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THE TEMPLE PRIMERS
MODERN CHEMISTRY
Systematic
By
WILLIAM RAMSAY, D.Sc
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Y>.: 4
MODERN CHEMISTRY
SFXOND PART
SYSTEMATIC CHEMISTRY
CHAPTER I
Methods of Preparing Elements— Their Physical
Properties,
Mixtures and Compounds.— \i\ the olden days, no
distinction was drawn between a compound and a mixture.
Indeed, all " impure " p-bstances artific'dly prepared were
termed "mixts." It was only after the true idea of elc-
mt had been arrived tt, and indeed not until Dalton had
formulated the laws which go by his name, that the distinc-
tion was drawn. The ultimate criterion for combination is
definiteness of proporticn, and this is generally connected
with uniformity in properties, or ' jmogeneity. A sub-
stance is said to be homogeneous when no one part of it
differs from any other part in composition. But this may
be predicated cf glass, or of air, which are mixtures, and not
compounds. A mixture may be homogeneous ; a com-
pound must.
Again, it is usually accepted that the separation of the
constituents of a mixture mr.y be effected by lechanical, or
at least by physical means ; whereas the separation of the
elements from a compound require chemical treatment.
Here it is difficult to draw a sharp distinction. The
VOL. II. .
48883
a MODERN CHEMISTRY
separation of carbon dioxide from soda-water by the appli-
cation of heat is similar in character to the separation of
suoar from water by evaporation of the water ; yet we
believe that a solution of carbon dioxide in water consti-
tutes a compound, while that of sugar in water is a mere
mixture of the two. It is necessary to be guided by analogy
in the former case ; and it is probable that the conijjound
named carbonic acid is really contained in a solution of
carbon dioxide in water, on account of the formula; and
behaviour of the c... _ ^nates.
The Atmosphere* — In the case of mixtures of gases,
the problem becomes an easier one. For in this case, each
gas retains its individual properties. The atmosphere, for
example, is believed to be a mixture of the gases
Nitrogen,
Oxygen,
Argon, &c..
78.16 per cent.
20.90
0.94
»»
If
1 00.00
if small amounts of water-vapour, of carbon dioxide, and
of ammonia, all of which vary considerably in amou '♦, be
subtracted.
This can be shown by several lines of argument.
First, The density of air agrees with the mean of the
densities of its constituents, taken in the proportion in which
they occur. Thus, the density of the mixture of atmos-
pheric nitrogen and argon differs by only i part in 40,000 from
that calculated from their relative weights, and the proportion
in which they occur. This is the case with compound gases
only when the constituents are present in equal proportions
by volume, as in hydrogei. chloride, HCl. The above
mixture is far from fulfilling that requirement.
Second, The constituents of air can be separated by
diffusion. Thomas Graham discovered that the rate of
escape of gases through an opening, or of passage through
THE ATMOSPHERE 3
a pcous {>artition is inveriely in the order of t*-- square
roots of their relative densities. Now, air hns been enricht'.i
in oxygen and in argon by diifi iion ; the lighter nitrogen
passes more rapidly in the proportion of —7— : — ;- : -
\/i4 V16 ViO
the last two fractions referring to the rates of oxygen and
argon respectively ; the oxygen and argon, being more slowly
diffusible, are left to the last.
Third, The constituents of air may be separated by
solution in water. While oxygen is soluble at aimo8j)heric
temperature in the proportion of about ' volumes in 1 00 of
water, nitrogen is much less soluble — anout 1.5 volumes;
and argon about 4. i volumes. Hence, on shaking air with
water, the relative volume^ dissolved are :
Oxygen, 3 x 20.90 ; Nitrogen, 1.5 x 78.16 ; and
Argon, 4. 1 X 0.94,
or in the proportion of 63 : 117 : 3.8. It is evident
that the relative proportion of nitrogen has considerably
decreased.
Fourth, The elements contained in air are not present in
any atomic ratio. To ascertain the relative number of
atoms of these elements it is necessary to divide the per-
centage amount of each by its atomic weight ; thus we have
Nitrogen, Z_! — = 5.58; Oxygen, ~'^ = 1.3 1 ;
14 i^
Argon, — "^ = 0.024 »
40
and these numbers bear to each other no simple ratio.
Lastly, it is possible by distilling liquid air to separate
the more volatile nitrogen from the less volatile oxygen
and argon.
For these reasons, and other similar ones, it is concluded
that air is a mixture.
4 MODERN CHEMISTRY
The Analysis of the Atmosphere is, however,
always performed by chemical means, for the difference in
physical properties of its constituents is not sufficiently
marked to allow of their being utilised for purposes of
separation. Many common elements unite easily with
oxygen to form non-volatile compounds, when they are
heated in air. One of the most convenient for this
purpose is metallic copper. By passing a known volume
of air over copper turnings, contained in a counter-
poised tube of hard glass, and heated to redness, the
oxygen of the air is removed, for it combines with the
copper to form non-volatile black oxide of copper. The in-
crease in weight of this tube gives the weight of the oxygen in
the measured volume of air. But it is customary to analyse
air volumetrically by absorbing the oxygen from a known
volume by means cf burning phosphorus, or of a solution of
potassium pyrogallate : the remainder consists of a mixture of
nitrogen, argon and its congeners. The separation of these
gases from each other is described in the next paragraph.
Reference has already been made in Part I. to the different
processes which may be used for the isolation of elements
from their compounds. But there exists a group of elements,
that of which the first member is helium, which form no com-
pounds, and which therefore are found only in a free state.
It is, therefore, convenient to begin with these.
The HELIUM Group. — These elements are all gases at
the ordinary temperature of the atmosphere, and they are
consequently all to be found in atmospheric air. They are
colourless, even in the liquid condition, and are devoid of
smell and taste. They are very sparingly soluble in water ;
for example, loo volumt. of water dissolve only 4.1 volumes
of argon at 15°. Their preparation consists, first, in the
separation of the other constituents of air from them, and,
second, in their separation from each other.
Air, which is a mixture, and not a compound, of nitro-
gen, oxygen, carbon dioxide, ammonia, water-vapour, and
the gases of the helium group, is a supporter of combustion,
THE HELIUM GROUP 5
owing to the combination of the oxygen which it contains
with most other elements. Now, when air passed through
a tube full of a mixture of caustic soda and lime, to remove
carbon dioxide, and then through a U-tube containing sul-
phuric acid, to deprive it of water-vapour and ammonia, is led
over red-hot copper, or over some other red-hot metal which
unites with oxygen, the oxygen is retained, and nitrogen with
members of the helium group alone passes on. The nitrogen
can be removed in one of two ways. The first plan is due
to Cavendish, who attempted to prove that atmospheric nitro-
gen was a homogeneous substance. He mixed atmospheric
nitrogen with oxygen, and passed electric sparks through
the mixture, having a little caustic soda present in the
tube. Under the influence of the sparks, the nitrogen and
oxygen combine, giving nitride peroxide, NO., ; this com-
pound is absorbed by the soda, with formation of sodium
nitrate and nitrite, NaNO, and NaNO„. Cavendish
obtained a residue of not "more than one-hundred-and-
twentieth of the nitrogen; and he concluded that if
atmospheric nitrogen was not homogeneous, it contained only
a trace of another gas. The second plan is to pass the
atmospheric nitrogen over red-hot magnesium, or, better, over
a mixture of magnesium powder and lime, which gives
calcium ; the magnesium or the calcium unites with the
nitrogen, and the inert gases pass on.
To separate these gases from each other, they are
compressed into a bulb, cooled to -185° by being immersed
in liquid air. The argon, krjrpton, and xenon condense to
a liquid, in which the neon and helium are dissolved. On
removing the bulb from the liquid air, its temperature rises,
and the helium and neon escape first, mixed with a large
amount of argon. Ar^on distils next, and krypton and xenon
remain till the last. By frequently repeating this process
of « fractional distillation," the argon, krypton, and xenon
can be separated from each other, and from the helium and
neon which still rtmain mixed with each other, for both
are gases at the temperature of boiling air.
6 MODERN CHEMISTRY
To separate helium from neon, recourse must be had to
hquid hydrogen. To liquefy hydrogen, the process is in
principle the same as that for liquefying air, described on
p. 26. The hydrogen, compressed by a pressure of 200
atmospheres, is cooled to -205° by passing through a coil of
copper pipe, immersed in liquid air boiling under low
pressure. On expandinp, its temperature is still further
lowered, and the still colder gas, in passing upwards, cools
the tubes through which the compressed gas is passing.
The hydrogen finally issues in the liquid staiv, as a colour-
less, mobile liquid, of the approximate temperature -240°.
By Its aid, if a mixture of neon and helium is cooled to
-240% the former freezes, while the latter remains
gaseous. The gaseous helium can be removed with the
pump ; and the neon, after it has been warmed, may also be
pumped off in a pure state.
Helium can also be prepared by heating certain specimens
of pitchblende or uraninite, a mineral consisting chiefly of
oxide of uranium. The gas, which appears to exist in some
sort of combination with the uranium oxide, escapes ; it
contains a trace of argon. All these gases give very striking
spectra, and that of helium was observed during the solar
eclipse of 1868 in the chromosphere, or coloured atmosphere,
of the sun. Although at that time it had not been dis-
covered on the earth, the name «♦ helium '* was given to
the bright yellow line, which is the most characteristic of
Its spectrum.
As regards the relative amount of these gases contained
in air, 100 volumes of air contain 0.937 volume of the
mixture. By far the largest portion of this mixture is
argon ; probably the volume of all the others taken together
does not exceed one-four-hundredth part of that of the
argon. Indeed, it may be said with truth that there is less
xenor m air than there is gold in sea-water.
Methods of Separating Elements from their
Compounds — The methods of preparation of the remain-
ing elements depend on considerations of the cost of the
SEPARATION PROCESSES 7
compound from which the element is to be prepared, and on
the ease of preparation. In the case of those elements which
are required on a commercial scale, like iron, for example,
the process of manufacture is regulated chiefly by the cost
of the ore, and of the operations necessary to produce the
metal in a state of purity sufficient for commercial purposes.
But if perfectly pure iron is required for scientific purposes —
for example, in order to determine its electrical properties —
then the question of cost does not come into consideration,
and processes are adopted which are necessarily very costly.
In the description which follows, however, we shall give
only the ordinary methods of preparation.
Again, the process chosen depends greatly on the physical
and chemical properties of the element which it is desired to
isolate. Some elements are volatile, and are more or less
easily separated by distillation from the material from which
they are produced ; some elements are attacked by water,
while others resist attack ; some fuse at comparatively low
temperatures, and can thus be separated, while others are
producible in a compact state only at the enormously high
temperature of the electric arc. It is necessary, therefore, to
know the properties of the element required before deciding
on a process for its isolation. The preparation of the
remaining elements will therefore be considered from this
point of view.
(i) Separation of the element by means of an
electric current.
(a) Prom a fused salt. — One condition is that the
salt shall fuse at a convenient temperature — that is, at or
below a red heat. Another is that, in the case of metals
which are commercially used, the salts must be cheaply
obtainable, and the metals easily separated from the salts.
It is interesting to note that this process led, in the hands
of Sir Humphry Davy, to the discovery of the metals
of the alkalies, potassium and sodium ; he first prepared
them by passing a current from a battery of high voltage
8
MODERN CHEMISTRY
through the hydroxide, melted on a piece of platinum foil.
The metal was visible only for an instant; for it floated
up from the electrode of platinum wire, and burst into
flame as soon as it came into the air.
As a rule, however, the chlorides are the most con-
venient salts for electrolysis. From the known fact that
the melting-point of a compound is lowered by the presence
of an «* impurity," it is often found advantageous to electro-
lyse a mixture of chlorides rather than a pure chloride ;
in this case one of the elements is liberated in preference
to the other. As the anode has to withstand the action
of chlorine, it is always made of carbon, which does not
unite with chlorine directly ; the kathode may be of iron,
a metal which has no tendency to form alloys with those
which are prepared in this way, at least at the temperatures
required. The kathode may be the iron pot in which the
chloride is kept fused.
The elements which are prepared in this way are:
lithium, sodium, potassium, rubidium, cjesium, beryllium,
magnesium, calcium, strontium, and barium. The first five
are easily fusible white soft metals, which take fire when
heated in air, and must therefore be kept in an atmosphere
free from oxygen ; they also attack water, liberating hydrogen,
with formation of the hydroxide MOH. Their density
18 so low that they float on their fused chlorides; they
must, therefore, be liberated in the interior of a bell-shaped
iron electrode or of a fireclay receptacle, down which an
iron kathode passes. Beryllium and magnesium are better
prepared from a mixture of their chlorides with potassium
chloride ; the latter melts and collects at the bottom of the
pot, which, in this case, may be the kathode. They are
hard white metals, magnesium melting at about 750°, and
beryllium about 1200°. They, too, take fire when heated
m air, and burn with a brilliant flame ; indeed, the chief
use of magnesium is for signalling purposes. The metal is
drawn, while hot, into wire, which is then rolled into
ribbon ; this ribbon burns with an exceedingly bright flame.
METALS OF THE ALKALIES 9
producing the oxide MgO. Calcium, strontium, and
barium are also white metals ; they have been produced by
electrolysis of their cyanides, M(CN)2, compounds which
fuse at a lower temjierature than the chlorides. They are
vc-y readily attacked by water, yielding the hydroxides
M(OH)2. The only two of these metals which find
commercial use are sodium and magnesium.
Alummium, which is also manufactured on a large scale,
u produced from its ore, bauxite, from which pure alumina,
the oxide, is first prepared. The alumina is dissolved in
fused cryolite, a fluoride of aluminium and sodium of the
formula NagAlFg, deposits of which occur in Greenland.
The aluminium sinks to the bottom of the crucible, and
when a sufficient quantity accumulates it is tapped out.
The "flux," 33 the cryolite is termed, is again melted,
and a further quantity of alumina »' dissolved in it. The
metal is fairly hard, white, susceptible of a high polish,
ductile and malleable. It is also very light (about two and
a half times as heavy as water), and not easily oxidised in air
at the ordinary temperature, nor is it attacked by water.
(^) Prom a dissolved salt.— Gallium, a tin-white,
hard metal, very rare, contained in some zinc ores, is
deposited from a solution of its hydroxide in catistic
potash. Copper prepared, as will be seen below, in a
crude state by displacement, is purified by electrolysis.
It is of the utmost importance to employ pure copper for
the conduction of electric currents ; for although copper
IS one of the best conductors, its resistance is enormously
increased by the presence of a very small trace of impurity.
To purify it, large rectangular blocks of crude copper are
suspended close to thin sheets of pure copper in an &r.id
bath of copper sulphate, CuSO^.Aq. The heavy block
is made the anode and the thin sheet the cathode; the
su/phation, SO4, in discharging at the anode, dissolves
copper from the thick block as sulphate; while the cu/>rion,
Cu, in yielding up its charge at the kathode, deposits on
lO
MODERN CHEMISTRY
the latter and increases its thickness. Th* ;«
arsenic, antimony and iron, re.airin 1':uo7:TI
sludge IS deposited containing silver and PoW isides
traces of many other elements. Copper is a vfry malSe
ductile red metal, melting at 1330% ^ malleable,
Objects of iron are often "niVt*.! »,U— j >?
with a..hi„ fi,™ o(.icJr.\£'t^':ti :ii:rz^
coated with copper before nickellJna q-i ^ ! are hrst
such X; r""°°. "'J"'" '•""«" *•'!='> "k^ place durk.
™ch electrolysis, the deposition of .iker may be chol™
7.ee p^Ts^T'' ,™P.'oyed is, as stated, the do^bi: c7a"d:
(•ee^p. .87) , m formula is KA8(CN)„ and the ion.
are K and Ag(CN),. There are, however, a. the same
:ii^:Mfd;-ei^-snLr:-^^^^^^^^^
amount ,s reduced, a fresh quantity is folS by .h.'
decomposition of the complex ion, A-fCNl Th.
fprm,„o„ and deposition of 'the silver io°n'g^i^„„ Z„
tinuously nntd all the silver required has b4rd^liSd
n'tf andX-d'' "'" ""^^ ''' electr ^.^,^0'^^,
cau^fx W;ir;:rt' z^^ ^^Ltf
enormous quantities of hydrogen. The X d'sSlrf to
i
i
i
i
ELECTRO-DEPOSITION , ,
b^'Tln^'^'i'V ''"'' ^i"'^'^ '"^^ ^^« compartments
r JrKo ^ T j!"P'?^*fi'" 5 ^^^ anode, which con««» of
b. formed of copper plates, m the other. The ions, of
at°ed"r; .h'"' ^^^"^^ .'°1 ^'•^^- '^'^^ <=hlorine is liber-
ated at the anode, and the sodium at the kathode. But as
soon as the sodion is discharged, it reacts with the water,
lormmg caustic soda, thus : 2Na + 2HOH = aNaOH + H c^
m^'F^'l 1^'°"!^"'°". °^ ^y^™«^"- »^°"''"«^ and iodine!^'
"r io^de^r^- '° '^' "^""^ ^'^ '' ^^'°""^' '^' bromide V %
chll^d. °^/°^r' °'" P°'''^''"'" b"'"S substituted for the^ \
Chloride. As fluorine at once acts on water, Hberating ^' >-'
oxygen ,n the form of ozone. O3, it cannot b; produced \
ITv"" TkT '°'""r °^ ' ^"°"^^ 5 b"' i' ^^' been found > ^
that liquid hydrogen fluoride ha« ionising power, so that on v ^'
passing a current between poles of plati'num-iVidium (an \
alloy of m^etals which is less attacked by fluorine than any
other conductor) through a solution of hydrogen-po-as-
smm fluoride, HKF, in pure liquid hydrogen' fluSide
n,P2, at -30, fluorine is evolved from the anode-
In J I . y^iJow gas with a strong characteristic smell,
somewhat resemb mg that of the other halogens, chlorine
CZe^ '°t"' ^bile hydrogen i, evolved at the
kathode, having been produced by the action of the potas-
sium on the hydro,. . fluoride. Fluorine boils at -^05%
chlorine at -35 bromine at 59% and iodine, which i/ a
solid at atmospheric temperature, melts at 114° and boils
nr i "^ * AiT "^°"" °^ 'bese elements also show a
as p;?rnH ,P^!°"°f " gr^nish-yellow; bromine, red both
as gas and liquid; lodme ,s a blue-black solid and a violet
gas. 1 hese three elements are somewhat soluble in water,
and more so in a solution of their soluble salts. It hal
recently been found that another ionising agent than water
cTJ ' H^^^f Lithium chloride is soluble' in pyrfd^ra
compound of the formula C,H,N, and may £%lectro.
deposited on a plaunum kathode from such a solution.
13
MODERN CHEMISTRY
The metal is not attacked by pyridine; the chlorine,
however, is rapidly absorbed.
(2) Separation of an element from a compound
by nse of temperature. j~u"u
This method is applied in practice only to tne pre- ra-
tion of oxygen, and of chlorine, bromine, and iodine ; but
many other elements may be thus made, where the com-
pound heated does not tend to re-form on coolinjj. These
cases will be considered first.
Ordinary coal-gas consists chiefly of methane, CH .
«hy ene, C,H,. r,rbon monoxide, CO, and hydrogen
the last amounting to nearly 50 per cent, of the'volume
ot the gas. This hydrogen owes its origin, at least in
part, to the decomposition of its compounds with carbon.
by their coming into contact with the red-hot walls of the
retort in which the coal is distilled. Carbon deposits in a
dense blacK mass on the iron, and is removed from time to
tirne with a chisel Hydrogen escapes and mixes with the
coal-gas. This form of carbon is used for the pencils for
arc-lights, and for the anodes of Bunsen's and other forms of
ceih and also for anodes in electro-chemical processes.
Ihe compounds of hydrogen with nitrogen (ammonia,
xNHJ, sulphur, selenium, and tellurium (sulphuretted
se eniuretted or telluretted hydrogen, H.,S, H.Se, H.Te)
all of which are gases at the ordinary temperature, are de-
composed if passed through a red-hot tube, giving hydrogen,
which escapes abng with nitrogen if ammonia be heattd
or a deposit of the sulphur, &c., in the cold part of the tub^
It one of the other gases mentioned be employed.
The oxides of the metals ruthenium, rhodium, palladium,
silver, osmium, indium, platinum, gold, and mercury are
decomposed at a red heat; and the chlorides, bromides.
:fst;a\1;lt^y" '- ''- '-<^-^-'^ -P^ ^'^ose
But none of these methods are practical plans of prepar-
ing the elements. On the other hand, as already staged.
DECOMPOSITION BY HEATING 13
this method is generally used for the production of oxygen.
This gas, although ,t had probably been obtained in an
impure state by the older experimenters, was first pro"
r;n?n r »PP;°>'""^te purity by Priestley and simul-
^neously by Scheele in 1774. Priestley produced it by
heattng niercunc ox.de HgO, which decomposes thus:
2rtgO = 2Hg + Og. And Lavoisier showed that it was
possib e to produce mercuric oxide by heating mercury to
Its boiling-point m a confined portion of air, and by sepa-
r. ung and we.ghmg the oxide, and subsequently heating it
till It decomposed again, he proved tha. the oxygen had
really been extracted from the air.
Certain oxides are not wholly decomposed into oxygen
and element when heated, but leave an oxide containing
less oxygf n than that originally heated. Among these il
3MnO, = Mn O, + O,. Lead dioxide undergoes a similaj
change: 2Pb6, = 2PbO + O,. The most important ap.
phcation of th.8 method, however, is the commercial plan
ot producing oxygen carried out in the « Brin Company's "
works. In their process, barium oxide, BaO, is heated
in iron tubes under pressure, air being pumped m. The
banum ox.de absorbs the oxygen of the airfthe nitrogen
being allowed to escape. After the operation has gone on
for about five minutes, a considerable amount of oxygen is
absorbed, barium dioxide, BaO^, being formed. The
stopcocks of the pipes leading to the pump are then
r^l \xr^ '^f «"' '' exhausted from the hot iron
ubes. When the pressure is reduced, the barium dioxide
loses oxygen, and again returns to the state of monoxide :
ZDau^ _ 2 i3aU + O^. The pumping is continued for about
live minutes, and the valves are again reversed. The pro-
cess ,3 thus a continuous one ; the oxygen is not pure, for
It contains about 7 per cent, of nitrogen; but for medical
use m cases of pneumonia, and for the oxv-hydrogen blow-
pipe. Its purity is sufficient.
This method of preparing oxygen is an instance of what
•4
MODERN CHEMISTRY
IS termed « maM-action." The temperature is kept con-
stant, but the pressure is raised when it is desired to cause
the oxide to absorb oxygen, and lowered when it is neces-
sary to remoTe the oxygen. When pressure is raised, the
number of molecules of oxygen in unit volume of the space
for the mass) is increased, and hence the number in contact
with the absorbing medium, the barium oxide. Combina-
tion, therefore, takes place between the two. On reducing
pressure, the number per unit volume is reduced, and the
compound decomposes. The phenomeno>j ib analogous
with the behaviour of a vapour when it is compressed ;
after a certain pressure has been reached— the vapour
pressure— the vapour condenses to a liquid, and if more
vapour be compressed into the same space, the pressure
does not rise further, but more vapour is condensed : this
18 analogous to the formation of more BaO,. On pumping
out vapour, the pressure does not fall, but the liquid
evaporates: this is the analogue of the decomposition of
the BaO^ into BaO. The law of mass-action is very
generally applicable. '
Certain oxides, for instance, pentoxide of iodine, LO„
and of nitrogen, NO^, decompose when heated. These
oxides form combinations with the oxides of many other ele-
ments, such as sodium or potassium oxide, e.^. Na^O.LO
or NalOg, K^O.N^O, or KNO„; a similar compound is
potassium chlorate, KCIO3 or K,O.CI.,0,, although the
simple oxide of chlorine is unknown. " Now, potassium
and sodium oxides are not decomposed by heat, and when
these salts are heated oxygen is evolved from the pentoxide
of chlorine or iodine. These elements, however, do not
escape, but replace the oxygen combined with the sodium
?-" ^P^fT""' J°""'"2 chloride of the metal, thus:
KoO-CIA = K.O f CI2 +5O, and K.,0 + C1,=.2KC1
+ U, or, summing up both changes in one equation,"2 KClO„
= 2KLI + 3O2. Nitrate of potassium, on the other hand,
loses only one atom of oxygen, leaving aitrite: 2KNO,
= 2KN02 + 0<,. 3
DECOMPOSITION BY HEATING 15
Oxygen ia a colourlem ga», without smtrll or taste; it
can be liquefied, at a high pressure and a low temperature,
to a pale blue lio^uid boiling at -182'. Most elements
unite directly with it, often with such a rise ' ' temperature
tnat incandescence is produced; in such a case the pheno-
menon is termed «« combustion.'* In many instances, for
example when iron rusts, the oxidation is not attended bv
any measurable rise of temperature, although in all case's
heat is evolved, but in some cases extremely slowly.
C^-lorine, bromine, and iodine are generally prepared by
heating together a chloride, bromide, or iodide with man-
ganese dioxide an'^ sulphuric acid diluted with water.
Here the first change is the formation of the halogen
hydride, HCl, HBr, 01 HI. The hydride, however; is
ionised in water, and the HCl.Aq., for example, at once
reacts with the MnOg, forming non-ionised water and
MnCL.Aq, thus: MnO, + 4HCI. Aq. = mV C 1,. Aq. +
2H2O. Tetrad manganese, however , appears not to be able
to co-exist with chlorine in solution ; hence the manganese
loses an electron and becomes Mn, the lost charge neutralis-
ing one of the charged chlorine ions, which escapes in an
electrically neutral state. Even then, however, the Mn^,
though capable of existence at low temperature, still loses
a charge, and a second chlorine atom is liberated in a non-
ionised state. Hence the whole change is : M n CI . Aq.
= MnCl^. Aq. + CI.,. Summing all these changes in one
equation, we have: MnO.. + zNaCl.Aq. + 2H,S0,.Aq
= MnSO,. Aq. + Na,SO,. Aq. + 2H2O + Cl^ ; or' if hydro-
chloric acid alone be warmed with manganese dioxide,
MnOg + 4HCI. Aq. = MnCl,. Aq. + iH.p + CI,.
(3) Separation of an element from a compo
displacement. — This is by far the most general i
'..xi
i6
MODERN CHEMISTRY
of preparing elementi. The elements commonly used at
displacing agents are : —
(a) Hydrogen at a red heat.— The oxide or chloride
H placed m a tube of hard glass, heated to 000° or 700*
in a tube-furnace, and a stream of dry hydrogen is passed
through the tube. Water or hydrogen chloride is formed,
and IS carried on by the current of hydrogen, and the
element ts left. Indium, thallium, g rmanium, tin, lead,
amimonv, and bismuth are left in fused globules, solidifying
to whitr ^trous metallic beads ; arsenic gasifies and con-
denses in me unheated part of the tube as a grey deposit
tellurium, which is also volatile, condenses as a lustrous
metallic solid ; while iron, cobalt, nickel, copper, and silver
do not fuse at that temperature. The first three remain as
grey powders, the copper as a red powder, and the silver
vr a white spongy condition. These metals can be fused
by heating them in a crucible to a sufficiently high tem-
p» rature ; it is well to use a « flux," or substance to make*
them flow, such as sodium carbonate or borax; the flux
fuses, and dissolves any film of oxide ofl^" the surface of the
meullic beads, ind they then join up to form a single mass
of molten metal.
{l>) Displacement by means of sodium at a red
hes,t.— -The chlorides of beryllium, magnesium, calcium,
strontium, barium, aluminium, scandium, yttrium, J. ntha-
num, ytterb'um, cerium, thorium, vanadium, niobium, and
tantalum are all reduced when added to sodium kept melted
m an iron crucible. For boron, silicon, and titanium the
double fluoride is more convenient, for the chlorides are
volatile liquids. The process for manufacturing magne-
sium, which is carried out on a large scale, may be more
minutely described as an example. The double chloride
of magnesium and potassium, MgClg.KCl, carefully dried,
is mixed with sodium in proportion to unite w :h the
chlorine of the MgClg, the sodium being in small lumps.
The iron crucible containing the mixture is heated; a
violent reaction takes place, and magnesium is liberated:
DISPLACEMENT i;
MgCL. KCl + 2Na ^ Mg + aNaCl + KCI. A. magneiium
I* volaiiie, and can be djstiJled, it U purified by this
oj)crat»on. The content* of the crucible are treated with
water; the potassium and sodium chloride* dissolve, and
the globules of magnesium are collected, dried, and placed
in a crucible, through the bottom of which a tube is fixed
reaching nearly to the lid, and projecting some distance
below the bottom. This crucible is placed in a furnace,
and on raising the temperature, the magnesium volatilises
up, passes down the tube, and the vapour condenses in the
cooler part of the tube which projects below the furnace.
This particular method of distillation is called Jestiilatlo per
destinsum. The other elements mentioned are too little
volatile to admit of purifica;ion by this means. In their
case, the cooled mass is treated with alcohol in order to
remove . .c excess of sodium, and then with water to
dissolve the resulting salt ; the element is left in the s'aie
of powder. *
\c) Displacement by means of magnesium at a red
neat. — This process is sometimes used to prepare the
clement from its oxide. A mixture is made of magnesiun.
lilings with the oxide of the element, and it is heated in an
iron crucible. The resulting mass is then treated wiih
hydrochloric acid to remove the oxide of magnesium, which
u thus converted into the soluble chloride. It is, of course,
essential that the liberated element shall not be attacked by
hydrochloric acid. The process works for the preparation
ot boron, silicon, and tiuniuin,
{d) Displacement by heating the oxide with car-
'*®^— This process is of the most general application. If
the element is yolatilf, it is distilled from an iron or fire-
clay retort; in this way sodium, poussium, rubidium,
arsenic, zinc, and cadmium are prepared. If non-voiatile
at a red heat, a mixture of the oxide with charcoal is
heated to bright redness in a clay crucible. On a manu-
facturing scale, coal or coke is substituted for the charcoal.
The process is applicable to the production of indium.
VOL. II. J
i8
MODERN CHEMISTRY
thallium, germanium, tin, lead, manganese, iron, cobalt,
nickel, and copper. To exemplify this method, four
mstances will be dcscribed-the preparation of phosphorus,
•odium, zinc, and iron.
Phosphorus.— The commonest natural compounds of
phosphorus are phosphorite or calcium phosphate,
yhy^^Jo* and gibbsite or aluminium phosphate, AlPO
It IS accordingly convenient and economical to prepare
phosphorus from one of them. The process depends on
the displacing action of carbon on the oxide at a high
temperature. There are two methods of effecting this.
1 he hrst is : the phosphorite is mixed with dilute sulphuric
acid ; the hydrogen of the sulphuric acid replaces the cal-
cium of the calcium phosphate : Ca3(P0J^. + 3H.,S0,.Aq
= sCaSO, + iHgPO^.Aq. Coke or chafcoal is" impreg-
nated with the phosphoric acid and heated to redness, when
the phosphoric acid loses water : H3PO^ = HPO + H O
The mixture of metaphosphoric acid, HPO„, wit'h carbon
is charged into retorts of Stourbridge clay, the mouths of
which are attached to a vertical copper tube, the lower
end of which dips under water. On raising the retorts to
a wnite heat, phosphorus distils over and condenses in the
water. 1 he final equation is : 4HP0„ + 1 2C = 2H , + P
+ 12CO. By the second method, thc'^calcium and alumi-
nium phosphates are mixed with silica and carbon, and
distilled from an electric furnace heated to whiteness by
an arc in its interior. ^
Sodium.— A mixture is made of « spongy iron " (see
p. 19) and pitch. This mixture is heated to redness in
order to decompose the pitch, which consists of compounds
of carbon and hydrogen. These compounds are decom-
posed, and a part of the carbon is left mixed with the
spongy iron, while the hydrogen escapes in combination
with the rest of the carbon. To this mixture, placed in
an iron crucible, caustic soda is added ; the lid of the
crucible, which is furnished with a curved tube sloping
downwards to a condenser, is fixed in place, and the
ZINC AND IRON
«9
crucible IS heated in a furnace to o-lght redness. The
carbon removes oxygen both from the hydrogen and the
sodium, and sodium and hydrogen pass over into the
condenser along with carbon monoxide, the sodium alone
condensing, for th^ others are gaseous and escape. The
equation is : aNaOH + 2C = 2CO + H., + iNa. The con-
denser consists of a flat hollow copper"yessel ; the sodium
18 raked out as it accumulates.
Zinc -The chief ore of zinc is the sulphide. To
convert it into the oxide, it is roasted on a flat hearth in a
current of air : 2ZnS + 3O, = zZnO + 2SO,. The oxide
rLn? 7;! r'" Z'^ (^'"^'^) ""'1 P'^^^'^ '^^ cylindrical
retorts of fireclay. These retorts ha\o pipes of rolled
sheet-iron luted to the open ends with fireclay ; they are
packed into a furnace in tiers, and the temperature is raised
to bright redness. The coal distils first, giving off coal-
gas, which expels air from the retorts. When the tem-
perature exceeds iooo% the zinc distils and condenses in
the iron pipes. It happens that almost all zinc ores
contam cadmium sulphide, which, like zinc sulphide, is
converted into oxide by roasting; and on distillation, the
cadmium, which ,s the more volatile metal, distils over
hrst and condenses in the outer portion of the tubes.
Ihese are untwisted and the metal removed with a chisel.
fh.^'^'A^uc °'^'.°^ ''■°" "^ '^^ carbonate and
^I ? 1 'u ^^ '''"^^' •' practically always mixed with
clay (clayband) or with coal (blackband), and generally
suTnhr 'r'^ln '""^ Ph^^Phorus in the form of^alcium
Milphate, CaSO,, and calcium phosphate, Ca,(POJ,.
