approximations; they are suffi-
cient however to prove a much reduced diffusibility in the ammoniated
salts of copper. * *
It will be remarked that the nitrate of ammonia and chloride of
ammonium approximate, 1580 and 16:59 grs. ; as do also the nitrate
and chloride of copper, 9.77 and 10-65 grs. ; the chlorides, which were
diffused at the higher temperature by 2°8, exceeding the nitrates in
both cases. -
4. Diffusion of Mia!ed Salts.
When two salts can be mixed without combining, it is to be expected
that they will diffuse separately and independently of each other, each
salt following its special rate of diffusion.
(1) Anhydrous sulphate of magnesia and sulphate of water (oil of
vitriol), one part of each, were dissolved together in 10 parts of water,
and the solution allowed to diffuse for four days at 61°5.
The water-jar was found to have acquired—
Sulphate of magnesia, . tº 5-60 grs.
Sulphate of water, . e 21:92 grs.
27-52 grS.
The experiment with the same diffusion cell and liquid being con-
tinued for a second period, this time of eight days, there was found to
be simultaneously diffused, of L
Sulphate of magnesia, . & 9:46 grs.
Sulphate of water, . & 29-32 grs.
38.78 grs.
It is obvious that the inequality should be greatest in the first period
of diffusion, or with the initial diffusion, as it actually appears above,
and become less and less sensible as the proportion of the low diffusive
salt comes to be increased in the solution phial.
In former experiments upon the solution of sulphate of magnesia
ON THE TIFFUSION OF LIQUIDS. 459
alone in water, as 1 salt to 10 water, compared with sulphate of water,
also as 1 to 10, the disparity in the diffusion of these two salts was less
considerable, being only as 1 to 2:385, instead of 1 to 3 or 4.
(2) A solution was also diffused of 1 part of anhydrous sulphate of
soda and 1 part of chloride of sodium in 10 parts of water, for four days
at 61°5. The salt which diffused out in that time consisted of—
Sulphate of soda, º ſº 9:48 grs.
Chloride of sodium, . ſº 17-80 grs.
- 27-28 grs.
The sulphate of soda in the last experiment had begun to crystallize
in the solution phial, from a slight fall of temperature, before the diffu-
sion was interrupted, a circumstance which may have contributed to
increase the inequality of the proportions diffused of these two salts.
(3) A solution of equal weights of anhydrous carbonate of soda and
chloride of sodium, namely, of 4 parts of the one salt and 4 parts of the
other, to 100 water, was diffused from 3 four-ounce phials of 1:25 inch
aperture, at a mean temperature of 57°9 and for seven days. The diffu-
sion product amounted to 17:10, 17:58, and 1813 grs. of mixed salt in
the three experiments. The analysis of the last product of 18; 13 grs.
gave—
Carbonate of soda, © 5'68 31-33
Chloride of sodium, . 12:45 68-67
18:13 100.00
Here the carbonate of soda presents a diffusion less than one-half of
that of chloride of sodium. The difference is again greater than the
peculiar diffusibilities of the same salts as they appear when the salts
are separately diffused. For in experiments made in the same phials
with solutions of 4 parts of each salt singly to 100 water, but with a
lower temperature by 3°6, namely, at 54°3, the diffusion product of the
carbonate of soda was 7:17 and 7:34 grs, in two experiments, of which
the mean is 7.25 grs. ; while the diffusion product of the chloride of
sodium was 11:18 and 10.73 grs. in two experiments, of which the mean
is 10.95 grs. The quantity of chloride of sodium diffused being taken at
100 in both sets of experiments, we have diffused—
Of carbonate of soda 66:18, when diffused singly.
Of carbonate of soda 45-64, when diffused with chloride of sodium.
The least soluble of the two salts appears in all cases to have its
diffusibility lessened in the mixed state. The tendency to crystalliza-
tion of the least soluble salt must evidently be increased by the admix-
ture. Now it is this tendency, or perhaps more generally the increased
460 ON THE DIFFUSION OF LIQUIDS.
attraction of the particles of a salt for each other, when approximated
by concentration, which most resists the diffusion of a salt, and appears
to Weaken the diffusive force in mixtures, as it is also found to do so in
a strong solution of a single salt.
(4) Equal weights of nitrates of potash and ammonia dissolved, as
in certain preceding experiments, in five times the weight of the mixed
salts of water, and diffused for eight days, gave in two experiments—
At 59°4. At 52°6.
Nitrate of potash, . 28°39 25'88
Nitrate of ammonia, . 36-16 30°36
*=mºse-rººms, ºst-sº-sº-sº-sº
64'55 56°24
The inequality in the diffusion of these two nitrates is singular, con-
sidering that in solutions of 1 salt to 10 water, they appeared before to
be equally diffusive. But on now comparing the diffusion of solutions
of 1 salt to 5 water, at 52°6, the salts no longer diffused in equal pro-
portions:—
Nitrate of potash gave * 57-93 grs.
Nitrate of ammonia gave . 82-08 grs.
The solution of nitrate of potash last diffused was nearly a saturated
one, while that of nitrate of ammonia is far from being so. The first
has its diffusibility, in consequence, impaired, and falls considerably
below the second.
The relatively diminished diffusibility of sulphate of magnesia, when
associated with sulphate of water, is probably connected with a similar
circumstance ; Sulphate of magnesia being less Soluble in dilute sul-
phuric acid than in pure water.
(5) The salt which diffused from a strong solution of sulphates
of zinc and magnesia, consisting of 1 part of each of these salts in the
anhydrous state and 6 parts of water, did not consist of the two salts in
exactly equal proportions. The mixture of salts, diffused for eight
days, as in the late experiments, gave the following results:—
Exp. I. II. III.
Sulphate of zinc, e 8'12 7-49 8-12
Sulphate of magnesia, . 8°68 8.60 8.75
16'80 16-09 16-87
There is therefore always a slight but decided preponderance of sul-
phate of magnesia, the more soluble salt, in the diffusion product.
These last experiments were made at an early period with another
object in view, namely, to ascertain whether in closely related salts,
such as the present Sulphates of magnesia and zinc, the two salts might
ON THE DIFFUSION OF LIQUIDS. 461
be elastic to each other, like the particles of one and the same salt, so
that one salt might possibly suppress the diffusion of the other, and
diffuse alone for both. The experiments lend no support to such an
idea.
It appears from all the preceding experiments, that the inequality of
diffusion which existed is not diminished but exaggerated in mixtures,-
a curious circumstance, which has also been observed of mixed gases.
5. Separation of Salts of different Bases by Diffusion.
It was now evident that inequality of diffusion supplies a method
for the separation, to a certain extent, of some salts from each other,
analogous in principle to the separation of unequally volatile substances
by the process of distillation. The potash salts appearing to be always
more diffusive than the corresponding soda salts, it follows, that if a
mixed solution of two such salts be placed in the solution phial, the
potash Salt should escape into the water atmosphere in largest propor-
tion, and the soda salt be relatively concentrated in the phial. This
anticipation was fully verified.
(1) A solution was prepared of equal parts of the anhydrous car-
bonates of potash and soda in 5 times the weight of the mixture of
water. Diffused from a small thousand-grain phial of 1:1 inch aper-
ture into 6 ounces of water, for nineteen days, at a temperature above
60°, it gave a liquid of density 1-0350, containing a considerable quantity
of the Salts. Of these mixed salts, converted into chlorides by the addi-
tion of hydrochloric acid, 9:39 grs, being treated with bichloride of
platinum in the usual manner, gave 1939 grs, of the double chloride
of platinum and potassium, equivalent to 591 grs. of chloride of potas-
sium ; and left in solution 3:44 grs. of chloride of sodium : loss 0.04 gr.
These chlorides represent 5'46 grs. of carbonate of potash and 3-12 grs.
of carbonate of soda. The salts actually diffused out were therefore in
the proportion of-
Carbonate of soda, . $9 & 36-37
Carbonate of potash, * & 63-63
100'00
(2) In another similar experiment from a six-ounce phial into 8%
ounces of water, the liquid of the water-jar, after twenty-five days'
diffusion, contained the two carbonates in nearly the same proportions
as before, namely—
Carbonate of soda, . e & 35-2
Carbonate of potash, te tº 64'8
*
100'0
462 ON THE DIFFUSION OF LIQUIDS.
(3) A partial separation of the salts of sea-water was effected in a
similar manner.
The sea-water (from Brighton) was of density 1-0265. One thou-
sand grs. of the liquid yielded 35-50 grs. of dry salts, of which 2,165
grs. were magnesia. The dry salts contain therefore 6'10 per cent. of
that earth.
Six thousand-grain phials, of 1:1 inch aperture, were properly filled
with the sea-water and placed in six tumblers, each of the last con-
taining 6 ounces of water. Temperature about 50°. The diffusion was
interrupted after eight days. The salts of the sea-water were now
found to be divided as follows:—
Diffused into the tumblers, . 92.9 grs., or 36:57 per cent.
Remaining in the phials, . 161-1 grs, or 63.43 per cent.
*-*m-smº ºmºmº-º-º-mm-
254'0 100'00
Rather more than one-third of the salts has therefore been trans-
ferred from the solution phials to the water-jars by diffusion.
Of the diffused salts in the tumblers, 46.5 grs. were found to contain
1.90 gr, magnesia, or 4.09 per cent. Hence we have the following
result—
Magnesia originally in Salts of sea-water, . 6:01 per cent.
Magnesia in Salts diffused from sea-water, . 4.09 per cent.
The magnesia, also, must in consequence be relatively concentrated in
the liquid remaining behind in the diffusion cells.
A probable explanation may be drawn from the last results of the
remarkable discordance in the analysis of the waters of the Dead Sea,
made by different chemists of eminence. I refer to the relative pro-
portion of the salts, and not their absolute quantity, the last necessarily
varying with the state of dilution of the saline water when taken up.
The lake in question falls in level 10 or 12 feet every year by evapora-
tion. A sheet of fresh water of that depth is thrown over the lake in
the wet season, which water may be supposed to flow over a fluid nearly
1:2 in density, without greatly disturbing it. The salts rise from below
into the superior stratum by the diffusive process, which will bring up
salts of the alkalies with more rapidity than salts of the earth, and
chlorides, of either class, more rapidly than sulphates. The composi-
tion of water near the surface must therefore vary greatly, as this pro-
cess is more or less advanced.
(4.) I may be allowed to add another experiment which is curious
for the protracted immobility of a column of water which it exhibits, as
well as for the separation occurring, which last may be interesting in a
geological point of view. A plain glass cylinder with a foot, 11 inches
ON THE DIFFUSION OF LIQUIDS. 463
in height, and of which the capacity was 64 cubic inches, had 8 cubic
inches poured into it of a saturated solution of carbonate of lime in car-
bonic acid water, containing also 200 grs. of chloride of sodium dis-
Solved. Distilled water was then carefully poured over the saline solu-
tion, so as to fill up the jar, a float being used and the liquid disturbed
as little as possible in the operation. The mouth of the jar was lastly
closed by a ground glass plate, and it was left undisturbed upon the
mantelpiece of a room without a fire, from March 20 to September 24
of the present year, or for six months and four days. Afterwards, on
removing the cover, the fluid was observed not to have evaporated sen-
sibly, and it exhibited no visible deposit. This I was not surprised at,
as no deposit appeared in a similar experiment with the jar uncovered,
after the lapse of six weeks. The liquid in the former jar was now
carefully drawn off by a small siphon with the extremity of both its
limbs recurved so as to open upwards, in four equal portions, which
may be numbered from above downwards. Equal quantities of the four
strata of liquids gave the following proportions of chloride of sodium
and carbonate of lime :-
Chloride of sodium. Carbonate of lime.
No. 1. 21 '91 0:10
No. 2. 23:41 0-22
No. 3. 23'55 0.38
No. 4. 23.99 0'42
The diffusion of the chloride of sodium has therefore not yet reached
complete uniformity, although approaching it, the proportion of that salt
obtained from the top and bottom strata being as 11 to 12. But the dif-
fusion of the carbonate of lime appears much less advanced, the propor-
tion of that substance being as 1 to 4 at the top and bottom of the
liquid column. The slight difference in density of the strata, it may be
further remarked, must have been sufficient to preserve such a column
of liquid entirely quiescent, as shown by the distribution of the carbo-
nate of lime, during the considerable changes of temperature of the
SeaSOD.
Chemical analysis, which gives with accuracy the proportions of acids
and bases in a solution, furnishes no means of deciding how these acids
and bases are combined, or what salts exist in solution. But it is pos-
sible that light may be thrown on the constitution of mixed salts, at
least when they are of unequal diffusibility, by means of a diffusion
experiment. With reference to sea-water, for instance, it has been a
Question in what form the magnesia exists, as chloride or as sulphate ;
or how much exists in the one form and how much in the other.
Rnowing, however, the different rates of diffusibility of these two salts,
which is nearly chloride 3 and sulphate 2, and their relation to the
464 ON THE DIFFUSION OF LIQUIDS.
diffusibility of chloride of sodium, we should be able to judge from the
proportion in which the magnesia travels in company with chloride of
sodium, whether it is travelling in the large proportion of chloride of
magnesium, in the small proportion of sulphate of magnesia, or in the
intermediate proportion of a certain mixture of chloride and sulphate of
magnesia. But here we are met by a difficulty. Do the chloride of
magnesium and sulphate of magnesia necessarily pre-exist in Sea-Water
in the proportions in which they are found to diffuse ? May not the
more easy diffusion of chlorides determine their formation in the diffu-
sive act, just as evaporation determines the formation of a volatile Salt
—producing carbonate of ammonia, for instance, from hydrochlorate of
ammonia with carbonate of lime in the same solution ? We shall see
immediately that liquid diffusion, as well as gaseous evaporation, can
produce chemical decompositions.
6. Decomposition of Salts by Diffusion.
(1.) At an early period of the inquiry, a solution was diffused of bi-
sulphate of potash, Saturated at 68° and of density 1280, from the six-
ounce phial of 1175 inch aperture, into 20 ounces of water. The period
of diffusion extended to fifty days. About the middle of that period, a
few small crystals of Sulphate of potash, amounting probably to 3 or 4
hundredths of a grain, appeared in the diffusion cell and never after-
wards dissolved away. When terminated, the liquid remaining in the
solution cell was found of density 1-154; that in the water-jar 1:0326.
A portion of the latter liquid, containing the salts diffused, gave by
analysis—
Sulphate of potash, . º 20:37 } º
Sulphate of water, e º 11:47 Bisulphate of potash.
Sulphate of water, te º 12-77
44'61
It thus appears that the bisulphate of potash undergoes decomposi-
tion in diffusing, and that the acid diffuses away to about double the
extent, in equivalents, of the Sulphate of potash. This greater escape
of the acid will also account for the deposition of crystals of the neutral
sulphate in the solution cell.
(2) A similar experiment was made with another double sulphate
of greater stability, common potash-alum. The solution of 4 anhydrous
alum in 100 water, was diffused from the six-ounce phial into 24 ounces
of water, at 64°2, for eight days. The quantity of salt diffused in that
time amounted only to 7-48 grs. It contained 1.06 gr. alumina, which
is equivalent to 5:33 grs. of alum. The diffused salt gave off no acid
ON THE DIFFUSION OF LIQUIDS. 465
vapours at 600. We may therefore suppose the excess of salt which is
diffused to be sulphate of potash. The diffusion product of alum, at
64", appears therefore to be— *
Alum, . . . 5:33 71°26
Sulphate of potash, . 2:15 28°74
7'48 100.00
In a second experiment, the diffusion product amounted to 6:39 grs.,
of which 0.95 gr, was alumina; and it is represented by 4.77 alum and
1-52 Sulphate of potash.
In connexion with the low diffusibility of the sulphate of alumina of
alum, it was found that the addition of caustic potash to fle alum solu-
tion, so as to convert it into an aluminate of potash, increased the diffu-
sibility of the alumina. The diffusion product from the 4 per cent.
Solution of alum so treated contained 1-62 gr. of alumina in one experi-
ment and 1:54 in another, or one-half more than from alum itself.
As alum is a Salt of great stability, it presents a severe test of the
influence in question. The decomposition of this double salt by diffu-
sion was further confirmed therefore in experiments made by means of
the four-ounce diffusion phials of 1:25 inch aperture, and the alteration
which the Salt undergoes in the process more exactly ascertained. The
experiments were made at a mean temperature of 57°-9, and lasted seven
days; the Solution employed being of 4 anhydrous alum to 100 water,
as before.
In three experiments, the salt diffused out amounted to 5'73, 5'80,
and 5'65 grs. ; of which the mean is 5'73 grs. The latter quantity gave
0-82 alumina and 3.22 sulphuric acid, which correspond to 4:11 anhy-
drous alum and 1-62 neutral sulphate of potash. Or, we have as the
diffusion product of alum, in 100 parts—
Alum, . ſº e g: * 71-73
Sulphate of potash, . gº º 28-27
100'00
This analysis corresponds closely with the diffusion product of the
former experiments, which gave 71-26 per cent. of alum, and 28.74 sul-
phate of potash. The solution of alum which remains behind in the
Solution phials must of course acquire an excess of sulphate of alumina.
The Salt, Sulphate of alumina, did not appear to be decomposed when
diffused alone. A four per cent, solution of the hydrated sulphate of
alumina, which is manufactured at Newcastle, when diffused in the same
circumstances as the preceding solutions of alum, gave 340 grs, of anhy-
drous sulphate of alumina, in which the acid was to the alumina as 2.95
2 G
466 ON THE DIFFUSION OF LIQUIDS.
equivalents of the former to 1 equivalent of the latter, or as nearly as
possible in the proportion of 3 equivalents of acid to 1 of base. As
the Newcastle salt contained almost exactly half its weight of water, the
3:40 grs. of anhydrous salt diffused out are equivalent to 6.80 grs. of
hydrated sulphate of alumina. The sulphate of alumina appears thus to
be more diffusive than the double sulphate of alumina and potash, in
the proportion of 6-80 to 573.
(3) It was interesting to observe what really diffuses from the
ammoniated sulphate of copper (CuO, SOs, 2NH,--HO), and to find if
the low diffusibility of that salt is attended with decomposition. The
diffusion of the ammoniated sulphate of copper was therefore repeated
from a 4 per cent. Solution in the six-ounce solution phial, for eight
days, at 64°2. In evaporating the water of the jar afterwards, the
ammoniated sulphate of copper present was necessarily decomposed, by
the escape of ammonia, and a subsulphate of copper precipitated. The
copper found, however, was estimated as neutral sulphate of copper.
The diffusion product of two experiments may be represented as follows,
in grains:—
I. II.
Sulphate of copper, © e 0°81 0-97
Sulphate of ammonia, . e 5*46 5'53
6-27 6'50
The abundant formation and separation of sulphate of ammonia in
these experiments prove that the ammoniated sulphate of copper is
largely decomposed in diffusion.
(4) Perhaps the most interesting result of this kind is a method
which diffusion suggests for the decomposition of the alkaline sulphates
by means of lime. -
Solutions were prepared, in lime-water, of 3 per cent of sulphate of
potash and of chlorides of potassium and sodium. Two solution phials
were filled with each of these solutions, and placed for diffusion in
water-jars filled with lime-water, at 49°, for seven days.
In the sulphate no deposition of crystallized sulphate of lime took
place within the solution phial, while the water-jar acquired an alkaline
reaction, which remained after precipitating the lime entirely by car-
bonic acid gas and evaporating twice to dryness. Hydrate of potash, it
will afterwards appear, is an eminently diffusive salt, having double
the diffusibility of sulphate of potash. The tendency of the former to
diffuse enables the affinity of the lime for sulphuric acid to prevail, and
the alkali is liberated and diffused away into the external atmosphere of
lime-water. By the latter, hydrate of lime is returned to the solution
cell and the decomposition continued. The salt diffused in the two
cells amounted to 2-60 grs., of which 0-62 gr., or 23.85 per cent, was
ON THE DIFFUSION OF LIQUIDS, 467 .
hydrate of potash. The chlorides of potassium and sodium, on the
contrary, were not sensibly decomposed. +
It is known that a precipitation of sulphate of lime may occur, with
a larger proportion of sulphate of potash in lime-water, in a close phial
without external diffusion. As the decomposition of the sulphate of
potash, in the latter case, has been referred to the insolubility of the
sulphate of lime, so the decomposition in the former circumstances
may be referred, in a similar sense, to the high diffusibility of hydrate
of potash.
7. Diffusion of Double Salts.
How is the diffusion of two salts affected by their condition of com-
bination as a double salt 2 A solution of the double sulphate of mag-
nesia and potash, in the proportion of 100 water to 4 anhydrous salt, was
operated upon in the four-ounce diffusion phials of 1:25 inch aperture,
with a period of diffusion of seven days, at 57°9 Fahr. The diffusion
product of the double salt was 8'09 and 7.81 grs. in two experiments:
mean 7-95 grs.
The constituent salts, sulphate of magnesia and Sulphate of potash,
were now dissolved separately, in the proportions in which they existed
in the double salt, namely, 1.65 gr. anhydrous Sulphate of magnesia in
100 water, and 2:35 grs. Sulphate of potash in 100 water, making up
together 4 parts of salts. The two solutions thus contain equivalent
quantities of the different sulphates.
The separate diffusion of the sulphate of magnesia was 2:09, 2:11,
and 2:40 grs. in three cells; and of the sulphate of potash, 5'83, 5-97,
and 5-54 grs. in three cells; the circumstances of the experiments being
the same as those of the double salt. The means of the two salts are
220 and 5.78 grs. ; and the sum of the two means 7-98 grs. The result
is, that the separate diffusion of the constituent salts is almost identical
with their diffusion when combined as a double salt :—
Diffusion of the double sulphate of magnesia and potash, 7.95 grs.
Diffusion of equivalents of sulphate of magnesia and } 798 grs
sulphate of potash in separate cells, ſ'98 grs.
It would thus appear that the diffusibility of this double salt is the
sum of the separate diffusions of its constituent salts.
It has been a question whether a double salt is formed at once when
its constituent salts are dissolved together, or not till the act of crystal-
lization of the compound salt. Equivalents of the same two sulphates,
making up 4 parts, were dissolved together without heat in 100 water.
Now the diffusion from this mixture, which has the composition of the
preceding solution of the double salt, exhibited notwithstanding a sen-
468 ON THE DIFFUSION OF LIQUIDS.
sibly different result of diffusion, giving 7-28, 7:37, and 7°26 grs. in three
cells: mean, 7.30 grs. The diffusion of the double salt was greater,
namely, 7-95 grs. Hence a strong presumption that the mixed salts last
diffused were not combined, and that the double Sulphate of magnesia
and potash is not necessarily formed immediately upon dissolving
together its constituent salts. -
In early experiments of a similar nature made upon the double salt,
sulphate of copper and potash, and upon a mixture of the two sulphates
newly dissolved together, a similar result was obtained. While the
diffusion of the mixed salts was 25-6 grs., that of the same weight of
the combined salts (the double sulphate) was 30 grs. The double salt
appears more diffusible, in both cases, than its mixed constituents.
These double salts appear to dissolve in water without decomposi-
tion, although the single salts may meet in Solution without combining.
Hence in a mixture of salts we may have more than one state of equi-
librium possible. And when a salt, like alum, happens to be dissolved
in such a way as to decompose it, the constituents are not necessarily
reunited by subsequent mixing. Many practices in the chemical arts,
which seem empirical, have their foundation possibly in facts of this
kind."
8. Diffusion of one Salt into the Solution of another Salt.
It was curious and peculiarly important, in reference to the relation
of liquid to gaseous diffusion, to find whether one salt A would diffuse
into water already charged with an equal or greater quantity of another
salt B, as a gas a freely diffuses into the space already occupied by
another gas b; the gas b in return diffusing at the same time into the
space occupied by a. Or whether, on the contrary, the diffusion of the
salt A is resisted by B. The latter result would indicate a neutralization
of the water's attraction, and a kind of equivalency or equality of power
and exchangeability of different salts, in respect of that effect, which
would divide entirely the phenomena of liquid from those of gaseous
diffusion.
(1) A solution of 4 parts of carbonate of soda to 100 water, of den-
sity 1-0.406, was placed in the six-ounce diffusion phial of 1175 inch
aperture, and allowed to communicate with 24 ounces of water.
Two similar diffusion phials, equally charged, were immersed in 24
ounces of a solution of chloride of sodium in the proportion of 4 parts
of the latter to 100 water, having the density 1-0282. The diffusion
proceeded for eight days, in all cases, at 64". The proportion of car-
bonate of soda found without in the water-jar afterwards, was ascertained
* The circulation in crystallizing tartaric acid necessary from the low diffusibility of
the acid 2
ON THE DIFFUSION OF LIQUIDS. 469
by an alkalimetrical process, the neutralization being effected at the
boiling-point. The following are the results:—
Experiment I. Diffusion product into
Water, . ſº º º tº
Experiment II. Diffusion product into
solution of chloride of sodium,
Experiment III. Diffusion product into } © -
solution of chloride of sodium, . 9:10 grs. of carbonate of soda.
} 9:06 grs. of carbonate of soda.
882 grs. of carbonate of soda,
It hence appears that 4 per cent. of chloride of sodium present in
the water atmosphere of the jar has no sensible effect in retarding the
diffusion into it, from the solution cell, of carbonate of Soda from a solu-
tion containing also 4 per cent. of the latter. -
(2) The experiment was varied by allowing the solution of carbonate
of Soda to diffuse into a solution of sulphate of soda, a salt more similar
to the former in composition and solubility. The solution of the latter,
containing 4 per cent, was of density 1.0352. The temperature and
period of diffusion were the same as before :—
Experiment IV. Diffusion product into
Solution of sulphate of soda, º
Experiment W. Diffusion product into
Solution of sulphate of soda, e
} 7:84 grs. of carbonate of soda.
} 7-82 grs. of carbonate of soda.
Here we find a small reduction in the quantity of carbonate of soda
diffused, amounting to one-eighth of the whole. The sulphate of soda
has therefore exercised a positive interference in checking the diffusion
of the carbonate to that extent. So small and disproportionate an effect
however is scarcely sufficient to establish the existence of a mutual
elasticity and resistance between these two salts.
Still it might be said, may not the diffusion of one salt be resisted
by another salt which is strictly isomorphous with the first 2
(3) A solution of 4 parts of nitrate of potash to 100 of water, of
density 1-0241, placed in the solution phial, was allowed to communi-
cate with Water containing 4 per cent of nitrate of ammonia in the
water-jar, which last solution was of density 1-0136; with all other cir-
cumstances as before. With one solution phial having the usual aper-
ture, 1175 inch, the diffusion product was 15:32 grs. of nitrate of potash.
With a second phial, having a larger aperture of 1190 inch, the diffusion
product was 18:03 grs. of nitrate of potash. No comparative experiment,
on the diffusion of nitrate of potash into water, was made at the same
time. But nitrate of ammonia, which appeared before to coincide in
diffusibility with nitrate of potash, gave on a former occasion, in similar
470 ON THE DIFFUSION OF LIQUIDS.
circumstances, and at 64°9, nearly the same temperature, a diffusion
product of 1580 grs. The quantity of nitrate of potash (15:32 grs.)
which diffused into the solution of nitrate of ammonia approaches so
closely to the number quoted, that we may safely conclude that the
diffusion of nitrate of potash is not sensibly resisted by nitrate of am-
monia, although these two salts are closely isomorphous. They are still
therefore inelastic to each other, like two different gases.
These experiments have been made upon dilute solutions, and it is
not at all impossible that the result may be greatly modified in concen-
trated solutions of the same salts, or when the solutions approach to
saturation. But there is reason to apprehend that the phenomena of
liquid diffusion are exhibited in the simplest form by dilute solutions,
and that concentration of the dissolved salt, like compression of a gas,
is attended often with a departure from the normal character. *
On approaching the degree of pressure which occasions the lique-
faction of a gas, an attraction appears to be brought into play, which
impairs the elasticity of the gas; so on approaching the point of Satura-
tion of a salt, an attraction of the salt molecules for each other, tending
to produce crystallization, comes into action, which will interfere with
and diminish that elasticity or dispersive tendency of the dissolved salt
which occasions its diffusion.
We are perhaps justified in extending the analogy a step further
between the characters of a gas near its point of liquefaction and the
conditions which we may assign to solutions. The theoretical density
of a liquefiable gas may be completely disguised under great pressure.
Thus, under a reduction by pressure of 20 volumes into 1, while the
elasticity of air is 1972 atmospheres, that of carbonic acid is only 1670
atmospheres, and the deviation from their normal densities is in the
inverse proportion. Of salts in solution the densities may be affected
by similar causes, so that although different salts in solution really
admit of certain normal relations in density, these relations may be con-
cealed and not directly observable.
The analogy of liquid diffusion to gaseous diffusion and vaporization
is borne out in every character of the former which has been examined.
Mixed salts appear to diffuse independently of each other, like mixed
gases, and into a water atmosphere already charged with another salt as
into pure water. Salts also are unequally diffusible, like the gases, and
separations, both mechanical and chemical (decompositions), are produced
by liquid as well as by gaseous diffusion. But it still remains to be
found whether the diffusibilities of different salts are in any fixed pro-
portion to each other, as simple numerical relations are known to prevail
in the diffusion velocities of the gases, from which their densities are
deducible. .
ON THE DIFFUSION OF LIQUIDS. - 4.71
II. DIFFUSION OF SALTS OF POTASH AND AMMONIA.
It was desirable to make numerous simultaneous observations on the
salts compared, in order to secure uniformity of conditions, particularly
of temperature. The means of greatly multiplying the experiments
were obtained by having the solution phial cast in a mould, so that any
number of solution cells could be procured of the same form and dimen-
sions. The phials were of the form represented (fig. 3), hold- Fig. 3,
ing about 4 ounces, or more nearly 2080 grs. of water to the
base of the neck, and the mouths of all were ground down,
so as to give the phial a uniform height of 3-8 inches. The
mouth or neck was also ground to fit a gauge-stopper of wood,
which was 0.5 inch deep and slightly conical, being 1:24 inch
in diameter on the upper, and 1:20 inch on the lower surface.
These are therefore the dimensions of the diffusion aperture
of the new solution cells. A little contrivance to be used in
filling the phials to a constant distance of half an inch from the surface
of the lip, proved useful. It was a narrow slip of brass plate, having a
descending pin of exactly half an inch in length fixed on one side of it

(fig. 4). This being laid across the mouth FIG. 4.
of the phial with the pin downwards in
the neck, the solution was poured into NY C \
the phial till it reached the point of the * T]
pin. The brass plate and pin being | -

removed, the neck was then filled up
with distilled water, with the aid of the little float as before described.
The water-jar, in which the solution phial stood, was filled up with
water also as formerly, so as to cover the phial entirely to the depth of
I inch. This water atmosphere amounted to 8750 grs., or about 20
ounces. A glass plate was placed upon the mouth of the water-jar itself
to prevent evaporation. Sometimes 80 or 100 diffusion cells were put
in action at the same time. The period of diffusion chosen was now
always exactly seven days, unless otherwise mentioned.
Solutions were prepared of the various salts, in a pure state, in cer–
tain fixed proportions, namely, 2, 4, 63, and 10 parts of salt to 100 parts
of water by weight. The density of these solutions was observed by
the weighing-bottle, at 60°. The solutions were frequently diffused at
two different temperatures; one, the temperature of the atmosphere,
which was fortunately remarkably constant during most of the experi-
ments to be recorded at present, and the other, a lower temperature,
obtained in a close box of large dimensions, containing masses of ice.
472 ON THE DIFFUSION OF LIQUIDS.
The results at the artificial temperature were obviously less accurate
than those of the natural temperature, but have still considerable value.
Three experiments were generally made upon the diffusion of each
Solution at the higher, with two experiments at the lower tempera-
ture.
(1) The carbonate and sulphate of potash and sulphate of ammonia
were first diffused during a period of seven days, of which the tempera-
tures observed by a thermometer placed near the water-jars were 64°5,
65°, 63°5, 63’, 63’, 63’-5, 65°, and 66°; mean temperature 64°2.
TABLE VII.-Diffusion of Carbonate of Potash, Sulphate of Potash,
and Sulphate of Ammonia.

At 64° 2. At 37° 6.
Parts of anhydrous salt to 100 water. S dººr.
Experiments. | Mean. Experiments. Mean.
Carbonate of potash.
2 1:01.78 5-36 3.80
5°55 5°45 3-91 3.85
4 I.0347 10°39 6-99
- 10°ll 10-25 7-19 7-09
63 1.0572 16:50 II -42
16’46 11°08 11:25
17:05 16.67
10 1-0824 24°42
24.94
24-70 24'69
Sulphate of potash.
2 1-015.5 5-62 3-93
5°42 5-52 3-98 3.95
4 1:03.18 10:49 7:50
10-65 10.57 7-31 7-40
6# 1-0512 17:07 11-62
16-89 11-71 11'66
17-54 17.17
10 1-0742 23°40
23°59
23-88 23.62
Sulphate of ammonia, NH,0.SOs.
- 2 1.0117 5-71 3-73
5*45 5'58 3-79 3-76
4 1-0229 10-72 7-54
10:30 10:51 7-86 7-70
6# I’0369 17:28 10-94 -
16-28 10-98 10.96
I6'80 16.79
10 1*0529 21°86
22:49
22-25 22:20
ON THE DIFFUSION OF LIQUIDS. 473
The diffusion product was obtained by evaporating the water of each
jar separately as before, and the result is expressed in grains.
It will be observed at once, on comparing the means of the experi-
ments, that the three salts under consideration are remarkably similar
in their diffusion, particularly with the smaller proportions of salt.
Thus the mean diffusion of the 2, 4, 6á, and 10 parts of the salts is
as follows:–
Diffusion at 64°2.

2 4 63. 10
Carbonate of potash ......... 5:45 10:25 16-67 24'69
Sulphate of potash ......... 5-52 10-57 17.17 23.62
Sulphate of ammonia ...... 5'58 10-51 16.79 22-20
Diffusion at 37°6.

2. 4. 63.
Carbonate of potash ........................ 3-85 7-09 11:25
Sulphate of potash ........................ 3-95 7-40 11-66
Sulphate of ammonia ..................... 3-76 7-70 10-96
The proportions diffused are sensibly equal, of the different salts, at
the higher temperature, with the exception of the largest proportion of
salt, 10 per cent, when a certain divergence occurs. This last fact is
consistent with our expectations, that the diffusion of salts would prove
most highly normal in dilute solutions. Some of the irregularities at
the lower temperature are evidently of an accidental kind.
(2) The neutral chromate and acetate of potash were diffused at a
temperature ranging from 63° to 65°, or at a mean temperature of 64°1,
which aſ most coincides with the higher temperature of the last experi-
ments’
A
A *
4.
sé
TABLE VIII.-
*
f*
f
474 ON THE DIFFUSION OF LIQUIDS.
TABLE VIII.-Diffusion of Chromate of Potash and Acetate of Potash, *
at 64°1.
*ś" |...º.º. Experiments. | Mean.
Chromate of potash.
2 1.0158 5-79
5-66
5'86 5-77
4 1-0313 Il-10
1I-35
11-13 11:19
63 1-0512 17.76
17.72
17:32 17:60
10 1-0750 24°49
24-92
24'85 24-75
Acetate of potash.
2 1-0095 5-93
5-75
5-88 5'85
4 1-0184 10°55
10-56
10-98 I0-70
63 1-0306 16-53
16:06
16-84. 16:48
10 1-0447 24-27
24'82
25°46 24'85

We have the same close correspondence in the diffusion products of
these two Salts as in the preceding group, and here the correspondence
extends to the 10 per cent. Solution.
Diffusion at 64°1.

2. 4. 63. 10.
Chromate of potash ......... 5-77 II -19 17:60 24-75
Acetate of potash............ 5'85 10'70 16°48 24'85
The 10 per cent. Solution of these two salts also agrees with the
same solution of carbonate of potash, which was 24.69 grs. Nor do the
lower proportions diverge greatly from the preceding group of salts.
ON THE DIFFUSION OF LIQUIDS. 475
(3) Another pair of salts were simultaneously diffused, but with an
accidental difference of 0°4 of temperature.
TABLE IX. —Diffusion of Bicarbonate of Potash, KO. CO, H-HO.CO,
at 64°1, and Bichromate of Potash, KO. 2CrO3, at 64°5.

At 64° ‘I and 64° 5.
Parts of anhydrous salt Density of
to 100 water. solution at 60°.
Experiments. Mean.
Bicarbonate of potash.
2 1-0129 5-74
5-77
5'91 5-81
4. I-0252 10-75
I 1' 16 -
11-13 I 1.01
Bichromate of potash.
2 I-0139 5-64
5-73
5-59 5-65
4 1.0273 11-55
II '54
11:39 11:49
Here again the two salts approach closely in diffusion, and also corre-
spond well with the two preceding series.
Mean Diffusion at 64°1 and 64°5.

2 4.
Bicarbonate of potash........................... 5-81 11-01
Bichromate of potash........................... 5-65 Il-49
It is singular to find that salts differing so much in constitution and
atomic weight as the chromate and bichromate of potash, may be con-
founded in diffusibility. The diffusion products of these two salts are,
for the 2 per cent. Solutions, 5-77 and 5'65 grs., and for the 4 per cent.
solution, 11:19 and 11:49 grs. The bicarbonate of potash also exhibits
a considerable analogy to the carbonate, but resembles still more closely
the acetate. It is thus obvious that equality, or similarity, of diffusion
is not confined to the isomorphous groups of Salts.
476 ON THE DIFFUSION OF LIQUIDS.
. (4.) The nitrates of potash and ammonia have already appeared to be
equi-diffusive at two different temperatures. They were diffused again
in the same proportions as the last salts, at a temperature varying from
63° to 67°5.
TABLE X.—Diffusion of Nitrate of Potash and Nitrate of Ammonia.
at 65°9.

Parts of anhydrous salt to 100 water. Pºu. Experiments. Mean.
Nitrate of potash.
2 1-0.123 7-34
7.58
7'49 7-47
4 1-0243 13-66
14:24
14:02 13.97
63 1*0393 22°l I
22.94
22-05 22:37
10 I •0581 32-06
32°90
32°50 32°49
Nitrate of ammonia, NH, O, NOs.
- 2 1°0080 7.85
7.71 -
7-64 7-73
4 1-0154 14:20
14-79
14'45 14.48
63 1.0256 23°66
23°35
22-22 22.74
10 1.0375 34.94
33.49
34-23 34-22
The solution of nitrate of ammonia of the water-jars was evaporated
carefully at a temperature not exceeding 120° Fahr, to prevent loss of
the salt by Sublimation or decomposition.
Diffusion at 65°-9.

2. 4. 62. 10.
Nitrate of potash ............ 7.47 13.97 22-37 32°49
Nitrate of ammonia ......... 7.73 14.48 22.74 34°22
Although these salts correspond closely, it is probable that neither
the diffusion of these nor the diffusion of any others is absolutely iden-
ON THE DIFFUSION OF LIQUIDS. 477
tical. The nitrate of ammonia appears to possess a slight superiority
in diffusion over the nitrate of potash, which increases with the large
proportion of salt in solution. They are both considerably more diffu-
sible than the seven preceding salts.
(5) A second pair of isomorphous salts was compared, the chlorides
of potassium and ammonium.
TABLE XI.—Diffusion of Chloride of Potassium and Chloride of
Ammonium.
- At 66°-2. At 64°7.
Parts of anhydrous salt to Density of solu-
0 water. tion at 60°.
Experiments. Mean. Experiments. Mean.
Chloride of potassium.
1.01.27 7-83 8-03
7.72 7-89 7.96
7.55 7-70
4 I •0248 15-22 15-21
15-59 14-82 15:01
15-07 15-29
6# 1-0401 24'88 24-83
& 24'64 24'62 24-72
25-09 24-87
10 I-0592 36.23
37:63 36-93
Chloride of ammonium.
1-0061 7-10 7-10
8-52 7-81 7-24 7.17
4. 1-0118 14-55 13-91
14-64 14-60 14-91 14:41
6% 1-0190 24-30 24°30 24-12
24-13 24-12
10 1-0272 36-53 36-53

These two salts agree well in diffusibility, and are also evidently
related to the preceding nitrates. The quantity of chloride of ammo-
nium diffused was determined by evaporation, which is troublesome and
may lead to Small errors, from the volatility and efflorescent tendency
of this salt. It would be easier and more accurate to determine this
and other chlorides by the use of a normal solution of nitrate of silver,
and so avoid evaporation.
Diffusion at 66°2.

| 2. 4. 63. 10.
Chloride of potassium....... 7-70 I5-29 24'87 36-93
Chloride of ammonium....... 7-81 14°60 24°30 36-53
478 ON THE DIFFUSION OF LIQUIDS.
The quantities diffused of these two chlorides are more closely in
proportion to the strength of the original solution, than with any of the
preceding salts of potash. Thus the quantities diffused from the 2 and
10 per cent. Solutions of chloride of potassium are 770 and 36.93 grs,
which are as 2 to 9-6, which is nearly as 2 to 10. Chloride of sodium
was observed before to be nearly uniform in this respect; but other
salts appear to lose considerably in diffusibility with the higher propor-
tions of Salt. It is possibly a consequence of the crystallizing attraction,
to which reference was lately made, coming into action in strong solu-
tions and resisting diffusion.
(6) The diffusion of chlorate of potash was observed at a tempera-
ture ranging from 63 to 65°, of which the mean was 64°1.
TABLE XII.-Diffusion of Chlorate of Potash.

|
r - At 64°1.
Parts of Salt to 100 water. S of...”. -
Experiments. Mean.
2 1-0 129 6-97
7-54
7-16 7-22
4. - 1-0246 13-03
13-64
13-27 13:31
6-5 (saturated solution). l-0395 21:30
20:29,
20-76 20-78
The solutions of chlorate of potash must be evaporated and the
residuary salt dried at a temperature not exceeding 212, otherwise a
very sensible quantity of chloride of potassium may be formed. The
chloride appears to be sensibly inferior in diffusibility to the nitrate of
potash. From the four per cent. Solution of the chlorate we have a
diffusion product of 1327 grs, and from the corresponding solution of
the nitrate 13.97 grs.; but the latter was obtained at a temperature 1°8
higher than the former. It remains a question whether chlorate of
potash does not really belong to the nitre group of salts, but has its
diffusion interfered with by some secondary agency, such as its sparing
solubility and consequent nearer approach to the Saturating proportion.
It is certainly true that the uniformity of diffusion generally increases
with the dilution of the solutions. This appears on comparing the diffu-
sion of the 4 per cent. solution of what may be called the sulphate of
potash group, with the diffusions of the 2 per cent, solutions of the
Same Salts. - - - -
ON THE DIFFUSION OF LIQUIDS. 479
Diffusion of Salts of the Sulphate of Potash Class.

4. 2.
Carbonate of potash............ 10-27 5.45
Sulphate of potash ............. 10-57 5-52
Sulphate of ammonia .......... I0-51 5-58
Acetate of potash................ 10-70 5'85
Bicarbonate of potash .......... 11.01 5'81
Chromate of potash............. II -19 5-77
Bichromate of potash .......... 11:49 5-65
Thus while the 4 per cent. solutions range from 10:27 to 11:49 grs.,
or from 100 to 1118, the 2 per cent. solutions range from 5:45 grs. to
5.85 grs, or from 100 to 1073.
As it appeared to be in dilute solutions that the greatest uniformity
of diffusion is to be expected, a series of experiments was instituted
upon the preceding salts, with the addition of acetºe of potash, which
appeared to belong to the same class, the solution efāployed being that of
1 salt to 100 water. The experiments were made in a vault, of which
the temperature was nearly uniform, falling in a gradual manner from
59° to 58°, with a mean of 58°5 during the period of seven days which
the diffusion lasted. Eight phials of each salt were diffused, and the
liquids of four water-jars evaporated together. -
Carbonate of potash gave 10:42 and 10:59 grs. of salt diffused: mean
10:51 grs, or 2.63 grs, for one cell.
Sulphate of potash gave 1072 and 1078 grs. of salt diffused: mean
1075 grs, or 2.69 grs, for one cell.
Acetate of potash, its diffusion product being treated with an excess
of hydrochloric acid, gave 8:30 and 8.04 grs of chloride of potassium,
equivalent to 109F and 10.57 grs. of acetate of potash; mean 10:74 grs.
of acetate of potash, or 2.68 grs, for one cell. The diffusion of these
three Salts %therefore remarkably similar:-
z -
1. Diffusion of 1 per cent solutions at 58°5.
Carbonate of potash, . tº tº 2-63 grs.
Sulphate of potash, . wº . 2:69 grs.
Acetate of potash, * & e 2.68 grs.
The 1 per cent. Solution of neutral or yellow chromate of potash in
good crystals gave 11:28 and 11:35 grs. ; mean 1131 grs, or 2-83 grs. for
each cell. It was remarked of the diffused chromate in this experiment,
that it contained a sensible quantity of green oxide of chromium. The
480 ON THE DIFFUSION OF LIQUIDS.
diffusion of a salt appears indeed to try its tendencies to decomposition
very severely. (The Author's copy has a ? here on the margin.)
The bicarbonate of potash gave 8.83 and 8:35 grs. of chloride of
potassium, the diffusion product being neutralized with hydrochloric
acid; equivalent to 11:25 and 11.21 grs. of bicarbonate of potash; mean
11:23 grs, or 2.81 grs. for one cell.
The bichromate of potash gave 11:54 and 11:49 grs. of salt diffused;
mean 11:51 grs, or 2.88 grs. for one cell. These last three Salts give
all a larger diffusion product than the preceding three, while they agree
well together. It is doubtful whether this excess in their diffusion is
occasioned by a partial decomposition in the act of diffusion, which
might be of such a kind as to increase the real or apparent diffusion in
every one of them, or whether it is a peculiar character of this little
subdivision, to which the ferricyanide of potassium, it will be afterwards
seen, falls to be added, while the ferrocyanide appears to belong to the
other group :-
Diffusion of 1 per cent. solutions at 58°5.
Chromate of potash, . to * 2.83 grs.
Bicarbonate of potash, . tº e 2.81 grs.
Bichromate of potash, . º * 2.88 grs.
The divergence from each other of two salts so closely isomorphous
as sulphate and chromate of potash, in the proportion of 100 to 1052, is
certainly remarkable, unless due to a slight decomposition of the latter.
(7) Ferrocyanide and Ferricyanide of Potassium.
Of these two salts the 1 per cent. solution only was diffused. The
time of diffusion was seven days, as usual; the mean temperature 54°5.
In evaporating the liquid of the water-jars, both salts were partially
decomposed, so that it became necessary to estimate the diffusion pro-
duct by a determination of the potash. Eight cells were employed for
one salt and six for the other, and the liquids of the water-jars evapo-
rated two together.
The diffusion product of ferrocyanide of potassium (anhydrous) was
5.02, 5:22, 5.02, and 5:20 grs.; mean 5'12 grs, or for one cell 2.56 grs.
The diffusion product of ferricyanide of potassium was 5'54, 5-64,
and 5.36 grs.; mean 5-51 grs, or for one cell 275 grs.
Three cells of a similar solution of Sulphate of potash which were
diffused for seven days at a mean temperature 1° lower, or of 53°5, gave
2:56, 2:53, and 2.62 grs. ; mean for one cell 2.57 grs., a number which
ON THE DIFFUSION OF LIQUIDS. 481
almost coincides with that of the ferrocyanide of potassium (2°56 grs).
The ferricyanide of potassium, on the other hand, is sensibly more dif-
fusive, as 107.6 to 100, and appears to rank with the bicarbonate and
bichromate of potash. The ferricyanide of potassium, again, is a Salt
which probably undergoes a slight decomposition in diffusion like those
Salts mentioned:— -
dº
Diffusion of 1 per cent. Solutions.
Sulphate of potash, : : 2.57 grs. at 53°5.
Eerrocyanide of potassium, * 2:56 grs. at 54°5.
Perricyanide of potassium, * 275 grs, at 54°5.
The salts of the nitre class may also be compared in the same man-
ner, and I shall now add a third series of results obtained from the
diffusion of 1 per cent. solutions of the same salts. The temperature of
diffusion of this new series was 64°5. Six phials of each salt were
diffused, and they were evaporated afterwards two and two. This
double diffusion product, however, is divided by 2 in the table.
Diffusion of Salts of the Nitre Class.

4. 2. 1.
Nitrate of potash ............ 13-97 7-47 3-72
Nitrate of ammonia ......... 14°48 7.73 3-75
Chloride of potassium ...... 15:01 7-70 3-88
Chloride of ammonium...... 14:41 7-81 3.89
Chlorate of potash ......... 13:31 7-22 3-66
Mean .................. 14-23 7-58 3-78
It is interesting to observe how the chlorate of potash rises in the
lower proportions and approaches to the normal rate of its class. The
diffusion products of all the salts are obviously more similar for the two
than for the 4 per cent. solutions, and again more similar for the 1 than
for the 2 per cent. Solutions. The extremes in the 1 per cent. solutions
are 3-66 grs. chlorate of potash, and 389 grs. chloride of ammonium,
which are as 1 to 1-0628. We have here an approach to equality in
diffusion, which appears to be as close as the experimental determina-
tions are of the specific heat of different bodies belonging to one class.
The numbers for the specific heat of equivalents of the metallic glements
are known to vary as 38 to 42.
The salts of potash thus appear to fall into two groups of very simi-
lar if not equal diffusibility. What is the relation between these
groups ? .
2 H
482 .ON THE DIFFUSION OF LIQUIDS.
The diffusion of 4 per cent. solutions of carbonate and nitrate of
potash was repeated at a temperature rising gradually from 63 to 65°
during the seven days of the experiment, with a mean of 64°1. The
diffusion products of the carbonate were 10:31, 10:05, and 10:44 grs, in
three different cells; mean 10:27 grs. Of the nitrate, 1398, 1386, and
1360 grs.; mean 13.81 grs. We have thus a diffusion in equal times
of— -
Carbonate of potash, º 10:27 1
Nitrate of potash, . te 13.81 1:3447
These experiments are almost identical with the former results, 10:25
carbonate of potash, and 13.97 nitrate of potash, which are as 1 to 1363.
But the numbers thus obtained cannot be fairly compared, owing to
the diminishing progression in which the diffusion of a salt takes place,
Thus when the diffusion of nitrate of potash was interrupted every two
days, as in a former experiment with chloride of sodium, the progress of
the diffusion for eight days was found to be as follows in a 4 per cent,
solution, with a mean temperature of 66°. - - -
Nitrate of Potash.
Diffused in first two days, . & 4:54 grs.
Diffused in second two days, º 4:13 grs.
Diffused in third two days, . . 4.06 grs.
Diffused in fourth two days, . tº 3.18 grs.
15'91
The absence of uniformity in this progression is no doubt chiefly
due to the want of geometrical regularity in the form of the neck and
shoulder of the solution phial. A plain cylinder, as the solution cell,
might give a more uniform progression, but would increase greatly the
difficulties of manipulation. - -
The diffusion of carbonate of potash will no doubt follow a diminish-
ing progression also ; but there is this difference, that the latter salt will
not advance so far in its progression, owing to its smaller diffusibility,
in the seven days of the experiment, as the more diffusible nitrate does.
The diffusion of the carbonate will thus be given in excess, and as it is
the smaller diffusion, the difference of the diffusion of the two salts will
not be fully brought out.
Thg only way in which the comparison of the two salts can be made
with #. fairness, is to allow the diffusion of the slower salt to pro-
ceed for a longer time, till in fact the quantity diffused is the same for
this as for the other salt, and the same point in the progression has
therefore been attained in both; and to note the time required. The
ON THE DIFFUSION OF LIQUIDS. & 483
problem takes the form of determining the times of equal diffusion of
the two salts. This procedure is the more necessary from the inappli-
cability of calculation to the diffusion progression. -
Further, allowing the Times of Equal Diffusion to be found, it is
not to be expected that they will present a simple numerical relation.
Recurring to the analogy of gaseous diffusion, the times in which equal
volumes or equal weights of two gases diffuse are as the Square roots of
the densities of the gases. The times, for instance, in which equal
quantities of oxygen and hydrogen escape out of a vessel into the air,
in similar circumstances, are as 4 to 1; the densities of these two gases
as 16 to 1. Or, the times of equal diffusion of oxygen and protocar-
buretted hydrogen are as 1.4142 to 1, that is as the square root of 2 to
the square root of 1 ; the densities of these gases being 16 and 8, which
: are as 2 to 1. The densities are the squares of the equal diffusion times.
. It is not therefore the times themselves of equal diffusion of two Salts,
but the squares of those times which are likely to exhibit a simple
numerical relation. -
(1.) While the 4 per cent solution of nitrate of potash was diffused
as usual for seven days, the corresponding solution of carbonate of
potash was now allowed to diffuse for 9-90 days; times which are as
1 to 1.4142, or as 1 to the square root of 2. -
The results were as follows: diffused of—
Nitrate of potash at 64°1, in seven days, 13.81 grs., . 100
Carbonate of potash at 64°3, in 99 days, 1392 grs., . 100.8
The three experiments on the nitrate of potash, of which 13.81 grs.
is the mean, were 1398, 13.86 and 13.60 grs, as already detailed. The
three experiments on the carbonate were 14:00, 13.97 and 1378 grs.
The difference in the means of the two Salts is only 0-11 gr. The results
appear to be as near to equality as could be reasonably expected from
the method of experimenting. 7 and 9.90 may therefore be considered
as the times of equal diffusion indicated for nitrate and carbonate of
potash. The times of equal diffusion, or the diffusibilities of nitrate
and carbonate of potash, would appear therefore to be in the proportion
of the square root of 1 to the square root of 2.
The explanation of such a relation suggested by gaseous diffusion
has been anticipated. It is that the two salts have different densities
in solution, that of nitrate of potash being 1, and that of carbonate of
potash 2. We are thus led to ascribe, what may be called Solution
Densities, to the salts. The two salts in question are related exactly
like protocarburetted hydrogen gas, of density 1, to oxygen gas of den-
sity 2. The parallel would be completed by supposing that the single
volume of oxygen to be diffused was previously mixed with 100 volumes
484 ON THE DIFFUSION OF LIQUIDS.
of air (or any other diluting gas), while the two volumes of protocar-
buretted hydrogen were also diluted with 100 volumes of air; the dilut-
ing air here representing the water in which the salts to be diffused are
dissolved in the solution cell. The time in which a certain quantity of
protocarburetted hydrogen would come out from a vessel containing 1
per cent. of that gas being 1 (the square root of density 1), the time
in which an equal quantity of oxygen would diffuse out from a similar
vessel, containing also 1 per cent., would be 1.4142 (the square root of
density 2). - -
(2) A solution of 4 parts of sulphate of potash in 100 water was
diffused simultaneously with the last solution of carbonate of potash,
and therefore in similar circumstances. The diffusion products of three
experiments were 14:46, 14:21, and 14:53 grs.; mean 14:40 grs. This
is in the proportion of 104.27 sulphate of potash to 100 nitrate of potash;
so that the approximation to equality of diffusion with nitrate of potash,
in the selected times, is not so close for the sulphate as for the carbonate
of potash. -
(3.) The diffusion was repeated of 2 per cent, solutions of the nitrate
and carbonate of potash at a lower temperature by about 10°. The
temperature of the solutions was rather unsteady; ranging from 56° to
52°25 for the first period of seven days, from 56° to 50°-5 for the period
of 9.90 days, and from 55° to 50°5 for a second period of seven days;
the external atmospheric temperature having fallen during the same
period more than 20 degrees. Six phials of each solution were diffused
and evaporated two together; so that the results are all double
quantities.
At a mean temperature of 54°3, the nitrate of potash gave in seven
days 12.60 and 12-13 grs. ; mean 12:36 grs.
Again, at a mean temperature of 52°4, the nitrate of potash gave i
seven days 1185, 12:40, and 11.95 grs. ; mean 12:06 grs. -
The carbonate of potash gave in 990 days, with a mean temperature
of 53°4, 1269, 12:40, and 12:12 grs. ; mean 12:40 grs.
The general results are—
Nitrate of potash, in seven days, at 54°3, . . 12:36 grs.
Carbonate of potash, in 99 days, at 53°4, . . 12:40 grs.
Nitrate of potash, in seven days, at 52°4, . . 12:06 grs.
As the first nitrate is 0°9 above the carbonate and the second nitrate 1°
below it, we may take the mean of the two nitrates as corresponding
to the temperature of the carbonate. We thus finally obtain, diffused
at 53°4, of -
Nitrate of potash in seven days, 12:22 grs., . . . 100
Carbonate of potash in 99 days, 12:40 grs., . . . . 101:47 .
ON THE DIFFUSION OF LIQUIDS. 485
The difference in the amount of the diffusion of the two salts in these
times is only 0.18 gr., or 1% per cent.
These last experiments may be held therefore as tending to the same
conclusion as the former series, although the circumstances were more
than usually unfavourable to their success. To find whether the same
relation existed between the salts through a considerable range of
temperature, an opportunity was taken during cold weather to repeat the
experiments at a low temperature. .
. (4.) Solutions of 1 salt in 100 water were diffused from eight solu-
tion cells, for each salt. The times were increased, but the same ratio
of 1 to 1.4142 was preserved between them. The liquids of the cells
Were found to retain a temperature ranging slowly between 41° and
38°8 during the whole period of the observations. Sulphate of potash
was substituted for the carbonate, as of these two equi-diffusive salts
the former had been found to be least in accordance with nitrate of
potash, in the 4 per cent. Solutions, and appeared therefore to afford the
severest test of the relation.
For nitrate of potash, at a mean temperature of 39°7, during nine
days, the diffusion product of two cells together was 6-97, 6'93, 6-77, and
6-64 grs. ; mean 6'83 grs. for two cells. :
For sulphate of potash, at the same mean temperature of 39°7, during
12728 days (twelve days, seventeen hours, twenty-eight minutes), the
diffusion, product of two cells together was 7:05, 6'93, 7:28, and 6-90
grs. ; mean 7.04 grs. for two cells.
The general results are—
Nitrate of potash in nine days at 39°7, . 6.83 grs. . 100
Sulphate of potash in 12728 days at 39°7, 7:04 grs. . 103-07
(5) Solutions of 2 salt in 100 water were diffused simultaneously
with the preceding experiments, and in precisely the same conditions of
time and temperature.
The diffusion product of nitrate of potash during nine days, at a
mean temperature of 39:7, was 7:03, 6-63, 6-83, and 6'83 grs. for one
cell; mean 6'83 grs. for one cell, or the same number as for two cells
with the 1 per cent. solution.
The diffusion product of sulphate of potash during 12-728 days was
6'84, and 6'80; mean 6:82 grs. for one cell. These experiments almost
coincide with the number for nitrate of potash.
Nitrate of potash, 6.83 grs., . gº 100
Sulphate of potash, 6-82 grs., . * 99-85
(6.) The existence of the relation in question was also severely
tested in another manner. Preserving the ratio in the times of diffusion
for the two salts, the actual times were varied in duration, in three
series of experiments, as 1, 2, and 3. The experiments were made in
4S6 ON THE DIFFUSION OF LIQUIDS.
the vault, with a uniformity of temperature favourable to accuracy of
observation. Eight cells of the 1 per cent, solution of each salt were
always diffused at the same time. - -
(a) Nitrate of potash diffused for 3-5 days, at 47°2, gave for two
cells, 3:55, 3:63, 3:33, and 3:51 grs. ; mean for two cells, 3:50 grs.
Sulphate of potash diffused for 4.95 days, at 47°3, gave for two cells,
3-54, 3:31, 3:51, and 3.63 grs. ; mean for two cells, 3:50 grs, or exactly
the same as for nitrate of potash above. :
(b) Nitrate of potash diffused for seven days, at 48°6, gave 6-1, 6-2,
5-9, and 5.92 grs. ; mean for two cells, 6.04 grs. . -
Sulphate of potash diffused for 9.9 days, at 49°1, gave 6'13, 5'92,
6:18, and 6:59 grs.; mean 6:20 grs, or, excluding the last experiment,
6:08 grs. - -
Chromate of potash diffused also for 99 days, at 49°1, gave 6:19,
6:18, 6:40, and 6:38 grs. ; mean for two cells, 6.29 grs. The diffused
chromate presented no appearance of decomposition on this occasion.
(c) Nitrate of potash diffused for 10-5 days, at 48’’, gave 8:36, 895,
8-82, and 8-84 grs.; mean for two cells, 874 grs. - º
Sulphate of potash diffused for 1485 days, at 48°6, gave 8-99, 8.94
8:66, and 8:56 grs. ; mean for two cells, 8-79 grs.
The mean results for the three different sets of periods of diffusion
are as follows:—
2
3:5 and 4.95 days Nitrate of potash, at 47°2, 3-50 grs., . 100
Sulphate of potash, at 47°3, 3:50 grs., . 100
Nitrate of potash, at 48°6, 6:04 grs., . 100
7 and 9:9 º Sulphate of potash, at 49°1, 620 grs., . 102.65
Chromate of potash, at 49°1, 629 grs., . 104-14
Nitrate of potash, at 48’’, 8.74 grs, ... 100
Sulphate of potash, at 48°6, 8-79 grs., . 100-57
The concurring evidence of these three series of experiments appears
to be quite decisive in favour of the assumed relation of 1 to 1.4142,
between the times of equal diffusion for the nitrate and sulphate of
potash, and consequently of the times for the two classes of potash salts,
of which the salts named are types. The same experiments are also
valuable as proving the similarity of the progression of diffusion, in
two salts of unequal diffusibility. I shall return again to the relation
between nitrates and Sulphates, under the salts of soda. . . . )
10.5 and 1485 days'
(8.) Hydrate of Potash.
(1) Eight cells of the 1 per cent solution of pure fused hydrate of
potash were diffused for seven days in the vault, with a temperature
ranging only from 59° to 58°, of which the mean was 58°6. The pro-
duct of four cells evaporated together was 17:57 grs. of hydrate of
ON THE DIFFUSION OF 1.IQUIDS. 487
potash, and of the other four cells 17:19 grs. ; mean 17:38 grs, or 4.345
grs, for one cell. The hydrate of potash was estimated from the chlo-
ride of potassium which it gave when Saturated with hydrochloric acid.
The diffusion product of sulphate of potash for seven days, at 58°5, or
almost the same temperature, was 10-75 grs. for the four cells, as already
stated, and consequently 2-64 grs. for one cell. It thus appears that
the hydrate of potash is greatly more diffusive than the sulphate of
potash in the same period of seven days, namely, as 4,345 to 2-64.
Such a result indeed is not inconsistent with the times of equal diffu-
sion of these two substances, differing as much as 1 to 2.
(2) Of pure fused hydrate of potash, a 1 per cent. Solution was
diffused from four cells for 4.95 days at a mean temperature of 53°7,
against a 1 per cent. Solution of nitrate of potash in six cells, for seven
days, at a mean temperature 0°-1 lower, or of 53°6. The hydrate of
potash which diffused, is calculated as before from the chloride of potas-
sium which it gave, when neutralized by hydrochloric acid. Hydrate
of potash diffused from two cells 5'97 and 6:28 grs. ; mean 6-12 grs, or
3.06 grs. for a single cell.
Nitrate of potash diffused from two cells 6:22, 6:54, and 5.93 grs. ;
mean 6:23 grs, or 3-11 grs. for a single cell. The diffusion of nitrate of
potash being 100, that of the hydrate of potash is 982, numbers which
are sufficiently in accordance. But the times were as 1 to 1.4142, and
their squares as 1 to 2. So far then as this series of experiments on
hydrate of potash entitles us to conclude, we appear to have for the
salts of potash a close approximation to the following simple series of
Squares of equal diffusion times:–
Squares of Times of Equal Diffusion, or Solution Densities.
Hydrate of potash, º * 1
Nitrate of potash, . º * 2
Sulphate of potash, tº e 4
(3) The hydrate of potash was also diffused at the lower tempera-
ture, 39°7, in company with the nitrate and sulphate of potash for a
period of 6.364 days (six days, eight hours, forty-four minutes).
The 1 per cent. Solution of hydrate of potash gave in eight cells,
evaporated two together, 6'93, 6'93, 6'93, and 6'89 grs. ; mean 6'92 grs.
The 2 per cent. Solution of hydrate of potash gave in three single
cells, 6-77, 6'49, and 7.10 grs. ; mean 679 grs.
The diffusion of nitrate of potash in nine days at the same tempera-
ture, as already detailed, was sensibly the same, or 6-83 grs. for both the
1 and 2 per cent. solutions. The times for the two salts were as 1 to
1:41:42. - -
The diffusion of hydrate of potash, at 39°7, may therefore be stated with
reference to that of nitrate of potash, for the selected times, as follows:–
488 ON THE DIFFUSION OF LIQUIDS.
Nitrate of potash, 1 and 2 per cent. Solutions, 100
Hydrate of potash, 1 per cent. solution, & 101.3
Hydrate of potash, 2 per cent. Solution, * 99.4
These experiments at the low temperature concur, therefore, with
those made at the higher temperature, in proving that the times of equal
diffusion of the two substances have been properly chosen.
III. DIFFUSION OF SALTS OF SODA.
(1) The only salts of soda which I have yet had an opportunity of
diffusing in a sufficient variety of circumstances are the carbonate and
sulphate. These salts appear to be equi-diffusive, but to diverge not-
withstanding more widely in the solutions of the higher proportions of
salt than the corresponding potash salts. It is a question whether this
increased divergence is not due to the less solubility of the soda salts,
and the nearer approach consequently to their points of Saturation in the
stronger Solutions. - .
TABLE XIII–Diffusion of Carbonate and Sulphate of Soda.