Ihe sulphur IS sometimes present in the form of i'4
pyrites, FeS,. The ore is roasted to expel carbon
dioxide thus : 4FeC03 + O, = 2Fe.03 + 4CO.,. If it
were then m its impure state smelted with "coal, the
iron would not flow, but would remain mixed with the
clay. However, this process, if the ore is pure and charcoal
IS used as fuel, yields a mass of iron sponge, which can be
heated and welded by hammering into a coherent mass.
20
MODERN CHEMISTRY
The process is still used by Africans, and was at one time
universal. On the large scale, however, it is necessary to
add Jime m order to form a flux with the clay. Clay con-
sists of a compound of silica, SiO.., and alumina, ALO„
and with hme it melts to a glassy "slag. Alternate layers
of coal, hme, and the roasted ore are fed in at the top of a
blast-furnace, a tall conical erection of firebrick, strength-
ened by being bound with iron hoops ; at the bottom there
IS a « crucible," or receptacle for the molten iron, which
can be discharged when required by forcing a hole in its
side with an iron bar. There are also holes which admit
water-jacktted tubes or "tuyeres," wiich convey a blast
of air heated to about 600^ to increase the temperature of
combustion of the coal. Here the reduction takes place
in the upper part of the furnace, owing to the carbon
monoxide formed by the combustion of the coal in the
lower part of the heated mass ; it ac:s on the oxide of iron
thus: Fe203+3CO = 2Fe + 3CO.. As the iron passes
down the furnace it melts, and is met by the fused slag ;
it then coheres and runs into the crucible, whence it is
drawn off from time to time.
Carbon unites with molten iron, forming a carbide ; hence
the product of the blast-furnace is not pure iron, but a
mixture of iron with its carbide, and also with its sulphide
and phosphide, if the ore has contained sulphates or phos-
phates. When such impure iron is brought in contact
with oxygen in a molten or semi-molten condition, the
carbon, sulphur, and phosp' orus are oxidised mostly before
the iron. If lime be present, sulphate and phosphate of
calcium are formed. The modern process of removing
these impurities is to pour the molten metal into a pear-
shaped iron vessel lined with bricks made of magnesia;
while it is molten, air is blown through the metal, and the
carbon burns to carbon dioxide ; the sulphur and phosphorus
are likewise oxidised and combine with lime, a layer of
which floats on the surface of the molten metal. When
these impurities have thus been removed in the " Bessemer
DISPLACEMENT BY OXYGEN
21
converter," the metal is poured into a mould. Steel is
a mixture of iron with a trace of its carbide, and it is
produced by mixing with the blown iron, before it is
poured, a quantity of iron containing carbon and manganese
(a metal which confers valuable properties on iron). The
quantity of carbon in steel may vary between 0.6 and i.c
per cent. ; with the content of carbon varies also the quality
of the steel ; that with a small proportion is soft, with
a high proportion hard.
(e) Displacement by means of Oxygen. — Oxygen
IS used in Deaco s process to liberate chlorine from
hydrogen chloride. The latter gas, mixed with air, is
passed through a chamber kept between the limits of
tempe« re 375°-400°, containing bricks soaked with
cupric chloride, CuCi,. At this temperature the cupric
chloride decomposes into cuprous chloride, CuCl, and
free chlorine, but the cuprous chloride is reconverted into
cupric chloride at the expense of the chlorine produced
by the mteraction of the hvdrogcn chloiiJc and the air
thus: 4HCl + 0,= 2H.,0 + 2a. The cupric chloride is
agam decomposed. This kind of action, where a limited
quantity of a substance, itself not permanently changed,
causes an apparently unlimited change in other reacting
bodies, IS termed « surface action," for its rate is dependent
on the extent of the surface of the agent ; and t e name
"catalysis" is sometimes given to such an action. The
action would take place independently of the catalytic
agent, but at a very slow rate ; the presence of the catalyser
has the effect of greatly increasing the rate at which the
change .akes place. The chlorine thus prepared is not
pure, but mixed with the nitrogen and argon of the air,
but It serves for some purposes. The rate of such action
of oxygen in displacing bromine or iodine from their
compounds witii hydrogen is much greater, and at a high
temperature the elements could be formed thus, but they
are not usually produced in this way.
The preparation of nitrogen may be also regarded as a
22
MODERN CHEMISTRY
displacement by means of oxygen. Ammonia burns m
oxygen, thus: 3NH3 + 30,= sH.O + N,, but at the
sar-'.e time some of the nitrogen unites with the oxygen
and forms NO^, nitric peroxide : this gas interacts with the
ammonia, forming ammonium nitrate and nitrite, NH^NO-
and NH^NO^,. If, however, the oxygen be not free, but
in combination with an easily reduced metal, such as copper,
it wi" combine with the hydrogen of the ammonia at a red
heat, setting free the nitrogen. Another method involves
the mutual displacement of nitrogen from its oxide by
means of hydrogen, and from its hydride, ammonia, by
oxygen: 2NH3 + N203 = 3H,0 + 2N,. This method is,
however, usually represented by the equation NH NO.,=
iH^.O + Ng; for ammonium mtrite, NH, NO.,, may "be
regarded as a compound of N2O3 with 2NH3 and HgO.
To obtain nitrogen by this method, since ammonium nitrite
is not easily obtained, a solution of ammonium chloride may
be warmed with one of sodium nitrite. The equation is
then : NaNO,. Aq + NH.Cl. Aq = 2H2O + Ng + NaCl. Aq.
Another convenient method is to warm together solu-
tions of sodium hypobromite and ammonium chloride ; the
former loses oxygen readily, which combines with the
hydrogen of the ammonia according to the equation:
SNaOBr.Aq. + 2NH,Cl.Aq. = 3NaBr.Aq. + 3H.,0 +
2HC].Aq. +N2.
Although sulphur, selenium, and tellurium burn in oxy-
gen, still thc-y may be displaced from their hydrides, HgS,
HgSe, and H^Te, by means of oxygen at a red heat,
provided the oxygen is present only in sufficient quantity to
combine with the hydrogen, thus : 2H2S + 02=2H20 +
So. Aqueous solutions of these compounds, too, are
decomposed on standing in contact with air, owing to
similar displacement. Oxygen may displace mercury from
its sulphide, cinnabar, HgS, which is the common ore of
mercury; here the sulphide is roasted in air, when the
sulphur combines with the oxygen to form sulphur dioxide,
a gas at ordiroiy temperature; and mercury is liberated,
DISPLACEMENT OF ELEMENTS 23
also in the gaseous form, but condensing at temperatures
below 358°.
(/) Displacement by use of Fluorine, Chlorine, and
Bromine. — Fluorine, chlorine, and bromine may also be
employed as displacing agents for nitrogen and oxygen.
A current of fluorine led through water displaces the
oxygen, forming hydrogen fluoride ; but the oxygen is in
an allotropic state (see Part i.), called «' ozone." Again,
if a stream of chlorine is passed through, or if bromine-
water be added to, a sjlution of ammonia, the hydrogen
and chlorine combine, while the nitrogen is set free:
aNHg.Aq + 3CK, = 6HC1 h N,; but as ammonia com-
bmes -ith hydrogen chloride, the" reaction 6NH3 + 6HCI
= 6NH4C1 occurs simultaneously; the complete equation
is the sum of these two : 8NH3. Aq + 3C1^ = 6NH^Cl.Aq
Chlorine, added to a solution of bromide or iodide of a
metal, displaces the bromine or iodine; here the non-
ionised chlorine becomes ionised at the expense of the
charge on the ionised bromine or iodine, while the latter
lose their charges, thus : 2KBr.Aq + Cl.^.Aq. = iKCl.Aq
+ Bro.Aq. Similarly, bromine displaces iodine from a
soluble iodide. But iodine displaces chlorine from the
nearly insoluble silver chloride. Here, the iodine is still
less soluble than the chloride; and as chloride dissolves,
the less soluble and therefore non-ionised iodide is formed.
is) Many metals are able to displace others. Thus,
iron placed in a solution of a copper salt displaces the
copper; copper displaces ^:lver; silver, gold. In all
these cases the action is doubtless an ilectrical one, and
dependent on the replacement of a metal of lower by one of
higher dectric potential ; that of higher potential becomes
ionised, while that of lower assumes the metallic state,
+ +- ++ - + -
thus: CuCl2.Aq + Fe = FeCl2.Aq + Cu; 2AgN0,.Aq +
Cu = Cu(N03)2.Aq +
*» MODERN CHEMISTRY
(^) There are some plans of obtaining dements which,
though they can be referred to one or other of the three
general methods exemplified already, are, on account of
their complexity, better treated separately. Among these
are the methods of separating hydrogen. The metals of
the alkalies and alkaline earths attack water, forming hydr-
oxides and liberating hydiogen : 2Na + 2H..O = 2NaOH +
H ; Ca + 2H,0 = Ca(0H).. + H,. Magnesium powder,
boiled with water, g.res off hydrogen slowly ; but zinc
requires the presence of an acid, and must not be pure.
/.^. there must be a foreign metal present to serve as the
anode. Ihe impurity usually present in commercial zinc
IS .ead ; the acid, for instance, sulphuric acid, is present in
dilute solution as ions of HH and SO, ; the SO, removes
the surface layer of the zinc as Zn, while the negative
charge is transferred to the lead, which is in metallic
contact with the zinc This charge is neutralised by the
positive charge of the KH, which, on being discharged,
escapes m an non-ionised state. It may then be collected
over water, m which it is very sparingly soluble. Hydro-
gen, while It is on the point of discharging and is still in the
ionised state, may be used to liberate certain elements from
their oxides or chlorides. Zinc and hydrochloric acid,
for instance, in a solution of stannous chloride, SnCl Aq
causes a deposition of tin owing to the exchange of charge;
the hydrogen retaining its charge instead of parting with it
to the lead or other impurity in the zinc, while the tin is
discharged in its stead. If zinc and hydrochloric acid are
placed in contact with silver chloride, AgCl, which is an
insoluble compound, the hydrogen remains charged, while
the silver parts with th- chlorine, the latter remaining in
solution with negative charge. Lastly, if generated in a
solution of ferric chloride,'"Fe C^.Aq. the zinc goes into
solution as before ; and the positive electricity is provided
PROPERTIES OF ELEMENTS 25
by the loss of a positive charge provided by the ferric ions
changing to the ferrous ions of ferrous chloride, Ftci.,.Aq,
and another molecule of HCl.Aq exists in solution. The
valency of the iron is lowered. Such processes are gene-
rally termed reduction ; the hydrogen is said to be in the
* nascent state," and is named the "reducing agen\"
Metallic iron, manganese, cobalt, and nickel at a red
heat remove oxygen from water with liberation of hydro-
gen : 3Fe + 4H.O = Fe30, + 3H.,; 2Co + 2H..O = CoO
+ U^. Conversely, a current of hydrogen passed over
these oxides at a red heat will combine with their oxvcen
reducing them to metal. This is an instance of mass-
action. From the equations given above, it is seen that
hydrogen is formed; it does not remain in the tube to
re-form water ; if it did, there would be a state of balance
or equilibrium, all four substances remaining toaether in
proportions depending on the temperature and ''on their
nature ; in the current of steam, however, the hydrogen is
carried on, and is no longer present to act on the oxide of
the metal. And in the converse action the hydrogen
conveys the steam away, so that it can no longer be
deprived of oxygen by the metal.
As already remarked, carbon monoxide has a similar
reducing aciion on the oxides of the more easily reducible
elements. The product in this case is the dioxide, CO
for example, FeP3 + 3CO = zFe + 3CO.,. This action
requires a red heat. Another reducing agent, applied by
fusing the oxide with it, is potassium cyanide, KCN-
It is converted into the cyanate, KCNO. The metal
thallium^ may be prepared by its help, Tl.,0 + KCN ^ 2TI
+ KCNO. As the cyanide is somewhat expensive, it is
used only m special cases.
An instance has already been given of the mutual reduc-
tion of two compounds in the case of nitrogen. Similar
mstances are known with lead and with sulphur. The
chief ore of lead is the sulphide, a natural product termed
26
MODERN CHEMISTRY
galena. It is roasted, i.e. heated in contact with air to a
red heat. After a ponion has been oxidised to sulphate,
PbS-f 20^ = PbS0.„ the temperature is raised, when the
sulphide and the sulphate mutually reduce each other:
PbS + PbSO^ = 2Pb + 2S02. With sulphur the partial
burning of sulphuretted hydrogen may be explained in a
similar manner; the reaction, 21^^8 + 0., = 2 H.,0 + S.„
rnay be represented as the formation of water and' sulphur
dioxide by the complete combustion of one-half of the
hydrogen sulphide, and its reaction with the remaining
sulphide, thus : 2H2S + SO, = 2H,0 + 3S. And, as a
matter of fact, that reaction does take place on mixing
the two gases in the required proportion of two volumes
of hydrogen sulphide with one of sulphur dioxide.
The Properties of the Elements.— It has been cus-
tomary to divide the elements into two classes, the metals
and the non-metals. As we have seen, this classification
is a completely arbitrary one ; for there are some elements
capable of existing in both states. The name " metal *'
was originally given to seven substances, all alike in possess-
ing that bright lustre known as "metallic." These were
gold, silver, mercury, copper, iron, lead, and tin. But in
the Middle Ages bismuth and antimony were isolated in a
fairly pure state, and these, together with zinc, were at first
not received into the class, but were regarded as spurious ;
for they were brittle and easily oxidisable. Although
there is no reason for retaining the division, yet it is often
convenient. Bodies which possess metallic lustre have the
power of conducting electricity better than transparent bodies,
and ihey are also relatively good conductors of heat.
The elements exist in various physical states. Those
which are gases at the ordinary temperature, however, have
all been condensed to the liquid state by sufficient reduction
of temperature. The lowering of temperature is most easily
produced by means cf liquid air, now a cheap commodity.
To liquefy air, it h compressed by a pump to a pressure of
1 50 atmospheres ; it then traverses a coil of copper pipe.
PROPERTIES OF ELEMENTS
27
and escapes from an orifice at the lower end. Now,
compressed air has some resemblance to a liquid, for
when it expands, as when a liquid changes to gas, heat is
absorbed. The rapidly escaping air becomes cold, and in
passing up over the coil of tube through which it has de-
scended, it cools the pipe, so that the air passing down
becomes colder and colder ; finally, it is so cooled that it
liquefies, and escapes from the orifice in a liquid state. It
may be poured from one vessel to another, with little loss
by evaporation ; and if other gases be allowed to stream
into a tube cooled by its aid, they too are liquefied. The
principle of liquefying hydrogen is the same, for its boiling-
point lies so low that it cannot be liquefied by the aid of
liquid air. That of helium is still lower, but it too has
yielded when compressed into a tube cooled by liquid
hydrogen.
The elements which are gases at the ordinary temperature
are hydrogen, helium, neon, argon, krypton, xenon, nitro-
gen, oxygen and ozone, fluorine, and chlorine. The first
seven are colourless, both in the gaseous and the liquid
state. Oxygen is a colourless gas, but forms a pale blue
liquid; gaseous ozone has a blue colour; fluorine is pale
yellow; and chlorine has a greenish-yellow colour. It
forms a white solid, which, however, melts to a bright
green liquid. Bromine is a dark red liquid at atmospheric
temperature, but above its boiling-point, 59% it is a deep
red gas. Iodine is a blue-black solid, melting to a black
liquid at 1 1 4°, and giving off a violet vapour. Ozone and
the " halogens," as fluorine, chlorine, bromine, and iodine
are called, have all a powerful odour, and act on the skin
in a corrosive manner. Chlorine and bromine are soluble
in water.
Among the other non-metallic elements are boron, a
black, dusty, infusible powder ; carbon, in its ordinary form
an amorphous (/.; '/"r///... -thallium, lead; some-
t' ^'"''^'\^»^ /""i'te only at a very high inuprraureL
rnod.um ruthenium, palladium, platinum, iridium
\o) lAquui metal : — mercury.
M Brittle metals :—
(i) TO/r, /W; -antimony, biimuth, tellurium, zirco-
Z:i:t^:r (---)---. «-anium; /I
(2) Gr^r./W. —lanthanum, cerium, yttrium, uraniu- >.
(3; ^rey powders, acqmrins rnetallic lustre under the bur.
ntsher .•— thorium, niobium, tungaten.
(4) ^/'^^-^/owJ./-/ ..—tantalum, titanium.
not We^a"^^^^ ""^^""'"' ^^^ ^^^°'-- ^-^^
Although the external properties of the elements does
th^ln!-! • '^' y" " '"'y ^ generally remarkVd that
the llhr!" '?'!;''? '' '""^^ ^°'""'" '■» descended. Amon^
thel ghtest of the elements arelithium, beryllium, magnesium^
and aluminium, at least in the solid .tate; whereas osmiZ'
.ndium, platinum, and gold are among the heaXt B^l
much more must be ascertained regarding the r Troper^^
before a satisfactory comparison can be mfde. ^'"P"^'^*
CHAPTER II
CImasltlcation of Compounds— The Hydrides,
Classification of Compounds. — Compounds of the
elements may he divided conveniently into si\ classes: —
The Hydrides ;
The Halides ;
The Oxides and Sulphides (with Selenides and
Tellurides] ;
The Nitrides and Phosphides (with Arsenides and
Antimonides) ;
The Borides, Carbides, and Silicides ;
The Alloys.
Com]iounds can be prepared by many methods ; it is not so
easy to classify them as it is to arrange into classes the
methods of ])reparation of elements. As a rule, the j)re-
paration is carried out by one of the following methods : —
a) The interaction of elements ;
b) The action of an element on a compound ;
{c) The action of heat on a compound ;
[il) The interaction of compounds ;
{e) The addition of one compound to another.
These methods shall be considered in relation to each of the
groups of compounds named above.
The Hydrides.
{a) The Interaction of Elements. — Lithium, sodium,
and potassium, when heated to 300^ in an iron tube m a
30
INTERACTION OP ELEMENTS
31
current of hydrogen, form white waxy cumpoumls ; that of
lithium has the turmula LiH ; as the sodium com|>ound has
the formula Na.jH, its existence is dirfkult to rtconcilc with
the usual valency of either hydrogen or soil •urn, for these
elements in all other com])ounds behave as monads. It would
repay further investigation. It decomposes at 421*.
Iron, nickel, paUaditun, and platinum, when heated
gently in hydrogen, absorb the gas. Meteoric iron, indeed,
his been known to give otT, on heating, 2.85 times its
volume of gas. This natural variety of iron contains about
6 per cent, of nickel. Palladium, gently warmed in an
atmosphere of hydrogen, absorbs over 900 times its volume
of that gas, corresponding to 4.6S per cent, of the weight
of the body produced. It is difficult to determine whether
or not the palladium is in chemical combination with the
hydrogen, or whether the hydrogen is in a state analogous
to solution, for it is known that a solid can exert solvent
power. There is a considerable rise of temjierature accom-
panying the absorption ; and if palladium, in a state of
sponge, is placed in contact with a mixture of oxygen and
hydrogen, the mixture may be made to explode. A ther-
mometer-bulb coated with palladium sjx)nge is a good test
for the presence of an explosive mixture of marsh-gas and
air in mines, for the rise of temperature produced is an in-
dication of danger. These metals absorb hydrogen moic
readily if they are made the negative electrodes of a
battery with which dilute sulphuric acid is electrolysed.
Iron shows a very curious behaviour under these circum-
stances. If a thin plate of iron is made to close the top of
a barometer -tube full of mtrcury and a small cell be con-
structed on it, hydrogen will pass through the iron, when
the plate is made the kathode, and will depress the mer-
cury in the tube. No other metal, so far as is known,
shows this peculiarity ; it would appear that the hydrogen
in the ionic state can penetrate the iron.
Carbon, heated to 1 200° in an atmosphere of hydrogen,
unites with it to form marsh-gas (methane), CH^. Only
32
MODERN CHEMISTRY
a small percentage of the hydrogen, however, enters into
combination ; a balance soon establishes itself between the
number of molecules of methane being formed and decom-
posed in unit time. At a higher temjjcraturc, that of the
electric arc, acetylene, C^,Ho, is formed, owing to
the decomposition of the methane into that gas and free
hydrogen :— 2 CH^ = C.3., + 3 H^. Other compounds of
carbon and hydrogen are formed simultaneously, and there
again a])pears to be a state of equilibrium produced between
the various hydrocarbons formed. With nitrogen, NH. ,
it appears to be impossible to induce hydrogen to enter into
direct combination at such temperatures ; but if electric
sparks he passed through a mixture of hydrogen and nitro-
gen, combination to a limited extent ensues. Should the
ammonia, NH.,, be removed by having water, or, better,
dilute sulphuric acid, present, the combination proceeds
until all the gases, if they were originally present in the
correct proportion — one volume of nitrogen to two volumes
of hydrogen — have combined. Conversely, if sparks be
passed through ammonia gas, there is nearly, but not quite,
complete decomposition into its constituents. This enables
the volume relations of ammonia to be demonstrated ; for
it is found that two volumes of ammonia gas can be decom-
posed into two volumes of nitrogen and six volumes of
hydrogen. This is symbolised by the equation —
2NH,^N., + 3H..
Weight 2(14 + 3) 2^' 3(2) grams.
Volume 2(22.4) 22.4 3(22.4) litres.
The hydrogen can be nearly completely removed by ab-
sorption with palladium-sponge, and the nitrogen remains.
Water, HgO, is more completely formed than any one
of the previously mentioned compounds by the interaction
of its elements. A mixture of oxygen and hydrogen, in
the proportion of one volume of oxygen to two of hydrogen,
is exploded by heat ; this is most easily done by passing an
electric spark through the mixture. While the position of
COMBINATION OF HYDROGEN 33
equilibrium for a mixture of nitrogen, hydrogen, and am-
monia lies at such a point that very little of the compound
is present, but chiefly the uncombined gases, the contrary is
the case with hydrogen and oxygen. Here nearly all the
oxygen and hydrogen combine, and ouly a trace remains
uncombined. Combination may be r^ade to take place
slowly at much lower temperaturr ; c.-n at ico° slow
combination occurs. Colloidal plaiinuin. prepart.ii by mak-
ing an electric arc between poles A j)lat!num under pure
water, which appears to consist c,' '-?"y iirely divided
platinum disseminated through the water, has the power of
causing union of oxygen and hydrogen left standing in
contact with it, even at the temperature of the atmosphere.
On the other hand, if water-vapour be raised to a very high
temperature, above 1800°, decomposition into its consti-
tuents takes place with considerable rapidity ; so that it is
possible to obtain a mixture of oxygen and hydrogen by
passing steam through a tube in which a spiral of platinum
wire is kept at a white heat by means of an electric current.
These actions are therefore termed " reversible," and they
are expressed by such equations as —
CH, ;!: C + 2H, ; 2H., + O., :^ 2H<,0 ;
N, + 3H, -- -
2SIH3.
Hydrogen also combines with sulphur when passed
through a flask containing boiling sulphur, and sulphuretted
hydrogen, HgS, decomposes when raised to a low red
heat.
Interesting relations are to be seen with the compounds
of the halogens with hydrogen. In preparing fluorine by
the electrolysis of hydrogen-potassium fluoride, KHF, in
presence of hydrogen fluoride, Hj;F2, it is possible, by stop-
ping the exit of the hydrogen, to cause a bubble to pass the
bend of the U-tube and to rise into the fluorine; the instant
the gases unite there is a sharp explosion. This shows
that these gases unite even in the dark to form H-T.,.
Chlorine and hydrogen, on the other hand, do not com-
VOL. II. c
34
MODERN CHEMISTRY
bine in the dark, but, when exposed to diffused daylight,
slow but complete combination ensues ; in bright sunlight,
or when illumined by the light from burning magnesium,
the mixture of gases explodes, forming HCl. Bromine and
hydrogen unite to form HBr when a current of hydrogen,
having bubbled through a wash-bottle of bromine, passes
through a red-hot tube ; with excess of hydrogen the union
is practically complete. Iodine and hydrogen, on the
contrary, unite very incompletely to produce HI ; and if
hydrogen iodide be heated, a large proportion of it is
decomposed into hydrogen and iodine. This change has
been investigated much more completely than other changes
of the same character already mentioned ; and as it is
characteristic of all such reversible reactions, we shall con-
sider it in somewhat greater detail.
The rate at which hydrogen iodide is produced from a
mixture of hydrogen and iodine at any constant tempera-
ture is much more rapid than that at which the reverse
change of hydrogen iodide into iodine and hydrogen takes
place. This rate was not difficult to determine. Weighed
quantities of iodine were placed in a tube filled with hydro-
gen, and after heating the sealed tube for a sufficiently long
time for equilibrium to be established, u was opened under
water. The hydrogen iodide formed at once dissolved in
the water, and the residual hydrogen was measured. The
amount of uncombined iodine remaining in the water was
then estimated by known processes. It was thus possible
to find the ratio of the combined to the uncombined hydro-
gen. Now, it was discovered many years ago that the rate
of chemical change depends on the amount of each of the
reacting substances present in unit volume — a condition ex-
pressed by the term "active mass." Thus, if we double
the amount of hydrogen in the mixture of the gtjses men-
tioned, we double its "active mass." Let /<, denote the
number of molecules in unit volume of the iodine gas, and
h.^ that of the hydrogen, and let ih't be that of the hydrogen
iodide formed by their interaction. Then, as the rate of
HYDRIDES OF CARBON 35
formation of hydrogen iodide is proponionil lx)th to / and to
A, It will be proportional to their product, 6 x i. And as
H +I,,= 2HI, the rate < f change of HI into H, and I
will he 2bi X 2hi or 4(/./)^'. If we call the rate of forma-
tion k, and that of decomposition k\ the jjroportion of
these rates to each other will be k i' = {/j x i)/^{/ji)\ if the
gases are present in molecular proportions. At the tem-
perature 440°, and at one atmosphere pressure, it was found
that, taking the total hydrogen as unity, 0.28 was free
and 0.72 combined, after a sufficient time had been al-
lowed for the change to complete itself. Now, the iodine
free must have been equal in number of molecules to the
free hydrogen, i.e. 0.28, and the same number of atoms
of iodine must have existed in combination as of hydro-
gen in combination; hence 0.28x0.28/4(0.72x0.72)
= 0.0375 = i/^'. This means that at 440' molecules of
hydrogen iodide decompose into hydrogen and iodine at
a rate only 0.0375 (or one twenty-sixth) of that at which
combination takes place between the two gases.
{l>) The action of an element on a compound leads
to the formation of many hydrides. This process has been
pretty fully treated in the description of the methods of
preparation of elements. For nie, on jiassing a current
of hydrogen over hot cupric c vater, H.,0, is formed,
while the oxide is reduced .0 copper, "CuO + H., =
Cu + HgO. The oxides mentioned on p. 16 are tlius
reduced. It is not so usual for sulphides to lose sulphur on
heating them in a stream of hydrogen ; indeed, it is only
those sulphides which themselves decompose when heated
that yield to such treatment ; but hydrogen fluoride, chlo-
ride, bromide, and iodide are formed on heating the halidcs
or many metals in a current of hydrogen. The process,
however, is not one which is used for the preparation of
these hydrides.
(c) The third method— that of heating a compound—
IS also not in use as a means of preparing hydrides, but it
is often employed in order to produce the compound from
36
MODERN CHEMISTRY
which the hydride is separated. Thus, all compounds
containing water of crystallisation, when heated, lose water
when raised to a high temperature ; and double compounds of
ammonia, too, lose ammonia on rise of temperature. Such
compounds as calcium chloride, CaCl.,, crystallise with
water. The formula of the hydrated compound is CaCl.,.
6H.,0 ; a similar compound with ammonia, CaCl.,.6NH3,
is also known ; compounds like these lose water or am-
monia when heated. By this plan Faxaday succeeded in
liquefying ammonia, which at ordinary temperatures is a
gas. Having sealed up the ammonio-chloride of calcium or
of silver, AgCl.NHg, in an inverted U-tube, one leg was
cooled with a freezing mixture, while the other was heated,
and the gas liquefied under the combined influence of cold
and prcssuce.
(//) Most of the hydrides can be prepared by the fourth
method — the interaction of compounds. The decom-
posing agent is either water, an acid, or an alkali.
(i) Water: — Marsh-gas, CH^, ethylene, C.2H4, acety-
lene, CoHot ammonia, NH3, and phosphoretted hydrogen,
PH3, may be produced by the action of water on some
compounds of carbon, nitrogen, and phosphorus. Alumi-
nium carbide, Al^Cg, yellow transparent crystals produced
by heating a mixture of carbon and oxide of aluminium to
whiteness in the electric furnace, on treatment wii-h water
yields pure methane, A1^C3+ i'zH.,0 = 3CH4 + 4Al(OH)3.
Manganese carbide, black crystals produced by heating in
the electric furnace a mixture of manganese oxide and
carbon, yields a mixture of equal volumes of hydrogen
and methane, MnyC + eR,© = 3Mn(0H), + CH^ + H._,.
Lithium, calcium, strontium, and barium carbides also
formed in a similar manner in the electric furnace yield
acetylene with water, Li.,C., + 2H.,0 = 2LiOH + C.,H., ;
CRC^ + 2H.p = Ca{OH)l + C.M.r The carbides of
cerium, CcC.^, lanthanum, L"aC.„ yttrium, YC.„ and
thorium, ThCg, yield a mixture of methane, ethylene,
CgH^, and acetylene, sometimes mixed with hydrogen ;
INTERACTION OF COMPOUNDS 37
and uranium carbide, U.^Co, gives methane, ethylene, and
hydrogen, but no acetylene."
Magnesium or calcium nitrides, prepared by heating
metallic magnesium or calcium in a current of nitrogen,
yield ammonia with water: Mg3N., + 6H.,0 = 2NH3 +
3Mg(0H)^, and calcium phosphide", produced by heat-
ing lime with phosphorus, on treatment with water simi-
larly gives ofF phosphoretted hydrogen: CagP., + 6H.,0 =
3Ca(OH)._, + 2PH3. The sulphides of magnesium" and
aluminium, MgS and Al,S3, are also decom|x)sed by water,
with production of hydr"ogen sulphide and the hydroxide
of the metal : MgS + 2H.OH = Mg(OH).. + H,S ; Al ,S,
+ 6H.OH = 2Al(OH),, + 3R,S. " ' ' - =^
The halides of a certain numfier of elements are at once
decomposed by water with formation of a hydride of the
halogen and a hydroxide of the element. Boron, silicon,
titanium, phosphorus, sulphur, selenium, and tellurium
chlorides, bromides, and iodides are thus resolved. The
method is practically made use of in preparing hydrogen
bromide, HBr, and iodide, HI, by help of phosphorus.
But the previous preparation of phosphorus bromide or
iodide is unnecessary. It is sufficient to add bromine to
water in conuct with red phospiiorus, and hydrogen bro-
mide is evolved ; or to warm a mixture of iodine, water,
and red phosphorus. The use of yellow phosphorus is not
advisable, for the action is apt to take place too violently if
it be used. It may be supjjosed that the ])hosphoru8 and
halogen unite to form the pentahalide, which is then imme-
diately decomposed by the water, thus: PBr.(or PIr) +
4H,0 = H3PO + 5HBr(or 5HI). The gaseous hydride
may be collected over mercury or by downward displace-
ment, or it may be dissolved in water and a solution of
hydrebromic or hydriodic acid prepared.
A commercial method of producing hydrogen chloride,
HCl, depending en the decomposition of magnesium
chloride when heated in a current of steam, has been
patented ; it results in the formation of a compound of
38
MODERN CHEMISTRY
oxide and chloride of maj-mKiuni, while the hydroKcn of
the water umte« with a part of the ehlorine ; the reNuhinu
gaseous hydro^jen chloride is passed up towerH. ami comes
into contact with water, thus yieldinj; a Bolulion of hydro-
chloric acul. ^
( 2) In many cases the contpound from which the hydride
IN forn.ed .s not decon.posed by water ; an acid, generally
hydrochloric acid, must be present. The reason of this i«
not easily explained ; it may k- that the very few ions of H
^ind on present in water are sufficient to effect the dccom-
positum m some cases and not in others, and that when
jin acid IS necessary the much lar);er number of ions of
hydroj-en present in its solution is recjuired ; also it is
kn.>wn that the heat evolved during; the decommjsition
ot those compounds which are altered by water is
greater than that which would k- evolved by those which
ri^at Its action were they to be attacked by water.
Many h>ch ides arc prepared by the help of acids. Maii-
nes.um kr.de, Mg^H., yields with hydrochloric acid a trace
, ^^■■^;, ^\".^ f ^'"s compound is a very unstable Pas,
almost all ol it decomposes into boron and hydrocen. The
similar comiK)und, Mj-.Si, produced by heating a mixture
ot sihca and magnesium powder to redness, when mixed
with hydrochloric acid yields hydride of silicon, SiH , as
'""J^T ' ^I'^ntancously inflammable gas :— Mp .Si +
4HCI. Ac, -. aMgCl.Aq + SiH,. Arseniuretted hydrogen.
AsH.„ and antimoniuretted hydrogen, SbH.. are prepared
from sodium or zinc arsenide or antimonide : Na,A8 +
3ZnCI,.Aq + 2bbH3. These gases, however, may be ob-
tained mixed with hydrogen if a solution of oxide of arsenic
or antimony in hydrochloric acid, which yields chloride of
arsenic or antimony, is treated with zinc. The first change
IS the rc^placement of the zinc by the arsenic or antimony,
thus : 2 AsC:i3. Aq + 32^n = sZnCl^ Aq + 2 As. Electrically
HYDRIDES
39
neutral /inc rci.I.KCH ,K,Nifiv,Iy char,..fd arsmic, ifwlf Ik-
cominK pos.uvcfy cl,ar,;nf. The armnic an.l the unattacked
/.inc form a couple.^and the hy.lrochlt.ric acid in clectrolyKed,
2HC! A.,-,.Zn .'/na.A<, , 2H; the hydrogen ion unites
with the amnic, ne|;atively charged in the drctric cunle,
fornung elcctrually neutral hydrule (,f arsenic, which e«ca,H.;
a« Kan, 3 H + As .-. AsH^, An element in thin form, capahle
ot combmation at the n.oment oflilK-ration, iH said to k- in the
nascent state, a word derived fron. " nas, :,re," to Ix- horn.
It ditters from an ordinary element in iH-in^ on the point of
losmg an electric charRc, and it n,ay cither Inr evolved in
the free state by comhinin;^ with itself, as M f H H on
fiivmg up its charge, or it may enter into some (,ther form
of combmation, as in the case explained. This j>roces8 of
preparing arsenic or antimony hydride is used as a test for
the elements arsensic or antimony. It was devised by
Marsh, and as the hydrides are very easily decomposed
by a h.^h temperature, the «as, if caused to pass throui-h a
red-hot tube, is decomposed, giving a deposit of arsenic
(grey) or antimony (l,lack). The former is more easily
oxidised than the latter, and dissolves in a solution of
bleaching-powder, in which the latter is insoluble. This
process is particularly applicable where poisoning with
arsenic or antimony is suspected.
H^S, H,Se, H,Te.— Hydrogen sulphide, selenide, and
te uride are prepared by treating a sulphide, selenide, or
tcllur.de with dilute sulphuric or hydrochloric acid: FeS
+ H,s6,.Aq ^ FeSO^.Aq + H,S ; Sb.S, + 6HCl.Aq
= 28bCl3.Aq + 3H.,S. Na2Se.Aq + H^SO^.Aq =
Na2Sb,.Aq + H.,Se.
>*<;/h yi^'ld salts with thJ
0XK1C8 jf metals All ac.ds contain hydrogen, and it is
now poss.be to define them in a very simple 'manner An
whtssdid'in^r/Trt "'"'■' 'f'' V'^"«- -«
. ""5" .'" w-^ter, or m some other so vent caoable
of causmg ,on.sat.on. This definition applies to the
alsftVol 7'"?K'''"^'r-'.^^^°""-' -^ '^'n ; and
also to tnose of sulphur, s^elenium, and tellurium ; for on
s^olution the^y ionise thus :^HF.Aq ; HCl.Aq ; HBr. Aq ;
Hl.Aq ; H SH.Aq ; H.sJh. Aq ; H.TeH Aa Rut
•t .s not confined to them, for the hydrog;n may b^'united
not wuh a s.m|^e element, hut^ wit^ a 'compTx gro"; of
elements, as in H.SO^.Aq or HNO^.Aq. Now in dilute
solution, a solufon of sulphuric acid L lei ionised' than one
of hydrochlcnc aod, in about the proportion of 12 and
"^"'^r .' ''''^'' ^^'^ ' «° ^hat ^a hydrox d'e such
nu^^rr'^'""'^',^ P^^^"^^^ to a mi^fure ofVq"
one^f hem r "l^'^'^^' '" ^"^"^ity requisite for o^y
one oi them, chloride of sodium will be formed in greater
h^d^de^itf" I^h''"" ^t'"^ ' y-' on heati
h-iKde with sulphuric acid, because hydrogen chloride
Which flasks and retom are usually made; for
HALIDES
hydrogen fluoride attacks the
41
,- ... ^ silica whiclj tlicv ccjntain
orm.ng w.th u silicon fluoride: SiO..,- .Hjv^ S.F ?
th '^;..n r . '^•'>'"^"«^^''^- ''"ly <'tl'«r nutal-which res sts
I , -.ct.cn of hydrogen fluoride. There is no such diffi-
culty with the other lud.des. Hydrogen chloride HCl 1
prepared by di^stilHng from a glass ^cllVx^,?,
c-onunon saU and oil of vitriol : NaCI + H..SO. . ilX.nSO
,+ n^l. Un a large scale thi.s preparation is carried out
m rotating c.rcular furnaces, he ni.xture of salt and \1trio
l^mg dehvered .n through a hup,)er ahove, and at the h gh
temperature the action goes further, and di-sodium sulphate
.8 produced: 2NaCl + H.,SO.,=.Na..SO, + 2HCl The
gas .s passed up towers filled with coke, and expos'ed to u
descendmg stream of water, in which it dissolves, tming
a saturated solution of hydrochloric acid, or. as i ZTtl
be called, "muriatic acid" (fn.m "muria," brtne
Hydrogen bromide. HBr, and iodide, HI, may similarly be
produced by disfllmg together bromide or iodide^of sodium o^
potassmm w.th exactly the right weight of sulphuri acid for
the equation zKBr (or 2KI) + H.SO^.Aq =^K.,SO .aV+
2HBr (or 2HI). But m these cases, ^he hydrogen bromide
All these halides come over as' gases, and may either be
collected over mercury or by 'downward dis/iac mem,^
/... by dehvermg them to the bottom of a jar containi^.
air, wh,ch owmg to its less density is forced^'upwards and
escapes at the mouth of the jar. they cannot bT col tod
over water, for they are readily soluble in it.
French 'teTf""^ — "' '''""'"^ ''>'^"^"'^ ^^'^ i^^^m the
French term for nitrogen, "azote"), is also liberated in
the gaseous form by warming its sodiu'm salt with sulphur"
acid. It, too, 13 readily soluble in water. ^
(3) Certain hydrides are set free by the action of an
43
MODERN CHEMISTRY
alkah, ;.. the hydroxide of one of the metals of the sodium
othe calaum group It is true that the chang. may be
produced by other hydroxides, but they are not so efficient,
and not so generally employed. Among these are ammonia,
WH,. and hydrazme, K,H,. These bodies unite with
acids ; for example, ammonia and hydrogen chloride form
ammomum chloride, NH.Cl. when mixed c-Nh'^HcI
~i » f .. . comiwund is produced by a change in
valency of the nitrogen atom ; in ammonia it is a triad. N'"
but on union with hydrogen chloride the valency of the
nitrogen becomes five, N^ On distillation of a mixture of
ammonium chloride with caustic soda or with slaked lime,
either in presence or ^absence of water, the following change
occurs :_NH,C1 + NaOH = NaCl + NH ^ H O
.^N; Cl + Ca;(OH), = CaCl,^.NH3^'lS^,a &
initial change IS the formation of ammonium hydroxide,
Wrt^UH; this substance, being unstable when heated
decomposes into ammonia and water. Hyd-azine, a com-
Krtde ' ^'■■-'' '' ''""''"''y ^•^^"'^d from its
The usual source of commercial ammonia is coal-gas.
On distillation of coal, all varieties of which contain nitrogen.
It may be imagined that when methane, the principal consti-
tuent of coal-gas, is strongly heated it splits into carbon and
hydrogen. This hydrogen, at the moment of its formation.
IS in the nascent state, and it unites with the nitrogen, which
IS also ,n the nascent condition. As ammonia is very easily
soluble in water, while the other constituents of coal-gas are
it^'Zfr« ''''J^' ^>f " ^^P"^^'* of ammonia by passing
It th ough « scrubber^," ..pes containing broken bricks kept
moist with water. The ammonia dissolves, while the coal-
gas passes on. The solution is next mixed with hydro-
chloric acid and evaporated to dryness. The residue of
ammomum chloride is then distilled with lime, as previously
described. The ammonia is received in water, and brought
XL fK^"' ' ;"i'^" ^°™ °^ ^ concentrated solution, to
which the name " liquor ammoniac " is given.
PROPERTIES OF HYDRIDES 43
(i) Certain double hydrides arc formed hy the addition
lh"h J A T r;:^r ^'"'"""'•■^ ^"-^ 'hydrazine unite
nmm chlonde NH.Cl ; but as these Ixxiies show analogy
with salts of the metals, they will be reserved until the latter
are considered.
Mthul^'^'A^'^"'^.''^ ^''^ "y1rides.~Hydrid.s of
.nH Zh T^ potassium, iron, nickel, palladium,
and phitinum differ from the others in character ; they are
solid bodies, decomposed by heat. Graham, indeed, who
investigated that of palladium, was struck with the met;,llic
nature of the substance, and was inclined to believe that it
might be regarded as an alloy of a metallic form of hydrogen,
o which he gave the name «h. drogenium;" and it was fo?
long believed that liquid hydrogen would show the character-
jst.c proj^erty of metals, metallic lustre. But this anticipation
has not been fulfilled. Liquid hydrogen is a colourless body ;
and solid hydrogen is described as having a white crystalling
appearance like ice froth. Bur it must be confessed tha!
hydrogen shows a marked similarity to metals in many of its
compounds, as will be frequently seen in the sequel.
cl.;jr ' Tk'"'"^ u^^^u ''^"'' "^"y ^ ^'^'^^-d '"to three
^nMlV-T ^"^ r^ '?''' "^''^ "^'^her acid nor bases,
and which therefore be described as neutral. To thi
class belong the hydrides of boron, carbon, silicon
arsenic, and antimony. That of phosphorus nearly falli
mfo the same category, for its compounds with acids are
very unstable. The next class-those which react with
bases-comprises water and the hydrides of sulphur
ThJr fl'L"'' '"4 '^". ,"'^ °^ ^"'P^""-' hydrosulphides.
These will be considered later, but an instance may be given
here :-When lime is moistened with water it is slaked
with formation of calcium hydroxide, thus : CaO + H O J
" .nnvS^'* 1 u ^'^"^'' °^ f^rioTme, chlorine, bro^e,
and iodine also belong to this class ; but in their case an
exchange takes place, thus: CuO + 2HCI. Aq = CuCl Aq
44 MODERN CHEMISTRY
r ^-? J . J^y'^^.^o'C acid is capable of similar reactions
termed ..c.ds. The last group of hydrides, ammonia and
^Jrazme. and m one or two isolated ca^es, hyZge^phoi-
pWde umte wuh a^.ds. forming salts, thus: ^H^'.^'l^^Z
al^' V '^"3t"^ = PHj. It api^ears that the pre-
sence of water .s necessary for at least the first of these
ZA'^ku'LVr '''''' ''' hydrogen "Urid 1
mixed with perfectly dry ammonia, no combination results
It .8 perhaps allowable to suppose that the presence of
moisture leads to ionisation of the hvdrocen chS a
that the ioni^ molecule is capab^'^f eTeHn^ to ^om'
bmatjion, while the non-ionised molecule is wifhout acZ
on the ammonia. These compounds will T treat^ n^
under the heading of "salts." ^^^ °*
^J.nl^^'^f'^f ^"''' *^^°°' «^con' phosphorus,
arsenic, and antimony are insoluble in water • those^ f
nitrogen, sulphur, selenium, tellurium and the l^io
gens are soluble With the exceptK'certain hyd^del
of carbon, to be afterwards described, and water all 7he
rest are gases at atmospheric temperature. The ^c that
water .s a l.qu.d. and not, as might be expected, aTas r
qmres comment. It is noteworthy that wLr^sX^le
the densny 9, corresponding to the molecular wei^t, 8
hence there can be no doubt that in the gaseous shelter
suUu^ which - ?"' ". '^ '"°""'*^^' compounZf
sulphur, which are m formula?, and in many properties
'p^tThirth?^""'^ °'.°^^^^"' J^°^^^«« higLrSg!
points than the correspondmg oxygen comoounds pL
instance bisulphide of Varbon! CS^'boils a?"", where"
carbon d.ox.de boils at about -8o\ But wtttr' Li L
1 00 , and, contrary to expectation, its analogue, sulphuretted
&"' T'^"- ^V^ liquid at a temperature r^uch
beJow o . Now, ,t has been found hy a method dcoend
Z::l'::^J'r'' - capUJary^tubes.thatwhinhe-
Identical with those which they possess in the gaseous state,
HYDROCARBONS 45
the molecular weight of water is considerably too great.
The conclusion follows, therefore, that the molecular
weight o water should be expressed by a more complex
formula than H,0 ; possibly by H,0,., or by one Iven
more comj^ex. Gaseous hydrogen fluoride,' unlike its
congeners, has a higher molecular weight than that ex-
pressed by the formula HF ; determination of its density
leads to the formula H^.F,. These facts are probably to l,e
explained by the view that oxygen may possess a higher
valency than 2. and fluorine than I. at relatively low tem-
peratures. It IS not unlikely that the structural formula of
I- -A • "\ ^^
liquid water is >0=0
-uf/ ^^\ * ^"^ ^^'^^ o^ hydrogen
fluoride HF=FH. where oxygen acts as a tetrad and
nuorine as a triad.
Hydrocarbons. -The hydrides of carbon, or
hydrocarbons, are very numerous, and form an im-
portant group of substances. In many respects they are
analogous to the metals, and they yield derivatives com-
parable with those of the metals, f he preparation of some
of them has already been described ; but in order to ijive a
more complete idea of their structure and functions, a short
description of other methods of forming them is annexed.
Methane or marsh-gas, if mixed with its own volume of
chlorine, and exposed to daylight— not sunlight, else the
mixture would explode-undergoes the reaction CH,+
«;i*^ ^- . L, . ^^^ resulting gas, termed chloro-
methane, is soluble m ether, a volatile liquid compound
of carbon, hydrogen, and oxygen. If pieces of metallic
sodium are added to the solution, the sodium withdraws
chlorine from the chloromethane and a gas is evolved.
On analysis. ,t gives numbers answering to the formula
yrtg. iiut if tnat were its formula, its molecular weight
m grammes would occupy 22.4 litres; but 15 grammes
occupy only 11.2 htres ; hence its molecular weight must
be 30, and not 15, and its formula cannot be CHg.but must
46
l)eC,H«.
MODERN CHEMISTRY
It IS reasonable to suppose that the mechanism of
H\ /j^
the reaction is this : H— C— CI + Na Na + CI — C - H •
n/ \h'
and that the two CH3 groups on liberation join together.
tormmg the complex group, H-C— C^ H. Similarly,
mixing C,Hg, which is named ethane, with its own
volume of chlorine, a reaction takes place like that with
methane, and chlorethane is formed, thus : C. H + CI =
C2H5CI + HCl. Chlorethane dissolved in ether and treated
with sodium yields not C^H, but C^H,^, and it may be
supposed that the constitution of the new hydrocarbon,
butane, is HC—C-C-CH. A mixture of chloro-
■H H H H
methane and chlorethane gives with sodium an intermediate
,. J . H H H
hydrocarbon, CgHg, propane, HC— C—CH. When
Ki • ^ H H H
chlorine and propane are mixed in equal volumes, two
Chloropropanes result; they have identical formulae and
molecular weights, and it is believed that the difference
between them consists in the position of the entering atom
of chlorine. In one case the chlorine replaces hydrogen
attached to one of the terminal atoms of carbon, thus :
H H H
^'2~£— f H» while in the other the medial hydrogen is
H H H
H CI H
replaced: HC— C-CH. These two chloropropanes
H H H
yield in their turn two methylpropanes or butanes.
1 wo such substances are said to be isomeric, or to exhibit
isomerism with each other. The following list gives the
names and formulae of some of this series of hydrocarbons ;
HYDROCARBONS
47
where the difference between their formulae is CH.,, they
are said to form a " homologous series."
H
H H
HCH
HC— CH
H
H H
Methane.
Ethane.
H H H
H H H H
HC C CH
HC— C— C— CH
H H H
H H H H
Propane.
Butane.
H H H
HC C CH
H H H H H
H H
HC C C C CH
HCH
H H H H H
H
Pentane.
Isobutane.
H
H
HCH
HCH
H H
H H
HC C CH
HC C CH
H H
H 1 H
HCH
I
HCH
H
H
Isopentane.
Tetramethyi-methanc.
Chloromethane, if mixed with its own volume of chlorine
and exposed to light, yields a dichloromethane, thus :
CH3C + CI, = CH3CI + HCl. This compound, which,
like chloromethane, is also a gas soluble in ether, on treating
Its solution with sodium, loses chlorine and is converted
into ethylene, thus: CH,,Cl2 + 4Na + CI,CH, = 4NaCI
H H " "
+ £=^- The carbon atom, it will be observed, is still
n H
a tetrad, but the two atoms are connected by a "double
48
MODERN CHEMISTRY
bond." Homologues of ethylene are known, of which the
following are a few : —
H H H H H
C=C HC— C=C
H H H H
Ethylene. Propylene.
H H H H
HC— C— C=C
H H H
H H H H
HC— C=C— CH
H H
Butylenes.
H H
HC— C— CH
H II H
HCH
These hydrocarbons are c! aracterised by the facility with
which they combine with the halogens, forming oils ; they
have, therefore, been termed « olefines," or " oil-makers."
They also unite with nascent hydrogen, and are converted
into paraffins, as the members of the former group are
termed. The equations which follow illustrate this : —
HgC CI H,CC1 CH.,
y + I = " I u ^
H,C CI H.,CC1 CH
CH,
+ 2H= I
CH,
By the further action of chlorine on dichloromethane,
trichloromethane, or chloroform, CHCL, is produced.
Chlorine can also be withdrawn from chloroform by sodium,
and acetylene, CgH^, is formed : HCCI3 + 6Na + CI3CH
= 6NaCl + HC^CH. Here the two carbon atoms are
represented as united by a treble bond, and each carbon
atom is still believed to remain tetrad. Acetylene is
also characterised by the ease with which it unites with
chlorine, forming a tetrachlorethane : HC=CH + 2CI2 =
ClgHC— CHCI3. Here, also, other members of the series
are known.
The passage of acetylene through a red-hot tube is
attended by «* polymerisation ; " that is, two or more mole-
cules unite to form a more complex one. In this case, three
j^ives on treatment with
HYDROCARBONS 49
molecules of acetylene combine to form a molecule of the
formula C^H,., a compound to which the name benzene is
applied. It is produced in large quantity by the distillation
of coal, and is separated from coal-tar oil by distillation.
Its carbon atoms are imagined to form a ring, because,
among other reasons, it yields only one mono-chloro-sub-
H H H
C— C.=C
stitution product : || I
C— c=c
H H H
H H CI
C— C=C
chlorine, CI,, |; ^ | ; and as all the hydrogen atoms
H H H
in the molecule are symmetrically arranged with respect to
the carbon atoms, this condition is fulfilled.
The four first members of the methane series are gases ;
those containing a greater number of atoms of carbon up
to eleven are liquids, and the higher members are solids.
The paraffin oil which is burned in lamps consists of a
mixture of the liquid members, and paraffin candles largely
consist of the solid members. They are all practicallv
insoluble in water. The olefines have similar physical pro-
perties, and benzene is a volatile liquid. Iodine, sulphur,
and phosphorus dissolve in the liquid hydrocarbons.
These and other hydrocarbons may be considered as
somewhat analogous to the metals ; the analogy appears in
the methods of formation and formulae of their derivatives.
voi . 11.
CHAPTER III
The Halldes of the Elements— Double Halides
— Endothermic Combinations— Hydrolysis
— Oxidation and Reduction— Mass- Action,
The Halides. — Compounds of fluorine, chlorine, bro-
mine, and iodine are thus named. They fall into classes
when the elements are arranged according to the periodic
system. Taking the chlorides as typical of the halides,
we have t k- following table : —
LiCl BeCU BCI;, CCli ... NCI, ... OCU
NaCl MgCL AICI3 SiCl, \X\ PCI^; SFg Sci," SCi:
HCl
FCl?
ClCl
KCl CaCU ScCla T'Cl. ... AsCL
RbCl SrCl.; YCl, ZrCl, SbCL SbCL
CsCl BaClo LaCla CeCl4
YbCl,,
ThCl^
ErCl.,
BiCi:
SeCU
TeCl4 TeCU ICl;, ICl
CuCl ZnCh GaClsGeClj VCl, VCl.,
AgCl CdClj InCla SnC^ NbCl., NbCLj
GdCl.,
TbCh
HgCl. TICI3 PbCl^ TaClj
PrCJ.,
CrCl., MnC'l,
M0CI4 MoCU
NdCL
wcig w'ci^ \\c\.:
... UC14
FeCI., FeCl.,
RuCia RuCL
CoCl., CoClo ...
RUCI3 ..." PdCl4
OSCI4 OSCI3 OsCil. IrCl'^ IrCi;.
PtCl,
50
NiCl,
PdCL
PtCL
THE HALIDES
5»
Besides these compounds, which present considerable
regularity, others exist which have Jess claim to order.
Thus, KI3 is also known; it is unstable, but Csl.. is re-
stively stable. Again, CuCl., and AuCL exist, also
HgCI. In the next group, GaCl,, InCl, and InCl. are also
known, as well as TlCl. The "following group "contains
bnCI, and PbCl ; PbCl is very unstable. Besides
VCl, and VCI3, VCl, and Vci., are also known ; and in
the next group, CrClg, MoCI,, and MoCI^, also WCI„
UCI3, and UCI5. These compounds are difficult to
classify.
The bromides and iodides, as well as the fluorides, corre-
sponding to many of these chlorides in formula, are also
known. Where they are of special interest, they will be
alluded to in the sequel.
The characteristic of the halides of the elements of
the lithium group is that they are all soluble white salts,
crystallising in cubes. In dilute solution they are all ion-
ised, and even in strong solution a large percentage of ions
are present. Hence they all react as metal ions and as halo-
gen ions. Thus, for instance, with silver nitrate, which is
the usual test for ionic chlorine, the following reaction takes
place : — NaCl.Aq + AgNOg.Aq = NaNOg.Aq + AgCl.
Practically insoluble, and therefore practically non-ionised,
silver chloride is precipitated, and free ions of sodium and
the nitrate group remain in solution. If concentrated
soiutions are mixed, that portion which is ionised reacts ;
and as it is removed from solution, the originally non-
lonised molecules of sodium chloride are ionised, because
the solution becomes more dilute as regards sodium chloride,
and they, too, enter into reaction. In a similar way, the
alkali metal ions react in presence of a suitable reagent.
Another point to be noticed is that these salts are not
hydrolysed, that is, do not react with water to give hydroxide
and acid to any appreciable extent, and the usual method
of preparing them depends on these facts. They may
52
MODERN CHEMISTRY
all be obtained by the addition of halogen acids to the
hydroxides or carbonates of the metals dissolved in water,
thus : KOH.Aq + HBr.Aq ^- KBr. Aq + H.,0. It will
be noticed that the water is not ionised, nor d8es it hydro-
lyse the potassium bromide; hence, on evaporation, as
concentration increases, the number of ions of potassium
and bromine becomes fewer and fewer, and after the
water has been removed the pure dry salt is left. With
a carbonate the action is similar. The equation
+ -
IS
Li,C03.Aq + 2HI.Aq = zLil.Aq + H.,0 + CO,. In
dilute solution the acid H.COg would be "liberated ;" it is a
very weak acid,/.jr. it is comparatively very slightly ionised into
2H.Aq and C03.Aq; and, moreover, it readily decom-
poses into H,0 and CO2; hence it is removed from the
sphere of action as it is formed, and on evaporation the
salt IS left behind, as in the previous example.
Sodium and potassium chlorides occur in nature; the
former m the sea, which contains from 3.8 to 3.9 per cent.
Deposits, which have undoubtedly been formed by the drying
up of inland seas, are found in many places. At Sussfurth in
b. Germany there are large deposits of all the salts present in
sea-water, including common salt, chlorides and sulphates of
magnesium, potassium, and sodium, and calcium sulphate ;
these have been deposited in layers in the order of their
solubilities, the less soluble salts being deposited first.
Bromides and iodides are also present in minute quantity in
the residues from the evaporation of sea-water.
Solutions of the halides of the beryllium groiip of elements
can also be made by acting on the hydroxides or carbonates
of the metals with the halogen acid. To take barium chlo-
I'^H n '^^''""PI^t' %'<^3.Aq + 2HCl.Aq = Baa,.Aq
+ n^U + CU,. Now barium carbonate is nearly insol-
uble m water, but the portion which dissolves is ionised •
and, as explained above, when the portion which is ionised has
THE HALIDES 53
reacted its place is taken by more of the carbonate entering
W.th the hydrox.des, the same kind of reaction takes place :
Ca(OH),.Aq + 2Hi3r.Aq -= c:B"r...Aq + 2H .O.
i hese salts are also white and soluble in water. There is
however, one exception, namely, calcium fluoride, CaF !
which occurs native as fluor- or Derbyshire spar. It fornfs
colourless cubical crystals, and is the chief compound of
flu^orine. It is produced by precipitation: CaCI,.Aq +
2KF.Aq = CaF.+ 2KCi.Aq. The calcium fluoride is
non-ionised, and comes down in an insoluble form.
Wa^er of CrystaWsation.-The other halides of
this group crystallise with water of crystallisation ; its
amount varies trorn 7 molecules, as in BaI...7H.,0, to i as in
iSnCl H,U. The retention of this so:called « water of
crystallisation has not yet been satisfactorily explained.
It was for long believed that such compounds were "mole-
cular, as opposed to atomic ; that is, that the water
molecules combined as wholes with the salt, and not by
virtue of their atoms ; but it is more probably to be explained
by the tetravalency of oxygen, although even wifh this
assumption it is not easy to ascribe satisfactory constitutional
formulae m all cases. It must at the same time be assumed
that the halogen atoms are of a higher valency than unity :
possibly triad, or even pentad. '
These salts are hydrolysed in solution to a small extent ;
hus a solution of magnesium chloride, besides containing a
large number of lons, has also reacted with the water to form
^ A'?''/i^T?'* hydrogen chloride: MgCl., + zHrOH)
= Mg(OH), + .HCI. As the solution ^tcomel con-
centrated on evaporation, the hydrogen chloride volati-
hses with a part of the water ; and a mixture, or rather a
compound, of the ox.de and chloride remain,. Hence these
chlorides cannot be obtained in a pure state by evaporating
their solutions. They exhibit another property, however!
54
MODERN CHEMISTRY
which makes it possible to obtain them in a pure state,
namely, the power of forming '* double halides." This pro-
perty is not well marked with the halides of calcium, barium,
and strontium, but the halides of beryllium, magnesium,
zinc, and cadmium are notable in this respect. We have,
for example, MgCl^.KCl/iH.O, ZnCL-NH^Cl, and many
similar bodies. In solution, such compounds are mainly
ionised into their simple ions, but on evaporation the non-
ionised salt separates in crystals, and is not subject to
hydrolysis. Hence such salts can be dried without decom-
position. The ammonium salts, when sufficiently heated,
lose ammonia and hydrogen chloride by volatilisation, and
the anhydrous halide is left]: MgCl2.NH^Cl = MgCl.,+
NHg + HCl. The mode of combination of these double
salts is possibly owing to the fact that the halogens are
XUCIK
capable of acting as triads ; thus Zn<
may be
^C1 = C1K
taken as the constitutional formula of that particular salt.
The mono-halides of copper, silver, and gold may be
attached to the first group ; and if that is done, the mono-
halides of mercury must also be included. These com-
pounds are all insoluble in water, and are consequently
obtained by precipitation or by heating the higher halides,
where these exist. Thus CuCl and AuCl are obtained
by cautiously heating CuCl., and AUCI3 ; they are white
insoluble powders. Cuprous chloride is more easily
obtained by removing half the chlorine from cupric chloride
dissolved in concentrated hydrochloric acid, by digesting
it with metallic copper: CuCio.iHCl.Aq + zHCl.Aq
+ Cu = CuoCl<,.4HCl.Aq, a brown compound, which is
decomposed by water into Cu.^Clo and 4HCl.Aq ; the
cuprous chloride is thrown down as a snow-white powder.
With silver and mercury^ the chlorides AgCl and HgCl are
formed by precipitation from the respective nitrates, AgNOg
and HgNOg, on addition of soluble chlorides. The bromides
and iodides are similarly formed, and are also insoluble.
THE HALIDES
55
There are several interesting points connected with these
halides. Fir«, as regards their colour; the chlorides are
white; cuprous bromide is greenish brown, while the brom-
ides of silver, gold, and mercury are yellow ; and cuprous
iodide is brownish, and the iodides of the other metals darker
yellow than the bromides. It appears as if the colour was
influenced both by the metal and by the halogen. Next,
the chlorides of copper and mercury give evidence of
possessing the double formulx Cu.,Cl.^ and Hg^Cl.,, which
would imply that the metals were only pseudo-monads,
and that the structural formulx should be Cl-Cu— Cu— CI
and CI— Hg— Hg— CI ; and this would correspond with
the fact that the chlorides CuCl., and HgCl., are also
known ; but, on the other hand, as AgCl in the state of gas
has the simple formula given to it, it may be that it is the
halogen which forms the bond of union between the two
half-molecules, thus : CuCI-=ClCu. Silver forms no higher
halides.
The fluorides of these elements differ from the others in
being soluble in water ; they are prepared from the oxides
with hydrofluoric acid. They are very difficult to dry,
for they undergo the reverse reaction, and are hydrolysed
into oxide and hydrogen fluoride on evaporation.
Copper and mercury also function as dyads ; that is,
their ions are capable of carrying a double electric ch"""'-
under certain circumstances. What the mechanism of tr.rs;
change is, we do not know ; but the change in valency car.
be induced by presenting to the element a larger amount :-f
halogen, if it is desired to increase the valency, or by remo r-
ing halogen if the opposite change is required. The addition
of halogen to the mono-halide is in each case an exothermic
change, and its converse is an endothermic one. Cuprous
or mercurous chloride, heated in a current of chlorine
changes to cupric or mercuric chloride, and the converse
change can be brought about by heating the higher halidc
in a current of hydrogen, or by exposing the lower halidc
to the action of nascent hydrogen ; but it is difficult to
56
MODERN CHEMISTRY
prevent the action in the lattei case from going too far and
yielding the metal. A solution of cupric chloride saturated
with sulphurous acid in presence of hydrochloric . "id, and
then diluted with water, gives a precipitate of cuprous
Cu,Cl,.4HCI.Aq + ri..SO,. Aq. the sulphurous acid re-
moves oxygen from water, liberating hydrogen in presence
of the cupric chloride, and the latter is deprived of half
Its chlorine and reduced to cuprous chloride. Similarlv,
stannous chloride forms a recfucing agent for mercuric
chloride : iHgCI.,. Aq + SnCI._,. Aq = H^XL. + SnCI .. Aq.
1 he converse change car be produced by expo'sirg the lower
hahde in presence of halogen acid to the action of nascent
oxygen : Cu^Cl, + iHCl.Aq + O = 2CuCl...Aq + H .O.
Ihis Gxyg^en in the case of copper may be molecular, 6,.
but for the formation of the higher halide of mercury, it
must be derived from some substance capable of par'ting
readily with oxygen, such as nitric acid.
Cupric iodide is very unstable, and readily yields up
iodine, forming cuprous iodide. On mixing cupric chloride
with potassium iodide, the cuprous iodide is precipitated :
2Cua.Aq + 4KI.Aq = CuX + 4KCl.Aq + I... It is to
be noticed that the dyad cupric ions ha-e lost two charges,
and that these have neutralised the two negative charges of
the lodme ions, causing them to be precipitated. (Inasmuch
as the cuprous iodide is insoluble, it should not have had the
ionic signs attached ; but they have b.en kept in order to
show the changed valency. ) Mercuric iodide is an insoluble
scarlet precipitate, and is therefore best produced by pre-
cipitation. It dissolves, however, in a solution of potassium
iodide, forming a double salt, of which more shortly.
Aunc chloride contains triad goid, and thus' has the
formula AuClg. It is nor nroduced by the direct action
of chlorine on gold, becau : the temperature of attack is
above the temperature at which the compound is decomposed.
Hut It IS possible to volatilise gold in a current of chlorine
THE HALIDES
57
because a few molecules escape decomposition and arc
volatilised along the tube through which the chlorine is
p -sed, and on cooling the gold is deposited, owing to the
decomposition of the chloride at a lower temperature. It
may appear paradoxical that the chloride is stable at a
higher temperature than that at which it decomposes ; but
it is to be presumed that the ditfercnce of temperature
between one favourable to an exothermic and to an endo-
thermic action is very small ; and as endothcrmic substances
increase in stability on rise of temperature, the chloride is
capable of volatilisation ; on cooling it becomes unstable and
undergoes decomposition with deposition of gold. The
usual method of preparing this salt is to dissolve gold in
a mixture of nitric and hydrochloric acids. This mixture
yields ionic chlorine, the negative charge of which neutralises
the positive charges of the gold ; but there are corresponding
negative charges set free, which are transferred to the ion
NO3 of the nitric acid, converting it into 2O, with its four
negative charges. The latter combines with the hydrogen,
forming electrically neutral vater: 3HCl4-HN03.Aq +
Au = 2H,0 + Au CI3 . Aq + NO.
Auric chloride forms dark red crystals ; it is soluble in
water, and when mixed with chlorides of the alkali metals
forms a set of salts termed aurichlorides. The potassium
salt, for example, has the formula K AuCl^ ; it is soluble in
water, but, unlike the "double salts," such as MoCl,..2KCl,
already alluded to, it is ionised by water, not tnto" simple
+
ions like these, but into the ions K and the complex group
AuCl^. At the same time there exists in the solution a small
number of simple ions, so that on electrolysis gold is deposited
at the kathode, but the primary effect of the current is to
send the aurichloric ions to the anode. The solution of mer-
curic iodide in potassium iodide, of which mention was
madebefore.is a half-way example of the same kind. Its solu-
58
MODERN CHEMISTRY
+ -
tion contain! ions of K and Kgl , but these are mixed with
a much larger proportion oi he imple ions, K and I and
Hg and I^. All grades of such salts arc known ; indeed it
is probable that the double sa' .>; si;:i as magnesium-potassium
chloride, contain a small r . vr i complex ions of MgCl^.