At 64°. At 37° 7.
Parts of anhydrous salt Density of
to 100 water. solution at 60°.
- Experiments. | Mean. Experiments. | Mean.
Carbonate of soda.
2 1-0202 4-15 2.78
4-08 2.62
4'21 4'14 2.73 2.71
4 1-0405 7.96 5-31
7-70 4.94
7.68 7-78 5-35 5-20
6; I'0653 12-16 8:50
• 12-06 8:45
- - e 12:45 12-22 8:05 8°33
10 1.0957 17-13 -
16-53
17:00 16-88
Sulphate of soda.
2 1.0179 4’35 2.96
- 4.32 3-03
- 4'25 4’31 3.09 3.03
4 1.0352 8'14 5:63
8-10 5-64
8-28 8-17 5-42 5-56
63 1.0578 13.26 . 8-77
13-63 8-84 8'80
. . 13-61 13:50
10 1.0847 1871
- 1973
18-9] 19'14
ON THE DIFFUSION OF LIQUIDS. 489
The range of the thermometer during the continuance of the experi-
ments at the higher temperature was from 64°5 up to 65° and falling
again to 63°; the mean of all the days being 64". The temperature of
the other series, or of the ice-box, was 42° the first day, 38° the second,
and 37 steadily for the remainder of the period; the mean being 37°7.
The mean results at 64° are as follows:—
| 2 4 63. 10
Carbonate of soda......... ' 4°14 7-78 12-22 16-88
Sulphate of soda ......... - 4’31 8-17 | 3:50 19°14
Another series of experiments was made upon a 1 per cent. Solution
of the same salts at a mean temperature of 64°9. Six phials of each
solution were diffused, and the water of two jars afterwards evaporated
together, so that the quantities stated are double.
The diffusion product in three experiments with the sulphate of
soda was 477, 475, and 4.80 grs. ; mean 477 grs. The diffusion pro-
duct in three experiments with the carbonate of soda was 4.61, 4-68,
and 4.67 grs.; mean 465 grs. The difference between the carbonate
and sulphate is 0.12 gr. ; it is less for the present proportion of 1 per
cent. of salt, than for 2 per cent., so that the diffusion of the salts may
be converging to a. perfect equality in very weak solutions. One-half
of the preceding quantities, or the mean results for a single diffusion
cell, are—
Diffusion of 1 per cent. Solutions at 64°9.
Carbonate of soda, 2.32 grS, . we 100
Sulphate of soda, 2.38 grs., . t 102°58
(2) The diffusion of the carbonate of soda was further compared
with the nitrate of the same base, to find whether their times of equal
diffusion are related like those of the corresponding potash salts. The
mean temperature of the first seven days, which was the period of
diffusion for the nitrate of soda, was 66.9 ; of the last three days, 65°2;
and of the whole period of 9.9 days occupied by the carbonate of soda,
66°4. The 4 per cent. solutions were employed.
The nitrate of soda gave a diffusion product, in three experiments,
of 11:48, 11:58, and 12-13 grs. ; mean 1173 grs.
The carbonate of soda, in three experiments, gave 11-66, 11:53, and
11:52 grs. ; mean 11:57 grs. A slight addition should be made to the
latter quantity to raise the diffusion product from 66°4 to 66°9. It
will appear from a subsequent experiment that the diffusion of the
carbonate of soda increases 0.096 gr. for a rise of one degree of tempera-
490 ON THE DIFFUSION OF LIQUIDS.
ture; which will give 0.05 gr, for the half degree in question. Bringing
the diffusion of the two salts to the same temperature of 669, we have
therefore diffused, of -
Nitrate of soda, in seven days, 11.73 grs., . 100
Carbonate of soda, in 99 days, 11-62 grs., . 99-06
The difference in the quantity diffused of the two salts is only 0-11 gr.,
or 1 per cent, which is quite within the unavoidable errors of observa-
tion.
(3.) The diffusion of a 2 per cent. solution of the same Salts was
repeated at the same inferior temperature of 54:3 as with the salts of
potash, and under the same difficulties from fluctuation of atmospheric
temperature. Two water-jars were evaporated together, so that the
results are double.
Nitrate of soda, diffused for seven days at a mean temperature of 54°3,
gave 10:15, 10:24, and 992 grs. in three experiments; mean 10:10 grs.
Carbonate of soda, diffused for 9.9 days at a mean temperature of
53°4, gave 9-93, 9:54, and 10:10 grs. in three experiments; mean 9:86
grs. But the latter amount is to be increased by 0.09 gr. to bring it to
the diffusion of 54°3. , We have then for the diffusion product of the
two salts at the same temperature of 54°3– *
Nitrate of soda, in 7 days, 10:10 grs., & 100
Carbonate of soda, in 99 days, 9.95 grs, . 98.51
The difference is again small, namely, 0-15 gr, or 1% per cent, and
within the limits of unavoidable error.
It appears therefore that the times of equal diffusion of the nitrate
and carbonate of soda are related like those of the nitrate and carbonate
of potash, or as the square root of 1 and 2, that is, as 1 to 1.4142.
Relation of Salts of Potash to Salts of Soda.
It appeared probable, from many of the experiments already re-
corded, that if any relation, in the times of equal diffusibility, existed
between the corresponding salts of potash and soda, it was that of the
square root of 2 to the square root of 3. They were accordingly diffused
for times having this ratio; namely, the nitrate of potash for seven
days, the nitrate of soda for 8-57325 days; the sulphate and carbonate
of potash for 9.9 days, and the sulphate and carbonate of soda for 12-125
days. If these times are rightly chosen, the eventual diffusion pro-
ducts of all the experiments should be equal. The 1 per cent. solution
was selected, and the number of experiments simultaneously made on
each salt was eight or six. The liquids of two water-jars were evapor-
ON THE DIFFUSION OF LIQUIDS. 491
ated together, so that each of the results in the table below represents
the diffusion of two cells. These experiments also afford another oppor-
tunity of testing the assumed relation between the nitrates and sul-
phates of the same base.
TABLE XIV.-Solution: 1 Salt to 100 Water, at 55°4–56°1.

Square of Diffusion product of two cells in grs.
Tempe-H. Time times.
rature. in days. Sol. density.
Exp. I. Exp. II. Exp.III. Exp. IV. Mean.
Nitrate of potash ...... 53-1 || 7
Nitrate of soda ......... 55-7 || 8.57
Sulphate of potash ...| 55-4 9-90
Sulphate of soda ...... 55-4 12-125
Carbonate of potash ... 55.4 9-90
-Carbonate of soda...... 55-4 12-125
6-67 || 6-87 || 6-90 || 6-57 || 6-75
6'59 || 6-80 || 6-94 || 6-57 || 6-78
6-73 || 6-77 || 6-96 || 6-68 6-78
6°43 || 6’94 || 6-80 || 6-68 || 6-72
6'54 6-64 || 6’40 || 6’ 67 || 6′56
6-40 || 6-63 || 6-60 6-67 6'54
:
The range of temperature during the period of these experiments
rather exceeded 3 degrees, so that they cannot be considered as fortu-
nate in that respect; but still the similarity between the different sets
of experiments, and the near equality of their means, is very remark–
able. The two nitrates and the two sulphates may be said to coincide,
the extreme difference of the means of the four salts not being quite so
much as 1 per cent. The two carbonates fall about 3.4 per cent. below
the sulphates and nitrates, but agree perfectly with each other, showing
a uniformity in their irregularity. This deviation of the carbonates
would appear essential, as it has been observed every time they have
been compared with the sulphates.
The double relation between salts of potash and salts of soda, and
between the nitrate and sulphate class of each of these bases, will, I
believe, be allowed to acquire considerable additional support from this
new series of observations. -
IV. DIFFUSION OF SULPHATE OF MAGNESIA.
In a set of preliminary experiments upon sulphate of magnesia in
comparison with sulphate of potash, the 4 per cent, solutions of both
salts were diffused for seven days at a mean temperature of 57°9, with
very little fluctuation, the extreme range being from 58°5 to 57°75.
The sulphate of magnesia is taken anhydrous in all the following
experiments. -
. The diffusion of Sulphate of potash in three cells was 9:16, 9:22, and
9:57 grs. ; mean 9:32 grs. -
49 2. ON THE DIFFUSION OF LIQUIDS.
The diffusion of sulphate of magnesia in three cells was 5:21, 498,
and 5:34 grs. ; mean 5:18 grs. The diffusion, in equal times, appears
here to be as 100 sulphate of potash to 55-58 sulphate of magnesia. We
know, however, that when unequally diffusible salts are diffused for
equal times, the diffusion of the slower is exaggerated. Consequently
the diffusion of sulphate of magnesia is likely to be represented in excess
in these experiments. - -
In a second preliminary series of experiments the same 4 per cent.
solutions were diffused, the sulphate of potash for eight days and the
sulphate of magnesia for nineteen days, with the view of discovering
their times of equal diffusibility. - - -
During the first period of eight days the temperature fluctuated con-
siderably, beginning at 54°, falling gradually in four days to 50°5, and
rising again in four days to 53°; the average of the whole period was
52°2. The diffusion of sulphate of potash from three cells was 9°36,
9°25, and 10°52 grs. ; mean 9:71 grs.
During the second period of nineteen days, which included the first
period, the mean temperature was 54°6. The diffusion of sulphate of
magnesia from three cells was 1181, 11-61, and 10.90 grs. ; mean 11:44
grs. The variation in the amounts diffused of both salts is greater than
usual, owing no doubt to the changes of temperature, which were imper-
fectly controlled. -
Dividing the quantity of salt diffused by the number of days, we
have of sulphate of potash 1214 gr. diffused per day, and of sulphate of
magnesia 0.602 gr. per day; or the latter salt exhibits sensibly half the
diffusibility of the former in equal times. This suggested the trial of
times for these two salts in the proportion of 1 to 2, with the view of
obtaining equal diffusions. -
(1.) A one per cent. Solution of sulphate of magnesia (anhydrous)
was diffused for the long period of 19.8 days, at a mean tempera-
ture of 54*7, in 8 cells. The diffusion products of four pairs of cells
were 7:07, 6-71, 7:07, and 7:35 grs. ; mean 7:05 grs, or for one cell,
3:53 grs. -
A similar solution of sulphate of potash diffused for 99 days, or half
the preceding period, at a mean temperature of 55°4, or 0°7 higher,
gave a mean product, for two cells, of 679 grS., as before stated, or
for one cell, of 3:40 grs. The diffusion of sulphate of potash being 100,
that of sulphate of magnesia is therefore 1037, a fair approximation to
equality. * - -
(2) In a second series of experiments upon 1 per cent. solutions of
the same two salts, diffused in the vault for fourteen and seven days.
respectively, with a mean temperature of 53°8 for the sulphate of
magnesia, and 54°3 for the sulphate of potash, the temperature was
...ON THE DIFFUSION OF LIQUIDS. 493
remarkably uniform, gradually falling from 55°2 to 53° during the longer
period, but without any injurious oscillation.
From eight cells, evaporated two together, the sulphate of magnesia
obtained was 6'12, 6-12, 6:04, and 6:03 grs.; mean 6:08 grs, or 3.04 grs.
for one cell. -
The sulphate of potash gave from eight cells, in experiments already
detailed, a mean result of 5-84 grs. of salt for two cells, or 2.92 grs. for
one cell. The diffusion is in the proportion of 100 sulphate of potash
to 104-11 sulphate of magnesia, the times being as 1 to 2 for the two
salts respectively.
From these two series of experiments, it appears that, at 54°, sulphate
of magnesia has nearly, if not exactly, half the diffusibility of sulphate
of potash, and consequently one-fourth of that of hydrate of potash.
Or, the times of equal diffusion for these three salts appear to be 1, 2,
and 4. The squares of these times and the solution densities are 1, 4,
and 16. Hydrate of potash may possibly therefore have the same rela-
tion to sulphate of magnesia in solution density and diffusibility that
hydrogen gas has to oxygen gas.
(3) A two per cent. solution of sulphate of magnesia, diffused for
fourteen days, gave at 53°9, for two pairs of cells, 9:57 and 10:00 grs.
of salt, of which the mean is 9-79 grs, or 4-85 grs. for one cell.
A similar solution of sulphate of potash diffused for seven days gave
a mean result of 4.97 grs. of salt for one cell, at 54°2, as already stated.
The result is a diffusion of 100 sulphate of potash to 97-59 sulphate of
magnesia.
(4.) A four per cent. Solution of Sulphate of magnesia, diffused for
fourteen days, gave at 53°7, in two pairs of cells, 18:00 and 1820 grs. of
salt; mean 1810 grs. for two cells, or 9:05 grs. for a single cell.
A similar solution of sulphate of potash, diffused for seven days at
54°2, gave a mean result of 9:30 grs. of salt for a single cell, as already
stated. This is a diffusion of 100 sulphate of potash to 97.4 sulphate of
magnesia. -
The diffusion of the 2 and 4 per cent. Solutions of sulphate of mag-
ºnesia is so nearly equal to the diffusion of the same proportions of
sulphate of potash in half the time, that they may be considered as
supplying additional support to the assumed relation between the diffu-
sibilities of these salts. - .
I may add, that a 4 per cent. Solution of anhydrous Sulphate of zinc
was diffused for fourteen days, simultaneously with the similar solution
of sulphate of magnesia, and of course at the same temperature of 53°7.
Two cells, evaporated two together, gave 17:40 and 17:36 grs. of ignited
! sulphate of zinc.; mean 1738 grs. The salt remained, after ignition,
| entirely soluble. . This is a diffusion of 8-69 grs. for one cell, while the
-
494 ON THE DIFFUSION OF LIQUIDS.
sulphate of magnesia gave 9:05 grs.; or of 100 sulphate of zinc to 104-14
sulphate of magnesia. This result is interesting, as we here find two
salts which are isomorphous, and of which the equi-diffusion is on that
account in a high degree probable, differing between themselves so much
as 4 per cent. w -
Another numerous series of experiments was made at a considerably
lower temperature, with the view of testing several of the same relations.
The temperature in commencing the diffusion was 41’’, but fell in the
course of three days to 38°8, and afterwards rose to 39, from which it
never varied afterwards more than a degree during the diffusion of the
salts of potash and soda. The mean temperature for their periods did
not vary above 0°-1 or 0°2 from 39°7, so that it may be supposed the
same for all these salts. For the sulphates of magnesia, the mean tem-
perature was 38°9, or 0°8 lower. The times chosen are as the square
roots of 2, 3, 6, and 16. - •
TABLE XV-Solutions of 1 and 2 Salt to 100 Water, at 39°7.
i

Diffusion product of two cells in I per cent.
solutions, and one cell in 2 per v
- & Square of -
* cent. solutions.
Time in times. - -
days. Sol density. +–


Exp. I. Exp. II. Exp. III. Exp. IV. | Mean.
Chloride of potassium, 2 per cent. 9 2 6-58 || 6-79 || 6-82. ... 6'73
Nitrate of soda, 2 per cent. ...... II -022 3 6-66 || 6'98 || 6-79 . ... 6'81
Chloride of sodium, 1 per cent... 11:022 3 6:33 || 6-63 || 6-73 || 7-06 || 6-69
Chloride of sodium, 2 per cent... 11:022 3 6:50 || 6-60 6'64 || 6-74 6.62
Sulphate of soda, 1 per cent......] 15:589 6 6-60 | 6′56 | 6′56 6'50 6'55
Sulphate of soda, 2 per cent. ... 15:589 6 6'50 5:43 || 6′33 ... | 6’42
Sulphate of magnesia, 1 per cent. 25.456 || 16 6:36 || 6’20 || 6-86 | 6′59 || 6:50
Sulphate of magnesia, 2 per cent. 25.456 16 6.42 678 || 6′50 | 6’84 || 6:63
Several other salts were diffused in the same circumstances as the
preceding, of which the diffusion products have been previously given.
Of these salts, both the 1 and 2 per cent. Solutions of nitrate of potash
gave 6'83 in nine days, or in the same time as chloride of potassium in
the table. The latter salt maintains a 'sensible equality of diffusion
with the present series at the low, as well as it was found to do at the
former high temperature. Chloride of sodium is here introduced for
the first time : it appears to be equi-diffusive with nitrate of soda. If
the sulphate of magnesia diffused be increased by 0:07, for its lower
temperature, this salt will be in close accordance with the salts of pot-
ash and Soda. -
Taking nitrate of potash 6'83, as 100, for a standard, the salt which
deviates most considerably is sulphate of soda, which for the 1 per cent.
ON THE DIFFUSION OF LIQUIDS. 495
solution is 6'55, or 959. A low temperature, however, must be unfav-
ourable to diffusion experiments, from increasing the tendency of salts
to crystallize.
In conclusion, I may sum up the results of most interest which this
inquiry respecting liquid diffusion has hitherto furnished. - -
1. I would place first the method of observing liquid diffusion. This
method, although simple, appears to admit of sufficient exactness. It
enables us to make a new class of observations which can be expressed
in numbers, and of which a vast variety of substances may be the
object, in fact everything soluble. Diffusion is also a property of a
fundamental character, upon which other properties depend, like the
volatility of substances; while the number of substances which are
soluble and therefore diffusible, appears to be much greater than the
number of volatile bodies.
2. The novel scale of Solution Densities, which are suggested by the
different diffusibilities of Salts, and to which alone, guided by the ana–
logy of gaseous diffusion, we can refer these diffusibilities. Liquid
diffusion thus supplies the densities of a new kind of molecules, but
nothing more respecting them.
The fact that the relations in diffusion of different substances refer
to equal weights of those substances, and not to their atomic weights or
equivalents, is one which reaches to the very basis of molecular chemis-
try. The relation most frequently possessed is that of equality, the
relation of all others most easily observed. In liquid diffusion we appear
to deal no longer with chemical equivalents or the Daltonian atoms, but
with masses even more simply related to each other in weight. Found-
ing still upon the chemical/atoms, we may suppose that they can group
together in such numbers as to form new and larger molecules of equal
weight for different substances, or if not of equal weight, of weights
which appear to have a simple relation to each other. It is this new
class of molecules which appear to play a part in solubility and liquid
diffusion, and not the atoms of chemical combination. -
3. The formation of classes of equi-diffusive substances. These
classes are evidently often more comprehensive than the isomorphous
groups, although I have reason to imagine that they sometimes divide
such groups; that while the diffusion of Salts of baryta and strontia,
for instance, is similar, the diffusion of salts of lead may be dif-
ferent. -
4. The separation of the whole salts (apparently) of potash and of
soda into two divisions, the Sulphate and nitrate groups, which sº
have a chemical significancy. The same division of the Salts in quéstion
S
^*..
... ºr
496 ON THE DIFFUSION OF LIQUIDS.
has been made by M. Gerhardt, on the ground that the nitrate class is
monobasic and the sulphate class bibasic. -
5. The application of liquid diffusion to the separation of mixed salts,
in natural and in artificial operations. -
6. The application of liquid diffusion to produce chemical decompo-
sitions. , -
7. The assistance which a knowledge of liquid diffusion will afford
in the investigation of endosmose. When the diffusibility of the salts
in a liquid is known, the compound effect presented in an endosmotic
experiment may be analysed, and the true share of the membrane in the
result be ascertained. -
But on the mere threshold of so wide a subject as liquid diffusion, I
must postpone speculation to the determination of new facts and the
enlargement of my data, of the present incompleteness of which I am
fully sensible. -
SUPPLEMENTARY OBSERVATIONS ON THE DIFFUSION OF
LIQUIDS.”
THE experiments of my former paper furnished strong grounds for
believing that isomorphous salts possess a similar diffusibility. All the
salts of potash and ammonia, which were compared, appeared to be
equi-diffusive; SO also were the salts of certain magnesian bases. A
single preliminary observation on the nitrates of lead and baryta, how-
ever, opposed the general conclusion, and demanded further inquiry. It
is scarcely necessary to say that any new means of recognising the exist-
ence of the isomorphous relation between different substances, must
prove highly valuable. Let us inquire therefore how far liquid division
is available for that purpose.
The salts were still diffused from weak solutions, that is from solu-
tions containing from 1 to 8 per cent. of Salt ; but now a measure of the
solution, equal to 100 grs, of water, was made to contain 1 grain of the
salt, to form what is called the 1 per cent. Solution; instead of 1 grain of
salt being added to 100 grs. of water, as before, without reference to the
condensation which generally occurs. The quantities 1, 2, 4, and 8 per
cent, thus indicate the parts of Salt present in a constant volume of liquid,
—as 10, 20, 40, and 80 grs. of the Salt in 1000 water grain-measures of
the solution. The same phials for the solution and jars for the external
water-atmosphere continued to be used, and the manipulations were
* Phil. Trans. 1850. Received May 2, —Read June 20, 1850.
ON THE DIFFUSION OF LIQUIDS. 497
similar. It is believed, however, that the temperature of the liquids
was maintained more uniform in the new experiments than the old,
partly by the better regulation of the temperature of the apartment,
and partly by placing the jars close together upon a table with upright
ledges, and covering the whole over with sheets of paper during the
continuance of an experiment. The mass of fluid in 80 or 100 jars,
which were employed at once and placed together, made the small
oscillations of temperature, which might still occur, slow and less
injurious.
The investigation is also extended to several new substances, such
as hydrocyanic acid, acetic acid, Sulphurous acid, alcohol, ammonia and
salts of organic bases without reference to isomorphous relations. It is
very necessary to have data which are minute and accurate respecting
the diffusion of a considerable variety of substances. This it is my
present object to endeavour to supply, leaving speculative deductions
in general respecting the nature and laws of liquid diffusion for a future
occasion.
The density of all the solutions was observed at a constant tempera-
ture, namely, 60 Fahr.
1. Hydrochloric Acid.
The period of diffusion arbitrarily chosen for this acid was five days.
The diffusate, or quantity of acid diffused, was determined by preci-
pitating the liquid of the external reservoirs with nitrate of silver,
and weighing the chloride of silver formed. In the 1 and 2 per cent.
solutions, the liquids of two jars were generally mixed and precipitated
together.
(1) Hydrochloric acid, 0.99 per cent. ; density 1-0043. Diffused at
53°5, in six cells, 7:52, 7:52, 7.42; mean 7:49 grs, for 2 cells. Calcu-
lated for 1 per cent, 7.56 grs. at 53°5 for two cells, or 7:41 grs. at 51°,
when corrected for that temperature. -
(2) Hydrochloric acid, 1.92 per cent. ; density 1-009. Diffused at
51°, in eight cells, 1471, 14:05, 14:54, 14:47; mean 1444 grs. for two
cells. Calculated for 2 per cent, 15.04 grs. at 51° for two cells.
(3) Hydrochloric acid, 1993 per cent. ; density 1-0094. Diffused
at 62°8, in six cells, two experiments on one-sixth part of the mixed
jars gave 8.203, 8:198; mean 8:20 grs, for one cell, or 16:40 grs. for two
cells. Calculated for 2 per cent, 1646 grs, at 62°8 for two cells.
(4) Hydrochloric acid, 3.90 per cent. ; density 1-0190. Diffused at
51°, in 8 cells, 29:18, 30.70, 30.70, 29.26; mean 2996 grs, for two cells.
Calculated for 4 per cent, 30.72 grs. at 51° for two cells.
2 I
498 ON THE DIFFUSION OF LIQUIDS.
(5) Hydrochloric acid, 7.90 per cent.; density 1-0380. Diffused at
51°, in four cells, 32.71, 33-64, 33-64, 33-74; mean 33°43 grs, for one
cell. Calculated for 8 per cent, 33-84 grs. at 51° for one cell.
Comparing the diffusibilities of the 2 per cent. solutions (2 and 3) at
51° and 62°8, an increase is observed from 15:04 to 16:40 grs, or from 100
to 109-1, which gives an increase of 0.77 per cent, for 1". This method
of estimating the effect of temperature is not exact, as the times only in
which an equal diffusion at the different temperatures takes place are
truly comparable. We may deduce from it, however, the effect of the
small difference of temperature of 2°5 of the 1 per cent, solution from
the others, as has been done, without sensible error. The diffusates at
the same temperature would then be as follows:— .
Diffusion of Hydrochloric Acid in five days at 51°Fahr.; two cells.
Grs. Ratio.
Erom 1 per cent. Solution, . g 7'41 0.97
Erom 2 per cent. Solution, . e. 15'04 2:00
From 4 per cent. Solution, . tº 30-72 4:08
From 8 per cent. Solution, . . 67-68 9:00
The increasing diffusibility with the larger proportions of acid here
observed is unusual, at least in the degree exhibited by the 8 per cent.
solution. Other substances, as will be immediately observed of nitric
acid, appear to lose proportionally in diffusibility as their solutions are
concentrated. -
Hydrochloric acid belongs to the most diffusive class of substances
known; it appears to exceed hydrate of potash at 53°5, as 7:56 to 6:12,
or as 100 to 80.9."
The rapidity with which hydrochloric acid diffuses, and the facility
with which that substance may be estimated, induced me to examine
the progression with which its diffusion takes place with increasing
times in a minute manner. The 2 per cent. Solution was diffused for
times increasing by six hours, from twelve hours or 0.5 day to 475 days,
six cells being diffused for every period. Instead of determining the acid
diffused separately in each jar or pair of jars, the contents of the six
jars of each experiment were mixed together, and a definite proportion
of the liquid precipitated by nitrate of silver, so as to obtain at once the
mean result. Another observation for 5.75 days is added, although
made at a sensibly higher temperature. .
1 Philosophical Transactions, 1850, p. 39.
ON THE DIFFUSION OF LIQUIDS. 499
Diffusion of Hydrochloric Acid, 2 per cent, solution; one cell.

Time. Temperature. Diffusate in grains. | Differences.
Days. O
0.5 53-75 0-909
0-75 53-75 1-312 •403
l 53-75 1766 *454
1.25 53-75 2-353 •587
I-5 - 53-75 2.596 •243
I-75 53-58 3-178 *582
2 53-58 3°410 •232
2.25 53°42 3.967 •557
2.5 * 53-58 4’339 -372
2.75 53-50 4-618 •279
3 53-50 4-969 •351
3.25 53-50 5-304 •335
3.5 54-85 5-857 •553
3-75 54-85 6-254. •397
4 54-85 6.407 • 153
4:25 54-85 6.795 •388
4-5 54.71 7:034 •239
4-75 54.71 7'473 •339
5.75 56'46 8°363
The differences are evidently affected by accidental errors of obser-
vation. The diffusion at 3-5 days is also increased by a rise of tem-
perature of more than 1 in that and the following experiments. The
diffusion always increases with the time, but less rapidly, according to
a gradually diminishing progression.
2. Hydriodic Acid, Hydrobromic Acid and Bromine.
Hydriodic Acid—Time of diffusion five days, as for hydrochloric
acid. The acid diffused was estimated from the iodide of silver which
it gave when precipitated by nitrate of silver.
Hydriodic acid, 1.98 per cent.; density 1:0142. Diffused at 53°5,
in eight cells, 14:90, 15-67, 15:25, 15-27; mean 1527 grs. for two cells.
Calculated for 2 per cent, 15.42 grs. at 53°5 for two cells, or 15:11 grs.
at 51°.
These experiments indicate a similarity of diffusion between the two
isomorphous substances, hydrochloric and hydriodic acids.
Diffusion from 2 per cent, solutions at 51° Fahr.
Hydrochloric acid, . e 15:04 100
Hydriodic acid, . ſe 49 15:11 100'46
Hydrobromic Acid.—Time of diffusion five days. The diffusate was
estimated from the bromide of silver.
500 ON THE DIFFUSION OF LIQUIDS.
(1) Hydrobromic acid, 1556 per cent.; density 1-0.112. Diffused
at 59°7, in eight cells. The whole diffusates mixed together gave by
analysis a mean of 12.90 grs. of hydrobromic acid in two cells; calcu-
lated for 2 per cent, 16:58 grs, in two cells, at 59°7. -
(2) The experiment was repeated at 59°8, with a solution con-
taining 1-578 per cent of hydrobromic acid, of density 1:01.16, with five
diffusion phials not employed above. The mean diffusate for a pair of
cells was 13:05 grs. of hydrobromic acid; that is, 16:53 grs. for a 2 per
cent. Solution, which is as nearly as possible the result of the preceding
Series of experiments. -
(3) Another solution containing exactly 2 per cent. of hydrochloric
acid was diffused for comparison in eight cells, in the same circum-
stances of time and temperature as (1); its density was 1:0104.
Diffusate from 2 per cent. solutions at 59°7 Fahr.
Hydrochloric acid, . © 16:55 100
Hydrobromic acid, . & 16-58 100-18
Hydrobromic acid appears therefore to coincide in diffusibility with
hydrochloric acid at this temperature. It may be remarked that these
three acids, hydrochloric, hydrobromic and hydriodic, do not exhibit the
same correspondence in another physical property, namely, the densities
of their aqueous solutions containing the same proportion of acid. The
densities of 2 per cent. solutions of hydrochloric and hydriodic acids
appear to be respectively 1:0104 and 1.0143, at 60° Fahr, and that of
hydrobromic acid will obviously be an intermediate number. The same
acids are also known to differ considerably in the boiling-points of solu-
tions containing the same proportion of acid. A considerable diversity
of physical properties appears here to be compatible with equal diffusi-
bility in substances which are isomorphous.
Bromine.—Pure water readily dissolves more than 1 per cent of this
substance. The solution prepared, however, contained only 0.864 per
cent of bromine, as was ascertained by treating it with sulphurous
acid and afterwards precipitating by nitrate of silver. Its density was
10070. It was evident, from the slow appearance of the brown colour
in the exterior cell, that bromine diffuses less rapidly than hydro-
bromic acid. -
The diffusion-time of bromine was made ten days, or double the
time of hydrobromic acid. Two cells contained together a diffusate of
5.80 grs. of bromine; another two cells a diffusate of 5.88 grs. ; mean
5.84 grs. at 60°l Fahr.; or 6-76 grs. for a 1 per cent. Solution. Doubling
the last result we have 13:52 grs, for a 2 per cent. Solution, which is
ON THE DIFFUSION OF LIQUIDS. 501
still considerably under the diffusate of hydrobromic acid (16:58 grs) in
half the time.
3. Hydrocyanic Acid.
Time of diffusion five days. The acid diffused was estimated from
the cyanide of silver which it gave with nitrate of silver.
Hydrocyanic acid, 1766 per cent, made up to a density of 1:01.42
with sulphate of potash. Diffused at 64°2, in six cells, 11:40, 11-86,
11.80; mean 11.68 grs. for two cells. Calculated for 2 per cent, 13:23
grs, at 64°2 in two cells, or about 13:10 grs. at 62°8, assuming this acid
to be affected in the same way by temperature as hydrochloric acid.
Hydrocyanic acid here appears less diffusive than hydrochloric acid,
at the same temperature 62°8, as 13:10 to 16:40, or as 79.6 to 100, and
not to belong therefore to the same class of diffusive substances.
4. Nitric Acid.
Time of diffusion five days. The quantity of this acid diffused was
always determined with great exactness by neutralization by means of
a normal solution of carbonate of soda.
1. Nitrate of water (HO. NOS), 1 per cent. ; density 1-0052. Dif-
fused at 50°8, in eight cells, 6-77, 6-77, 7:26, 6-97; mean 6.94 grs, of
nitrate of water in two cells at 50°8, and 6.99 grs. by estimate at 51°2.
2. Nitrate of water, 1 per cent. ; density 1-0052. Diffused at 53°-5,
in six cells, 7:32, 7:32, 7:20; mean 7-28 grs. in two cells.
3. Nitrate of water, 1.92 per cent. ; density 1:01.12. Diffused at
51°2, in eight cells, 14:34, 14:24, 14:10, 13.96; mean 14:16 grs. in two
cells. Calculated for 2 per cent, 1474 grs. at 51°2 in two cells.
4. Nitrate of water, 2 per cent. ; density 1:0106. Diffused at 63°2,
in eight cells, 16-97, 16-64, 16-81, 16-64; mean 16-76 grs. in two cells.
5. Nitrate of water, 3.88 per cent.; density 1-0209. Diffused at
51°2, in eight cells, 27-76, 28-34, 27.90, 27.62; mean 27.90 grs, in two
cells. Calculated for 4 per cent, 28-76 grs. at 51°2 in two cells.
6. Nitrate of water, 7.96 per cent. ; density 1-0.432. Diffused at
51°2, in four cells, 29-17, 29-17, 29:17, 27.76; mean 28:82 grs, in one
cell. Calculated for 8 per cent, 28.96 grs, at 51°2 in one cell.
For the difference of temperature between 51°2 and 63°2, the diffu-
sion rises, in the 2 per cent. solution, from 1474 to 16-76 grs., or from
100 to 1137; which gives an increase of 1:142 per cent. for one degree
of temperature.
The diffusion of the different proportions of this acid at one tem-
perature is as follows:—
502 ON THE DIFFUSION OF LIQUIDS.
Diffusion of Nitrate of Water in five days at 51°2; two cells.
Grs. Ratio.
From 1 per cent. solution, º 6'99 0.95
From 2 per cent, solution, e 14*74 2
From 4 per cent. solution, & 28°76 3.90
From 8 per cent. Solution, e 57.92 7.86
The 2 per cent. solution is taken as the standard of comparison for
the ratios, instead of the 1 per cent. solution, from the greater accuracy
with which the diffusion of the former can be observed.
The usual approach to equality of diffusion, between chlorides and
nitrates, is observable in hydrochloric and nitric acids, at least in the
1 and 2 per cent. Solutions.
Diffusion from 1 per cent, solution at 53°5.
Hydrochloric acid, & • • 7:56 100
Nitrate of water, . e º 7-28 96.3
Diffusion from 2 per cent, solution.
Hydrochloric acid at 51°, tº 15:04 100
Nitrate of water at 51°2, wº 14*74 98.0
The 2 per cent. solutions of both acids were also diffused at higher
temperatures.
Diffusion from 2 per cent. Solution.
Hydrochloric acid at 62°8, º 16’46 100
Nitrate of water at 63°2, . tº 1676 101'8
Here the diffusibility of the two acids is as nearly as possible equal.
Diffusion from 4 per cent. solution.
Hydrochloric acid at 51°, . e 30-72 100
Nitrate of water at 51°2, we 28°76 93.7
Diffusion from 8 per cent. solution.
Hydrochloric acid at 51°, † 67-68 100
Nitrate of water at 51°2, . º 57-92 85-3
The wide divergence between these two acids, in the 8 per cent.
solution, is produced by the remarkably increased diffusion of hydro-
chloric acid in that high proportion. .”
ON THE DIFFUSION OF LIQUIDS. 503
5. Sulphuric Acid.
The time of diffusion arbitrarily chosen for this acid was ten days.
The diffusate of this acid was determined in the same manner as that
of nitric acid.
1. Sulphate of water (HO.SOs), 0.993 per cent. ; density 1:0065.
Diffused at 51°7, in eight cells, 887, 8.87, 8.87, 8:69; mean 8.82 grs. of
sulphate of water for two cells. Calculated for 1 per cent, 8-91 grs.
at 51°7 for two cells, and 8-69 grs. at 49°7.
2. Sulphate of water, 1.89 per cent. ; density 1-0130. Diffused at
49°7, in eight cells, 16-13, 16:16, 15:58, 16:03; mean 1598 grs. for two
cells. Calculated for 2 per cent, 1691 grs. at 49°7 for two cells.
3. Sulphate of water, 2 per cent. ; density 1:01:33. Diffused at
63°5, in eight cells, 1980, 2005, 19.67, 19:41; mean 1973 grs. for
two cells.
4. Sulphate of water 387 per cent.; density 1-0261. Diffused at
49°7, in eight cells, 32-72, 32-72, 33:06, 32:58; mean 32-77 grs, for two
cells. Calculated for 4 per cent, 3389 grs. at 49°7 for two cells.
5. Sulphate of water, 7.90 per cent. ; density 1-0513. Diffused at
49°7, in four cells, 34'08, 34-76, 33-74, 33-63; mean 34.05 grs. for one
cell. Calculated for 8 per cent, 34-48 grs. at 49°7 for one cell.
In the 2 per cent. Solution the diffusion rises, with the difference of
temperature between 49°7 and 63°5, from 1691 to 1973 grs, or from
100 to 116-68. This is an increase of 1209 per cent, for one degree of
temperature.
The diffusion of the different proportions of sulphuric acid is a
follows:–
Diffusion of Sulphate of Water in ten days at 49°7; two cells.
6. Grs. Ratio.
From 1 per cent. Solution, . e 8-69 1*03
From 2 per cent. solution, . . 16.91 2
From 4 per cent. Solution, . . 33.89 4'01
From 8 per cent. Solution, . . 68°96 8-16
The diffusibility of different strengths of this acid appears to be
pretty uniform, but with a slight tendency to increase in the higher
proportions, like hydrochloric acid.
Sulphuric acid is greatly inferior in velocity of diffusion to hydro-
chloric acid, but still appears to possess considerably more than half
the diffusibility of the latter.
6. Chromic Acid.
Time of diffusion ten days. The diffusates from four cells of the
2 per cent. Solution were mixed together, and the quantity of chromic
504 ON THE DIFFUSION OF LIQUIDS.
acid diffused for two cells reduced by means of hydrochloric acid and
alcohol, and weighed as oxide of chromium.
1762 per cent. of anhydrous chromic acid, density 1-01404, diffused
at 67°3, gave 1978 grs, of chromic acid in two cells. Calculated for
2 per cent, 22:43 grs. of chromic acid, in two cells, at 67°3. The diffu-
sion of sulphuric acid at 63°5, was 1973 grs, which would give about
21 grs. of that acid at 67°3.
7. Acetic Acid.
Time of diffusion ten days. This acid cannot be determined accu-
rately by the acidimetrical method, owing to the acetates of potash and
Soda being essentially alkaline to test-paper, like the carbonates of the
Same bases, although neutral in composition. The weight of carbonate
of baryta dissolved by the acid was had recourse to.
1. Acetate of water (HO.C, H2O3), 2 per cent. ; density 10030.
Diffused at 48°8, in eight cells, 12.62, 10.94, 11:10, 11:39 grs. of acetate
of water; mean 11:51 grs. for two cells.
2. Acetate of water, 4 per cent. ; density 1-0060. Diffused at 48°8,
in eight cells, 22:12, 21.71, 21:59, 22.67; mean 22:02 grs. for two cells.
3. Acetate of water, 8 per cent, ; density 1.0117. Diffused at 48°8,
in four cells, 21:19, 2013, 21.84, 20:44; mean 20.90 grs. for one cell.
The diffusion of the different proportions of acetic acid is as follows:—
Diffusion of Acetate of Water in ten days at 48°8; two cells.
GrS. Ratio,
Erom 2 per cent. Solution, . o 11' 31 2
From 4 per cent. Solution, . e 22:02 3-83
From 8 per cent. Solution, . . & 4 1-80 7.26
The diffusibility diminishes with the larger proportions of acid. This
acid appears to be considerably less diffusive than sulphuric acid. I
was led to over-estimate the diffusion of acetic acid in a preliminary
observation of my former paper, by trusting to the acidimetrical method
of determination. Hydrochloric acid appears to diffuse about two
and a half times more rapidly than acetate of water, at the same
temperature.
8. Sulphurous Acid.
The time of diffusion chosen for this acid was ten days, for com-
parison with sulphuric acid. The usual number of eight cells of the
1 and 2 per cent. solutions were diffused, and four cells of the 4 and 8
per cent, solutions. The whole diffusates of each proportion were then
mixed together, and the proportional quantity of liquid representing two
ON THE DIFFUSION OF LIQUIDS. 505
cells in the 1 and 2 per cent. solutions, and one cell in the 4 and 8, was
converted into sulphuric acid by a slight excess of bromine, and deter-
mined from the sulphate of baryta.
1. 0.982 per cent. of sulphurous acid, density 1.0056, diffused at
68°1, gave 7.94 grs. in two cells. Calculated for 1 per cent, 8-09 grs.
of sulphurous acid in two cells at 68°1.
2. 1965 per cent of sulphurous acid, density 1:01055, diffused at
68°1, gave 16-66 grs. for two cells. Calculated for two 2 per cent,
1696 grs. of sulphurous acid in two cells at 68°1.
3. 393 per cent. of sulphurous acid, density 1-01991, diffused at
68°1, gave 1621 grs. for one cell. Calculated for 4 per cent, 16:50
grs. of sulphurous acid in one cell at 68°1.
4. 7-86 per cent. of sulphurous acid, density 1-0384, diffused at 68°1,
gave 32°60 grs. for one cell. Calculated for 8 per cent, 33-19 grs. of
sulphurous acid in one cell at 68°1.
Diffusion of Sulphurous Acid in ten days at 68°1; two cells.
Grs. Ratio.
From 1 per cent. Solution, sº 8-09 0°954
From 2 per cent. Solution, † 16.96 2
From 4 per cent. Solution, * > 33-00 3-891
From 8 per cent. Solution, . 66°38 7.827
This substance appears to be less diffusive than sulphuric acid at the
same temperature; the diffusion of sulphurous acid at 68°1 considerably
resembles that of sulphuric acid at 49°7 (p. 503).
9. Ammonia.
The time of diffusion chosen was 4,041 days, or that of hydrate of
potash with chloride of sodium at seven days. The usual number of
eight cells of the 1 and 2 per cent. Solutions were diffused, and four
cells of the 4 and 8 per cent. solutions. The whole diffusates of each
proportion were then mixed together, and the quantity of ammonia dif-
fused for two cells determined by an alkalimetrical experiment, which
was always repeated twice. It was necessary for diffusion to have the
ammoniacal solution made denser than water, which was effected by the
addition of common salt.
1. 1:005 per cent. of ammonia, density made up to 1:00352 with
chloride of sodium, diffused at 63°4, gave 4.96 grs. for two cells; calcu-
lated for 1 per cent, 4.93 grs. of ammonia in two cells at 63°4.
2. 2:01 per cent. of ammonia, density made up to 1-00617 with
chloride of sodium, diffused at 63°4, gave 9:64 grs. for two cells; calcu-
lated for 2 per cent, 9:59 grs, of ammonia in two cells at 63°4.
506 º ON THE DIFFUSION OF LIQUIDS.
3. 402 per cent. of ammonia, density made up to 1.01141 with
chloride of sodium, diffused at 63°4, gave 9-91 grs, for one cell; calcu-
lated for 4 per cent, 9.86 grs, of ammonia, in one cell, at 68°4.
4, 8:04 per cent. of ammonia, density made up to 1:0215 with
chloride of sodium, diffused at 63°4, gave 20-71 grs. for one cell; calcu-
lated for 8 per cent, 20-61 grs. of ammonia in one cell at 63°4.
Diffusion of Ammonia in 404 days at 63°4; two cells.
Grs. Ratio.
Erom 1 per cent. solution, e 4-93 1-029
From 2 per cent. Solution, . 9°59 2
From 4 per cent. solution, e 1972 4-117
From 8 per cent. solution, º 41-22 8-605
Ammonia appears to have a diffusibility approaching to that of
hydrate of potash. It appears somewhat less diffusive than hydrocyanic
acid at the same temperature, in the proportion of 12 to 13 nearly; or
to possess about three-fourths of the diffusibility of hydrochloric acid.
10. Alcohol.
Time of diffusion ten days. The quantity of alcohol diffused was
determined by careful distillation.
1. Alcohol, 2 per cent.; density made up to 1-0237 with chloride of
sodium. Diffused at 40°7, in eight cells, 1780, 16.70; mean 1725 grs.
for four cells, or 8-62 grs, for two cells.
2. Alcohol, 4 per cent. ; density made up to 1:0203 with chloride of
sodium. Diffused at 48°7, in eight cells, 34:30, 30-20; mean 3225 grs.
for four cells, or 16-12 grs. for two cells.
3. Alcohol, 8 per cent. ; density made up to 1-0154 with chloride of
sodium. Diffused at 48°7, in four cells, 30-80, 402; mean 35-50 grs.
for two cells, or 17.75 grs. for one cell.
The results accord less closely with each other than usual, owing, I
believe, chiefly to the difficulties of manipulation when the density of
the liquid placed in the phials to be diffused approaches so nearly to
that of water. This is more particularly true of the 8 per cent, solution.
Diffusion of Alcohol in ten days at 48°7; two cells.
Erom 2 per cent. solution, © 8.62
From 4 per cent. Solution, tº 16:12
From 8 per cent, solution, e 35°50
It would be unsafe to draw any conclusion as to the proportionality
of the diffusion of alcohol to the strength of the solution from these
experiments.
ON THE DIFFUSION OF LIQUIDS. 507
Alcohol does not appear to belong to the same class of diffusive sub-
stances as acetic acid, which might be expected from their similarity
of composition, but possesses a considerably lower diffusibility.
Diffusion from 2 per cent. Solutions in ten days.
Acetate of water at 48°8, º 11:51 100
Alcohol at 48°7, . © sº 8-62 74°9
The diffusion of alcohol approaches to one-half of that of sulphate
of water at nearly the same temperature, p. 503.
Alcohol may be substituted for water to dissolve certain salts, and
also as an atmosphere into which these salts may diffuse. From experi-
ments which have been commenced on this subject, it appears that the
diffusion of hydrate of potash, iodide of potassium, chloride of calcium,
and others is about four times slower into alcohol of density 0-840 than
into water. The salts likewise often exhibit the same relations in their
diffusibility in alcohol, as in water, with some singular exceptions, such
as chloride of mercury.
11. Nitrate of Baryta.
Time of diffusion 11:43 days.” The salt diffused was precipitated
by sulphuric acid, and calculated from the weight of the sulphate of
baryta formed. -
1. Nitrate of baryta, 1 per cent. ; density 1:0083. Diffused at 51°5,
in eight cells, 6.71, 671, 6'84, 6-68; mean 673 grs. for two cells.
2. Nitrate of baryta, 0.993 per cent. ; density 1-00886. Diffused at
64°1, in eight cells, 7-64, 7-70, 774, 7-61; mean 7-67 grs. for two cells.
Calculated for 1 per cent, 7.72 grs. for two cells.
3. Nitrate of baryta, 2 per cent.; density 1.01686. Diffused at
64°1, in eight cells, 15-63, 14.81, 14:41, 15:32; mean 15:04 grs. for
two cells. -
4. Nitrate of baryta, 4 per cent.; density 1-03319. Diffused at
64°1, in four cells, 15:36, 1478, 1479, 14:30; mean 1480 grs. for
one cell.
5. Nitrate of baryta, 8 per cent. ; density 1.06556. Diffused at
64°1, in four cells, 26:46, 26-77, 28.63, 27-13; mean 27:25 grs. for
one cell. .
The diffusion from the 1 per cent. solution increases by a rise of
temperature from 51°5 to 64°1, from 6-73 grs. to 772, or from 100 to
1147, which is an increase of 1:17 per cent, for 1°.
* This time is to that of sulphate of magnesia (16-166 days) as the square root of 8
is to the square of 16; but does not appear to express the true relation between these
salts.
508 ON THE DIFFUSION OF LIQUIDS,
Diffusion of Nitrate of Baryta in 1143 days at 64°1; two cells.
Grs. Ratio.
From 1 per cent. solution, e 7.72 1-026
From 2 per cent. solution, e 15'04 2
From 4 per cent. Solution, tº 29'60 3'936
From 8 per cent. Solution, º 54'50 7.247
12. Nitrate of Strontia.
Time of diffusion 11-43 days. Of anhydrous nitrate of strontia 0.82
per cent. ; density 1-0063. Diffused at 51°5, in 8 cells, 5'59, 5-62, 5:44,
5'69; mean 5-59 grs. for two cells; calculated for 1 per cent, 6.79 grs.
at 51°5 for two cells.
The diffusion of nitrate of strontia almost coincides with that of the
isomorphous nitrate of baryta at the same temperature.
Diffusion from 1 per cent solutions at 51°5 in 11-43 days.
Nitrate of baryta, . e º 6-73 100
Nitrate of strontia, . º º 6.79 100-89
13. Nitrate of Lime.
Time of diffusion 11-43 days. The diffusate was evaporated to dry-
ness with an excess of sulphuric acid, and the nitrate of lime, which is
always supposed anhydrous, was estimated from the sulphate of lime
produced. *
1. Nitrate of lime, 1:17 per cent. ; density 1-0088. Diffused at 51°5,
in eight cells, 7:39, 7'76, 7-69, 7-80; mean 7.66 grs, for two cells; calcu-
lated for 1 per cent, 6.54 grs. at 51°5 for two cells.
2. Nitrate of lime, 0.985 per cent. ; density 100802. Diffused at
64°1, in eight cells, 7:47, 7:38, 7.63, 772; mean 7:55 grs, for two cells;
calculated for 1 per cent, 7-66 grs. at 64°1 for two cells.
3. Nitrate of lime, 1.97 per cent. ; density 1-01508. Diffused at
64°1, in eight cells, 15:04, 1474, 14:55, 1483; mean 1479 grs, for two
cells; calculated for 2 per cent, 1501 grs. at 64°1 for 2 cells.
4. Nitrate of lime, 3.94 per cent. ; density 1-0296. Diffused at 64°1,
in four cells, 14:30, 15:29, 13-79, 1393; mean 14:33 grs. for one cell;
calculated for 4 per cent, 14.52 grs, at 64°l for one cell.
5. Nitrate of lime, 7-88 per cent. ; density 1-0582. Diffused at 64°1,
in four cells, 27-95, 27'10, 26-80, 26-73; mean 27-14 grs. for one cell;
calculated for 8 per cent, 27°55 grs, at 64°1 for one cell.
By a rise of temperature from 51°5 to 64°1, the diffusion of the 1
ON THE DIFFUSION OF LIQUIDS. 509
per cent. solution increases from 6-54 to 7-66 grs, or from 100 to 117:1;
which is an increase of 1.357 per cent, for 1".
Diffusion of Nitrate of Lime in 11:43 days at 64°1; two cells.
Grs. Ratio.
From 1 per cent. Solution, © 7-66 1-021
Prom 2 per cent. Solution, 2 15:01 2
Erom 4 per cent. Solution, . 29'04 3'872
From 8 per cent solution, º 55:10 7'334
The results throughout for this salt are almost identical with those of
nitrate of baryta (p. 508), although these two salts differ greatly in solu-
bility, and in one being a hydrated, and the other an anhydrous salt.
14. Acetate of Lead.
Diffused for 16-166 days; the time chosen before for sulphate of
magnesia, with seven days for chloride of sodium. The solution con-
tained 0-965 per cent of anhydrous salt, with the density 10080. As
this solution of acetate of lead was found to be precipitated by pure
water, about 2 per cent. of strong acetic acid was introduced into the
solution, and the same acid was added in a less proportion to the water
jars. The salt of lead diffused was afterwards determined by means of
sulphuric acid. Diffused in eight cells, at 53°1, 7:45, 7:29, 7.46 and
8:07 grs. ; mean 7:56; or 7:84 for 1 per cent. in two cells.
15. Acetate of Baryta.
Diffused for 16-166 days. The solution contained 0-977 per cent of
anhydrous salt, with the density 1:0073. The same addition of acetic
acid was made to it as to the preceding acetate of lead, in order that
the circumstances of diffusion might be similar for both salts. The salt
diffused was estimated also in the form of sulphate.
Diffused at 53°5, in eight cells, 7:30, 7:38, 7.40, and 7.21 grs. in two
cells; mean 733; or 7:50 for 1 per cent. in two cells.
Diffusion of 1 per cent solutions in 16-166 days; two cells.
Acetate of baryta at 53°5, o 7:50 100
Acetate of lead at 53°1, . º 7.84 104°53
Pſere, of two isomorphous salts, that of greatest atomic weight sen-
sibly exceeds the other in diffusibility.
510 ON THE DIFFUSION OF LIQUIDS.
16. Chloride of Barium.
Time of diffusion 11:43 days. The diffused salt was weighed as
sulphate of baryta.
1. Chloride of barium, 0.99 per cent. Diffused at 50°9, in eight
cells, 791, 7:27, 7-42, 7-12; mean 7:43 grs. of chloride of barium for two
cells; calculated for 1 per cent, 7-50 grs. at 50°-9 for two cells.
The diffusion of this salt being manifestly more rapid than that of
the chloride of calcium, a shorter time was tried, which is to seven days,
the time of chloride of Sodium, as the square root of 3 to the square root
of 4-5. Time of diffusion 8:57 days.
2. Chloride of barium, 1.01 per cent. ; density 1-0095. Diffused at
63”, in eight cells, 6:46, 6:44, 6:41, 627; mean 639 grs. for two cells;
calculated for 1 per cent, 6-32 grs. at 63 for two cells,
3. Chloride of barium, 2:02 per cent. ; density 1-0183. Diffused at
63”, in eight cells, 1198, 12:03, 1275, 12:03; mean 12:20 grs, for two
cells; calculated for 2 per cent, 12:07 grs. at 63 for two cells.
4. Chloride of barium, 4:04 per cent. ; density 1-0359. Diffused at
63”, in four cells, 12:43, 12:30, 11-87, 11.86; mean 12:10 grs, for one
cell; calculated for 4 per cent, 11.98 grs, at 63 for one cell.
5. Chloride of barium, 8:08 per cent. ; density 1-0712. Diffused at
63”, in four cells, 23:17, 23:05, 22.98, 23.62; mean 23'20 grs, for one cell;
calculated for 8 per cent, 22.96 grs. at 63 for one cell.
Diffusion of Chloride of Barium in 8:57 days at 63°; two cells.
GrS. Ratio.
Erom 1 per cent. Solution, º 6:32 1-047
From 2 per cent. Solution, * 12-07 2
From 4 per cent. Solution, º 23-96 3-970
From 8 per cent. Solution, º 45°92 7-608
17. Chloride of Strontium.
Eirst time of diffusion 11-43 days. The diffused salt was weighed
as sulphate of strontia.
1. Chloride of strontium, 0.803 per cent. ; density 1.0076. Diffused
at 51°, in eight cells, 6:36, 6:06, 5.93, 5-73; mean 6:02 grs. of chloride of
strontium for two cells; calculated for 1 per cent, 7.52 grs, at 51° for
two cells. - -
Second time of diffusion 8:57 days.
2. Chloride of strontium, 1 per cent. ; density 1-00936. Diffused at
63”, in eight cells, 6-10, 6:17, 6:02, 6-09; mean 6:09 grs, for two cells.
3. Chloride of strontium, 2 per cent. ; density 1-01806. Diffused at
ON THE DIFFUSION OF LIQUIDS. 511
63”, in eight cells, 11-62, 11.71, 11:53, 11.79; mean 11-66 grs. for two
cells. -
4. Chloride of strontium, 4:01.4 per cent.; density 1.03537. Diffused
at 63, in four cells, 12:09, 11.75, 11:64, 1179; mean 1182 grs, for one
cell; calculated for 4 per cent, 1178 grs. at 63 for one cell.
5. Chloride of strontium, 8:02.8 per cent.; density 1-06959. Diffused
at 63, in four cells, 22:29, 22:34, 22:03, 22:57; mean 22:31 grs. for one
cell; calculated for 8 per cent, 22:23 grs. at 63 for two cells.
Diffusion of Chloride of Strontium in 8:57 days at 63”; two cells.
- Grs. Ratio.
from 1 per cent. Solution, e 6'09 1-045
From 2 per cent. Solution, º 11'66 2
Erom 4 per cent. Solution, º 23:56 4:041
From 8 per cent. solution, e 44'46 7.626
The series of ratios in the preceding table will be found on compari-
son to correspond closely with the ratios of chloride of barium. It may
be useful to compare further the amounts diffused from similar solutions
of these two isomorphous compounds.
Diffusion in 8:57 days at 63°; two cells.
Chloride of barium, 1 per cent., 6:32 100
Chloride of strontium, 1 per cent, 6-09 96.36
Chloride of barium, 2 per cent., 12-07 100
Chloride of strontium, 2 per cent, 11-66 96-90
Chloride of barium, 4 per cent, 23.96 100
Chloride of strontium, 4 per cent., 23:56 99-16
Chloride of barium, 8 per cent, 45°92 100
Chloride of strontium, 8 per cent, 44.46 96.83
The near coincidence of the 4 per cent. Solutions probably arises
from an accidental error of observation in the chloride of barium, for the
latter departs here from the progression of its ratios. We appear then
to have a small but constant difference of about 3% per cent, in the dif-
fusion of these two isomorphous salts, the chloride of barium, which
possesses the highest atomic weight, having the advantage.
The diffusion of the 1 per cent, solution of the same salts for the
longer period of 11:43 days, gives 7:50 for chloride of barium at 50°9,
and 7°52 for chloride of strontium at 51°, or nearly the same tempe-
rature. For the first time we have in the barytic salts a divergence
between chlorides and nitrates, for the nitrates of the same bases have a
number about 68 only at the same temperature. I am led however to
512 ON THE DIFFUSION OF LIQUIDS.
believe that this discrepancy becomes much less at low temperatures by
experiments which are at present in progress.
18. Chloride of Calcium.
Time of diffusion 11:43 days. The salt diffused was weighed as
sulphate of lime.
1. Chloride of calcium, 1.065 per cent. ; density 1:0091. Diffused
at 50°9, in eight cells, 6.95, 7:09, 6-78, 6.94; mean 6'94 grs. of chloride
of calcium for two cells; calculated for 1 per cent, 6.51 grs. at 50°9 for
two cells. -
2. Chloride of calcium, 1.03 per cent. ; density 1-0089. Diffused at
63°8, in 8 cells, 8:08, 8:13, 8:28, 8.19; mean 8'17 grs, for two cells;
calculated for 1 per cent, 7.92 grs. at 63°8 for two cells.
3. Chloride of calcium, 2:06 per cent. ; density 1-0171. Diffused at
63°8, in eight cells, 1570, 15:33, 16:48, 15:82; mean 1583 grs. for two
cells; calculated for 2 per cent, 15:35 grs. at 63°8 for two cells.
4. Chloride of calcium, 412 per cent. ; density 1-0334. Diffused at
63°8, in four cells, 15:24, 16:20, 1589, 16:20; mean 1588 grs, for one
cell; calculated for four per cent, 15:39 grs, at 63°8 for one cell.
5. Chloride of calcium, 8.23 per cent. ; density 1-0652. Diffused at
63°8, in four cells, 32.97, 31-17, 30-64, 31.90; mean 31.67 grs. for one
cell; calculated for 8 per cent, 30.78 grs. at 62°8 for one cell.
The diffusion of the 1 per cent. solution of chloride of calcium is
increased by a rise of temperature from 50°-9 to 63°8, from 6:51 to 7.92,
or from 100 to 121-6, which is an increase of 1674 per cent for 1".
Diffusion of Chloride of Calcium in 11:43 days at 63°8; two cells.
Grs. Ratio.
From 1 per cent. Solution, * 7-92 1:03.2
Brom 2 per cent. Solution, * 15-35 2
Erom 4 per cent. Solution, e 30-78 4'010
IFrom 8 per cent. Solution, e 61°56 8-021
We may now observe how far the diffusion of the chloride of calcium
is analogous to that of nitrate of lime. At the inferior temperatures,
the results for the 1 per cent. Solution of these two salts were as
follows:—
Chloride of calcium at 50°9, . 6'51 100
Nitrate of lime at 51°5, . e 6'54 100'46
While at the higher temperatures, namely, 63°8 for the chloride of
calcium, and 64°1 for the nitrate of lime, the results for the different
proportions of Salt are—
ON THE DIFFUSION OF LIQUIDS. 513
Chloride of calcium, 1 per cent, . 7.92 100
Nitrate of lime, 1 per cent., * 7-66 96.72
Chloride of calcium, 2 per cent., 15-35 100
Nitrate of lime, 2 per cent, . 15:01 97.79
Chloride of calcium, 4 per cent., 30-78 100
Nitrate of lime, 4 per cent, 29'04 94'35
Chloride of calcium, 8 per cent., 61'56 100
Nitrate of lime, 8 per cent., e 55:10 89°51
The correspondence between the 1 and 2 per cent. Solutions of chlo-
ride and nitrate is sufficiently close, but in the 4 and 8 per cent, the
salts diverge, as happens also with hydrochloric and nitric acids them-
selves. The mitrate in both cases falls off, while the chloride sustains
throughout the high diffusibility of the lower proportions.
19. Chloride of Manganese.
Time of diffusion 11-43 days. The salt diffused was estimated by
means of nitrate of silver.
The 1 per cent. solution, of density 1:0085, gave at 50°8, in eight
cells, 6-67, 6-26, 6-79, and 6-81 grs. ; mean 6-63 for two cells.
20. Nitrate of Magnesia.
Time of diffusion 11-43 days. The salt diffused was estimated as
sulphate.
The 1 per cent, solution, of density 1:0073, gave at 50°8, in eight
cells, 6'29, 6:39, 6:52, and 6-76 grs. ; mean 6:49 for two cells.
21. Nitrate of Copper.
Time of diffusion 11-43 days. The salt diffused was estimated from
the oxide of copper obtained by ignition.
The 1 per cent, solution, of density 1.0075, in eight cells, at 50°8,
gave 6:52, 6:36, 6:18, and 6.70 grs. ; mean 6’44 for two cells.
Comparing the preceding salts with chloride of calcium diffused at
the same temperature, 50°8, we have the following results:—
Chloride of calcium, tº & 6'51 100
Chloride of manganese, . * 6'63 10I '85
Nitrate of magnesia, * º 6°49 99.69
Nitrate of copper, . * g 6'44 98-92
This group of salts, belonging to the same isomorphous family of
bases, the magnesian, again correspond closely in diffusibility.
* 2 K
514 ON THE DIFFUSION OF LIQUIDS.
The following additional magnesian chlorides were diffused, all 1 per
cent. Solutions, either in six or in eight cells. The salt diffused was
estimated by means of nitrate of silver.
22. Chloride of Zinc at 51°, solution of density 1:0091, gave 6:55,
6:20, 6:21, and 6:28 grs. ; mean 629 for two cells.
23. Chloride of Magnesium at 50°6, density 10077, gave 6:40, 5'84,
and 6:29; mean 6:17 for two cells.
24, Chloride of Copper at 50°6, solution of density 1-0093, gave 6:08,
6:08, and 6.02 grs. ; mean 6:06 for two cells.
The results referred to chloride of calcium, at nearly the same tem-
perature, 50°8, are as follows:—
Chloride of calcium, º e 6'51 100
Chloride of zinc, te tº º 6'29 96'61
Chloride of magnesium, . e 6-17 94.77
Chloride of copper, . -> º 6'06 93-08
These salts present a greater latitude in their diffusibility, if belong-
ing to the same class, than is usual.
25. Protochloride of Iron.
A solution of this salt of 1023 per cent. was diffused at 53°5, a
somewhat higher temperature than the corresponding chlorides. It
gave 6:45, 6:48, 6:48, and 6:28 grs. in two cells; mean 6'44 or 6:30 for
1 per cent. in two cells. This salt appears therefore to belong to the
last group.
26. Sesquichloride of Iron.
A full series of observations was made upon the diffusion of the
different proportions of this salt from 1 to 8 per cent, but in all of them
decomposition was determined by the diffusion, with turbidity also in
the solution phial except in the 8 per cent. Solution.
The mean diffusion from the 1 per cent. Solution in 11-43 days, at
63°3, was 4:13 grs. of sesquichloride of iron with 1:28 gr. of free hydro-
chloric acid, in two cells. This result indicates that one-half nearly of
the sesquichloride of iron is decomposed in the diffusion.
The mean diffusion from the 8 per cent. solution, at 63°3, was 55-88
grs. of sesquichloride of iron, with 6'66 grs. of free hydrochloric acid, in
two cells. It appears from this experiment that perchloride of iron
approaches the chloride of calcium in diffusibility. That the proto- and
persalts of the magnesian metals should have a similar rate of diffusion
is not unlikely from other analogies which they exhibit.
ON THE DIFFUSION OF LIQUIDS. 515
27. Sulphate of Magnesia.
The time chosen for the diffusion of this salt, namely 16-166 days,
is a multiple by 2 of the time of sulphate of potash, and by 4 of the
time of hydrate of potash. The diffusate was evaporated to dryness
and weighed. -
1. 1:012 per cent. of anhydrous sulphate of magnesia, density 1-0108,
diffused at 65°4, in eight cells, 7:34, 7-66, 7:43, 7-18; mean 7:40 grs.
for two cells; calculated for 1 per cent, 7.31 grs. of Sulphate of magnesia
in two cells at 65°4.
2. 2.024 per cent of sulphate of magnesia, density 1-02089, diffused
at 65°4, in eight cells, 1291, 13:13, 12.83, 12-93; mean 1295 grs. for
two cells; calculated for 2 per cent., 1279 grs. of sulphate of magnesia
in two cells at 65°4.
3. 4-048 per cent. of sulphate of magnesia, density 1-04033, diffused
at 65°4, in four cells, 12:06, 12:56, 10-63, 12:24; mean 11-87 grs, for one
cell; calculated for 4 per cent. 1173 grs. of Sulphate of magnesia in one
cell at 65°4.
4. 8096 per cent. of sulphate of magnesia, density 1-07830, diffused
at 65°4, in four cells, 22:25, 20:56, 21-80, 22:06; mean 21-67 grs, for
one cell; calculated for 8 per cent., 21:41 grs. of Sulphate of magnesia
in one cell at 65°4. -
5. 8:07 per cent. of sulphate of magnesia, density 1-07830, diffused
at 62°8, in four cells, 21:12, 21-20, 22:13, 21.77; mean 21:55 grs. for one
cell; calculated for 8 per cent., 21:33 grs. of sulphate of magnesia in one
cell at 62°8.
6. 16:14 per cent. of sulphate of magnesia, density 1-15054, diffused
at 62°8, in four cells, 37-08, 38-39, 38:65, 37.50; mean 37.90 grs. for
one cell; calculated for 16 per cent, 37-53 grs. of sulphate of magnesia
in one cell at 62°8.
7. 24:22 per cent. of sulphate of magnesia, density 1-21882, diffused
at 62°8, in four cells, 49.38, 50:40, 53:36, 53.00; mean 51.53 grs, for
one cell; calculated for 24 per cent., 51-02 grs. of sulphate of magnesia
in one cell at 62°8.
Diffusion of Sulphate of Magnesia in 16:16 days at 65°4; two cells,
Grs. Ratio.
From 1 per cent. Solution, . § ſº 7-31 1°144
From 2 per cent. Solution, . ū. . 12-79 2
Erom 4 per cent. Solution, . te . 23°46 3:671
From 8 per cent. Solution, . tº . 42'82 6-701
From 8 per cent. solution at 62°8, . 42'66 |
From 16 per cent, solution at 62°8, 75-06 1759
From 24 per cent. solution at 62°8, . 102.04 2:340
516 ON THE DIFFUSION OF LIQUIDS.
28. Sulphate of Zinc.
Time of diffusion 16-166 days. The diffused salt was evaporated to
dryness and weighed. - - *
1. 1001 per cent of anhydrous sulphate of zinc, density 1.01093,
diffused at 65°4, in eight cells, 6.66, 6-76, 6:51, 6'80; mean 668 grs.
for two cells; calculated for 1 per cent, 6-67 grs, of sulphate of zinc in
two cells at 65°4.
2. 2002 per cent. Sulphate of zinc, density 1-02120, diffused at
65°4, in eight cells, 12:16, 12:19, 12:52, 12:05; mean 1223 grs, for two
cells; calculated for 2 per cent, 12'22 grs. Of Sulphate of zinc in two
cells at 65°4. - -
3. 4:005 per cent. of Sulphate of zinc, density 1.041.46, diffused at
65°4, in four cells, 11-63, 1170, 11:00, 11-95; mean 11:57 grs, for one
cell ; calculated for 4 per cent., 11:56 grs. of sulphate of zinc in one cell
at 65°4. -
4, 8:01 per cent of sulphate of zinc, density 1-08063, diffused at
65°4, in four cells, 21-22, 20:52, 21:06, 21.84; mean 21:16 grs. for one
cell; calculated for 8 per cent, 21-13 grs. Of Sulphate of zinc in one cell
at 65°4. ‘. * .
5. 8:04 per cent of sulphate of zinc, density 1-08084, diffused a
62°8, in four cells, 20.70, 18:57, 20:32, 20:36 ; mean 1999 grs, for one
cell; calculated for 8 per cent., 1981 grs. of Sulphate of zinc in one cell
at 62°·8. - . , -
6. 16:08 per cent of sulphate of zinc, density 1-15734, diffused at
62°8, in four cells, 3670, 37:15, 37-51, 38'21; mean 37.39 grs. for one
cell; calculated for 16 per cent., 37°20 grs. of Sulphate of zinc in one
cell at 62°8. - - - .
7. 24.11 per cent, of sulphate of zinc, density 123156, diffused at
62°·8, in three cells, 51-12, 50:14, 51-66; mean 50.97 grs, for one cell;
calculated for 24 per cent., 50.71 grs. of Sulphate of zinc in one cell at
62°8. - -
Diffusion of Sulphate of Zinc in 16:16 days at 65°4; two cells.
Grs. Ratio.
Erom 1 per cent. Solution, . © ę 6-67 1.091
From 2 per cent. Solution, . * . 1222 2.
From 4 per cent. Solution, . wº . 23-12 3.784
From 8 per cent. Solution, . * . 42'26 6'916
From 8 per cent solution at 62°8, . 39.62 I
From 16 per cent. Solution at 62°8, 74.40 1878
From 24 per cent. Solution at 62°8, . 101°42 2'560
It will be remarked that the diffusion of these two isomorphous
ON THE DIFFUSION OF LIQUIDS. 517
salts, sulphate of magnesia and Sulphate of zinc, differs so much, in the
1 per cent, solution, as 731 to 6-67, that is, as 100 to 91.25; or 8.75
per cent. This, I have no doubt, however, is an accidental error, the
disturbances from changes of temperature and other causes of dispersion
being in direct proportion to the duration of the experiment, and there-
fore much increased with these long times; while the 1 per cent, solu-
tion also appears to be generally the proportion most exposed to such
errors. The sulphate of zinc appears to be the truest throughout, in its
diffusion, of these two salts. The approach to equality becomes close
in the 4 per cent, and larger proportions of salt, particularly with the
unusually high proportions of 16 and 24 per cent, which were observed
in these salts. The diffusion of both salts falls off remarkably in the
higher proportions. The result of the comparison of these two mag-
nesian sulphates is no doubt favourable to the similarity of diffusion of
isomorphous salts.
29. Sulphate of Alumina.
The time of diffusion chosen was 16-166 days, or the same as that
for sulphate of magnesia. The usual number of eight cells of the 1 and
2 per cent. solutions were diffused, and four cells of the 4 and 8 per cent.
solutions. The whole diffusates of each proportion were then mixed
together and the quantities of alumina and sulphuric acid, diffused for
two cells, determined separately.
1. 1045 per cent. of sulphate of alumina, density 101160, diffused
at 65°4, gave 180 gr. of alumina and 393 grs. of sulphuric acid, in all
5-73 grs. for two cells. Calculated for 1 per cent., 1:72 gr. alumina and
3-76 grs. Sulphuric acid, in all 5:48 grs, of sulphate of alumina in two
cells at 65°4.
2. 2.091 per cent. of sulphate of alumina, density 1-02251, diffused
at 65°4, gave 332 grs, of alumina and 7:35 grs, of sulphuric acid, in all
10.67 grs. for two cells. Calculated for 2 per cent, 3.18 grs. of alumina
and 7:03 grs, of sulphuric acid, in all 10:21 grs. of sulphate of alumina
for two cells at 65°4.
3. 4-182 per cent of sulphate of alumina, density 10438, diffused at
65°4, gave 3.17 grs. of alumina and 6.91 grs, of sulphuric acid, in all
10:08 grs, for one cell. Calculated for 4 per cent, 3.03 grs. of alumina
and 6-61 grs. of Sulphuric acid, in all 9'64 grs, of sulphate of alumina for
one cell at 65°4. *
4, 8.364 per cent. of Sulphate of alumina, density 1-08518, diffused
at 65°4, gave 537 grs. of alumina and 12:15 grs, of sulphuric acid, in all
17:52 grs, for one cell. Calculated for 8 per cent., 5.14 grs. of alumina
and 11-62 grs, of Sulphuric acid, in all 16-76 grs, of sulphate of alumina
for one cell at 65°4.
518 ON THE DIFFUSION OF LIQUIDS.
Diffusion of Sulphate of Alumina in 16-166 days at 65°4; two cells.
Grs. Ratio.
From 1 per cent. solution, . º 5°48 1.074
From 2 per cent. solution, . © 1021 2
From 4 per cent. solution, . º 19°28 3.780
From 8 per cent. solution, . © 33-52 6'572
The diffusion of sulphate of alumina, it will be observed, is very
sensibly less than that of sulphate of zinc at the same temperature.
30. Nitrate of Silver.
Time of diffusion seven days. The quantity of salt diffused was
ascertained by precipitation with hydrochloric acid, and weighing the
chloride of silver formed.
1. Nitrate of silver, 0.996 per cent. ; density 1-0089. Diffusion at
51°4, in eight cells, 5:39, 5:39, 574, 5.50; mean 5:50 grs. for two cells;
calculated for 1 per cent, 5.52 grs. at 51°4 for two cells.
2. Nitrate of silver, 1.98 per cent. ; density 1.0161. Diffusion at
53”, in eight cells, 11:27, 11:16, 11:05, 11.06; mean 11-13 grs, for two
cells; calculated for 2 per cent, 11:24 grs. at 53° for two cells.
3. Nitrate of silver, 1967 per cent.; density 1-01696. Diffusion at
63°41, in eight cells, 13.85, 13:29, 13-70, 12.73; mean 13:39 grs. for two
cells; calculated for 2 per cent, 13.61 grs. at 63°4 for two cells.
4. Nitrate of silver, 3.93 per cent.; density 1-032. Diffusion at 63°4,
in four cells, 1327, 1270, 12.90, 12.90; mean 1294 grs. for one cell;
calculated for 4 per cent, 13:17 grs. at 63°4 for one cell. -
5. Nitrate of silver, 7.88 per cent.; density 1-066. Diffusion at 63°4,
in four cells, 26:45, 25-49, 24:57, 25.73; mean 25-56 grs, for one cell;
calculated for 8 per cent, 25.94 grs. at 63°4 for one cell.
A rise of 10°4 of temperature, or from 53° to 63°4, increases the
diffusibility of this salt from 11:24 to 13.61, or from 100 to 121-2; which
is an increase of 2:04 per cent for 1".
Diffusion of Nitrate of Silver for seven days at 63°4; two cells.
Grs. Ratio.
From 2 per cent. solution, . © 13-61 2
Prom 4 per cent. Solution, . Q 26°34 3-87
From 8 per cent. Solution, . º 51°88 7.62
31. Nitrate of Soda.
Time of diffusion seven days. The quantity of salt diffused was
ascertained by evaporation to dryness. -
# ON THE DIFFUSION OF LIQUIDS. 519
1. Nitrate of soda, 1987 per cent. ; density 1-0130. Diffusion at 53°.
in eight cells, 11:37, 10:44, 1076, 10:40; mean 1074 grs. for two cells;
calculated for 2 per cent, 10.81 grs. for two cells.
2. Nitrate of soda, 1998 per cent. Diffusion at 63°4, in eight cells,
12:53, 12:38, 12:39, 12:06; mean 12:34 grs, for two cells; calculated for
2 per cent, 12:35 grs. for two cells.
3. Nitrate of soda, 3.98 per cent. ; density 1-027. Diffusion at 63°4,
in four cells, 12:21, 11:32, 12:10, 11:31; mean 1173 grs. for one cell;
calculated for 4 per cent., 11.78 grs, for one cell.
4. Nitrate of soda, 7.96 per cent. ; density 1-053. Diffusion at 63°4,
in four cells, 24.96, 22:53, 23:16, 24.38; mean 23-76 grs. for one cell;
calculated for 8 per cent, 23.87 grs. for one cell.
A rise of temperature from 53° to 63°4 increases the diffusibility of
nitrate of soda from 10-81 to 12:35, or from 100 to 114.3, which is an
increase of 1:37 per cent for 1. The increase on the nitrate of silver
for the same rise of temperature appeared to be considerably greater,
namely, 2:04 per cent, for 1". -
Diffusion of Nitrate of Soda in seven days at 63°4; two cells.
Grs. Ratio.
From solution of 2 per cent, . 12'35 2
From solution of 4 per cent., . 23:56 3'82
From solution of 8 per cent., . 47 '74 7-73
The ratios of the last column of the preceding Table are sensibly the
same as those already obtained for nitrate of silver. But the diffusi-
bility of nitrate of soda appears to be increased less rapidly by tempera-
ture than nitrate of silver. Hence the diffusibility of these two salts
appears more similar at low than high temperatures.
Diffusion from 2 per cent. Solutions in seven days at 53°.
Nitrate of silver, . * 11:24 I00
Nitrate of soda, . ſº 10°81 96.17
Diffusion from 2 per cent, solutions in seven days at 63°4.
Nitrate of silver, . gº 13-61 100
Nitrate of soda, . & 12'35 90-74
32. Chloride of Sodium.
Time of diffusion seven days. The salt diffused was treated with
nitrate of silver, and the chloride of silver weighed.
1. Chloride of sodium, 1 per cent. Diffused at 50°5, in eight cells,
5-96, 5-69, 5:54, 5'50; mean 5’70 grs, of chloride of sodium for two cells.
520 ON THE DIFFUSION OF LIQUIDs,
2. Chloride of sodium, 0.985 per cent. Diffused at 53°4, in eight
cells, 5'86, 5'86, 5-77, 5-76; mean 5'81 grs, for two cells; calculated for
1 per cent., 5'89 grs. at 53°4 for two cells.
3. Chloride of sodium, 1 per cent. ; density 100776. Diffused at
63°4, in eight cells, 6:30, 6:18, 6:52, 6:30; mean 6-32 grs. for two cells.
4. Chloride of sodium, 2 per cent. ; density 101483. Diffused at
63°4, in eight cells, 12:37, 12:08, 12:45, 12:53; mean 12:37 grs. for two
cells. &
5. Chloride of sodium, 4 per cent. ; density 1-02879. Diffused at
63°4, in four cells, 12:56, 12-65, 12:55, 12:17; mean 12:48 grs. for one
cell.
6. Chloride of sodium, 8 per cent. ; density 1-0562. Diffused at
63°4, in four cells, 25.11, 25.36, 22.82, 23:59; mean 24:22 grs, for one cell.
The rise of temperature from 50°5 to 63°4 increases the diffusion of
the 1 per cent. solution of chloride of sodium from 5:70 to 6:32, or from
100 to 110.9, which is an increase of 0.843 per cent, for 1".
Diffusion of Chloride of Sodium in seven days at 63°4; two cells.
Grs, Ratio.
From 1 per cent. solution, ſº 6:32 1-023
From 2 per cent. Solution, . 12:37 2
From 4 per cent. Solution, wº 24-96 4'036
From 8 per cent. solution, te 48°44 7-832
These numbers resemble closely those obtained in the diffusion of
chloride of barium during the longer period of 8:57 days.
The chloride of sodium and nitrate of soda will be seen to exhibit the
usual approach to parallelism between the chloride and nitrate of the
same metal, by the following comparison —
I)iffusion of Chloride of Sodium and Nitrate of Soda, both at 63°4.
Chloride of sodium, 2 per cent., * * 12:37 100
Nitrate of soda, 2 per cent, . te I 2'35 99.83
Chloride of sodium, 4 per cent, te 24'96 100
Nitrate of soda, 4 per cent., . * 23'58 94'48
Chloride of sodium, 8 per cent, tº 48'44 100
Nitrate of soda, 8 per cent, . tº 47-74 98’55
As usual the chloride is slightly more rapid in its diffusion than the
nitrate. .
33. Chloride of Potassium.
Time of diffusion 571 days. The salt diffused was treated with
nitrate of silver, and the chloride of silver weighed.
ON THE DIFFUSION OF LIQUIDS. 521
1. Chloride of potassium, 1 per cent. ; density 1:00697. Diffused
at 62°, in eight cells, 670, 6-75, 6:53, 6-77; mean 669 grs. of chloride
of potassium for two cells.
2. Chloride of potassium, 2 per cent. ; density 1:01333. Diffused
at 62°, in 8 cells, 13:36, 13:35, 13.60, 12.96; mean 1332 grs. for two
cells. -
3. Chloride of potassium, 4 per cent, ; density 1-0258. Diffused
at 62°, in four cells, 12:51, 1321, 13:46, 1271; mean 1297 grs. for
One cell. -
4. Chloride of potassium, 8 per cent. ; density 1-0503. Diffused at
62", in four cells, 26.88, 26.64, 26.15, 27-63; mean 26'82 grs, for one cell.
Diffusion of Chloride of Potassium in 571 days at 62°; two cells.
GTS. Ratio.
From 1 per cent. solution, & & 6'69 1°005
From 2 per cent. Solution, e e 13:32 2
From 4 per cent, solution, * tº 25-94 3.895
From 8 per cent. solution, e e 53-64 8'054
The ratios are in remarkably close accordance with the proportions
of salt diffused. r
The times 5’71 and seven days chosen for the chloride of potassium
and sodium, it will be observed, are as the Square roots of 2 and 3. A
certain deviation from this ratio of the times of equal diffusion, appears
on comparing the experimental results obtained at present for these salts.
Diffusion of Chloride of Potassium in 571 days at 62°, and of Chloride
of Sodium in 7 days at 63°4.
Chloride of potassium, 1 per cent, . 6-69 100
Chloride of sodium, 1 per cent, º 6-32 94'47
Chloride of potassium, 2 per cent, . 13:32 I 00
Chloride of sodium, 2 per cent., * I2-37 92'86
Chloride of potassium, 4 per cent, . 25°94. 100
Chloride of sodium, 4 per cent, 4. 24-96 96.23
Chloride of potassium, 8 per cent, . 53-64 100
Chloride of sodium, 8 per cent, e 48°44 90'30
The difference would be about 1 per cent, greater if the diffusion of
both salts were reduced to the same temperature. The chloride of pot-
assium deviates of course from the nitrate of Soda in a similar manner.
But chloride of potassium corresponds more closely with nitrate of silver
than with chloride of sodium and nitrate of soda, at the temperature of
the experiments.
522 ON THE DIFFUSION OF LIQUIDS.
Diffusion of Chloride of Potassium for 571 days at 62°, and of Nitrate
of Silver for 7 days at 63°4.
Chloride of potassium, 2 per cent, . 13:32 100
Nitrate of silver, 2 per cent, . ſº 13-61 102.18
Chloride of potassium, 4 per cent., . 25'94 100
Nitrate of silver, 4 per cent, . tº 26'34 101'54
Chloride of potassium, 8 per cent., . 53-64 100
Nitrate of silver, 8 per cent., . tº 51.88 96.71
The coincidence in rate would appear even closer in the 2 and 4 per
cent, solutions, if the diffusion of the nitrate of silver was diminished
about 1 per cent., on account of its higher temperature. It might thus
be supposed that the nitrate of silver followed the sodium rate more
accurately than the nitrate of soda and chloride of sodium themselves do.
A series of observations were made upon the diffusion of the 1 per
cent. solution of chloride of potassium at a nearly constant temperature
of 56°, but for different times, varying from five days to eight days, and
eighteen hours, to discover the progression, which proved to be pretty
similar to that of the 2 per cent. Solution of hydrochloric acid. Six cells
were diffused for each period, of which the mean result is given: the
times advance by ten hours. -
Diffusion of Chloride of Potassium, 1 per cent. solution ; two cells.
Time. Temperature. Diffusion in two cells. Differences.
5 days. 55-71 5'89
5 days 10 hours. 55'90 6.25 0.36
5 days 20 hours. 55-79 6'55 0°30
6 days 6 hours. 55-79 6-71 O'16
6 days 16 hours. 55'90 6'95 0'24.
7 days 2 hours. 55-9 7'48 0.53
7 days 12 hours. 55'9 7.58 0° 10
7 days 22 hours. 56'03 8:08 0.50
8 days 8 hours. 56:28 8'34 0-26
8 days 18 hours. 56°15 8.60 0-26
When the quantities of chloride of potassium are placed beside the
same quantities of hydrochloric acid in the former Table, it is found
that the times of diffusion of the salt and acid exhibit an approximately
constant ratio. The squares of these times of equal diffusion are as 1 to
2.04 for the shortest period of the chloride of potassium, and as 1 to
2-10 for the longest period but one. The variation in the differences
towards the middle of the Table is too great to be explained, except, I
ON THE DIFFUSION OF LIQUIDS. 523
fear, by some error of observation, although no ordinary precaution was
neglected in the execution of this laborious series of experiments.
34. Iodides and Bromides of Potassium and Sodium.
Iodide of Potassium.—Time of diffusion 5:716 days. The diffusate
was estimated by means of nitrate of silver.
(1) Iodide of potassium, 1977 per cent. ; density 1:01.45. Diffused
at 53°5, in eight cells, 11:415, 11:506, 10:942, and 11.062 grs.; mean
11:24 for two cells, and 11:36 for two per cent.
Comparing this salt with the isomorphous chloride of potassium, we
have—
Diffusion of 2 per cent, solutions in 5:716 days.
Chloride of potassium at 55°, . 11:48 100
Iodide of potassium at 53°5, . 11'36 99.65
The diffusion of the iodide would slightly exceed that of the chloride,
instead of falling below it as in the Table, if the temperatures were
made equal.
. (2) Again, iodide of potassium 1971 per cent. ; observed density
101486. Diffused at 59°8, in eight cells, and the mean diffusate of the
whole cells determined, it gave 12:33 grs. of iodide of potassium for two
cells; or 12:51 grs. for a 2 per cent. solution.
Bromide of Potassium.—Time of diffusion and mode of estimating
diffusate as above. The solution contained 1975 per cent. of salt, and
had a density of 1:01.4850. Diffused at 59°8, in eight cells, it gave a
mean diffusate of 12:30 grs, for two cells; or 12:46 grs. for 2 per cent.
For comparison, a solution of chloride of Potassium, containing
exactly 2 per cent. of salt and having the density 1:01:33, was diffused
in the same circumstances of time and temperature as the two preceding
salts. The mean diffusate of eight cells was 12:24 grs. for two cells.
Hence the following result of the diffusion of three isomorphous
Salts:–
Diffusion of 2 per cent. solutions in 5:716 days, at 59°8.
Grs. Ratio.
Chloride of potassium, . * 12:24 100
Bromide of potassium, . * 12:46 101-80
Iodide of potassium, º º 12:51 102.21
-ms-
Mean, 12°40
Iodide of Sodium.—Time of diffusion seven days, temperature 59°8.
A solution of 2011 per cent, and density 1.01618, diffused in eight cells,
524 ON THE DIFFUSION OF LIQUIDS,
gave a mean diffusate of 12:24 grs, for two cells; that is, 12:18 grs, for
2 per cent, solution, -
Bromide of Sodium.—Time of diffusion and temperature as above.
A solution of 2:146 per cent, of density 1-01726, diffused in eight cells,
gave a mean diffusate of 1280 grs.; that is, 11.93 grs, for 2 per cent.
A comparative experiment was made with a solution of chloride of
Sodium, containing 1917 per cent. of salt and of density 1.01376, in
eight cells, at 60°. The diffusates for four pairs of cells were 11'65,
1175, 11-63, and 11:47 grs. ; mean 11-63 grs, which gives by propor-
tion 12:14 grs. for a 2 per cent. solution. As the present salt differs
only 0°2 Fahr, in diffusion-temperature from the two preceding salts,
which is inadequate to produce an assignable difference of diffusion, the
three salts may be supposed to be diffused at the same temperature,
without sensible error.
Diffusion of 2 per cent. Solutions for 7 days.
- GrS. Ratio,
Chloride of sodium at 60°, © , 12:14 100
Bromide of sodium at 59°8, . 11.93 98.27
Iodide of sodium at 59°8, º 12:18 100'33
Mean, 12:08
In both these isomorphous groups of salts of potassium and sodium,
there is certainly a near approach to equality of diffusion. The times for
the salts of the two bases being in the empirical proportion of the square
roots of 2 and 3, the mean diffusates also approach pretty closely;
namely, 12:40 grs. for the salts of potassium and 12:08 grs. for the salts
of sodium, which are as 100 to 97.42. Here the members of each
group are certainly very similar to each other in density, and probably
other physical properties, which was not the case with the equidiffusive
group containing the hydrogen acids of the same salt-radicals (p. 499).
35. Chloride of Ammonium.
Time of diffusion 5.716 days. The salt diffused was estimated by
means of nitrate of silver.
Solution 0.988 per cent. ; density 10036. Diffused at 53°, in eight
cells, 6:09, 6-07, 5-67, 5-87; mean 592 grs, and 5.99 for one per cent, in
two cells. This is somewhat more than 5'68, one-half of the diffusate
of the 2 per cent, solution of iodide of potassium, at nearly the same
temperature. The diffusion, however, of the small proportions of salts of
ammonium, such as the 1 per cent. Solution, is apt to be given in excess,
from their low density. *
ON THE DIFFUSION OF LIQUIDS, 52
5.
36. Dichloride of Copper.
Time of diffusion seven days, or that of chloride of sodium. The
salt diffused was obtained by evaporation to dryness, in an air-bath,
after treating the liquid with an excess of chlorine, in the form of
chloride, from which the dichloride was calculated. -
It was an object of interest to discover whether the dichloride of
copper (Cu,Cl), which should be isomorphous with the chloride of
sodium, may separate from the protochloride of copper and other mag-
nesian salts, and assume the high diffusibility of the salts of alkaline
metals. But the salt in question is entirely insoluble in water. A solu-
tion, however, was obtained by dissolving an equivalent quantity of the
red suboxide of copper recently precipitated, in hydrochloric acid, of
density 1-033, so as to give one grain of dichloride in every hundred
water-grain measures of the solution. This acid solution did not preci-
pitate by dilution with water. The salt was diffused into pure water at
a mean temperature of 53°2.
1. Dichloride of copper diffused, 6-66, 6:57, 7:01, and 6:48 grs. ; mean
6-68 grs, in two cells. Chloride of sodium at 53°4, nearly the same
temperature, gave 5-90 grs. in the same time. Reducing the result to
temperature of 51° by an approximative correction, we should have 6'48
grs. of dichloride of copper for that temperature, at which chloride of
calcium gave 6:51 grs. in 11:43 days, and protochloride of copper (CuCl)
6:06 grs. at nearly the same temperature, also in 11:43 days.
So far as we can judge from an experiment at a single temperature,
it would appear that the diffusion of dichloride of copper is more rapid
than that of the chloride (CuCl), in a proportion which supposes the
former compound to possess half the “solution density” of the latter,
the times of equal diffusion, 7 and 11:43 days, being when Squared as
1 to 2. -
With the view of discovering whether the large proportion of hydro-
chloric acid, amounting to 7 per cent, present in the preceding solution
of dichloride of copper, modified the diffusion of the salt, a portion of
the same acid solution was treated with chlorine gas, to convert the
copper salt into chloride, and diffused into water, after the excess of
chlorine was removed by agitation of the solution with air. The pro-
portion of Salt present was thus increased in weight from 1 to 1:36 per
cent. The time of diffusion was 11:43 days, and the temperature 53°.
2. Chloride of copper diffused from a 1:36 per cent. Solution of the
salt in hydrochloric acid, 5'83, 5-66, and 5:30 grs. in two cells; mean
5-60 grs. - - - -
The corresponding diffusion from a 1 per cent. Solution may be sup-
posed to be less than 5-6 grs, in the proportion of 1:36 to 1, without any
526 ON THE DIFFUSION OF LIQUIDS.
great error. The results thus become chloride of copper diffused, 3.98,
385, and 358 grs. ; mean 380 grs. in two cells.
It hence appears that the diffusion of chloride of copper is much
diminished by the presence of a great excess of hydrochloric acid in the
same solution. Different causes suggest themselves for this result, such
as the possibility of a combination existing of chloride of copper with
chloride of hydrogen, in the acid solution; or the influence which must
be admitted of the more soluble substance, in a mixture of two similar
substances, in repressing the diffusion of the less soluble. The present
result, however, is entirely opposed to the idea that the high diffusibility
of the dichloride of copper, observed before, is due to the hydrochloric
acid present.
3. The diffusion of chloride of sodium also appears to be repressed
by contact with a large excess of hydrochloric acid. One per cent. of
chloride of sodium raised the density of dilute hydrochloric acid from
1.035 to 1:0408. Diffused into pure water for seven days at 52°9, in
eight cells, the diffusates of chloride of sodium were 380, 3.87, 4:00, and
3.86 grs. ; mean 388 for two cells. The diffusion of chloride of sodium
is thus reduced in a corresponding measure with that of chloride of
copper by association with seven times its weight of hydrochloric acid.
These results are interesting in a very different point of view. I
have always watched for the appearance of some absorbent or imbibing
power on the part of the acids, more analogous to an endosmotic attrac-
tion for water, as usually conceived. If such an attraction existed, it
would complicate the phenomena of diffusion, for the volume of water
absorbed by the acid would displace and project a portion of the latter
into the reservoir, the phial not being extensible. The high diffusibility
of hydrochloric and nitric acids would be thus explained. But by such
a mechanical displacement the chloride of sodium would be thrown out
in the preceding experiment, as well as the hydrochloric acid, which is
not the case.
4. Even in hydrochloric acid of density 1-124 (25 per cent), the dif-
fusion of I per cent. of chloride of sodium for seven days, at 56°6, was
found to amount to 47 grs. Only in two cells, and is less than from a
solution in pure water.
5. In comparing the influence of nitric acid with that of hydro-
chloric acid upon the diffusion of chloride of sodium, it was found that
in a 7 per cent. Solution of nitric acid, the chloride of sodium (1 per
cent) was entirely decomposed in the diffusive process, at 56°6, and
gave hydrochloric acid in the full diffusive equivalent of that acid,
together with nitrate of Soda.
ON THE DIFFUSION OF LIQUIDs. 527
37. Bicarbonate of Potash.
Time of diffusion 8.083 days, or double that of hydrate of potash.
The water of the jars was partially charged with carbonic acid gas, to
prevent the decomposition of this and the other bicarbonates in the act
of diffusion. The usual number of eight cells of the 1 and 2 per cent.
solutions were diffused, and four cells of the 4 and 8 per cent. solutions.
The whole diffusates of each proportion were then mixed together, and
the quantity of bicarbonate of potash diffused for two cells, converted
into the chloride of potassium, evaporated to dryness and weighed.
1. 1:05.9 per cent. of bicarbonate of potash (HO.CO3 + KO. C.O.),
density 1:00788, diffused at 68°2, gave 7-66 grs. for two cells. Calcu-
lated for 1 per cent., 723 grs. of bicarbonate of potash in two cells.
2. 212 per cent. of bicarbonate of potash, density 101489, diffused
at 622, gave 1488 grs. for two cells. Calculated for 2 per cent., 14:05
grs. of bicarbonate of potash in two cells.
3. 4.236 per cent. of bicarbonate of potash, density 1-0288, diffused
at 68°2, gave 14-15 grs. for one cell. Calculated for 4 per cent, 1336
grs. of bicarbonate of potash in one cell. -
4. 8472 per cent. of bicarbonate of potash, density 1-05600, diffused
at 68°2, gave 27:55 grs. for one cell. Calculated for 8 per cent, 26-01
grs. of bicarbonate of potash in one cell.
Diffusion of Bicarbonate of Potash in 8'08 days at 68°2; two cells.
Grs. Ratio.
From 1 per cent. Solution, e 7:23 1.029
From 2 per cent. solution, º 1 4-05 2
From 4 per cent. Solution, & 26-72 3.806
From 8 per cent. Solution, * 52-01 7'408
38. Bicarbonate of Ammonia.
Time of diffusion 8.083 days. The usual number of eight cells of
the 1 and 2 per cent, solutions of this substance were diffused, and four
cells of the 4 and 8 per cent. solutions. The whole diffusates of each
proportion were then mixed together, and the quantity of bicarbonate
of ammonia, diffused for two cells, determined by an alkalimetrical
experiment, which was always repeated twice.
1. 1:109 per cent of bicarbonate of ammonia (HO.CO, +NH,0.CO.),
density 1-00553, diffused at 68°2, gave 7-66 grs, for two cells. Calcu-
lated for 1 per cent, 6.91 grs. of bicarbonate of ammonia in two cells.
2. 2:218 per cent of bicarbonate of ammonia, density 1-0.1056, dif–
fused at 68°2, gave 15-14 grs. for two cells. Calculated for 2 per cent,
13.65 grs. of bicarbonate of ammonia in two cells. .
528 ON THE DIFFUSION OF LIQUIDS.
3. 4:436 per cent. of bicarbonate of ammonia, density 1-02000, dif-
fused at 68°2, gave 1498 grs, for one cell. Calculated for 4 per cent,
13:50 grs. of bicarbonate of ammonia in one cell. -
4. 8:872 per cent. of bicarbonate of ammonia, density 1-03856, dif-
fused at 68°2, gave 27-78 grs, for one cell. Calculated for 8 per cent,
25:05 grs. of bicarbonate of ammonia in one cell.
Diffusion of Bicarbonate of Ammonia in 8'08 days at 68°2; two cells,
GTS. Ratio.
Erom 1 per cent. Solution, º 6'91 1*013
Erom 2 per cent. Solution, ſº 13-65 2.
From 4 per cent. Solution, & 27-00 3'959
From 8 per cent. Solution, g 50'10 7:346
The amount and progression of the diffusion of this Salt correspond
well, for all the proportions diffused, with the preceding isomorphous
bicarbonate of potash,
39. Bicarbonate of Soda.
Time of diffusion 9.875 days. The usual number of eight cells of
the 1 and 2 per cent, solutions were diffused, and four cells of the 4 and
8 per cent, solutions. The whole diffusates of each proportion were then
mixed together, and the quantity of bicarbonate of soda, diffused for two
cells, converted into chloride of sodium, evaporated to dryness and
weighed.
1. 1-135 per cent. of bicarbonate of soda, HO.CO2 + NaO.CO2,
density 1.00892, diffused at 68°1, gave 8:30 grs. for two cells. Calcu-
lated for 1 per cent, 7.31 grs. of bicarbonate of soda in two cells.
2. 2.27 per cent of bicarbonate of soda, density 101703, diffused at
68°1, gave 15.68 grs. for two cells. Calculated for 2 per cent, 13.81
grs. of bicarbonate of soda in two cells. *.
3. 4:54 per cent of bicarbonate of soda, density 1-03306, diffused at
68°1, gave 15-16 grs, for one cell. Calculated for 4 per cent, 13.35 grs.
of bicarbonate of soda in one cell.
4, 9:08 per cent of bicarbonate of soda, density 1-06386, diffused at
68°1, gave 29-73 grs. for one cell. Calculated for 8 per cent, 26-19 grs.
of bicarbonate of Soda in one cell.
Diffusion of Bicarbonate of Soda in 987 days at 68°1; two cells.
- Grs. Ratio.
From 1 per cent. Solution, e 7-31 1'059
Erom 2 per cent. Solution, & 13.81 2
From 4 per cent. Solution, e 26'70 3.869
From 8 per cent. Solution, e 52°38 7.590
ON THE DIFFUSION OF LIQUIDS. & 529
A remarkable approach to equality in the diffusion of the bicarbonates
of potash and soda, in the times chosen, is observed equally in all the
proportions of salt from 1 to 8 per cent.
The results for the three bicarbonates may be stated as follows, the
diffusate of the 2 per cent. solution of bicarbonate of potash being made
equal to 200, as a standard of comparison.
Diffusion of Bicarbonates of Potash and Ammonia in 8'08 days, at 68°2,
and of Bicarbonate of Soda in 9:875 days, at 68°1 :—
Bicarbonate i Bicarbonate | Bicarbonate
of potash. of ammonia. of soda.
|
|
From 1 per cent. solution ............... 102-9 98.3 I 04:0
From 2 per cent. solution ............... 200-0 194-3 196'4.
From 4 per cent. solution ............... 380-6 | 384-3 380-0
From 8 per cent. solution ............... 740-8 712.6 748-3
Or, making the diffusate from each proportion of the bicarbonate
of potash equal to 100:-
Bicarbonate Bicarbonate Bicarbonate
of potash. of ammonia. of soda.
From 1 per cent. Solution ............... 100 95-53 101.07
From 2 per cent. Solution ............... 100 97.15 98-20
From 4 per cent. Solution ............... 100 100-97 99.84
From 8 per cent. solution ............... 100 96-19 101-03
The bicarbonate of ammonia is slightly lower in general than the
bicarbonate of potash, possibly from a small loss of the former salt by
evaporation in the different operations. The times chosen for these two
bicarbonates is to that of the bicarbonate of soda, as the square root of
2 to the square root of 3, and the remarkable agreement observed in the
diffusion of these salts gives support therefore to that relation. In
alluding to this relation, however, it is proper to add that the carbo-
nates of potash and soda deviate from it in a sensible degree, and the
hydrates of potash and soda very considerably. If the relation there-
fore has a real foundation, it must be masked in the salts last named by
differences existing between them in certain properties, the discovery
and investigation of which is of the last importance for the theory of
liquid diffusion.
40. Hydrochlorate of Morphine.
Time of diffusion 11-43 days. The crystallized salt was assumed
to be of the composition Cs. HisNOs. HCl + 6HO, with the equivalent
2 L
530 ON THE DIFFUSION OF LIQUIDS.
374-5. The quantity diffused was determined from the chlorine, which
was precipitated as chloride of silver in an acid solution. Hydrochlorate
of morphine, 1.88 per cent of the salt supposed anhydrous, diffused at
64°1, in six cells, 11:03, 1072, 11-01; mean 1092 grs. of the anhydrous
salt for two cells. Calculated for 2 per cent, 11.60 grs. at 64°1 for
two cells.
41. Hydrochlorate of Strychnine.
Time of diffusion 11-43 days. The crystallized salt was assumed to be
of the composition Ca2H22N2O4. HCl + 3HO, with the equivalent 397.5.
Hydrochlorate of strychnine, 2 per cent, density 1:0065, diffused at
64°1, in six cells, 11:54, 11-62, 11:31 ; mean 11:49 grs. for two cells.
The quantities refer to anhydrous Salt, and were estimated from the
chlorine, as with hydrochlorate of morphine.
These two analogous Salts appear to approach very closely in
diffusibility.
Diffusion from 2 per cent. Solutions at 64°1; two cells.
Hydrochlorate of morphine, . 11'60 100
Hydrochlorate of Strychnine, . 11:49 '99'05
For a similar period of 11:43 days, but at a lower temperature, 53°4,
the 1 per cent. Solution of hydrochlorate of morphine gave a mean result
of 5:49 grs. from two cells, and the hydrochlorate of strychnine 5-77
grs, from two cells. But the weights of chloride of silver from which
these numbers are deduced were too small to admit of much precision.
The diffusion of these salts of organic bases in 11-43 days, is
exceeded by the diffusion of chloride of ammonium or potassium in
571 days, or half the former time. The vegeto-alkalies appear thus to
be divided from ammonia and potash.
The new observations of the present paper are favourable to the
existence of a relation amounting to close similarity or equality in diffu-
sibility between certain classes of substances.
The chlorides and nitrates of the same metal generally exhibit this
correspondence, as in the chloride of calcium and nitrate of lime, the
chloride of sodium and nitrate of Soda, and also in hydrochloric and
nitric acids. *
Isomorphous salts exhibit the same relation, as has been observed in
the chlorides, bromides and iodides of potassium, sodium and hydrogen,
in various salts of baryta, strontia and lead, in numerous magnesian salts,
in the salts of silver, soda, and probably those of suboxide of copper, and
in several additional Salts of potash and ammonia.
ON THE DIFFUSION OF LIQUIDS. 531
Corresponding salts of two of the vegeto-alkalies are found also to
be equidiffusive.
Before discussing the relations between the different groups of
equidiffusive substances which are thus formed, it will be necessary to
examine their diffusion at widely different temperatures, a subject
attended with considerable difficulty.
ADDITIONAL OBSERVATIONS ON THE DIFFUSION OF LIQUIDS.1
The experiments on diffusion to be presently described are in con-
tinuation of those detailed in my last publication on the subject, the
same method of observing being followed without change. The diffu-
sion is generally made from solutions in four different proportions, so as
to exhibit pretty fully the characters of the property in question for
each salt, so far as is possible at a constant temperature. The salts
operated upon are of two bases only, potash and soda ; but the acids are
considerably varied, so as to include hydrates, carbonates, sulphates,
sulphites, hyposulphites, sulphovinates, oxalates, acetates, and tartrates.
Salts of almost every class of acids come thus to be represented, either
in the present or former series of experiments on diffusion, while at the
same time much information is elicited respecting the diffusive relation
of the two important bases named.
Comparison of Salts of Potash and Soda.
Hydrate of Potash-Time of diffusion 4,041 days. The usual
number of eight cells of the 1 and 2 per cent, solutions of this substance
were diffused, and four cells of the 4 and 8 per cent. Solutions. The
whole diffusates of each proportion were then mixed together, and the
quantity of hydrate of potash diffused for two cells determined by an
alkalimetric experiment, which was always repeated twice.
1. One per cent. of hydrate of potash, density 1-00978, diffused at
63°4, gave 6-56 grs. of hydrate of potash for two cells.
2, 2005 per cent. of hydrate of potash, density 1-01878, diffused at
63°4, gave 1288 grs. for two cells; calculated for 2 per cent, 1284 grs.
of hydrate of potash in two cells.
3. 4.01 per cent. of hydrate of potash, density 1-0366, diffused at
63°4, gave 12:56 grs, for one cell; calculated for 4 per cent, 12:52 grs.
of hydrate of potash in one cell.
4. 802 per cent. of hydrate of potash, density 1-07069, diffused at
63°4, gave 26:20 grs, for one cell; calculated for 8 per cent., 26-12 grs.
of hydrate of potash in one cell.
* Third Memoir, Phil. Trans, 1851. Received March 27,-Read May 22, 1851.
532 ON THE DIFFUSION OF LIQUIDS.
Diffusion of Hydrate of Potash in 404 days at 63°4; two cells.
Grs. Ratio.
IFrom 1 per cent, solution, . 6'56 1-022
From 2 per cent. Solution, . 12-84 2
Trom 4 per cent. solution, . 25'04 3'900
From 8 per cent. Solution, . 52°24 8'137
Hydrate of Soda.-Time of diffusion 4:9497 days; the times chosen
as hitherto for the corresponding potash and soda salts being always,
when squared, in the proportion of 2 to 3. The usual number of eight
cells of the 1 and 2 per cent. Solutions were diffused, and four cells of the
4 and 8 per cent. Solutions. The whole diffusates of each proportion
were then mixed together, and the quantity of hydrate of soda diffused
for two cells determined by alkalimetric experiments.
1. 1043 per cent. of hydrate of soda, density 1.01256, diffused at
63°3, gave 6'06 grs, for two cells; calculated for 1 per cent, 5.81 grs.
of hydrate of soda in two cells.
2. 2:087 per cent. of hydrate of soda, density 1-0242, diffused at
63°3, gave 11:58 grs. for two cells; calculated for 2 per cent, 11-09
grs. of hydrate of soda in two cells.
3. 4-177 per cent. of hydrate of soda, density 1-04666, diffused at
63°3, gave 10.90 grs, for one cell; calculated for 4 per cent, 10:43 grs.
of hydrate of soda in one cell.
4. 8:35 per cent. of hydrate of soda, density 1.08846, diffused at
63'3, gave 21-10 grs, for one cell; calculated for 8 per cent, 20:22 grs.
of hydrate of soda in one cell.
Diffusion of Hydrate of Soda in 495 days at 63°3; two cells.
GrS. Ratio.
From 1 per cent. Solution, . S-81 1-048
From 2 per cent. Solution, . 11'09 2
From 4 per cent. Solution, . 20'86 3.765
From 8 per cent. Solution, . 40°44 7:30
The nearest approach to equality of diffusion in the hydrates of
potash and Soda, is exhibited by the 1 per cent, solutions, which are as
6:56 to 5'81, or as 100 to 88-57, being a difference of so much as 11:43
per cent.
Comparative Diffusion of Hydrate of Potash in 4:04.1 days at 63°4, and
of Hydrate of Soda in 495 days at 63°3.