These halides have be n < ni;.i,'ered at length because
they form types of the otl rs. ' .,e will be made of the
examples given in treating <>t tin icinainin'^ halHes.
We have seen that the hali '« . mav r • djr-r- either ionisa-
tion or hydrolysis, or both . once. ! hi ligation may be
more or less complete, and *k h;.Ji. -Pi<
KCI=CK \:i NH,C1=CK ^Cl
Hahdes of certain complex groups are also known.
When these contain oxygen or hydroxyl, (OH), they are
generally termed basic salts or halo-acids; they will be
considered later. The others may be divided into two
classes : those like ammonium halides, and those derived
from hydrocarbons.
Ammonium and phosphonium halides. — These hal-
ides, which are formed by direct addition of the hydrogen
halide to ammonia or to phosphine, closely resemble in
colour, in crystalline form (cubic), and in reactions, the
halides of the lithium group of metals. On mixing a solution
of ammonia and hydrochloric acid, for example, the combina-
tion occurs: NH3.Aq + HCl.Aq = NH^Cl.Aq ; and on
evaporating the solution to dryness, ammonium chloride is
left in an anhydrous state. From the conductivity of
ammonia solution, it is known to contain a certain amount of
NH^OH in an ionised condition ; and the equation .nay be
written: NH.OH.Aq + HCI.Aq = NH^Cl.Aq + H,0.
VOL. II. g
66
MODERN CHEMISTRY
As the hydroxy! ion is removed from the solution by the for-
mation of practically non-ionised water, more and more am-
monium hydroxide is formed to maintain equilibrium between
the NHg. Aq and the NH^OH.Aq ; and the whole is ulti-
mately transformed. The rate of transformation, however,
is a very rapid one. Combination has been shown not to
take place between perfectly dry ammonia and dry hydrogen
chloride ; hence it does not seem unlikely that ionisation
may occur, either in the gaseous state, or more probably on
the surface of the vessel in the condensed layer of moisture
which appears always to adhere to all solid surfaces. Once
started, combination occurs continuously until the reaction is
complete. Ordinarily "dry" ammonia, however, at once
gives a dense cloud with hydrogen chloride, bromide, or
iodide. Again, perfectly dry ammonium chloride has the
vapour-density 26.25, corresponding to the molecular
weight (N=i4 + H4 = 4 + Cl = 35.5) = 53-5; whereas, if
moist, the density is half that amount, corresponding with
a mixture of NH3 = 1 7 and HCl = 36.5. These compounds
have densities of 8.5 and 18.25 respectively, and a mix-
ture in equal proportions of each has a density the mean of
the two, viz., 13.125. It appears necessary that ionisation
+ -
into NH4 and CI should take place before dissociation into
NHg and HCl is possible. The electrically neutral body
+
NH^Cl can volatilise unchanged ; the ions NH^ and CI
are incapable of volatilisation as such, and in volatilising
unite their opposite charges, and form the two electrically
neutral compounds HCl and NHg.
Phosphine, PHg, also unites wi'.h hydrogen chloride,
but only under high pressure, at the ordinary temperature.
On ihe other hand, phosphonium iodide, PH^I, is pro-
duced by the union of phosphine with hydrogen iodide
under atmospheric pressure ; it forms white, cubical
crystals, which, like ammonium chloride, dissociate when
heated. The hydrides of arsenic and antimony form no
such compounds.
PHOSPHINE GROUPS 67
It must be assumed that these compounds are formed
with change of valency of the nitrogen or phosphorus ; the
triad becomes pentad ; the N"'H3 becomes H.NTI. On
distilhng with sodium hydroxide or slaked lime, water is
tormed, and the element is reduced to its original triad con-
dition, thus : NH^Cl.Aq + NaOH. Aq = NH^H.Aq +
NaCLAq, and NH,OH.Aq = NH3 + H.,O.Aq, two
electrically neutral bodies. 3 j m»
Carbon shows no such tendency to change valency.
1 he hydrocarbons of the methane series are "saturated"
M* ^^%T'^ "° tendency to take up any other element.
Hence halogen must replace hydrogen. This can be done
either directly, by the action of the halogen on the hydro-
carlxjn, as for instance, CH, + CI., = CH3CI + HCl ; or
indirectly Ly the action of the halogen acid on the hydr-
oxide : CH30H + HC1 = CH3C1 + H.,0. Such hydr-
ox^es are termed alcohols ; that derived from ethane,
S^«; ''.^^'^^^'•"l^y anhydrous alcohol of commerce ; its
formula '« C H^OH, and the corresponding chlorid; of
ethyl IS C,H,C1. It will be remembered that the struc-
tural formula of ethane is H^C~Cf H, and that of
ethyl chloride is H-)C-C(1-C1. There is, however, a
difference between the formation of ethyl chloride, for
example, and of sodium chloride. Whereas sodium chloride
is ionised m solution in water, ethyl chloride is insoluble,
and IS therefore non-ionised. Hence the action is a slow
one; the alcohol ir saturated with hydrogen chloride,
allowed to stand for some hours, and distilled ; ethyl
chloride, being volatile passes over ; it is a gas, condensing
at about 12 to a mobile colourless liquid. It is probable
that the hydrogen chloride is ionised in solution in alcohol ;
the alcohol IS also possibly ionised to a minute extent •
68
MODERN CHEMISTRY
water is formed by the union of the hydrogen and hydroxyl
+ -
ions, and non-ionised ethyl chloride distils over : C^H-OH
+ -
+ HCl.Alc = H.,0 + C.^iCI. But this suggestion, it
must be admitted, is somewhat speculative, and is based
only on analogy with reactions of a more familiar nature.
The formation of some of the halogen compounds of the
olefines, and of hydrocarbons of the acetylene and benzene
series, has already been alluded to on p. 48.
CHAPTER IV
HydnxUea and Acids-" laaoluble Subataacea '*-
ladlcaton-Prepantloa oi Baalc Oxldea-Pro-
pertlea of the Baalc Oxidea and Hydroxldea-
Sulphldes-The "Solublllty^Product"- Basic
Oxidea and Hydroxidea of Complex Qroupa:
Alcohola, Aldehydea, Etbera; and Sulpblnea,
Aminea and Pboapblnea.
The Oxides and Hydroxides, Sulphides and
Hydrosulphides, Selenides and Tellurides.—
Owing to the dyad valency of oxygen, sulphur, selenium,
and tellurium, compounds of these elements are more
numerous than those of the halogens. And whereas double
hahdes of hydrogen and other elements are not numerous,
bemg conhned to such bodies as H^SiF , HBF H PtCl
and a iew others, those of the oxides are very numerous,'
and form two important classes, the "hydroxides" and
the " acids.
Hydroxides and Adds.— Members of both these
classes may be regarded as hydroyxl, that is, water minus
one atom ot hydrogen, -OH, in combination with elements,
but they differ raaically in that the true hydroxides ionise
into^element and hydroxl, thus: NaOH.Aq, Ca(o'H).,.Aq,
^' i^^)3'f whereas acids ionise into hydrogen and a
D^egatively charged radical, thus: HOCl.Aq, HNO^.Aq,
H(HSOJ.Aq, Hio^.Aq, and many others. There
69
70
MODERN CHEMISTRY
are certain hydroxides in which the ionisation may talce
either form ; such compounds are said to be either "basic "
or "acid" according to circumstances; thus, aluminium
+ + + -
hydroxide, Al(OH)3, is basic; with hydrochloric acid
+ + + -
It reacts in the following manner: Al(OH)3.Aq +
3HCl.Atie S& CO
OXIDES AND
HYDROXIDES
o o K S
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U C5 S
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74
MODERN CHEMISTRY
SOo and MoOg ; but manganese also forms 03Mn(0K),
termed potassium permanganate, which is analogous in formula
as well as in crystalline form with potassium perchlorate,
03C1(0K). It is convenient, however, also to include
chromium and manganese in the iron group of elements.
Cr(OH).,
OCrdroxides are
prepared from the carbonates by boiling a solution witii
slaked lime (calcium hydroxide) : Na.,C03.Aq +
Ca(OH),Aq = 2NaOH.Aq + CaC03; or by heating to
redness a mixture of the carbonate with ferric oxide, when
the ferrite is formed : K.JCO^ + Fe.Pg = 2 K FeO., 4- CO.,.
On treatment with water, potassium ferrite is decomposed,
thus: KFe02 + 2H20.Aq=KOH.Aq + Fe(OH)3.
INDICATORS
75
t
I
In either case, the solution of hydroxide is evajwrated to
dryness in an iron vessel and fused.
These Jiydroxides are said to be basic, for they are
neutralised by acids, forming salts. Thus, with hydro-
chloric acid, KOH.Aq + HCl.Aq=KCl.Aq + H,0,
the point of neutralisation— that is, when the acid anc! iiase
are present in theoretical quantity to form the Fill and water
— is determined by the addition of an " indicator."
Indicators, — The most important indicators are litmus,
phenol-phthalein, and methyl -orange. I.itmus is a weak
acid, red in colour, the salts of which are blue. When
dissolved in water, the molecule is hardly at all ionised,
hence the red colour of the acid is alone visible. If a base
such as sodium hydroxide is added, which, in aqueous solu-
tion, is largely ionised into Na.Aq and OH.Aq, the
hydroxyl ions combine with that portion of the hydrogen
ions of the litmus acid which exist in solution ; when these
are withdrawn, more hydrogen ions take their place, and the
solution acquires the colour of the ion of the litmus acid,
VIZ., blue. Conversely, if an acid be added to a base in
which the blue litmus ione are present, the hydrogen ions of
the acid combine with the hydroxyl ions of the base, forming
water, so long as any are present; after they are all in
combination they convert the ion of the litmus acid into the
red acid, non-ionised, and there is a marked colour-change.
As the colours of the litmus acid and of its ion are both
very bright, the presence of a mere trace of the indicator
suffices. Phenol-phchalein, like litmus, is also a weak acid,
that is, it is hardly ionised at all in dilute solution ; the acid
IS colourless, but the ions are pink, hence the addition of a
trace of free alkali causes the colourless solution to become
pmk. But this indicator gives results only with strong bases,
like the hydroxides of the alkalies ; with ammonium hydr-
oxide, present in a solution of ammonia in water, it is not a
good indicator, for NH^OH is too weak a base, i.e. the
hydroxyl and ammonium ions are present in too small amount
76
MODERN CHEMISTRY
to liberate the ions of the phenol-phthalein, unless much
ammonium hydroxide is present in solution. Hence the
presence of a trace of free ammonium hydroxide is not
revealed by that indicator. Phenol-phthalein is therefore
serviceable only with strong bases, but it may be used for
weak acids. Methyl -orange, on the other hand, is a com-
paratively strong acid ; with a weak base it forms the ions
of a salt, and it may therefore be used for weak bases like
ammonium hydroxide, or for strong bases like the hydrox-
ides of the alkali metals ; but it is too strong an acid to
serve well as an indicator of excess of a weak acid, such as
carbonic or acetic acid. Its colour-change is from orange
to orange-pink.
Prepantioa of Basic Ojr/des.— The hydroxides of
the metals of the sodium group, as already mentioned, do
not lose water on heating, and the* ox ides, therefore, cannot
be thus obtained. Neither do their carbonates lose carbon
dioxide, nor their nitrates oxides of nitrogen, save at an im-
practicable temjierature. But all other basic oxides may be
prepared by heating the hydroxides, carbonates, or nitrates
of the metals, and a few may be obtained by heating the
sulphates. Oalcitun and strontium oxides are generally
prepared from the carbonates, which are found as minerals,
named limestone and strontianite respectively. The opera-
tion of preparing «* quicklime " or calcium oxide is techni-
cally, but wrongly, called " burning." Alternate layers of
lime and coal are placed in a tower of brick or stone,
termed a limekiln ; the coal is set on fire, and its heat
expels the carbon dioxide from the carbonate : CaCO^ =
CaO+CO^,. If calcium carbonate be heated in a closed
vessel, however, so that the carbon dioxide does not escape,
the dissociation proceeds until the amount of carbon dioxide
in the vessel has reached a certain proportion, which is per-
fectly definite for each temperature, or until the carbon
dioxide has attained a certain «♦ concentration." The reaction
then stops. But if the carbon dioxide be removed as it is
formed, the reaction goes on to the end, until all carbon
BASIC OXIDES 77
dioxide has escaped. The draught in the kiln removes the
carbon dioxide, hence the product is calcium oxide. Stron-
tium carbonate is causticised in the same way as limestone ;
but the temperature for witherite (BaCOg) is inconveniently
^•gj> 5 ^baryta is consequently prepared by heating the nitrate,
^'^(NOa)^ ; it may be supposed to split into BaO and
N^.Oj; the latter, however, decomposes even at moderate
temjieratures into NO., and O ; hence the equation is •
2Ba(N03), = 2BaO + 4NO., + 0... These oxides are
whitish-grey solids, volatile at the tenij)erature of the elec-
tric arc, and combining with water with great rise of tem-
perature to form hydroxides. The hydroxides are sol-
uble in water — barium hydroxide most, calcium least. An
aqueous solution of the former deposits crystals of a hydrate.
Ba(0H),.8H,0. i ^ y .
The sparing' solubility of calcium hydroxide makes it
possible to precipitate it by the addition of caustic alkali to a
soluble salt of calcium, provided too much water is not pre-
sent : CaCI,.Aq + 2NaOH.Aq = Ca(OH)..+ 2NaCI.Aq.
Of course, a saturated solution of calcium hydroxide remains,
hence the precipitation is not complete. This plan is appli-
cable to the preparation of all hydroxides which are insoluble
in water, unless they dissolve in excess of the caustic alkali ;
if they do, they are said to display " acid " properties]
Beryllium and magnesium hydroxides are thus piecipiuted •
Mga.Aq + 2KOH.Aq = Mg(OH).,+ 2KCl.Aq. The
hydroxide may be hitered off and dried", and the white mass,
on Ignition, leaves the oxide as a white powder. By this
means, too, the hydroxides of copper (cupric, Cu(OH ) ),
■ilver, AgOH, auc, Zn(OH}.„ cadmium, Cd(OHJ.„
aluminium, A1(0H)3, scandium, yttrium, lanthanum,
and ytterbium, gallium, indium, and thallium, with
similar formulx, titanium, zirconium, thorium, with
formula OM(OH),, (where M stands for an element of
that group; germanium, tin (stannous, Sn(OH)„ and
stannic, Sn0...nH,0), lead (plumlxjus, Pb(OH),); bis-
muthous, Bi(OH)3, chromic, Cr(0H)3, and chromous
78
MODERN CHEMISTRY
:
Cr(OH)2, nianganic and manganous, ferric and ferrous,
cobaltons and nickeloos : in short, from all elements which
form «• basic " hydroxides. And from almost all these the
oxides may be obtained by heating the hydrates to redness.
Excess of the precipitant, however, must be avoided in many
cases, for some of these hydroxides display acid properties
if in presence of excess of alkali. Thus, for example, if
excess of sodium hydroxide or potassium hydroxide be
added to the solution of a soluble salt of zinc, such as the
chloride, nitrate, or sulphate, the first change, as already
shown, is the precipitation of the hydroxide ; but on additi m
of excess of alkali, the precipitate redissolves, forming the
compound Zn(OK)^,.Aq, of which the ions are K, K, and
ZnOo ; this compound is thrown down by alcohol, in which
it is insoluble. It is generally named zincate of potassinm.
Cadmium forms a similar compound, but that of aluminium
has the formula OAl(OK) ; the hydroxide, AI(OH)3, »"
losing water is transformed into the condensed hydroxide,
OAl(OH), which may be termed aluminic acid, of which
the hydrogen atom is exchangeable for meuls. Stannous
and plumbous hydroxides dissolve in excess of alkali, doubt-
less forming compounds similar to that of zinc ; and chromic
hydroxide is soluble in cold solution of caustic alkali, form-
ing, no doubt, a compound analogous to that of aluminium ;
but It is decomposed on warming, with reprecii)itation of the
hydroxide. The hydroxides of all these elements may also
be precipitated by a solution of ammonium hydroxide, and
some of them are redissolved ; but the compounds formed
are of a different nature from those descrilied in the case of
zinc, &c., and will be afterwards considered.
Properties of the Hydroxides.~As regards the
l)roperties of the hydroxides, that of copper (cupric) is light
blue, and of silver, brown ; chromic hydroxide is grey-
green, and chromouh, yellowish ; manganic, brown, and
manganous, very pale pink ; ferric, rust brown, and ferrous,
white when pure, but usually dirty green ; cobaltous, dingy
I
PROPERTIES OF HYDROXIDES 79
red, and nickelous, grass-green. The others are all white
amorphous bodies, and they all yield oxides on heating.
Cupric oxide is black ; even when lx)iled with water the
hydroxide loses water and changes colour. Argentous
oxide is brown ; when heated to redness it loses oxygen,
leaving a residue of metallic silver. Zinc oxide is yellow*
when hot and white when cold; cadmium oxide is a
brown powder; the oxides of aluminium, scandium,
yttrium, lanthanum, ytterbium, gallium, and indium, and of
titanium, zirconium, thorium, germanium, and stannic oxide
are white powders ; thallium oxide is a yellow jjowder ; tin
monoxide is a black powder ; that of lead (litharge, massi-
cot) is a yellow substance, fusible at a red heat ; bismuth
sesquioxide is a yellowish powder; chromic, ferric, and
manganic are resi)ectively green, rust-red, and brown;
chromous oxide is unknown, for any attempt to dry it
results in the decomposition of water, the absorption of its
oxygen by the chromous oxide which becomes chromic
oxide, and the evolution of hydrogen. Ferrous hydroxide
can be dried, but only with rigid exclusion of air ; it
is a black powder. Manganous oxide is greyish-green,
cobaltous, olive-green, and nickelous also greyish-green.
Manganous hydroxide must also Ix.- dried in absence
of air.
These hydroxides and oxides are named bases. There
are some basic oxides, which are j)recipitated by adding a
hydroxide, such as that of sodium, to a soluble salt, and to
which there is no corresponding hydroxide. This is the
case with the oxides of mercury. On referring to the
table of halides on p. 50, it will lie seen that the chloride
of mercury has the formula HgCI.,. This compound,
commonly called corrosive sublimate, wlien treated in solu-
tion with sodium hydroxide, gives a precipitate, not of
hydroxide, as might iy» expected, but of oxide: HgCI .Aq
+ 2NaOH.Aq =. HgO + iNaCl.Aq + H.,0. Simifarly,
a soluble mcrcurous salt, such as mercurous nitrate,
Hg._,(NO.,)^„ on treatment with an alkali gives a i)recipitate
^.--.■c^-? r^;-i2a£te*!»:^2ai^: ;s-:
8o
MODERN CHEMISTRY
of mercurous oxide: Hg.,(N03).,.Aq + 2NaOH.Aq =
HggO + iNaNOj.Aq + H.^0. These arc cases of relative
stability ; for, as has been already remarked, on boiling a
solution from which cupric hydroxide has been precipitated,
the blue hydroxide is changed into black oxide ; other
hydroxides lose their water at a still higher temperature ;
while those of the alkaline metals may be volatilised without
decomposing.
Oxides produced by Heating Carbonates,—
Most of the basic oxides may also be prepared by heating
the carbonates, a class of salts afterwards to be discussed.
The carbonates of the alkali metals, however, are not thus
decomposed ; like their hydroxides, they may be volatilised
without decomposition. But all other carbonates are de-
composed by exposure to a red heat. The process has
already been described as a method of manufacturing quick-
lime. Most carbonates, however, do not require the same
high temperature; a dull red heat suffices. And the
oxides do not, as a rule, recombine with the carbon dioxide
expelled, as does lime ; hence there is no danger of re-car-
bonating the oxide.
Oxides produced by Heating Nitrates.—Thc
nitrates, too, of nearly all the basic metals, yield the respec-
tive oxides vvh.ci: they are heated to bright redness. The
nitrates of the alkali metals in this instance, as in others, do
not behave in this way. When heated they lose oxygen,
but only at a very high temperature, forming the nitrites, a
class of salts afterwards to be described. Thus, potassium
nitrate undergoes the decomposition : zKNOg^ 2KNO0 +
O.,. The product of heating the other nitrates, however, is
the oxide, while a mixture of oxides of nitrogen is evolved.
This may be supposed to take place in two stages : first,
the nitrate may be imagined to decompose into the oxide
and nitrogen pentoxide, thus : Zn(N03)., = ZnO -f-N.^O. ;
the last compound is very easily decomposed by heat, and
yields a lower oxide of nitrogen: 2N.,05 = 4NO., 4- 0„ ;
while if the temperature is over 600°, which is usually
SULPHIDES AND HYDROSULPHIDES 8i
exceeded in decomposing the nitrates, the nitric peroxide is
NO and O * products, therefore, are NO.^,
A metal which forms two oxides, one containing more
1217 M '^t °i^'[' '^ '^' ""^^^^ «*' '^' J«^" oxide is
heated, yields the higher oxide. Cases of this are mercury.
tm. and iron. Mercurous nitrate, carefiilly heated, gives
HaNo'"Tn''lTX"«^'°'.^"^ '"^^^'""c oxide. HgO
HgNO, = HgO + NO., ; similarly SnCNO J , yields SnO
and not SnO ; and FefN03),. fIoJ, ancf ii^t' Fea " ^'
Oxides produced by Heating Suip/iates.^
1 he sulphates require a higher temperature than the nitrates
tor their decomposition, consequently they are not generally
used as a source of oxides. But the equivalents of mag-
nesium, zinc, and some other metals have been determined
by estimating the weight of oxide obtainable on heating a
weighed amount of sulphate ; and ferrous sulphate has b^n
distilled ,n fireclay retorts for many years Jast at Nord-
hausen. in f>axony, for the purpose of making « Nordhausen
su^huric acid." H,S,0„ and red oxide of iron, Fe.O "
which, made in this way. has a fine colour, and is used 'as a
pamt. When a sulphate is heated, the gas which escapes
IS not entirely SO3, as might be imagined from the
equation: MgSO, = MgO + SO3 ; the high temperature
decomposes most of the sulphur trioxide into the dioxide.
bU and oxygen ; and the oxygen, in the case of ferrous
sulphate, oxidises the FeO into Fe. O .
Sulpliides and Hydrosuiplii'des.—The analogy
between the elements oxygen and sulphur is well shown
by comparing the sulphides of the elements of which the
oxides have been described. Elements of the lithium
group form both hydrosulphides and sulphides ; thus we
know sodium hydrosulphide. NaSH. analogous to the
hydroxide NaOH. and sulphide, similar in formula to
the oxide Na^O, Na,S. Hydrogen sulphide is a
weak acid ; fience, on passing hydrogen sulphide ^brQu«h
VOL. 11.
82
MODERN CHEMISTRY
a concentrated solution of sodium hydroxide at 95° until
saturation is complete, white crystals ot NaSH.2H.jO
deposit on evaporation. The equation is : NaOH.Aq
+ - + -
+ HSH. Aq =. NaSH. Aq + H ,0. On mixing the solu-
tion with an equivalent quantity of sodium hydroxide and
evaporating, the sulph: le is produced: NaSH.Aq +
+ - + - -
NaOH. Aq = Na., S. \q + HoO. Here it must be sup-
posed that the hydrogen of the hydrosulphide i» present as
an anions and that it reacts with the hydroxyl of the caustic
soda, forming water, while the sodium sulphide remains in
solution in an ionised form, and can be recovered on
evaporation in crystals with gH.^O. Similar compounds
exist with potassium.
Caldnm, strontium, and barium also form hydro-
sulphides and sulphides, analogous in formula to the
hydroxides and oxides. They are similarly prepared to
the sodium compounds, but, as the metals are dyads, their
formulx are M(SH)o and MS; and there is an inter-
mediate compound between the hydroxide and hydro-
sulphide, having, in the case of calcium, the formula
HSCaOH. They are also soluble in water. Magnesium,
too, forms a hydrosulphide, probably Mg(SH),; it is
prepared by passing sulphuretted hydrogen into water in
which magnesium oxide is suspended. It is unlike the
hydrosulphides of the alkalies, for while they do not
decompose with water, it, on the contrary, when its solution
is heated to 80°, reacts with water, yielding hydroxide
and sulphuretted hydrogen: Mg(SH)^.Aq -t- 2HOH =
Mg(OH)., + 2H.,S. The probable explanation of this
change is "that water is not wholly non-ionised, but that
there are present some hydrogen ions ; these are not so
inconsiderable in number, compared with those of the weak
acid H.jS ; on raising temperature, a certain amount of
hydrogen sulphide is liberated, and, being volatile, it escaj)es,
THE SOLUBILITY-PRODUCT 83
and is no longer present to act on the magnesium hydroxide
and reconvert it into sulphide.
Sulphides of boron, aluminium, chromium, and
■ilicon are at once decomposed by water, and cannot,
therefore, be produced in aqueous solution. Thev are
white substances fornied by heating the elements to a' Wwh
temjjerature m a current of sulphur vapour.
The sulphides of copper, silver, gold, cadmium,
mercury, rndium, thallium, tin. lead, arsenic, anti-
mony, and bismuth, and of the metals of the palladium
and platinum groups, me all insoluble in water, or, to be
more accurate, very sparingly soluble. They form no
hydrosulphides. Hence they are precipitated from soluble
salts of these metals by addition of sulphuretted hydrogen ;
they form flocculent precipitates, usually characterised
by striking colours, and are therefore generally used as a
means of recognising the metal. CuS. Ac S Au S
HgS, Tl,S, Us/pbS, PtS... and the' othr'sulrdi*
oi the platinum group of metals are black ; CdS, SnS' and
AsA are yellow .^In,S.„ SnS, and Bi^S, are brown, and
&b bg IS orange. These sulphides are n6t attacked by dilute
acids. On the other hand, the sulphides of zinc, manganese,
iron, cobalt, and nickel are not precipitated by hydrogen
sulphide, but they are thrown down by a soluble sulphide
or hydrosulphide, such as those of ammonium or sodium.
1 hey, too, form flocculent precipitates; ZnS is white, MnS
pink and FeS, CoS. and NiS are black. The reason of
the difference in the behaviour of the two classes of sulphides
18 an interesting one, and will be now explained.
Solubility Product,~lt has already l^en mentioned
on p. 14 that the rate of chemical change depends on the
amount of each of the reacting; substances present in unit
volume. 1 his last is generally termed the « concentration "
of these substances, for the more concentrated the solution
the greater the mass present in unit volume. Now, if two
kinds of ions, such as N^ and CI, are present in solution.
1
84
MODERN CHEMISTRY
necessarily in equal numbers, the solution will also conuin
a certain number of molecules of non-ionised NaCl, formed
by their union, and the relative number of ions and mole-
cules will depend on the concentration ; the number of ions
in proportion to the number of non-ionised molecules will
be greater, the greater the dilution. For each diluti-.
(and for each temperature) a state of balance will result;
the position of this equilibrium will depend on the relative
rate at which ionisation and union of ions to form mole-
cules go on ; if ionisation takes place twice as quickly as
combinations of ions to form molecules, then two-thirds
of the dissolved substance will exist as ions, the remain-
ing third being non-ionised molecules. It the solution is
made more concentrated by evaporation, the conditions are
changed, and the rate of ionisation is reduced compared
with the rate of union of ions with each other. Suppose
that concentration be pushed so far that solid salt separates
the limit of concentration will be reached, since it is
out
now impossible to alter the number of ions and of molecules
in unit volume of the solution. The ratio will now remain
constant, and if e and c be the concentrations ot the ions
(and they are, of course, equal), and if C be that of the
non-ionised molecules, then cc =k.C^ k being a factor ex-
pressing the relative proportions of the non-ionised mole-
cules. If i is very small, then there are many molecules
and few ions present ; if, on the contrary, i is large, the
ions are numerous and the molecules few. The expression
k.C is termed the ••solubility-product."
To take a specific case : — A solution of ammonia in
water consists partly of the ions NH^ and OH, and
partly of non-ionised molecules of NH^OH ; it is a
weak base — ^that is, the number of non-ionised molecules
is much greater than that of the ions. In a solution con-
taining 1.7 grams of ammonia per litre (one-tenth normal
solution), only 1.5 per cent, of the total number of mole-
cules exist in the ionic state. Hence a solution of ammonia,
uallkc one of caustic soda or potash, gives no precipitate
INSOLUBILITY OF SULPHIDES 85
of hydroxide when added to a solution of salts of the
^H;r^m"T^ ^«T' ""'^^ '' "'^'"'"' "rontium, or
barmm chlorides. Wuh salts of the weaker base magnesia,
however, ammonia produces a precipitate of magnesium
hydroxide. It is possible still firther to reduce the ion-
«sat,on of ammonia solution ; this can be done by the
addition of an ammonium salt, such as the chloride, which.
l.ke most such salts, is highly ionisnl. The reason is. th';
while (concentration of NH ) x (concentration of OH) -
fddijT"'""^" °^NH,Ok). if more ammonium ion be
wifh Nh' ""^^Z '^- ^'y^'""^ •°"'' ^'^ ^'•"'"'"h h union
with NH lons, forming non-ionised ammonium hydroxide,
because the increase of the number of ammonium'ions wil
increase the value of the product on the left-hand side of the
equation, and in order that it may balance that of the right,
t relative number of molecules of NH.OH must be in-
creased ; and we may see that if ammonium chloride i. added
to a solution ot magnesium chloride, ammonia solution will
the Zr ^ ' precipitate of magnesium hydroxide;
the ammonia is too weak a base, that is, it contains too few
hydroxyl ions, which are the reason of its basic nature.
.n}riV 7"^ '""'" '"^ '^^ consideration of the insolubility of
8u phides of the copper group in acids and the solubility of sich
sulphides as that 0/ zinc. No substance, as has been before
remarked. IS wholly insoluble in water ; zinc sulphide, how!
ever, belongs to the ^very sparingly soluble compounds.
Hence the product c{Zn)xc(S) has a very small value,
for . ,s equal to /.qZnS). which must nec^sarily be very
small, seeing that the compound is so sparingl/ soluble!
Now, the ions of H,S are H, H, and's"; but though the
.onisation IS very small, hydrogen sulphide being a' very
weak acid, they are yet sufficient to reach the value of
the very small solubility-produce i.C(ZnS). If, however.
the concentration of the V-ions is still further diminished
MICROCOPY RESOLUTION TEST CHART
(ANSI and ISO TEST CHART No. 2)
1.0
I.I
Ik
Li
1^
Z5
2.0
1.8
M APPLIED IIVMGE Inc
S^ '653 tost Main Street
Sr^ Rochester. New York 1A609 USA
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86
MODERN CHEMISTRY
by addition of some compound rich in H-ions, such as
+ - ++ - -
HCl.Aq, then the product f(Zn) Xf'( S ) will be less
than i.C(ZnS), and there will be no precipitate ; or if
hydrochloric acid be added to precipitated zinc sulphide,
it will be dissolved. On the other hand, the addition of
acetic acid, a weak acid, and poor in hydrogen ions, does
not bring about solution of zinc sulphide ; indeed, the pre-
cipitation of zinc from a solution of its acetate by hydrogen
sulphide is almost complete.
The solubility-product of copper sulphide, and of the
other sulphides which are not soluble in dilute acids, is
still less ; hence hydrogen sulphide precipitates them from
acid solution, for the concentration of the S-ions of the
hydrogen sulphide may be very much diminished without
+ +
the product ciCn) xc'( S ) becoming less than i.C(CuS),
for CuS is still less soluble in water than ZnS.
Oxides and Hydroxides of Compiex Groups,
— ^The oxides and hydroxides of complex groups show
analogy in their formulae, and often in their methods of
preparation with the basic oxides and hydroxides. A few
instances of these will now be given.
Ammonia (see p. 42) is very soluble in water ; at the
ordinary temperature, no less than 800 volumes of the gas
dissolve in one volume of water, forming a very pungently
smelling solution named liquor ammonU. This solution con-
sists for the most part of a mixture of liquid ammonia with
water ; it probably also contains ammonium hydroxide,
NH4OH, and, as already mentioned, less than 1.5 per cent.
+
of the ions NH. and OH. It is, therefore, a weak base.
Hydrazine, N2^4> ^^° forms a hydrate, N^H^OH,
a fuming liquid with slight smell (and consequently in all
probability fairly highly ionised) ; it boils at 119°, and is
very corrosive, attacking wood, cork, and even glass. It has
a strong reducing action, so that if added to a solution of
ALCOHOLS
«7
cupric sulphate which contains cupric ions, Cu, it gives an
immediate precipitate of cuprous oxide, Cu.,0, nitrogen
being evolved. Like ammonia, it precipitates" such hydr-
oxides aj that of aluminium, iron, &c. Hydroxylamine,
Wrtg^H, IS a soniewhat similar body, produced by passing
n,tr,c ox'de, NO (see p. 97), through a mixture of granu-
I. J ^^"^ Mrochlonc acid, to which a little platinic
chloride has been added ; the nascent hydrogen reduces
the mtric oxide to hydroxylamine; it unites with the
Sh nwri" '''!?k ^^'■'"'"^ hydroxylamine hydrochloride,
NH3OHCI. After removal of the tin Dy addition of
8odium hydroxide and filtration, the solution is evaporated
to dryness and mixed with alcohol ; hydroxylamine hydro-
chloride dissolves, while sodium chloride remains. A solution
MH n^!"y "t'^A^rf ^y ^'^^^'^^ °^ "'^" hydroxide :
NH3OHCI Aq + AgOH. Aq = AgCl + NH3OH. Aq. If
sodium methox.de (see p. 88) be added to a solution of the
hydrochloride m methyl alcohol, the base is liberated, and
can be separated from the alcohol by fractional distillation ;
it IS a volatile white solid. This compound is interesting
because the OH group is under no circumstances an ion ; ite
solution in water musil contain ions of NHtoH and OH
since It reacts like ammonium hydroxide. '
AIcohoJs.^Thc hydroxides of the hydrocarbon
Wdicles are, as mentioned on p. 67, termed alcohols.^
Ut these there are very many, but a few only will be
chosen to serve as examples : methyl alcohol. CH OH
!Sil''''H-'i: ^"3-CH,0H, as types of monohfdS
alcohols, which may be taken as the analogues of the
hydroxides of the monad metals; glycol.
CHjOH
L
OH
dihydric alcohol, may be likened to Urium hyWide,
' A special class of such hydroxides derived frnm h*n.>»> n u
88
MODERN CHEMISTRY
CHoOH
Ba(OH)<, ; and glycerine (glycerol), CHOH , is a
CH2OH
trihydric alcohol, as aluminium hydroxide is a trihydroxide.
These substances dilfer from the hydroxides, however, by
their being non-electrolytes, and therefore non-ionised.
Or perhaps it is more correct to say that their conductivity
is of the same order of magnitude, but less in value, than
that of pure water. The corresponding halides, for ex-
ample, CH3CI, C^H^Clo, and C3H5CI3, are also regarded
as non-ionised ; they are practically insoluble in water.
Nevertheless, methyl chloride has been transformed into
methyl alcohol by heating with water to a high temperature
in a sealed tube under pressure — CH3CI + HOH =
CH3OH + HCl ; and the others, but preferably the bro-
mides, may be similarly changed into hydroxiJes by heating
with silver hydroxide, or with silver oxide and water :
CHoBr CHJDH
CHBr + 3AgOH.Aq = CHOH .Aq + 3 AgBr. Is it
CH^Br CH2OH
possible that at a higher temperature the ionisation is suffi-
cient (though it must be exceedingly small) to produce the
interaction ?
The metals sodium and potassium dissolve in the alcohols,
with evolution of hydrogen, forming compounds somewhat
analogous to the hydroxides ; instead of hydrogen, however,
they contain a hydrocarbon group : socUlim methozide,
for example, has the formula Na(0CH3). Such sub-
stances are white solids, like caustic soda.
Aldehydes, — The alcohols, if oxidised by boiling
them with chromic acid, yield a class of bodies analogous
to the oxides, termed aldehydes: CH3-CH2-OH + O
- (CH3 - CH)"0 + H^O. It will be noticed that ethane,
CHo — CHo, has lost two hydrogen atoms, and that the
residue, CHg — CH,„ is now a dyad group, capable of com-
bination with an atom of dyad oxygen. The aldehydes are
volatile liquids, with strong c _ jur, and those containing few
AMINES AND PHOSPHINES
89
atoms of carbon are miscible with water. They form easily
decomposable compounds with water, which are di-hydr-
oxides; e.g. ordinary aldehyde forms CH3— CH<( ;
they are called aldehydrols. When brought into contact
with solutions from which hydrogen is being evolved, the
aldehydrols lose oxygen, and are converted into alcohols :
CH3CH/ + 2H = CHg-CH.OH + H.,0.
The alcohols cannot be termed basic substances ; still, it
is evident that they show analogy with the true bases ^n
many respects.
Amines and Phosphines. — Derivatives of nitrogen,
phosphorus, sulphur, and ven of iodine and of oxygen,
containing hydrocarbon groups, are however known,
which are true bases, though weak ones. If ammonia
m alcoholic >lution be heated with excess of methyl
iodide, tetr^-methyl-ammonium iodide is formed:
NH3 + 4CH3I = N(CH3),I + 3HI. This iodide, digested
with water and silver hydroxide, exchanges iodine for
hydroxyl, and after removal of the silver iodide by filtra-
tion the solution may be evaporated to dryness. The
residue is a white solid, of the formula N(CH.j)pH ;
it is termed tetra - methyl -ammoniiun- hydroxide; in
its reactions it shows great analogy with caustic potash,
having a caustic taste, and producing precipitates with
the usual salts of the metals. In solution it is more
ionised than ammonium hydroxide, though less than that
of potassium.
Phosphine, as remarked on p. 66, combines with
hydrogen iodide, forming a salt, PH J, phosphonium iodide,
resembling ammonium chloride. But as it is decomposed
by water into phosphine, PH3, and hydrogen iodide, an
attempt to convert it into phosphonium hydroxide, PH^OH;
cannot be made. Substituted phosphonium compounds^
90
MODERN CHEMISTRY
however, are known, ,n which a hydrocarbon radicle, such
romt ^y'\ '■^P'^"" hydrogen. Sodium and phosphorus
comt .e when heated togethe; under an oil call^ xylene
forming PNa, ; this body, treated with methyl iodTde^S
?;CH^ f^°f '"%^(^?3).; with more methyl 'iSe
^i^ ''^* " J u™^?' ^^'^ "' '°'"^'°" •" water, which is
not decomposed by the solvent, yields with silver hydroxide
tetra-methyl-phosphonium hydroxide, PfCH ) OH a
base resembling the corresponding ammonium comJitind. '
Ihese compounds exist owing to the double valency of
nitrogen and of phosphorus, which can function either as
triad or pentad Double valency is to be noticed a"so with
oxygen and with sulphur, although with the former tetrad
combinations are far from stable, while with the latter both
dyad and tetrad compounds can be formed.
^rAers.— Oxide of methyl and oxide of ethyl, which
are usually named methyl and ethyl ethers, are forr;.rd by
mixing solutions in alcohol of methyl or ethyl iodide with
sodmm -ethoxide or ethoxide : CH3I. Ale + NaOCH3. Ak
«";jnl + ^aCOCHg. Ale. The ether has a low boiling-
point and can be separated by fractional distillation from
the alcohol in which ij is dissolved. Methyl ether is a
gas; ethyl ether a volatile liquid, boiling at%7\ Such
compounds can also be prepared more readily by distilling a
HCrSO 'h';''°''' with sulphuric acid, ^hich yiell^
HCH qn'\^rS?:U"'^'W^"^P*'^'^'^"'^ '^^ alcohol:
HCH SO + CH3OH = H3COCH3 + H„SO,. Now
methyl ether and hydrochloric acid 'combine at a low
tempe. iture, y'«Wing^^'^0<(^ ; but it is impossible to
replace the chlorine by hydroxy!.
Similar sulphur compounds, however, are stable. Methyl
iDhide, produced by the action of methyl iodide on
sium sulphide,
CH3I K KI CI^.
+ \s= + '\
CH3I K/ KI Ch/
potas-
S, unites with
:h
us
e,
Js
le
is
le
a
>f
IS
h
1
ETHERS
CH CH
methyl iodide, forming ^\s/ ' ,
CH Z' NT ' compound con-
taining tetrad sulphur ; wi'th silver hydroxide it yields
CH
CH
CH,
OH
a compound exhibiting basic properties.
From iodine, too, iodonium compotm-lg have h«.n
prepared ,n which the iodine functions' a!^ triad ^n^
hydrox.de with basic properties is known. '
CHAPTER V
Neutral Oxides— Peroxides— Action of Nitric
Acid on Metals; on Oxidisabie Substances
—Complexity of Oxides— Spinels and Simi-
lar Compounds,
The properties of all chemical compounds show gradation ;
and there is a slow transition from basic oxides and hydr-
oxides, like those which we .ave been considering in the
last chapter, to acid oxides and hydroxides. The transition
takes place along two paths ; first, there are some oxides
which are neither basic nor acid ; and second, a number of
oxides exist which are either basic or acid, according to
circumstances. We shall consider first the neutral oxides.
Peroxides. — In the potassium and calcium groups of
elements, peroxides are known. When sodium is burned
m air a light yellow powder is formed, sodium dioxide,
of the formula Na.p^ ; potassium yields a totroxide,
i^O^. Both of these substances react with water, giving
off oxygen ; but if they are very slowly added to the water,
so that the temperature does not rise much, a solution is
obtained. The corresponding barium compound is formed
when barium monoxide is heated under pressure in air (see
ft ' fl/r»S? ^^^"'^" *° ^^^^"^ " forms a hydrate, probably
^a=O(OH)2.7H20. On treatment with acid, hydrogei.
dio^dde, H2O2, is formed ; and if sulphuric acic' be added
m theoretical amount to the barium dioxide, nearly
insoluble barium sulphate is formed, along with a fairly
pure soluUoD of hydrogen c oxide : BaO=(OH)2.Aq
93
NEUTRAL OXIDES 9^
+ H,SO,.Aq = BaSO, r 0=OH.,. Aq. It can be purified,
and indeed obtained anhydrous by cfistillation under very low
pressure. It then forms a somewhat viscous, colourless
liquid, with a sharp taste.
There is some doubt as to the constitution of hydrogen
dioxide, and consequently of the c'=oxides from which it is
derived. It is unlikely that barium ever acts as a tetrad,
and much more probable that this character is to be attri-
buted to oxygen ; hence the formula of its dioxide is more
hkely to be Ba=0=0, than 0==Ba^ O ; and consequently
hydrogen dioxide has more probably the formula O^OHj,
than HO=OH. Indeed, hydrogen dioxide is possibly a
weak acid, since the hydrated dioxides of calcium and
barium are precipitated on addition of concentrated solu-
tions of hydrogen dioxide to the hydroxides suspended in
water. These substances have all bleaching power, for they
readily part with their second atom of oxygen, and it is
capable of oxidising coloured insoluble substances to colour-
less soluble ones.
Neutral Oxides, Class /.—The next neutral oxides
met with are carbon monoxide, CO, nitrous oxide,
N20, and nitric oxide, NO. These are all gases, but
condense at low temperatures to colourless liquids, and at
still lower, freeze to white solids.
Carbon monoxide is prepared by burning carbon i"
supply of oxygen insufficient to convert it into the dioxiae ;
or by passing the dioxide over a layer of carbon, heated to
redness. It appears that the monoxide is always the first
product ; for if moisture be excluded during the combustion
of carbon in oxygen, the amour. :^ of dioxide relatively to the
monoxide is very small ; and it is known that if water-vapour
be absent, carbon monoxide cannot be induced to explode with
oxygen. If even the minutest amount of moisture be present,
on passing a spark the union takes place with explosion This
phenomenon is not easily accounted for ; it is readily repre-
sented by the equation 2CO + HgO + 0„ - 2CO, + HgO.
Can it be that at the very low pressure of the water-vapour
94
MODERN CHEMISTRY
a trace is ionised into H and OH, and ♦' he OH furnishes
the oxygen for the CO, the hydrog shining with
oxygen to re-form the molecule of water i For it has
been found that no moisture is requisite to nromote the
union of oxygen and hydrogen if these gasc . be heated
together. Phosphorus and sulphur, too> show reluctance in
uniting with oxygen, in absence of moisture. In ordinary
moist air, carbon monoxide burns with a blue flame. It is
nearly insoluble in and has no action or. water.
Other methods of preparing carb«,in monoxide are : by
withdrawing the elements of water from formic acid by
adding it drop by drop to warm concentrated sulphuric
acid ; HC - OH + H2SO4 = CO + H^SO^.H^O ; by heat-
ing a mixture of oxalic acid with concentrated sulphuric
CO.OH '
acid; I H-H.SO^-CO + CO., + H„SO,.H,0;
CO.OH . 2 4 2 »
the carbon dioxide is stparated from the monoxide by
bubbling the mixture of gases through a solution of caustic
potash, which absorbs the dioxide, allowing the monoxide
to pass ; and lastly, by heating a mixture of potassium ferro-
cyanide and fairly concentrated sulphuric acid ; K.Fe(CN)
+ 6H SO, + 6H O = 2K2SO, + FeSO, . ^NHJ.So"
+ 6C0. In the last reaction, it may be taken that hydro-
cyanic acid,^ HCN, is first liberated, and that it reacts
with water, forming ammonia and carbon monoxide : HCN
+ H2O = NH3 + CO ; the ammonia subsequently combines
with t^-e sulphuric acid.
If carbon monoxide is passed over metallic nicke or
iron in a fine state of subdivision produced by reducing
their oxides, volatile compounds are formed of the formulae
Ni(C0^4, and Fe(C0)5; on exposing the latter to light
gold-coloured crystals are formed, of the formula Fe2(CO),.
The nickel carbonyl boils at 43% and the iron penta-
carbonyl at 103°; di-ferro-hepta-carbonyl decomposes
NITROUS OXIDE 95
when even moderately heateci At .80^ the.e compounds
are de. omposed mto metal and carbon monoxide, thc^iietal
being deposited as a mirror on the hot surf .ce.
Nitrous oxide. iX.O. is ,nost readily prepared by
r^n.iNU N,O + 2H0. It ,s somewhat soluble in
water, and ,s best colfected by downward displacement!
The aqueou. so:ut»on has a sweetish taste; and the gas. if
emn ^^ f! /"'" '"^^n^ibiiity ; it is therefore frequen ly
employed by dent.sts as an ana-sthet-'c. If a mixture with
a.r s respired ,t prcKluces with some persons a state of
exctement. wh.ch has procured for it the nam. " laughin«-
fudH.n K '^"".*^"^"^,^Y'"•<^ com,x,und, and if submitted to
^dden shock It exp odes with violence. It may be sup-
posed that the L.minate used to explode it decompoi
some molecules m the neighbourhood ; 'these, on decom^ot
I. J. evolve heat, and decompose their neighbours, and the
explosion rapidly travels throughout the g!s ; theVc^uct!
are nitrogen and oxygen. A candle will burn in nitrou
oxide. for the temperature of the flame is sufficiently hTgh
to decompose the gas. and the combustion proceeds as 1
dilute oxygen. Although nitrous oxide is not acted on by
v/ater or bases ,t has claims to be regarded as the anhydride
of hypomtra^acd. from a solution of which it is lil^rated
by heat ^ ^_ ^^ - ^)>0 + H,0. As neither ammo-
nium nitrate nor hyponitrous acid can be reproduced by
bringing together nitrous oxide and water, its production by
?eacdol"' '' '°'"P"""^^ '' ^^^"^^' an'«irreversibl'e
of ^hf T ''^^'^'^^^ ^,^'^ on MetMls.-The product
of the action of nitric acid on metals varies according to the
metal acted on the concentration of the acid, a^nd the
temperate .-. The acid in aqueous solution is more or less
ionised, the ions eing H and NO,. If a metal of which
96 MODERN CHEMISTRY
the ions are hif hly electropositive is presented to these ions
of nitric acid the hydrogen ions impart their charge to the
non-ionised metal, which metal enters into solution as ions,
while hydrogen is evolved. This is the case when nitric
acid acts on magnesium, and theoretically also on aluminium,
manganese, zinc, cadmium, iron, cobalt, and nickel, tor all
these metals in the ionic state have higher electro-affinity
than hydrogen, and that in the order given. It may \x
termed the normal action of acids on metals, and repre-
sented thus: M+iH-M + H.^. But along with this
action others take place in which the nitric ion is "re-
duced " or deprived of oxygen. Some examples of this
will now be given.
When silver is attacked by nitric acid, nitric peroxide,
NOg, is produced, and partly evolved as gas. The react-
H NO,
substances are Ag, and + and - ; one of the
H NO,
mg
NOg groups lose* oxygen, being converted into electrically
neutral NO3 and an ion of oxygen, O, which combines
with the two hydrogen ions, forming water, non-ionised,
H.,0. But this leaves a negatively charged nitrate group
without a corresponding positively charged partner ; more-
over, the charge of th' decomposed nitrate group is still
available. An atom of silver, therefore, goes into solution
as a positively charged ion, and restores electric equilibrium
in the solution. With less concentrated acid the nitrate ion
parts with two atoms of oxygen, requiring three negative
electrons, in addition to the one originally attached to the
group NOg; to effect this three positive electrons must
attach themselves to three atoms of silver, which then go
+
into solution as ions, hence the charge is : 3 Ag + 4H +
4N63 = NO + 2H2O + 3 Ag + 3N63, the balance of elec-
OXIDES OF NITROGEN
97
t.on. The ^equations are : 4M" + loH + loNO, = N r.
+ 5H,0-f4M + «Nu,; 5M"-fi2H+„N63ll^ ..
6H,0 + 5M+ ,oN03 ; 4M"4- .oH+ ,oN6, = NH +
ac;J yields fa.rly pure nitric oxide; i^" more concentS
Oxidation by means of Nitric Add.— Action of
the .ame nafure occurs when an elemer apable of cTanf
jng us valency. /.. the number of elect -s^s L' ted wifh
«s .omsed atom, .s treated in the ionic condition uith nh c
1 acid. For example, the ferrous ion. fV, on treatment
with nitric acid at ^,00" becomes ferric. F:.' while nitric
oxide is evolved: 3Fe4-6R + 4H + 4N63 = NO + 2H,0
S'uch^'o^^^-^^''^^' ^ '^•"g ^"y monovalent anion
ie weXay!'" "' ""'"^ ^P°'^" °^ '' "oxidationsTn
.nwater^, on bnngmg ,t mto contact with oxy|en. unless
98 MODERN CHEMISTRY
moisture is absolutely excluded union takes place to form
nitric peroxide, N0„, along with a trace of N0O3, nitrous
anhydride. On suS^ciently cooling n.tr.c oxide it con-
denies to a colourless liquid, and at a still lower temperature
it forms a white solid. ,^ »u^ rla«
Nitrous anhydride, ^^rictly speaking, bebngs to the c as
of acid-forming oxides ; its formula is N.Og. When n.t c
oxide and nitri? peroxide are brought together, only a minute
quantity of N^O, is formed ; that is, because on converting
k into the gaseous state it decomposes almost completely
into these products. On cooling such a mixture however
a blue liquid condenses, which has the formula N2O3. it
will be afterwards alluded to. . . • u .. .»
Nitric peroxide, as usually seen mixed with air at
ordinary temperatures, is an o-ng--lou-d gas When
pure it condenses to an orange-red l/^^^' ^'^ "8 .^5 " '
[t freezes at -10° to a colourless solid. The liquid has a
molecular weight correspondmg to the fo;"^f ^,0 and
the gas, at temperatures not much exceeding the boiling-
tLf consists mainly of the same substance. But as the
Uperature rises the colour grows darker, untxU at 140,1^
forms a blackish-red gas, consisting wholly of NO . VVith
progressive increase of temperature NO dissociates m its
Ln into NO and 0„ and at 6oo<' the change is complete.
As temperature falls the action is reversed.
NZral Oxides, Class //.-The next class of
oxSes comprises those which may be termed neutral
L ause the/can act either as bases or as acids, according
as they are'treated with an acid or with a base. Their
hydroxides may be comprised m the same class. A case
of this kind has already been explained on p. 70 ; it is
there shown that aluminium hydroxide, when treated with
acZ yields salts of aluminium,' while with bases alum.nates
^'^/^mntexi^v— It appears probable that such oxides
hav^'Zicdaf^ormul/n^ore c^ex than those usually
ascribed to them; for instance, aluminium oxide is certainly
NEUTRAL OXIDES „
more complex than is implied by the usual formula Al O .
u may be A1,0 or Al,p,„ but .here is no mrs a. p ^f,!
Thf Z'S ' n f"'' <":--■''"">• "' *e moK
melf fo- ra„:^^ ^^J^. hi,h
.":rt;t:r.he'tit;;L^.' ';^'%:f^ -f-r-"^
Ss^iti' C„H,„ &c., are also known ; and the boil np On
increases with the molecular weight Now th^ Tm"^ J
of the elements are, as a rule, easli; volatU^'and WW
mek.ng.po,nts ; and where it happens that bo h chloride and
ox de have a simple molecular formula as for ^v i
chl orTde'r t"'^' ^.^^^' ^"^ car^dirxidt CO the
chloride has always a higher boiling-point than the o;ide
It would appear to follow, therefort, that if the oxide of
the metals had as simple molecular formula as the chlor des
s notTi "T'' ''""^''^''y ''^^^ ^he latter. As ttl
^ not the case the presumption is that the oxides posse s
to henr'ThisT^KT^" ^'.r.' ■■" ^^^ ^^b'^ °f -Sng
arises. ^'^^'^'^^^ ^'" ^ ^^^'^ ^«^h as occasion
Among the oxides and hydroxides which exhibit th.
centrated solution of potassium hydroxide with a LX M
colour; zinc and cadmium h/droid«« li, k ^ "^
in excess of ^]lo\; ~"™ . '*y«'0»aes, which disso ve
AirhJ.k ^ ^^a^z-nu .8H O; and aluminium hydroxide
which dissolves in alkali, forming an aluminateT MA^o'l
lOO
H-ODERN CHEMISTRY
Mi
i
stannous and plumbous hydroxides, Sn(OH). and
PbToHlo, dissolve in alkalies, forming compounds no
doubt analogous to zincates. Chromous, ferrous, manganous,
cobaltous, and nickelous hydroxides are not thus soluble
C^omic hydroxide, however, is soluble m soda, probaWy
foTming a compound like sodium alummate ; un hke he
Kr, chromium hydroxide is thrown down on bo.lmg the
'° fitt^'such compounds, when they do not contain sodivun
or Votassium. are often insoluble in water, and then they
c nSo~epared by the action of the one hydroxide on
the other. The oxides combine when heated together m
the dry condition, and sometimes when the compound
formed^s decomposed by water (hydrolysed) it is con-
venTent* to prepare it either from the ox.de or from the
""^'soinels -A considerable number of compounds,
anabgou! to the aluminates, is produced in this way, and
manv of them are found in nature as minerals. To this
rs'b^Lng the "spinels," so called because one of their
number the native aluminate of magnesium, had receivea
rtm^ Viewed as a combination of oxide, such corn-
pounds possess the general formula ^oO .MO, and they
can be prepared by heating the sesquioxide (a n^nie g.^en
to oxides when the proportion between the metal and the
oxygen islsone to one'and a half, or, more correctly, as
two to three) with the monoxide. The spinels all crysta -
Ze in regular octahedra ; they are therefore said to
use in icguia Viewed as aluminates,
be isomorphous with each other, vieweu as
- thev may be written M" MO3 , ; compare NaAlO .
Alngthem are true spinel, MgfAlO,),; fra^mite,
yTpfo r chrysoberyl, BeCAlO^Lj ^""^ chromite,
/,n(t'eU2J.2». '^"^' ,, plVrO ^ But it is not neces-
or "chrome-iron ore, Fe(Cr02)2. ,/^".^ "" . „„_,.
sary that the metals of a spinel should be different ones
71 metal is capable of existing in two torms, -^. - ^>f^
and triad, it may form a similar compound. (Su'rh are
magnetite, or "magnetic iron ore, Fe (Fe U.j.. ^na
SPINELS
hausmanite. Mn''(Mn"'0,)„ the first atom of iron or
or iron sesquioxide (hematite), may be in^ rS an
PeliFeO^C "'"* Al(Al6,)3/or ferric fer'rite!
A common test for zinc and aluminium is to heat
ogether before the blow-pipe the salt suspected to contain
the metal w.th cobalt nitrate ; it is probable that the gr^n
z,t::e'ctz^O^ ^'"V\'"m" 'h ^---n"of': cXlt
ofrs^ov,^r '^^^^V'^'°''•^dness in air the first product
of Its oxidation ,s htharge, PbO ; on continuing the ap-
pl cation of heat at a carefully regulated temperature the
yelJow htharge becomes red, and the product ofthe aa on
1 Lr;"r;[r"'^^^'*'7'^^- now, on tre^n^^
? lead dioxide hj^rated, remains as an insoluble ;esX!
^ zPbo! ^O rt' °^ "^""^^'^^ ^"^ "'^^ °f di Jxide,
2rbU + I'bO the former reacts with nitric acid forming
i'he ;?' •''k^''' '^' ^'"^^ '■^'"^•"^- Now, If the diox Sf
^ piumbate, K,Pb03 ; and red lead may be regarded as a
I basic plumbous piumbate, 0<^ ,,'>(PbOj ; "basic,"
I ™^'"'' f""^ J''" *"«'" "'O'ns of lead arc partly oxide
I U [iiad ' ^^ '" ''"''• *''"' *^ »=""<' a.om oHead
view. Lompounds of antimony and bismuth, having the
,02 MODERN CHEMISTRY
formula Sb,0, and Bi,0., may be similarly regarded
as 0=Sb(sfot) and d=ii(Bi03) ; of this, however,
there is no proof. j;^^ij«a » tn
Manratnese and chromium also form 'dioxides, to
which the simple formula MnO, and CrO. are usually
attributed ; they, too, may be written .^Cr
,-^"
O
and
O
chromous
.0
1/ ^Mn". They would then be termed
cnromous i;hromate and manganous '"fg^"^^*^' ^"f.^
ideas must be regarded as speculative,but there can be litt e
doubt that the formulae are more complex than they are
usually written. The former is a snufF-coloured powder,
produced by the action of nitric oxide on a chromate ; the
latter, formed by oxidising and precipitating a manganous
salt simultaneously, is best prepared in a hydratea state by
the action of a hypobromite on a "^^"g^^?^^ gl'^ ^Mr Aa
^NaOBr.Aq+2NaOH.Aq = 0=Mn(OH 2.+ NaBr.Aq
+ 2NaCl.Aq. It is a common black mmeral m the anhy-
drous state, and is known as pyrolusite. It will be re-
membered that the ordinary method of preparmg chlorme is
to heat this mineral with dilute hydrochloric acid, and also
that on heating alone it furnishes oxygen, being itself con-
verted into Mn^O,, a brown powder, which may be formu-
lated as a spinel, viz. (0=Mn-0)2=Mn.
In concluding this chapter on neutral oxides, it may be
mentioned that there are a few which, actmg generally as
feeble bases, yet display feebly acid properties if in the
presence of a strong base like soda or potash, buch are
[he oxides of gold, the metals of the platmnm group,
and of titanium, zirconium, and thorium. The chlorides
of these elements are soluble in water, as also the sulphates
and nitrates of the last three. Sulphates of gold and plati-
num, however, are hydrolysed byj-ater, g>y"g °^'^%^"^
sulphuric acid, thus : Pt(SO,)2 + 2HOH = PtO^ + zH^SO,.
NEUTRAL OXIDES 103
Salts of these elements, on treatment with soda, yield no pre-
cipitate, for they are dissolved by the alkali ; the compounds
tormed are indefinite, but it may be supposed that they
contain aurate, MAuO^.Aq, or platinate, titanate, zirconate,
or thorate, MPtO,.Aq, &c. Iron and calcium titanates
occur native ; FeTi03 ''« termed ilmenite, and CaTiO,
perowskite. The first is isomorphous with and crystal-
ises along with native ferric oxide ; the ore is known as
titanic iron ore." It is the commonest compound of
titanium.
CHAPTER VI
Anhydrides — Acids and Salts — Basic and Acid
Chlorides— The Borates— The Carbonates and
Thiocarbonates — Other Acids containing Car-
bon; their Salts with Alcohol Radicals— The
Silicic Acids and the Silicates.
Basic Salts.— Many compounds are known which are
at the same time chloride and oxide, or chloride and hydr-
oxide of elements. Where the element with which the
oxygen and chlorine is combined is one which forms a basic
oxide, the compounds in question are termed basic chlorides.
Similarly, there are basic bromides and iodides. For ex-
ample, zinc oxide heated with zinc chloride forms oiychlo-
rides, of which the simplest example is Cl-Zn-Q-Zn-Cl;
aluminium chloride, evaporated with water, has its chlo-
rine gradually replaced by hydroxyl, forming successively
a.=Al(OH), C1-A1=(CH),, and finally, A1(0H)3,
though at a temperature sufficient to complete the reaction,
the aluminium would probably form the condensed hydr-
oxide 0=A10H instead of the trihydroxide. We shall
ste later that other grou: , playing a part analogous to
that of the chlorine in a basic salt, may also exist m basic
SHltS*
Acid Ctllorides. — Another class of double oxides and
chlorides exists, most of which are easily volatile, and-
which therefore are of known molecular weight. These
are the so-called "acid chlorides "—oxychlorides of those
elements which form acids. These are related to acids, in
as much as by replacement of their chlorine by hydroxyl,
104
BORATES
'05
acids are formed. It will therefore be convenient to con-
sider them along with the acids to which they are related.
A general idea has already been given of the nature of
acids in describing the hydroxides of zinc and ot aluminium.
As a rule, acids are condenrnd hydroxides; that is,
hydroxides which, having lost the elements of water, are
partly oxides, partly hydroxides. They also possess the
property of ionising into one or more hydrogen ions and an
electro-negatively charged radical. In following the order
of the periodic table, after such feebly acidic hydroxides as
those of zinc and aluminium, hydroxide of boron claims
attention.
Borates. — In certain lakes in California the water,
when evaporated, deposits crystals of the formula
Na.^B40y.ioH20 ; this substance is named borax. It is a
white, crystalline salt, easily soluble in hot water, but sparingly
soluble in cold. When mixed with 6ulphu;ic acid nacreous
scales separate of the formula B(0H)3, or, as it is usual in
writing the formulae of acids to place the hydrogen atoms
first, H3BO3. Boracic acid hardly deserves the name of
acid; in aqueous solution it exists almost entirely in the
non-ionised state. No ions are volatile ; but this compound
issues in Tuscany and in the Lipari Islands along with
steam from cavities in the ground, termed sujioni ; it is
easily recognised, for it imparts a green colour to a flame
held in the steam. When heated to 100° boracic acid loses
water and is changed into metaboracic acid, 0=B DH,
a vitreous substance; and at a red-heat boron xiie,
B^,0„, is left as a transparent, colourless glass. Its con-
stitution is 0-B-O- B=0,
The boiates of the alkalies are prepared by mixing
boracic acid with the hydroxide of the alkali metal;
although there are very few hydrogen ions in an aqueous
solution of boracic acid, however dilute, yet some of those
present combine with the hydroxyl ions of the alkali, forming
water, thus: H3B03.Aq + sN^OH.Aq = NtgBOg.Aq +
,o6 MODERN CHEMISTRY
iH O. But there arc so few ions present, that those of
the water, which, it will be remembered, is ionised, although
to an extremely hiinute extent, are yet sufficiently numerous
to bear some proportion to those of the Voracic acid ; hence
the reaction given above is perceptibly reversed, and on
dissolving borax in water it is " hydrolysed, that is, split
by the hydrogen and hydroxyl ions of the water into non-
ionised boracic acid and caustic soda, the latter, of course,
lareely ionised as usual. It is therefore possible to estimate
the sodium of borax by aH-Mtion of a solution of a strong
acid, such as hydrochloric ur sulphuric acid of known con-
centration, just as if no boracic acid were present, provided
methyl-orange be used as an indicator. (^«!^ P- 750
Thus the addition of 36.5 grams (H=i; U- 35.5 J
of hydrdchloric acid, dissolved in a litre of vater (such a
solution is termed a "normal solution"), to 191 grams ot
a solution of crystallised borax in a litre of water (1/2
all 1/2 of 382) gives a solution which is neutral to methyl-
°'*Fu!ed borax has the property of dissolving oxides of the
metals, forming complex borates; certain of these are
coloured, and their formation is often made use ot tor
detecting the presence of such metals as copper (blue),
silver (yellow), chromium (green), ferric iron (yellow),
ferrous iron (bottle-green), manganese (amethyst, when
heated in a tlame containing excess of oxygen), cobalt
(blue), and nickel (reddish). Borax is also used tor
soldering easily oxidisable metals, such as iron, copper, or
brass ; the tilm of oxide which prevents the metal touching
and alloying with the solder is thus removed. Both borax
and boracic acid have considerable antiseptic properties, and
are used for preserving eggs, milk, and other animal and
vegetable substances.
Carbonates and Thiocarbonates.—The car-
bonates and the thiccarbonates are cenvatives of carbon
dioxide (or rather of carbon oxy-hydroxide, commonly
CARBONATES
107
0»
called carbonic acid), and of carbon disulphide. Carbon is a
tetrad, and the analogue of carbon tetrachloride would be the
tetrahydroxide, C(OH)^; but this body is unstable, and
its first anhydride, 0=C(OH).„ is known only in aqueous
solution. However, carbonyl" chloride, 0=CC1.„ exists;
it is produced by the direct union of carbonic oxide with
chlorine, when a mixture of both gases is exposed to
sunlight ; it was formerly known as " phosgene gas,"
meaning "made by light"; but it is more conveniently
prepared by passing a mixture of the two gases over
animal charcoal heated to redness. It condenses to a
liquid, boiling at 8.4°. It is immediately decomposed by
water, thus: 0=001., + 2HOH = 0=C(0H)2+ 2HCI;
if sufficient water is present, the carbonic acid can remain
in solution. The existence of the oxychloride establishes
the formula of -arbonic acid.