From solutions of
1 per cent. || 2 per cent. || 4 per cent. || 8 per cent.
Hydrate of potash ......... 100 100 I00 100
Hydrate of soda ............ 88-57 86°37 83.30 77°41
ON THE DIFFUSION OF LIQUIDS. 533
The marked departure from the usual ratio of diffusion, here ex-
hibited, must not be overlooked in considering the relation between
potash and soda salts.
Carbonate of Potash.--Time of diffusion 8.083 days, or double the
time of hydrate of potash. The usual number of eight cells of the 1 and
2 per cent. solutions were diffused, with four cells of the 4 and 8 per
cent. solutions, and the diffusates of each proportion determined by
alkalimetric experiments as with the preceding alkaline hydrates.
1. 1.002 per cent. of carbonate of potash, density 1-00957, diffused at
63°7, gave 6'15 grs. for two cells; calculated for 1 per cent, 6.13 grs.
of carbonate of potash in two cells.
2. 2:005 per cent. of carbonate of potash, density 1-01843, diffused
at 63°7, gave 1195 grs. for two cells; calculated for 2 per cent, 11-92
grs. of carbonate of potash in two cells.
3. 4.01 per cent. of carbonate of potash, density 1-03577, diffused at
63°7, gave 11:48 grs, for one cell; calculated for 4 per cent., 11:44 grs.
of carbonate of potash in one cell.
4, 8:02 per cent of carbonate of potash, density 1-06935, diffused at
63°7, gave 2279 grs. for one cell; calculated for 8 per cent, 22.72 grs.
of carbonate of potash in one cell.
5. 2:005 per cent of carbonate of potash, density 1-01843, diffused at
68°2, gave 12.64 grs. for two cells; calculated for 2 per cent., 12.62 grs.
of carbonate of potash in two cells.
Diffusion of Carbonate of Potash in 8'08 days at 63°7; two cells.
Grs. Ratio.
Erom 1 per cent. solution, . . 6-13 1-028
From 2 per cent. solution, & I 1-92 2
From 4 per cent, solution, * 22°88 3-839
From 8 per cent. solution, & 45-44 7-624
Comparative Diffusion of Hydrate of Potash in 4.04 days at 63°4, and
Carbonate of Potash in 8'08 days at 63°7.

From solutions of
1 per cent. 2 per cent. 4 per cent. 8 per cent.
100 100 100
Hydrate of potash ......... 100
92.81 . 91.36 86-97
Carbonate of potash......... 93-48
The diffusion of hydrate of potash appears to be excessive when
compared with the carbonate of potash, as well as when compared with
the hydrate of soda.
534 ON THE DIFFUSION OF LIQUIDS.
Carbonate of Soda.—Time of diffusion 9:8994 days. The usual
number of eight cells of the 1 and 2 per cent, solutions of this substance
were diffused, and four cells of the 4 and 8 per cent. Solutions, and the
diffusates determined by alkalimetric experiments.
1. 1:003 per cent. of carbonate of soda, density 1-0.1120, diffused at
63°4, gave 6.04 grs. for two cells; calculated for 1 per cent, 6.02 grs. of
carbonate of soda in two cells.
2, 2007 per cent. of carbonate of soda, density 1-0216, diffused at
63°4, gave 1174 grs, for two cells; calculated for 2 per cent, 1170 grs.
of carbonate of soda in two cells.
3. 4-015 per cent of carbonate of soda, density 1:04.156, diffused at
63°4, gave 1074 grs, for one cell; calculated for 4 per cent, 1071 grs.
of carbonate of Soda in one cell.
4. 803 per cent, of carbonate of soda, density 1-0800, diffused at
63°4, gave 1993 grs. for one cell; calculated for 8 per cent, 1987 grs.
of carbonate of soda in one cell.
In the two following additional experiments the diffusate was treated
with hydrochloric acid, and estimated from the weight of chloride of
sodium produced.
5, 2007 per cent of carbonate of soda, density 1-02166, diffused at
68°1, gave 12:06 grs, for two cells; calculated for 2 per cent, 12:02 grs.
of carbonate of soda in two cells at 68°1.
6. 2.13 per cent of carbonate of soda, density 1-0.2246, diffused at
59°6 in eight cells, 11-12, 11:34, 11:17, 11:58; mean 11:38 grs. for two
cells; calculated for 2 per cent., 10'65 grs. of carbonate of soda in two
cells at 59°6.
Diffusion of Carbonate of Soda in 99 days at 63°4; two cells.
Grs. Ratio.
From 1 per cent. Solution, - 6:02 1-028
From 2 per cent. Solution, - 11-70 2
From 4 per cent. Solution, . 21:42 3:661
From 8 per cent. Solution, º 3974 6-792
The similarity of diffusion between the carbonates of potash and
soda is remarkable in the 1 per cent. Solution, which are as 6:13 to 6:02,
or as 100 to 98°2; also in the 2 per cent. Solutions, which were observed
at two different temperatures.
Diffusion of 2 per cent solutions of Carbonate of Potash in 8.083 days,
and Cârbonate of Soda in 9.9 days.
Grs. Ratio.
Carbonate of potash at 63°7, . 11:92 I 00
Carbonate of soda at 63°4, º II '70 98’ 15
Carbonate of potash at 68°2, . 12°62 100
Carbonate of soda at 68°1, º 12:02 95.24
ON THE DIFFUSION OF LIQUIDS.
Comparative Diffusion of Carbonate of Potash in 8'083 days at 63°7,
and Carbonate of Soda in 99 days at 63°4.

Carbonate of potash
Carbonate of soda............
* * * * is e a # s
From Solutions of
1 per cent. 2 per cent. 4 per cent. 8 per cent.
100 100 100 100
98.20 98.15 93-63 87°44
The carbonate of soda appears to preserve more analogy to the
hydrate of soda in its diffusion than the carbonate of potash to the
hydrate of potash.
Comparative Diffusion of Hydrate of Soda in 4.937 days at 63°3, and
Carbonate of Soda in 99 days at 63°4.

From solutions of
1 per cent. 2 per cent. || 4 per cent. || 8 per cent.
Hydrate of soda ............ 100 100 100 100
Carbonate of soda............ 103-62 105'50 102’68 98-27
Here we have a nearly equal diffusion with the times as 1 to 2 for
the hydrate and carbonate of soda respectively.
Sulphate of Potash-Time of diffusion 8.083 days.
diffused salt was evaporated to dryness and weighed.
1. 1:005 per cent of sulphate of potash, density 100844, diffused at
60°3, in eight cells, 6:11, 621, 6:12, 6-32; mean 6.19 grs. in two cells;
calculated for 1 per cent, 6.16 grs. of sulphate of potash in two cells.
2. 2:01 per cent. of sulphate of potash, density 1.01653, diffused at
60°3, in eight cells, 11-61, 11:58, 11:50, 11.97; mean 11-66 grs. in two
cells; calculated for 2 per cent, 11.60 grs. of sulphate of potash in two
cells.
3. 402 per cent of sulphate of potash, density 1.03240, diffused at
60°3, in four cells, 10.80, 11:33, 11:20, 12:07; mean 11:35 grs. for one
cell; calculated for 4 per cent, 11:35 grs. of sulphate of potash in one
cell.
4. 804 per cent of sulphate of potash, density 1-06306, diffused at
60°3, in four cells, 21.91, 21-93, 22:00, 22:47; mean 22:08 grs, for one
cell; calculated for 8 per cent., 21.96 grs. of sulphate of potash in one
cell.
The solution of
536 ON THE DIFFUSION OF LIQUIDS.
Diffusion of Sulphate of Potash in 8.083 days at 60°3; two cells.
GrS. Ratio.
From 1 per cent. Solution, e 6-16 1°062
From 2 per cent, solution, * 11.60 2
From 4 per cent. solution, § 22-70 3'914
From 8 per cent. solution, e 43-92 75-72
The diffusion of sulphate of potash above, at 60°3, appears to be
similar to that of carbonate of potash at 63°7, a higher temperature by
3°4 (p. 533). The numbers for the sulphate of potash and hydrate of
potash (p. 531) would probably correspond closely at the same tem-
perature, the times of diffusion of the two substances being taken as
2 to 1.
Sulphate of Soda.-Time of diffusion 9.9 days. The diffusate was
evaporated to dryness and weighed.
1. One per cent of sulphate of soda, density 1-00940, diffused at
59°9, in eight cells, 6-31, 6:47, 621, 6-32; mean 6:33 grs, for two cells.
2, 1995 per cent of sulphate of soda, density 1-01832, diffused at
59°9, in eight cells, 12:02, 12:10, 11.66, 12.16; mean 11-98 grs, for two
cells; calculated for 2 per cent, 12:00 grs. of sulphate of soda in two
cells at 59-9.
3. 3.99 per cent. of sulphate of soda, density 1.03594, diffused at
59°9, in four cells, 10:00, 10.80, 11:53, 11:53; mean 10.96 grs. for one
cell; calculated for 4 per cent., 1098 grs. of sulphate of soda in one
cell at 59°-9.
4. 7-98 per cent of sulphate of soda, density 1-06960, diffused at
59°9, in four cells, 20:50, 21:36, 20:01, 20-68; mean 20-64 grs, for one
cell; calculated for 8 per cent., 20-69 grs. of Sulphate of soda in one
cell at 59°9.
Diffusion of Sulphate of Soda in 99 days at 59°9; two cells.
Grs. Ratio.
Erom 1 per cent. Solution, . e 6:33 I'055
From 2 per cent. Solution, . * 12:00 2
IFrom 4 per cent. Solution, . ſº 21.96 3'66
from 8 per cent. Solution, . p 41°38 6'896
The 2 per cent. Solution of sulphate of soda above, at 59:9, appears
to be more diffusive than the corresponding solution of carbonate of
soda at 59°6, as 12:00 to 10'65 grs, or as 100 to 88-75.
The assumed relation in the times of equal diffusion for salts of
potash and soda appears to derive support from the sulphates, particu-
larly in the lower proportions of salt.
ON THE DIFFUSION OF LIQUIDS. 537
Comparative Diffusion of Sulphate of Potash in 8.083 days at 60°3,
and Sulphate of Soda in 99 days at 59°9.
From solutions of

1 per cent. || 2 per cent. || 4 per cent. || 8 per cent.
Sulphate of potash ......... 100 100 100 100
Sulphate of soda ............ 102.74 || 103°45 96-74 94-21
Another set of experiments made upon these two Salts, simul-
taneously with certain oxalates and acetates which follow, may be
placed here to illustrate the same relation. The preceding times of
diffusion were observed.
5, 2013 per cent of sulphate of potash, diffused at 59°8, in eight
cells, gave 11.90, 11.94, 11:41, 11-71; mean 11-74 grs. for two cells;
calculated for two per cent, 11.67 grs. of sulphate of potash in two cells.
6. Two per cent. of sulphate of soda, density 1-01846, diffused at
59°6, in eight cells, gave 11:58, 11:56, 11.94, 11.97 ; mean 1176 grs. of
sulphate of soda in two cells.
The present results, from 2 per cent. solutions of these salts, are as
follows:—
Sulphate of potash in 8.083 days at 59°8, 11-67 100
Sulphate of soda in 99 days at 59°6, . 1176 100-94
The diffusion in the selected times appears therefore to be, as nearly
as possible, equal at the present temperatures.
Another experiment may be recorded at present, of which the object
was to ascertain the influence of free sulphuric acid upon the diffusion
of Sulphate of soda.
7. Sulphate of soda, 2:02 per cent, to which an equivalent quantity
of sulphuric acid was added, had the density 1-02703. This solution,
diffused into pure water, in eight cells, at 59°6, for the same time as the
preceding sulphate of soda, gave a diffusate of 9-70, 10:06, 10:17, and
10:29 grs. of sulphate of soda ; mean 10:05 grs. in two cells; calculated
for 2 per cent, this diffusate becomes 9-95 grs. The presence of one
equivalent of sulphuric acid appears therefore to diminish the diffusion
of sulphate of soda considerably, namely, from 11:76 to 9.95 grs., or from
100 to 84.61. The free sulphuric acid diffused in the experiment was
not determined.
Sulphite of Potash.--It was curious to observe how far this and
other salts of the oxygen acids of sulphur correspond with the sulphates.
Time of diffusion 8.083 days. The diffusate was treated with sulphuric
acid and estimated in the form of neutral sulphate of potash.
538 ON THE DIFFUSION OF LIQUIDS.
1.90 per cent. of sulphite of potash, density 1-01753, diffused at
59°5, in eight cells, gave 11:36, 1072, 11:22, and 10.90 grs, in two cells;
mean 11-05 grs. in two cells; calculated for 2 per cent., 11-63 grs.
Making the comparison for 2 per cent. solutions we have—
Sulphate of potash at 60°3, . tº 11'60 100
Sulphite of potash at 59°5, . º 1 1:63 100:26
The two salts appear to have the same diffusibility.
Sulphite of Soda.—Time of diffusion 9.9 days. The diffusate was
estimated in the same manner as the preceding salt.
2:26 per cent of sulphite of soda, density 1-02330, diffused at 59°6,
in eight cells, gave 12-93, 13:35, 13:56, and 13.62 grs. in two cells; mean
13:37 grs. in two cells; calculated for 2 per cent., 11.83 grs.
The comparative diffusion of the sulphites of the two bases is as
follows:–
Sulphite of potash in 8:083 days at 59°5, 11:63 100
Sulphite of soda in 99 days at 59°6, . 11.83 100.72
The sulphites of potash and soda appear therefore to exhibit the
usual relation of these two bases. -
Hyposulphite of Potash-Time of diffusion 8.083 days. The diffu-
sate was evaporated to dryness with sulphuric acid, ignited and estimated
from the Sulphate produced.
1925 per cent. of anhydrous hyposulphite of potash, density 1-0150,
diffused at 59°8, in eight cells, gave 11-66, 11-67, 12:01, 12:26 grs.;
mean 11.90 grs, for two cells; calculated for 2 per cent., 12:37 grs. of
hyposulphite of potash in two cells. - -
Comparing this salt with the Sulphate of the same base, we have—
Sulphate of potash at 60°3, . 11'60 100
Hyposulphite of potash at 59°8, 12:37 106° 44
A slight error in excess may possibly have been introduced from the
circumstance that the hyposulphite of potash employed was not abso-
lutely free from Sulphate.
Hyposulphite of Soda.-Time of diffusion 99 days. The diffusate
was estimated in the same manner as the preceding salt.
2:136 per cent. of anhydrous hyposulphite of soda, density 1-01778,
diffused at 59°9, in eight cells, gave 13'11, 1277, 1292, 11.99 grs; mean
1270 grs. for two cells; calculated for 2 per cent, 1189 grs. of hypo-
sulphite of soda in two cells. -
The comparative diffusion of the salts of potash and soda appears
thus:–
ON THE DIFFUSION OF LIQUIDS. 539
Hyposulphite of potash in 8.083 days at 59°8, 12:37 100
Hyposulphite of soda in 99 days at 59°9, . 11.89 96.21
The relation of the sulphate and hyposulphite of soda appears still
closer.
Sulphate of soda at 59°6, º 11.76 } 00
Hyposulphite of soda at 59°9, . 11-89. 101 - 10
Sulphovinate of Potash.--Time of diffusion 8.083 days. The diffu-
sate was evaporated to dryness and ignited with sulphuric acid.
1966 per cent. of sulphovinate of potash, of density 1:00977, dif-
fused at 59°8, in eight cells, gave 12:57, 12:48, 12:12, and 12:39 grs. ;
mean 12:39 grs. for two cells; calculated for 2 per cent., 12.60 grs. of
sulphovinate of potash in two cells.
The diffusion of this salt appears in excess when compared with
sulphate of potash.
Sulphate of potash at 60°3, . I 1-60 100
Sulphovinate of potash at 59-8, . 12-60 108.62
Sulphovinate of Soda.-Time of diffusion 9.9 days. The diffusate
was estimated in the same manner as the preceding salt. -
2:063 per cent of sulphovinate of soda, of density 1-00944, diffused
at 59°6, in eight cells, gave 13:32, 13:50, 1378, and 13:15 grs. ; mean
13:44 grs, for two cells; calculated for 2 per cent., 13:03 grs. of sulpho-
vimate of soda in two cells.
Comparing the two sulphovinates together, we have—
Sulphovinate of potash in 8.083 days at 59°8, 12.60 100
Sulphovinate of soda in 99 days at 59°6, . 13:03 10341
Neither of these sulphovinates appeared to suffer decomposition in
the act of diffusion, at least to any considerable extent. But the ex-
periments on both of these salts are less precise than usual, from the
difficulty of obtaining them entirely free from sulphates.
Oxalate of Potash-Time of diffusion 8.083 days. The diffusate was
evaporated to dryness, ignited, and then converted into chloride of
potassium.
1. 0.981 per cent. of anhydrous oxalate of potash, density 100775,
diffused at 59°8, in eight cells, 6:24, 6-22, 5.91, 597; mean 6:08 grs, for
two cells; calculated for 1 per cent, 6.20 grs. of oxalate of potash in
two cells.
2. 1.92 per cent. of oxalate of potash, density 1-01463, diffused at
59°9, in eight cells, 11:54, 11-63, 11.94, 11-63; mean 11-68 grs. for two
cells; calculated for 2 per cent, 12:17 grs. of oxalate of potash, in two
cells. -
540 - ON THE DIFFUSION OF LIQUIDS.
3. 384 per cent of oxalate of potash, density 1-02864, diffused at
59°9, in four cells, 11:10, 11:16, 11:09, 10.92; mean 11-07 grs, for one
cell; calculated for 4 per cent, 11:52 grs, of oxalate of potash in one cell.
4. 7-68 per cent of oxalate of potash, density 1-05604, diffused at
59°9, in four cells, 20:45, 20.63, 20.99, 2015; mean 20:55 grs. for one
cell; calculated for 8 per cent., 21.41 grs, of oxalate of potash in one cell.
Diffusion of Oxalate of Potash in 8.083 days at 59°9; two cells.
Grs. Ratio.
From 1 per cent. solution, * 6:20 I'019
From 2 per cent, solution, {- 12:17 2
From 4 per cent. Solution, . 23:04 3.789
From 8 per cent. solution, * 42'82 7-042
The oxalate of potash corresponds well with sulphate of potash,
Comparative diffusion in 8088 days of Sulphate of Potash at 60°3, and
- Oxalate of Potash at 59°9.

From solutions of
1 per cent. || 2 per cent. || 4 per cent. |8 per cent.
Sulphate of potash ......... 100 100 100 100
Oxalate of potash............ 100-65 | 104-91 || 101-50 97.47
The sensible excess in the diffusion of the 2 per cent, solution of
oxalate of potash is, I believe, to be accounted for by this proportion
having been estimated in the form of carbonate of potash instead of
chloride of potassium. -
Oa'alate of Soda.-Time of diffusion 99 days. The diffusate was
evaporated to dryness, ignited, and then converted into chloride, as with
the preceding oxalate of potash.
1. 0.925 per cent. of oxalate of soda, density 1-00882, diffused at
59°9, in eight cells, 5.99, 5'81, 5-69, 5'59; mean 577 grs, for two cells;
calculated for 1 per cent, 6.24 grs. Of Oxalate of soda in two cells.
It was found impossible to form a 2 per cent. Solution of this salt
from its sparing solubility, so that the observations respecting it are
limited to the lowest proportion of salt.
The comparative diffusion from 1 per cent. Solutions of these alkaline
oxalates is as follows:—
Oxalate of potash in 8.083 days at 59°9, 620 100
Oxalate of soda in 99 days at 59°9, . 6'24. 100'65
ON THE DIFFUSION OF LIQUIDS. 54 I
Here again a nearly equal diffusion is observed in times of which
the Squares are as 2 to 3.
Acetate of Potash.--Time of diffusion 8.083 days. The diffusate was
converted into chloride of potassium and weighed in that form.
1. 0-951 per cent. of anhydrous acetate of potash, density 100540,
diffused at 60°3, in eight cells, 6:01, 6:18, 6.27, 6-06; mean 6:13 grs. for
two cells; calculated for 1 per cent, 6’44 grs. of acetate of potash in
two cells.
2. 1:903 per cent of acetate of potash, density 1-00976, diffused at
60°3, in eight cells, 11.90, 11.91, 11.65, 12:24; mean 11-92 grs. for two
cells; calculated for 2 per cent, 12:52 grs, of acetate of potash in two
cells.
3. 3807 per cent. of acetate of potash, density 1-01928, diffused at
60°3, in four cells, 10-91, 11:08, 11:48, 11:18; mean 11-16 grs. for one
cell; calculated for 4 per cent, 11.72 grs. of acetate of potash in one cell.
4. 7-614 per cent. of acetate of potash, density 1-03743, diffused at
60°3, in four cells, 22:62, 21-72, 23:23, 22:42; mean 22:50 grs, for one
cell; calculated for 8 per cent, 23.63 grs. of acetate of potash in one cell.
Diffusion of Acetate of Potash in 8'08 days at 60°3; two cells.
Grs. Ratio.
From 1 per cent. Solution, 6°44 I'028
From 2 per cent. Solution, 12:52 2
From 4 per cent. Solution, 23'44 3-744
From 8 per cent. Solution, 47-26 7-549
The acetate will be found to exceed sensibly the Sulphate and oxalate
of potash in diffusibility at the preceding temperature.
Comparative diffusion of Sulphate and Acetate of Potash in 8.083 days,
at 60°-3.
From solutions of
1 per cent. 2 per cent. || 4 per cent. |8 per cent.
Sulphate of potash ......... 100 100 I00 100
Acetate of potash............ I04-55 | 107-93 || 103-26 107.58

The acetate of potash appears to possess that increased diffusibility
which is observed in bicarbonate of potash. But a parallelism still
holds between the acetate and sulphate, and the diffusion of the two
salts would probably coincide if that of the acetate were observed at a
temperature 3’ or 4° lower than the sulphate.
542 - ON THE DIFFUSION OF LIQUIDS.
Acetate of Soda.-Time of diffusion 9.9 days. The diffusate was
converted into chloride of sodium and weighed in that form.
1. 0-958 per cent. of anhydrous acetate of soda, density 1.00530,
diffused at 59°6, in eight cells, 6:33, 6:56, 6-63, 6:05; mean 639 grs.
for two cells; calculated for 1 per cent, 6.67 grs. of acetate of soda in
two cells. -
2. 1:917 per cent. of acetate of soda, density 1:01032, diffused at
59°6, in eight cells, 1170, 12:04, 11.90, 12:19; mean 1196 grs, for two
cells; calculated for 2 per cent, 12:46 grs. of acetate of soda in two cells.
3. 3-835 per cent. of acetate of soda, density 1-02039, diffused at
59°6, in four cells, 12:19, 11-74, 12:15, 11-93; mean 12:00 grs. for one
cell; calculated for four per cent, 12:52 grs. of acetate of soda in one cell.
4. 7-67 per cent of acetate of soda, density 1-03968, diffused at 59°6,
in four cells, 23:49, 22:26, 23.87, 22:49; mean 23:03 grs. for one cell;
calculated for 8 per cent, 24.02 grs. of acetate of soda in one cell at 59°9.
Diffusion of Acetate of Soda in 99 days at 59°6; two cells.
GrS. Ratio.
From 1 per cent. Solution, . • 6-67 1-070
From 2 per cent. Solution, . º 12°46 2
From 4 per cent. Solution, . -> 25'04 4°019
From 8 per cent. Solution, . Q 48:04 7-7I1
The diffusion of acetate of soda presents a general parallelism to
that of acetate of potash for the times chosen, the temperatures of the
two series of experiments differing only 0°7.
Comparative diffusion of Acetate of Potash in 8'083 days at 60°3, and
- Acetate of Soda in 9.9 days at 59°6.

From solutions of
I per cent. 2 per cent. 4 per cent. 8 per cent.
Acetate of potash ............ 100 100 100 100
Acetate of soda ............... 103-57 99.52 106'82 101-65
Tartrate of Potash.--Time of diffusion 8'08 days. The diffusate
was evaporated to dryness, ignited, and then converted into chloride of
potassium.
1-82 per cent. of anhydrous tartrate of potash, density 1.01227,
diffused at 59°9, in eight cells, 996, 10:02, 10:06, 9,87; mean 9°98 grs.
for two cells; calculated for 2 per cent., 1096 grs. of tartrate of potash
in two cells.
ON THE DIFFUSION OF LIQUIDS. 543
Tartrate of Soda.-Time of diffusion 9.9 days. The diffusate was
evaporated to dryness, ignited, and then converted into chloride of
Sodium.
2:03 per cent. of anhydrous tartrate of soda, density 1-01460, dif-
fused at 59°6, in eight cells, 1084, 1077, 10.81, 10:82; mean 10-81
grS. for two cells; calculated for 2 per cent., 10'65 grs. of tartrate of
Soda in two cells.
Diffusion of 2 per cent. solutions of Tartrate of Potash in 8:08 days at
59°9, and Tartrate of Soda in 99 days at 59°6.
Tartrate of potash, . * ſº 10.96 100
Tartrate of soda, . tº * 10'65 97.18
The tartrate of soda happens to correspond absolutely with the
carbonate of Soda, the diffusate of the latter salt obtained at the same
temperature being also 10'65 grs. (p. 534).
The double Tartrate of Potash and Soda afforded an interesting
instance of decomposition produced by diffusion. Instead of the usual
diffusion cells, a single plain cylindrical jar was employed about 5
inches in diameter and 10 inches in height. A portion of a 4 per cent.
Solution of Rochelle salt, amounting to 5000 grs. of liquid, was covered
over by nine times as much pure water, in this jar, and the salt allowed
to diffuse upwards for three weeks at 56°. The upper third of the fluid
column, amounting to 17,000 grs. of liquid, was then drawn off, evapo-
rated to dryness, and the salt ignited and converted, by the addition of
hydrochloric acid, into chloride, which weighed 3-14 grs. The salt
proved to be a mixture of the two chlorides in the proportion of 2:43
grs. of chloride of potassium and 0.71 gr. of chloride of sodium. This
gives the following as the composition of the diffusate:—
Tartrate of potash, . & & 3-68
Tartrate of soda, & * * I 17
4-85
It hence follows that the proportion of potash, or of tartrate of
potash, in the diffusate is nearly three times greater than existed in the
original Rochelle salt. It will be recollected that the Salt decomposed
is, strictly speaking, a bibasic tartrate of potash and soda, and not a double
tartrate of potash and soda. The diffusate was observed to be exactly
neutral to test-paper. This mode of diffusing upwards in water from
the lower part of a deep jar obviously gives the greatest degree of sepa-
ration attainable in consequence of unequal diffusibility.
I may confine myself at present to the conclusion that of the nine
pairs of potash and soda salts, of which the diffusion is compared in this
544 ON DECOMPOSITION BY LIQUID DIFFUSION.
paper, the potash salt uniformly exceeds in diffusibility the corre-
sponding soda salt; that the ratio between the two classes is always
sensibly the same, or exhibits only a small range of variation at the
temperature of the experiments, which was near 60°; with the peculiar
exception of the hydrates of potash and soda.
XIII.
ON THE APPLICATION OF LIQUID DIFFUSION TO
PRODUCE DECOMPOSITIONS.
From Chem. Soc. Journ. vol. iii. p. 60, 1851.
THE experiments to be described in the sequel of this paper were
conducted in the same manner as those contained in a late communica–
tion to the Royal Society." A set of phials, of nearly equal capacity,
were made use of, all cast in the same mould,
and further adjusted by grinding to a uniform
size of aperture. The dimensions for a phial,
(see Fig) were 38 inches in height, with a neck
0.5 inch in depth; aperture 1.25 inch in dia-
meter, and capacity to base of the neck, 2080
grains of water, or between 4 and 5 ounces.
For each phial a plain glass jar was also pro-
vided, 4 inches in diameter and 7 inches in
depth. The method of observing the diffusion of a salt will be best
explained by an example.
For my present object, it was necessary to observe the spontaneous
diffusion into pure water of several salts, already dissolved in 100 times
their weight of water. The phial was filled with such a solution of sal-
ammoniac, for instance, to the base of the neck, or, more correctly, to a
distance of exactly 0.5 inch from the ground surface of the lip. The
neck of the phial was then filled up with distilled water, a light float
being placed on the surface of the solution, and care taken to avoid
agitation, after the phial had been placed within the jar. The latter
was then filled up with distilled water, so as to cover the open phial to
the depth of an inch, which required about twenty ounces of water.
The saline liquid in the “solution-phial” is thus allowed to communi-
cate freely with the water of the “water-jar.” The water of the latter
forms an atmosphere into which salts spread or diffuse, escaping from
the solution-phial with different degrees of velocity. The phial and jar
1 “On the Diffusion of Liquids.” Read December 21, 1849.

ON DECOMPOSITION BY LIQUID DIFFUSION. 545
together form the “diffusion-cell.” The diffusion is interrupted by
placing a small plate of ground glass upon the mouth of the phial, and
raising the latter out of the jar. The amount of salt diffused, or the
“diffusion-product,” is learned by evaporating the water of the jar to
dryness, or with this and the following chlorides, by precipitating with
nitrate of silver.
The diffusion was always allowed to proceed for a period of exactly
seven days, unless another time is expressly mentioned. The experi-
ments were conducted in a vault, of which the temperature did not vary
more than one degree on either side 50 F.
The 1 per cent. Solution of sal-ammoniac, in the solution-phial,
would contain 20:8 grains of salt. Of this quantity of salt, 3.49 grs.
were found to diffuse out into the water-jar in the time mentioned, in
one experiment, and 3.36 grains in another experiment. The mean of
these two diffusion-products is 3:42 grs., which is, therefore, the quantity
of hydrochlorate of ammonia diffused out of the solution-phial, contain-
ing a 1 per cent. Solution of that salt, in a period of seven days.
The diffusion of a 1 per cent. solution of chloride of sodium, in
similar circumstances, gave, in eight cells, the following products: 3:02,
2.83, 2-86, 2.68, 274, 270, 2-80, and 2.94 grs., of which the mean is 2.85
grs. These results for the chlorides of ammonium and sodium approach
to the theoretical ratio of 1.4142 to 1-7.320, that is, of the square root of
2 to the square root of 3.
Anhydrous chloride of calcium gave 2:01 and 2:04 grs. in two experi-
ments; mean 2:02 grs.
Anhydrous chloride of magnesium gave 2:15 and 1.90 grs. ; mean
2:03 grs. These two earthy chlorides appear, therefore, to be equally
diffusible. I may place along with these results, the diffusion-products
which the alkaline hydrates, and a few other salts would have afforded
in similar circumstances, the latter numbers being deduced from experi-
ments detailed in the paper on the diffusion of liquids already referred to.
Salt Diffused from a 1 per cent. Solution in Equal Times.
Hydrate of potash, . & & * 4:84 grs.
53 soda, º g & tº 4'03 ,
Chloride of ammonium, & tº ſº 3:42 ,
33 potassium, * * e 3:42 ,
35 Sodium, . tº & & 2.85 ,
Sulphate of soda, {º & & ſº 2:35 ,
Chloride of calcium, . e & º 2:02 ,
39 magnesium, g © e 2:03 ,
Sulphate of lime, * * & & 1-21 ,
55 magnesia, . e g e 1.21 ,
2 M
546 ON DECOMPOSITION BY LIQUID DIFFUSION.
The alkaline hydrates have the highest diffusibility, being twice as
diffusive as the Sulphates of the same bases, and four times as diffusive
as the Sulphates of magnesia and lime. The Salts of potash and am-
monia, of the same acid, have an equal diffusibility, which is greater
than the diffusibility of the corresponding salts of soda.
Now it has been shown that, when two salts are dissolved together
in the solution-phial, they diffuse independently, each salt maintaining
its own rate of diffusion. Hence the possibility of separating salts to a
certain extent, by diffusion, in a manner analogous to the separation of
substances of unequal volatility by distillation. Further, decomposi-
tions may be effected by diffusion, such as the decomposition of alum,
the sulphate of potash being separated from the sulphate of alumina,
from the higher diffusibility of the former substance. -
It appeared probable, also, that, in a mixture of several salts, the
acids and bases would have a tendency to arrange themselves so as to
form the most diffusive compounds, when an opportunity for diffusion
was presented. This would be analogous to the sublimation of car-
bonate of ammonia, when carbonate of lime and hydrochlorate of
ammonia are heated together. As the order of affinity is often deter-
mined in mixed salts by volatility or insolubility, according to the
canons of Berthollet, so it may be regulated and determined, in a similar
sense, by diffusibility.
The application which I have particularly in view, is the possible
decomposition of the sulphates of potash and soda, and of the chlorides
of potassium and sodium, by means of lime, when the affinity of that
base for an acid is aided by the high diffusibility of the hydrate of
potash or of Soda. -
1. A solution was made of 1 part of sulphate of potash in 100 parts
of lime-water, with which six phials were filled, and placed to diffuse
in jars containing lime-water, instead of water simply, for the usual
period of seven days. To obtain the salts diffused, the fluid of the jars
was treated with an excess of bicarbonate of ammonia and evaporated
twice to dryness. The filtered liquid contained only sulphate and car-
bonate of potash, without a trace of lime. The proportions of these
salts found, indicated a diffusion-product from two phials of
Hydrate of potash, º º 1:08 grs. 23.69
Sulphate of potash, e e 3.48 , 76-31
*=-
4'56 , 100'00
The diffusion-product of the remaining four cells was similar:
Hydrate of potash, e º 2:19 grs. 21.66
Sulphate of potash, e º 7-94 , 78'34
10:13 , 100.00
ON DECOMPOSITION BY LIQUID DIFFUSION. 547
More than a fifth part of the diffused Salt appears thus to be hydrate
of potash, and a considerable decomposition of the sulphate of potash
has therefore taken place.
2. Sulphate of soda dissolved in lime-water, was diffused into lime-
water, in a precisely similar series of experiments.
The diffusion-product obtained in a set of four cells, appeared to
consist of -
Hydrate of soda, . & & 0.90 grs. 11:45
Sulphate of soda, . e & 6-87 , 88°55
7-77 , 100'00
Of another set of four cells, the diffusion-product was repre-
sented by—
Hydrate of soda, . i.e. tº 0.93 grs. 1322
Sulphate of soda, . & gº 6:10 , 86-78
7:03 100'00
The hydrate of soda formed and diffused, is very sensible, amount-
ing on an average to about 12 per cent. of the whole diffused salt.
It may be remarked that, although sulphate of soda may be justly
Supposed to require a less powerful affinity to decompose it than sul-
phate of potash, still the latter salt appears to yield to the action of the
lime to a greater extent than the former, in these experiments; the
weight of hydrate of potash diffused being fully double that of the
hydrate of soda. The result in question may be confidently referred to
the superior diffusibility of the hydrate of potash, and establishes,
beyond doubt, the nature of the agency by which the decomposition, in
both cases, is principally, if not wholly, effected.
The low diffusibility of the sulphate of lime (one fourth of that of
hydrate of potash) retains a large proportion of that Salt behind in the
solution-phial, where, indeed, it was deposited in crystals. It is proper
to remark, that a similar deposition of sulphate of lime took place in
lime-water containing so much as 1 per cent. of sulphate of potash or
sulphate of soda, in the course of two or three days, in a close vessel,
quite irrespective of diffusion. One of the solution-phials was found to
contain so much as 2.04 grains of hydrate of potash, formed in conse-
quence of this deposition of sulphate of lime, without any diffusion,
in the course of seven days. The same decomposition of sulphate of
potash, with deposition of sulphate of lime, was observed by Scheele,
and afterwards referred, by Berthollet, to the insolubility of the latter
salt, which enables the affinity of lime for sulphuric acid to prevail
over that of potash for the same acid.
548 ON DECOMPOSITION BY LIQUID DIFFUSION.
3. Similar solutions, of 1 per cent of chlorides of potassium and
sodium in lime-water, were diffused into lime-water.
Eight cells of chloride of potassium gave 25-51 grains of diffused
salt, containing only 0.04 grain of hydrate of potash.
Eight cells of chloride of sodium gave 20-77 grains of diffused salt,
containing no more than 0-08 grain of hydrate of soda.
The decomposition of the alkaline chlorides is so small as to be
barely sensible, not exceeding, in the most favourable case, more than
wºoth part of the salt diffused. Lime, therefore, appears incapable,
although aided by diffusion, to decompose the chlorides of potassium
and sodium to a sensible extent.
4. Solutions in lime-water were diffused of 0.25 and 0.5 per cent of
the alkaline sulphates, not with the view of increasing the product of
alkali, but for the purpose of observing the diffusion, where no deposi-
tion of sulphate of lime is possible, owing to the dilute condition of the
solutions. The experiments, however, come to be more liable to de-
rangement from currents produced by small changes of temperature,
and other accidental causes of dispersion, where the solution in the
phial differs so little in density from the water of the jar.
One set of four cells, containing the quarter per cent. Solution of
sulphate of potassa in lime-water, gave 0.321 gr. of hydrate of potash.
Another similar set gave 0.614 gr. of hydrate of potash. The hydrate
of soda diffused from four cells of the quarter per cent. Solution of sul-
phate of soda was 0.260 gr. The diffusion was always into lime-water.
The half per cent. Solution of sulphate of potash in lime-water gave
0.62 gr. hydrate of potash in two cells; or twice as much alkali as the
quarter per cent. Solution. The diffusion-product was altogether 2:60
grs, so that 23.85 per cent of the salt diffused consisted of hydrate of
potash. No sulphate of lime crystallized, or was deposited in the phial
or jar, in any of these experiments, so that the decomposition of the
sulphate of potash by lime cannot be referred in any degree to the in-
solubility of sulphate of lime, but must be ascribed entirely to the high
diffusibility of hydrate of potash.
5. Carbonate of lime dissolved in carbonic acid water, or a saturated
solution of bicarbonate of lime, was now applied to form a 1 per cent.
solution of sulphates of potash and soda. These solutions were diffused
from the phials into pure water, as the liquid atmosphere of the jars.
Decomposition of the alkaline Sulphate always took place, and without
any visible deposit of Sulphate of lime, but to a less extent than in the
preceding experiments with hydrate of lime. The proportion of potash
salts diffused in two pairs of cells was 4.86 and 5-84 grs. ; of which 0:26
and 0.30 gr. was carbonate of potash, or 5.35 and 6.2 per cent. of car-
bonate of potash. *
oN DECOMPOSITION BY LIQUID DIFFUSION. 549
The proportion of soda-salts diffused in two pairs of cells was 3:40
and 378 grs, of which 0:26 and 0.29 gr. was carbonate of soda ; or 7-65
and 7.67 per cent of carbonate of soda. The excess of carbonate of soda
diffused over the carbonate of potash, in these experiments, is probably
accidental.
The experiments on the decomposition of an alkaline sulphate by
means of carbonate of lime, aided by diffusion, are chiefly interesting, as
they illustrate a decomposition which may occur among the salts of the
soil, and with the formation of an alkaline carbonate, from a reaction
between carbonate of lime and an alkaline Sulphate, although the solu-
tions may be too dilute to admit of any separation of sulphate of lime
in the solid state.
But the decomposition of the chlorides of potassium and sodium is
a more important problem than that of the sulphates of potash and
soda. The direct diffusion of these chlorides with hydrate of lime
appears to be inadequate to produce this effect, for no more than a trace
of fixed alkali was obtained in the experiments already described. It
was further observed, that a saturated solution of the chlorides of potas-
sium and sodium in lime-water did not afford the Smallest appreciable
quantity of alkali by diffusion. Bicarbonate of lime had no greater
effect upon the alkaline chlorides. But the conjoint action of lime-
water and the sulphate of lime upon these chlorides gave better
results. .
6. Lime-water and solution of Sulphate of lime, both saturated solu-
tions, were mixed together in equal volumes, and the liquid was em-
ployed to dissolve 1 per cent. of chloride of sodium. The phials charged
with this solution were allowed to diffuse into pure water. After
separating the hydrate of lime from the water of the jars, the latter
exhibited only the faintest possible alkaline reaction due to soda. The
proportion of alkali was too minute to be appreciated by the alkali-
metrical method, although a quantity so small as 0.01 gr, could be
determined. To enable the hydrate and sulphate of lime to act upon
the chloride of sodium, it was found necessary first to heat the solution
before diffusion.
7. The solution of sulphate of lime, with an addition of 2 per cent.
of chloride of sodium, was kept at the boiling point for half an hour.
No deposition of sulphate of lime occurred then, or after the liquid
cooled. Two or three days afterwards, this solution was mixed with an
equal volume of lime-water, and diffused into pure water, for the short
period of three and a half days. The liquid of the jars was evaporated
to dryness, as usual, with an excess of pure carbonate of ammonia, to
precipitate the salts of lime. The hydrate of soda diffused in three
cells amounted to 0.234 gr., and the sulphuric acid to 0.209 gr. Allow-
550 ON DECOMPOSITION By LIQUID DIFFUSION.
ing the sulphuric acid to have diffused as sulphate of soda, and putting
out of consideration the undecomposed chloride of sodium which was
also diffused, we have a diffusion-product of
Hydrate of soda, . º & 0.234 gr.
Sulphate of soda, tº § 0.371 ,
- 0-605 ,
These quantities are necessarily small, from the form of the experi-
ment, but could easily be increased by enlarging the diffusing surface,
which is at present limited to the area of the aperture of the solution-
phial. They are amply sufficient, however, to establish the fact that
the united affinities of hydrate and sulphate of lime are sufficient to
decompose chloride of sodium, when aided by diffusion of the hydrate
of soda formed. Of chloride of potassium, we have reason to believe
that the decomposition would be more considerable in similar circum-
stances. -
Two phials of the same liquid, as in the last experiment, were dif–
fused into water for the longer period of seven days and eighteen hours.
The whole lime found afterwards in the water-jar, and precipitated by
the addition of carbonate of ammonia, was represented by 1:01 grain of
carbonate of lime. The soluble salts filtered from the last amounted
to 6:14 grains, and contained carbonate of soda equivalent to 0-646 gr.
of hydrate of soda, and sulphuric acid equivalent to 0.373 gr. of sul-
phate of soda. It is difficult to decide in what form the lime reached
the water-jar, but this earth was probably diffused out of the solution-
phial, partly as hydrate of lime, partly as sulphate of lime, but princi-
pally as chloride of calcium. The last two salts would destroy a portion
of free alkali in the evaporation, but the hydrate of Soda obtained, even
after this deduction, amounted to 10:52 per cent. of the whole salts
diffused. With a smaller quantity of chloride of sodium than 2 per
cent. in the original mixture, the alkali, although not increased in abso-
lute quantity, might no doubt come to form a considerably larger pro-
portion of the diffusion-product. - -
The experiments also throw a curious light upon the condition of
mixed salts. It follows, from the absence of hydrate of soda in the
diffusion product of the first experiments, that cold solutions of sul-
phate of lime and chloride of sodium may be mixed without decomposi-
tion, or without any sensible formation of Sulphate of soda. But on
heating, this change is induced, and it is permanent; sulphate of soda
is formed, and continues to exist in the cold solution : for it is the
decomposition of that salt alone, by hydrate of lime, which appears to
afford the diffused hydrate of Soda. More than one condition of equi-
librium is therefore possible for mixed solutions of sulphate of lime and
sº
ON THE CONCENTRATION OF ALCOHOL. 551
chloride of sodium. It would be interesting to submit such a mixture
to a diffusion experiment, after being kept for different periods. The
effects of time and temperature are so often convertible, that we might
anticipate a gradual formation of sulphate of soda. If such be the case,
we have an agency in the soil, by which the alkaline carbonates re-
quired by plants may be formed from the chlorides of potassium and
sodium, as well as from the sulphates of potash and soda ; for the
sulphate of lime generally present will convert those chlorides into
Sulphates. - -
The mode in which the soil of the earth is moistened by rain is
peculiarly favourable to separations by diffusion. The soluble salts of
the soil may be supposed to be carried down together, to a certain
depth, by the first portion of rain which falls, while they find after-
wards an atmosphere of nearly pure water, in the moisture which falls
last and occupies the surface stratum of the soil. Diffusion of the salts
upwards into this water, with its separations and decompositions, must
necessarily ensue. The salts of potash and ammonia, which are most
required for vegetation, possess the highest diffusibility, and will rise
first. The pre-eminent diffusibility of the alkaline hydrates may also
be called into action in the soil by hydrate of lime, particularly as
quicklime is applied for a top-dressing to grass lands.
XIV.
ON THE CONCENTRATION OF ALCOHOL IN SöMMERING's
- EXPERIMENTS.
From Brit. As80c. Rep. 1854 (Pt. ii.), p. 69.
THE author stated that when an open vessel is filled with a mixture
of alcohol and water and exposed to the air, the alcohol goes off first
and leaves the water; but if, as in Sömmering's experiments, a bladder
be completely filled with dilute alcohol, the liquid will decrease in bulk,
and the water pass through the membrane, leaving a much larger per-
centage of alcohol in the bladder. Sömmering describes the action of
membrane to be improved by coating it with isinglass. Prof. Graham
removed the membrane entirely, and made use of a septum of gelatin
itself. Cotton calico was coated several times with a solution of isin–
glass and allowed to dry. A retentive vessel was thus prepared, in
which alcohol in different states of dilution was placed, and kept between
552 LIQUID DIFFUSION APPLIED TO ANALYSIS.
100° and 12” Fahr, for twenty-four hours. Evaporation took place,
which was uniformly attended by concentration of the spirit:--
180 grammes of alcohol 0-860 gave 150 grims of 0.854
180 32 35 0-860 gave 146 , of 0.852
180 25 22 0.880 gave 146 , of 0.871
180 25 3) 0-900 gave 154 , of 0.888
or, the septum of gelatin alone acted exactly like the coats of bladder.
Eurther, it was observed that dry gelatin (isinglass) placed in alcohol
0-860 increased 11 per cent. in weight, and at the same time lowered
the gravity of the spirit to 0.857. There can be no doubt, therefore,
that gelatin per se separates water from alcohol, and the colliferous
tissues possess the same property. In the bladder experiment, the water
thus absorbed by the membrane evaporates from the outer surface, and
its place being constantly supplied from the dilute alcohol within, the
latter comes to be rapidly concentrated.
XV.
LIQUID DIFFUSION APPLIED TO ANALYSIS."
From Phil. Trans. 1861, pp. 183-224, [Roy. Soc. Proc. xi. 1860-62, pp. 243-247;
Annal. de Chimie, lxv. 1862, pp. 129-207; Chemical News, iv. 1861, pp. 86, 87;
Chem. Soc. Journ. xv. 1862, pp. 216-270; Liebig, Annal. cxxi. 1862, pp. 1-77,
cxxiii. 1862, pp. 90-112 ; Nuovo Cumento, xv. 1862, pp. 92-94; Paris Comptes
Rendus, liii. 1861, pp. 275-279; Phil. Mag. xxiii. 1862, pp. 204-223, 290-306,
368-380; Poggend. Annal. cxiv. 1861, pp. 187-192.] -
THE property of volatility, possessed in various degrees by so many
substances, affords invaluable means of separation, as is seen in the
ever-recurring processes of evaporation and distillation. So similar
in character to volatility is the Diffusive power possessed by all liquid
substances, that we may fairly reckon upon a class of analogous analy-
tical resources to arise from it. The range also in the degree of diffu-
sive mobility exhibited by different substances appears to be as wide as
the scale of vapour tensions. Thus hydrate of potash may be said to
possess double the velocity of diffusion of sulphate of potash, and sulphate
of potash again double the velocity of sugar, alcohol, and sulphate of
magnesia. But the substances named belong all, as regards diffusion,
* Received May 8,-Read June 13, 1861.
LIQUID DIFFUSION APPLIED TO ANALYSIS. 553
to the more “volatile” class. The comparatively “fixed” class, as
regards diffusion, is represented by a different order of chemical sub-
stances, marked out by the absence of the power to crystallize, which are
slow in the extreme. Among the latter are hydrated silicic acid, hydrated
alumina, and other metallic peroxides of the aluminous class, when they
exist in the soluble form; with starch, dextrin and the gums, caramel,
tannin, albumen, gelatine, vegetable and animal extractive matters.
Low diffusibility is not the only property which the bodies last enume-
rated possess in common. They are distinguished by the gelatinous
character of their hydrates. Although often largely soluble in water,
they are held in solution by a most feeble force. They appear singularly
inert in the capacity of acids and bases, and in all the ordinary chemical
relations. But, on the other hand, their peculiar physical aggregation
with the chemical indifference referred to, appears to be required in sub-
stances that can intervene in the organic processes of life. The plastic
elements of the animal body are found in this class. As gelatine
appears to be its type, it is proposed to designate substances of the class
as colloids, and to speak of their peculiar form of aggregation as the
colloidal condition of matter. Opposed to the colloidal is the crystalline
condition. Substances affecting the latter form will be classed as
crystalloids. The distinction is no doubt one of intimate molecular
constitution. -
Although chemically inert in the ordinary sense, colloids possess a
compensating activity of their own arising out of their physical proper-
ties. While the rigidity of the crystalline structure shuts out external
impressions, the softness of the gelatinous colloid partakes of fluidity,
and enables the colloid to become a medium for liquid diffusion, like
water itself. The same penetrability appears to take the form of cemen-
tation in such colloids as can exist at a high temperature. Hence a
wide Sensibility on the part of colloids to external agents. Another
and eminently characteristic quality of colloids, is their mutability.
Their existence is a continued metastasis. A colloid may be compared
in this respect to water while existing liquid at a temperature under its
usual freezing-point, or to a supersaturated saline solution. Fluid colloids
appear to have always a pectous" modification; and they often pass under
the slightest influences from the first into the second condition. The
solution of hydrated silicic acid, for instance, is easily obtained in a state
of purity, but it cannot be preserved. It may remain fluid for days or
weeks in a sealed tube, but is sure to gelatinize and become insoluble at
last. Nor does the change of this colloid appear to stop at that point.
* IImrrós, curdled. As fibrin, casein, albumen. But certain liquid colloid substances
are capable of forming a jelly and yet still remain liquefiable by heat and soluble in
water. Such is gelatine itself, which is not pectous in the condition of animal jelly;
but may be so as it exists in the gelatiferous tissues.
\ .
554 LIQUID DIFFUSION APPLIED TO ANALYSIS.
\ .*
For the mineral forms of silicic acid, deposited from water, such as flint,
are often found to have passed, during the geological ages of their exist–
ence, from the vitreous or colloidal into the crystalline condition (H. Rose).
The colloidal is, in fact, a dynamical state of matter; the crystalloidal
being the statical condition. The colloid possesses ENERGIA. It may
be looked upon as the probable primary source of the force appearing in
the phenomena of vitality. To the gradual manner in which colloidal
changes take place (for they always demand time as an element), may the
characteristic protraction of chemico-organic changes also be referred.
A simple and easily applicable mode of effecting a diffusive separa-
tion is to place the mixed substance under a column of water, contained
in a cylindrical glass jar of five or six inches in depth. The mixed
solution may be conducted to the bottom of the jar by the use of a fine
pipette, without the occurrence of any sensible intermixture. The
spontaneous diffusion, which immediately commences, is allowed to go on
for a period of several days. It is then interrupted by siphoning off the
water from the surface in successive strata, from the top to the bottom
of the column. A species of cohobation has been the consequence of
unequal diffusion, the most rapidly diffusive substance being isolated
more and more as it ascended. The higher the water column, suffi-
cient time being always given to enable the most diffusive substance
to appear at the summit, the more completely does a portion of that
substance free itself from such other less diffusive substances as were
originally associated with it. A marked effect is produced even where
the difference in diffusibility is by no means considerable, such as the
separation of chloride of potassium from chloride of sodium, of which
the relative diffusibilities are as 1 to 0.841. Supposing a third metal
of the potassium group to exist, standing above potassium in diffusibility
as potassium stands above sodium, it may be safely predicted that the
new metal would admit of being separated from the other two metals by
an application of the jar-diffusion above described. -
& A certain property of colloid substances comes into play most oppor-
tunely in assisting diffusive separations. The jelly of starch, that of
animal mucus, of pectin, of the vegetable gelose of Payen, and other solid
colloidal hydrates, all of which are, strictly speaking, insoluble in cold
water, are themselves permeable when in mass, as water is, by the more
highly diffusive class of substances. But such jellies greatly resist the
passage of the less diffusive substances, and cut off entirely other colloid
substances like themselves that may be in solution. They resemble
animal membrane in this respect. A mere film of the jelly has the
separating effect. Take for illustration the following simple experiment.
A sheet of very thin and well-sized letter-paper, of French manu-
facture, having no porosity, was first thoroughly wetted and then laid
LIQUID DIFFUSION APPLIED TO ANALYSIS. 555
upon the surface of water contained in a small basin of less diameter
than the width of the paper, and the latter depressed in the centre so as
to form a tray or cavity capable of holding a liquid. The liquid placed
upon the paper was a mixed solution of cane-sugar and gum-arabic,
containing 5 per cent. of each substance. The pure water below and
the mixed solution above were therefore separated only by the thickness
of the wet sized paper. After twenty-four hours the upper liquid
appeared to have increased sensibly in volume, through the agency of
osmose. The water below was found now to contain three-fourths of
the whole sugar, in a condition so pure as to crystallize when the liquid
was evaporated on a water-bath. Indeed the liquid of the basin was
only in the slightest degree disturbed by sub-acetate of lead, showing
the absence of all but a trace of gum. Paper of the description used is
sized by means of starch. The film of gelatinous starch in the wetted
paper has presented no obstacle to the passage of the crystalloid sugar,
but has resisted the passage of the colloid gum. I may state at once
what I believe to be the mode in which this takes place.
The sized paper has no power to act as a filter. It is mechanically
impenetrable, and denies a passage to the mixed fluid as a whole. Mole-
cules only permeate this septum, and not masses. The molecules also
are moved by the force of diffusion. But the water of the gelatinous
starch is not directly available as a medium for the diffusion of either
the sugar or gum, being in a state of true chemical combination, feeble
although the union of water with starch may be. The hydrated com-
pound itself is solid, and also insoluble. Sugar, however, with all
other crystalloids, can separate water, molecule after molecule, from any
hydrated colloid, such as starch. The sugar thus obtains the liquid
medium required for diffusion, and makes its way through the gelatinous
septum. Gum, on the other hand, possessing as a colloid an affinity for
water of the most feeble description, is unable to separate that liquid
from the gelatinous starch, and so fails to open the door for its own
passage outwards by diffusion.
The separation described is somewhat analogous to that observed in
a soap-bubble inflated with a gaseous mixture composed of carbonic acid
and hydrogen. Neither gas, as such, can penetrate the water-film.
But the carbonic acid, being soluble in water, is condensed and dissolved
by the water-film, and so is enabled to pass outwards and reach the
atmosphere ; while hydrogen, being insoluble in water, or nearly so, is
retained behind within the vesicle.
It may perhaps be allowed to me to apply, the convenient term
dialysis to the method of separation by diffusion through a septum of
gelatinous matter. The most suitable of all substances for the dialytic
septum appears to be the commercial material known as vegetable
556 LIQUID DIFFUSION APPLIED TO ANALYSIS.
parchment or parchment-paper, which was first produced by M. Gaine,
and is now successfully manufactured by Messrs. De la Rue. This is
unsized paper, altered by a short immersion in sulphuric acid, or in
chloride of zinc, as proposed by Mr. T. Taylor. Paper so metamorphosed
acquires considerable tenacity, as is well known; and when wetted it
expands and becomes translucent, evidently admitting of hydration. A
slip of 25 inches in length was elongated 1 inch in pure water, and 12
inch in water containing 1 per cent. of carbonate of potash. In the
wetted state parchment-paper can easily be applied to a light hoop of
wood, or, better, to a hoop made of sheet gutta percha, 2 inches in depth
and 8 or 10 inches in diameter, so as to form a vessel like a sieve in
FIG. 1. —Hoop Dialyser. form (fig. 1). The disc of parch-
§ ment-paper used should exceed in
i º #º f diameter the hoop to be covered by
sºliºiº. º 3 or 4 inches, so as to rise well round
the hoop. It may be bound to the
hoop by string, or by an elastic band,
G|| † sº but should not be firmly secured. The
jº º parchment-paper must not be por-
ºiliº º ous. Its soundness will be ascer-
（IIT tained by sponging the upper surface
àE with pure water, and then observing
= that no wet spots show themselves
on the opposite side. Such defects may be remedied by applying liquid
albumen, and then coagulating the same by heat. Mr. De la Rue
recommends the use of albumen in cementing parchment-paper, which
thus may be formed into cells and bags very useful in dialytic experi-
ments. The mixed fluid to be dialysed is poured into the hoop upon the
surface of the parchment-paper to a small depth only, such as half an
inch. The vessel described (dialyser) is then floated in a basin contain-
ing a considerable volume of water, in order to induce the egress of the
diffusive constituents of the mixture. Half a litre of urine, dialysed for
twenty-four hours, gave its crystalloidal constituents to the external
water. The latter, evaporated by a water-bath, yielded a white Saline
mass. From this mass urea was extracted by alcohol in so pure a
condition as to appear in crystalline tufts upon the evaporation of the
alcohol.
º
sºlº
º:
:
|
S
1. Jar-diffusion.
The mode of diffusing more lately followed, which I have already
alluded to as jar-diffusion, is extremely simple, and gives results of more
precision than could possibly be anticipated. The salt is allowed to rise


LIQUID DIFFUSION APPLIED TO ANALYSIs. 557
from below into a cylindrical column of water, and after a fixed time,
the proportion of salt which has risen to various heights in the column
is observed. The water was contained in a plain cylindrical glass jar,
of about 152 millimetres (6 inches) in height and 87 millimetres (3:45
inches) in width. In operating, seven-tenths of a litre of water were
first placed in the jar, and then one-tenth of a litre of the liquid to be
diffused was carefully conveyed to the bottom of the jar by means of a
fine pipette. The whole fluid column then measured 127 millimetres
(5 inches) in height. So much as five or six minutes of time were occu-
pied in emptying the pipette at the bottom of the jar, and extremely
little disturbance was occasioned in the Superincumbent water, as could be
distinctly seen when the liquid introduced by the pipette was coloured.
The jar was then left undisturbed, to allow diffusion to proceed; the
experiments being always conducted in an apartment of constant, or
nearly constant, temperature. When a certain time had elapsed, the
diffusion was interrupted by drawing off the liquid from the top, by
means of a small siphon, slowly and deliberately as the liquid had been
first introduced, in portions of 50 cubic centimetres, or one-sixteenth of
the whole volume. The open end of the short limb of the siphon was
kept in contact with the surface of the liquid in the jar, and the portion
of liquid drawn off was received in a graduated measure. By evapo-
rating each fraction separately, the quantity of Salt which had risen into
equal sections of the liquid column was ascertained. From the bottom
of two jars, A and B for instance, a 10 per cent solution of chloride of
sodium was diffused for a period of fourteen days. The whole quantity
of salt present in each jar was 10 grammes, which was found at the end
to be distributed as follows in the different sectional strata of fluid,
numbering them from the top downwards:—
In the first or highest stratum, 0.103 and 0-105 gramme of salt in
A and B respectively; in the second stratum, 0.133 and 0-125; in the
third stratum, 0.165 and 0.158; in the fourth stratum, 0.204 and 0.193;
in the fifth stratum, 0.273 and 0.260; in the sixth stratum, 0.348 and
(0.332; in the seventh stratum, 0.440 and 0.418; in the eighth stratum,
0.545 and 0.525; in the ninth stratum, 0.657 and 0.652; in the tenth
stratum, 0-786 and 0-747; in the eleventh stratum, 0.887 and 0.875; in
the twelfth stratum, 0.994 and 0.984; in the thirteenth stratum, 1-080
and 1.000; in the fourteenth stratum, 1:176 and I-198; in the fifteenth
and sixteenth strata together, 2.209 and 2.324 grammes. With differ-
ences so moderate in amount between corresponding strata in the two
experiments, this method of observing diffusion may claim a consider-
able degree of precision.
In similar experiments made at the same time and temperature with
sugar, gum-arabic and tannin of nut-galls, the final distribution of each
558 LIQUID DIFFUSION APPLIED TO ANALYSIS.
substance was different in each case, and the results may be placed
together in illustration of unequal diffusibility, as exhibited by this
method of observation. Two experiments were made on each substance,
as with chloride of sodium, but the mean result only need be stated.
TABLE I.—Diffusion of 10 per cent solutions (10 grammes of substance
in 100 cub. cent. of fluid) into pure water, after fourteen days, at
10° (50°Fahr)

Number of *
sº§:* Cºlºr Sugar. Gum. Tannin,
I *104 •005 •003 •003
2 • 129 •008 •003 •003
3 • 162 •012 •003 •004
4 • 198 •016 *004 •003
5 •267 •030 •003 •005
6 •340 •059 *004 •007
7 '429 •] 02 •006 •017
8 ‘535 • 180 •031 •03]
9 '654 •305 •097 •069
10 •766 '495 “215 •145
II ‘881 •740 '407 •288
12 •99] l:075 •734 •556
13 1-090 1°435 1-157 1*050
14 1-187 1758 . 1731 1719
15 and 16 2°266 3.783 5-601 6:097
9-999 10:003 9-999 9-997
The superimposed column of water being 111 millimetres (4.38
inches) in height, the chloride of sodium, it will be observed, has diffused
in sensible quantity to the top, and could have risen higher; the upper
layer being found to contain 0-104 gramme of Salt, or 1 per cent. of the
whole quantity present. The apex of the diffusion column of sugar
appears to have just reached the top of the liquid in the fourteen days of
the experiment, for '005 gramme only of that substance is found in the
first stratum, followed by 008, '012, '016, and 0.30 in the following strata.
Again, no gum appears to be carried by diffusion higher than the seventh
stratum (2:2 inches), which stratum contains 006 gramme, followed by
-031 gramme in the eighth stratum. The minute quantities of substance
shown in the first to the sixth stratum, and which do not altogether
exceed 020 gramme, are no doubt the result of accidental dispersion,
arising probably from a movement of the upper fluid occasioned by
slight inequalities of temperature. The diffusion of tannin is even less
advanced than that of gum ; but the former numbers are apparently influ-
LIQUID DIFFUSION APPLIED TO ANALYSIS. 559
enced by a partial decomposition, to which tannin is known to be liable,
and which gives rise to new and more highly diffusible substances.
Experiments continued, like those last described, for a constant time,
do not exhibit the exact relative diffusibilities, although these could be
obtained by proceeding to ascertain, by repeated trial, the various times
required to bring about a similar distribution and equal amount of diffu-
sion in all the salts. The numbers observed, however, may afford data
for the deduction of the relative diffusibilities by calculation.
A particular advantage of the new method is the means which it
affords of ascertaining the absolute rate or velocity of diffusion. It
becomes possible to state the distance which a salt travels per second in
terms of the metre. It is easy to see that such a constant must enter
into all the chronic phenomena of physiology, and that it holds a place
in vital science not unlike the time of the falling of heavy bodies in the
physics of gravitation. It may therefore be not amiss to place here in
a short tabular form the results observed of the diffusion of a few more
substances, conducted in the same manner as the preceding.
TABLE II.-Diffusion of 10 per cent. solutions for 14 days.