Carbonic acid is a very easily decomposable substance ;
if liberated, unless a great deal of water be present, it splits
into its anhydride, COg, and water: 0=C(OH)2 = C02
+ HgO. The anhydride u a colourless gas, which con-
denses to a solid at about -80° ; it can he liquefied only
under pressure. Carbon dioxide, or carbonic anhydride,
is produced by heating a carbonate ; as already remarked,
all carbonates, except those of the alkaline metals, are
decomposed by heat, forming oxides, and evolving carbon
dioxide. It is also produced when carbon or carbon
monoxide is burned with excess of oxygen. Lastly, it is
produced in large quantities during the process of fermenta-
tion. Glucose, or grape sugar, either produced by the
hydrolysis of starch or extracted from fruits like grapes,
when mixed in dilute aqueous solution with yeast, a vegetable
organism, decomposes into ethyl alcohol and carbon dioxide,
thus: CgHj,0^ = 2C2H,OH + 2CO,. The carbon di-
oxide being heavier than air, collects in the fermenting
tuns ; it is now often collected and compressed until it
liquefies ; and the liquid on expansion solidifies to a snow-
like solid, used for producing low temperatures.
io8
MODERN CHEMISTRY
• i
A solution of carbonic anhydride in water contains
carbonic acid, 0=C(OH).„ which is a very weak acid
owing to the small extent of its ionisation. It is probable,
too, that liquid carbon dioxide exists in the solution, mixed,
but not combined with the water. Carbonic acid reacts
with sodinm, potassium, calcium, or barium hydroxide,
forriing carbonate of the metal : H^CO^. Aq + iNaOH. Aq
= Nt,c6,.Aq + 2H.p ; H,C63. Aq + ct(OH ),. Aq =
CaCdj+iH^O. In such actions it is only the ionised
portion of the acid which reacts, and the hydrogen ions
form water ; when these are removed another portion
becomes ionised in order to restore equilibrium ; it reacts in
its turfi until all has become transformed. On evaporation
of the solution the alkaline carbonate is left as a white crystal-
line salt; hydrated sodium carbonate, Na^COg.ioHjO,
is ordinary washing-soda. All other carbonates are insol-
uble in water, and are consequentry thrown down as
precipitates on adding a solution of sodium carbonate tr
any ionised solution of other metals. They form Hocculent
precipitates, generally possessing the colour of the ion
of the metal ; thus copper carbonate is blue, ferrous
green, cobalt pink, and so on. But with the exception of
the carbonates of the metals of the sodium and calcium
groups all other precipitated carbonates are " basic," that
is, they are partly hydroxides, partly carbonates. Copper
carbonate, for example, may be assigned the formula
/0-Cu-OH
0=C\ ; it will be noticed that each atom
^O-Cu-OH
of copper is combined with the oxygen of the carbonic
residue on the one hand, and with hydroxyl on the other.
The paint known as " white lead " consists of a basic
carbonate of lead, more complex than the example given
above, of the formula
HO-Pb-0-(CO)-0-Pb-0-(CO)-0-Pb-OH.
Native Carbonates. — Manv carbonates exist in the
ACID CARBONATES
109
native state ; some are widely distributed minerals. Among
these are Iceland ur calc-spar, amgonite, limestone,
chftlk, and marble, all of them caleinm carbonate;
strontianite, SrCO, ; witherite, BaCO., ; gpathic iron
ore, FeCO.,, also named clay-band when contaminated
with clay, and black-band when mixed with shale.
Magnesite is Mf '^O, ; dolomite, a mixture of magne-
sium and calcium carbonates ; calamine, ZnCOy ; and
cemssite, PbC03. Malachite and azurite are basic car-
/O-Cu-OH
bonates of copper, 0=C\ , and
^O-Cu-OH
HO-Cu-0-C- O-Cu- 0~C-0-Cu-OH.
We see here again that with weak bases, such as the
hydroxides of most metals, the carbonates tend to become
basic, that is, to be hydrolysed. This is why the preci-
pitates obtained on adding a soluble carbonate to a salt of
such metals are basic, and not normal carbonates.
"Acid** Carbonates. — The name «*acid carbon-
ate " is given to a double carbonate of hydrogen and a
metal. Such bodies are prepared by the method which
always is adopted for the preparation of double salts — by
ONa
mixture. Hydrogen sodium carbonate, 0=C
/'
OH
the corresponding potassium compound ; hydrogen cal-
O O
1:
cium carbonate HO-C-O-Ca-O-C-OH, a ferrous
carbonate of similar formula, and many others -^re all
formed when carbonic acid and the respective normal car-
bonate are mixed, the mixture being kept cold. On raising
the temperature of all of these, carbon dioxide escapes, and
the neutral carbonate is again formed. " Acid " carbonate
of sodium is the common " baking-soda ; " hydrogen calcium
no
MODERN CHEMISTRY
I
li
carbonate is a constituent of many natural waters, and is the
/ cause of what is termed " tem|)orary hardness " ; for on
\ boiling the water the neutral carbonate is precipitated, and
j the water ceases to be "hard." The same result may be
effected, paradoxical as it may appear, by the addition of
lime-water ; for then sufficient calcium hydroxide is present
to form normal calcium carbonate with the hydrogen carbon-
ate, thus : Ca(HC03)^.Aq + Ca(OH),.Aq ^. iCaCOa +
2H..0.Ac|. Hydrogen ferrous carbonate is a constituent
of cnaly'ieate springs ; on exposure to the atmosphere the
iron is oxidised to ferric hydroxide, and the carbonic acid,
being too weak an acid to form a carbonate with such a
weak base as that, escapes : 2Fe(HCOjj).,.Aq+ 5Hj,0 +
O = 2Fe(OH)., + 4H,,C0.,.Aq. The fer'ric hydroxide is
deposited as a brown scum on the banks of the streams
flowing from such wells.
Carbonates of Radicals. — Although normal hydr-
oxide of carbon is unknown, yet if the hydrogc 'e replaced
by ethyl, -C^H^, the compound is stable. The compound,
which is produced by the action of carbon tetrachloride
on sodium cthoxide, CCl^ + 4Na-0-C.,H. = 4NaCl +
C(0-C,HJ^, is the analogue of C(OH)'^. It is a
volatile liquid, and is named ethyl orthocarbonate. And
a corresponding carbonate of ethyl, 0=C(OC.,H.).„ the
analogue of carbonic acid, 0=C(OH).^, is formed by treating
carbonyl chloride with alcohol: 0=CCI.j + 2HO-C^H,=
0=C(OC^,H.)^, + 2nCl. These compounds are volatile,
and can be weighed in the state of \apour, hence their
molecular weights are known, and this is an additional
proof of the correctness of the formulae ascribed to carbonic
acid and the carbonates,
Thiocarbonates. — The sulphocarbonates, or thiocar-
bonates (from the Greek theion, sulphur) form a class
of salts analogous to the carbonates, both in their formula:
and in the method of their preparation. Carbon disulphide,
a volatile liquid, boiling at 46°, possessing a disagreeable
smell, is produced when sulphur vapour is led over charcoal
THIOCARBONATES
I'l
heated to redness in a fireclay tube ; in fact, the carlwn is
burned in sulphur ga*. When siiaken with a concentrated
aqueous solution of the sulphide of sodium or potassium, it
dissolves, forming the compound Na^CS^, or K.,CS .
These thiocarbonates, like the carbonates," are white, crvstaj-
hne salts ; on adding acid, thiocarbonic acid separates as
an oil ; it slowly decomposes, esjwcially if warmed, into
hydrogen sulphide and carbon disulphide. Many of its salts
are insoluble, and may be i)repared by preci uion.
The formula of carbon dioxide is CO.^," that of carbon
disulphide CS ; and it is evident that an intermediate
substance should exist of the formula COS. This sub-
stance is carbon oxysolphide. It is a gas, prepared by
heating thiocyanic acid, HSCN, the ammonium salt of
which is produced when ammonia is passed through a
mixture of carbon disulphide and alcohol : CS., + 2NH.,.AIc
= H.^S + (NH4)SCN. Ale. On evaporation" of the alcohol
the ammonium thiocyanate cryitallises out. This salt, dis-
tilled with sulphuric acid, yields in passing the acid HSCN,
which, on account of the high temperature, reacts with
water, forming ammonia (which yields ammonium sulphate
with the sulphuric acid) and carbon oxysulphide, COS •
HSCN + H,0 = NH3 + COS.
Like nitrous oxide, carbon disulp' ^de is an endothermic
compound, and can consequentlv be aecomposed by shock ;
when a fulminate is exploded in it, it is resolved into carbon
and sulphur. On the other hand, carbon dioxide and oxy-
sulphide are exothermic comix)unds, heat being evolved
during their formation.
Acids containing Carbon. — An enormous number
of acids containing carbon is known, in which the acidic
carbon atom is combined with oxygen and hydroxyl, and
also with hydrocarbon residues, such as methyl or ethyl, or with
some more complex group of carbon atoms. The simplest
O
of these is formic acid, H-C-OH. Acetic acid is
112
MODERN CHEMISTRY
O
i i>
methyl-formic acid (CH3)-C-0H ; ethyl-formic acid is
H
named propionic acid ; its formula is CH„— CH.,— C— OH.
0=C-OH
Oxalic acid is to be regarded as di-carboxyl, I ,
0=C-OH
the name carboxyl being a contracted form of ♦' carb(onyl
hydr)oxyl" ; it is commonly written — CO--OH.
Formic acid (from /orw/Va, an ant) is contained in ants
and stinging nettles. Sodium formate is produced when
carbon n^onoxide is left in contact with sodium hydroxide ;
the reaction takes a considerable time : CO + NaOH =
H— CO— ONa. It is also formed by heating oxalic acid,
better in presence of glycerine: (CO— OH)., = CO., +
H— CO— OH. It is a colourless, pungently smelfing liquid,
boiling at 99°, and a fairly strong acid in aqueous solution ;
it is poisonous. Its salts are crystalline, and possess the
colours of the metallic ions which they contain. When
warmed with concentrated sulphuric acid, or with other
substances capable of withdrawing water, it yields carbon
monoxide. Yet CO is not the true anhydride of formic
acid, seeing that an anhydride can be obtained only from
loss of the elements of water from hydroxyl groups, for
formic acid contains the group H-C.==h ; the real anhydride
O o
II li
would be H— C— O— C— H ; it is unknown.
Acetic acid is the acid constituent of vinegar, and is a
solid, melting at 17° to a liquid, boiling at 118°. It can
be formed synthetically by bringing into contact carbon
dioxide and sodium methide, a compound of the formula
Na-CH,; the equation is: Na-CHa + COg =
HgC-CO-ONa ; the sodium salt, distilled with sulphuric
acid, yields acetic acid. It is produced on a large scale by
the distillation of wood ; the distillate consists mainly of
0, decomposes into CO and COg.
CO ,. , I.
Salts of these acids with alcohol radicals, such as
methyl and ethyl, are prepared by saturating a solution of
the acid in the respective alcohol with hydrogen chloride,
and then distilling: (COOH)., + 2CH3OH = (COOCH3).,
+ 2HOH. The hydrogen chloride serves to withdraw
water, and prevent it acting on the product. Such salts,
which are generally colourless liquids or solids, possessing
a pleasant smell, are called "esters.^' As a rule they are
s])aringly soluble in water, and are not ionised n solution,
thus differing from salts of the metals. When boiled with
alkalies, the ester being returned by means of an inverted
condenser into the boiling-flask, they change into salts of the
alkalies, and the alcohol: CH,-CO-0-CH^CH,+
KOH.Aq =^ CK,-CO-OK.Aq + CHg-CH.-OH.
This change is also effected by heating with water in a
SILICIC ACIDS
IIS
sealed tube ; it is accelerated by the presence of hydrogen
ions, and therefore by the presence of strong acids, such as
hydrochloric acid. Decomposition of this kind by alkrlies
is called " saponification " ; if effected by water the term
*' hydrolysis " is applied to it.
Silicic Acids and Silicates.— V/hile the character-
istic of carbon 's to form compounds in which many atoms
of carbon are linked together (hydrocarbons, for example,
H H H H H
havmg formulae like H-C-C-C- ... -C-C-H)
H H H H H
atoms of silicon are characterised by linking by means of
atoms of oxygen. This peculiarity leads to the existence
of a large number of silicates, and probably, too, of a
large number of silicic acids. The existence of some of
these is rendered certain by a study of the oxychlorides.
Silicon tetrachloride, SiCl^, when passed over fragments
of felspar (a silicate of aluminium and calcium) heated to
whiteness in a porcelain tube, exchanges chlorine for oxygen,
and yields a liquid boiling at about 137% of the formula
0<
.SiCl.,
^SiCL
This liquid, passed along with oxygen through
a hot glass tube, gave two othti liquids, which could be
separated by fractionation; the one, boiling at 153% had
the formula Si^O.^C „ and the other, boiling at 200',
Si^O^Clj^. The vapour-densities of th-se liquids were
determined, and led to the formula; given above. The
signification of this will appear presently.
Si(OH)^. When silica, in the form of flint, or fine
sand, or powdered rock-crystal is either fused with caustic
soda or potash, or heated under pressure with a solution
of one or other of the alkalies, an orthosilicate is pro-
duced, possessing the formula Si(ONa)^ or Si(OK)^.
These silicates are soluble in water, and as they resemble
glass in appearance, they are usually named "soluble glass."
If hydrochloric acid is added to the solution of one of
1,6 MODERN CHEMISTRY
them, no apparent change occurs ; in reality, orthosiUcic
acid is produced, a compound which is hardly ionised at
all, being one of the very weakest of acids.
Osmosis.— T'o separate the ions of sodium chloride
and of hydrochloric acid advantage is taken of a discovery
made by Oraham, that a vegetable or animal membrane like
parchment or parchmentised paper is readily permeated by
crystalline bodies, while it is very slowly permeated by
•♦colloidal" or gum-like compounds. By placing in a
drum, floating on water, the mixture of orthosilicic acid
and salt,' the sodium and chlorine ions pass through, ot
course in equivalent proportions, leaving the cc id behind.
Fresh water is substituted from time to time, until^ ail
chlorine ions have been removed from the silicic acid. The
water can be removed by evaporation in vacuo, and a clear
but very viscous liquid remains, which is believed to con-
tain Si(OH)^.Aq. On raising the temperature of this
viscous liquid it gelatinises, and is then insoluble m water ;
the resulting compound may have a formula analogous to
carbonic acid, 0=Si(OH),; it is termed metasilicic
acid. On further drying, water is gradually expelled, and
finally a flint-like mass is left, which on ignition yields
a white powder of SiO^, or silica. As already mentioned,
silica is found in nature; when pure, it crystallises m
hexagonal prisms, and is termed quartz, rock-crystal, or
Irish diamond. It is used for spectacle lenses and optical
instruments.
The major part of the rocks which constitute the
surface of the earth consists of mixtures of silicates.
Occasionally they are found in definite crystals, and on
analysis their formulae can be determined. From their
formulae, the formula- of the silicic acids from which
they may be supposed to be derived can be deduced;
and tables foll^^w, in which the formulae of these silicic
acids and of some of the minerals constituting their salts
are given.
SILICATES U7
r
r
f
.OH
\;^OH
OH
/^>Be
^^>Be
0^
Beryl.
i
f
•
11
e
/%Mg, Fe)
\o>(Mg, Fe)
ySiO^^Al
Al SiO, Al
SiO,-Al
Olivi
ine.
Xenolite.
Orthosllicates. — These are orthosilicates ; the
comma between the Mg and the Fe means that these
metals can replace each other in any proportions. Xenolite,
it will be observed, is the silicate of a triad metal, aluminium ;
and four atoms of aluminium replace twelve molecules of
hydrogen in three molecules of orthosilicic acid. But
doi'Sle silicates are common, in which three of the atoms of
hydrogen in three molecules of orthosilicic acid may be
replaced by three monad atoms ; or by one dyad and one
monad atom ; oi we may have a monad group, such as
-A1=0, or - AlF^o, replacing each atom of hydrogen ;
or, lastly, the aluminium may be partly hydroxide, thus
constituting a basic silicate. Examples of such compounds
are : —
SiO,-.KH,
Al SiO-Al
^.■';o,==Ai
Muscovite, or Potash mica.
SiO,-CaH
Al^ SiO,_ CaH
\iO, Al
Prehnite.
Ii8
MODERN CHEMISTRY
SiO,z(Al = 0)3
Al-SiO, -Al
^SiO^ Al
Fibrolite.
SiO,- ( AlF^),
Al-SiO^-;Al
^SiO.'Al
Topaz.
OH
Al SiO^- Hg
"^SiO.-Al
i Kaolin or China-clay.
In such silicates, the aluminium is often partially replaced
by triad metals, such as triad chromium, iron, or man-
^^Iweias/Z/ca^CS.— Metasilicates are derivatives of the
acid H SiO. ; the constitutional formula is 0=Si(0H)2,
like that of carbonic acid. Examples of metasilicates
are: —
.O.
.0.
0=Si Ca
\o/
Wollastonite.
= Si (Mg, Fe", Mn", Ca)
No/
Augite or Hornblende.
o o
/ \ «
= Si Al-O-Si-ONa
\o/
Jade.
The potassium salt is Leucite.
Disillcates. The molecules of orthosilicic acid may
lose one molecule of water, the remaining atom of oxygen
of the two hydroxl groups serving to unite the two molecules
SILICATES
119
together, and a similar loss of water may be repeated twice,
thus : —
Si
/OH
/>0H
Si^.
X^OH
OH
OH
OH
OH
Two molecules of
orthosilicic acid.
OH
SiO«
SiO„
'OH
2nd anhydride.
Sil
ica.
The final loss of water yields anhydrous silica. These
acids are not known as such ; but certain minerals may be
regarded as their salts. It is probable that okenite is a
disilicate, thus CaH^Si.^O- ; and also petalite, a derivative
of its second anhydride, AlLi(Si„05)o. Similarly, three
molecules of orthosilicic acid, by losing two molecules of
watf r, may unite to form trisilicic acid ; and it again by
successive loss of one, two, and three molecules of water
may yield a first, a second, and a third anhydride. The
120
MODERN CHEMISTRY
well-known felspars albite and orthoclasc are salts of the
third anhydride of trisilicic acid, thus : —
,o.
o
o
Al O Si-0-Si-0-8i-0Na
Albite.
Al(^0
o o
ll il
Si-0-Si-O-Si-OK
Orthoclase.
The method of ascertaining the tormula of a silicate
requires notice. In order to determine the relative number
of molecules of silica, SiO.„ and of the oxides of the various
metals in combination with it, each percentage is divided
by the molecular weight o'' the oxide in question ; the
quotients are then divided by the smallest, and the ratio
between the resulting quotients compared. To take an
instance : —
An analysis of a specimen of muscovite gave the follow-
ing numbers : —
SiO,= 45.07 per cent.; AUO^ = 38.41 ; KoO^ 12.10;
H20--"4.42; together =100.00. Dividing by 60.4;
by" 102.3 ; by 94.3 ; by 18.0, the quotients 0.746, 0.375,
o'.i28, 0.245 are obtained. Again dividing the quotients
bv 0.128, the smallest of these quotients, the ratios are:
6, 3,
nearly. Therefore the formula is 6SiOo,
3AU03, K.,0, 2H.,0, or, adding the various constituents
together and dividing by 2, Si^Oj^AlgKH,. The group
Si^Oj., is 3 X SiO^; the compounds is, therefore, an ortho-
silicate ; and three atoms of triad aluminium, one of monad
potassium, and two of monad hydrogen are equivalent to
the twelve atoms of hydrogen of the three molecules of
orthosilicic acid. It sometimes happens, however, that one
SILICATES
131
metal, such as magnesium, may replace more or less of
another, such as calcium and iron. In that case, the
quotients obtained on dividing the j)ercentages by the mole-
cular weights are added before the final ratio is obtained.
The products of Nature's laboratory are seldom, if ever,
pure ; and it rarely happens that a natural mineral gives
results so easily interpreted as the case given above. For
the mineral no doubt separates from a matrix in which
many compounds are present ; and so it happens that one
metal may take the place of another possessing the same
valency, and capable of forming compounds of the same
crystalline form. The alkali metals are mutually re])lace-
able ; also the triads Al, Fe, Mn, Cr, and others. There
are even instances where silicon is partially replaced by
titanium ; hence the interpretation of the results of analyses
presents a problem of no small difficulty. The work of
F. W. Clarke, of the U.S. Geological Survey, has con-
tributed not a little to a solution of this problem.
CHAPTER VII
ANHYDRIDES, ACIDS, AND SALTS
PhosphoHc, Vanadic, Arsenic, and Anticnonic Acids
— Nitrous, Phosphorous, Arsenious Acids — PhoS'
phailc Acld—Hyponltrous and Hypophosphorous
Acids, and their Salts.
The remaining hydroxides, which all exhibit well-marked
acid functions, may be divided into two classes, those of
elements of odd valency, and those derived from elements
of even valency. A scheme has alreadj been given on
p. 71, which illustrates the derivation of the acids of the
halogens from the imaginary hydroxides corresponding to
X^", X^', X'", and X', where X stanas for halogen, and
the Roman numerals for the valencies in the compounds.
Elements of Odd Valency. — The highest valency
shown by elements of the nitrogen group, apart from a
somewhat questionable pernitric acid, is five. This is
illustrated by the formula: of the pentoxides, N.,0., P.O.,
As.,Oj, SK,Oj, and V.,Oj. But these compounds possess
very different stability, and the elements show different
behaviour in uniting with oxygen. Nitrogen and oxygen
do not unite except when electric sparks are passed through
a mixture of the two gases, or when a high-tension current
is passed through air. It is doubtful whether heat alone
is the cause of this union ; it is more probable that energy
must be imparted to the combining gases in an electrical
form. The act of combination, in which the p -oduct is
the pe'-'^xide NO.,, is attended by absorption of heat (7700
PHOSPHORIC ACIDS
123
calories tor the union of 14 grams of nitrogen with 32 grams
of oxvgen) ; and this energy must be supplied if union is
to take place. On the other hand, phosphorus burns
brilliantly in air, and if excess of oxygen be j)resent, the
so-called pentoxide is produced ; according to the vapour-
density, however, the formula is P^0,„. If air be slowly
passed over heated phosjjhorus, on the other hand, the
lower oxides P40^5 and P.,0^ are formed. It is not pos-
sible to dehydrate phosphoric acid, HPO3, completely, so
as to obtain P.Oy When arsenic burns in air, arsenious
oxide, As^0,.,"i8 the product ; with antimony, vSb^O, ; but
vanadium pentoxide, VjO,,, is formed when the element
or one of the lower oxides is heated in air.
The pentoxides behave differently when treated with
water. While N.^Os and PjOj,, unite with water with a
hissing noise to form HNO., and HPO.,, As.O,,, slowly
reacts to produce H,,AsO^, and probably H^VO^ is the
result of dissolving V.,Oj in water ; the corresponding
Sb^Cj is insoluble in water.
Add ChloiiJes, — The clue to the constitution of the
acids of these elements is afforded by tlie oxychlorides, as
in the case of carbon and silicon. No oxychloride con-
taining pentad nitrogen is known, but phosphoryl chloride,
0=PCl3, and antimonyl chloride, 0=iSbCl.(, are pro-
duced by the action of a small quantity of water on the
respective pentachlorides : Cl.^=PCI.j + H.,0 = 0=PCly +
2HCI. The former is a colourless liquid boiling at 107',
and the latter a white, crystalline solid. Phosphoryl
chloride reacts with hydrogen sulphide, yielding the corre-
sponding phosphoryl sulphide : 0--PCl3 + H.,S = 8=PCl3
+ H.,0, and hydrogen sulphide acts on antimony pcn-
tachloride, with formation of S=SbCl.j. O-VCl^ is
produced by direct union of VO with chlorine. It is a
yellow liquid boiling at 137°. The vapour-densities of
phosphoryl and vanadyl chlorides lead to the ascribed
formulae.
Ortho-, Pyro; and yWe^a-^c/ds.— With water,
124
MODERN CHEMISTRY
thcic substances exchange chlorine for hydroxyl, thus :
O-FCI3 + 3H-OH - 0-.P(OH), + 3HCI. This
ebtablithes the formula of ortho-phosphoric add. The
name ought, in strictness, to be applied to P(OH)j; but,
as the true ortho-phosphoric acid is unknown, it has been
transferred to what should be termed its first anhydride.
The corresponding nitric acid is unknown. We have thus
'^'.'wAV^.^-^^^'a. 0=P(OH)3, 0=As(OH)„ and
U^obfOH),;.
On heating these bodies the elements of water are lost, and
the *' meta-acids " are formed; at a temperature of alx>ut
O
II
200°, 0=P(0H)3 yields P-OH, and 0-A8(OH)3,
o
o
II
As - OH ; the former is a glass, the latter a pearly
il
O
substance. On adding water to metaphosphoric acid
it dissolves as such, and, on neutralisation, it yields a
series of metaphosphates ; but metarsenic acid, when
treated with water, is reconverted into orthoarsenic acid ;
a similar change can be produced with metaphosphoric
acid, but only after prolonged boiling.
Di- Acids. — We are unacquainted with any normal di-
acid of this group, but a number of anhydrides are known.
If Z stand for any element of this group, the series should
run as follows : —
/OH
(OH).,=Zc OH
(OH)..=Zf^OH
\OH
Di-acid.
/OH
0=Z^OH
(OK),=Z^OH
\0H
1st Anhydride.
PHOSPHORIC ACIDS 125
/OH 0-Z— OH
O-Z^OH I \
>o 60
0=Z( OH I /
\OH 0=2— OH
and Andryhide. 3rd Anhydride.
Neither the di-acid nor the first anhydride are known
in any case, but the second anhydride, which is generally
called the •• pyro " acid, because it is formed in certain
cases by heating the ♦• ortho " acid, is known with phos-
phorus, arsenic, antimony, and vanadium. Pyrophos-
phoric acid is formed at 215''; but the change is not
complete, and if a higher temperature be employed the
meta-acid is also produced. Pyroarsenic acid is formed
by heating the ortho-acid to 140°- 160°. Pyroantimonic
acid, however, is best prepared by the action of boiling
water on antimonyl chloride, 0=SbCl3; the ortho-acid,
which is probably formed r.ist, loses the elements of water,
forming the pyro-acid, H.^iSb^O-. Pyro-phosphoric acid
is a syrupy glass-like substance ; pyro-arsenic acid forms
hard crystals, and pyro-antimonic acid is a sparingly soluble
white powder.
Basicity. — The basicity of these acids is deduced from
the formulae of double salts. Thus, there are three ortho-
phosphates of sodium and hydrogen ; they have tht-
formula? H._,NaP04, HNa^FO^, and Na.^PO, ; the hydro-
gen calcium salts are : ' H^Ca(POJ,i, HCaPO^, and
C2i.^(^P0^),y It is therefore argued that sincp the hydro-
gen atoms of ortho-phosphoric acid are replaceable in three
stages by metals, there are therefore three atom- of hydro-
gen. These salts are made by mixture; 2rj^P0..Aq-r
Na^PO^.Aq = sH.^^aPO^.Aq, and so on. The acid is,
therefore, said to be tri-basic. The arsenates are j)recisely
similar ; but only simple vanadates are known, and no
ortho-antimonates. A pyrophosphate is known ot the
formula HKo(NH4)P20-, which demonstrates ^Se tetra-
126
MODERN CHEMISTRY
basic character of pyrophosphoric acid, and the other
pyro-acids are classified accordingly.
Metaphosphoric Acids. — The formula of the third
anhydride of the di-acid, H^Z.,Oy, given on the pre-
ceding page, is a multiple by two of that of the meta-
acid, and it is evident that the fourth anhydride of the
tri-acid, the fifth of the tetra-acid, and so on, will all
be multiples of the simpler formula of the meta-acid.
These acids and some of their salts appear to be known
in the case of the phosphoric acids, and what is usually
termed '" meta-phosphoric acid," and given the formula
HPO3, is probably the seventh anhydride of hexa-phosphoric
acid, H,.PgOj3, for one of its double salts has the formula
Na,Ca,("P,0,,),. . , „
Complex salts are known m the case of almost all
these elements. Among such compounds are : H^N^Ojj,
H^^A^u^ Agj,P,,0,i, Na,V,Oj,; while niobates and
tantalates are particularly prone to form such complex salts.
Compounds of a complicated kind, too, in which one of
these elements replaces another partially, have been made ;
as an example, K,.(PyVj2)Oj,y.2iH^O may be instanced.
They are made by mixture.
The source of the nitrates is the attack of ammonium
salts resulting from the decomposition of urea (the chief
form in which all animals part with the nitrogen they
absorb as a constituent of their food) by a bacterium named
the "nitrate ferment." This organism exists only in the
dark ; it is an inhabitant of the soil, and causes the oxida-
tion of ammonia, from whatever source, into a nitrate. As
potash and lime are the commonest bases in the soil, nitrates
of potassium and calcium are the chief compounds formed.
Vast tracts of country in Chili and Peru contain beds of
sodium nitrate, possibly formed by the attack ot the debris
of previous generations of animal organisms by the nitrate
ferment. By distilling a mixture of sodium or potassium
nitrate with sulphuric acid in glass vessels, or, on a large
scale, in iron vessels on which concentrated nitric acid is
PHOSPHORIC ACIDS
127
without r;<-tion, nitric acid comes over into the receiver :
Na/'t /, + H ,SO - HNO3 + HNaSO^. It is not econo-
mic I tc use the quivalent quantity of sulphuric acid, for
the :eai:':iori Ixtvi ;en hydrogen, sodium sulpliate, and sodium
nitrate take- *)lrce at a tem))erature so high that much of
the nitric acid is decomposed: 4HNOy = 2H.,0 + 4NO„
+ O2. Nitric acid is a colourless fuming liquid, with
very corrosive properties. In aqueous solution it is one of
the strongest acids, for it is highly ionised. It is also a
powerful oxidising agent ; this has been referred to on
p. 97. Its anhydride, N._,0.., is produced on distilling
a mixture of nitric acid with phosphoric anhydride ; the
distillate separates into two layers ; the upper one consists
mainly of NgO^, and the anhydride separates in crystals
when it is cooled; the lower layer contains H.,N^O,j, a
liquid solidifying at - 5° ; it is the last anhydride of tetra-
nitric acid. The anhydride decomposes spontaneously in a
few days into the peroxide, N.^O^, and oxygen.
Nitrates. — The nitrates are all soluble salts, possess-
ing the colours of their metallic ions. As a rule, they
crystallise easily. They are all decomposed by heat ; those
of the metals of the alkalies into nitrite and oxygen ; and
all others into the oxide of the metal and nitric oxide and
peroxide, NO a' d NO.,. They are formed by dissolving
the metal, the oxide, or the carbonate in dilute nitric acid.
All metals are attacked by nitric acid, except gold and the
metals of the platinum group. The chief nitrates are those
of potassium, KNO3, saltpetre or nitre ; of sodium, NaNOg,
Chili saltpetre ; ammonium nitrate, NH^NO.j, from which
nitrous oxide, N.,0, is obtained on heating ; lead nitrate,
Pb(N03).„ and silver nitrate, AgNOg, still known by its
old name " lunar caustic," the word " lunar " referring to
the ancient alchemical connection between silver and the
moon. It is used as a caustic for removing growths and
warts ; metallic silver is deposited, blackening the place
rubbed.
Phosphates, — The source of phosphoric acid and
[28
MODERN CHEMISTRY
the phosphates is chiefly calcium phosphate, Ca3(P0^).„
a mineral known as phosphorite, and AlPO^, aluminium
phosphate, or gibbs'te. Phosphoric acid i ; produced from
phosphorite by heating it with dilute sulphuric acid ; spar-
ingly soluble calcium phosphate is formed, while ortho-
phosphoric acid goes into solution. The solution, on
evaporation, deposits white crystals of H.jPO^ ; the
residual liquor deposits crystals of H3P0^.H._,0 ; com-
mercial or " glacial phosphoric acid " is a mixture of both
kinds. Its solution contains many hydrogen ions, and it
is therefore a strong acid. But, inasmuch as phosphoric
+ _ +
acid can ionise in three ways, into 3H and PO_j, into 2H
_ _ + -
and HPO^, and into H and H.,PO^, there are three kinds
of anions. The first of these, PO^, are present in very
small relative amount ; the second and third, HPO^ and
H.,PO^, are relatively much more numerous. There is a
state of balance between the quantities of these ions present
in any solution ; and if, for example, kations of calcium or
lead or silver be added to a solution of phosphoric acid, or
to one of hydrogen di-sodium phosphate, Na^,HPO^, the
PO, ions present enter into combination with the kations,
forming Ca3(P0J,, Pb3(P0J„ or Ag3P0, ; the PO,
ions are increased at the expense of the HPO. and H.iPO,
ions, and the solution becomes more acid. On adding an
alkali, e.g. caustic soda, to a solution of phosphoric acid,
neutrality occurs when the salt Na.,HPO, has been reached;
+ - _ -
the ions are then mainly 2Na and HPO,. On adding
more soda, the solution becomes alkaline, indicating the
presence of free OH ions ; and it is only on concentration
that these OH ions combine with the few H ions of the
PHOSPHATES
129
if
I
~r T - - —
ionised, Na^.HPO,, forming non-ionised water, and «'tri-
basic" sodium phosphate, Na.PO^, is left as a residue.
Similar remarks apply to the ortho-arsenates. The
ortho- vanadates are hydrolysed by water into pyro- and
meta-vanadates.
The chief orthophosphates are: Na.,HP0^.i2H,0,
obtained by neutralising phosphoric acid with sodium car-
bonate ; HNa(NHJP0,.4H.,0, named « microcosmic
salt ; the human organism u^ed to be known as the
" microcosm," and this salt crystallises out of concentrated
urine; Ca^fPOJ.,, prepared by precipitation, and found native
/Ca-PO, Ca
as phosphorite; F-Ca-PO,/ , a .widely
Ca-PO, Ca
spread mineral termed apatite; (NHJMgP0^.6H .O, a
white precipitate produced by adding ammonium" and
magnesium ions to those of a soluble phosphate : (NH ) +
' -p6,=. (NHJMgPO,. It is the usual test for the
ce ot magnesia, and serves at the same time to dis-
t ..i^uish phosphoric acid ; arsenates give a precisely similar
precipitate. The precipitate is nearly insoluble in am-
moniacal water, and it may be filtered off and washed with
water containing ammonia with very little loss. Like
almost all phosphates, it is soluble in water containing
hydrogen ions ; and by the addition of ammonium hydr-
oxide their number is greatly diminished. On ignition,
It yields magnesium pyrophosphate, Mg.P.O-. thus •'
2Mg(NHJPO, = Mg,P:o;+2NH;+H.,ci. '
Ai^enates.~The important arsenates correspond
exactly m formula and crystalline form to the phosphates ;
the only striking difference is in the colour of the silver
salt ; while ortho-phosphate of silver is yellow, the ortho-
arsenate is brick-red.
Vanarfa^es.— Ortho- vanadates are prepared by fusing
vanadium pentoxide with the required amount of a carbonate-
VOL. 11. . *
13°
MODERN CHEMISTRY
on addition of nitric acid to one of its salts, metavanadic
acid separates out as a brov/n-red powder ; on ignition, a
sparingly soluble red powder is left: 2HV03==H.,0 +
V.,0,^. Ortho-antimonates are unknown.
ThiO' Acids. — Thio-compounds are known, analogous
to these salts. Mention may be made of mixed oxy-thio-
phosphates, e.g. Na.jPO.^S 'and Na^POS.,, which result
from the action cf alkaline hydroxides on phosphorus penta-
sulphide, a grey solid produced by direct combination of phos-
phorus with sulphur. They are easily decomposed by hot
water ; hence the thio-arsenates and the thio-antimonates
are bettei* known. Arsenious sulp lide, A8._,S.,, a yellow pre-
cipitate formed by the action of hydrogen sulphide on a solu-
tion of arsenious chloride, and antimony trisulphide, Sb._,S.5, an
orange precipitate similarly formed, dissolve in solutions ot poly-
sulphides of the alkalies; these solutions, on evaporation,deposit
crystals on cooling : As.^S.^ = 2K.,S,\.Aq = zK^AsS^.Aq -I-
S,„_...,. Sodium thio-antimonate, Na3SbS^.9H._,0, has long
been known as «' Schlippe's salt." One of the sulphur atoms
may be replaced by selenium, giving Na.5SbS,Se.9H.,0,
thus showing the similarity in character between sulphur
and selenium.
Pyrophosphoric Acid. — When hydrogen di-sodium
orthophosphate is heated to redness, water is lost, and
tetra-sodium pyrophosphate is left as a white deliquescent
mass : 2HNa,P0^ = Na^P.O^ + H,0. This salt is soluble
in water. 0"n adding to' it lead nitrate, a precipitate of
lead pyrophosphate is thrown down ; it is filtered off,
suspended in water, and a current of hydrogen sulphide
is passed through the liquid. Lead sulph.'de is formed,
and, on removing it by filtration, the solution contains
pyrophosphoric acid. With silver nitrate, a pyrophosphate
gives a white precipitate of silver pyrophosphate, a reaction
which distinguishes this acid from orthophosphoric acid,
for silver orthophosphate is yellow. Magnesium pyro-
phosphate has already been alluded to. The pyrophosphates
of the metals, those of the alkalies excepted, are insoluble
META-SALTS
131
in water, but, tor reasons similar to those given in describ-
ing the ortho phosj)hates, they dissolve in acidt,.
Pyroantimonate of potassium is a salt obtained by
fusing the metantimonate, K^bOy, with caustic potash,
and crystallisation of the resulting fused mass from water.
It is easily soluble, but on adding its solution to that of a
sodium salt, a precipitate of the sparingly soluble di-hydiogen
di-sodium pyroantimoniate, H^.Na^Sb.O.. is produced. It
is one of the very few sparingly sofublc salts of sodium.
Metii' Salts. — On heating to redness di-hydrogen
sodium orthophosphate, H.NaPO., or microcosmic salt,
PI(NHjNaP0^.4H._,0, water, Jr, in the latter case,
ammonia in addition, is lost, and the residue consists of
sodium hexa-metaphosphate, (NaPO.,),.. It is a glass
soluble in water ; its salts are mostly gelatinous. The acid,
uhrch IS probably also hexa-metaphosphoric acid, is a
soluble glass, formed on igniting ortho-phosphoric acid;
It yields salts like that mentioned on p. 126. Unlike the
other two phosphoric acids, it coagulates a solution of
V hite-of-egg or albumen in water. Its silver salt is white
and gelatinous. Mono-metaphosphates are insoluble salts,
produced by igniting together oxides, carbonates, sulphates,
or nitrates with excess of phosphoric acid, and removing
the excess of phosphoric acid with water. The salts of
the alkalies are sparingly soluble. Metarsenates are ])ro-
duced in a similar manner to the hexa-metaphosphates, but,
on treatment with water, they combine with water and
re-form the orthoarscnates of metal and hydrogen from
which they were obtained. Some pyro- and nTeta-thio-
arsenates have been prepared.
Compounds containing less Oxygen. — The
elements of the nitrogen group are characterised by their
possessing more than one valency. They are also, in
most cases, capable of forming compounds with hydrogen.
These two characteristics, taken together, lead' to the
possibility of their forming a number of isomeric com-
pounds, i.e. compounds having an identical composition,
ki
132
MODERN CHEMISTRY
but being, at the same time, different chemical mdividuaU.
Some such compounds are known, at least m their de-
rivatives. The conception will be clearer after inspection
of the following table : —
HO /OH
X -OH
HO OH
(I)
OH
ON' OH
\
OH
(9)'
O-N.
OH
^O
(15)
HO. Al
^N OH
HO^ OH
(2)
/
H
0=N OH
OH
(10)
JI
0=N(
(16)
^O
HO, .H
X H
HO OH
(3)
Al
0-N H
OH
CD
HO II
N II
HO H
(4)
H
0=N -H
^ II
I-')
/OH
N -OH
\OH
(5)
n(-oh
\OH
(6)
N^H
\OH
(7)
/H
N-H
\H
(8)
.OH
H
^0
—
—
(13)
(14)
For convenience' sake, the compounds have been written
as derivatives of nitrogen, but the type is followed by other
elements of the group.
(i) is the true "ortho" acid, unknown in all cases.
(0) is its first anhydride, known in " orthophosphoric ''
acid and in ♦' orthoarsenic " acid. (15) is nitric acid,
and corresponds to mono-metaphosphoric acid, metavana-
dic acid, the metarsenates, and the metantimonates. (2)
and (10) are unknown bodies, but (10) corresponds to
phosphorous acid, and (16) to the nitrites. (3) is also
unknown, but ( 1 1 ) is represented by hypophosphorous acid
and the hypophosphites. (4) is unknown. (12), how-
PHOSPHOROUS ACID
»33
ever, may possibly be the formula of hydroxylamine ; its
name, in that case, should Ix- *« oxy-ammonia." In all
these compounds the element is a pentad. The other
compounds contain triad element. (5) probably represents
the formula,- of the arsenites ; ( 1 3 ) is an alternative formula
for nitrites. (6) nnd (14) are unknown. (7) is an alter-
native formula for hydroxylamine.
Phosphorous Acid. — We shall first consider numbers
(S) and (1^1). In phosphorous trichloride, PCI,, phos-
phorus is undoubtedly a triad. On heating this compound
to 60 ', and passing over it a current of dry air, and subse-
quently leading the air through ice-cold water, crystals
separate, which are washed with ice-water and dried in
a vacuum. They have the formula H,,PO,. The acid,
however, is di-basic ; the formula of its sodium salt, for
example, is Na.^HPOy. Agrin, phosphorous anhydride
^4^0' produced by the combustion of phosphorus in a
limited supply of air, constitutes a crystalline substance,
melting at 22.5' ; it is acted on only very slowly by cold
water, and then yields phosphorous acid. These facts point
to a molecular change from P(OH).. to O PH(OH).,.
But this view is rendered certain by consideration of the
ethyl salts of the acids.
Constitution of Phosphorous Acid. — Phosphorous
trichloride, if treated with a solution of sodium ethoxide,
Na(OC.,H.)„, in alcohol, yields tri-ethyl phosphite,
(CA)3PO;or P (OC,H J y, corresponding to PfOHJg.
It IS a liquid, boiling at 191". On the other hand, a
compound analogous to hydrogen phosphide, PH,, is
known, of the formula PH^,(C2H-), named di-e'thyl
phosphine, which, on oxidatio'n, yields a di-basic acid
analogous to phosphorous acid, O -P(CoH.)(OH).„ named
ethyl-phosphinic acid, from which the ethyl salt' can be
prepared, O- P(C,H.)(OC,H,)^, isomeric with ethyl
phosphite. Iilthyl phosphite is a derivative of triad phos-
phorus, whereas di-ethyl ethyl-phosphinate is derived from
pentad phosphorus. The anhydride of phosphinic acid,
134
MODERN CHEMISTRY
O
O PH(OH).„ would Ix?, not P..O.,, bur :i-P O, like
(i6). But this substance is not toimcd on heating phos-
phorous acid, tor it decomposes into phosjjhoric acid and
phosphoretted hydrogen, thus: 4H;,PO.. = PH., - 3H3PO^.
One of the varieties of the salts of nitrous acid, however,
has a corresponding formula.
Nitrites. — When a nitrate of one of the metals ot the
alkalies is heated with metallic lead, lead monoxide is
formed, and a nitrite, thus : KNO3 + Pb = PbO + KNO..
The nitrite is left as a white fusible salt, easily soluble in water.
On acidifying a very dilute solution with sulphuric acid, a
dilute solution of nitrous acid is formed ; but on warming it,
a somewhat complex action takes place. First, the anhy-
dride is produced : 2HNOo.Aq = H.,O.Aq + Np3, next,
the anhydride is attacked "by the water and decomposed :
3N.,03 + H.,0 = 2HN03 + 4NO ; and some of the anhy-
driJe volatilises with decomposition into nitric oxide and
peroxide: N.,03- NO + NO^. The nitrites are white,
easily soluble 'crystalline salts; those of lead, Pb(NO._,),_,,
and silver, AgNO._„ are sparingly soluble. All are decom-
posed by the stronger acids ; for nitrous acid is a weak acid,
and, moreover, it is easily decomposed, as has been pomied
out. None of these changes throws any light on the constitu-
tion of nitrous acid, however. To gain this knowledge it is
necessary to study the alkyl salts ; for example, ethyl nitrite.
Constitution of the Nitrites. — Ethy\ nitrite,
made by distilling together a mixture of sodium nitrite,
sulphuric acid, and alcohol, is a volatile colourless liquid
with a fragrant odour. On boiling it with a solution of
sodium hydroxide it is hydrolysed, the ethyl group being
again replaced by the metal sodium, thus : 0=N-0(C^HJ
+ NaOH.Aq = 0=N-ONa.Aq + C.H.pH. And if
ethyl nitrite be placed in a Hask along with tin and hydro-
chloric acid — in other words, exposed to the action ot
nascent hydrogen — the products are ammonia (with some
NITRITES 135
H H H
hv-Jroxylaminc) and alcohol : O -= N - H or O + N - H +
I I i
H H H
HO' C, H.J. Sodium nitrite therefore apjwars to possess
the formula ON-ONa. But silver nitrite, heated in a
sealed tube with ethyl iodide, yields a compound of the
same composition as, but not identical with, ethyl nitrite,
O
J
and the formula N— (C.,H.) is ascribed to it ; for, on heat-
I
O
ing with caustic soda, it is not hydrolysed, but one of the
atoms of hvdrogen of the ethyl group is replaced by the
O
I
element sodium, giving N-(C.,H^Na) ; and further, with
I
O
nascent hydrogen, the two atoms of oxygen are removed
and replaced by hydrogen, yielding ethylamine, a compound
H
analogous to ammonia, N-(C..H,) ; this shows that the
I
H
ethyl group in the compound, which is named nitroethane,
is in direct union with the nitrogen atom. It ai)pear?, then,
O
that silver nitrite has the formula N— Ag, and not
o
0=N-OAg. It also follows that two nitrous acids
O
must exist, 0=N-OH and N-H, the former (13) a
6
136
MODERN CHEMISTRY
derivative of triad, and the latter (i6) of pentad nitroger.
But the acids are unknown, and it is only possible to guess
the constitutional formulae of the salts through the reactions
just described.
Arsenltes. — Arseiiites, derived from the acid
HgAsOjj,, such as hydroj^en cupric arsenite or " Scheele's
green," HCuAsO,,, produced by adding to a solution oi
copper sulphate jxjtassium arsenite, arsenious oxide, and a
little ammonia ; pyro-arsenites, such as K jA'=._,0.,, and
metarsenites, KAsO^, ; also ortho- and meta-thioarf:enites,
K.AsSy.and KAsS..^ are known. They show no signs ot
isomerism like that of the phos])hites and nitrites, and they
are doubtless salts of A8(OH)3 and O As-OH, and
the corres|)onding sulphur acids, although the acids corre-
sponding to I'le sulphur salts are unknown. Metantimonite
of sodium, NaSbO.,, and nieta-thio'ntimonite, NaSbS^,, are
formed by dissolving antimonious oxide, Sb^O,., or the sul-
phide, Sb.,Sjj, in caustic soda, and precipitating with alcohol.
Hypophosphites. — Hypophosphorous acid, H.jPOo,
is a monobasic acid ; sodium hypoi)hosphite has. the formula
Na(H.,PO.,). This leads to a formula analog' *o that
given iii ( 1 1 ). When heated, too, the acid yiclus , sphine
and phosphoric acid: 2H3PO, = PH^ + H3PO,. This
would lead to the supposition that some of the hydrogen
was already in combination with the phosphorus. Its salts
also yield phosphine, together with a phosphate and tree
hydrogen. The acid is prepared by the action of sulphuric
acid on the barium salt ; that salt is prepared by boiling
together yellow 'jhosphorus and caustic baryta : 2P^
+ 3Ba(0H),.Aq -»- 6H,0 = 2PH3 + 3Ba(H.PO,),.Aq.
With sulphuric acid insoluble barium sulphate is formed,
while hypophospliorous acid remains in solution. It forms
white crystals, melting at 17.4°. The acid has reducing
power ; with silver nitrate, for example, metallic silver is
precipitated and phosphoric acid is formed. With hydrogen
iodide phosphorous acid and phosphonium iodide are formed :
3H(H,PC )+HI = 2H,(HP03) + PH,L
bi
HYPOPHOSPHATES
U7
Two acids are known Ulonj^inj; to this j^roup of ele-
ments ; thiv have not Ixrii tabulated on p. 132, U-cause
their structure may l>e comiiared with th:it ot hydra/.ine or
liquid phosphine, H,N-NH.. or HJ' PH.,, in which two
atoms of nitrogen — -or of phosphorus — are in direct union
with each otlier. These are phosphatic acid, or, as it is
O P (OH),
sometimes termed, hypophosphoric acid, 1 »
OP (OH).,
N-(OH) "
and hyponitrOUS acid, H . Tlie first of these is
N-(OH)
produced in small quantity along with ortho-phosphonc and
phosphorous acids, when phosphorus is oxidised by exposure
to moist air. It is, however, lu'st made from its silver salt,
by addition of the equivalent quantity of hydrochloric acid.
Silver hjpophosphate is produced by dissolving 6 grams of
silver in 1 00 grams of nitric acid diluted with its own
weisiht of water, and adding to the solution, warmed on a
waterbath, 8 or 9 grams of phosi'horus. i soon as the
violent evolution of nitrous gases ceases the liquid is cooled,
and silver hypophosphate crystallises out. The acid has
no reducing properties, hence it probably contains no hydro-
gen capable of conversion into hydroxyl by the addition of
oxvgen. The sodium salt, Na^P^O^, is converted into
pyrophosphate by the action of a solution of bromine in
water ; the change is evidently due to the addition of
0=P (OH)^ 0=P=(OH),
oxygen, thus
+ 0=0 .The
(OH),
a compound of
0=P=(OH).. 0=P=
" 0=P=0
anhydride of this acid would be | ;
O P=0
the formula P.,0^ is produced by the incomplete combustion
rf phosphorus in oxygen ; but as it yields orthophosphoric
»38
MODERN CHEMISTRY
and phosphorous acids on treatment with water, it is in all
O
probability phosphory! phosphate, O-P-O P
O
Hyponitrites .ire produced by the action of sodium
amalgam, that is, a solution of sodium in mercury contain-
ing alx)ut 4 ))er cent, of the former, on a solution of potas-
sium ().• sodium nitrite. After the mixture has stood for
some days, it is rendered slightly acid with acetic acid, and
silver nitrate is added. .A yellow preci])itate of silver
hyponiti ite is produced ; other hyponitrites may be pre-
pared from it by the addition of the calculated quantity of
the respective chloride. The acid can also be lilx-rated by
the addition to a very dilute aqueous solution of the equiva-
lent amount of hydrochloric acid. On warming ibe solution
ot the acid, nitrous oxide is evolved ; but nitrous oxide
does not unite with water to form the acid.
That the acid has the formula H.,N.,0.„ and not HNO,
is shown by its formation tiom hydroxylamine and nitrous
acid. On mixing dilute solutions of hydroxylamine sulphate
and sodium nitrate, the hydroxylamine nitrate loses watei,
thus: HO-NH, + 0=N-OH = H,0 + HO-N=N-OH;
the silver salt is thrown down on adciition of silver nitrate.
CHAPTER VIII
The Ox} -Acids of the Halogens; Perchlorates and
Perlodates; Chlorates, Bromates, and lodates;
Chlorltes ; Hypochlorites, Hypobromites, and
Hypolodltes— Acids and Salts of Sulphur, Sele-
nium, and Tellurium; ot JHolybdenium, Tung-
sten, and Uranium- Perchromates, Persulphaies,
Perborates, and Percarbonatem.
Thf tbrmulx uf the acids of the halogens present some
analogy with those of the nitrogen group, for, like the
latter, the halogens also possess uneven valency. But while
the highest valency of elements of the nitrogen group n
that of a j)entad, chlorine and iodine function as heptads in
perchlorfc and periodic acids. The valency ot the halogen,
is five in chloric, bromic, and iodic acids ; three in chlorous
acid ; and one in the hypochlorites, hypobromites, and
nypoiodites. A short table, analogous to that given on
p. 132, shows the relation lx?tween these compounds: —
I(OH),.(ONa), corresi^nding to I (OH)., ortho-
periodates ;
O-I(OAg).,, corresponding to O I (OH)., para-
periodates ;
o
^
o
V.
>,I(0Ag)3, corresponding to ^^li'OH)., meso-
( middle) periodates ;
'39
H^^^^^^^^^
M
ll
vn
m
140 MODERN CHEMISTRY
^\ <^%
O y>I(OAg), corresponding to 0-/I(OH), meta-
periodates.
O y>I-0— Iv-0, unknown periodic anhydride.
Perchloric acid, 03Cl(OH), corresponding to meta-
periodic acid, is the only representative of these among
the other members of the halogen group. But the
periodaftes, like the phosphates, form still more condensed
acids ; thus, salts of a di-ortho-perioHic acid, H^IgOj^,
and of a di-meso-periodic acid, H^I^Og, as well as of a
tetra- and hexa-periodic acid, Hjoip^j, and H.,^IgO„i,
are known.
I(OH)5, ortho iodic acid; orthobromic and ortho
chloric acids are unknown.
0=I(0H)3, and similar bromine and chlorine acids, are
unknown.
O
o.
o.
^I(OH), ^Br(OH), and '^^Cl(OH), iodic,
bromic, and chloric acids.
O
I— O— I
^
o
v\ , iodic anhydride, is the only an-
hydride known.
A tri-iodic acid, HIgOg, has been prepared.
0=C1— (OH), chlorous acid, is the only representative
of triad halide.
I-(ONa), Br-(ONa), and Cl-(ONa), hypoiodite,
-chlorite, and -bromite of sodium and of some other
metals are fairly stable in solution.
Hypochlorites. — The starting-point for these com-
pounds is the hypohalite ; it is produced by the action of a
hydroxide on the element in cold aqueous solution, thus :
HYPOCHLORITES
141
2NaOH.Aq + CU Br.., or I., = NaCl, NaBr, or Nal.Aq
+ H.,0 + NaOCi; NaOBr, or NaOI.Aq.
Chlorine monoxide, Cl.p, is tormed ()n i)assing
over dry mercuric oxide, prepared by precipitation from
mercuric chloride with caustic soda, dry chlorine gas ; the
tube containing the oxide must be cooled with ice, tor the
monoxide Is a dark brown, very unstable liquid, boiling
at 6°. The equation is: 2HgO + 2C1.^ = Hg.Cl.O +
Cl-O-Cl. Its density at 10" corresponds with the formula
given. If the mercuric oxide be made into an emulsion
with water, and chlorine be passed through, the acid is
produced in aqueous solution ; it is a pale yellow liquid,
with a not unpleasant smell, recalling that of chlorine. If
concentrated, it decomposes into water, chlorine, and oxygen.
It reacts at once with h\ drochloric acid, forming water and
chlorine : H-O-Cl. Aq + H-Cl.Aq = CI, + H,O.Aq.
The most important hypochlorite is a double compound,
obtained by the action of chlorine on slaked lime, termed
«'cliloride of lime" or " bleaching-powder." It is a
white, non-crystalline powder, smelling of hypochlorous acid.
Its formula is Cl-Ca-O-Cl. That it is a compound, and
not a mixture of calcium chloride and hypochlorite, is
proved by the fact that bleaching-powder is not deliquescent,
whereas calcium chloride is a very deliquescent salt ; calcium
chloride and hypochlorite are both very soluble salts, but
bleaching-powder is only sparingly soluble, but if a saturated
solution of bleaching-powder be cooled, crystals of hypo-
chlorite separate out, thus proving that it is dissociated in
aqueous solution into these two salts. Its smell, as well as
that of other hypochlorites, is due to the fact that hypo-
chlorous acid is a very feeble acid, and is only slightly
ionised ; hence the calcium and other salts are hydrolysed
by the ions of water, and the solution contains free base
and free acid ; and the latter reveals its presence by its smell.
No ion has a smell ; hence one does not smell solutions ot
salts, but only volatile non-ionised compounds.
When bleaching-powder is distilled with just enough
142
MODERN CHEMISTRY
acid to liberate the hypochlorous acid, that acid comes over ;
but if excess of such an acid as sulphuric or hydrochloric
be added, chlorine is liberated, owing to the reaction
between hydrochloric and hypochlorous acids. The addition
of a trace of a salt of cobalt to bleaching-powder results in
the liberation of oxygen when it is warmed ; this reaction,
which is termed " catalytic," is supposed to be due to the
alternate formation and decomposition of an oxide of cobalt
of the formula Co^Oh. ; but the reaction is still obscure.
The bleaching action of bleaching-powder in presence of
acid is ascribed to the liberation of oxygen, and the oxida-
tion thereby of the insoluble brownish colouring matter of
unbleaqhed cotton or linen to soluble compounds which can
be removed by washing.
Chlorates. — Hypochlorites, when heated, undergo
conversion into a mixture of chlorate and chloride:
SNaOCl.Aq = NaClOy.Aq + zNaCl.Aq. The usual
method of preparing chlorates, however, is to pass a current
of chlorine through hot " milk of lime " — that is, calcium
hydroxide suspended and partially dissolved in water.
Potassium chloride equivalent to one-sixth of the lime is
also present. The following reaction occurs : 6Ca(OH),.Aq
+ 2KCl.Aq + 6Cl, = 6CaCl,.Aq + 2KC10,.Aq + 6H..O.
On evaporation, the sparingly soluble potassium chlorate cle-
posits in crystals, leaving the very soluble calcium chloride in
solution. The potassium chlorate is purified by recrystallisa-
tion. It is a white, lustrous salt, crystallising in flat plates.
It fuses readily, and, at a somewhat higher temperature than
its melting-point, it evolves oxygen. At the same time some
of the chlorate is oxidised by the oxygen, and perchlorate
is formed: 2KC103 = 2KCI + 30,, and KCIO, + O =
KCIO,. ' '
Perchlomtes. — On ceasing to apply heat, therefore,
after the salt has become pasty, and treating with water,
the potassium chloride is dissolved, leaving the much less
soluble perchlorate; the perchlorate may be purified by
recrystallisation.
CHLORINE PEROXIDE
143
Owing to the fact that very few potassium salts are
insoluble in water, it is not convenient to prepare chloric
acid from the potassium salt ; for this pur})08e it is
better to use the barium salt, made from baryta-water
and chlorine ; a solution of this salt, when mixed with
the equivalent amount of dilute sulphuric acid, yields a
precipitate of barium sulphate, and chloric acid remains in
solution.
Chlorine Peroxide. — The solution, freed from barium
by filtration, may be concentrated by distilling away the
water at a low temperature in a vacuum ; the acid remains
as a colourless, syrupy liquid, which decomposes at 100°
into perchloric acid, water and chlorine peroxide, CIO., ;
the last compound is unstable at that temperature, and
explodes into chlorine and oxygen. But the peroxide may
be prepared by warming, not above 40°, a mixture of potas-
sium chlorate and concentrated sulphuric acid ; the chloric
acid decomposes as it is formed: 3HC10.j = HCIO^ +
H.,0 + 2CIO.,. It is a dark red liquid, boiling at 10.6"
to a reddish-brown gas. Unlike nitric peroxide, it does
not form double molecules ; Cl.,0^ is unknown. 'It re-
sembles that compound, however, in its action on water ;
while nitric jjeroxide gives a mixture of nitrous and nitric
acids, chlorine peroxide, added to an alkali, forms a chlorite
and a chlorate : 2CIO., + 2K0H.Aq = KC10,.Aq +
KClOyAq.
The chlorates, like the nitrates, are all readily soluble
in water ; lead and siher chlorites, like the corresponding
nitrites, are sparingly soluble salts ; and lead perchlorate is
the only salt which does not easily dissolve. As already
mentioned, chloric acid is readily decomposed when its
aqueous solution is warmed ; chlorous acid is still less
stable ; but perchloric acid, which may be prepared by
distilling together potassium perchlorate with concentrated
sulphuric acid, is relatively stable, seeing that it can be
distilled without decomposition. It is an oily liquid, with
acid taste ; it is apt to explode when brought into contact
I !
,44 MODERN CHEMISTRY
with any oxidisable matter. The corresponding perbromic
acid is unknown.
hypobromites.—KTVohTomileB are produced, along
with bromides, on mixing solutions of alkalies with bromine ;
the solution turns yellow, and acquires a smell like that ot
seaweed. On warming, a change analogous to that suffered
by hypochlorites occurs; the hypobromite yields bromide
and bromate, and the latter can be separated by crystal-
Bromates.— The bromates are white salts soluble in
water ; they do not, however, decompose into bromide and
perbrdmate when heated; the perbromate is unstable, pnd
bromide and oxygen are the only products. Bromic acid,
too, when warmed changes to water, hydrobromic acid,
bromine, and oxygen ; as no compound analogous to ClO^
is produced, bromous acid ii unknown.
//^poiod/tes. — The formation of hypoiodites is
analogous to that of hypochlorites; but the salts are
known only in solution mixed with iodide. Again, like
the hypochlorites, they change on heating; they yield a
mixture of iodide and iodate ; and from barium lodate
iodic acid can be prepared. But it is more readily obtained
by boiling iodine with nitric acid ; for iodine is more easily
oxidised than either chlorine or bromine ; or chlorine and
water may be used as an oxidising agent.
Iodic Acid.— Iodic acid is a white crystalline com-
pound, easily soluble in water; it is a strong acid, and its
salts are produced by neutralisation with hydroxides or
carbonates. When it is mixed in solution with hydriodic
acid, mutual decomposition ensues and iodine is liberated :
HI03.Aq4-5HI.Aq=3l,+ 3HoO.Aq.
Periodic Acid. — The oxidation of iodic acid to
periodic acid is accomplished by means of a solution of
sodium hypochlorite; it is easier to dissolve iodine in a
solution of sodium carbonate, when hypoiodite is formed,
and to saturate the solution wi^h chlorine. The iodate at
first formed is converted into the periodate : NalOg. Aq +
THERMAL DATA 145
NaOCl.Aq = NaCl.Aq + NalO^. Aq. As the periodate is
sparingly soluble in water, it crystallises out on concentrat-
ing the solution. On mixing the solution of the sodium
salt with silver nitrate, tri-hydrogen di-argentic periodate
is precipitated ; it is dissolved in hot dilute nitric acid and
evaporated, when mono-argentic periodate, AglO^, crystal-
lises out. On mixing with water, this salt undergoes the
change : 2AgI0 + 4H..O = HgAg.JO, + HJO,.Aq.
1 he silver salt, which is insoluble in water, is removed by
filtration, and the periodic acid deposits in crystals on
evaporation. The acid forms white prisms ; on heating it
to 130% it decomposes into iodine pantozide, I^Oj^, a
white solid, also produced on heating iodic acid to 170°,
together with water and oxygen; at 180° the pentoxide
decomposes slowly into iodine and oxygen.
Thermal Data. — From the short description which
has been given, it is seen that the oxides of iodine and their
compounds are, as a rule, more stable than those of bromine
and chlorine, and this is connected with the heat which is
evolved or absorbed during their formation. This heat is
seldom determined directly; never when the compounds
are produced with absorption of heat. Thus, when chlorine
combines with oxygen to form Cl.,0, enough heat is ab-
sorbed to cool 17,800 grams of wa'ter through 1% or what
is the same thing, on decomposing Cl.,0 heat enough is
liberated to raise the tem{)erature of "17,800 grams of
water through 1°. This is termed the heat of formation
of the substance. The heat of formation of chloric
acid from chlorine, oxygen, and water involves a heat-
absorption of 20,400 calories, and these substances are
both very unstable. On the other hand, the combination
of lodme with oxygen is attended with an evolution of
heat of 25,300 calories, and an additional 2600 calories
are liberated when it combines with water to form Iodic
acid. Perchloric acid, too, is formed with evolution of
heat (4200 calories), and thus iodic, periodic, and per-
chloric acid are comparatively stable. The heat-change
VOL. II. ^
,46 MODERN CHEMISTRY
^™«s^^S::;V™rB?.meHrso/B«„ valency
-Omenta of the molyMenm and of .he su^ptar
S';SfVl-anatLyhere<<-.^,^^^^
ox,des MoO.and UO »« a o^ Jhydride of a feeble
rjrand Jo^lid'leO:"^ weU-defiLd acid, sulphu-
Oxiaes OT ^"'y"" » . . __When su phur, selenium,
„?.:u:^r?!^f.^fa»e.e-.^^^^^^
Xhtlr^i::^.^"^^^ Rrr£-s'°^s
fLnins sulphur; .is^con^^^^^^^^^
';iS.T, ™?h-e aS:A,SO,, oncc^ling th^ jo-ou
Sf 'iSp^ya a a whj^^^K al» di...e. .
water, and from the -^™""**°'0"^„r naturally be
?""• .n^t^hratds"dld'iave .h:suuctural forLl.
™ag,ncdthat*eseac.ds ,^^^^^ ^^ ^^
Xs-6 and O-Se-O moreover, the chlondes
O S cf'and 0-Se=Cl., thionyl and selenosyl ch o-
°d«,ie Wn; and these react at once w.th water.
ISOMERIC SULPHITES
U7
forming the acids. It is to be presumed that there is ex-
change of chlorine lor hydroxyl, as usual: 0-S=CL +
2HOH = 0=S=(0H)^, + 2HC1. But there is evi-
dence, similar in kind to that adduced in the case of nitrous
and phosphorous acids, to show that while sodium sulphite
has the formula 0=S=(ONa).„ silver sulphite is better
expressed by ^S<; , sulphur being a hexad.
O^ ^OAg
Isomeric Sulphites.— The evidence is this:— Sul-
phur alcohol or ethyl-hydrosulphide (also termed " mer-
captan"), when oxidised by boiling with dilute nitric
acid, is converted into ethyl-sulphonic acid, thus:
O
C2H5SH + 30 = CoH5S-OH, a monobasic acid, of
ii
O
O
which the ethyl salt is C.^Hj-S-O-C.^H.,. Now sodium
O
sulphite, warmed with ethyl iodide, yields an isomeric com-
O
pound of the formula C,H -O-S-O-C^H^. This is
known, because when saponified by boiling with alkali, it is con-
H
verted into alcohol and a sulphite, thus: C^.H^O-S-OC^Hj
+ 2KOH=2aH,OH + 0=S
/
OK
\^ ; whereas the sap-
onification of ethyl sulphonate yiel' potassium ethyl-
n
sulphonate and alcohol, thus: CoHj-S— O— C2H5 +
148 MODERN CHEMISTRY
O
KOH = C0H5-S-OK + CHjOH. And, moreover, this
O
acid, when distilled with phosphoric chloride, yields an
O
acid chloride, CHj-S-Cl, which can be reduced with
1;
O
nascent hydrogen to ethyl hydrosulphide, the substance from
which the acid was originally obtained by oxidation. It is
therefore concluded that the carbon is directly united to the
sulphur atom in this case, while in ethyl sulphite the carbon
of the ethyl group is united through oxygen. It follows
that sulphurous acid must have the formula 0=Sv ,
whereas sulphonic acid should be represented by \^\^
The silver salt is a sulphonate, while the potassium salt is
a sulphite. This peculiarity is not shown by selenium or
tellurium. It appears certain that they are represented by
/OH .OH
the formula 0=Se< and O^Te^ ; but it is
\0H ^OH
not known which formula is to be ascribed to a solution
of sulphur dioxide in water.