Number of
ºve mi.º.o. tº a.º.
1 •007
2 •011
3 •018
4 •027
5 •049
6 •085 ...... •003
7 *133 ...... •005
8 •218 •010 •010
9 •331 •015 •023
10 - •499 •047 •033
11 •730 •l 13 •075
12 1-022 "343 “215
13 I-383 •855 •705
14 1-803 1-892 I-725
10-000 I0-000 10-000
The Sulphate of magnesia was anhydrous. The albumen was puri-
fied by Wurtz's method. The caramel was partly purified by precipita-
tion by alcohol, as recommended by Frémy, and further by other means
which will again be referred to. It will be remarked that the diffusion
of sulphate of magnesia exhibited above is very similar to that of sugar
in a former Table, but is slightly less advanced. The similarity in
560 LIQUID DIFFUSION APPLIED TO ANALYSIS.
diffusibility of these two substances had already been observed in the
experiments of former papers. The fall in rate on passing from these
crystalloids to the colloids tannin, albumen, and caramel, is very striking.
The elevation in the liquid column attained by albumen or by caramel
is moderate indeed compared with that of crystalline substances. Of
albumen, which will be looked upon with most interest, no portion
whatever was found in the seven higher strata. It appeared to the
extent of 0.010 gramme in the eighth stratum, 0.015 in the ninth
stratum, 0.047 in the tenth stratum, 0.113 in the eleventh stratum,
0.343 in the twelfth stratum; while the great mass of this substance
remained in the four lower strata. The diffused albumen did not
appear to lose its coagulability, or to be otherwise altered. It will be
seen immediately that the diffusion of sugar advances as much in two
days as the albumen above in fourteen days (Table IV.).
The diffusion of caramel is the slowest of all, and does not much
exceed in fourteen days the diffusion of sugar in a single day.
It was considered useful to possess examples of the progress of dif-
fusion, in one or two selected substances, for successive periods of time,
so as to exemplify the continuous progress of diffusion in these sub-
stances. Such a chronological progress of diffusion in a particular
substance becomes a standard of comparison for single experiments on
the diffusion of other substances. The substances selected were chloride
of sodium and cane-sugar.
TABLE III.-Diffusion of a 10 per cent. solution of Chloride of Sodium
in different times.


Number of In four days, In five days, In seven days, In fourteen
stratum. at 9° to 10°. at 11°75. at 9°. days, at 10°.
1 •004 •004 •013 "104
2 •004 •006 •017 • 129
3 •005 •011 •028 • 162
4 •011 •020 •051 • 198
5 •023 •040 •081 •267
6 •040. •075 *134 •340
7 •080 *134 “211 •429
8 •145 •233 •318 •535
9 •261 •368 *460 •654
10 •436 ‘589 •640 •766
11 •706 -762 •850 •881
12 1.031 I-090 1.057 •991
13 1-416 1.357 1.317 1.090
14 1-815 1.697 1.527 1-187
15 and 16 4'023 3°613 3°294 2°266
10'000 9-999 9.998 9-999
LIQUID DIFFUSION APPLIED TO ANALYSIS. 561
TABLE IV.-Diffusion of a 10 per cent, solution of Cane-sugar in
"different times.



Number of In one day, In two days, In six days, In seven days, In eight days, In fourteen
stratum. at 10° 75. at 10°. at 9°. ’ at 9°. at 9°. days, at 10°.
l ...... . ...... •001 •002 •002 •005
2 ...... . ...... •002 •002 •003 •008
3 | ...... . ...... •002 •003 •003 •012
4 ...... I ...... •002 •004 •004 •016
5 ...... . ...... •003 •004 •007 •030
6 ...... ...... •005 •007 •012 •059
7 | ...... . ...... •011 •020 •031 •] 02
8 002 002 •024 •051 -072 • 180
9 •002 •008 •071 • 121 *154 •305
10 •005 •027 -170 •260 •304 •495
11 •024 -107 •376 •507 *555 •740
12 •133 *344 -727 •897 •858 1.075
13 '597 •930 1.282 1-410 1°365 1-435
14 I '850 1-940 1:930 1-950 1955 1758
15 and 16 7:386 6-641 5:392 4:760 4'674 3.783
9-999 9-999 9.998 9.998 9-999 10-003
The scheme of the diffusion of the chloride of sodium may afford
terms of comparison for the metallic salts, acids and other highly
diffusible substances, while the scheme of sugar will be found more
useful in appreciating the diffusion of organic and other less diffusible
substances. In comparing the two Tables together, it appears that
a fourteen days' diffusion of Sugar is greater in amount than a four
days' diffusion of chloride of sodium, but less than a five days' dif-
fusion of the same substance. The diffusion of chloride of sodium
appears to be pretty nearly three times greater (or more rapid) than
that of Sugar.
The following experiments were made upon hydrochloric acid and
chloride of sodium at a somewhat lower temperature and for times
which are different, but which give a nearly equal diffusion for each
substance.
TABLE TV. bis—
2
N
562 LIQUID DIFFUSION APPLIED TO ANALYSIS.
TABLE IV. bis—10 per cent. solutions.

Hydrochloric acid, Chloride of sodium,
Number of stratum. in grammes. in grammes.
Three days at 5°. Seven days at 5°.
I •003 •003
2 •006 •009
3 •012 •010
4 •022 •026
5 •043 •055
6 •086 •082
7 •162 • 165
8 *308 •270
9 •406 '403
I 0 •595 •595
11 •837 •823
12 1-080 1-085
13 - 1-163 1:270
14 1-578 I-615
15 and 16 3.699 3'589
10:000 10'000
The diffusion of hydrochloric acid in three days corresponds closely
with the diffusion of chloride of sodium in seven days. The times of
equal diffusion for these two substances, at the temperature of the
experiment, appear accordingly to be 1 (hydrochloric acid) and 2:33
(chloride of sodium). Hydrochloric acid and the allied hydracids, with
other monobasic acids, are the most diffusive substances known. The
general results of several series of experiments may be expressed approxi-
mately by the following numbers:–
Approximate times of equal diffusion.
Hydrochloric acid, . ë * 1
Chloride of sodium, . e e 2-33
Sugar, . º we te e 7
Sulphate of magnesia, e e 7
Albumen, º e • . . 49
Caramel, º º * e 98
It is curious to observe the effect of changing the liquid atmosphere
in which diffusion takes place, which is water in all these experiments,
and replacing it by another fluid, namely alcohol. Two substances
were diffused in the usual manner, but with this difference, that the
substances were dissolved in alcohol, and the solutions placed under a
column of the same liquid in the jar. The alcohol was of sp. gr. 0-822
(90 per cent.) .
LIQUID DIFFUSION APPLIED TO ANALYSIS.
§63
TABLE W.-Diffusion in Alcohol of 10 per cent, solutions of Iodine and
of Acetate of Potash in seven days.
f
Number of stratum. Iodine at 14". Aeºn,
l •028 •055
2 •033 •057
3 •046 •06]
4 •038 •063
5 •037 •064
6 •039 •066
7 •081 •070
8 • 143 •071
9 •263 •072
10 •417 •095
11, •637 •285
12 •936 | •619
13 I-235 | 1:157
14 1.506 : I-907
15 and 16 4-561 5-358
10-000 10-000
TABLE V. bis—Diffusion in Alcohol of a 10 per cent, solution of Resin,
for seven days, at 14°5.

Number in stratum.
Diffusate, in grammes.
15 and 16
-017
-017
•018
•017.
•019
•020
•022
•024
•025
•08U
•210
•498
•992
1:700
6:34.1
10-000
564 LIQUID DIFFUSION APPLIED TO ANALYSIS.
The experiments were conducted in the absence of light, and there
is no reason to believe that the iodine acted chemically upon the alcohol.
The diffusion is more advanced in the iodine than in the acetate of
potash, but in both is moderate in amount, confirming the early experi-
ments with phials, which appeared to show that the diffusion process
was several times slower in alcohol than in water. The small quantities
of iodine found in each of the six superior strata are nearly equal, and
were no doubt accidentally elevated by the mobility of this fluid, arising
from its high dilatability by heat compared with that of water at the
same low temperature. The diffusion may be considered then as com—
fined to the nine lower strata, and considerably resembles that of Sugar
in water for eight days.
The diffusion of acetate of potash is still less advanced than that of
iodine, and is probably confined to the six lower strata, the salt found
in the higher strata presenting in its distribution the appearance of
having been carried there by a movement of the fluid consequent upon
heat-dilatation, and not by diffusion. The diffusion of acetate of
potash in alcohol observed during seven days approximates to that of
sugar in water during six days (Table IV.)
I now proceed to observations of the simultaneous diffusion of two
substances in the same fluid. The great object of this class of experi-
ments was to separate salts of unequal diffusibility, and to test the
application of diffusion as an analytical process. A mixture of two
salts being placed at the bottom of the jar, it may be expected that the
salts will diffuse pretty much as they do when they are diffused sepa-
rately; the more diffusive salt travelling most rapidly, and showing
itself first and always most largely in the upper strata. The early ex-
periments of diffusion from phials had shown indeed that inequality of
diffusion is increased by mixture, and the actual separation is conse-
quently greater than that calculated from the relative diffusibilities of
the mixed substances. Chlorides of potassium and sodium diffuse
nearly in the proportion of 1 to 0.841, according to the earlier experi-
ments. They may afford, therefore, the means of observing the amount
of separation that may be produced by a very moderate difference in
diffusibility. A mixture of 5 grammes of each salt in the usual 100
cub. cent. of water was diffused.
TABLE VI.—
LIQUID DIFFUSION APPLIED TO ANALYSIS. 565
TABLE VI.-Diffusion of a mixture of 5 per cent of Chloride of Potas-
sium and 5 per cent. of Chloride of Sodium, for seven days, at
12° to 13°.
Number of stratum. |Chloride of potassium. Chloride of sodium. Total diffusate.
l •018 •014 •032
2 •025 •015 •040
3 •044 •014 •058
4 •075 •017 •092
5 • 101 •034 • 135
6 •] 41 *063 •204
7 •185 *104 •289
8 •252 • 151 '403
9 "330 •212 *542
10 •349 •351 -700
11 •418 •458 •876
12 •511 •559 1-070
13 •552 •684. 1.236
14 •615 •772 1-387
15 and 16 1-385 I-551 2°936
5'001 4'999 10-000

In the upper part of the Table chloride of potassium always appears
in excess, but not in so large a proportion in the first three strata as in
the fourth. This inequality may be partly owing to mechanical dis-
persion of the mixed solution, but is to be referred chiefly, I believe, to
errors of analysis from a loss of the chloride of potassium difficult to
avoid in the determination of minute proportions of that salt by means
of chloride of platinum. Of 92 milligrammes of salt found in the fourth
stratum, 75 milligrammes, or 81°5 per cent, are chloride of potassium.
The first six strata contain together 561 milligrammes, of which 404
milligrammes, or 72 per cent, that is nearly three-fourths, are chloride
of potassium. We have to descend to the tenth stratum before the
salts are found in equal proportions. The progression is then inverted,
and chloride of sodium comes to preponderate in the lower strata.
It is evident that the preceding experiment might be so con–
ducted as to diffuse away the chloride of potassium and leave below
a mixture containing chloride of sodium in relative excess, to as great
an extent, as the chloride of potassium is found above, in the last
experiment. -
Further, the mixture in which chloride of potassium was concen-
trated in the experiment described, so as to form 72 per cent. of the
whole mixture, might be subjected again to diffusion in the same
manner. In an experiment upon a mixture of 7.5 grammes of chloride
566 LIQUID DIFFUSION APPLIED TO ANALYSIS.
of potassium and 2.5 grammes of chloride of sodium, the six upper
strata gave 640 milligrammes of salt, of which 610 milligrammes, or
95.3 per cent, were chloride of potassium. It is obvious that by repeat-
ing this diffusive rectification a sufficient number of times, a portion
of the more diffusive salt might be obtained at last in a state of sensible
purity.
The preceding example illustrates the separation of unequally diffu-
sive metals or bases; the following example, on the other hand, the
separation of unequally diffusive acids united with a common base.
Chloride of sodium and sulphate of soda diffuse separately in the phial
experiments in the proportion of 1 to 0707.
TABLE VII.-Diffusion of 5 per cent of Chloride of Sodium and
5 per cent of anhydrous Sulphate of Soda, for seven days, at
10° to 10°75.
Number of stratum. ºn. sº8, º
l •009 | ...... •009
2 •013 •001 *014
3 •024 •002 •026
4 •038 •003 *04]
5 •060 •006 •066
6 •095 :012 -107
7 *141 •029 -170
8 •203 •059 •262
9 •278 •II 5 *393
10 - "360 •205 *565
Il •473 •317 •790
12 '560 •507 1-067
13 •637 •694 I'331
14 •718 ‘909 I-627
15 and 16 1°390 2°141 3’531
4°999 5'000 9-999

Here the separation is still more sensible than before with the bases.
The six upper strata contain 263 milligrammes of salt, of which 239
milligrammes, that is 90.8 per cent, are chloride of sodium. The salt
of the upper eight strata amounts to 695 milligrammes, of which 583
milligrammes, or 83.9 per cent, are chloride of sodium.
How long the diffusion should be continued in a liquid column of
limited height, such as in these experiments, so as to produce the
greatest separation, is a question of some interest, which can only
LIQUID DIFFUSION APPLIED TO ANALYSIS. 567
be answered by experiment. The last diffusion was accordingly re-
peated, with the difference that it was continued for double the former
time.
TABLE VIII.-Diffusion of 5 per cent of Chloride of Sodium and 5 per
cent of Sulphate of Soda, for fourteen days, at 10 to 11”.

Number of stratum. chlºº, sº Tºº
l .077 •005 •082
2 •089 •009 •098
3 • 105 •014 •119
4 • 130 •026 • 156
5 • 161 •044 •205
6 • 199 •072 -271
7 •240 • 111 -35I
8 •289 "I'73 •462
9 •337 •241 •578
10 •392 “334 •726
11 °433 °433 •866
12 •487 •539 1-026
13 ‘525 •646 I-171
14 *555 •745 I -300
15 and 16 •979 1.609 2.588
4°998 5-001 9-999
The salt contained in the three upper strata amounts to 299 milli–
grammes, of which 271, or 90.6 per cent. of the whole, are chloride of
sodium. The upper five strata yield 660 milligrammes of salt, of which
562 milligrammes, or 85.1 per cent, are chloride of sodium. These
proportions are not dissimilar to those deduced from the former Table,
and show that little is gained in the way of separation by extending the
diffusion-period from seven to fourteen days; unless indeed the column
of fluid be increased in height at the same time.
It might be worth observing whether the separation of two unequally
diffusive metals can be favoured by varying the acid, or form of combi-
nation; whether, for instance, the hydrates of potash and soda would
not separate to a greater extent than has been observed of the chlorides
of potassium and sodium, the separate diffusibilities of the former sub-
stances being as 1 to 0-7, while that of the latter are as 1 to 0.841. I
have not, however, pursued this branch of the subject.
The separation of the same metals from each other may possibly be
favoured in another manner. In the preceding experiments (Table VI)
the two metals were in union with the same acid, or rather both were
568 LIQUID DIFFUSION APPLIED TO ANALYSIS.
in the state of chloride. But the metals might be used in combination
with different acids, and these acids themselves might be of equal or of
unequal diffusibility. If of equal diffusibility, such as nitric and hydro-
chloric acids, no reason appears why the acids should affect the amount
of separation. But if the acids are unlike in diffusibility, the case is
not so clear. If, for instance, the potassium were in the form of chloride
and the sodium of that of sulphate, might not the diffusion of the
potassium be promoted by the highly diffusive chlorine with which it is
associated, and the diffusion of the soda, on the other hand, be retarded by
its association with the slowly diffusive sulphuric acid 2 Will, in fine,
the separation of the metals be greater from a mixture of chloride of
potassium and sulphate of soda, or even from sulphate of potash and
chloride of sodium, than from the two chlorides, or from the two
sulphates? The inquiry, it will be remarked, raises the whole question
of the distribution of acid and base in solutions of mixed salts. It will
be illustrated by a comparison of the diffusion of chloride of potassium
mixed with sulphate of soda, with the diffusion of sulphate of potash
mixed with the chloride of sodium, the salts being taken in equivalent
proportions.
TABLE IX.-Diffusion of a mixture of 5:12 per cent. of Chloride of
Potassium and 4.88 per cent. of Sulphate of Soda (equivalent
proportions), for seven days, at 14.

l •028 •002 •024
2 •035 •002 •030
3 •048 •004 •045
4 •064 •009 •066
5 •092 •016 -097
6 • 128 •032 • 149
7 • 174 •058 •215
8 •242 •I 05 •316
9 & e º ge tº e *441
10 •615
| 1 •815
12 1-042
13 tº tº tº º is 1°290
14 we ſº tº * tº g 1.517
15 and 16 tº º º tº º º 3°346
I0-008
LIQUID DIFFUSION APPLIED TO ANALYSIS. 569
TABLE X—Diffusion of a mixture of 4:01 per cent. of Chloride of
Sodium and 5.99 per cent of Sulphate of Potash (equivalent pro-
portions), for seven days, at 14°.

Number of stratum. # º: sº 3. º
I •028 •002 •023
2 *034 •002 •030
3 •049 •004 •044
4 *064 •009 •065
5 •092 •015 •096
6 • 128 •031 * •149
7 •172 *059 •219
8 •242 *104 •315
9 e e & e - - •435
10 •600
11 •797
12 1*025
13 © e e - e. e. 1 *261
14 to e e © º e 1°480
15 and 16 tº e ºs - e - 3°467
10-016
The weight of the mixed salt was always 10 grammes. The diffu-
sions exhibited in the two Tables are strikingly similar, and indeed may
be considered as identical. It thus appears that the diffusion of the
metals is not affected by the acid with which they are in combination.
The result is quite in harmony with Berthollet's view, that the acids
and bases are indifferently combined, or that a mixture of chloride of
potassium and Sulphate of Soda is the same thing as a mixture of sul-
phate of potash and chloride of sodium, when the mixtures are in a
state of solution. With two acids very unequal in their affinity for
bases, the result possibly might be very different.
2. Effect of Temperature on Diffusion.
Diffusion is promoted by heat, and separations may accordingly be
effected in a shorter time at high than at low temperatures. In a series
of observations made upon hydrochloric acid, the diffusion of that sub-
stance was carefully determined at 15°-5 (60°F), and at three higher
points, advancing by 11°11 (20°F). The ratios of the diffusions observed
were as follows:—
Diffusion of hydrochloric acid at 15°55 (60°F), I
}} }} at 26°66 (80°F), 1:3545
35 52 at 37°77 (100°F), 17732
}} 35 at 48°88 (120°F), 2:1812
570 LIQUID DIFFUSION APPLIED TO ANALYSIS.
\
The increments of diffusibility, 0.3545, 0.4187, and 0.408 for equal
increments of temperature, are probably affected by small errors of
observation, but they appear to indicate that the diffusion increases at a
higher, although not greatly higher, rate than the temperature. The
average increase of diffusibility for the whole range of temperature
observed is 0.03543, or 3's for each degree (0.01969, or #o nearly for
1°F)
The preceding experiments were made by diffusing a 2 per cent.
solution of hydrochloric acid from wide-mouth phials immersed in a jar
FIG. 2. of water, as in my former experiments." The times were
e—s observed in which an equal amount of the acid (0.777
| - gramme from three phials) was diffused out. These
------------ ~1 times of equal diffusion were 72 hours at 15°55 (60°F);
53-15 hours at 26°66 (80° F); 40.6 hours at 37°77
(100°F); and 33 hours at 48°88 (120°F)
The diffusate from a 2 per cent. solution of chlo-
ride of potassium in similar circumstances was 0-6577

S-E- gramme,
In 101.75 hours, at 15°55 (60°F); and
In 4193 hours, at 48°88 (120°F)
The diffusate from a 2 per cent. solution of chloride of sodium was
0.6533 gramme,
In 12475 hours, at 15°55 (60°F);
In 49-60 hours, at 48°88 (120°F).
In equal times the diffusate would be
For chloride of potassium at 15°55 (60°F), 1
35 35 at 48°88 (120°F), 2.426
For chloride of sodium at 15°55 (60°F), I
35 33 at 48°88 (120°F), 2:5151.
As the ratio between the diffusates of hydrochloric acid, at the same
two temperatures, was I to 2-1812, it appears that the acid is less
increased in diffusibility than the salts at the higher temperature; chlo-
ride of sodium also is slightly more increased than chloride of potassium.
The more highly diffusive the substance the less does it appear to gain
by heat. Chloride of sodium appears to be sensibly 23 times more
diffusible at 48°88 (120°F) than at 15:55 (60°F): this gives an average
increase of 0:014, or ºr for 1 degree (0.025 for 1°F., or #3. The inequa-
lity of diffusion which the three substances referred to exhibit at a low
temperature becomes therefore less at high temperatures; and it would
* Philosophical Transactions, 1850, p. 25.
LIQUID DIFFUSION APPLIED TO ANALYSIS. 57.1
appear to be the effect of a high temperature to assimilate diffusi-
bilities. Heat, then, although it quickens the operation of diffusion,
does not appear otherwise to promote the separation of unequally diffu-
sive substances.
The results in such experiments are less disturbed by changes of
temperature, if at all gradual, than might be supposed. A sensible
separation was obtained of hydrochloric acid and chloride of sodium from
each other, in a solution containing 2 per cent of each substance, when
the water-jar was heated up from 15°55 to 95°C. in two hours, and
maintained at the latter temperature during four hours more. Diffusion
appeared to be accelerated about six times at the higher temperature.
At low temperatures, again, diffusion is proportionally slow. The
ratio of diffusibility of the following salts at two different temperatures
appeared to be,
For chloride of potassium at 5°-3 (41°5 F), 1; at 16°-6 (62°F. ), 1.4413
For chloride of sodium at 5°-3 (41°5 F), 1 ; at 17°4 (63°4 F.), 14232
For nitrate of soda at 5°-3 (41°5 F), 1; at 17°4 (63°4 F.), 14475
For nitrate of silver at 5°-3 (41°5 F), 1; at 17°-4 (63°4 F.), 13914
The salts are unequally affected to a sensible extent; and it will be
observed that the superiority of chloride of potassium over chloride of
sodium, in diffusibility, is increased at the low temperature.
Within the range of temperature of the preceding experiments, the
diffusibility of chloride of sodium being taken as 1 at 17°4 (63°4 F.), it
becomes 0-7026 at 5°3 (41°5 F); or it diminishes 0.0246, or #4, for a
40-72
e 9 /ſ). I wº Q
depression of 1 (0-0136, or #3, for a depression of 1°F)
3. Dialysis.
Passing from liquid diffusion in the water-jar, I may advert first to
the diffusion of crystalloids through a gélatinous or colloid mass, the
circumstance of the experiment being varied as little as possible from
those of jar-diffusion.
Ten grammes of chloride of sodium and 2 grammes of the Japanese
gelatine, or gelose of Payen, were dissolved together in so much hot
water as to form 100 cub. cents. of fluid. Introduced into the empty
diffusion-jar and allowed to cool, this fluid set into a firm jelly, occupy-
ing the lower part of the jar, and containing of course 10 per cent. of
chloride of sodium. Instead of placing pure water over this jelly, it
was covered by 700 cub, cents, of a solution containing 2 per cent of
the same gelose, cooled so far as to be on the point of gelatinizing ; the
jar at the same time being placed in a cooling mixture, in order to
expedite that change. The jar with its contents was now left undis-
572 LIQUID DIFFUSION APPLIED TO ANALYSIS.
turbed for eight days at the temperature 10°. After the lapse of this
time the jelly was removed from the jar in successive portions of 50
cub. cents, each from the top, and the proportion of chloride of sodium
in the various strata ascertained. The results were very similar to
those obtained in diffusing the same salt in a jar of pure water. The
diffusion in the gelose appeared more advanced in eight days than dif-
fusion in water for seven days, as will be seen by comparing the gelose
experiment below with a water experiment on chloride of sodium which
had been conducted at nearly the same temperature (Table III.)
TABLE XI.-Diffusion of a 10 per cent. solution of Chloride of Sodium
in the jelly of gelose, for eight days, at 10°.
Number of Diffusate,
stratum. in grammes.
•015
•015
•026
•035
•082
*130
"212
‘350
*486
•630
•996
I-172
1:190
14 I 203
15 and 16 3:450
:
9-992
Diffusion of a crystalloid thus appears to proceed through a firm
jelly with little or no abatement of velocity. With a coloured crystal-
loid, such as bichromate of potash, the gradual elevation of the salt to
the top of the jar is beautifully illustrated. On the other hand, the
diffusion of a coloured colloid such as caramel through the jelly, appears
scarcely to have begun after eight days had elapsed. The diffusion of a
salt into the solid jelly may be considered as cementation in its most
active form.
Numerous experiments were made on the diffusion of crystalloids
through various dialytic Septa, such as gelatinous starch, coagulated
albumen, gum-tragacanth, besides animal mucus, and parchment-paper,
which all tended to prove how little the diffusive process was interfered
with by the intervention of colloid matter. Salts appeared to preserve
their usual relative diffusibility unchanged. The same partial separa-
LIQUID DIFFUSION APPLIED TO ANALYSIS. 573
tion of mixed salts was observed as in the water-jar. With a mixture,
for instance, of equal parts of chlorides of potassium and sodium in the
dialyser, the first tenth part of the mixture which passed through was
found to consist of 59:17 per cent. of chloride of potassium and 40-83
per cent. of chloride of sodium. Double salts also, such as alum, and
the sulphate of copper and potash, which admit of being resolved into
pairs of unequally diffusive salts, were largely decomposed upon the
dialyser, as they are in the water-jar. The effect of heat in promoting
diffusion appeared, however, to be diminished in dialysis, at least with
a parchment-paper septum. Thus the diffusion from a 2 per cent. solu-
tion of chloride of sodium in a constant period of three hours was,
O Ratio.
At 10, . . 0.738 grm. 1
At 20, . . 0-794 grim. 1-07
* At 30, e tº 0.892 grim. 1:20
At 40, . . 1.017 grm. 1.37
The rate of diffusion in water alone, without the septum, would have
been doubled by an equal rise of temperature instead of being increased
one-third only as above.
The Small glass bell-jar (fig. 3) formerly used as an osmometer, was
FIG. 3.-Bulb Dialyser.
conveniently applied to dialytic experiments.
Two sizes of the bulb were employed, 3:14 and
4'44 inches in diameter respectively, and of which
the dialytic septa possessed an area very nearly
of T&oth and złoth of a square metre (15.6 and
7-8 square inches). With 100 cub. cents of fluid
in the osmometer (the volume usually employed),
the septum of the smaller instrument was
covered to a depth of about 20 millimetres (0.8
inch), and the septum of the larger to a depth
of 10 millimetres (0.4 inch). The thinner the
stratum, the more exhaustive the diffusion in a
given time. It is generally unadvisable to cover
the septum deeper than 10 or 12 millimetres (half an inch), where a con-
siderable diffusion is desired within twenty-four hours. The following
º
2:
s
*
ſ
* .
:
i
º,
º
23
*2
*3.
23
.e.


574 LIQUID DIFFUSION APPLIED TO ANALYSIS.
practical observations may be found useful in applying the dialyser to
actual cases of analysis. They refer to the parchment-paper septum,
which is much the most convenient for use.
With a 2 per cent. solution of chloride of sodium, containing 2
grammes of the salt, and covering a septum of nearly 0.01 square metre
(15.6 square inches) in area, to a depth of 10 millimetres, the salt which
diffused in five hours amounted to 0-75 gramme, and in twenty-four
hours to 1-657 gramme, leaving behind 0.343 gramme, or 17.1 per cent.
of the original salt. The following experiments, made with the same
osmometer and solution, show the effect of reducing the volume of liquid
placed in the dialyser. The proportion of salt which diffused out in
twenty-four hours was—
From 100 cub. cents, of solution 86 per cent.
Erom 50 cub. cents, of solution 92 per cent.
From 25 cub. cents. of solution 96 per cent.
In all cases the volume of water outside into which the salt escaped
was ample, being from five to ten times greater than the volume of fluid
placed in the dialyser, and it was changed during the continuance of
the experiment. A much less volume of external water suffices, pro-
vided it is changed at intervals of a few hours. The temperature was
10° to 12°. It will be observed that these volumes correspond to a
depth of liquid in the dialyser of 0-4, 0-2, and 0.1 inch respectively.
The time of travelling through the thickness of the parchment-paper
itself may be observed, and is worthy of remark.
Of the quality of parchment-paper always used in these experiments,
a square metre, when dry, weighed 67 grammes; and when charged with
water, 108.6 grammes. Taking the specific gravity of cellulose at 1:46,
that of the lighter woods, the parchment-paper described will, in the
humid state, have a thickness of 0.0877 millimetre, or ſºn of a milli-
metre. Wet parchment-paper so thin is highly translucent. Gelatinous
starch, slightly coloured with blue litmus, was applied by a brush to one
side of the wet parchment-paper. Immediately afterwards a drop of
water, containing Tºoth part of hydrochloric acid, was applied on the
point of the finger to the other (the lower) side of the paper. The time
required by the acid to affect the litmus, in five successive trials, was
6 seconds, 5.5 seconds, 6 seconds, and 5 seconds. The mean is 5-7
seconds, which is therefore the time required by hydrochloric acid,
diluted already 1000 times, to travel a distance of 0.0877 of a milli-
metre, by the agency of diffusion. The temperature was 15°.
With hydrochloric acid diluted twice as much as before (water con-
taining 0-0005 dry acid), the average time of passage was 10.4 seconds,
or nearly double the preceding time.
Water containing Tºoth of sulphuric acid (an acid less rapidly
LIQUID DIFFUSION APPLIED TO ANALYSIS. 575
diffused than hydrochloric acid) reddened the litmus in 91 seconds, and
When doubly diluted in 16:5 seconds.
These results are not affected, it is believed, by any sensible diffusive
movement on the part of the litmus. The diffusion of that colouring
matter, in a colloid medium, is so slow that it may be entirely disre-
garded. The acid, therefore, is not met in its way by the litmus, but
really travels the entire distance expressed by the thickness of the
parchment-paper. The first experiments related give a diffusive velocity,
in water, to hydrochloric acid, already diluted one thousand times, of
0.0154 millimetre per second, and 0.924 millimetre in one minute.
The few following dialytic experiments may be recorded for the sake
of the practical points which they bring out. They were made in the
Smaller Osmometer, with 100 cub. cents. of a solution containing 10
grammes of each of the various substances. The area of the parchment-
paper Septum was 0.005 square metre, and the depth of the stratum of
fluid placed upon it 20 millimetres. The substances diffused were all
Crystalloids, with the exception of gum-arabic. -
TABLE XII.-Dialysis through Parchment-paper during twenty-four
hours, at 10° to 15°.
º g tº , Osmose, Relative
Ten per cent, solutions. *º, §: *.Fº OSIDOS6.
Gum-arabic, . . . . . 0-029 •004 5-0 *263
Starch-sugar, . e & de 2°000 *266 17-0 "894
Cane-sugar, ſº g gº * 1:607 *214 15:3 •805
Milk-sugar, * tº tº tº 1°387 • 185 15-0 •789
Mannite, . tº ë & te 2:621 *349 17-6 •926
Glycerine, . & & tº . . . .3°300 *440 17-6 ‘926
Alcohol, . © tº de tº 3-570 •476 7:6 "400
Starch-sugar (second experiment), 2: 130 •284 16-8 ‘884
Chloride of sodium, . * . 7:500 l 19-0 l
The experiments were all made through the same portion of parch-
ment-paper, and in the order of the Table; gum-arabic first, and chloride
of sodium last. After every experiment the bulb was immersed in
water for twenty-four hours, to purify the septum, before it was again
used. The diffusion of starch-sugar was repeated early and late in the
series of experiments, with little change in the result, showing consider-
able uniformity in the action of the parchment-paper; the first diffusate
of starch-sugar being 2 grammes, and the second 2.13 grammes. Yet
the parchment-paper had been in contact with water or some solution
for a whole fortnight between the two observations referred to.
A layer of animal mucus, taken from the stomach of the pig, 12
millimetres in thickness (10 grammes of humid mucus being spread
over 0:005 square metre of surface), was applied, between two discs of
576 LIQUID DIFFUSION APPLIED TO ANALYSIS.
calico, to the diffusion-bulb used above, the parchment-paper being first
removed. -
TABLE XIII–Dialysis through Animal Mucus during twenty-five
hours, at 10° to 15°. -

- - Osmose,
Ten per cent. solutions. . ºº, Pººl ". Fº
Gum-arabic, e t t wº •023 •004 + 29
Starch-sugar, . e & e 1°821 •360 + 7:6
Cane-sugar, e te tº e 1753 •347 + 4-6
Milk-sugar, º & & & 1.328 •262 + 7-1
Mannite, . º e * e- 1°895 •375 + 5°0
Alcohol, . º * º e 2-900 •573 + 7-2
Starch-sugar, . & º e 1765 *349 + 7-0
Glycerine, . e g º e 2°554 “505 + 7.5
Chloride of sodium, . {º º 5'054 l — 0:2
The relative diffusibilities of the different substances present a con-
siderable degree of similarity in the two Tables, and are equally analo-
gous to the diffusibilities of the same substances observed in pure water.
The intervention of a colloid septum cannot be said to have impeded
much the diffusion of any of these substances except the colloid gum.
The dialysis through parchment-paper of several other organic sub-
stances, both crystalloids and colloids, may be brought together, in
comparison with the chloride of sodium as a standard. The larger
osmometer bulb was used, and the parchment paper was now changed
in each experiment. The substance in solution amounted to 2 grammes,
the depth of fluid in the dialyser to 10 millimetres (0.4 of an inch), and
the surface of the septum to 0-01 square metre (15.6 square inches).
TABLE XIV.-Dialysis through Parchment-paper during twenty-four
hours, at 12°.

Two per cent. solutions. iº, Pºnal
Chloride of sodium, . & © 1.657 I
Picric acid, º & © e 1°690 1.020
Ammonia, - e º g l'404 •847
Thein, º º e º o 1 - 166 •703
Salicin, . { } & de ſº '835 “503
Cane-sugar, º º e & •783 '472
Amygdalin, & tº e e •517 •311
Extract of quercitron, º e “305 *184
Extract of logwood, . * & 280 • 168
Catechu, . e e ſº e •265 •159
Extract of cochineal, . e 4- •086 •05]
Gallo-tannic acid, e & e •050 •030
Extract of litmus, . º e •033 •019
Purified caramel, e e e •009 •005
- L10 UID DIFFUSION APPLIED TO ANALYSIS. 57.7
Picric acid and thein were actually diffused from 1 per cent, solu-
tions, and the numbers observed are multiplied by 2. The crystalliz-
able principles, thein, Salicin, and amygdalin, appear greatly more
diffusible than gallo-tannic acid, or than gum, as has been already seen.
Such inequality of rate is likely to facilitate the separation of vegetable
principles by the agency of dialysis. • -
4. Preparation of Colloid Substances by Dialysis.
The purification of many colloid substances may be effected with
great advantage by placing them on the dialyser. Accompanying
crystalloids are eliminated, and the colloid is left behind in a state of
purity. The purification of soluble colloids can rarely be effected by
any other'known means, and dialysis is evidently the appropriate mode
of preparing such substances free from crystalloids.
Soluble Silicic Acid.—A solution of silica is obtained by pouring
silicate of soda into diluted hydrochloric acid, the acid being maintained
in large excess. But in addition to hydrochloric acid, such a solution
contains chloride of sodium, a salt which causes the silica to gelatinize
when the solution is heated, and otherwise modifies its properties. Now
such soluble silica, placed for twenty-four hours in a dialyser of parch-
ment-paper, to the usual depth of 10 millimetres, was found to lose in
that time 5 per cent. of its silicic acid, and 86 per cent. of its hydro-
chloric acid. After four days on the dialyser, the liquid ceased to be
disturbed by nitrate of silver. All the chlorides were gone, with no
further loss of silica. In another experiment 112 grammes of silicate
of soda, 67.2 grammes of dry hydrochloric acid, and 1000 cub. cents. of
water were brought together, and the solution placed upon a hoop
dialyser, 10 inches in diameter. After four days the solution had
increased to 1235 cub. cents, by the action of osmose; colloid bodies
being generally highly osmotic. The solution now gave no precipitate
with nitrate of silver, and contained 60.5 grammes of silica, 67 grammes
of that substance having been lost. The solution contained 4.9 per cent.
of silicic acid. -
The pure solution of silicic acid so obtained may be boiled in a flask,
and considerably concentrated, without change; but when heated in an
open vessel, a ring of insoluble silica is apt to form round the margin of
the liquid, and soon causes the whole to gelatinize. The pure solution
of hydrated silicic acid is limpid and colourless, and not in the least
degree viscous, even with 14 per cent. of silicic acid. The solution is
the more durable the longer it has been dialysed and the purer it is.
But this solution is not easily preserved beyond a few days, unless con-
siderably diluted. It soon appears slightly opalescent, and after a time
- 2 O
578 LIQUID DIFFUSION APPLIED TO ANALYSIS.
the whole becomes pectous somewhat rapidly, forming a solid jelly
transparent and colourless, or slightly opalescent, and no longer soluble
in water. This jelly undergoes a contraction after a few days, even in
a close vessel, and pure water separates from it. The coagulation of the
silicic acid is effected in a few minutes by a solution containing in ºth
part of any alkaline or earthy carbonate, but not by caustic ammonia,
nor by neutral or acid salts. Sulphuric, nitric, and acetic acids do not
coagulate silicic acid, but a few bubbles of carbonic acid passed through
the solution produce that effect after the lapse of a certain time. Alco-
hol and sugar, in large quantity even, do not act as precipitants; but
neither do they protect silicic acid from the action of alkaline carbonates,
nor from the effect of time in pectizing the fluid colloid. Hydrochloric
acid gives stability to the solution : So does a small addition of caustic
potash or Soda.
This pure water-glass is precipitated on the surface of a calcareous
stone without penetrating, apparently from the coagulating action of
soluble lime-salts. The hydrated silicic acid then forms a varnish,
which is apt to scale off on drying. The solution of hydrated silicic
acid has an acid reaction, Somewhat greater than that of carbonic acid.
It appears to be really tasteless (like most colloids), although it occasions
a disagreeable persistent sensation in the mouth, after a time, probably
from precipitation.
Soluble hydrated silicic acid, when dried in the air-pump receiver,
at 15°, formed a transparent glassy mass of great lustre, which was no
longer soluble in water. It retained 21.99 per cent, of water after being
kept two days over sulphuric acid.
The colloidal solution of silicic acid is precipitated by certain other
soluble colloids, such as gelatine, alumina, and peroxide of iron, but not
by gum nor caramel. As hydrated silicic acid, after once gelatinizing,
cannot be made soluble again by either water or acids, it appears neces-
sary to admit the existence of two allotropic modifications of that sub-
stance, namely, soluble hydrated silicic acid, and insoluble hydrated
silicic acid, the fluid and pectous forms of this colloid.
The ordinary soluble silicate of soda is not at all colloidal, but dif-
fuses as readily through a septum as the sulphate of soda does. Several
crystalline hydrated silicates of soda are known (Fritzsche).
The amorphous silicic acid obtained by drying and calcining the
jelly, and the vitreous acid obtained by igneous fusion, have both a
specific gravity of about 22, according to H. Rose," and appear to be the
same colloidal substance; while the specific gravity of crystalloidal
silicic acid (rock-crystal and quartz) is about 2.6.
Soluble silicic acid forms a peculiar class of compounds, which like
- * Annales de Chimie, 3 sér. t. Ivii. p. 163.
LIQUID DIFFUSION APPLIED TO ANALYSIS. 579
itself are colloidal, and differ entirely from the ordinary silicates. The
new compounds are interesting from their analogy to organic substances,
and from appearing to contain an acid of greatly higher atomic weight
than ordinary silicic acid. Like gallo-tannic acid, gummic acid, and the
other organic colloidal acids, silicic acid combines with gelatine; the
last substance appearing to possess basic properties. Silicate of gelatine
falls as a flaky, white and opake precipitate, when the solution of silicic
acid is gradually added to a solution of gelatine in excess. The precipi-
tate is insoluble in water, and is not decomposed by washing. Silicate
of gelatine prepared in the manner described, contains 100 silicic acid
to about 92 gelatine. This is a greater proportion of gelatine than in
the gallo-tannate of gelatine, and requires for soluble silicic acid a higher
equivalent than that of gallo-tannic acid. In the humid state the
gelatine of this compound does not putrefy.
The acid reaction of 100 parts of soluble silicic acid is neutralized by
1.85 part of oxide of potassium, and by corresponding proportions of
soda and ammonia. The colli-silicates or co-silicates thus formed are
soluble and more durable than fluid silicic acid, but they are pectized
by carbonic acid or by an alkaline carbonate, after standing for a few
minutes. The co-silicate of potash forms a transparent hydrated film
on drying in vacuo, which is not decomposed by water, and appears to
require about ten thousand parts of water to dissolve it. The silicate
of soda which Forchhammer obtained by boiling freshly precipitated
silicic acid with carbonate of soda, and collecting the precipitate which
falls on cooling, contains 274 per cent. of soda, and is represented by
NaO + 36 SiO, (Gmelin). This silicate is probably a co-silicate of soda
in the pectous condition. Soluble silicic acid produces a gelatinous
precipitate in lime-water, containing 6 per cent. and upwards of the
basic earth. This and the other insoluble earthy co-silicates appear not
to be easily obtained in a definite state. They gave out a more basic
silicate to water on washing. The composition of these salts, and that
also of the co-silicate of gelatine, were found to vary according as the
mode of preparation was modified. When a solution of gelatine was
poured into silicic acid in excess, the co-silicate of gelatine formed gave,
upon analysis, 100 silicic acid with 56 gelatine, or little more than half
the gelatine stated above as found in that compound prepared with the
mode of mixing the solutions reversed. The gallo-tannate of gelatine
is known to offer the same variability in composition.
The gelatine used in the preceding experiments was isinglass (colle
de poisson), purified by solution in hydrochloric acid and subsequent
dialysis. As the acid escapes by diffusion, a jelly is formed in the
dialyser. This jelly is free from the earthy matter, amounting to about
0.4 per cent. in isinglass, and is not liable to putrefaction.
580 LIQUID DIFFUSION APPLIED TO ANALYSIS.
Cosilicic acid also precipitates both albuminic acid and pure casein.
Soluble Alumina.--We are indebted to Mr. Walter Crum for the
interesting discovery that alumina may be held in solution by water
alone in the absence of any acid. But two soluble modifications of
alumina appear to exist, alumina and metalumina. The latter is Mr.
Crum's substance.
A solution of the neutral chloride of aluminium (Al, Cls), placed on
the dialyser, appears to diffuse away without decomposition. But when
an excess of hydrated alumina is previously dissolved in the chloride,
the latter salt is found to escape by diffusion in a gradual manner, and
the hydrated alumina, retaining little or no acid, to remain behind in a
soluble state. A solution of alumina in chloride of aluminium, consisting
at first of 52 parts of alumina to 48 of hydrochloric acid, after a dialysis
of six days, contained 66.5 per cent. of alumina; after eleven days 76.5
per cent. ; after seventeen days 92.4 per cent, and after twenty-five days
the alumina appeared to be as nearly as possible free from acid, as traces
only of hydrochloric acid were indicated by an acid solution of nitrate
of silver. But in such experiments the alumina often pectizes in the
dialyser before the hydrochloric acid has entirely escaped.
Acetate of alumina with an excess of alumina gave similar results.
The alumina remained fluid in the dialyser for twenty-one days, and
when it pectized was found to retain 34 per cent. of acetic acid, which
is in the proportion of 1 equivalent of acid to 282 equivalents of
alumina.
Soluble alumina is one of the most unstable of substances, a circum-
stance which fully accounts for the difficulty of preparing it in a state of
purity. It is coagulated or pectized by portions, so minute as to be
scarcely appreciable, of sulphate of potash and, I believe, by all other
salts; and also by ammonia. A solution containing 2 or 3 per cent. of
alumina was coagulated by a few drops of well-water, and could not be
transferred from one glass to another, unless the glass was repeatedly
washed out by distilled water, without gelatinizing. Acids in small
quantity also cause coagulation; but the precipitated alumina readily
dissolves in an excess of the acid. The colloids gum and caramel also
act as precipitants. ;
This alumina is a mordant, and possesses indeed all the properties
of the base of alum and the Ordinary aluminous salts. A solution con-
taining 0.5 per cent. of alumina may be boiled without gelatinizing, but
when concentrated to half its bulk it suddenly coagulated. Soluble
alumina gelatinizes when placed upon red litmus paper, and forms a
faint blue ring about the drop, showing a feeble alkaline reaction. Solu-
ble alumina is not precipitated by alcohol nor by sugar. No pure solution
of alumina, although dilute, remained fluid for more than a few days.
LIQUID DIFFUSION APPLIED TO ANALYSIS. 581
Like hydrated silicic acid, then, the colloid alumina may exist either
fluid or pectous, or it has a soluble and insoluble form, the latter being
the gelatinous alumina as precipitated by bases. It is evident that the
extraordinary coagulating action of salts upon hydrated alumina must
prevent the latter substance from ever appearing in a soluble state when
liberated from combination by means of a base.
Colloidal alumina possesses also, I believe, a high atomic weight,
like cosilicic acid. The chloride of aluminium with excess of alumina
referred to above appears to be, either in whole or in part, a colloidal
hydrochlorate of alumina, containing the latter substance with its large
colloidal equivalent, and may be really neutral in composition. The
soluble basic persalts of iron, tin, etc., are likewise all colloidal, and
have no doubt a similar constitution. Such colloidal salts are them-
selves slowly decomposed on the dialyser, being resolved into the crystal-
loidal acid which escapes and the colloidal oxide which remains behind.
Soluble Metalumina.-Mr. Crum first pointed out a singular relation
of acetic acid to alumina, which has never been explained. Sulphate of
alumina, when precipitated by acetate of lead or baryta, gives a bin-
acetate of alumina, with one equivalent of free acetic acid; the neutral
teracetate of alumina not appearing to exist. It was further observed
that, by keeping a solution of this binacetate in a close vessel at the
boiling-point of water for several days, nearly the whole acetic acid came
to be liberated, without any precipitation of alumina occurring at the
same time. Mr. Crum boiled off the free acetic acid, or the greater
part of it, and thus obtained his soluble alumina. The same result may
be arrived at by dialysing a solution of acetate of alumina that has
been altered by heat. In three days the acetic acid was reduced on the
dialyser to 11 per cent, giving 1 equiv. acetic acid to 8 equivs. alumina;
in six days to 7:17 per cent. acid; in thirteen days to 2-8 per cent. acid, or
1 equiv. acid to 33 equivs. alumina. The alumina exists in an allotropic
condition, being no longer a mordant; and forming, when precipitated, a
jelly that is not dissolved by an excess of acid. Metalumina resembles
alumina in being coagulated by minute proportions of acids, bases, and on
most salts. Mr. Crum found the solution of metalumina to require larger
quantities of acetates, nitrates, and chlorides to produce coagulation than
of the former substances. The solution of metalumina is tasteless, and
entirely neutral to test-paper, according to my own observation.
Like alumina, the present colloid has therefore a fluid and a pec-
tous form, the liquid soluble metalumina, and the gelatinous insoluble
metalumina.
Soluble Peroxide of Iron.—A solution of hydrated peroxide of iron
may be obtained by a process exactly analogous to that for soluble
alumina. Perchloride of iron in solution is first Saturated with hydrated
582 LIQUID DIFFUSION APPLIED TO ANALYSIS.
peroxide of iron, added by small quantities at a time; or carbonate of
ammonia may be added in a gradual manner to perchloride of iron, so
long as the precipitated oxide continues to be redissolved on stirring.
These red solutions of iron have lately been carefully investigated by
Mr. Ordway (Silliman's Journal, 3 ser. xxxix. 197), by M. Bechamp
(Annales de Chimie, 3 Sér. lvii. 293), and by M. Scheurer-Kestner (ib.
lv. 330). It is observed that the act of solution of the hydrated peroxide
by the chloride of iron is a gradual process, demanding time. The
quantity of oxide taken up will go on increasing for a long time, if diges–
tion in the cold is continued. Mr. Ordway found chloride of iron to take
up so much as 18 equivalents of peroxide of iron in the course of five
months. This slowness of action is highly characteristic of colloids.
Only monobasic acids, such as hydrochloric and nitric, serve for prepar-
ing such solutions; sulphuric and other polybasic acids giving insoluble
subsalts with excess of ferric oxide, or of any other aluminous oxide.
The red liquid so obtained is already a colloidal hydrochlorate of peroxide
of iron, but requires to be dialysed for a sufficient time. Such a com-
pound possesses an element of instability in the extremely unequal
diffusibility of its constituents. Beginning with perchloride of iron,
containing five or six equivalents of peroxide in solution, the whole solid
matter also amounting to 4 or 5 per cent. of the liquid, and the latter
forming a stratum of the usual depth of about half an inch in the dialyser,
it was found that hydrochloric acid diffused out accompanied only by a
small proportion of the iron. After eight days, the deep red solution
in the dialyser contained peroxide of iron and hydrochloric acid, in the
proportion of 97.6 per cent of the former to 2.4 per cent. of the latter.
In nineteen days the hydrochloric acid was reduced to 1.5 per cent,
which gives 1 equiv. of acid to 30.3 equivs. peroxide of iron. The last
solution was transferred to a phial, in which it remained fluid for twenty
days, and then spontaneously pectized. wº
The peracetate of iron, prepared by double decomposition, is incap-
able of dissolving hydrated peroxide of iron, as is well known, but still
may be made a source of soluble peroxide; as the salt referred to is itself
decomposed to a great extent by diffusion on the dialyser. About one-
half of the iron was lost by a diffusion of eighteen days, in a particular
experiment, leaving on the dialyser a red liquid, in which ninety-four
parts of peroxide of iron were still associated with six parts of acetic
acid.
Water containing about 1 per cent. of hydrated peroxide of iron in
solution has the dark red colour of venous blood. The solution may be
concentrated by boiling to a certain point, and then pectizes. The red
solution is coagulated in the cold by traces of sulphuric acid, alkalies,
alkaline carbonates, sulphates and neutral salts in general, but not by
LIQUID DIFFUSION APPLIED TO ANALYSIS. 583
hydrochloric, nitric, and acetic acids, nor by alcohol or sugar. The
coagulum is a deep red-coloured jelly, resembling the clot of blood, but
more transparent. Indeed, the coagulation of this colloid is highly
suggestive of that blood, from the feeble agencies which suffice to effect
the change in question, as well as from the appearance of the product.
The coagulum formed by a precipitant, or in the course of time, without
any addition having been made to the solution of peroxide of iron, is no
longer soluble in water, hot or cold; but it yields readily to dilute acids.
It is, in short, the ordinary hydrated peroxide of iron. Here, then,
"again, we have a soluble and insoluble form of the same colloidal sub-
stance. Native hematite, which presents itself in mammillary concre-
tions, is no doubt colloidal. *.
Soluble Metaperoxide of Iron.—The soluble peroxide of iron of M.
Péan de Saint-Gilles' appears to be the analogue of metalumina. It was
also prepared by the prolonged action of heat upon a pure solution of
the acetate. The characteristic properties of this substance, which indi-
cate its allotropic ‘nature, are the Orange-red colour and the Opalescent
appearance of its solution. The metaperoxide of iron is entirely preci-
pitated of a brown ochreous appearance by a trace of sulphuric acid, or
of an alkaline salt, and is insoluble in all cold acids, even when the
latter are concentrated. The solubility of metaperoxide of iron in water
appears to be more precarious, if possible, than that of the colloid
alumina. It would no doubt be more safely prepared by diffusing away
the acetic acid of the altered acetate of iron, than it is by boiling off that
acid; as the solution is said to become precipitable by heat before the
whole acetic acid is expelled.
Ferrocyanide of Copper—Many of the insoluble ferrocyanides are
crystalline precipitates, but the compound above named, and the different
arieties of prussian blue, appear to be strictly colloidal.
Certain anomalous properties long observed in these compounds
come thus to be explained. The ferrocyanide of copper, precipitated
from ferrocyanide of potassium and sulphate of copper, is a reddish-
brown gelatinous precipitate, and carries down a portion of the potash
salt. It is obtained of greater purity, like the other insoluble ferrocy-
anides, by the use of ferrocyanic acid as the precipitant. Ferrocyanide
of copper is then darker in colour, and still more highly gelatinous. It
is well known that this substance appears as a transparent almost colour-
less jelly, when precipitated from strong solutions. This colloidal matter
assumes colour on the addition of water, in consequence of further hydra-
tion, following in this respect the analogy of the crystalloid salts of
copper. The ferrocyanide of copper, when once precipitated, may be
washed without loss, and exhibits no symptoms of solubility. But it
* Comptes Rendus, 1855, p. 568.
584 LIQUID DIFFUSION APPLIED TO ANALYSIS,
has been remarked that the same salt, when produced by mixing the
precipitating salts dissolved in not less than two or three thousand
times their weight of water, gives a wine-red solution with no preci-
pitate. This is the soluble condition of the colloid. When the red
solution is placed in the dialyser the salt of potash diffuses out, and the
whole ferrocyanide of copper is retained behind in solution.
Precipitated ferrocyanide of copper is not dissolved by oxalic acid,
nor by oxalate of potash, but dissolves freely in about one-fourth of its
weight of neutral oxalate of ammonia. The ferrocyanide of copper
must be washed beforehand, to insure solubility. A solution holding
3 or 4 per cent. of ferrocyanide of copper is of a dark reddish-brown
colour, intermediate in tint between the acetate and meconate of iron.
The solution is transparent, but assumes a peculiar appearance of opacity
when seen by light reflected from its surface. The same appearance
was observed by Péan de Saint-Gilles in his metaperoxide of iron.
When a red solution, such as that described, was dialysed, the oxalate
of ammonia came away in a gradual manner; 30.6 per cent. of the
oxalate of ammonia were found in the colourless diffusate of the first
twenty-four hours; 31 per cent. of the same salt in the diffusate of the
next three days, and 18.2 per cent. in the diffusates of the following
seven days, making altogether 79.8 per cent, or four-fifths of the whole
oxalate of ammonia originally introduced. A small portion of the
ammoniacal salt is retained with force, as might be expected from a
ferrocyanide. Although the diffusate appeared colourless, it was found
to contain a little oxide of copper, namely, 0-041 gramme (of which
0.022 gramme diffused out in the first twenty-four hours), from 2
grammes of ferrocyanide of copper placed in the dialyser. -A
The liquid ferrocyanide of copper, both before and after being dia-
lysed, may be heated without change, but it is pectized by foreign sub-
stances with extreme facility. This effect is produced by a minute
addition of nitric, hydrochloric, and Sulphuric acids in the cold, and of
oxalic and tartaric acids with the aid of a slight heat. It is remarkable
that acetic acid does not pectize the ferrocyanide of copper and many
other colloids. Sulphate of potash, Sulphate of copper, and metallic salts
generally appear to pectize the red liquid. The oxalate of ammonia, if
any is present, remains in solution.
Neutral Prussian Blue.—The blue precipitate from perchloride of iron
and ferrocyanide of potassium, or ferrocyanic acid, is a bulky hydrate,
which dries up into gummy masses, so far resembling a colloid. The
precipitate dissolves readily with the aid of a gentle heat, in one-sixth
of its weight of Oxalic acid, giving the well-known solution of prussian
blue, used as an ink. Prussian blue is equally soluble in the oxalate
and binoxalate of potash. When the Solution of prussian blue in oxalic
LIQUID DIFFUSION APPLIED TO ANALYSIS. 585
acid was placed on the dialyser, no colouring matter came through, but
28 per cent of the oxalic acid diffused away in the first twenty-four
hours, accompanied by traces of peroxide of iron. The oxalic acid
appears to leave the colloidal solution very slowly and incompletely,
8 per cent, diffusing away in the second twenty-four hours, 11 per cent.
in the next four days, and 2 per cent. in the following six days. The
colloidal solution of prussian blue was pectized by small additions of
sulphate of zinc and several other metallic salts, but required larger
quantities of the alkaline salts for precipitation.
Ferridcyanide of Iron.—The blue precipitate from the ferridcyanide
of potassium and a protoSalt of iron is soluble in Oxalic acid and the
binoxalate of potash, but not in the neutral oxalates. This blue liquid
is quite incapable of passing through the dialyser, and is equally col-
loidal with ordinary prussian blue. So also is basic prussian blue pre-
pared by the spontaneous oxidation of precipitated ferrocyanide of
protoxide of iron. This last colloid might probably be purified with
advantage upon the dialyser.
The ammonio-tartrate of iron, ammonio-citrate of iron, and similar
pharmaceutical preparations are chiefly colloidal matters.
Sucrate of Copper—The deep blue liquid obtained by adding potash
to a mixed solution of chloride of copper and sugar appears to contain a
colloidal substance. Placed on a dialyser for four days, the blue liquid
became green, and no longer contained either potassium or chlorine; it
in fact consisted of oxide of copper united with twice its weight of
sugar. The external liquid remained colourless, and gave no indication
of copper when tested with Sulphuretted hydrogen. The colloidal solu-
tion of sucrate of copper was sensitive in the extreme to pectizing agents.
Salts and acids generally gave a bluish-green precipitate; even acetic
acid had that effect. The precipitate, or pectous sucrate, after being well
washed, consisted of oxide of copper with about half its weight of sugar,
and is therefore a subsucrate. When the green liquid is heated strongly,
it gives a bluish-green precipitate, and does not allow the copper to be
readily reduced to the state of suboxide. The subsucrate of copper
possesses considerable vivacity of colour, and might be used as a pig-
ment. A solution of sucrate of copper absorbs carbonic acid from the
air with great avidity.
The sucrate of copper dries up into transparent films of an emerald
green colour. These films are not altered in appearance or dissolved in
cold or boiling alcohol. In water they are resolved into sugar and the
pectous subsucrate of copper.
Sucrate of Peroa;ide of Iron.—The perchloride of iron with an addi-
tion of sugar is not precipitated by potash, provided the temperature is
not allowed to rise. The peroxide of iron combined with the sugar is
586 LIQUID DIFFUSION APPLIED TO ANALYSIS.
colloidal, and remains on the dialyser without loss. At a certain stage,
however, the sugar appears to leave the peroxide of iron, and a gelatinous
subsucrate of iron pectizes. The subsucrate of iron thrown down from
the soluble sucrate, by the addition of sulphate of potash, consisted of
about 22 parts of Sugar to 78 parts of peroxide of iron.
Sucrate of Peroxide of Uranium.–A similar solution may be obtained
by adding potash to a mixture of the nitrate or chloride of uranium with
Sugar, avoiding heat. The solution is of a deep Orange-yellow colour,
and on the dialyser soon loses the whole of its acid and alkali. This
fluid sucrate has considerable stability, but is readily pectized by salts,
like the sucrate of copper. The subsucrate pectized has considerable
solubility in pure water.
Sucrate of Lime.—The well-known solution of lime in Sugar forms a
solid coagulum when heated. It is probably, at a high temperature,
entirely colloidal. The solution obtained on cooling passes through the
septum, but requires a much longer time than a true crystalloid like the
chloride of calcium.
The blue solution of tartrate of copper in caustic potash contains a
colloidal compound, which has not been fully examined.
Soluble Chromic Oxide.—The definite terchloride of chromium, being
a crystalloid, diffuses away entirely when placed in solution upon the
dialyser. This salt dissolves, with time, a certain portion of freshly-
precipitated hydrated chromic oxide, and becomes of a deeper green
colour. Such a solution, after dialysis for twenty-two days, contained
8 hydrochloric acid to 92 chromic oxide; and after thirty days, 4:3 acid
to 95.7 oxide, or 1 equiv. acid to 10-6 equivs. oxide. After thirty-eight
days, the solution gelatinized in part upon the dialyser, and then con-
tained 1-5 acid to 98-5 oxide, or 1 equiv. acid to 31-2 equivs. chromic
oxide. This last solution, which may be taken to represent soluble
chromic oxide, is of a dark green colour, and admits of being heated,
and also of being diluted with pure water without change. It was
gelatinized with the usual facility by traces of salts and other reagents
which affect colloid solutions, and was then no longer soluble in water,
even with the assistance of heat. It appeared to be the green hydrated
oxide of chromium, as that substance is usually known. A metachromic
oxide may possibly be obtained by heating and dialysing the acetate,
but I have not attempted to form it.
Mr. Ordway succeeded in dissolving an excess of the hydrated uranic
ocide and of glucina in the chloride of uranium and of glucinum respec-
tively. The dialysis of such solutions may be reasonably expected to
yield soluble uranic oxide and soluble glucina.
It appears, then, that the hydrated peroxides of the aluminous type,
when free, are colloid bodies; that two species of each of these hydrated
LIQUID DIFFUSION APPLIED TO ANALYSIS. 587
oxides exist, of which alumina and metalumina are the types; one
derived from an unchanged salt, and the other from the heated acetate
of the base; further, that each of these species has two forms, one soluble
and the other insoluble, or coagulated. This last species of duality
should be well distinguished from the preceding allotropic variability of
the same peroxide. The possession of a soluble and an insoluble (fluid
and pectous) modification is not confined to hydrated silicic acid and
the aluminous oxides, but appears to be very general, if not universal,
among colloid substances. The double form is typified in the fibrin of
blood.
The precipitated and gelatinous peroſcide of tin is largely soluble in
the bichloride of the same metal. Such a solution, when placed in the
dialyser, allows the whole chlorine of the salt and a portion of the tin
to diffuse away. Peroxide of tin, or stannic acid, remains behind, but
not in a soluble state. It forms in the dialyser a semi-transparent
gelatinous cake, which after a few days is entirely free from chlorine.
The original solution, containing excess of stannic acid, was diluted to
various degrees, but was dialysed always with the same result. The
coagulum was insoluble in hot or cold water, but dissolved readily in
dilute acids. It was evidently the peroxide of tin unaltered.
The metastannic acid, or nitric acid peroxide of tin of Berzelius,
forms a solid compound with a small quantity of hydrochloric acid.
This compound is not dissolved by an excess of acid, but is soluble in
pure water. The solution placed in the dialyser is readily decomposed,
and leaves behind a semi-transparent gelatinous mass of pure hydrated
metastannic acid, insoluble both in water and acids. There appears,
then, to be no soluble form of either hydrated stannic or metastannic
acid, although both are colloidal substances.
Precipitated titanic acid was dissolved in hydrochloric acid and
submitted to dialysis. The hydrochloric acid readily diffused away,
leaving hydrated titanic acid, gelatinous and insoluble, upon the
dialyser. The proportion of titanic acid, which escaped from the
dialyser and was lost, amounted to 0.050 gramme out of 2.5 grammes.
Titanic acid thus resembles stannic acid in not presenting itself in
the form of a fluid colloid.
Metallic protoxides are not soluble in their neutral salts, and cannot
therefore be submitted to dialysis in the same conditions as the preced-
ing peroxides. It was observed, however, that oxide of copper and
oxide of zinc, when dissolved in ammonia, are capable of diffusing
through a colloidal septum, and are therefore not colloids themselves.
The water outside the dialyser should be charged with ammonia in such
an experiment.
588 LIQUID DIFFUSION APPLIED TO ANALYSIS.
5. Dialysis of Organic Colloid Substances.
Tannin.—The tannin employed was that extracted from gall-nuts
by the ether process of Pelouze. A two per cent. Solution of this sub-
stance, covering a surface of paper-parchment of the area of about Tāoth
of a square metre, or 15-6 Square inches, to a depth of 10 millimetres,
was diffused at 10° to 13° of temperature. The diffused matter
amounted, in successive periods of twenty-four hours, to 073, '040, 021,
-021, '024, and 024 gramme, derived from the two grammes in solution.
Probably the earlier diffusates were increased by the presence of a little
gallic acid, which, being a crystalloid, would no doubt be rapidly
eliminated by diffusion. The latter observations indicate that tannin
passes through a paper-parchment septum about 200 times less rapidly
than chloride of sodium does, in similar circumstances as to temperature
and strength of solution. The diffusates from the tannin solution gave
a precipitate with gelatine, and therefore contained tannin unaltered.
But the diffusates probably contained also throughout some products of
decomposition of a crystalloid character.
To the low diffusibility of tannin may be ascribed the remarkably slow
penetration of skins by that substance in the ordinary operation of tan-
ning leather. Tannin appears to form compounds of much stability with
certain other colloids, as tanno-gelatine, and the compound with albumen
which appears to be the primary basis of the vegetable cell (Frémy).
Gum.—The diffusate obtained from a solution containing 2 grammes
of gum-arabic, in experiments corresponding in their conditions with
the experiments upon tannin just related, was 013 gramme per day.
The power of gum to penetrate the colloid septum appears, therefore, to
be one-half less than that of tannin, and 400 times less than the diffusi-
bility of chloride of sodium. Gum gave the same amount of diffusate
with a mucus septum as with parchment-paper. When substances of
the crystalloid class are mixed with the gum, the diffusion of the latter
appears to be still further reduced, and may even be entirely extin-
guished. The separation of colloids from crystalloids by dialysis is, in
consequence, generally more complete than might be expected from the
relative diffusibility of the two classes of substances.
Vegetable gum, which Frémy has shown to be a gummate of lime,
can be purified by a dialytic method, which may be found applicable
with advantage in other cases. Oxalic acid, it is known, precipitates
lime from the gum very imperfectly. Hydrochloric acid may be used
to separate that base from a solution of gum placed upon the dialyser,
with more effect. It is only necessary to add to a strong solution of
gum 4 or 5 per cent of hydrochloric acid, and to dialyse till the gum
solution gives no precipitate with nitrate of silver. In an experiment
LIQUID DIFFUSION APPLIED TO ANALYSIS. 589
made upon a 20 per cent. Solution of gum, the ash was reduced to 0:1
per cent. of the gum in five days. The gummic acid possesses a sen-
sible acid reaction, about equal to that of carbonic acid. This acid.
reaction was neutralized in 100 parts of gummic acid by 2.85 parts of
potash. This amount of potash is very nearly equivalent to the lime
originally present in the gum (1:72 lime, or 3.07 carbonate of lime,
being equivalent to 2.89 potash). When the gummate of potash itself
was dialysed without addition, the potash gradually diffused away,
possibly in the state of carbonate, and left the gum again possessed of
an acid reaction. Gummic acid, well dried at 100°, becomes insoluble
in water, but swells up in that liquid, like gum-tragacanth. We appear
to have here the pectous form of gummic acid.
It is worthy of inquiry whether such native gums as are insoluble
in water are not the pectous form of Soluble gum, rather than allotropic
varieties of that substance. So also of the metagummic acid of Frémy,
formed by the action of strong sulphuric acid on mucilage. This last
substance is insoluble in water, but was found by Frémy to afford, when
neutralized by lime and alkalies, a soluble gum undistinguishable from
gum-arabic.
Gummic acid produces a remarkable compound with gelatine. When
solutions of these two colloids are mixed, oily drops fall and form a
nearly colourless jelly on standing. This jelly is very fusible, melting
at 25°, or by the heat of the hand. The gummate of gelatine may be
washed without decomposition, but is soluble to a certain extent in
pure water, and still more so in a solution of gelatine. Prepared with
gummic acid in excess, the compound, when dried at 100°, consisted of
100 gummic acid with 59 gelatine. The drops and the jelly contained
83.5 per cent. of water. Solution of gelatine is not precipitated by
unpurified gum, nor by the gummate of potash.
Deatrin.—A 2 per cent. Solution of dextrin, prepared from starch,
was diffused in the same conditions as the preceding substances, but
through a mucus septum. It gave in twenty-four hours 034 gramme
of diffusate from 2 grammes, or about three times more diffusate than
was given by gum-arabic.
Caramel.—The dialytic examination of this substance adds to the
accurate information on the subject lately supplied by M. A. Gélis,"
and places caramel indisputably in the colloid class. The crude caramel
obtained by heating cane-sugar at 210°–220°, when placed on the dialyser,
allows certain intermediate coloured substances (Caramelane and Cara-
melene of Gélis) to diffuse out with considerable facility, while the
compound containing the largest proportion of carbon remains behind.
The latter substance, as obtained by me, possessed five times the colour-
* Annales de Chimie, etc., sér. 3, t. lii. p. 352. -
590 LIQUID DIFFUSION APPLIED TO ANALYSIS.
ing power of the original crude caramel, weight for weight. This highest
soluble member of the caramel series may also be obtained, more quickly,
by precipitation from its aqueous solution by means of alcohol. But I
found it necessary to repeat the precipitation four times, or till the mass
thrown down, from being plastic at first became pulverulent. A solu-
tion containing 10 per cent. of the caramel so purified is gummy; and
on standing, it formed a tremulous jelly entirely soluble in hot or cold
water. Evaporated in vacuo, the solution dries up into a black shining
mass, which is tough and elastic, while it still possesses a certain pro-
portion of water, like gum containing some water. Once thoroughly
dried at a low temperature, this soluble caramel may be heated, after-
wards, to 120° and retain complete solubility. But if a solution of
the same caramel be directly evaporated to dryness by the heat of a
water-bath, the whole matter is rendered insoluble in hot or cold water.
The soluble and insoluble caramel have the same composition, and
appear to illustrate the usual double form of colloids. The proportion
of carbon in the fluid caramel was found as high as 54.59 per cent.,
which comes nearer to C2H18O1s (requiring C 55-17) than any other
formula in which the oxygen and hydrogen are assumed to be present
in the proportion of water. In the analysis by Gélis of his carameline,
the proportion of carbon did not exceed 5133 per cent, which does not
apply to the present substance.
Fluid caramel is wholly tasteless, and appears to be neutral. It
exhibits the same excessive sensibility to crystalloidal reagents which is
witnessed in fluid silicic acid and alumina. The solution is precipitated
or pectized by mere traces of any mineral acid, by alkaline sulphates,
chloride of sodium, by most other salts, and by alcohol. The caramel
then forms a brownish black pulverulent substance, insoluble in hot or
cold water. The presence of sugar and of the intermediate brown sub-
stances protects fluid caramel in a remarkable way from the action of
crystalloids, and accounts for the preceding properties not being observed
in crude caramel. This colloid appears also to be precipitated by certain
substances of its own class, such as peroxide of iron.
Pectous caramel may readily have its solubility restored. Placed in
dilute potash, the caramel Swells and appears gelatinous, and is dissolved
on the application of heat. When this solution is dialysed, the potash
is quickly reduced to the proportion of about 9 per cent, which forms a
neutral compound. If an excess of acetic acid now be added, the whole
potash is soon diffused away, and pure soluble caramel remains on the
dialyser. Even carbonic acid will carry away the potash.
The extremely low diffusibility which has been assigned to caramel
in former Tables, belongs to that substance as last described; the brown
intermediate substances which accompany it in crude caramel being
LIQUID DIFFUSION APPLIED TO ANALYSIS. 591
2nsiderably more diffusive, although they again are much less diffusive
lan any variety of crystallizable or uncrystallizable sugar. When the
Olasses of the cane-sugar are diffused, much the greater portion of the
louring matters remains in the dialyser.
With the parchment-paper septum the fluid caramel appeared even
SS dialysable than gum, the diffusate in twenty-four hours from a 2
per cent. Solution of the former being 009 gramme only, while that of
the latter was 013. Caramel may be stated, approximately, to be 600
times less dialysable than chloride of sodium, and 200 times less so than
sugar. Hence liquids coloured with caramel, such as porter and coffee,
may be dialysed for a day with the passage of very little colouring
matter.
Before leaving caramel, the analogy may be referred to which the
insoluble form of that substance presents to coal. Caramelization
appears the first step in that direction,-the beginning of a colloidal
transformation to be consummated in the slow lapse of geological ages.
Albumen.—The purification of albumen is effected with much
advantage upon the dialyser. The solution of egg-albumen is mixed
freely with acetic acid and then dialysed. The earthy and alkaline salts
are speedily got rid of, and in three or four days the albumen burns
without leaving a trace of ash. Although the acetic acid used in the
process appears to diffuse off entirely, albumen prepared in the manner
described has a faint acid reaction. It also coagulates milk when mixed
with the latter and heated. Albumen so prepared retains its constituent
sulphur.
The passage through parchment-paper of pure albumen prepared by
the unobjectionable process of M. Wurtz is so slow, that several days are
required to produce a sensible result. Thus the diffusate from a solution
of 2 grammes of albumen in 50 grammes of water was 0.052 gramme
in eleven days, which gives 0.005 gramme in a single day. Albumen,
then, appears to be about 2% times less dialysable than gum, and 1000
less so than chloride of sodium.
Even combination with an alkali does not appear to enable albumen
to pass through the colloid septum. To half a gramme of pure albuminic
acid dissolved in 50 grammes of water, '05 gramme of hydrate of soda
was added (one-tenth of the weight of the albumen), and the liquid was
placed upon parchment-paper. No albumen could be discovered in the
diffusate of several days, but it gave '069 gramme of carbonate of soda,
equivalent to 053 gramme of hydrate of soda ; that is the whole soda
originally added to the albumen. The separation of the soda from the
albumen may possibly have been aided by the presence of carbonic acid
in the water, but certainly the entire separation of the alkali from
albumen by diffusion through a colloidal film is a remarkable fact.
592 LIQUID DIFFUSION APPLIED TO ANALYSIS.
Hydrate of potash was found to diffuse away from albumen in the same
Iſla DIlòT.
A solution of Emulsin is precipitated by albuminic and gummic
acids, but not by unpurified albumen or gum-arabic. The precipitates
are white and opaque, pulverulent, and not gelatinous. They are solu-
ble in acetic acid.
A thin stratum of pure albumen coagulated by heat appears to inter-
cept completely the passage of liquid albumen of the egg. Forty
grammes of undiluted egg-albumen, representing 5-6 grammes of dry
albumen, were placed on a dialyser of the small size, composed of two
sheets of calico well impregnated with albumen and coagulated by heat
of steam, as in the albumenized osmometer." After twelve days the
volume of liquid within the instrument had increased to 117 grammes
by osmose, while a diffusate had passed through the dialyser of 0:243
gramme, or 4:34 per cent. of the original dry albumen. This diffusate
consisted of Salts chiefly, with some organic matter, but no portion of
the latter was coagulable by heat.
Neither gelatinous starch, animal gelatine dissolved in water, nor
extract of flesh, appears to be capable of diffusing through a colloid
septum in a sensible degree, although salts and other crystallizable sub-
stances, which are mixed with the former, diffuse the septum readily,
and may thus be separated from the former substances.
6. Separation of Arsenious Acid from Colloidal Liquids.
Dialysis may be advantageously applied to the separation of arseni-
ous acid and metallic salts from organic solutions in medico-legal
inquiries. The process has the advantage of introducing no metallic
substance or chemical reagent of any kind into the organic fluid. The
arrangement for operating is also of the simplest nature.
The organic fluid is placed, to the depth of half an inch, on a dialyser
formed of a hoop of gutta percha 10 or 12 inches in diameter, covered
with parchment-paper (fig. 1, page 556). The dialyser is then floated
in a basin containing a volume of water about four times greater than
the volume of organic fluid in the dialyser. The water of the basin is
generally found to remain colourless after the lapse of twenty-four hours,
and after being concentrated by evaporation, it admits of the application
of the proper reagents to precipitate and remove a metal from solution.
One-half to three-fourths of the crystalloidal and diffusible constituents
of the organic fluid will generally be found in the water of the basin.
In the few illustrative experiments which follow, the 4-inch bulb
dialyser, having an area of 16 Square inches, or about Tºoth part of a
* Philosophical Transactions, 1854, p. 189.
LIQUID DIFFUSION APPLIED TO ANALYSIS. 593
square metre, was generally made use of (fig. 3, p. 573). The volume
of liquid placed in the bulb was 50 cubic centimetres, and accordingly
covered the dialyser to a depth of 5 millimetres, or about 0:2 inch. The
outer volume of water (in the jar) was not less than 1 litre, or twenty
times the volume of the solution on the dialyser.
1. A solution of arsenious acid, in pure water, was first placed on
the dialyser, the water containing 0.5 per cent. of arsenious acid, or 0.25
gramme of that substance, for twenty-four hours. The dialyser being
then removed, the outer fluid was concentrated by heat, and then preci-
pitated by sulphuretted hydrogen. It gave 0300 gramme of tersulphide
of arsenic, equivalent to 0.241 gramme of arsenious acid. It appears,
then, that about 95 per cent of the arsenious acid had diffused from the
dialyser into the water-jar in twenty-four hours.
2. Water, with one-fourth of its volume of fluid egg albumen and
0.25 gramme, or 0.5 per cent. of arsenious acid, was now placed on the
dialyser as before. The diffusate gave, with sulphuretted hydrogen,
after being acidulated with hydrochloric acid, 0.267 gramme of tersul-
phide of arsenic, equivalent to 0.214 gramme of arsenious acid.
3. The water contained 10 per cent. of gum-arabic and 1 per cent.
arsenious acid, the latter amounting to 0.5 gramme. From the diffusate
was derived 0-505 gramme of tersulphide of arsenic, equivalent to 0.406
gramme of arsenious acid. The dialyser still gave out arsenious acid
when immersed for a second day in water. The outer fluid contained
no gum.
It may be added that a similar 1 per cent. solution of arsenious acid,
without the gum, gave a diffusate of 0.45 gramme arsenious acid in the
same time, that is, nine-tenths of the whole acid.
4. A solution in hot water of l per cent. isinglass and 0.5 per cent.
of arsenious acid (0.25 gramme), formed a jelly upon the dialyser on
cooling. The diffusate from this jelly gave 0.260 tersulphide of arsenic,
equivalent to 0.209 arsenious acid, with no gelatine. The escape of the
arsenious acid appears then to have been slightly retarded by the fixing
of the gelatinous solution. This is probably due to the arrest of
mechanical movement within the gelatinous stratum, and not to any
sensible impediment offered by the jelly to diffusion.
In another experiment, similar to the last, but continued for four
days instead of twenty-four hours, the terSulphide of arsenic weighed
0.320 gramme, equivalent to 0.257 arsenious acid.
5. A quantity of white of egg, amounting to 50 grammes, to which
0.01 gramme of arsenious acid in solution had been added, was coagu–
lated by heat. The solid mass was then cut up into small pieces and
placed on the dialyser, mixed with 50 grammes of water; after the
usual period of twenty-four hours, the diffusate gave 0.01 gramme
2 P
594 LIQUID DIFFUSION APPLIED TO ANALYSIS.
of tersulphide of arsenic, equivalent to 0:008 gramme arsenious acid.
Here, of the mass upon the dialyser, the arsenious acid formed only
isºth part, yet four-fifths of it are recovered.
6. One hundred grammes of milk, charged with mºth part of
arsenious acid (0.01 gramme), and forming a stratum on the dialyser of
10 millimetres, gave a diffusate which yielded 0-010 tersulphide of
arsenic, equivalent to 0:008 gramme of arsenious acid. The outer liquid
was colourless, and gave no indication of casein, but it contained of
course the salts and the Sugar of the milk.
7. The same experiment was repeated with sized writing-paper, as
the septum, applied to the same bulb. The result was a slight increase
in the quantity of arsenious acid recovered. *
It appears, then, that arsenious acid separates on the dialyser from
gum, from gelatine, albumen, fluid or coagulated, and from casein, and
is obtained in a solution fit for the application of reagents.
8. Half a litre of dark-coloured porter, with 0.05 gramme of arsenious
acid added Gºth part of arsenious acid) was placed on a hoop dia-
lyser, 8 inches in diameter, and the whole floated in an earthenware
basin containing 2 or 3 litres of water. After twenty-four hours the
latter fluid had acquired a slight tinge of yellow. It yielded, when
concentrated and precipitated by sulphuretted hydrogen, upwards of
one-half of the original arsenious acid in a fit state for examination.
9. In a similar experiment on 200 grammes of defibrinated blood
charged with ºth part of arsenious acid (0.05 gramme), and placed in
a similar dialyser to the last for twenty-four hours, the diffusate of
arsenious acid was recovered with the same facility, and appeared to be
equally considerable.
10. Animal intestines, charged with the usual minute proportion of
arsenious acid, were cut into small pieces and digested in water, about
32° C., for twenty-four hours. The whole was then thrown upon a
dialyser for an equal time. Arsenious acid diffused out so free from
colloidal matter that the action of reagents was not interfered with. A
high temperature in digesting the intestines is quite unnecessary, and
appeared indeed to increase the difficulty of diffusing out the arsenious
acid afterwards.
The tartrate of potash and antimony, mixed in the Small proportion
of ºth, with defibrinated blood and with milk, was separated by
10,000
dialysis quite as effectually as arsenious acid above.
Strychnine also was separated from organic fluids in the same
manner, a small addition of hydrochloric acid being first made to the
fluid on the dialyser.
Dialysis then appears of general application in the preparation of a
LIQUID DIFFUSION APPLIED TO ANALYSIS. 595
liquid for examination by chemical tests, whether the poison looked for
be mineral or organic. All soluble poisonous substances, whatever
their origin, appear to be crystalloids, and accordingly pass through
colloidal septa.
7. Colloidal Condition of Matter.
I may be allowed to advert again to the radical distinction assumed
in this paper to exist between colloids and crystalloids in their intimate
molecular constitution. Every physical and chemical property is char-
acteristically modified in each class. They appear like different worlds
of matter, and give occasion to a corresponding division of chemical
science. The distinction between these kinds of matter is that subsist–
ing between the material of a mineral and the material of an organized
Iſla SS.
The colloidal character is not obliterated by liquefaction, and is there-
fore more than a modification of the physical condition of solid. Some
colloids are soluble in water, as gelatine and gum-arabic ; and some are
insoluble, like gum-tragacanth. Some colloids, again, form solid com-
pounds with water, as gelatine and gum-tragacanth, while others, like
tannin, do not. In such points the colloids exhibit as great a diversity
of property as the crystalloids. A certain parallelism is maintained
between the two classes, notwithstanding their differences.
The phenomena of the solution of a salt or crystalloid probably all
appear in the solution of a colloid, but greatly reduced in degree. The
process becomes slow; time, indeed, appearing essential to all colloidal
changes. The change of temperature, usually occurring in the act of
solution, becomes barely perceptible. The liquid is always sensibly
gummy or viscous when concentrated. The colloid, although often
dissolved in a large proportion by its solvent, is held in solution by a
singularly feeble force. Hence colloids are generally displaced and
precipitated by the addition to their solution of any substance from the
other class. Of all the properties of liquid colloids, their slow diffusion
in water, and their arrest by colloidal septa, are the most serviceable in
distinguishing them from crystalloids. Colloids have feeble chemical
reactions, but they exhibit at the same time a very general sensibility
to liquid reagents, as has already been explained.
While soluble crystalloids are always highly sapid, soluble colloids
are singularly insipid. It may be questioned whether a colloid, when
tasted, ever reaches the sentient extremities of the nerves of the palate,
as the latter are probably protected by a colloidal membrane, imper-
meable to soluble substances of the same physical constitution.
It has been observed that vegetable gum is not digested in the
stomach. The coats of that organ dialyse the soluble food, absorbing
596 LIQUID DIFFUSION APPLIED TO ANALYSIS.
crystalloids and rejecting all colloids. This action appears to be aided
by the thick coating of mucus which usually lines the stomach.
The secretion of free hydrochloric acid during digestion—at times
most abundant—appears to depend upon processes of which no distinct
conception has been formed. But certain colloidal decompositions are
equally inexplicable upon ordinary chemical views. To facilitate the
separation of hydrochloric acid from the perchloride of iron, for instance,
that salt is first rendered basic by the addition of peroxide of iron. The
comparatively stable perchloride of iron is transformed, by such treat-
ment, into a feebly-constituted colloidal hydrochlorate. The latter
compound breaks up under the purely physical agency of diffusion, and
divides on the dialyser into colloidal peroxide of iron and free hydro-
chloric acid. The super-induction of the colloidal condition may pos-
sibly form a stage in many analogous organic decompositions.
A tendency to spontaneous change, which is observed occasionally
in crystalloids, appears to be general in the other class. The fluid
colloid becomes pectous and insoluble by contact with certain other
substances, without combining with these substances, and often under
the influence of time alone. The pectizing substance appears to hasten
merely an impending change. Even while fluid a colloid may alter
sensibly, from colourless becoming opalescent ; and while pectous the
degree of hydration may become reduced from internal change. The
gradual progress of alteration in the colloid effected by the agency of
time, is an investigation yet to be entered upon.
The equivalent of a colloid appears to be always high, although the
ratio between the elements of the substance may be simple. Gummic
acid, for instance, may be represented by C13 Hu Oil, but judging from
the small proportions of lime and potash which suffice to neutralize this
acid, the true numbers of its formula must be several times greater. It
is difficult to avoid associating the inertness of colloids with their high
equivalents, particularly where the high number appears to be attained
by the repetition of a smaller number. The inquiry suggests itself
whether the colloid molecule may not be constituted by the grouping
together of a number of smaller crystalloid molecules, and whether the
bases of colloidality may not really be this composite character of the
molecule.
With silicic acid, which can exist in combination both as a crystal-
loid and colloid, we have two series of compounds, silicates and cosili-
cates, the acid of the latter appearing to have an equivalent much greater
(thirty-six times greater in one salt) than the acid of the former. The
apparently small proportion of acid in a variety of metallic salts, such
as certain red salts of iron, is accounted for by the high colloidal equi-
valent of their bases. The effect of such an insoluble colloid as prussian
LIQUID DIFFUSION APPLIED TO ANALYSIS. 597
blue in carrying down small proportions of the precipitating salts, may
admit of a similar explanation.
Gelatine appears to hold an important place as a colloidal base.
This base unites with colloidal acids, giving a class of stable compounds,
of which tanno-gelatine only appears to be hitherto known. Gelatine
is precipitated entirely by a solution of meta-phosphoric acid added drop
by drop, 100 parts of gelatine uniting with 3-6 parts of the acid. The
compound formed is a semi-transparent, soft, elastic, and stringy solid
mass, presenting a startling resemblance to animal fibrin. It will be
an interesting inquiry whether metaphosphoric acid is a colloid, and
enters into the compound described in that character, or is a crystalloid,
as the small proportion and low equivalent of the acid would suggest.
Gelatine is also precipitated by carbolic acid.
The hardness of the crystalloid, with its crystalline planes and
angles, is replaced in the colloid by a degree of softness, with a more or
less rounded outline. The water of crystallization is represented by
the water of gelatination. The water in gelatinous hydrates is aptly
described by M. Chevreul as retained by “capillary affinity,” that is, by
an attraction partaking both of the physical and chemical character.
While it is here admitted that chemical affinity of the lowest degree
may shade into capillary attraction, it is believed that the character of
gelatinous hydration is as truly chemical as that of crystalline hydration.
Combination of a colloid with water is feeble, it is true, but so is com-
bination in general with the colloid. Notwithstanding this, anhydrous
colloids can decompose certain crystalloid hydrates. The water in
alcohol of greater strength than corresponds with the density 0.926,
which represents the definite hydrate C, H, O, -i- 6HO, is certainly in
a state of chemical union. But alcohol so high as 0-906, contained in a
close vessel, is concentrated in a notable degree by contact with dry
mucus, gelatine, and gum, and sensibly even by dry parchment-paper.
Dilute alcohol divided from the air of the atmosphere by a dry septum
of mucus, gelatine, or gum, is also concentrated by evaporation, as in
the well-known bladder experiment of Sömmering. The selective power
is here apparent of the colloid for water, that fluid being separated from
alcohol, and travelling through the colloidal septum by combination with
successive molecules of the latter, till the outer surface is reached and
evaporation takes place. The penetration in this manner of a colloid by
a foreign substance may be taken as an illustration of the phenomena
of cementation. Iron and other substances which soften under heat,
may be supposed to assume at the same time a colloidal constitution.
So it may be supposed does silica when fused into a glass by heat, and
every other vitreous substance.
Gelatinous hydrates always exhibit a certain tendency to aggregation,
598 LIQUID DIFFUSION APPLIED TO ANALYSIS.
as is seen in the jelly of hydrated silicic acid and of alumina. With
Some the jelly is also adhesive, as in glue and mucus. But unless they
be soluble in water, gelatinous hydrates, when once formed, are not in
general adhesive. Separated masses do not reunite when brought into
contact. This want of adhesiveness is very remarkable in the gelose of
Payen, which resembles gelatine so closely in other respects. Layers of
a gelose solution, allowed to cool and gelatinize in succession in a dif-
fusion-jar (p. 571), do not adhere together.
Ice itself presents colloidal characters at or near its melting-point,
paradoxical although the statement may appear. When ice is formed
at temperatures a few degrees under 0°C., it has a well-marked crystal-
line structure, as is seen in water frozen from a state of vapour, in the
form of flakes of snow and hoar-frost, or in water frozen from dilute
sulphuric acid, as observed by Mr. Faraday. But ice formed in contact
with water at 0°, is a plain homogeneous mass with a vitreous fracture,
exhibiting no facets or angles. This must appear singular when it is
considered how favourable to crystallization are the circumstances in
which a sheet of ice is slowly produced in the freezing of a lake or river.
The continued extrication of latent heat by ice as it is cooled a few
degrees below 0° C., observed by M. Person, appears also to indicate
a molecular change subsequent to the first freezing. Further, ice,
although exhibiting none of the viscous softness of pitch, has the elas-
ticity and tendency to rend seen in colloids. In the properties last
mentioned, ice presents a distant analogy to gum incompletely dried, to
glue, or any other firm jelly. Ice further appears to be of the class of
adhesive colloids. The redintegration (regelation of Faraday) of masses
of melting ice, when placed in contact, has much of a colloid character.
A colloidal view of the plasticity of ice demonstrated in the glacier
movement will readily develop itself.
A similar extreme departure from its normal condition appears to
be presented by a colloid holding so high a place in its class as albumen.
In the so-called blood-crystals of Funke, a soft and gelatinous albumi-
noid body is seen to assume a crystalline contour. Can any facts more
strikingly illustrate the maxim that in nature there are no abrupt
transitions, and that distinctions of class are never absolute 7
8. Osmose.
Little has been said in the present paper respecting osmose, a subject
closely connected with colloidal septa. It now appears to me that the
water movement in Osmose is an affair of hydration and of dehydration
in the substance of the membrane or other colloid Septum, and that the
diffusion of the saline solution placed within the Osmometer has little
LIQUID DIFFUSION APPLIED TO ANALYSIS. 5.99
or nothing to do with the osmotic result, otherwise than as it affects the
state of hydration of the septum.
Osmose is generally considerable, through membranous and other
highly hydrated septa, with the solution of any colloid (gum, for in-
stance) contained in the osmometer. Yet the diffusion outwards of the
colloid is always minute, and may sometimes amount to nothing.
Indeed, an insoluble colloid, such as gum-tragacanth, placed in powder
within the osmometer, was found to indicate the rapid entrance of
water to convert the gum into a bulky gelatinous hydrate. Here no
outward or double movement is possible.
The degree of hydration of any gelatinous body is much affected by
the liquid medium in which it is placed. This is very obvious in
fibrin and animal membrane. Placed in pure water, such colloids are
hydrated to a higher degree than they are in neutral Saline Solutions.
Hence the equilibrium of hydration is different on the two sides of the
membrane of an osmometer. The outer surface of the membrane
being in contact with pure water tends to hydrate itself in a higher
degree than the inner surface does, the latter surface being supposed to
be in contact with a saline solution. When the full hydration of the
outer surface extends through the thickness of the membrane and
reaches the inner surface, it there receives a check. The degree of
hydration is lowered, and water must be given up by the inner layer of
the membrane, and it forms the osmose. The contact of the Saline
fluid is thus attended by a continuous catalysis of the gelatinous
hydrate, by which it is resolved into a lower gelatinous hydrate and
free water. The inner surface of the membrane of the osmometer con-
tracts by contact with the saline solution, while the outer surface
dilates by contact with pure water. Far from promoting this separa-
tion of water, the diffusion of the salt throughout the substance of the
membrane appears to impede osmose, by equalizing the condition as to
saline matter of the membrane through its whole thickness. The
advantage which colloidal solutions have in inducing osmose, appears
to depend in part upon the low diffusibility of such solutions, and their
want of power to penetrate the colloidal septum.
The substances fibrin, albumen, and animal membrane swell greatly
when immersed in water containing minute proportions of acid or of
alkali, as is well known. On the other hand, when the proportion of
acid or alkali is carried beyond a point peculiar to each substance, con-
traction of the colloid takes place. Such colloids as have been named
acquire the power of combining with an increased proportion of water,
and of forming superior gelatinous hydrates, in consequence of contact
with dilute acid and alkaline reagents. Even parchment-paper is
more elongated in an alkaline Solution than in pure water. When so
600 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
hydrated and dilated, the colloids present an extreme osmotic sensibility.
Used as septa, they appear to assume or resign their water of gelatination
under influences apparently the most feeble. It is not attempted to
explain this varying hydration of colloids with the osmotic effects
thence arising. Such phenomena belong to colloidal chemistry, where
the prevailing changes in composition appear to be of the kind vaguely
described as catalytic. To the future investigation of catalytic affinity,
therefore, must we look for the further elucidation of osmose.
XVI,
ON THE CAPILLARY TRANSPIRATION OF LIQUIDS IN
RELATION TO CHEMICAL COMPOSITION."
From Phil. Trans. 1861, pp. 373-386. [Roy. Soc. Proc. xi. 1860-62, pp. 381-384;
Chem. Soc. Journ. xv. 1862, pp. 427–445; Paris Comptes Rendus, liii. 1861,
pp. 774-777.]
THE passage of liquids under pressure through a capillary tube is
here spoken of as liquid transpiration, in accordance with the analogy of
gaseous transpiration. The subject owes the development which it has
already acquired chiefly to the investigations of the late Dr. Poiseuille.”
The precision of the results attainable by the mode of experimenting
pursued by that physicist has been remarked on by every one who has
followed him in the inquiry. The observations on this subject which
we owe to M. Poiseuille and other inquirers are very numerous, but
have not, so far as I am aware, been connected hitherto with any specu-
lative views of the chemical or molecular constitution of liquids.
The isolated discovery of M. Poiseuille, that diluted alcohol has a
point of maximum retardation, coinciding with the degree of dilution
at which the greatest condensation of the mixed liquids occurs, appears
to offer a starting-point for new inquiries. The same result may be
otherwise expressed, by saying that the definite compound of 1 equiv.
of alcohol with 6 equivs. of water, C.H.O., + 6HO,” is more retarded
than alcohol containing either a greater or a smaller proportion of water.
The rate of transpiration appears here to depend upon chemical compo-
sition, and to afford an indication of it. A new physical property may
1 Received June 20,—Read June 20, 1861.
* Mém. Savans étrangers, tom. ix. p. 433; Ann. Chim. 3 sér, tt. 7 et 21.
* Halving the equivalent of alcohol, the hydrate of greatest retardation becomes
C.H.O + 3HO.
IN RELATION TO CHEMICAL COMPOSITION. 601
thus become available for the determination of the chemical constitu-
tion of substances. Methylic alcohol being found to exhibit the same
remarkable feature in its transpiration, although the 6-hydrate of that
alcohol is not distinguished by extraordinary condensation of volume,
the inquiry was extended to the hydrated acids. The results obtained
with the latter substances give a certain degree of generality to the
relation subsisting between the transpirability and chemical composition
of liquids.
The apparatus employed was very similar to that of M. Poiseuille.
It consisted of a small but rather stout glass bulb, A (see figure), about
two-thirds of an inch in dia-
meter, having a capacity of
from 4 to 8 cub. cent., blown
upon a thick glass tube,
with a bore of about 2 milli-
metres. A scratch (c) was
made upon the glass tube
above, and another (d) below
the bulb, to indicate the
available capacity of the
instrument. The lower tube
was bent at a right angle to
the upper, and a fine capil-
lary tube, B, from 3 to 4
inches in length, was sealed
to the curved extremity of
the tube. The bulb and
capillary were always held
immersed in a vessel of water
during the experiment, in
order to secure uniformity –
of temperature. The force
employed to impel the liquid through the capillary was the weight of
one atmosphere of 760 millimetres of mercury, and was obtained from
compressed air contained in a large reservoir provided with a mercurial
gauge, as in Poiseuille's experiments. The time was noted in Seconds
which the level of the liquid in the bulb took to fall from the mark c to
the mark d. This time varied from about 300 to 900 seconds in differ-
ent liquids. In successive experiments made upon the same liquid, the
variation in the time, or error of observation, did not exceed one or two
seconds. The experiment was always repeated two or three times, and
a mean taken. The temperature of the liquid transpired was always
20° (68°F), when not otherwise stated.

N-
d.
602 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
The liquid may be introduced into the bulb through the open upper
tube by means of a tube-funnel; but it was found more convenient in
practice, although requiring a much longer time, to fill the bulb by aspi-
ration through the capillary. With this view the compressed air was
shut off by a stop-cock, and the upper tube of the bulb was then allowed
to communicate with the receiver of an air-pump, instead, by which
exhaustion was produced, while the open end of the capillary was im-
mersed in a portion of the liquid. The liquid which entered the bulb
in this manner was sure to be free from any solid matter which could
cause obstruction in the capillary during the subsequent passage of the
liquid outwards, while the disconnecting of the bulb from the rest of the
apparatus, for the purpose of filling the former, was also avoided.
Mitric Acid.
A bulb provided with a capillary tube, distinguished as capillary C,
was used in the transpiration of nitric acid and of several other liquids.
The dimensions of this bulb C were as follows:–Capacity of bulb, 8.075
cub. cent. ; length of capillary tube, 28 millims. ; diameter of bore,
0.0942 millim. The time of passage of water through the tube, under
the pressure of one atmosphere and at the fixed temperature of 20°,
was 348 seconds. The time of the passage of the most highly concen–
trated nitric acid through the same capillary was found to be 344-5
seconds, or slightly less than the time of water. This is the proto-
hydrate of nitric acid, HO. NO, or NHO's. With the addition of water
to the acid, the transpiration of equal volumes of liquid becomes gra-
dually slower; till as much as three additional equivalents of water
were added, when the transpiration-time rose to its maximum, 732
seconds. The last hydrate is the well-known definite compound
NHOs -- 3PIO, having the specific gravity 14, and which possesses the
highest boiling-point of any compound of nitric acid and water. Diluted
beyond this point nitric acid begins to pass more freely, and the tran–
spiration-time approaches again to that of water. With the addition of
twice its weight of water, or about 7 equivalents, the acid passed through
the capillary in 472 seconds.
The experiments made upon nitric acid are recorded in the following
Table. It will be observed that the retardation is considerable for a
certain distance on both sides of the maximum point. No unusual
retardation appears to occur with the proportions of water correspond-
ing to 2 and 4 equivalents. The specific gravity of the acid liquid is
added in the last column of the Table, whenever that property was
observed.
IN RELATION TO CHEMICAL COMPOSITION. 603
TABLE I.--Transpiration of Nitric Acid, at 20° C., by Capillary C."
(Transpiration-time of water, 348 seconds.)
Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(NHO's). per cent. at 15°.
In seconds. Water = I.
0. 0 344'5 0-9899 1°5046
25-47 20-38 692 19885 1°4358
28:56 ... 2 eqs. HO 21'43 705 2-0258
30 23:07 712 2.0459
40 * 28'50 725 2.0833
42.85... 3 eqs. HO 29.99 732 2-1034 I 3978
45 31-03 730 2-0977
50 33-33 728-5 2°0919 I'3816
55 35°48 718 2.0632
57-12... 4 eqs. HO 36-35 712 2.0459
60 37.50 709.5 2-0387 1.3598
70 41-17 683 1.9626 1.3407
80 44'44 661 1-8994 I-3239
90 47-36 635-5 I '8261
100 50-00 593 17040 1-2943
200 66'66 472 1-3563
It appears, then, that a certain hydrate of nitric acid is marked
out by its low transpirability so distinctly, that nitric acid could be
identified by that physical property. Such a property may prove to be
typical of a class of acids to which nitric acid belongs. The hydration
of nitric acid probably advances by three equivalents at a time, NHO's +
3HO, as in the magnesian nitrates, NMOs -- 3HO + 3HO. The tran-
spiration of the assumed second hydrate of nitric acid was not made
the subject of experiment. A certain steadiness is observed in the
transpiration of this acid on either side of the point of maximum
retardation.
* In the following Tables, the particular capillary employed is in each case desig-
nated by a particular letter. Capillary C, which was more employed than any other,
became reduced in length during the course of the experiments, the end being ground
off on several occasions on account of the choking of the tube. This capillary is then
described as C shortened. It did not seem requisite to give in every case the dimen-
sions of the bulb and capillary tube, as all the experiments were conducted on the
same plan, and the transpiration of water is in every case given as a standard of com-
parison. Direct experiments were also made, which proved that the transpiration-
times were sensibly inversely proportional to the effective pressure applied to the
liquid, as found by Poiseuille; which indicates that the capillaries offered sufficient
resistance to the passage of the liquid.
604 ON TEIE CAPILLARY TRANSPIRATION OF LIQUIDS
Sulphuric Acid.
TABLE II.—Transpiration of Sulphuric Acid, at 20°, by Capillary G.
(Transpiration-time of water, 109 seconds.)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(SHO4). per cent. at 15".
In seconds. Water = I.
0 0 2360 21-6514 1-8456
2.5 2:43 2412 22° 1284 1-8398
5 4-76 2451 22:4862 1°8346
10 9-09 2516 23:08:25 I-8120
12.5 I I I I 2548 23:3761 I-7976
15 13-04 2587 23-7.340 l'7800
17.5 I4'89 2591 23-7706
1836... I eq. HO 15° 13 2466 22-6238 17590
20 16-66 2398 22:0000 I-7473
30 23:07 1523 13°9724 1-6700
36-73 ... 2 eqs. HO 26'86 1189 I0-9090 I-6335
40 28'50 1056 9-6880 l"6146
50 33-33 810 7'4302 1-5600
60 37.50 626 5-7431 l'5118
70 41' 17 535 4-9082
80 44'44 450 4°1284
100 50-00 382 3-5045
120 54'54 332 3-0.458
140 58.33 290 2’6605
160 61-53 260 2.3889
180 64°28 24l 2.2110 ;
200 66'66 227 2-0825
The transpiration of sulphuric acid is very slow, being twenty-four
times less rapid than that of water, as might be expected from the
viscous quality of the acid fluid. It is surprising, however, that the
first additions of water do not promote the transpiration, although they
lessen in a sensible degree the viscosity of the liquid. The transpira-
tion-time increases from 2360 to 2591 seconds, and then attains the
maximum, when 17°5 parts of water have been added to 100 parts of
oil of vitriol. The proportion of water named approaches closely to 1
equivalent (1836 parts). Indeed, it is quite possible that the acid mix-
ture which exhibits the least transpirability might have contained a
full equivalent of water, for a portion of aqueous vapour may have
been absorbed from the air during the process of filling the bulb. That
the crystallizable hydrate of sulphuric acid, SHO,--HO, is the liquid
of least transpirability is, I believe, the proper inference from these
IN RELATION TO CHEMICAL COMPOSITION. 605
observations. With increasing proportions of water the transpiration-
time rapidly diminishes, till the time is reduced to 227 seconds in a
mixture of oil of vitriol with twice its weight of water.
A more minute examination than has been attempted would be
required to show whether the existence of other definite hydrates of
sulphuric acid may be indicated by a perceptible retardation in the
time of transpiration.
Acetic Acid.
TABLE III.-Transpiration of Acetic Acid, at 20°, by Capillary C.
(Transpiration-time of water, 348 seconds.)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
4H4O4). per cent. at 15°.
In seconds. Water = 1.
0-8 0-8 445-5 i 2801
15 ... 1 eq. HO 13-04 890 2:5574 1.0735
20 16-66 921.5 2-6480 1-0742
25 20:00 931 2.6753
27.5 21:56 933 2.6810
30 ... 2 eqs. HO 23:07 941 2-7040 1.0752
32°5 24°52 934 2.6839 1-0746
35 25-92 928 2-6666
40 28-50 912 2-6207
45 31:04 895 2°5718
50 33-33 882 2-5344 1.0720
60 ... 4 eqs. HO 37:50 852 2-4482 1-0700
90 ... 6 eqs. HO 47-36 769 2-2098 -
The glacial acetic acid made use of in these experiments still retained
0.8 per cent of water. Its transpiration-time was 445-5 seconds. With
the addition of 1 equiv. of water the time rose to 890 seconds; and with
2 equivs. of water to 941 seconds, when it attained its maximum. This
last is the characteristic hydrate of acetic acid, C.H.O., + 2 HO. It is
marked out with great precision in these transpiration experiments.
The times rise very gradually on either side, and appear to culminate
exactly at that point. It is also the compound of water and acetic acid
of maximum density, as is well known. The transpiration-time of the
hydrate referred to is so much as 2.7 times longer than that of pure
water. With 6 equivalents of water acetic acid is still transpired 2-2
times more slowly than water.
600 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
Butyric Acid.
TABLE IV—Transpiration of Butyric Acid, C.H.O., at 20,
by Capillary C shortened.
(Transpiration-time of water, 290 seconds)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(Csbis04). per cent. at 15°.
In seconds. Water = 1.
0 0 454 1.565 •9740
10:22 ... 1 eq. HO 9:27 828 2.855 •9901
20:45 ... 2 eqs. HO 16.98 95] 3.279 •9975
30-67 ... 3 eqs. HO 23:47 969 3'34.1
38-69 ... 4-8 eqs. HO 27.85 863 2.975
In the transpirability of its hydrates butyric acid presents a con–
siderable analogy to acetic acid, as might be expected from the relation
of these acids in composition. The time of the pure acid (CsPIsO.) is
1565, referred to that of water as 1, and it rises to 2-855 by the addition
of 1 equivalent of water. By a second equivalent of water the time is
increased to 3.279. Here, however, the progression does not imme-
diately turn, as with acetic acid, but the time rises to 3-341 with 3
equivalents of water. With 3-8 equivalents of water the time is 2.975,
and has accordingly very sensibly receded, the maximum point being
passed. It is conceivable that the relation to acetic acid is slightly
modified in butyric acid by the interference of some other physical
property, such as unctuosity, that is unequally developed in the two
acids.
Valerianic Acid.
The hydration of this acid cannot be carried beyond 2 equivalents,
but up to that point the transpiration is retarded by every addition of
water, as in acetic and butyric acids. While the pure basic hydrate
(CoPſioC),) is transpired in 2:155 times the water period, the time
increases to 3-634 with 1 equivalent of water added, and to 3-839 with
2 equivalents.
IN RELATION TO CHEMICAL COMPOSITION. 607
TABLE W.-Transpiration of Valerianic Acid, at 20° C.,
by Capillary C shortened.
(Transpiration-time of water, 290 seconds.)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(C10H10O.). per cent. at 15°.
In Seconds. Water=1.
0 0 625-2 2-155 •9350
8-82... I eq. HO 8-10 1054 3-634 *9484
17-64... 2 eqs. HO 15-84 1113-5 3-839 •9519
Formic Acid.
Formic acid appears to diverge considerably from the other members
of the acetic acid series in certain physical and chemical characters.
While the acetic hydrate is lighter than water, and is increased in
density by the addition of water, the formic hydrate has a higher density
than water, and has its density uniformly lowered by dilution, as will
be seen in the Table which follows. The transpiration-time of formic
acid in a concentrated state is also highest, and diminishes with dilution
in the same regular manner as the density, showing no evidence of the
acetic maximum at the point of 2 equivalents of water. Indeed, formic
acid does not appear to affect that particular degree of hydration so
characteristic of the acetic acid series. Hence it is, also, that we have
no subformiate of lead corresponding with the subacetate of lead, and
have occasion to remark a general absence of basic formiates. The
physical properties of liquid formic acid are more suggestive of hydro-
chloric acid than they are of acetic acid.
The most concentrated formic acid that could be prepared still con-
tained 3.6 per cent. of water. The transpiration-time of that liquid, it
will be seen, is 1718 referred to water as 1; and of the 2-hydrate 1:486.
There is evidence of retardation between the points of 3 and 4 equi-
valents of water, but it is difficult to say with which of these two
hydrates the retardation should be connected. More numerous and
minute observations would be required to settle the point. We can
only draw the negative conclusion from the Table, that the maximum
retardation does not coincide with the 2-hydrate as in acetic acid.
608 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
TABLE VI.-Transpiration of Formic Acid, at 20°,
by Capillary C shortened.
(Transpiration-time of water, 293 seconds.)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(C2H2O4). per cent. at 15°.
In seconds. Water = 1.
3-73 3-6 503.5 1-718 1.2265
19:56 ... 1 eq. 16:35 484-5 1:653 1.2019
39°13 ... 2 eqs. 20-93 435-5 1'486 l’l'765
58-69 ... 3 eqs. 36'98 4ll 1-402 l" 1524
68’47 ... 3-5 eqs. 40-64 40] '5 1.368 l”].466
78.26 ... 4 eqs. 43-90 402-5 1.372 I-1408
97-82 ... 5 eqs. 49°44 388-5 1.325 1-1275
117:35 ... 6 eqs. 53-99 376.5 I'284 l" l.203
136'95 ... 7 eqs. 57-79 359 1.225 l’IO62
Hydrochloric Acid.
The most concentrated form of this acid that was dealt with, acid of
sp. gr. 1'1553, contained already upwards of 8 equivalents of water. Its
transpiration-time was 17356, referred to the time of water as 1. With
further dilution the time diminished, till at the proportion of 12 equiva-
lents of water the time had fallen to 15287. About this point the rate
of diminution is reduced, and the transpiration-time even becomes
stationary for a short portion of the range of hydration. The retardation
observed appears to coincide with the formation of a 12-hydrate of
hydrochloric acid. The existence of such a compound is further sup-
ported by the fact that solutions of hydrochloric acid tend to the same
composition by evaporation at the atmospheric temperature. The
degree of hydration of most stability at high temperatures, and having
the highest boiling-point, is known to be at or near the proportion of
the 16-hydrate. The existence, however, of the latter hydrate, at the
ordinary temperature, is not supported by the transpiration experiments
now recorded, conducted as these were at a low temperature.
IN RELATION TO CHEMICAL COMPOSITION. 609
TABLE VII-Transpiration of Hydrochloric Acid, at 20°, by Capillary C.
(Transpiration-time of water, 348 seconds.)

Transpiration-time.
Water added to 100 acid Water, Specific gravity,
(HCl). per cent. at 15°.
In Seconds. Water = 1.
221-8 69.23 604 1-7356 1-1553
250 71-42 569 1:6336 1 - 1411
280 73-67 536 1:54.04 1° 1303
290 74°36 532 1-5287
295.89... 12 eqs. HO 74-74 532 I-5287 1°1246
300 75:00 520 1-4942
310 75-60 516 1-4827 1 1202
380 79.20 486 1.3965 1-1021
394 ... 16 eqs. HO || 79-97 479 1-3764 1.0992
410 80-39 469 1.3476 1-096]
Alcohol.
The fundamental discovery made by Poiseuille of a point of maxi-
mum retardation in the transpiration of diluted alcohol is fully con-
firmed in the following series of observations. The transpiration-time
rises from that of absolute alcohol, 1:1957 (water being 1), to 2.7872,
when the alcohol is united with 6 equivalents of water, and then falls
off again by further additions of water.
TABLE VIII.—
2 Q
610 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
TABLE VIII-Transpiration of Alcohol, at 20°, by Capillary D.
(Transpiration-time of water, 470 seconds.)

Transpiration-time.
Water added to 100 Water, Specific gravity,
Alcohol. per cent. at 15°.
In seconds. Water = 1.
O 0 562 1-1957
I 0-99 578 1-2297 •7069
3 2.91 615 1.3085 •8030
5 4-76 650 l'3829 •8083
7 6'54 695 1.4787
10 9-09 734 1-5617
20 16-66 851 I '8106 •8396
30 23:07 950 2-0212 •8557
40 28'50 I029 2-1893 •8683
50 33-33 1093 2.3253 •8800
60 37:50 1152 2-4510 •8897
70 41-17 1213 2-5808 •8983
72°5 42-02 1230 2-6,170 •9003
75 * 42-85 1231 2-6,191 •9021
78.26 ... 4 eqs. HO 43-94 1239 2-636] •9045
80 44'44 1238 2-6340 •9058
82.5 45°20 1242 2-64.25 •9073
85 45'94 1244 2.6468 •9088
90 47-36 1256 2.6723 •9120
100 50.00 1268 2-6978 •9183
110 52°38 1282 2.7276 •9235
112.5 52-94 1287 2-7382 •9249
115 53-49 I298 2.7617 •9255
117:39... 6 eqs. HO 54-04 1310 2.7872 •9271
120 54'54 1307 2.7808 •9288
I22 55.05 1300 2-7659 •9292
125 55-55 1297 2.7595 •9304
130 56-52 1297 2.7595 •9328
140 58-33 1295 2-7553 •9363
150 60-00 1280 2-7234 •9396
160 61°53 1255 2.6702 *9430
170 62-92 1250 2-6505 •945],
180 64°28 1246 2-6510 •9482
190 65°51 1240 2-6382 •9500
200 66-66 1235 2.6276 •952]
250 71.42 1165 2.4787 •9601
300 75:00 I 094 2.3276 •9652
350 77.77 1026 2-1829 •9689
400 80:00 973 2:0702 •9716
450 81:80 934 1.9872 •9738
500 83:33 908 1-93.19 •9759
It will be observed that after attaining its maximum the transpira-
tion-time falls off in a very gradual manner, till another equivalent at
least of water has been added. With still further dilution the shorten-
ing of the transpiration-time is considerably more rapid. The Table
appears to indicate a slight retardation at the proportion of four equi-
valents of water; but this would require confirmation. It is remarkable
IN RELATION TO CHEMICAL COMPOSITION. 611
that hydrated liquid compounds appear in general to show only one
decided transpiration maximum, as with the 1-hydrate in sulphuric acid,
the 2-hydrate in acetic acid, the 3-hydrate in nitric acid, the 6-hydrate
in alcohol, and the 12-hydrate in hydrochloric acid.
A considerable number of experiments were made upon specimens
of methylic alcohol prepared at different times, with some discrepancy in
the results. Although always derived from crystallized methylic oxalic
ether, the liquid varied sensibly in transpirability. As the cause of
this variation has not yet been ascertained, I shall confine myself at
present to one statement, namely, that a particular specimen of methylic
alcohol gave 0.63 as the transpiration-time of the anhydrous substance
(water being 1), and 1-8021 as the time of the 6-hydrate, C.H.O2+
6HO, and that for a considerable distance on either side of that point
of hydration the transpiration was slightly less and nearly constant, as
it is in vinic alcohol. It may be inferred, therefore, with some proba-
bility, that alcohols have a maximum of retardation at the same stage
of dilution.
Three alcohols in a state of purity were transpired through the same
capillary, with water for comparison, at 20°. The time of water was
297 seconds.
TABLE IX—Transpiration of Alcohols, at 20°.

Transpiration-time.
speciegºvits, Boiling point.
In seconds. Water = 1.
Methylic alcohol, . . 187:25 0-630 •7973 66 C.
Vinic alcohol, e e 355°l 1’ 195 ‘7947 78-5
Amylic alcohol, . e 1084 3°649 '8204 132
It will be remarked that the transpiration-time of an alcohol in-
creases with the elevation of its temperature of ebullition. A similar
observation applies to the transpiration of ethers.
TABLE X.—Transpiration of Ethers, at 20°, by Capillary C shortened.
(Transpiration-time of water, 290 seconds.)

Transpiration-time.
—A- S peºgwig, Boiling point,
In Seconds. Water = 1.
Formiate of ethyl, . 1482 0-511 •9174 55.5
Acetate of ethyl, . . . 160:5 0-553 •8853 74
Butyrate of ethyl, e 217.5 0-750 •8490 114
Valerianate of ethyl, . 237.5 0-827 ’8750 133'5
6 12 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
The transpiration-times of the homologous acids, previously observed,
appear also to follow in progression.
Transpiration of Acids, at 20°.
Acid. Acid +2HO.
Acetic acid, . * > 1°2801 2.740
Butyric acid, . gº 1°565 3.279
Valerianic acid, e 2° 155 3-839
The increase of the transpiration-time of an alcohol, ether, and acid,
as each rises in its series, may be connected with the increasing weight
of their molecule.
Acetone.
The transpiration of this liquid is remarkably rapid. It is also
greatly retarded by the addition of water. The time will be found to
rise from 0.401, that of anhydrous acetone, to 1604, the time of the
12-hydrate, taking the equivalent of acetone as CeBIgO2, or of the
6-hydrate with the equivalent C.H.O.
TABLE XI-Transpiration of Acetone, at 20°, by Capillary C.
(Transpiration-time of water, 348 seconds.)

Transpiration-time.
Water added to 100 acetone Water Specific gravity,
(C6H6O2). per cent. at 15°.
In seconds. Water = 1.
0. 0. I39-6 0°401 •7943
15:51 ... l eq. 13°42 212°5 0-610 •8384
31:03 ... 2 eqs. 23°68 283.5 0°814 ‘8604
46'55 ... 3 , 31.76 355-5 1-021 •8850
62°06 ... 4 , 38-29 457 1°313 •8990
77'58 ... 5 ,, 43-68 464 1°333 •9123
85.34 ... 5-5, 46'04 469 1.347 •917.3
93-10 ... 6 ,, 48°21 482 1-385 •92.19
100 50-00 500 1-436 •9251
108.61 ... 7 ,, 52-06 515-5 1-479 •9300
124°13 ... 8 ,, 55°33 531-5 1.527 •9320
139-65 ... 9 , 57.85 537-7 1°543 ‘9413
155-16 ... 10 , 60-81 552.7 1-586 •9468
170.67 ... 11 , 63-05 555°5 1°594 •9504
186’18 ... 12 , 65°05 558-5 1:604 •9526
201'71 ... 13 , 66'85 556-5 1:599 •9563
21724 ... 14 , 68°41 557 I •600 •9588
232.75 ... 15 ,, 69-94 553-5 1.590 ‘9608
248.27 ... 16 ,, 71.28 549 1.577 •9632
263-79 ... 17 ,, 72°23 547 1:571 •9649
279°31 ... 18 , 73°63 546 1-568 •9662
294-82 ... 19 , 74.67 539-5 1'550 •9676
372.24 ... 24 , 78-82 5] 9 1°491 •9736
IN RELATION TO CHEMICAL COMPOSITION. 613
The transpiration-time of acetone attains a maximum at what is
represented in the Table as the compound with 12 equivalents of water.
The time is nearly stationary for some distance on either side of that
point, the range from 10 to 15 equivalents of water being 1586 to
1:590, with 1604 as a maximum for the intermediate twelfth equi-
valent.
Glycerine.
This liquid is too viscid in a state of purity to be transpired by
means of the bulb and capillaries employed in these experiments. The
observations to be recorded were confined to diluted solutions of glyce-
rine approaching in composition to the 18-hydrate, CsPIsOs + 18HO.
It was imagined that glycerine as a triatomic alcohol might affect com-
bination with water in the proportion named.
TABLE XII−Transpiration of Glycerine, at 20°, by Capillary C.
(Transpiration-time of water at the same temperature,
348 seconds.)

Transpiration-time.
Water added to 100 Glycerine Water, Specific gravity,
(CeBis0s). per cent. at 15°.
In seconds. Water = 1.
170 62-96 | 199 3°445 1°1010
176-07... 18 eqs. 63-77 II60 3-333 1.0980
I80 64'28 1131-5 3-251 1-0960
190 65-51 1068-5 3-070 1°0934
192 65.75 1054 3.031 1-0927
195 66-10 1049 3-014 1-0914.
197 66-32 1039 2.977 1-0912
200 66-66 1026 2-948 l'O905
The transpiration-time of 18-hydrate is 3:333, referred to water as 1.
There is no indication of a maximum at that point, but the numbers
descend according to their place in the Table without any interrup-
tion.
The idea having suggested itself that the viscous property of glyce-
rine solutions might overpower or conceal the expected deviation, the
transpiration was repeated at a higher temperature, when the solutions
possess greater fluidity.
614 ON THE CAPILLARY TRANSPIRATION OF LIQUIDS
TABLE XIII–Transpiration of Glycerine, at 60°, by Capillary C.
(Transpiration-time of water at the same temperature,
186 seconds.)

Transpiration-time.
Water added to 100 Glycerine Water, Specific gravity,
sHsOs). per cent. at 15°.
In seconds. Water = 1.
170 62.96 435-5 2-341 1° 1010
172.5 63-30 432 2-322 1.0999
175 63-63 428 2-301 1.0980
176-08... 18 eqs. 63-77 425 2°284 1.0976
177 63-96 422°5 2.271 1-0970
180 64'22 420 2.258 1-0960
Still no retardation appears at the point of 18 equivalents, but the
time continues to shorten as the proportion of water is increased,
according to a pretty uniform progression. The information respecting
the constitution of glycerine which transpiration affords is therefore of
a negative character.
The existence of a relation between the transpirability of liquids
and their chemical composition appears to be established. It is a rela-
tion analogous in character to that subsisting between the boiling-point
and composition, so well defined by M. Kopp. Perhaps the most inter-
esting part of the present subject to develop would be the transpiration
of homologous series of substances. Judging from the limited obser-
vations recorded above on the alcohols, ethers, and acids, the order of
succession of individual substances in any series would be indicated by
the degree of transpirability of these substances, as clearly as it is by
their comparative volatility. In carrying out the inquiry, it would
probably be found advantageous to operate at a fixed temperature, which
is somewhat elevated. A large number of substances are liquid at 100°,
of which the transpiration-time could be easily obtained. º
In hydrated substances transpiration also affords a manifestation of
definite combination at once striking and precise. I need only refer
to the manner in which the “constitutional” hydrate of sulphuric acid
SHO, + HO, of acetic acid C.H.O., + 2HO, of nitric acid NHO's H-3HO,
and of alcohol C, HsO2 + 6HO is each indicated by its maximum tran-
spiration-time. The indication of the alcohol-hydrate is particularly
distinct, although that hydrate must be a comparatively feeble com-
IN RELATION TO CHEMICAL COMPOSITION. 615
pound. Indeed the extent to which transpiration is affected by the
annexation of constitutional water appears to be by no means in pro-
portion to the intensity of combination.
The increased resistance to transpiration observed in these definite
hydrates may be connected with their larger molecules. But another
speculative view of the retardation can be suggested, in which the phe-
nomenon is referred to a physical agency. When one of these definite
hydrates, say the 6-hydrate of alcohol, is being forced through the capil-
lary, it may be imagined that a small portion of the hydrated compound
is molecularily decomposed by the friction. A certain portion of the
impelling force would thereby be lost, being converted into the latent
heat which alcohol and water require to assume when separated from
each other, and the transpiration be consequently retarded ; for as alcohol
and water evolve heat on combining, so they must absorb heat when
their union is dissolved by any cause. But the change of temperature
representing the lost force appears to be too small to be rendered
sensible to observation. It would be capable of raising the tempera-
ture of the transpired liquid not more than about one forty-third part
of a degree, according to an accurate estimate for which I am indebted
to Professor Stokes. In consequence of this circumstance the physical
hypothesis now suggested has neither been verified nor disproved.
To this paper are appended two series of observations made on tran-
spiration at different temperatures, the first series being the transpiration
of water, and the second that of absolute alcohol. Each series of expe-
riments is repeated with two capillary tubes, one having nearly double
the resistance of the other. The numbers from the two capillaries
exhibit a fair amount of agreement. The times given are those actually
observed, no correction being made for the Small variation of the capil-
lary in diameter at different temperatures.
The dimensions of Capillary D were as follows:–Capacity of bulb,
4135 cub. cent. ; length of capillary tube, 37.5 millims. ; diameter of
bore, 0.10325 millim. Time of passage of water, at 20°, under pressure
of one atmosphere, 470 seconds.
The dimensions of Capillary E were as follows:–Capacity of bulb,
3.725 cub. cent. ; length of capillary, 53 millims. ; diameter of bore,
0.0858 millim. Time of passage of water, at 20°, under pressure of one
atmosphere, 913 seconds.
616
ON THE CAPILLARY TRANSPIRATION OF LIQUIDS

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TABLE XV-Transpiration of Alcohol at different Temperatures.
By capillary tube D. By capillary tube E.
Time and velocity of water Time and velocity of water Time and velocity of water Time and velocity of water
Time in at 20°=1. at 0°=1. Time in at 20°=1. at 0°–1.
Temperature. Seconds. g seconds.
Time. Velocity. Time. Velocity. Time. Velocity. Time. Velocity.
Ö C. 860 1.8297 0°5465 1-0238 0.9767 1642 1-7984 0°5560 1:0079 0.9920
I 840 17893 0°5588 1-0012 0-9988 1601 17535 0.5702 0-9828 l:01.74
3 807 1-7170 0-5824 0-9607 1-0409 1537 l'6834 0°5940 0-9435 1-0598
5 772 1:6425 0-6089 0.9190 1:0880 1473 1-6133 0-6198 0-9042 I-1059
7 738 1:5702 0.6368 0.8785 | 1382 1410 l'5443 0-6475 0-8656 1-1553
10 700 1'4893 0-6714 0.8333 l 2000 1350 1°4786 0-6755 0-8226 1-2066
15 624 1.3276 0-7532 0.7428 I ‘3461 1213 1.3285 0-7526 0.7446 l‘3429
20 562 1-1957 O'8362 0.6690 1'4946 1092 1 : 1960 ()'8360 0-6703 1.4917
25 520 I 1063 O'9038 0-6190 l'6154 1001 1.0963 0.9120 0.6145 1-6273
30 476 1-0.127 0.9873 O'5566 1-7646 915 1.0022 0.9978 0.56.17 I '7803
35 428 0-9106 1.0981 0.5095 l'9626 843 0.9233 1-0830 0.5175 I '9323
40 391 0-8319 I-2020 0'4654 2° 1483 772 ()'8455 I” l826 0.4739 2-1 101
45 360 0.7659 1-3055 0.4285 2°3333 707 0.7743 1.29.13 0°4340 2'3041
50 331-5 0-7053 1.4.177 0-3946 2.5339 645 0-7064 1°41'55 0.3959 2-5100
55 307 0-6531 1-5309 0.3654 2.7301 592 0-6484 1'5422 0°3634 2.7517
60 285 O'6063 1:6491 0.3392 2-9473 551 0-6035 1-6569 0-3382 2°9564
65 262 O'5574 1-8005 O°3] 19 3°2061 510 0.5585 17901 0.3130 3' 1941
70 241 0.5127 1-9502 0.2869 3.4854 468 0.5125 l'9465 0-2873 3:4807


0 | 8 ON THE PROPERTIES OF SILICIC ACID
XVII.
ON THE PROPERTIES OF SILICIC ACID AND OTHER
ANALOGOUS COLLOIDAL SUBSTANCES.
From the Journal of the Chemical Society, 1864.
THE prevalent notions respecting solubility have been derived chiefly
from observations on crystalline salts, and are very imperfectly appli-
cable to the class of colloidal substances. Hydrated silicic acid, for
instance, when in the Soluble condition, is, properly speaking, a liquid
body, like alcohol, miscible with water in all proportions. We have no
degrees of solubility to speak of with respect to silicic acid, like the
degrees of solubility of a salt, unless it be with reference to silicic acid
in the gelatinous condition, in which it is usually looked upon as desti-
tute of solubility. The jelly of silicic acid may be more or less rich in
combined water, as it is first prepared, and it appears to be soluble in
proportion to the extent of its hydration. A jelly containing 1 per
cent. of silicic acid, gives with cold water a solution containing about 1
part of silicic acid in 5000 water; a jelly containing 5 per cent. of
silicic acid gives a solution containing about 1 part of acid in 10,000
water. A less hydrated jelly than the last mentioned is still less
soluble ; and, finally, when the jelly is rendered anhydrous, it forms
gummy-looking white masses, which appear to be absolutely insoluble,
like the light dusty silicic acid obtained by drying a jelly charged with
salts, in the Ordinary analysis of a silicate.
The liquidity of silicic acid is only affected by a change, which is
permanent (namely, coagulation or pectization), by which the acid is
converted into the gelatinous or pectous form, and loses its miscibility
with water. This change may be brought about by time alone. The
liquidity is permanent in proportion to the degree of dilution of silicic
acid, and appears to be favoured by a low temperature. It is opposed,
on the contrary, by concentration, and by elevation of temperature. A
liquid silicic acid of 10 or 12 per cent. pectizes spontaneously in a few
hours at the Ordinary temperature, and immediately when heated. A
liquid of 5 per cent, may be preserved for five or six days; a liquid of
2 per cent. for two or three months; and a liquid of 1 per cent. has not
pectized after two years. Dilute solutions of 0.1 per cent or less are
no doubt practically unalterable by time, and hence the possibility of
soluble silicic acid existing in nature. I may add, however, that no
solution, weak or strong, of silicic acid in water has shown any disposi-
tion to deposit crystals, but always appears on drying as a colloidal
AND OTHER ANALOGOUS COLLOIDAL SUBSTANCES. 619
glassy hyalite. The formation of quartz crystals at a low temperature,
of so frequent occurrence in nature, remains still a mystery. I can only
imagine that such crystals are formed at an inconceivably slow rate,
and from solutions of silicic acid which are extremely dilute. Dilution
no doubt weakens the colloidal character of substances, and may there-
fore allow their crystallizing tendency to gain ground and develop
itself, particularly where the crystal once formed is completely insoluble,
as with quartz.
The pectization of liquid silicic acid is expedited by contact with
Solid matter in the form of powder. By contact with pounded graphite,
which is chemically inactive, the pectization of a 5 per cent. silicic acid
is brought about in an hour or two, and that of a 2 per cent. silicic acid
in two days. A rise of temperature of 1*1 C. was observed during the
formation of the 5 per cent, jelly.
The ultimate pectization of silicic acid is preceded by a gradual
thickening in the liquid itself. The flow of liquid colloids through a
capillary tube is always slow compared with the flow of crystalloid
Solutions, so that a liquid-transpiration tube may be employed as a
colloidoscope. With a colloidal liquid alterable in viscocity, such as
silicic acid, the increased resistance to passage through the colloidoscope
is obvious from day to day. Just before gelatinizing, silicic acid flows
like an oil.
A dominating quality of colloids is the tendency of their particles to
adhere, aggregate, and contract. This idio-attraction is obvious in the
gradual thickening of the liquid, and when it advances, leads to pectiza-
tion. In the jelly itself, the specific contraction in question, or synaeresis,
still proceeds, causing separation of water, with division into clot and
serum, and ending in the production of a hard stony mass of vitreous
structure, which may be anhydrous, or nearly so, when the water is
allowed to escape by evaporation. The intense synaeresis of isinglass
dried in a glass dish over sulphuric acid in vacuo, enables the contract-
ing gelatine to tear up the surface of the glass. Glass itself is a colloid,
and the adhesion of colloid to colloid appears to be more powerful than
that of colloid to crystalloid. The gelatine, when dried in the manner
described upon plates of calcspar and mica, did not adhere to the crystal-
line surface, but detached itself on drying. Polished plates of glass
must not be left in contact, as is well known, owing to the risk of per-
manent adhesion between their surfaces. The adhesion of broken
masses of glacial phosphoric acid to each other is an old illustration of
colloidal synaeresis.
|
\,
*.
Bearing in mind that the colloidal phasis of matter is the result of
a peculiar attraction and aggregation of molecules, properties never
entirely absent from matter, but greatly more developed in some sub-
620 ON THE PROPERTIES OF SILICIC ACID
|
}
A
|
f
|
stances than in others, it is not surprising that colloidal characters
spread on both sides into the liquid and solid conditions. These char-
acters appear in the viscidity of liquids, and in the softness and adhe-
Siveness of certain crystalline substances. Metaphosphate of soda, after
fusion by heat, is a true glass or colloid; but when this glass is main-
tained for a few minutes at a temperature some degrees under its point
of fusion, the glass assumes a crystalline structure without losing its
transparency. Notwithstanding this change, the low diffusibility of the
salt is preserved, with other characters of a colloid. Water in the form
of ice has already been represented as a similar intermediate form, both
colloid and crystalline, and in the first character adhesive and capable
of reunion or “regelation.”
It is unnecessary to return here to the fact of the ready pectization
of liquid silicic acid by alkaline salts, including some of very sparing
solubility, such as carbonate of lime, beyond stating that the presence
of carbonate of lime in water was observed to be incompatible with the
co-existence of soluble silicic acid, till the proportion of the latter was
reduced to nearly 1 in 10,000 water.
Certain liquid substances differ from the salts in exercising little or
no pectizing influence upon liquid silicic acid. But, on the other hand,
none of the liquids now referred to appear to conduce to the preserva–
tion of the fluidity of the colloid, at least not more than the addition of
water would do. Among these inactive diluents of silicic acid are found
hydrochloric, nitric, acetic, and tartaric acids, syrup of Sugar, glycerin,
and alcohol. But all the liquid substances named, and many others,
appear to possess an important relation to silicic acid, of a very different
nature from the pectizing action of salts. They are capable of displacing
the combined water of the silicic acid hydrate, whether that hydrate
is in the liquid or gelatinous condition, and give new substitution-
products.
A liquid compound of alcohol and silicic acid is obtained by adding
alcohol to aqueous silicic acid, and then employing proper means to
withdraw the water from the mixture. For that purpose the mixture
contained in a cup may be placed over dry carbonate of potash or quick-
lime, within the receiver of an air-pump. Or a dialysing bag of parch-
ment paper containing the mixed alcohol and silicic acid may be sus-
pended in a jar of alcohol: the water diffuses away, leaving in the bag
a liquid composed of alcohol and silicic acid only. A point to be
attended to is, that the silicic acid should never be allowed to form more
than 1 per cent. of the alcoholic solution, otherwise it may gelatinize
during the experiment. If I may be allowed to distinguish the liquid
and gelatinous hydrates of silicic acid by the irregularly formed terms
of hydrosol and hydrogel of silicic acid, the two corresponding alcoholic
AND OTHER ANALOGOUS COLLOIDAL SUBSTANCES. 621
bodies now introduced may be named the alcosol and alcogel of silicic
acid.
The alcosol of silicic acid, containing 1 per cent. of the latter, is a
colourless liquid, not precipitated by water or salts, nor by contact with
insoluble powders, probably from the Small proportion of silicic acid
present in solution. It may be boiled and evaporated without change,
but is gelatinized by a slight concentration. The alcohol is retained
less strongly in the alcosol of silicic acid than water is in the hydrosol,
but with the same varying force, a small portion of the alcohol being
held so strongly as to char when the resulting jelly is rapidly distilled
at a high temperature. Not a trace of silicic ether is found in any
compound of this class. The jelly burns readily in the air, leaving the
whole silicic acid in the form of a white ash.
The alcogel, or solid compound, is readily prepared by placing masses
of gelatinous silicic acid, containing 8 or 10 per cent. of the dry acid in
absolute alcohol, and changing the latter repeatedly till the water of the
hydrogel is fully replaced by alcohol. The alcogel is generally slightly
opalescent, and is similar in aspect to the hydrogel, preserving very
nearly its original bulk. The following is the composition of an alcogel
carefully prepared from a hydrogel which contained 9:35 per cent. of
silicic acid :—
Alcohol, e e º * 88:13
Water, e º º e 0-23
Silicic acid, . o * e 11 *64.
100:00
Placed in water, the alcogel is gradually decomposed—alcohol diffusing
out and water entering instead, so that a hydrogel is reproduced.
Further, the alcogel may be made the starting-point in the formation
of a great variety of other substitution jellies of analogous constitution,
the only condition required appearing to be that the new liquid and
alcohol should be intermiscible, that is, interdiffusible bodies. Com-
pounds of ether, benzole, and bisulphide of carbon have thus been pro-
duced. Again, from etherogel another series of silicic acid jellies may
be derived, containing fluids soluble in ether, such as the fixed oils.
The preparation of the glycerin-compound of silicic acid is facilitated
by the comparative fixity of that liquid. When hydrated silicic acid
is first steeped in glycerin, and then boiled in the same liquid, water
distils over, without any change in the appearance of the jelly, except
that when formerly opalescent it becomes now entirely colourless, and
ceases to be visible when covered by the liquid. But a portion of the
silicic acid is dissolved, and a glycerosol is produced at the same time as
the glycerin jelly. A glycerogel prepared from a hydrate containing
622 ON THE PROPERTIES OF SILICIC ACID
9:35 per cent of silicic acid, was found by a combustion analysis to be
composed of—
Glycerin, . e g . 87°44
Water, wº e g º 3-78
Silicic acid, , * º tº 8'95
100-17
The glycerogel has somewhat less bulk than the original hydrogel.
When a glycerine jelly is distilled by heat, it does not fuse, but the
whole of the glycerine comes over, with a slight amount of decomposi-
tion towards the end of the process.
The compound of sulphuric acid, Sulphagel, is also interesting from
the facility of its formation, and the complete manner in which the water
of the original hydrogel is removed. A mass of hydrated silicic acid
may be preserved unbroken if it is first placed in sulphuric acid diluted
with two or three volumes of water, and then transferred gradually to
stronger acids, till at last it is placed in concentrated oil of vitriol. The
sulphagel sinks in the latter fluid, and may be distilled with an excess
of it for hours without losing its transparency or gelatinous character.
It is always somewhat less in bulk than the primary hydrogel, but not
more, to the eye, than one-fifth or one-sixth part of the original volume.
This sulphagel is transparent and colourless. When a sulphagelis heated
strongly in an open vessel, the last portions of the monohydrated sul-
phuric acid in combination are found to require a higher temperature
for their expulsion, than the boiling-point of the acid. The whole silicic
acid remains behind, forming a white opaque, porous mass, like pumice.
. A sulphagel placed in water is soon decomposed, and the original hydro-
gel reproduced. No permanent compound of sulphuric and silicic acids,
of the nature of a salt, appears to be formed in any circumstances. A
sulphagel placed in alcohol gives ultimately a pure alcogel. Similar
jellies of silicic acid may readily be formed with the monohydrates of
nitric, acetic, and formic acids, and are all perfectly transparent.
The production of the compounds of silicic acid now described, indi-
cates the possession of a wider range of affinity by a colloid than could
well be anticipated. The organic colloids are no doubt invested with
similar wide powers of combination, which may become of interest to
the physiologist. The capacity of a mass of gelatinous silicic acid to
assume alcohol, or even olein, in the place of water of combination,
without disintegration or alteration of form, may perhaps afford a clew
to the penetration of the albuminous matter of membrane by fatty and
other insoluble bodies, which seems to occur in the digestion of food.
Still more remarkable and suggestive are the fluid compounds of silicic
acid. The fluid alcohol-compound favours the possibility of the exist-
AND OTHER, ANALOGOUS COLLODIAL SUBSTANCES. 623
ence of a compound of the colloid albumin with olein, soluble also and
capable of circulating with the blood.
The feebleness of the force which holds together two substances
belonging to different physical classes, one being a colloid and the other
a crystalloid, is a subject deserving notice. When such a compound is
placed in a fluid, the superior diffusive energy of the crystalloid may
cause its separation from the colloid. Thus, of hydrated silicic acid,
the combined water (a crystalloid) leaves the acid (a colloid) to diffuse
into alcohol; and if the alcohol be repeatedly changed, the entire
water is thus removed, alcohol (another crystalloid) at the same time
taking the place of water in combination with the silicic acid. The
liquid in excess (here the alcohol) gains entire possession of the silicic
acid. The process is reversed if an alcogel be placed in a considerable
volume of water. Then alcohol separates from combination, in conse-
quence of the opportunity it possesses to diffuse into water; and water,
which is now the liquid present in excess, recovers possession of the silicic
acid. Such changes illustrate the predominating influence of mass.
Even the compounds of silicic acid with alkalies, yield to the decom-
posing force of diffusion. The compound of silicic acid with 1 or 2 per
cent. of soda is a colloidal solution, and, when placed in a dialyser over
water in vacuo to exclude carbonic acid, Suffers gradual decomposition.
The soda diffuses off slowly in the caustic state, and gives the usual
brown oxide of silver when tested with the nitrate of that base.
The pectization of liquid silicic acid and many other liquid colloids,
is effected by contact with minute quantities of salts in a way which is
not understood. On the other hand, the gelatinous acid may again be
liquefied and have its energy restored by contact with a very moderate
amount of alkali. The latter change is gradual, 1 part of caustic soda,
dissolved in 10,000 water, liquefying 200 parts of silicic acid (estimated
dry) in 60 minutes at 100° C. Gelatinous stannic acid also is easily
liquefied by a small proportion of alkali, even at the ordinary tempera-
ture. The alkali, too, after liquefying the gelatinous colloid, may be
separated again from it by diffusion into water upon a dialyser. The solu-
tion of these colloids, in such circumstances, may be looked upon as ana-
logous to the solution of insoluble organic colloids witnessed in animal
digestion, with the difference that the solvent fluid here is not acid, but
alkaline. Liquid silicic acid may be represented as the “peptone” of
gelatinous silicic acid; and the liquefaction of the latter by a trace of
alkali, may be spoken of as the peptization of the jelly. The pure jellies
of alumina, peroxide of iron, and titanic acid, prepared by dialysis, are
assimilated more closely to albumin, being peptized by minute quan-
tities of hydrochloric acid.
Liquid Stannic and MetaStannic Acids.-Liquid stannic acid is pre-
\
l
t
|
624 ON THE PROPERTIES OF SILICIC ACID
pared by dialysing the bichloride of tin with an addition of alkali, or by
dialysing the stannate of soda with an addition of hydrochloric acid. In
both cases a jelly is first formed on the dialyser; but, as the salts dif-
fuse away, the jelly is again peptized by the small proportion of free
alkali remaining: the alkali itself may be removed by continued diffu-
Sion, a drop or two of the tincture of iodine facilitating the separation.
The liquid stannic acid is converted, on heating it, into liquid meta-
stannic acid. Both liquid acids are remarkable for the facility with
which they are pectized by a minute addition of hydrochloric acid, as
well as by salts.
Liquid Titanic Acid is prepared by dissolving gelatinous titanic acid
in a small quantity of hydrochloric acid, without heat, and placing the
liquid upon a dialyser for several days. The liquid must not contain
more than 1 per cent. of titanic acid, otherwise it gelatinizes spontane-
ously, but it appears more stable when dilute. Both titanic and the two
stannic acids afford the same classes of compounds with alcohols, etc.,
as are obtained with silicic acid.
Liquid Tungstic Acid—The obscurity which has so long hung over
tungstic acid is removed by a dialytic examination. It is in fact a
remarkable colloid, of which the pectous form alone has hitherto been
known. Liquid tungstic acid is prepared by adding dilute hydrochloric
acid carefully, and in slight excess to a 5 per cent. solution of tungstate
of soda, and then placing the resulting liquid on a dialyser. At intervals
of two days, the addition of hydrochloric acid must be repeated two or
three times, and the dialysis continued in order to remove the whole
alkali. It is remarkable that the purifted acid is not pectized by acids,
salts, or alcohol at the ordinary temperature. Evaporated to dryness,
it forms vitreous scales, like gum or gelatin, which sometimes adhere so
strongly to the surface of the evaporating dish as to detach portions of
it. It may be heated to 200°C. without losing its solubility, or passing
into the pectous state, but, at a temperature near redness, it undergoes
a molecular change, closing at the same time 2:42 per cent. of water.
When water is added to unchanged tungstic acid, the acid becomes pasty
and adhesive, like gum ; and it forms a liquid with about one-fourth its
weight in water, which is so dense as to float glass. The solution effer-
vesces with carbonate of Soda. The taste of tungstic acid dissolved in
water is not metallic or acid, but rather bitter and astringent. Solutions
of tungstic acid containing 5, 20, 50, 66'5, and 79.8 per cent. of dry
acid, possess the following densities at 19°: 1:0475, 12168, 18001,
2:396, and 3.243. Evaporated in vacuo, liquid tungstic acid is colour-
less, but becomes greenish in air, apparently from the deoxidating
action of organic matter. Liquid silicic acid is protected from pectizing
when mixed with tungstic acid, a circumstance probably connected
AND OTHER ANALOGOUS COLLOIDAL SUBSTANCES. 625
with the formation of the double compounds of these two acids which
M. Marignac has lately indicated.
Molybdic Acid has hitherto been known (like tungstic acid) only in
the insoluble form. Crystallized molybdate of soda dissolved in water
is decomposed by the gradual addition of hydrochloric acid in excess,
without any immediate precipitation. The acid liquid thrown upon a
dialyser may gelatinize after a few hours, but again liquefies spontane-
ously, when the salts diffuse away. After repeated additions of hydro-
chloric acid, and a diffusion of several days, about 60 per cent. of liquid
molybdic acid remains behind in a pure condition. In the dialysis of
both tungstic and molybdic acids, the osmose is very great, the acid
solutions increasing to two or three times their original volume. The
consequent dilution causes the purification to be slow, as compared with
that of silicic acid where the osmose is inconsiderable. The solution of
pure molybdic acid is yellow, astringent to the taste, acid to test-paper,
and possesses much stability. The acid may be dried at 100°, without
immediately losing its solubility. Dry molybdic acid has the same
gummy aspect as tungstic acid. Heated short of the point at which it
volatilizes, pure molybdic acid in powder will still dissolve in a solution
of carbonate or bicarbonate of potash, with effervescence of carbonic
acid gas. Both acids lose their colloidality when combined with soda,
and give a variety of crystallizable salts. The pure liquid acids also
become insoluble, when heated for some time with hydrochloric or other
strong acids.
2 R
UN CLASSIFIED PAPERS,
I.
ON THE HEAT OF FRICTION.
From Annals of Philosophy, xii. 1826, pp. 260-262.
EDINBURGH, Sept. 7, 1826.
IT is generally allowed, that the heat extricated in friction is inex–
plicable upon the theory of the materiality of heat, as at present enter-
tained. It would be easy to show that this heat does not arrive at the
bodies rubbed together, by the Ordinary and admissible methods of
conduction or radiation, or, that no reduction of bulk takes place, or
diminution of capacity for heat. Yet the materiality of heat is involved.
in the principal doctrines of chemistry, while the simplicity and easy
application of the theory render its establishment exceedingly desirable.
In these circumstances, an attempt to reconcile the substantial existence
of heat with its appearance in friction, may not be unworthy of attention,
even although the suppositions on which it is founded should be alto-
gether novel; elucidating, as they do, other departments of science.
Heat is observed by us, either radiant in motion, and possessed of
great velocity; or in union with matter, and capable of regaining this
velocity.
Probably this velocity is necessary to its entering into bodies and
uniting with them; at least we never observe heat do so without it.
For, when communicated by radiation, this is evident; and in conduc-
tion, which in close contact Supplies the place of radiation, it is evident
that heat is communicated with a force. Indeed, conduction may be
reduced with considerable plausibility to an internal radiation.
It appears that this motive power, which is essential to the communi-
cation of heat and our perception of it, is really never annihilated. It
disappears when heat passes into a body, but it is merely overpowered
for a time, and not altogether lost; for upon reduction of temperature,
the heat emanates from the body, evincing its pristine velocity. We
may compare the state of the heat in union with matter to that of a bent
ON THE HEAT OF FERICTION. 627
Spring, or a compressed elastic substance, the attraction of the matter
for heat being the restraining force. Sensible heat, therefore, we never
find destitute of this motive power, nor to lose it—at least heat is never
so divested of it as to be incapable of resuming it.
These observations prepare us for the conception of heat in a different
state from that in which it is generally supposed to exist. Let us sup-
pose that the calorific principle is capable, likewise, of existing destitute
of this motive power; and yet not in combination with matter, which
this motive power seems necessary to effect. We may suppose it cap-
able of existing in a state similar to our ordinary conceptions of the
electric fluid. As a fluid, powerfully repelling its own particles, and
attracting those of other matter, spread equally over the surfaces of all
bodies, independently of their composition or temperature, without
combining with these bodies, diffused (to borrow an illustration from
chemistry) like a drop of oil upon the surface of water, without being in
combination with it. To the matter of heat in this quiescent state, we
shall, for the sake of convenience, give the name superficial heat, from
its covering the superficies or surfaces of bodies. It is merely heat to
which there has not been imparted that original velocity, upon which
the characteristic properties of sensible heat depend. Superficial heat,
it is evident, must be insensible. But project it with the necessary
velocity, and you render it sensible. This might result from extraordi-
nary accumulation of our idio-repulsive body, or its concentration upon
a particular spot. Dissipation, by means of radiation, appears to be a
natural effect of the repulsion between the particles of Superficial heat,
aggravated to a great degree.
Now in friction, circumstances are favourable to the conversion of
superficial into sensible heat, in this manner. The surfaces of the
bodies rubbed together are brought rapidly into exceedingly close con-
tact, so that as surfaces they virtually cease to exist. From the violent
approximation, the idio-repulsive power of the Superficial heat investing
both the surfaces, is powerfully exerted; so that a portion of the super-
ficial heat is expelled as radiant heat, and impinges upon the rubbing
surfaces. But more superficial heat is supplied from the earth; and as
long as the friction is continued, superficial heat is converted into sen-
sible, and the bodies become hotter and hotter. Hence the heat attend-
ing friction; and the reason why more heat is elicited, when the surfaces
are smooth than when they are rough, their approach in the former case
being more close, and the investing superficial heat more condensed.
In a course of experiments upon the heat produced in friction, M.
Haldat attempted to insulate his apparatus for that purpose, by means
of non-conductors of electricity. Upon reference, however, to his paper,"
* Nicholson's Journal, vol. xxvi. p. 30.
628 ON THE HEAT OF FRICTION.
it will be found, that notwithstanding the body of the apparatus was
electrically insulated with great care, yet the insulation of the machine
and contrivance by which motion was conveyed to the rubbing surfaces,
was overlooked. The result of this imperfect insulation was a diminu-
tion of one-third in the amount of heat evolved. New experiments
upon this subject are very desirable.
The theory which we have applied to friction admits of very great
extension. We may suggest that the phenomena of electricity are caused
by an accumulation, or a deficiency, of our superficial heat. That the
electric fluid is really superficial heat, and convertible into sensible heat
in the manner explained.
Hence we never perceive anything which we can call the radiation
of electricity. We never find that one electrified body communicates
any of its electricity to another body at a distance by this means. For
it follows from the doctrines illustrated, that should ever electricity
(Superficial heat) emanate from bodies in this manner, it should be in
the shape of radiant heat.
We Scarcely need adduce instances, in which heat, in its sensible
form, does attend the accumulation of electricity. When a powerful
current of the electric fluid is concentrated, by being passed along a thin
wire, the wire is heated to a great degree, so as to become strongly
radiant. In this way, charcoal, or any other body, may be kept in the
voltaic arc in a state of intense ignition. Here, from the great repulsive
force that must attend such an accumulation of superficial heat, which
will be much enhanced by the retardation of the passage of the fluid,
occasioned by the imperfect conducting power of the substance, a large
portion is expelled with the necessary velocity, and becomes thereby
sensible heat. According to this theory, electrical light and heat are
derived from the same source as the heat of friction; and in neither case
is there any production or actual generation of these principles.
The simplicity of this theory is its chief recommendation. That
heat, possessed of a substantial existence, should be found alone, uncom-
bined with matter, and that this combination, of a most elementary kind,
should, at all times, be brought about by the calorific principle imping-
ing with force upon the material body, are not hard postulates. Most
material substances, however strong their affinities for each other,
require peculiarly favourable circumstances to enable these affinities to
act, otherwise the bodies appear to a certain extent repulsive of each
other. Moreover, when we attribute to the matter of heat diffused over
the surfaces of bodies, an attraction for these substances which yet does
not amount to the production of a combination, we are but extending to
heat properties, which all other material substances evince, in adhesion,
capillary attraction, etc.
ALCOHOL DERIVED FROM THE FERMENTATION OF BREAD. 629
It is hoped, likewise, that the theory of superficial heat is not charge-
able with that barrenness and want of practical application, which
generally characterize premature speculations upon abstract subjects.
The knowledge of the existence of such an agent, of its influence in
friction and electricity, and of its convertibility into sensible heat, affords
a clew of no small importance to guide us in our researches. Its appli-
cation in galvanism, we shall, perhaps, hereafter, have an opportunity of
exhibiting.
II.
ALCOHOL DERIVED FROM THE FERMENTATION OF BREAD.
From Annals of Philosophy, xii. 1826, p. 363.
(To the Editors of the Annals of Philosophy.)
EDINBURGH, Sept. 25, 1826.
GENTLEMEN, Two facts of considerable importance in determining
the nature of the panary fermentation have been made known by your
ingenious correspondent upon the art of baking bread. He has shown
that the fermentation depends upon the Saccharine ingredient of the
flour, by renewing it when exhausted by the addition of sugar; and
provided for the little alteration in the proportion of sugar existing in
the flour, before and after fermentation, by exhibiting the influence of
the baking in converting a portion of the starch into sugar. From the
known laws of the decomposition of Sugar, it is presumed, with consider-
able reason, that the fermentation is the vinous. The production of
alcohol in the course of the fermentation of bread in baking, which we
have found to take place, and rendered appreciable, is perhaps a most
irrefragable proof of which this theory is susceptible.
To avoid the use of yeast, which might introduce alcohol, a small
quantity of flour was kneaded, and allowed to ferment in the usual way,
to serve as leaven. By means of the leaven a considerable quantity of
flour was fermented; and, when the fermentation had arrived at the
proper point, formed into a loaf. The loaf was carefully enclosed in a
distillatory apparatus, and subjected for a considerable time to the bak-
ing temperature. Upon examining the condensed liquid, the taste and
smell of alcohol were quite perceptible, and by repeatedly rectifying it
a small quantity of alcohol was obtained of strength sufficient to burn,
and to ignite gunpowder by its combustion.
630 EFFECTS OF ANIMAL CHARCOAL ON SOLUTIONS.
The experiment was frequently repeated, and in different bakings
the amount of alcohol obtained, of the above strength, found to vary from
0-3 to 1 per cent. by weight of the flour employed. When the fermented
flour was allowed to sour before baking, the amount of alcohol rapidly
diminished; and in all cases, the disagreeable empyreuma completely
disguised the peculiar smell of the alcohol, when in its first diluted
state, and in vapour.—I am, Gentlemen, with great respect, your most
obedient servant, THOMAS GRAHAM.
III.
EFFECTS OF ANIMAL CHARCOAL ON SOLUTIONS.
From Quart. Journ. Science, i. 1830, pp. 120-125. [Dingler, Polytechn. Journ. xl.
1831, pp. 443-446; Poggend. Annal. xix. 1830, pp. 139-144.]
THE property of withdrawing matters from a state of solution,
possessed by the charcoal of bone-black, has been investigated in the
case of soluble colouring matters of a vegetable and animal origin. It
is known, that the discolouring faculty resides entirely in the charcoal,
for the earthy matters and portions of azote combined with it, possess
by themselves no such power, and the charcoal discolours without them.
This property is also greatly exalted by the state of extreme division
and porosity of animal charcoal, arising from the interposition of foreign
particles of earthy and saline matter between the particles of carbona-
ceous matter in bone, which effectually prevents the aggregation of the
carbon during calcination. The bright, hard charcoal from the calci-
nation of dried blood has no discolouring power; but the charcoal from
the calcination of dried blood, mixed with carbonate of potash, as in the
manufacture of prussiate of potash, proves the most efficient discolour-
ing form of charcoal we possess, after the alkaline carbonate is washed
out. A very intense heat, however, destroys entirely the discolouring
power of bone-black.
The colouring matters are not destroyed or decomposed by the
charcoal, but merely withdrawn from a state of solution, in combination
with the surface of the charcoal, and may be again dissolved out and
made to appear by the action of a more powerful solvent.
M. Lowitz first discovered this property of charcoal in 1791. He
EFFECTS OF ANIMAL CHARCOAL ON SOLUTIONS. 631
used only charcoal of wood. M. Guilbert observed, that the discolouring
power of wood charcoal was improved by exposing it for a considerable
time, in a wet state, to the rays of the sun. In 1810, M. Figuier, Pro-
fessor of Chemistry at Montpellier, discovered that animal charcoal
discoloured with much greater power. It has subsequently been used
very extensively by the sugar-refiners of France in clarifying their
syrups. Of bone or ivory-black, one-sixth of the weight of the raw
sugar is boiled with it for ten minutes. The charcoal and impurities
are separated by filtering, and the syrup is filtered a second time to
separate a little charcoal which comes through the first filter (Payen).
In the Journal de Pharmacie, tom. iv. pp. 301-7, there is a distinct
account of the mode of preparing bone-black, by M. Cadet de Gassi-
court; and in the same work, tom. viii. pp. 257-277, an excellent memoir
on charcoal, considered as a discolouring substance, by A. Bussy, which
was crowned by the Society of Pharmacy of Paris, and contains every-
thing known on the subject. It is followed by another memoir on the
same subject by M. Payen, to which a second prize was adjudged. [The
substance of the preceding memoir is given in this Journal, vol. xiii.
pp. 406–16.]
But the action of animal charcoal on solutions has been considered
hitherto only in reference to the removal of colouring matters. More
determinate results, however, might be expected in solutions of Saline
and other chemical bodies, of which the composition is known. The
investigation is also interesting, from the light which it may throw upon
the state of combination in which bodies exist in cases of ordinary solu-
tion, as Salt in water, to which the doctrine of definite proportions seems
wholly inapplicable. If a solid body, such as carbon, destroy such a
combination, and take down the saline matter attached to its surface,
we may conclude that there is an analogy between the combination of
the salt with the water, and the combination of the salt with the char-
coal, and that the former as well as the latter processes have something
of a mechanical character.
The same property is possessed by other solid bodies, in a state of
minute division, as when newly precipitated, although not in so great a
degree. And, in analytic researches, its interference must be guarded
against, as it may contribute, in some cases, to increase the weight of
precipitates.
The animal charcoal, employed in the following experiments, was
prepared from common bone, or ivory-black, by boiling dilute muriatic
acid upon it, and afterwards washing it with hot water till the water
came off tasteless. No more than 10 or 12 per cent. of charcoal remained
after dissolving out the earthy salts. On burning this charcoal, it left
a grey ash, amounting to about one-twelfth of the original weight,
632 EFFECTS OF ANIMAL CHARCOAL ON SOLUTIONS.
insoluble in water and acids, and almost entirely silica. Charcoal pre-
pared in this way, M. Bussy found to go no farther in discolouring than
one and a half times its weight of the original ivory-black.
In my first experiments, it was found that the prepared charcoal,
in great excess, had no sensible effect in impoverishing a Saturated solu-
tion of common salt at natural temperatures. The proportion of Salt
remaining in solution was always as great as water was found capable
of retaining, at the same time, at the lowest temperature which had
occurred during the experiment.
A solution of nitrate of lead, with the charcoal repeatedly agitated,
and occasionally tested with carbonate of soda, gave a distinct precipitate
the first day, a much less distinct the second, and the merest trace the
third day. But, on heating the water, the charcoal part of the nitrate
was re-dissolved, and afforded a copious precipitate, with carbonate of
soda and with sulphuretted hydrogen.
The dinitrate of lead, which is soluble, was taken down completely
by the charcoal, so that no trace of it was perceived by means of sulphu-
retted hydrogen. But on heating the water over it to 200”, part was
re-dissolved, as in the previous case, but again taken down completely
by the charcoal on cooling. The action of the charcoal on the cold solu-
tion of the dinitrate was immediate, and much more energetic than in
the case of the nitrate. The former salt, however, is much less soluble
in water than the latter. Other soluble subsalts were tried.
2. Three grains diacetate of lead in one ounce water, with twenty
grains common ivory-black; taken down completely, and not re-dis-
solved in any degree on boiling,
Four grains trisacetate of lead; same results.
Four grains tartar emetic in one ounce water, with twenty grains of
the prepared charcoal, in the cold; agitated occasionally for several
days; still a copious precipitate, with hydrosulphuret of ammonia.
After a second addition of twenty grains of the charcoal, only a trace of
antimony, with sulphuretted hydrogen.
Lime-water was deprived entirely of the lime which it contains, in
the cold, as Dr. Paris previously observed, so that the liquid remaining
did not act on reddened litmus.
Arsenious acid was not taken down entirely in six weeks by great
excess of the charcoal, no heat being applied.
No quantity of the charcoal could take down bisulphate of copper.
Ammonia was added in excess to bisulphate of copper, so as to form
the deep-blue solution of ammonio-Sulphate: the latter was readily
taken down by the charcoal, and the liquid became perfectly colourless.
Strong ammonia was digested in the cold upon the charcoal containing
the salt of copper, and also boiled upon it, without dissolving a trace
EFFECTS OF ANIMAL CHARCO AL ON SOLUTIONS. 633
of it, as the ammonia did not become blue even when poured off and
exposed to the air. In a certain experiment, the deep-blue colour of
five grains bisulphate of copper in half an ounce of caustic ammonia,
diluted with one and half ounces water, was much impaired by twenty
grains of the charcoal. Increasing the charcoal every second day, by
five grains at a time, with thirty-five grains, the colour had become very
slight, and was entirely destroyed by forty grains; nor did the super-
natant ammonia contain any protoxide of copper.
Five grains of nitrate of silver, in the same quantity of ammonia
and water, with twenty grains of the charcoal. Next day no trace of
silver in solution could be detected : two and a half grains nitrate of
silver added; agitated occasionally with the charcoal, but after several
days there was still silver in solution. On examining the phial con-
taining the above materials some time afterwards, shining metallic
spangles were perceived among the charcoal.
The solution of chloride of silver in ammonia was also taken down
completely by the charcoal.
A solution was made of ten grains hydrated protoxide of lead in
caustic potash, which was diluted with water till it amounted to three
ounces. Twenty grains of the charcoal, added to the above solution, in
a phial, which was then corked up, took down so much of the oxide of
lead that the white colour of the latter substance was quite discernible
among the charcoal. Here we have the colour of the charcoal disguised
in the compound. Making successive additions of charcoal, the oxide
of lead in solution was reduced to a trace by ninety grains; the last
additions of charcoal floated over the heavy portion containing the oxide
of lead; the supernatant solution, which had a greenish tinge, was
poured off, and the charcoal washed, thrown on a filter, and dried at a
heat which did not exceed 212°. When dry, innumerable metallic par-
ticles were visible in it; so that the oxide of lead is easily reducible by
the charcoal attached to it.
The oxide of zinc was withdrawn entirely by the charcoal from
Solution in caustic ammonia.
A deep-red solution was made of five grains iodine in fifteen grains
pure hydriodate of potash, dissolved in two ounces water. Forty grains
of the charcoal were added before the colour of the iodine was wholly
removed from the solution; the liquid acquired a faint acid reaction:
the carbon was washed, and dried in a filter on the sandbath without
exhaling any iodine vapours; but on heating it strongly in a flask by
a lamp, iodine rose in vapour, and condensed on the sides of the flask
with some moisture. The iodine was afterwards re-absorbed by the dry
charcoal when cold.
Labarraque’s disinfecting fluid (chloride of soda with bicarbonate
634 NOTE ON THE PREPARATION OF CHLORATE OF POTASH.
of soda) may be boiled without being materially injured; but I was
surprised to find that ebullition for a few seconds of a large quantity
of that fluid, in contact with a few grains of the charcoal, completely
destroyed its bleaching power.
The same effect took place in the cold, on agitating the fluid and the
charcoal together for a few minutes. No gas was emitted in either case.
On evaporating the saline solution to dryness, it was found to contain
no notable quantity of chlorate of soda. Twenty grains of carbon were
adequate to destroy the bleaching power of a pint of the disinfecting
fluid recently prepared.
A solution of common bleaching powder, chloride of lime, was
destroyed by charcoal with nearly equal facility, particularly when
hot.
A pound of water, recently impregnated with an equal bulk of chlo-
rine gas, was heated rapidly to the boiling point, in contact with twenty
grains of the charcoal, in a glass flask provided with a perforated cork
and bent glass tube, for the purpose of collecting any gas which might be
given off. Gas was collected, but it was entirely carbonic acid, and
most of the charcoal disappeared: muriatic acid was found in the liquid.
On collecting the unconsumed charcoal in this and other cases, and
washing it several times after being dried on a sandbath, it gave out a
few drops of strong muriatic acid, when heated in a glass tube by means
of a lamp.
IV.
NOTE ON THE PREPARATION OF CHLORATE OF POTASH.
From Chem. Soc. Mem. 1841-43, pp. 5-7.
IT is well known that the ordinary processes for this important salt
are attended with some practical difficulties. When a stream of chlorine
gas is passed through a strong solution of carbonate of potash, the
absorption of the gas is rapid and complete, till one-half of the alkaline
carbonate is decomposed; but the remaining portion, which is in the
state of bicarbonate, is not so easily acted upon. To decompose the
latter salt completely, chlorine must be applied in excess, and the de-
composition is attended by the formation of free hypochlorous acid, as
has been proved by Mr. Detmer. The liquid is also at the end highly
bleaching, and contains much hypochlorite of potash. The boiling
NOTE ON THE PREPARATION OF CHLORATE OF POTASH. 635
necessary to convert the latter into chlorate of potash and chloride of
potassium occasions, according to M. Morin, a considerable loss of
Oxygen, and thus lessens the product of chlorate. When a strong solu-
tion of caustic potash is substituted in this process for the carbonate,
the absorption of chlorine proceeds without interruption; but the liquid
When Saturated bleaches strongly from hypochlorite formed. A long-
Continued boiling is required to destroy this property completely, and
as Oxygen escapes, the chlorate obtained must be deficient in quantity
in a corresponding proportion. The process which the author recom-
mends, and which is attended with none of these inconveniences, con-
sists in mixing carbonate of potash intimately with an equivalent
quantity of dry hydrate of lime, and exposing the mixture to chlorine
gas. This mixture, although quite dry, absorbs the gas with prodigious
energy, the temperature rises much above 212°, and water is freely
evolved. When saturated it may be moderately heated, which destroys
a mere trace of hypochlorite it contains. The whole lime is found in
the state of carbonate, and the potash as chlorate and chloride of potas-
sium. The solution of the two latter salts is neutral, without any
bleaching property, and free from lime. The chlorate of potash may be
crystallized from it in the usual way. Carbonate of potash, when
moistened and exposed to chlorine, without the hydrate of lime, absorbs
the gas with great avidity, and certainly answers better than a strong
solution of the same salt; but the absorption becomes slow after the
Salt is in the state of bicarbonate, and subsequently a large quantity of
the bleaching hypochlorite of potash is produced. In the new process
described above, there is no reason to believe that the carbonate of
potash is decomposed by the dry hydrate of lime till the chlorine is
presented to the mixture; then, while the lime attracts the carbonic
acid, the chlorine acts simultaneously upon the potash, and the car-
bonate of potash is thus readily decomposed. The same principle of
calling in a secondary agency to promote combination may be taken
advantage of in many other cases. One of these, of some interest, is
the promotion of the absorption of sulphuretted hydrogen by hydrate of
lime, through the influence of other salts. Thus hydrate of lime, dry
or slightly damped, ceases to absorb sulphuretted hydrogen long before
it is saturated with that gas; but if mixed with an equivalent of
hydrated Sulphate of soda, the absorption takes place with greatly
increased avidity, and goes on till two equivalents of Sulphuretted
hydrogen are taken up for one equivalent of lime. But here, with the
assistance of sulphuretted hydrogen, the hydrate of lime decomposes
the sulphate of soda, sulphate of lime being formed, while caustic soda
combines with the sulphuretted hydrogen.
The author has found that the last mixture may be applied with
636 LETTER TO M. DUMAS.
advantage, from its great absorbing power, in purifying coal-gas, where
the highest degree of purification is desirable, and where the products,
sulphate of lime and hydrosulphuret of sulphuret of sodium, can be
economically applied. He recommends it to be introduced into the
last of the dry-lime purifiers.
V.
LETTRE DE M. GRAHAM À M. DUMAS
SUR QUELQUES CONSIDÉRATIONS QUI DERIVENT DE LA LOI DES
SUBSTITUTIONS ET SUR UN SYSTÈME DE NOTATION APPLICABLE
AUX FORMULES DES TYPES.
From Annal. de Chimie, iv. 1842, pp. 177-186.
LoNDRES, 30 novembre 184l.
* EN vous priant d'accepter la dernière partie de mon ouvrage, je
désire en même temps appeler votre attention sur quelques considéra-
tions qui dérivent de votre loi des substitutions, et sur un système de
notation que je crois particulièrement applicable aux formules des types,
de façon à les distinguer de celles que appartiennent à la théorie des
radicaux."
Toute théorie de combinaisons serait incomplète si elle ne tenait
compte, dans la constitution assignée aux éléments et aux combinaisons,
de la propagation de l'action chimique à une distance qu'on peut apprécier
dans une couple voltaïque. Cette considération nous a déjà amenés à
conclure que même un élément isolé, tel qu'un métal dans l'état où nous
l'employons, possède une structure moléculaire compliquée, ses atomes
se groupant réellement de manière à représenter des combinaisons
binaires. Ainsi, quand nous combinons deux éléments différents, nous
avons réellement à défaire une combinaison préexistante, mais moins
stable, avant d'unir les éléments dissemblables. Par suite, même dans
les cas où la combinaison paraît la plus directe, elle est réellement due
à une double décomposition, ou bien à la substitution d'un élément à un
autre dans un cadre de combinaisons préexistantes. De plus, l'aptitude
des combinaisons, de toute sorte, à se décomposer sous une action élec-
trique intense, paraît indiquer une simplicité et une identité de composi-
tion plus grandes qu'on ne l'admettait généralement.
LETTER TO M. DUMAS. 637
Nous repoussons l'idée de voir des atomes de même sorte appartenir
indifféremment à divers systèmes de combinaison, car la différence de
nature paraît la cause déterminante de la combinaison des corps.
L'intensité de la combinaison augmente certainement par la différence
des éléments, mais cela ne prouve pas que cette différence soit une con-
dition essentielle de la combinaison. L'état de combinaison paraît, en
vérité, l'état naturel de la matière, en même temps que la source de sa
cohésion et de son agrégation : c'est l'inertie qui lui permet de conserver
cette disposition, et, pour la détruire, il faut l'application d'une force
telle que celle de la chaleur, pour déterminer la séparation des molé-
cules.
En regardant comme binaire la combinaison fondamentale et élémen-
taire de chaque composé, l'un des éléments étant négatif et l'autre
positif, on peut exprimer cette différence, en séparant par un trait le
symbole des deux éléments, mettant l'élément positif au-dessous et
l'autre en-dessus : Eau # acide carbonique # ; hydrate de potasse
# carbonate de potasse # , gaz oléfiant # OU1 # éther #.
alcool H,oo
H
4
La plupart de ces formules signifient seulement que certains éléments
pris collectivement sont négatifs, et que certains autres, collectivement
aussi, sont basiques. Ainsi, dans l'éther, 4 atomes sont basiques C4, et
6 (HgO) sont négatifs. Mais on doit supposer que beaucoup de com-
posés admettent une division poussée plus loin : le gaz oléfiant, par
H2 H2 , HHHH
, Ou meme ©
exemple, peut se représenter par 2C2H2 ou C,C TCCCC ' 06)
2N-/2
qui peut se résumer ainsi :
1. L'élément basique ou positif est en combinaison immédiate avec
l'élément ou les éléments électro-négatifs placés au-dessus dans la
formule ;
2. Ces combinaisons binaires s'associent de nouveau pour former la
molécule composée, par suite d'une attraction réciproque de tous les
éléments basiques et de tous les éléments électro-négatifs. C'est là ce
qui maintient réunis les 3 atomes similaires qui forment l équivalent
d'azote ou de phosphore ; les trois atomes de cyanogène dans l'acide
cyanurique; les différents multiples de C2H2 groupés ensemble pour
former la molécule de gaz oléfiant et des hydrocarbures ses isomères
ou bien encore, les multiples de CgH4 dans la molécule d'essence de
térébenthine.
Une molécule organique est donc représentée comme l'association de
63S LETTER TO M. DUMAS.
deux ou plusieurs combinaisons binaires, d'une constitution simple
relativement, souvent susceptibles d'être isolées et douées d'une grandè
stabilité.
Parmi les corps placés en haut dans les formules, on peut s'attendre
- à trouver le chlore, l'oxygène, l'azote, l'hydrogène, et en bas le carbone,
ou le carbone et l'hydrogène. Les premiers éléments paraissent électro-
négatifs dans l'ordre où ils sont placés :
Chlore,
Oxygène,
Soufre,
Azote,
Hydrogène.
On trouve dans les cas de substitution que les corps placés à la fin du
tableau précédent, sont remplacés par ceux qui les précèdent. L'azote
paraît plus électro-négatif que l'oxygène, mais seulement dans certaines
doubles décompositions où il intervient comme élément de l'ammoniaque,
ce qui ne suffit pas pour déterminer son rang; de même qu'on pourrait
aussi placer l'oxygène avant le chlore, d'après la conversion du chloro-
forme FoCls en acide formique par la potasse.
Combinaisons du méme type.—Ce sont des corps qui renferment le
même nombre d'atomes élémentaires tant électro-négatifs que basiques.
Type gaz oléfiant #, chlorure de carbone Cl,
4 4
Type éther #º ; chlorure d'éthyle H,ol, éther hydrochlorique
4 4
chloré H.Cl,
C4
Type alcool H,oo, acide acétique H,o,o, acide chloracétique
4 C4H2
ClaOgO
C,H ©
Type aldéhyde #, chloral #
Ammoniaque.—Sa formule paraît être § et non pas #. L'hydro-
3
gène étant basique, ne serait pas remplacé par le chlore, et l'on n'a pas
observé de sels chlorés d'ammoniaque analogues aux éthers chlorés. La
connaissance que nous avons de la composition du chlorure d'azote ne
suffit pas pour décider la question. On se souvient que dans la formule
ci-dessus N équivaut à Oa ou Hs ; le précipité blanc de mercure de
LETTER TO M. DUMAS. 639
#
Wöhler HgCl + NHa, et le précipité blanc ordinaire HgCl + HgNH2
peuvent être assimilés et représentés respectivement par et
C1N
HgH,Hg. -
Le composé noir produit par l'action de l'ammoniaque liquide sur le
CIN ClHgN
Hg2H2Hg2 Hg2H,Hg
la présence de l'amidogène n'est pas nécessaire dans les amides métal-
liques, mais paraît indispensable à la constitution de l'oxamide et de
l'urée. Pour l'oxalate d'ammoniaque et l'oxamide, les formules sont
O,ON et O.N
| C,HHa " C,H,
HgHs
calomel est représenté par ou peut-être par Ainsi,
Cyanogène et cyanures.—La formule du cyanogène est § car l'acide
2
, et non pas · N . Que son hydrogène ne soit
2 C,H
pas basique, c'est ce que prouve la formation du chlorure de cyanogène
par substitution de chlore et production d'acide hydrochlorique. C'est
ce qui explique aussi la faible action de la potasse sur l'acide hydro-
cyanique, son hydrogène étant électro-négatif, tandis que le même
hydrogène est promptement remplacé par le mercure, le cyanure de
NHg
2
énergiques, comme cela arriverait si sa composition ressemblait à celle
hydrocyanique est N
mercure étant Ce dernier sel n'est pas décomposé par les acides
Mais le cyanure de mercure est prompte-
du cyanure de potassium #
ment décomposé par le soufre et l'hydrogène sulfuré, ainsi que par l'acide
hydrochlorique, le soufre et le chlore formant du sulfure et du chlorure
de mercure, tandis que l'hydrogène laissé à la place du mercure employé
reproduit l'acide hydrocyanique #.
2
Les 2 atomes de cyanure d'hydrogène qui existent dans l'acide ferro-
cyanique FeCy + 2HCy ont au contraire la constitution d'un hydracide
ordinaire, l'hydrogène étant aisément remplacé par les métaux basiques,
le potassium, etc. Il contient donc Nº . Mais le fer du cyanure de
4-1-4-2
* Rien ne prouve mieux la difficulté de concilier les théories anciennes et nouvelles
que cette nécessité admise par M. Graham de considérer le cyanure de mercure et celui
de potassium comme deux corps renfermant deux radicaux différents.
640 LETTER TO M. DUMAS.
fer n'étant pas précipité par la potasse, doit être électro-positif, et le
cyanure métallique se représente par #.
2
NFe N* .
Acide ferrocyanique ° 7-N -- 2
. NFe Nº
Ferrocyanure de potassium C - . : =.
C2 C4K2
Les formules de l'acide ferricyanique (Hs + Fe2Cye) et du ferricyanure
NFe2.Ns et NºFe2Ns
de potassium (K,+ Fe,Cy) sont Ce CeHs " CºCºKs
En donnant au sulfocyanogène C2NS2 la formule moléculaire #,
2
ses combinaisons seront
Acide hydrosulfocyanique hydraté #
2
. NS
Sulf de pot - 2
ocyanure de poUasslum C,K
2
L'acide cyanique hydraté et le cyanate de potasse seront représentés
par des formules analogues :
Acide cyanique hydraté #
NO
C te de pot #;
yanate de potasse G#
2
Les deux corps isomères, le cyanate de potasse et l'urée, ont une
formule moléculaire différente.
) ſ$ NO,N
Cyanate d'ammoniaque #- ;
C2HHs
Urée N92 N .
C2H2 H2
On représentee l'urée comme renfermant 1 at. de cyanogène, 2 at.
d'eau et 1 at. d'amidogène. D'après l'opinion générale elle contient 2
atomes d'oxyde de carbone et 2 d'amidogène, ce qu'on peut représenter
O,NN
C,H,H,
Mais le cyanogène existant probablement dans l'urée, la première
formule est préférable. On peut alors comparer l'urée à l'allantoïne,
qui contient 2 atomes de cyanogène et 3 atomes d'eau.
N2Os O ·NO,N
ll —.
C4H8 C2 Hg C2
par la formule
Allantoïne
LETTER TO M. DUMAS. 641
En doublant son atome, cette matière et sa combinaison avec l'oxyde
j) 9 N4O6 N4O6
d'argent deviennent C Hº et C,H,Ag
D'après la différence d'action de la potasse sur des corps isomériques,
tels que la liqueur des Hollandais et le chlorure d'éthyle protochloré, on
ne peut douter de la différence de leur formule moléculaire,
H,ClCl .
C,H '
Chlorure d'éthyle protochloré #.
- 4
Tandis que les autres composés chlorés de chlorure d'éthyle sont
Liqueur des Hollandais
º, et º, ceux du gaz oléfiant sont, d'après l'action des alcalis,
4 4
H,Cl,Cl et HCl Cl Car la liqueur des Hollandais et les deux autres
| C,H C,H
corps cédent à la potasse HCl, et abandonnent trois composés du même
HaCl H,Cl, et HCls
C, ' C, ' ^ C,
Les éléments qui sont électro-négatifs ou basiques ensemble dans
un composé, exercent entre eux une influence réciproque, bien qu'on
* puisse supposer qu'ils ne sont pas combinés comme ceux dont l'état
· électrique est opposé, car on trouve une tendance à s'organiser en
couples. Ainsi, la combinaison chlorée d'oxyde d'éthyle a pour formule
type
HgCl2O ©
- - , Ou InleuX
empyrique CºH"Cl*O, et pour formule moléculaire
4
H,Cl,HO
C4 -
négatifs encore, 2 de chlore et 1 d'oxygène. On ne peut douter que ces
trois atomes d'hydrogène ne soient à l'abri de l'action ultérieure du chlore
et moins aisément chassés que les deux autres.
La formule moléculaire de l'huile d'amandes amères ou de l'hydrure
de benzoïle, paraît être Ho, celle de l'acide benzoïque hydraté H,OsO
l4 l4
, où les 3 atomes d'hydrogène sont associés à 3 autres plus
>
celle de l'huile de spiraea isomérique avec la dernière Hs9 ; celle de
· l4
H,o,ol et celle de l'ac. salicylique hydraté
l'acide chlorosalicylique
- 14
H,Oe ou H,O.0
C14 H C14 H
2
S
642 LETTER TO M. DUMAS.
Dans l'huile de spiraea, le seul atome basique d'hydrogène peut se
déplacer, comme dans un hydracide, par la formation d'un sel, tandis que
pour l'acide benzoïque hydraté dans la même circonstance, l'hydrogène
et l'oxygène disparaissent à la fois. -
L'acide bromobenzoïque hydraté et bibasique est une association de
deux acides, dont l'un perd l at. d'hydrogène remplacé par le brome
O + C14HgO4 et H + C14 H. BrO4 Les formules seront # pour le
- - l4
H,O,BrO
Pour la benzamide Bz + Ad ou bien C,H,O,+ NH2, la formule peut
être #, où N remplace les 3 O de l'acide benzoïque hydraté.
premier, et pour le second.
14-4-4-2
L'hydrobenzamide CiaHºN# provient de l'action de l'ammoniaque
sur l'hydrure de benzoïle. La formule moléculaire est H Nº, ou bien
14 .
celle de l'huile dans laquelle N# remplace 2 O.
La salicylimide HO + C14HgON# provient de l'action de l'ammo-
HgO,N# Oll H，N#OO
C14H ClaH '
c'est-à-dire celle de l'acide salicyleux où N# remplace 2 O.
La chlorosalicylimide C14HgClgOgN#, serait H.ClaN#O2 Ol1 CliioNº,
C14H & C14 H
le chlore remplaçant 3 atomes d'hydrogène électro-négatif.
niaque sur l'acide salicylique. Sa formule est
Formation des acides.—La formule de la benzine est #. celle de la
: 12
H,SO, ou H,O,
12 12S
tion d'acide sulfurique HºOºOºO OUl H.SO.0.0
· C12SSH C12SH
L'acide sulfureux est un corps analogue à la sulfobenzide ; l'acid
hyposulfurique renferme un hydrate d'acide sulfurique. L'acide sul-
O,OsO
· sulfobenzide
; l'acide sulfobenzique se forme avec fixa-
fureux est # L'acide hyposulfurique hydraté est
La benzile neutre C14 HgO2 ou C2sH10O4 devient du benzilate de
potasse en fixant les éléments de l'hydrate de potasse. Benzile HioO4 $
28 2
HioO,OO
benzilate de potasse | C, HK
En saturant la potasse par un acide
ON THE USEFUL APPLICATION OF REFUSE-LIME OF GAS-WORKS. 643
HioO,OO
28
par les bases, cet acide perd 1 atome d'eau et le remplace par 1 atome
d'oxyde métallique.
Chlorisatine.—Dissoute dans la potasse, elle se convertit en chlori-
satinate.
énergique, on forme l'acide benzilique hydraté Neutralisé
H,ClOaN
Ca»
H,ClOºOON
Cie HK
H,ClOaNOO
Cie HH
Les acides concentrés lui enlèvent son eau et reproduisent la chlori-
satine neutre. Il est clair que les acides anhydres tels que SOa, POg,
appartiennent à la classe de la sulfobenzide et de la chlorisatine, et doi-
vent à la présence d'un atome d'eau le pouvoir de se combiner aux bases.
Chlorisatine
Chlorisatinate de potasse ; avec un acide énergique on
obtient l'acide chlorisatinique
Hydrate d'acide sulfurique # ; hydrates d'acide phosphorique
O4O OgO2 OgOs
PH' PH,' PH
Nous avons d'autres séries de combinaisons dont les termes différent
par les proportions d'eau ou de ses éléments, comme l'amidon, la gomme
et le sucre d'amidon ; la gomme étant l'amidon plus 1 atome d'eau, et le
sucre représentant l'amidon plus 2 atomes d'eau. On ne peut cependant
· aujourd'hui assigner une formule moléculaire probable au radical de
l'amidon et de bien d'autres séries de combinaisons, faute de savoir le
rôle que joue l'hydrogène dans leur constitution ; là, en effet, il n'est
point remplacé par un autre élément plus décidément basique ou négatif.
VI.
NOTE ON THE USEFUL APPLICATIONS OF THE REFUSE-
LIME OF GAS-WORKS.
From Chem. Soc. Mem. ii. 1843-45, pp. 358, 359. [Erdm. Journ. Prak. Chem. xxxvi.
1845, pp. 48, 49 ; Franklin Inst. Journal, xi. 1846, pp. 281, 282.]
I HAD lately occasion to examine the lime as removed from a dry
lime purifier. The gas before reaching the latter had been washed with
644 ON THE USEFUL APPLICATION OF REFUSE-LIME OF GAS-WORKS
dilute sulphuric acid, which accounts for the absence of ammonia and
cyanogen compounds. The lime had not been exposed more than a
few hours to the air before it was operated upon. Still, to my surprise,
it did not blacken an acid salt of lead, and contained no sulphuret of .
calcium. It was not dried, but analysed in a damp state, exactly as it
is sent out of the works to be used as manure.
Composition of Gas-Lime.
Hyposulphite of lime, - & 12:30
Sulphite of lime, . º © 14-57
Sulphate of lime, . º º 2.80
Carbonate of lime, . º - 14'48
Hydrate of lime, . º º 17.72
Sulphur, © & º º 5'14
Sand, . © e º e '71
Water combined, . o º 8’49
Water (free), . © te º 23.79
100°
With no more than a trace of ammonia and cyanogen. }
The lime in the porous condition in which it is taken from the dry-
lime purifiers, absorbs oxygen so rapidly from the air as to heat, and
hence the state of oxidation in which the sulphur is found. If the lime
be very damp, or diffused through a quantity of water, as it comes from
the wet-lime purifiers, then the absorption of oxygen is much slower.
The fluid portion then contains in solution the bisulphuret of calcium of
Herschel, which may be crystallized from it; and at first very little else.
After the first rapid absorption of oxygen, the further oxidation of
the gas-lime is decidedly slow. A specimen kept in an open vessel,
and repeatedly moistened and rubbed to powder when it dried, was
found after three months’ exposure to retain 7 per cent. of sulphurous
acid, besides all the free Sulphur Originally present. The hyposulphur-
ous acid had entirely disappeared. Hence, if added to soil as manure,
gas-lime must be powerfully deoxidising, a property which will gene-
rally impair its utility.
It appears advisable, where the refuse-lime does not possess any
value from ammonia, to dry it strongly, or roast it. It would thereafter
consist of nearly equal weights of sulphate and carbonate of lime, and
be in the condition most valuable as a manure. *
Refuse-lime, such as was examined, may be recommended as a con-
venient and most economical source of the hyposulphites. The lime,
after being taken from the purifiers, should be exposed to air for two or
three days, till it loses all smell of sulphuretted hydrogen. The highly
ON THE EXISTENCE OF PHOSPEIORIC ACID, 645
soluble hyposulphite of lime may then be dissolved out by little more
than an equal weight of cold water. The solution may be evaporated at
120°, and the hyposulphite of lime crystallized out; or, the solution, by
adding carbonate of soda, converted into hyposulphite of soda, which is
a more stable salt, may be evaporated at a higher temperature, and
crystallizes more easily.
From the refuse-lime, one-sixth of its weight of crystallized hypo-
sulphite of lime has been obtained in a state of purity by a single
crystallization. When the gas is washed with sulphuric acid to remove
ammonia, before being conducted into the lime-purifier, it yields the
refuse-lime more suitable for this purpose. The preparation of the
hyposulphites in quantity is becoming the more important, as besides
their use in electro-plating and photography, they are likely to be
applied largely to the extraction of chloride and bromide of silver from
silver ores.
VII.
NOTE ON THE EXISTENCE OF PHOSPEIORIC ACID IN THE
DEEP-WELL WATER OF THE LONDON BASIN.
From Chem. Soc. Mem. ii. 1843-45, pp. 392, 393. [Bibl. Univ. lx. 1845, pp. 385, 386.]
THIS water is obtained on piercing the London clay, which forms an
impervious bed, generally exceeding 200 feet in thickness, and flows
from fissures in the subjacent chalk. It is always highly soft and
alkaline, and remarkable for the predominance of soda salts over earthy
Salts among its solid constituents. I have never found it to contain a
sensible quantity of potash, although salts of the vegetable alkali appear
among the constituents of the water of the deep Artesian well of Grenelle.
When evaporated considerably, a small deposit takes place in the
London deep-well water, which consists chiefly of carbonate and phos-
phate of lime. The remaining liquid gives with nitrate of silver a pre-
cipitate of chloride and carbonate of silver, which is white without any
shade of yellow ; but if a portion of the water, amounting to an ounce
or two, be evaporated to dryness in a platinum capsule, without remov-
ing the precipitate, and the heat afterwards continued so as to raise the
temperature of the resulting dry saline matter to low redness, then, on
redissolving by distilled water, and adding nitrate of silver, a precipitate
is obtained, in which the yellow colour of the phosphate of silver is very
646 OBSERVATIONS ON ETHERIFICATION.
perceptible. The earthy phosphate is decomposed by ignition with the
alkaline belonging to the water, and the soluble phosphate of soda is
produced.
The following are the results of the analysis of the water from the
deep well in the brewery of Messrs. Combe and Delafield, Long Acre.
An imperial gallon of the water contained 56.45 grains of solid matter,
100 parts of which gave—
Carbonate of soda, . * © 20-70
Sulphate of soda, . e e 42'94
Chloride of sodium, . © * 22:58
Carbonate of lime, . º º 10-96
Carbonate of magnesia, . º I '92
Phosphate of lime, . e fe 0°34
Phosphate of iron, . tº tº 0°43
Silica, . * * º tº O'79
100°66
The growth of green confervae in this water is extremely rapid, and
occasions inconvenience when the water is kept in open tanks. It is a
subject perhaps worthy of inquiry, whether the value of some waters
for irrigation may not depend upon their containing phosphoric acid,
this constituent having hitherto been generally overlooked in Waters.
VIII.
OBSERVATIONS ON ETHERIFICATION.
From Chem.Soc. Journ. iii. 1851, pp. 24-28. [Journ. de Pharm. xviii. 1850, pp. 124-130;
Liebig, Annal. lxxv. 1850, pp. 108-116.]
IN the ordinary process of etherizing alcohol by distilling that liquid
with sulphuric acid, two distinct chemical changes are usually recog-
nised ; namely, first, the formation of sulphovinic acid, the double sul-
phate of ether and water; and secondly, the decomposition of the com-
pound named, and liberation of ether. The last step, or actual separa-
tion of the ether, is referred to its evaporation, in the circumstances of
the experiment, into an atmosphere of steam and alcohol vapour, assisted
by the substitution of water as a base to the sulphuric acid, in the place
of ether. The observation, however, of M. Liebig, that ether is not
brought off by a current of air passing through the heated mixture of
OBSERVATIONS ON ETHERIFICATION. 647
Sulphuric acid and alcohol, is subversive of the last explanation, as it
demonstrates that the physical agency of evaporation is insufficient to
Separate ether. Induced to try whether ether could not be formed
Without distillation, I obtained results which appear to modify con-
siderably the views which can be taken of the nature of the etherizing
process.
The spirits of wine or alcohol always employed in the following
experiments, was of density 0.841, or contained 83 per cent. of absolute
alcohol.
Ea.pt. I.-One volume of oil of vitriol was added to four volumes of
alcohol, in a gradual manner, so as to prevent any considerable rise of
temperature. The mixture was sealed up in a glass tube, 1 inch in dia-
meter and 6-6 inches in length, of which the liquid occupied 5-2 inches,
a space of 1:4 inch being left vacant, to provide for expansion of the
liquid by heat. The tube was placed in a stout digester containing
water, and safely exposed to a temperature ranging from 284 to 352”
(140° to 178° C) for one hour.
No charring occurred, but the liquid measured on cooling, 5:25
inches in the tube, and divided into two columns, the upper occupying
I-75 inches, and the lower 3-5 inches of the tube. The former was
perfectly transparent and colourless, and on opening the tube, was found
to be ether, so entirely free from sulphurous acid, that it did not affect
the yellow colour of a drop of the solution of bichromate of potash. The
lower fluid had a slight yellow tint, but was transparent. It contained
some ether, but was principally a mixture of alcohol, water, and sulphuric
acid. The salt formed by neutralizing this acid fluid with carbonate of
soda, did not blacken when heated, from which we may infer that little
or no sulphovinic acid was present.
The principal points to be observed in this experiment, are its entire
success as an etherizing process, without distillation, without sensible
formation of sulphovinic acid, and with a large proportion of alcohol in
contact with the acid, namely, two equivalents of the former nearly, to
one of the latter. When the proportion of the alcohol was diminished,
the results were not so favourable.
Ea:pt. 2.- A mixture of one volume of oil of vitriol and two volumes
of alcohol, sealed up in a glass tube, was heated in the same manner as
the last. The liquid afterwards appeared of an earthy-brown colour by
reflected light, and was transparent and red by transmitted light. Only
a film of ether was sensible after twenty-four hours, floating upon the
surface of the dark fluid.
Eacpt. 3.−With a still smaller proportion of alcohol, namely one
volume of oil of vitriol with one volume of alcohol, which approaches
the proportions of the Ordinary etherizing process, a black, opaque liquid
648 OBSERVATIONS ON ETHERIFICATION.
was formed at the high temperature, thick and gummy, without a per-
ceptible stratum of ether, after standing in a cool state.
Crystals of bisulphate of soda, containing a slight excess of acid, were
found to etherize about twice their volume of alcohol, in a sealed tube,
quite as effectually as the first proportion of oil of vitriol, when heated
to the same temperature. The two liquids found in the tube were
colourless, no Sulphurous acid appeared, and only a minute quantity of
sulphovinic acid. Crystals of bisulphate of soda, which were formed in
an aqueous Solution and without an excess of acid, had still a sensible
but much inferior etherizing power.
Eacpt. 4.—A mixture was made of oil of vitriol with a still larger
proportion of alcohol, namely, 1 volume of the former and 8 of the latter,
or nearly 1 equivalent of acid to 4 equivalents of alcohol. This mixture
was sealed up in a tube and heated for an hour between 284 and 317°
(140° and 158° C), which appeared sufficient for etherizing it. A second
exposure for another hour to the same temperature did not sensibly
increase the ether product. The column of ether measured 1.25 in the
tube, and the acid fluid below 2:5 inches. Both fluids were perfectly
colourless. t
It thus appears to be unnecessary to exceed the temperature of 317°
(158°C.) in this mode of etherizing, and that the proportion of alcohol
may be increased to eight times the volume of the oil of vitriol without
disadvantage.
Eajot, 5.—The proportions of the first experiment were again used,
namely, 1 volume of oil of vitriol with 4 volumes of alcohol, and the
mixture heated as in the last experiment to 317° (158°C). The upper
fluid, or ether, measured 1-1 inch in the tube, the lower fluid 2.65 inches.
The latter had a slight yellow tint, like nitrous ether, but only just
perceptible. It gave, when neutralized by chalk:—
Sulphate of lime, . q 83-11 grains.
Sulphovinate of lime, . © 4'91
22
The last Salt was soluble in alcohol, and crystallized in thin plates.
Here again the formation of sulphovinic acid in a successful etheriz-
ing process is quite insignificant.
New results at 317°, from the other proportions of 1 volume of oil
of vitriol with 1 and 2 volumes of alcohol, were quite similar to those
obtained in experiments 2 and 3, at the higher temperature of 352°.
In none of these experiments did there appear to be any formation of
olefiant gas, and the tubes could always be opened, when cool, without
danger.
Neither glacial phosphoric acid nor crystallized biphosphate of soda
etherized alcohol to the slightest degree, when heated with that sub-
OBSERVATIONS ON ETHERIFICATION. 649
stance in a sealed tube, to 360° (182°C). Even chloride of zinc produced
no more, at the same temperature, than a trace of ether, perceptible to
the sense of smell.
Eagt. 6.—To illustrate the ordinary process of ether-making, a mix-
ture was prepared, as usually directed, of
100 parts of oil of vitriol,
48 , of alcohol (0.841),
18.5 , of water.
This liquid was sealed up in a glass tube, and heated to 290° (143°C)
for one hour. It became of a dark greenish-brown colour, and opales-
cent, with a gummy-looking matter in Small quantity. No stratum of
ether formed upon the surface of the fluid.
The tube was opened and the fluid divided into two equal portions.
One of the portions was mixed with half its volume of water, and the
other with half its volume of alcohol, and both sealed up in glass tubes
and exposed again to 290 for one hour.
It would be expected, on the ordinary view of water Setting free
ether from sulphovinic acid, that much ether would be liberated in the
mixture above, to which water was added. The ether which separated,
however, amounted only to a thin film, after the liquid had stood for
several days. In the other liquid, on the contrary, to which alcohol was
added, the formation of ether was considerable, a column of that liquid
appearing, which somewhat exceeded half the original volume of the
alcohol added. In fact, the sulphovinic acid was nearly incapable of
itself of yielding ether, even when treated with water. But it was
capable of etherizing alcohol added to it, in the second mixture, like
bisulphate of soda or any other acid Salt of sulphuric acid.
The conclusions which I would venture to draw from these experi-
ments are the following:—
The most direct and normal process for preparing ether appears to
be, to expose a mixture of oil of vitriol with from four to eight times its
volume of alcohol of 83 per cent to a temperature of 320° (160° C), for
a short time. Owing to the volatility of the alcohol, this must be done
under pressure, as in the Sealed glass tube. The sulphuric acid then
appears to exert an action upon the alcohol, to be compared with that
which the same acid exhibits when mixed in a small proportion with
the essential oils. Oil of turpentine, mixed with one-twentieth of its
volume of sulphuric acid, undergoes an entire change, being chiefly
converted into a mixture of two other hydrocarbons, terebene and colo–
phene, one of which has a much higher boiling point and greater vapour-
density than the oils of turpentine. This hydrocarbon does not combine
with the acid, but is merely increased in atomic weight and gaseous
650 OBSERVATIONS ON ETHERIFICATION.
density without any further derangement of composition, by a remark-
able polymerizing action (as it may be termed) of the sulphuric acid.
So of the hydrocarbon of alcohol; its density is doubled in ether, by the
same polymerizing action. Chloride of zinc effects, with alcohol, at an
elevated temperature, a polymeric catalysis of the latter, of the same
character, but in which hydrocarbons are formed, of even greater density,
and free from oxygen.
This view of etherification is only to be considered as an expression
of the contact—theory of that process which has long been so ably advo-
cated by M. Mitscherlich.
The formation of sulphovinic acid appears not to be a necessary
step in the production of ether; for we have found that the etherizing
proceeded most advantageously with bisulphate of soda, or with sul-
phuric acid mixed with a large proportion of alcohol and water, which
would greatly impede the production of sulphovinic acid. It appears,
indeed, that the combination of alcohol with sulphuric acid, in the form
of sulphovinic acid, greatly diminishes the chance of the former being
afterwards etherized; for, when the proportion of oil of vitriol was
increased in the preceding experiments, which would give much sulpho-
vinic acid, the formation of ether rapidly diminished. The previous
conversion of alcohol into Sulphovinic acid, appears, therefore, to be
actually prejudicial, and to stand in the way of its subsequent trans-
formation into ether.
The operation of etherizing has attained a kind of technical per-
fection in the beautiful continuous process now followed. The first
mixture of alcohol and sulphuric acid is converted into sulphovinic
acid, the sulphate of ether and water, which acid salt appears to be the
agent which polymerizes all the alcohol afterwards introduced into fluid.
Bisulphate of soda, with a slight excess of acid, acts upon alcohol in
the same manner, and its substitution for the acid sulphate of ether
would have a certain interest, in a theoretical point of view, although a
change of no practical importance in the preparation of ether.
Sulphuric acid does not appear to be adapted for the etherizing of
amylic alcohol. M. Balard, by distilling these substances together,
obtained a variety of hydrocarbons, some of them of great density, but
no ether. The polymerizing action of the sulphuric acid appears to
advance beyond the ether stage. I have varied the experiment by
heating amylic alcohol, in a close tube, to 350° (176°C.) with oil of
vitriol, to which 1, 2, 3, 4, and even 6 equivalents of water had been
added, without obtaining anything but the hydrocarbons of Balard. The
formation of these was abundant, even with the most highly hydrated
acid, and with a very moderate colouration of the fluid.
END.
IN DE X.
GRAHAM'S
CHEMICAL AND PHYSICAL RESEARCHES.
IN DE X.
ABSORPTION and dialytic separation of gases
by colloid septa (1866), 235.
Absorption of gases by liquids (1826), 1.
Absorption of gases by metals, 253-290.
Absorption of gases, chemical theory of, 4.
Absorption of moisture and carbonic acid
from the atmosphere, 17.
Absorption of vapours by liquids, experi-
ments on, 17.
Acetate of baryta, diffusion of, 509.
Acetate of lead, diffusion of, 509.
Acetate of potash, diffusion of, 541.
Acetate of soda, diffusion of, 542.
Acetic acid, diffusion of, 504.
Acetic acid, neutralization of, by hydrate of
potash, 437.
Acetic acid, transpiration of, 605.
Acetone, transpiration of, 612.
Acids, various, neutralization of, by hydrate
of potash, 424.
Aerated water, 13.
Aikin's Chemical Dictionary, 15.
Air. See Absorption, Diffusion, Effusion,
Motion, Percolation, and Transpiration.
Albumen, dialysis of, 591.
Alcoate of chloride of calcium, 314.
Alcoate of chloride of zinc, 319.
Alcoate of nitrate of lime, 317.
Alcoate of nitrate of magnesia, 316.
Alcoate of protochloride of manganese, 318.
Alcoates, an account of the formation of
(1828), 309.
Alcogel, 621.
Alcohol, 200.
Alcohol derived from the fermentation of
bread (1826), 627.
Alcohol, diffusion of, 506.
Alcohol, on the concentration of, in Sömmer-
ing's experiments (1854), 551.
Alcohol, methylic, transpiration of, 611.
Alcohol, transpiration of, 609.
Alcosol of silicic acid, 621.
Alumina, soluble, 577.
Ammonia, 184, 257.
Ammonia, diffusion of, 505.
Ammonia, transpiration time of, 185.
Ammonia, transpiration times of, at different
pressures, 186.
Ammoniated salts of copper, diffusion of,457.
Andrews, Dr., 301, 401, 404.
Animal charcoal, effects of, on solutions, 630.
Arrott, Mr., 436, 437.
Arsenious acid from colloid liquids, separa-
tion of, 592.
Arseniates, phosphates, and modifications of
phosphoric acid, researches on the (1833),
321.
Arseniate, tribasic, of magnesia and water
(arseniate of magnesia), 388.
Arsenic and phosphoric acids, neutralization
of, by hydrate of potash, 441.
Atmosphere, different altitudes of, 9.
Atmosphere, finite extent of the, 6.
BALARD, M., 650.
Becker, Mr., 296.
Bellani de Monza, 36.
Berzelius, J., 13, 261, 321, 333, 357, 394.
Bechamp, M. : solutions of iron, 582.
Becquerel, M. E., 298.
Bicarbonate of ammonia, diffusion of, 527.
Bicarbonate of potash, diffusion of, 527.
Bicarbonate of soda, diffusion of, 528.
Bichloride of mercury deliquesces in alcohol
vapour, 23.
Bichromate of potash, 412.
Bichromate of potash, neutralization of, by
hydrate of potash, 437.
Bimoxalate of potash, 371, 439.
Binoxalate of soda, 373.
Bisulphide of carbon, transpiration times,
190.
654
INDEX.
Biphosphate of soda, 336.
Biphosphate of soda, second variety of, or
bipyrophosphate of soda, 337.
Biphosphate of soda, third variety of, 339.
Biphosphate of soda, fourth, or insoluble
variety of, 340.
Biphosphate of soda, fifth variety of, or
metaphosphate of soda, 341.
Bipyrophosphate of soda, second variety of
biphosphate of soda, 337.
Bisulphate of soda, 417.
Brewster, Sir D., 375.
Brockedon, Mr. : graphite, 210.
Bromide of sodium, diffusion of, 524.
Bromine, diffusion of, 500.
Bromine and hydrochloric acid, transpira-
tion, 194.
Buddle, Mr., on mine gases, 87.
Bunsen, Professor, 215.
Bussey, A., 631.
Buttini, M., 309.
Butyric acid, transpiration of, 606.
CAILLETET, M. : penetration of iron, 285.
Caramel, dialysis of, 589.
Carbonate of potash, diffusion of, 533.
Carbonate of soda, diffusion of, 534.
Carbonic acid and platinum, 256.
Carbonic acid and nitrous oxide, 93.
Carbonic acid gas, 15, 16.
Carbonic oxide, diffusion of, 63.
Carburetted hydrogen, 92.
Carburetted hydrogen of marshes, diffusion
of, 64.
Castor oil, vapour of alcohol absorbed by, 23.
Chalk of Roche Guyon, 10, 12.
Chevraud, M.: chalk not nitrifying, 13.
Clark, Mr., 322, 324, 334, 335.
Chlorate of potash, on the preparation of, 634.
Chloride of ammonium, diffusion of, 524.
Chloride of barium, diffusion of, 510.
Chloride of calcium, 396.
Chloride of calcium, diffusion of, 512.
Chloride of copper, 395.
Chloride, double, of copper and ammonium,
396. .
Chloride of magnesium, water of, 396.
Chloride of manganese, do., 398.
Chloride of manganese, diffusion of, 513.
Chloride of potassium, diffusion of, 520.
Chloride of sodium, diffusion of, 449, 519.
Chloride of strontium, diffusion of, 510.
Chlorides, water of, 394.
Chlorine and platinum, 257.
Chlorine, diffusion of, 59.
Chlorine, transpiration time, 192.
Chromate of potash, 412.
Chromic acid, diffusion of, 503.
Chromic oxide, soluble, diffusion of, 586.
Coal gas, 200, 257.
Colloidal condition of matter, 595.
Congelation of sulphate of soda, 27.
Contents, xxiii.
Contents Analytically, xxvii.
Copper, absorption of, 273.
Crum, Mr. Walter, 580, 581.
Crystallization of saline solution, 24.
Crystallization of soda-alum, on the water
of (1836), 365.
Cyanogen, diffusion of, 60.
Cyanogen, transpiration times of, 187.
DALTON, Dr., 5, 6, 22, 81,302, 303, 445.
Davy, Sir H., on nitrous gas, 320.
Davy, Sir H., Essay on Flame, 41, 42, 85.
De la Rue, Mr. : parchment paper, 556.
Dialyser, 556.
Dialysis, 555, 571.
Dialysis of organic colloid substances, 588.
Dialysis, preparation of colloid substances
by, 577.
Decomposition of salts by diffusion, 464.
Deville, M. H. Ste.-Claire, 253, 254, 258,
278, 289.
Dextrin, dialysis of, 589.
Dichloride of copper, diffusion of, 525.
Diffusion of gases, experimental researches
on (1829), 28.
Diffusion of gases into atmospheric air, 29.
Diffusion of mixed gases into atmospheric
air, 30.
Diffusion of gases into other atmospheres
than common air, 34. 4.
Diffusion of carbonic acid gas, 57.
Diffusion of gases, on the law of, 44.
Diffusion volumes of gases, table of equiva-
lent, 64.
Diffusion of gases, supplementary observa-
tions on the law of, 69.
Diffusion of mixed gases into a vacuum,
with partial separation—atmolysis, 224.
Diffusion of chloride of sodium, 449.
Diffusion of liquids, on the (the Bakerian
lecture, 1850), 444.
INDEX.
655
Diffusion of liquids, additional observations
on the, 531.
Diffusion of liquids, supplementary observa-
tions on the, 496.
Diffusion of ammoniated salts of copper, 457.
Diffusion, decomposition of salts by, 464.
Diffusion of double salts, 467.
Diffusion, effect of temperature on, 569.
Diffusion of salts of soda, 488.
Diffusion, separation of salts of different
bases by, 461.
Diffusion of salts of potash and ammonia,
471.
Diffusion of mixed salts, 458.
Diffusion of one salt into the solution of
another salt, 468.
Diffusion of various salts and other sub-
stances, 452.
Doebereiner, M., 42, 44, 45.
Dulong, the nitrous acid of, 79.
Dumas, M., on absorption, 335.
Dumas, M., letter of Mr. Graham to, 636.
Dumas, M. : absorption of hydrogen, 273.
Dutrochet, M. : endosmose, 40.
EFFUSION of air, carbonic oxide, oxygen, and
of a mixture of carbonic oxide and oxygen
at different pressures by plate B, 100.
Effusion into a vacuum by a glass jet, 90.
Effusion of carbonic acid, air, and of mix-
tures of carbonic acid and air, at different
pressures by plate B, 100.
Effusion of mixtures containinghydrogen, 101.
Effusion of air of different elasticities or
densities by brass plate B, 104.
Effusion of air of different temperatures, by
plate F, 107.
Effusion of nitrogen and oxygen, and of
mixtures of these gases under different
pressures, by a second perforated brass
plate B, 97.
Effusion into a vacuum by a perforated
brass plate A, 94.
Energia, 554.
Ether, hydrochloric (chloride of ethyl), 198.
Ether, hydrochloric methylic (chloride of
methyl), 198.
Ether, methylic (oxide of methyl), transpira-
tion time, 197.
Ether (oxide of ethyl), transpiration time,
195.
Etherification, observation on (1851), 646.
Ethers, transpiration of, 611.
Evaporation, loss of liquid by, 21.
Expansion of gaseous bodies by heat, 7.
Experiments with compound capillary P, 174.
Experiments on diffusion, 49-62.
FARADAY, M., 284, 598.
Faraday, M., on condension of sulphuric
acid into a liquid, 3.
Faraday, M., on gaseous liquefaction, 1.
Fermentation of bread, alcohol derived from
the (1826), 627.
Ferrocyanide of copper, diffusion of, 583.
Ferrocyanide of iron, diffusion of, 585.
Ferro and ferricyanide of potassium, 480.
Fire-damp, composition of, 85.
Fluoboric gas, 3.
Fluosilicic gas, 3.
Figuier, M. : animal charcoal, 631.
Formic acid, transpiration of, 607.
Fownes, Mr., 99, 126.
Fremy, M., 559, 588.
Friction, on the heat of (1826), 626.
Funke, M. : blood-crystals, 598.
GASEs, on the motion of (1846), 88, 164.
Gases, molecular action of, 13.
Gases, on the molecular mobility of (1863),
210.
Gases, a new property of, 84.
Gases, effusion of, 90.
Gases in coal pits, 87.
Gases, increase of capacity for heat in, 7.
Gases liquefied, table of, 3.
Gases under pressure, 1.
Gas-lime, composition of, 644.
Gay-Lussac, M., 13, 301, 303, 444.
Glauber's, M., formation of saltpetre, 9.
Glycerine, transpiration of, 613.
Glycerosol, 621.
Gold, absorption by, 273.
Graphite for diffusion, 210.
Gregory, Dr., 375.
Greiner's, M., thermometer, 403.
Guilbert, M. : charcoal, 631.
Gum, dialysis of, 588.
HALDAT, M. : heat of friction, 627.
Heat of friction, on the (1826), 626.
Heat disengaged in combinations, experi-
ments on, 402.
Henry, Dr., 41, 42, 43, 45, 85, 320.
656
INDEX.
Hess, Prof., 400, 401, 404.
Huggins, Mr. : hydrogen in stars, 283.
Humboldt, Alex, von ; air and water, 13.
Hydrate of soda, diffusion of, 532.
Hydrate of potash, do., 486.
Hydrate of potash, neutralization of, by
nitric and hydrochloric acids, 424.
Hydrate of potash, neutralization of, by
sulphuric acid, 431.
Hydrated sulphate of lime, 364,
Hydrates of salts and metallic oxides, with
observations on the doctrine of isomerism
(1834), 349.
Hydration of magnesian sulphates, 407.
Hydration of oil of vitriol, 404.
Hydriodic acid, diffusion of, 499.
Hydriodic acid, hydrobromic
bromine, diffusion of, 499.
Hydrobromic acid, diffusion of, 499.
Hydrochlorate of morphine, diffusion of, 529.
Hydrochloric acid and hot platinum, 257.
Hydrochloric acid, diffusion of, 497.
Hydrochloric acid, transpiration of, 608.
Hydrochloride of strychnine, diffusion of,
530.
Hydrocyanic acid, diffusion of, 501.
Hydrocyanic acid, transpiration times, 187.
Hydrogen, effusion of, 91.
Hydrogen gas, diffusion volume of, 48.
Hydrogenium, 290.
Hydrogenium, chemical properties of, 298.
Hydrogel of silicic acid, 620.
Hydrosol of silicic acid, 620.
Hydrosulphuric acid and heated platinum,
258.
Hydrosulphuric acid, transpiration times,
188.
Hyposulphite of potash, diffusion of, 538.
Hyposulphite of soda, diffusion of, 538.
acid, and
INDIA-RUBBER between double cotton cloth
vulcanized, 246.
India-rubber, thin balloons of, 248.
India-rubber tubing, vulcanized, 247.
Inflation of a bladder, singular, 40.
Iodide of sodium, diffusion of, 523.
Iodides and bromides of potassium and
sodium, diffusion of, 523.
Iron, absorption by, 278.
Iron, meteoric, of Lenarto, 282.
Interdiffusion of gases—double diffusion,
232.
Interdiffusion of gases without intervening
septum, 233.
JACQUELIN, M. : bisulphate of potash, 417.
Jar, diffusion-, 556.
KANE, Dr. : chloride of mercury and am-
monia, 436.
Kopp, M. : boiling points, 614,
LABARRAQUE's, M., disinfecting fluid, 633.
Latour, Caignard : state of vapour, 301.
Lavoisier, M., 10, 12.
Leslie, Prof. : the atmosphere, 8.
Leslie, Prof. : frigorific apparatus, 310, 312.
Liebig, Justus: formation of ether, 646.
Liquefaction of gases, 2.
Liquids, absorption of gases by (1826),
Liquids, miscible, 1.
Liquid diffusion to produce decomposition,
on the application of (1849), 544.
Liquid diffusion, characters of, 449.
Liquid diffusion applied to analysis (1861),
552.
Liquids mixed, density altered, 6.
Liquid stannic acid, 623.
Liquid titanic acid, 624.
Liquid tungstic acid, 624.
Liquids in relation to chemical composition,
on capillary transpiration of (1861), 600.
Liquids, on the diffusion of (the Bakerian
lecture, 1850), 444.
Longchamp's theory of nitrification, 9, 11,
12, 13.
Lowitz, M. : charcoal, 630.
Luminosity of the atmosphere, 8.
MARBLE does not exhibit any tendency to
the formation of nitre, 13.
Margueritte, M., 280, 281.
Matter, colloidal condition of, 595.
Matter, speculative ideas respecting the con-
stitution of (1864), 299.
Matthiessen, Dr., 293, 296.
Metalumina, soluble, 581.
Metaperoxide of iron, soluble, diffusion of,583.
Metaphosphate of barytes, 344.
Metaphosphate of lime, 345.
Metastannic acid, 587, 623.
Methylic ether (oxide of methyl), transpira-
tion time, 197.
Mixed salts, diffusion of, 458.
INDEX.
657
Miller, Prof. : hydrogen in stars, 283.
Mitchel, Dr., 235, 336, 337.
Mitscherlich, M., 321, 387, 393,650.
Molybdic acid, 625.
Motion of gases, 88.
Muriatic acid, evaporation, 21.
Muriatic acid, power to absorb moisture, 22.
Muriatic acid gas, diffusion of, 61.
NAPHTHA, transpiration of, 200.
Neutralization of various acids by hydrate
of potash, 424.
Neutralization of acetic acid by hydrate of
potash, 437.
Neutralization of arsenic and phosphoric
acids by hydrate of potash, 441.
Neutralization of bichromate of potash by
hydrate of potash, 437.
Neutralization of hydrate of potash by
sulphuric acid, 431.
Neutralization of hydrate of potash by nitric
and hydrochloric acids, 424.
Neutralization of oxalic acid by hydrate of
potash, 438.
Newcastle coal mines, on the composition of
the fire-damp of the, 85.
Newton, Sir I. : weight of bodies, 300.
Nitrates, water of, 378.
Nitrate of baryta, diffusion of, 507.
Nitrate of copper, water of, 378.
Nitrate of copper, diffusion of, 513.
Nitrate of lime, diffusion of, 508.
Nitrate of magnesia, diffusion of, 513.
Nitrate of magnesia, water of, 383.
Nitrate of silver, diffusion of, 518.
Nitrate of soda, diffusion of, 518.
Nitrate of strontia, diffusion of, 508.
Nitrate and submitrate of bismuth, 382.
Nitrate of zinc, water of, 383.
Nitrates, double, and submitrates, 384.
Nitre, artificial production of, 17.
Nitric acid, formation of, 11.
Nitric acid, transpiration of, 602,
Nitric acid, diffusion of, 50l.
Nitric oxide, action of, 80.
Nitrification, process of, 14.
Nitrogen, diffusion of, 63.
Nitrous phosphuretted hydrogen, properties
of, 82.
OccLUSION of hydrogen gas by metals
(1868), 283.
Occlusion of hydrogen gas by meteoric iron
(1867), 281.
Oils, essential, and phosphuretted H., 77.
Olefiant gas, 63, 78, 93, 181.
Ordway, Mr., 582, 586.
Osmium-iridium, absorption by, 272.
Osmose, 598.
Otto, Dr., 391, 392.
Oxalates, water of the 368.
Oxalates of ammonia, 392.
Oxalate of barytes, 370.
Oxalate of copper and potash, 374.
Oxalate of chromium and potash, of peroxide
of iron and potash, of peroxide of iron
and soda, etc., 375.
Oxalate of chromium and potash, 375.
Oxalates, double, 373.
Oxalate of lime, 370.
Oxalate of magnesia, 369.
Oxalate of peroxide of iron and potash, 377.
Oxalate of peroxide of iron and soda, 377.
Oxalate of potash, 371, 438.
Oxalate of potash, diffusion of, 539.
Oxalate of soda, 373.
Oxalate of soda, diffusion of, 540.
Oxalate of water, or hydrated oxalic acid, 368.
Oxalate of zinc, 369.
Oxalic acid, neutralization of, by hydrate of
potash, 438.
Oxygen gas, diffusion of, 62.
Oxygen and hydrogen, diffusion of, 224.
Oxygen and nitrogen, effusion, 92; with
platinum, 256.
Oxygen and nitrogen, diffusion of, 225.
PALLADIUM, on the relation of hydrogen to,
and on hydrogenium (1869), 290,
Palladium, alloy of, absorption by, 269.
Palladium, absorption by, 266.
Palladium, density of, 290.
Palladium, electrical conductivity of, 296.
Palladium, magnetism of, 296.
Palladium, tenacity of, 296.
Palladium with hydrogen at a high tempera-
ture, 298.
Péan de Saint-Gilles, M., 583, 584.
Peligot's, M., salts, 363.
Percolation of air through gutta percha and
other septa, 253.
Peroxide of iron, diffusion of, 581.
Peroxide of tin, precipitated and gelatinous,
587.
2 T
658
INDEX.
Person, M. : heat of ice, 598.
Phillips, Mr. Richard, 306, 350.
Phosphate, tribasic, of magnesia and water
(phosphate of magnesia), 389.
Phosphate, tribasic, of magnesia and ammonia
(ammonia.co-magnesian phosphate), 390.
Phosphate, tribasic, of soda, ammonia, and
water, 387.
Phosphates, 384.
Phosphates and pyrophosphates, on the
natural, 334.
Phosphates, tribasic, containing oxides of
the magnesia class, 388.
Phosphates, tribasic, of zinc and water
(phosphate of zinc), 388.
Phosphoric acid in the deep-well water of
the London basin, on the existence of, 645.
Phosphoric acid, the modifications of, 345.
Phosphorus, luminous, 38.
Phosphorus, observations on the oxidation
of, 36.
Phosphuretted hydrogen, 71.
Platinum, absorption and detension of hy-
drogen by, 260.
Platinum, fused, 261.
Poiseuille, M., 162, 213, 600, 609.
Powell, Mr., 101.
Preface, v.
Priestley, Dr. : nitrous gas, 320.
Protochloride of iron, 396.
Protochloride of iron, diffusion of, 514.
Protosulphate of iron, 411.
Protosulphate of iron and ammonia, 419.
Protosulphate of iron and potash, 420.
Protosulphate of manganese, 411.
Protoxide of nitrogen, diffusion of, 60.
Prussian blue, neutral, diffusion of, 584.
quadROXALATE of potash, 372, 440.
REFLECTION of the sun's rays, 8.
Refuse-lime of gas-works, on the useful
applications of the (1845), 643.
Regnault, M., 112, 162.
Richter, M. : absolute alcohol, 309.
Riffault, M., 390, 391.
Roberts, Mr. W. C., 299.
Robinson, Prof. : velocity of fluids, 212.
Rose, H., 71, 351, 393.
SAINT-VENANT, M. de : motion of air, 98.
Saline solutions, exposed to air, 21.
Salts—on the exception to the law that salts
are more soluble in hot than in cold water
(1827), 303.
Salts, oxalates, nitrates, phosphates, sul-
phates, and chlorides, on the constitution
of (1837), 367.
Salts of different bases, separation of, by
diffusion, 461.
Salts of potash to salts of soda, relation of,
490.
Salts of potash and ammonia, diffusion of,
471.
Salts of potash and soda, comparison of, 531.
Salts, double, diffusion of, 467.
Salts and other substances, diffusion of, 452.
Salts of soda, diffusion of, 488.
Salts, solubility of, 309.
Saussure, 6, 45.
Scheurer-Kestner, M. : iron solutions, 582.
Secchi, Father : star gases, 283.
Septa, at a red heat, action of metallic, 253.
Septum of caoutchouc, action of a, 235.
Sesquichloride of iron, diffusion of, 514.
Silicic acid, soluble, 577.
Silicic acid, and other analogous colloidal sub-
stances, on the properties of (1864), 618.
Silk cloth varnished with rubber, 250.
Silver, absorption by, 275.
Soda-alum, on the water of crystallization of
(1836), 365.
Solution of sulphate of soda, 26.
Solutions, the crystallization of saline (1831),
24.
Solutions, effects of animal charcoal on, 630.
Specific gravities of gases, table of, 111.
Spongy platinum, application of, to eudio-
metry, 41.
Sprengel, Dr. Hermann, 244, 245.
Steam and sulphuric acid, 2.
Subarseniate and subphosphate of soda, 322.
Subarseniates and subphosphates of barytes,
331.
Subarseniates and subphosphates of lead,
333.
Subarseniates and subphosphates of lime, 332.
Subnitrate of copper, 379.
Subphosphates and subarseniates of potash,
330.
Sucrate of copper, diffusion of, 585.
Sucrate of lime, diffusion of, 586.
Sucrate of peroxide of iron, diffusion of,
585.
INDEX.
659
Sucrate of peroxide of uranium, diffusion
of, 586.
Sulphagel, 622.
Sulphates, 392.
Sulphates, as illustrated by late thermo-
metrical researches, on the constitution
of (1842), 400.
Sulphate of alumina, diffusion of, 517.
Sulphate of ammonia, cold produced by, 416.
Sulphate of soda, diffusion of, 536.
Sulphate of soda, congelation of, 27.
Sulphate of water with saline water, 355.
Sulphate of water with sulphate of potash,
356.
Sulphate of zinc, heat of solution, 409.
Sulphate of zinc, diffusion of, 516.
Sulphate of zinc and ammonia, 420.
Sulphate of zinc and potash, 419.
Sulphate of zinc with saline water: sulphate
of zinc, 358.
Sulphate of zinc with sulphate of potash :
sulphate of zinc and potash, 358.
Sulphate of zinc with sulphate of soda: sul-
phate of zinc and soda, 359.
Sulphate of manganese with saline water :
sulphate of manganese, 362.
Sulphate of magnesia and heat, 408.
Sulphate of magnesia and potash, 418.
Sulphate of magnesia with saline water :
sulphate of magnesia, 363.
Sulphate of magnesia, diffusion of, 491,
515.
Sulphate of potash, sulphate of soda, 357.
Sulphate of potash and heat, 412.
Sulphate of potash, diffusion of, 535.
Sulphate of soda and heat, 415.
Sulphates and chromates of the potash
family, 412.
Sulphate of copper and heat, 410.
Sulphate of copper and ammonia, 420,
Sulphate of copper with saline water: sul-
phate of copper, 360.
Sulphate of copper with sulphate of soda :
sulphate of copper and soda, 361.
Sulphate of copper and potash, 420.
Sulphate of copper with sulphate of potash :
sulphate of copper with potash, 360.
Sulphates, double, 417.
Sulphate of iron with saline water: sulphate
of iron, 362.
Sulphate of iron with sulphate of potash :
sulphate of iron and potash, 363.
Sulphate of manganese and ammonia, 419.
Sulphite of potash, diffusion of, 537.
Sulphite of soda, diffusion of, 538.
Sulphovinate of potash, diffusion of, 539.
Sulphovinate of soda, diffusion of, 539.
Sulphuric acid, diffusion of, 503.
Sulphuric acid, transpiration of, 604.
Sulphuric acid, transpiration times, 191.
Sulphuretted hydrogen gas, diffusion of, 61.
Sulphurous acid, diffusion of, 504.
Sulphurous acid, transpiration times, 190.
Sulphurous acid gas, diffusion of, 60.
Superphosphates, 336.
TARTRATE of potash, diffusion of, 542.
Tartrate of soda, diffusion of, 543.
Terchromate of potash, 413.
Thomson, Dr., 22, 81, 303, 320, 323, 330,
360.
Thouvenel, M., 11, 14, 45.
Titanic acid, 587.
Transpiration of gases, 108.
Transpiration of different gases by a capil-
lary tube of copper, 129.
Transpiration of different gases by a glass
capillary tube E, 135.
Transpiration of various gases and vapours,
179.
Transpiration of protocarburetted hydrogen
(into air) by capillary M, 180.
Transpiration of air of different densities or
elasticities, 201.
Transpiration of equal volumes of air, 202.
Transpiration of air and other gases of dif-
ferent temperatures, 203.
Transpiration of air of different densities or
elasticities, by glass capillary tube E,
135.
Transpiration of air of different densities—
table, 109.
Transpiration of air of different tempera-
tures, 110.
Transpiration of different gases by capillary
tubes A, B, C, preliminary experiments
on, lll.
Transpiration times of carbonic acid, 176.
Transpiration times of hydrogen, 177.
Transpiration by capillary tube H, 121.
Transpiration of olefiant gas, 140.
Transpiration times of olefiant gas, 182.
Transpiration time of olefiant gas (into air),
182.
660
INDEX.
Transpiration time of olefiant gas (into a
vacuum), 184.
Transpiration of nitric oxide, 142.
Transpiration of sulphuretted hydrogen,
143.
Transpiration, capillary tubes for, 164.
Troost, M., 253, 278, 289.
Tube, atmolyser, the, 228.
Turner, Dr., 41, 42, 43, 85.
VALERIANIC acid, transpiration of, 606.
Vapour of water, 257.
Vogel, M. : binoxalates, 374.
Voltaic circle, on the theory of the, 398.
WANKLYN, Mr., hydride of iron, 288.
Wantzel, M. : motion of air, 98.
Water : effect of vapour on motion of gases
199.
Water as a constituent of salts, 352.
Wedgewood's porcelain basins, 18.
Wedgewood's stoneware tubes, 46.
... Wehrle, M. : meteoric iron, 282.
Williamson, Dr. : atomic motion, 302.
Wollaston, Dr. : limit of atmosphere, 6.
Wrede, Baron : weight of gases, 112.
Wurtz, M., on the constitution of hypophos-
phites, 414, *
Wurtz, M., hydride of copper, 288.
ZINC, phosphates, tribasic (phosphate of
zinc), 388.
Zinc, sulphate, with saline water, sulphate
of zinc, 358.
'UN 4 - 1915
PRINTED BY T. AND A. CONSTABLE, PRINTERS TO HER MAJESTY,
AT THE EDINBURGH UNIVERSITY PRESS,
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