Sulphites.— The stdpliites, selenites, and telluritesof
the alkalies are soluble salts; those of most of the other metals
are sparingly soluble in water. Double salts with hydrogen
(" acid salts ") are, however, soluble, e.g. calcium hydrogen
sulphite, Ca(HSOj,)., ; and they are all decomposed by the
stronger acids, sulphurous acid being liberated, li the solution
is dilute ; if strong, sulphur dioxide, its anhydride, comes
off in the state of gas. Similarly, selenious and tellurous
-SCM) CHLORIDES 149
acids are liberated on addition of a strong acid to a solution
of a selcnite or tellurite. Pyrosulphites, similar in kind to
O O
.1 II
pyrophosphates, such as KO-S-0-S-OK, crystallise
out on passing a current of sulphur dioxide through a
solution of the carbonate of the alkali.
Sulphurous acid is a reducing agent, depriving reducible
compounds of their oxygen; it itself is oxidised to sulphuric
acid by the process. Owing to this property, it is used to
bleach woollen goods ; this it does by converting the in-
soluble colouring matter into a soluble colourless compound,
which can be removed by washing. It is also an antiseptic ;
and sulphites are added to liquors undergoing fermentation,
when it is desired to check the action of the ferment.
Selenious and tellurous acids, treated in boiling solution
with sulphurous acid, deposit selenium or tellurium, thus ;
H,Se03.Aq + 2H,,S03.Aq = Se + 2H,SO,.Aq + H,0 ;
and with sulphuretted hydrogen, sulphurous acid gives a
precipitate of sulphur : H^SOg.Aq + 2H,S.Aq =38 +
2H.^0.Aq. This brings to mind the mutual action of
hydrochloric and hypochlorous acids, and of hydriodic and
iodic acids, where the eu » also liberated.
Acid Chlorides. — .Salphur dioxide combines with
chlorine when a mixture jf the two gases is exposed to
sunlight, or when it is p.- ssed over gently heated charcoal.
O. CI
The product, sulphuryl chloride, ^S<; , is a colourless
O^ \C1
filming liquid, boiling at 7 7 °. On adding it to water, it imme-
diately yields sulphuric acid by replacement of the chlorine
O^ /CI H— OH O..^ /OH HCl
byhydroxyl: ^S^ + = ^S< +
O^ \C1 H— OH O^ \0H HCl
Selenium and tellurium form similar compounds ; and so
also do molybdenum, tungsten, and uranium, as well as
chromium. Molybdyl, tungstyl, and uranyl chlorides
,50 MODERN CHEMISTRY
are produced by passing chlorine over tne dioxide, heated
to redness; they are not decomposed ^Y water, but when
tailed with alkalies they are converted into molybdates,
mngsute or uranates. Ohromyl chloride, on the other
3 fs formed by distilling together « ch-^-J ^"^ -'^
and concentrated sulphuric ac.d. This «"^»""" \^^"
action of hydrogen chloride on chromium tr.oxide. thus
CrO + 2HCI = CrO.,Cl.. 4- H,0. The presence of the
sulphltic aciH. is necessary in order to ->thdraw and retain
wa?er, for chromyl chloride is at once attacked by water,
Xomic acid being formed. It is a deep red fuming liquid,
ha Jy ^is inguishf ble from bromine in appearance ; it boils
at 1 18'. A manganyl chloride is said also to have been
^Thetnstitution of the acids is inferred from that of the
chlorides • and in the case of chromium, an intermediate
i is known between chromyl chloride and potas-
S chromate, termed chiorochromate ; us formula is
a CI
\Ct/ ; with sulphur, the corresponding acid,
SilorosulphuHc, or, better blorosulphonic acid is known,
^S ^ . These I aies are produced by the method of
2ixture;^" former by crystallising together arhydro-chro-
mateand chloride of potassium = ^^'"Xqj^ KO^^ ^^O
Ov /OK O^ yOK
^KCl- ^Cr/ + yCr{ ; the latter, by the
union of hydrochloric acid with sulphur tnoxide, thus :
O O. /OH .
\S = + HC1= ^S/ . The former consists of
O^ 0<^ ^Cl ^., ,
red crystals ; the latter is a fuming liquid, readily acted on
CHROMATES
I5»
by water, with formation of sulphuric and hydrochloric acids.
We have thus with sulphur and with chromium the series :
o^\ci'
O,. .OH
O^ '^OH
Chromates, — The starting-point for the chromates is
chrome iron ore, Fe(Cr02)., a spinel (see p. lOo). It
is heated in a powdered state with a mixture of lime and
potassium carbonate, in a reverberatory furnace, where the
atmosphere is a strongly oxidising one. The product is a
mixture of calcium and potassium chromates and ferric
oxide: 2Fe(CrO..)., + 4K,C03+70 = Fe,0, + 4K,CrO,
+ 4CO.,. The fritted mass is treated with water, when
the chromate dissolves, leaving the ferric oxide insoluble.
On evaporation, potassium chromate crystallises out. If
it is desired to produce " bichromate " or anhydrochro-
mal -^ potassium, K.,Cr.,0-, the solution of the chromate
is treated with dilute' sulphuric acid ; calcium sulphate is
precipitated, and is removed by settling ; on evaporation,
sparingly soluble sulphate of potassium crystallises c ut ; and
after removal of the crystals, on further evaporation, " bi-
chrome " crystallises. The conversion of the chromate into
the anhydrochromate is represent^-d by the equation :
2K..CrO,.Aq + H,SO,.Aq = K ,Cr,O..Aq + K ,SO,.Aq.
This conversion is' accompanied by a colour-change ; for
the ions of chromate, CrO^, are yellow, whereas those of
anhydrochromate, Cr.^0-, are orange. On addition of
potassium hydroxide to the bichromate, the opposite change
takes place ; vhe anhydro-chromate ion is changed into the
+ -- +- +--
chromate ion : K.,Cr.,O..Aq + 2K0H.Aq= 2K.,CrO^.Aq
+ H2O.
I-; 2
MODERN CHEMISTRY
Chromic Acid. — Chromic acid is liberated on add-
rv.y to a concentrated solution of potassium anhydrochro-
!'i ite a sufficient excess of sulphuric acid : K.iCr.O^.Aq +
I ; SO^ = K.,SO^. Aq + H,.0 + 2CrO.,. The" acid, in con-
ci 1 ;rated solution, loses water, and deposits the triozide or
auliydride ir crystals of a deep red colour. Chromium
tnoviur "^ ■'. |jowerful oxidising agent ; hence it may not be
hiv '.'b' J to contact with filter-paper ; it must be filtered
thioi. n . ! lat of asbestos or glass wool. The excess of
si.lphui ic acid and potassium sulphate are washed out with
conctnf.ated nitric acid, in which the anhydride is almost
insoluble ; the nitric acid is then volatilised by gentle heat.
This anhydride dissolves in water, but it is doubtful whether
the acid HoCrO^ is contained in the solution ; it is more
+ + - -
probable that the ions are HH and CfoO-,- from the colour,
and other tests, such as the conductivity.
Oxidation by means of a solution of chromic anhydride
is carried out either by boiling the substance to be oxidised
with a mixture of bichrome and dilute sulphuric acid, or
with a solution of chromic anhydride in pure acetic acid ;
the chromate ion, CrO^ or Cr.O;, is changed into the
+ + + ' \ + - -
chromic ion Cr ; the action is: K.^CT,^OyAci +
4H.s6,.Aq J'Cr!^(S0j3.Aq + K,s6,.Aq + 4H,0 +
3O. If the sulphuric acid is hot and concentrated, oxygen
is evolved as gas ; if dilute, substances present in solution,
if they are capable of being oxidised, are attacked by the
oxygen. When chromic anhydride is heated, it is con-
verted into chromium sesquioxide, Cr^O^, with evolution
of oxygen.
Manganates. — Oxides of manganese, if heated with
caustic alkalies in a current of air, or with potassium or
sodium nitrate, are converted into manganate ; the manga-
nate, however, is much more easily decomposed than the
chromate, and, indeed, is stable only in presence of excess
PERMANGANATES
»53
of alkali. Manganic acid is incapable of existence ; an
attempt to liberate it, by addition of an icid to its sotlium
salt, results in the formation of a pennanganate and a
manganous salt, thus: 5Na.,MnO .Ac| 4-6H,SO Aq =
SNa^SO^.Aq + MnSO^.Aq + 4H]VlnO^.Aq + 4H.,0.
PemtMnganatei. — While the manganates are bright
green, the permr lates, which are analogous to the per-
chlorates, are aim t black ; they dissolve in water with a
deep purple colour ; the l^est known is the potassium salt,
a solution of which is sold under the name of " Condy's
Fluid." It is also a useful oxidising agent. If an oxidis-
able body is boiled with its solution, it loses oxygen, thus :
zKMnO^.Aq + 3H,,0 = iKOH.Aq + 2MnO(OH).,
+ 3O ; if an acid, such as sulphuric acid, is present, the
eauation is : iKMnO .Aq + 3H.,S0..Aq = K..SO,.Aq +
2MnSO,.Aq + 50 + 3H,0. ' ' ^ - 4 M
Ferrates are also known ; they are still more unstable
than manganates.
Equations Simplified.— A word may be added
here with regard to the somewhat complicated equations
such as those given. It is convt lient to assume the exist-
ence of the anhydride of the acid as a constituent of the
salt ; thus potassium bichromate may for this purpose be
regarded as consisting of K._,0 in union with aCrOg. On
acting on it with sulphuric acid in r.rt .nee of an oxidit,able
compound, the K.,0 may be supposed react with the acid
thus: K20 + H;S0,= K.,S0, + H.i'). The chromium
salt formed may be regarded! (and this was formerly the j)oint
of view) as a comjx)und of 3SO3, the anhydride of sulphuric
acid, with Cr^Og, viz., Cr,0,.3S03, or Cr.,(SOj . The
formation of CrjjOg from zCrOg involves the loss of 3O ;
nence the equation given above. Similarly, the oxidising
action of potassium permanganate may be formulated thus :
KaO.MnjO^ = KgO + zMnO., + 36 ; and K.pMn.,0,
= KgO + 2MnO -f 5O. With'water present in the former
action, the K._,0 becomes KOH, and the manganese dioxide
becomes hydrated ; with sulphuric acid present in tht latter.
,54 MODERN CHEMISTRY
the K O is converted into K..SO,, and the MnO into
MnSd" This old method of representing chemical
changes had much to recommend it on the score of simpli-
city ; and it often is found convenient, although it is only
a partial expression of the truth.
Molybdates, Tungstates, and ^^"""-/^^'-J,^^
formulae of the molybdates, tungstates, and uranates
are analogous to those of the chromates ; tor example,
K MoO,rNa,WO,, (NHJ.,UO,. The common ore ot
mffiumis thedisulphiii; crystalline scales resembhng
graphite, MoS.., termed molybdenite. On heating it in
the air, or on boiling it with concentrated nitric acid, it is
oxidised to the trioxide, MoO^, a white slippery powder
Wolfram, (Fe,Mn)WO„ is the chief ore of tungsten ; on
boiling with concentrated nitro-hydrochloric acid calcium
nitrate and chloride go into solution, and tungstic acid,
H WO„ remains as an insoluble yellow pwder. Un
heiting t, it loses water, and yields the anhydride a
powde^r with similar colour, WO3. Pitchblende is the
name of the comm'onest ore of uranium ; its forniula is
U O . On fusing it with a mixture of mtrate and car-
bonate of soda, sodium uranate Na,UO, is formed ; and on
adding acid, uranic acid, H,UO, is precipitated, as a
yellow powder. On heating it to 300% a scarlet powder,
of the formula UO3, remains. Ignition changes it into
U,0«, possibly uranium uranate, U(UO J., ot the same
formula as the natural mineral. The chief mo ybdate is
that of ammonium, (NHJ^MoO,, white crystals obtained
by dissolving the acid in ammonia solution; " is used in
precipitating phosphoric acid as phospho-molybdate of
ammonium, a representative of many very complicated njolyb-
dates; its formula is i6Mo03.PA-3(NHJ O-hH^O ;
it is a derivative of one of the condensed mofybdic acids.
Sodium tungstate, NaiWO,, produced by fusmg the tn-
oxide with sodium carbonate, is used as a mordant in dye-
ing, and it has the property of rendering cotton and linen
fabrics uninflammable. The chief characteristic of uranium
SULPHUR TRIOXIDE
155
trioxide is that of forming uranyl salts, such as uranyl
nitrate, (U0..)(N03)^, and acetate, (U0..)(C.,H30.,)..,
"0
i|
where uranyl, U = acts as a dyad radical. The uranates
,1
O
are ill-defined compounds.
Sulphur Trioxide. — The constitution of sulphury]
chloride and its conversion into sulphuric acid has already
been alluded to. And it may be assumed that that of sulphur
trioxide, SOo, is expressed by the formula O^S^ , sulphur
acting as a hexad. Although sulphur dioxide unites directly
with chlorine, it does not combine with oxygen, unless the
two gases are brought intimately into contact by passing them
over line! divided platinum ; such platinum is best prepared
by dipping asbestos (a native magnesium silicate, possessing
a fibrous structure) int j platinic chloride, and subsequent
ignition, when the chloride is decomposed into chlorine,
which escapes, and a deposit of spongy platinum on the
asbestos. On a large scale, sulphur dioxide, made by
burning sulphur or iron pyrites, FeSg, in air, is concentrated
by solution in water, the gas being forced in under some
pressure ; the solution, on being exposed to reduced pressure,
gives up the gas, which is thus freed from the nitrogen of
the atmosphere. The sulphur dioxide is then mixed with
air and passed over the platinised asbestos heated to a
definite high temperature. Combination ensues, and the
sulphur trioxide is condensed in cooled receivers. It is a
white, crystalline, fuming substance, dissolving in water
with a hissing noise and with great evolution of heat. It
also unites directly with hydrogen chloride, with formation
of chloro-sulphonic acid, Cl-SO^,-OH, a fuming very
corrosive liquid.
Sulphuric Acid. — The product on dissolving sulphur
trioxide in water is sulphuric acid, H^SO^j if smaller
156
MODERN CHEMISTRY
quantities of water be used than are necessary tor the
formation of HoSO^, various pyro- or anhydro-sulphuric
acids are produced, the simplest of which is the acid,
H0-(S0o)-0-(S0o)0H, analogous to some extent in for-
mulatopyrophosphoricacid, (0H)o-^P0-0-PO=(0H)o,
but more closely resembling potassium dichromate. It,
too, is a fuming liquid, evolving much heat on addition of
water. j i i • •
Sulphuric acid, however, is ordinarily made by brmgmg
together sulphur dioxide in presence of steam with nitric
peroxide, NO.,, and oxygen. For this purpose, sulphur
or iron pyrites' is burned in air ; the products of combus-
tion are passed through a flue provided with a chamber in
which it is possible to place, when required, a pot containing
a mixture of sodium nitrate and sulphuric acid ; the product
is nitric acid, which is at once attacked by the sulphur
dioxide, yielding sulphuric acid and nitric peroxide, thus :
2HN03 + SO., = H,SO^ + 2NO.,. The gases next pass
up a tower, termed the " Glover tower," after its in-.ontor.
In this tower they meet a spray of dilute sulphuric acid, the
decomposition product with water of a compound which
will afterwards be alluded to, hydrogen nitrosyl sulphate.
The hot gases, in contact with the dilute acid, evaporate
much of its water, which as steam finds its way along with
them up the tower. From the Glover tower the gases
enter the first -^C •\ series of leaden chambers, in which a
reaction occurs between the sulphur dioxide, the nitric
peroxide, and the steam, thus : SO., + NO., + HgO = H^SO^
+ NO. Excess of air is admitted along with the sulphur
dioxide, so that there is present in the leaden chamber a
considerable excess of oxygen. By its aid, the nitric oxide
is re-oxidised to peroxide, which is again attacked by the
sulphur dioxide, so that the nitric oxide serves as a carrier
of oxygen to the sulphur dioxide. The nitrogen of the air
conveys the gases from chamber to chamber ; and when it
has passed through a sufficient series (from nine to thirteen)
of chambers, all the sulphur dioxide has been converted
SULPHURIC ACID
«57
into sulphuric acid, and deposited on the floors of the
chambers, whence it is run off from time to time ; it is
called " chamber-acid." Formerly, the nitric oxide and
peroxide used to escape into the air and be lost, besides
causing a nuisance ; to save it, Gay-Lussac devised a
means of trapping it by passing the escaping gases up a
tower which bears his name ; a stream of concentrated
sulphuric acid flows down this tower, moistening the coke
or flint with which it is filled. On coming into contact
with the mixture of nitric oxide and peroxide, a salt of
sulphuric acid is formed — hydrogen nitrosyl sulphate,
HO— SO.,— O— N=0, the group — N=0 having replaced
one of the hydrogen atoms of the sulphuric acid. This
compound dissolves in the excess of sulphuric acid ; it is
conveyed by means of a special pump to the Glover tower,
where it is mixed with water, and is decomposed, thus :
2H0-S0,-0-N0 + H.p = 2HO~SO,-OH = NO +
NO.,. Although this compound is formed by the action
of concentrated sulphuric acid on a mixture of NO and
NO.,, yet excess of water causes the action to proceed in
the opposite sense ; this affords a good example of the
action of mass.
After the chamber acid has been evaporated in leaden
vessels until a portion of the water is expelled, it is further
concentrated in vessels of platinum, glass, or iron. The
dilute acid is without action on lead, and the concentrated
acid does not attack platinum or iron, although iron is at
once dissolved by dilute acid. The heavy oily liquid
remaining after evaporation still goes by its old name of
" oil of vitrol." Its composition is not quite expressed by
the formula H.,S04, however, for that substance is unstable,
and parts with a trace of sulphuric anhydride when heated,
leaving a trace of water in the oil of vitrol. It can be
made by dissolving the right amount of anhydride in the
acid to combine with that water ; the resulting acid melts
at 10.5°; oil of vitrol has a much lower melting-point.
The molecular weight of liquid sulphuric acid, determined
158
MODERN CHEMISTRY
by its rise in a capillary tube, is very high, and appears to
correspond to about 30H2SO4 ; on dilution it is no doubt
considerably lowered, and in dilute solution it is mostly in
the state of ions.
When heated to about 250% sulphuric acid, as oil of
vitrol is usually termed, begins to emit fumes of anhydride ;
apparent ebullition takes place at about 350°, and the acid
distils over. This is, however, really dissociation into
anhydride and water ; for the density of the vapour is not, as
might be expected, half the molecular weight, 98, but only
24.5, one quarter of that number. And this agrees with
the theoretical density of a mixture in equal proportions of
the vapours of the anhydride and water, for (40 + 9) / 2 =
24.5. A considerable rise of temperature takes place on
mixing sulphuric acid with water ; it is not improbable that
the first anhydride of the true ortho-acid is formed ; the
compound of the formula HgSO-.HgO, which may be
0=S=(OH)^, melts at 8°. The point of maximum
contraction of a mixture of sulphuric acid and water occurs
when the proportion corresponds to H.^SO^.jHoO ; this is
possibly S(OH),., but it does not easily sofidify. Water
can be' withdrawn from sulphuric acid by distilling it with
phosphorus pentoxide, when sulphuric anhydride is formed
and distils over.
Oxidising Action of Sulptiuric Ac/d.— Sulphuric
acid can behave as an oxidising agent, being itself reduced.
This change is produced when it is heated with most other
elements. Thus with carbon, C + 2H.,S04 = COg + 2SO0
+ K,0; with sulphur, S + H,S04 = 3802 + HgO; with
copper, mercury, iron, lead, silver, &c., a sulphate is formed,
and' sulphur dioxide is liberated ; this may be viewed as the
reducing action of hydrogen, at the high temperature re-
quired for the reaction, thus : Cu + H^SO^ = CUSO4 + 2H
and H.,SO^ + 2H = 2H,0 + S02. The reduction goes
further, "and some sulphur'is liberated, while copper sulphide
is formed: CuS04 + SH = CuS + 4H,0 ; H2SO, + 6H
= S + 4H20.
SELENIC AND TELLURIC ACIDS
159
Hydriodic, and to a less extent hydrobromic acid also,
are oxidised by sulphuric acid: H.^S04 + 2HI = I., +
2H2O + SO2 ; and alcohol and many other compounds" of
carbon have a reducing action on sulphuric acid.
Selenic .4c/ink, Cr green, Fe yellow, Ni ureen, Co
+ +
red, Cu blue, and the others col. ailess.
Sulphates of" the alkali- and alkaline-earth metals are
stable at all tcmi)eratures lower than that of the electric arc ;
but all other sulphates decompose, the primary jModuct lieing
the oxide of the metal and sulphuric anhydride ; the latter,
however, being unstable at a red-heat, dccomjjoses partly
into sulphur dioxide and free oxygen. This decomposition
is made use of in the preparation of " Nordhausen sulphu-
ric acid," a fuming liquid, consisting chietiy of H.,S.,0. ;
it is made by distilling partially dried ferrous sulphate 'from
fireclay retorts: 2FeS0^= Fe,034- SO. + SO.^ ; the
pyrosulphuric acid is produced by the union of the anhy-
dride with water : 2SOy + H^,0 = H^,S^.O-. The iron
oxide has a fine red colour, and is sold as "a paint under the
name " Venetian red."
Salts of Alkyl RatHcals.— Salts of the alkyl radi-
cals are as a rule volatile ; they are produced by distilling
the alcohols with the res|)ective acid. Ethyl nitrite, for
example, is formed by distilling a mixture of alcohol,
sodium nitrite, and sulphuric acid : NaNO , + H .SO,. Aq -f
C,H,OH = C.H,NO,. + NaHSO,.Aq. ■ It is' a volatile
liquid, with a pleasant odour, which, when boiled with
potash, is hydrolysed, with formation of scxlium nitrite and
ethvl alcohol : C.HjNO., + KOH.Aq - K -0-N O.Aq
+ C.,H,OH. The nitrate, C.H.ONO^, cannot be pre-
pared from nitric acid and alcohol unless the presence
of nitric i)ero\ide i-. excluded ; for this purjx)se urea,
CO(NH^,)^„ is added in small proportion to the mixture ; its
presence prevents the oxidation of the alcohol, and brings
about the normal action C..H.OH + HNO., = C..H-NO.. +
H._,0. The nitrate resembles the nitrite i'ipropert'4s, t)n
mixing alcohol with sulphuric acid there is a considerable rise
in temi)erature, and hydrogen ethyl sulphate is produced :
C.H.OH + HO SO,-OH = HO- SO,-OC.,H., + H..0.
A considerable excess of sulphuric acid "must 6e present in
1 64
MODERN CHEMISTRY
order to ensure the nearly complete conversion ot the
alcohol into the ethyl salt. To remove this excess, calcium
carbonate is added, which forms sulphate of calcium and
a double sulphate of ethyl and calcium, Ca(C._,H,SO^)^, ;
the former is nearly insoluble in water, while the latter is
readily soluble ; from the calcium salt the acid may be pro-
duced by addition of the theoretical amount of sulphuric
acid. On evaporation it is a syrupy liquid ; it decomposes
when heated into ethylene, sulphur dioxide, carbon mon-
oxide, and carbon dioxide. As seen by the formula of the
calcium salt, the acid is a monobasic one. The i)otassium
salt, f9r example, has the formula K(C._,Hr,]SO^ ; the salts
are all soluble. Similar acids are formed from other alkyl
radicals, such as methyl, amyl, &c.
ThiosulphateS' — Some other acids of sulphur remain
to be noticed. Among these is thiosulphuric acid,
H.,S.^O.j, of which the sodium salt is produced by digesting
together sodium sulphite with sulphur, just as, with oxygen,
sodium sulphate is formed. In the latter case it may be
supposed that the atom of oxygen inserts itself between the
sodium atom and the sulphur atom with which it is in com-
O O
I r
bination, thus : Na-Q-S-Na + O = Na-O-S-Q-Na ;
O
O
O
Na-0-S-Na + S = Na-0--S-S-Na ; hence the name
i '
O O
«♦ thio " sulphate, the «* thion," or sulphur, replacing the
oxygen of sulphuric acid. The sodium salt forms large
transparent crystals of the formula Na..8..0„.5H.,0 ; the
barium salt is sparingly soluble, and forms a crystalline
precipitate on adding a solution of the sodium salt to one ol
barium chloride ; the lead salt is insoluble, and the silver
salt is a white precipitate, which rapidly turns dark on
lODOMETRY
165
application of heat, being converted into silver sulpliitle :
f^&2^P:i + H^O.Ai] - Ag.S + H.SO^.Aq. On acidify-
ing any one ot' the soluble salts, the ac d is momentarily
liberated; but it immediately decomposes into sulphurous
acid and sulphur, H^.S.Oy. Ac| ^ H.,SOy. Aq + S, the latter
rendering the liquid mifky. The sodium salt, when a solu-
tion of iotiinc in one of potassium iodide is added to it,
undergoes the reaction : iNa^S^Oa. Ac] + I.,.Aq = iNal.Aq
4- Na.,S^Og.Aq. The salt formed is named tetrathionate
of sodium. It will be considered shortly.
lodometry. — A solution of sodium thiosulphate con-
taining 24S grams, made up to a litre with water, reacts
quantitatively with one containing 127 grams of iotline jier
litre ; the colour of the iodine disapjH-'ars, and the vanishing
of the \v X trace of iodine can be ascertained by the addition
of some starch paste, which gives a blue colour so long as
any free iodine remains unconverted into ions ; such a solu-
tion is commonly used in estimating 'odine, or in determin-
ing the quantity present in solution of any substance which
has the proj^rty of liberating iodine from acidified iodide,
i.e. from hydriodic acid, such as free chlorine, a hvjx)-
chlorite, or, indeed, anv oxidising agent.
On boiling together solutions of sodium thiosulphate with
ethyl iodide, sodium ethyl thiosulphate is formed ; its
O
formula is Na— O— S-S-CH^, for, when mixed with
O
barium chloride, the barium salt, which is unstaSle, decom-
poses into barium dithionate and erhyl disulphide. thus :
.0-SO,-S(C,H,) ^ u SO.. S(C,H,)
Ba
\
= Bac
+ I
0-SO.-S(C,HJ ^O-SO, '"^(C.H.)
This decomposition renders two suppositions probable :
O SH
that thio-sulphuric acid has the formula S^ ,
O^ \OH
1 66
MODERN CHEMISTRY
S., .OH
and not jSc , and that dithionic acid is constitu-
O- ^OH
0,S-OH
tionailv represented by I
0,S-OH
Hydrosulphites. — Hydrosulphurons acid, H.S.O^,
sometimes called " hyposulphurous acid," is produced
as zinc salt by the action of metallic zinc on sulphurous
acid. The liquid turns brown, and i^ssesses great reducing
power. The sodium salt, which is better known, is pro-
duced by digesting zinc turnings with a concentrated solu-
tion of hydrogen sodium sulphite: Zn^^+HNaSOg-Aq -
Na.,Zn(S03)2 + NaoS..,O^.Aq-f aH.jO; the sodium zinc
sulphite crystallises out' on addition of alcohol, leaving the
hydrosulphite in solution. On cooling the solution, slen-
der crystals of the hydrosulphite separate. The solution
absorbs free oxygen so rapidly that it turns warm ; it is
used as a reducing agent in indigo-dyeing ; indigo-blue is
converted by the hydrogen of water (of which the oxygen
enters into combination with the hydrosulphite, convert-
ing it into sulphite) into a colourless substance, termed
indigo-white ; this body being soluble, penetrates the fibre
of fabrics dipped into the solution, and on exposure to air,
indigo-blue, with its usual colour, is deposited as an in-
soluble precipitate in the cloth. By help of sodium hydro-
sulphite, too, a ferrous salt may be deprived of ferric so
completely that it gives a nearly white precipitate with
alkalies ; the usual colour of the impure ferrous hydroxide
is a dirty green.
Thionates Manganese dithionate is produced by
passing a current of sulphur dioxide through freshly pre-
pared manganese dioxide suspended in water, made by
boiling potassium permanganate with alcohol. The equa-
tion MnOo.nH20 + zSO^.Aq = MnSgO^.Aq represents the
change. On addition of barium hydroxide to the man-
ganese salt, manganous hydroxide is thrown down, and
THIONATES
167
barium dithlonate is left in solution. From it, the acid
may be prepared by the addition <>♦ the requihite amount of
sulphuric acid ; and the other s % by addition ot the
appropriate sulphate. The acid, concentrated by evapora-
tion at a low temperature, is a sour, syrupy liquid ; when
heated, it decom]X)se8 into sulphur dioxide and sulphuric
acid.
Trithiouic acid, H .S^O^, is also known ; it is a still
more unstable liquid.
Tetratliionate of sodium, as already remarked, is pro-
duced by adtiition of a solution of iodine to a thiosulphate ;
it is j-recipitated on addition of alcohol. The acid forms
a colfiurlc s solution, widi strong acid taste. The
method of it6 foriu ition gives a clue to its constitution :
NaO-S{0 )-S-Na I Nal NaO-S(0,J-S
- ! - + I •
NaO-8(0,,) -S Na 1 Nal NaO-S(0.,)-S
Pentathionic acid, H.^S^O^, is produced by passing a
current of hydrogen sulphide through a dilute scl ur'(;4i of sul-
phurous acid, along with tri- and tetrathirvptc a-
+ 5S0..Aq. = H.SjO^.Aq + +H,0 + y i , u
usually given. Hxcess of hydrogen snt-'i't;* , 1
long time, results in the reaction ,:ii,- •
2H.,O.Aq + 3S. The tri-, tctra-, asi ;- ^
when heated, yield a sulphate, sulphur I'.ioxju
sulphur.
Highly Oxidised Acids.— 0( recent y
siderable number of salts of acids more highly oxidised
than any of those already mentioned has been prepared. It
has long Iwen known that on addition of hydrogen dioxide
to a solution of potassium bichromate acidified with
sulphuric acid, a bright blue colour is produced, and that
this coloured substance can be extracted by ether from its
aqueous solution. The compound has recently been
identified as perchromic acid, CrO^(OH); for, on
adding to the cooled blue solution a solution of ammonia
in ether, a violet precipitate of CrO^(0-NH^).H._,0^ is
i*". ■
:H,S
uition
.•:Cv
'or a
.
1
■' '' ' i ^
:!i;>
■ '^CSf
*:!*
-t X'Ci^
A con-
168
MODERN CHEMISTRY
thrown down ; and if an etherial solution ot" potassium
hydroxide be added, the potassium salt of similar formula
is precipitated. These bodies are explosive.
Fersulphates of potassium and ammonium are produced
by passing a current of electricity through concentrated
solutions of the sulphates in water. The persulphate is
sparingly soluble, and deposits in white crystals. The
formula ap])ears to be M._,S^O^ (M== monad metal).
The acid has bleaching powers, and gradually decomposes
into sulphuric acid and ozone.
Perborate of sodium, NaB03,4H.,0, is similarly pre-
pared, ,or it may be produced by cooling a solution of
borax to which some caustic soda and hydrogen peroxide
have been added. It, too, is a sparingly soluble salt, pos-
sessing bleaching properties.
Percarbonate of sodium, NaXO^. iAH.,0, is similarly
prepared by addition of alcohol" to a solution of sodium
carbonate, to which a solution of hydrogen peroxide has
been added. It is a white, extremely unstable compound,
possessing, ?.". the other similar salts, great oxidising
power.
H
CHAPTER IX
The Nitrides and Pliosptiides, Arsenides and
Antimonides — Complex Amines and titeir
Salts— Acid Amides— The Cyanides and the
Double Cyanides.
Analogy between Oxides and Nitrides.— Nitro-
gen and phosphorus are best characterised by the compounds
in which they act as triads. For just as an oxide or
hydroxide may, as was customary during the era of the
theory of "types," be regarded as water in v/hich the
atoms of hydrogen are more or less completely replaced by
atoms of a metal ; so from analojiy it is to be inferred that
conijjounds should be jireparable which should he similarly
related to ammonia and to hydrogen phosphide. The
following graphic formulas will render the conception
clear : —
H-O-H _
H-NH. ^
H-O-H j
H-O-H (
H-NHo I
H-NH3 j ~*
Na-O-H
Na-NH,
.0-H
O-H
NH,.
C
Ca<
\
^NHg
Na-O-Na;
- Na- N^^Na, ;
-- Ca=0 ;
-* Ca/
,N=Ca
•^N=-Ca
MODERN CHEMISTRY
I
Ci
OH
^0
c./''
OH
^ C< -.
OH
^OH
\o
NH..
-. c.^'^" .
NH.:
Cr-N.
NH,
\nh.,
170
H-O^H )
H -0-H
H-O-H )
H-NH., )
h-nh: >
h-nh: )
But although most elements combine with oxygen directly,
there are only a few which burn in nitrogen. Among these
are lithium, calcium, and magnesium ; boron and titanium
also pdssess this property. The nitrides of the other
elements are practically unknown. These nitrides are
attacked by water ; the three first with violence at the
ordinary temperature ; the two last, when heated in a
current of steam. The products are the hydroxide of the
metal and ammonia ; or with boron and titanium, owing to
the high temperature of action, the oxide, thus : Mg^N,
+ 3H,O.Aq = 3Mg(OH), + iNHg.Aq.
Nitrides. — Lithium nitride, Lij,N, is a dark-coloured
substance ; it is formed at the ordinary temperature on expos-
ing metallic lithium to the air. Calcinm nitride, CaoN.,, is a
greyish-yellow substance ; and magnesium nitride, Mg^N.,,
a yellow powder. Combination takes place readily with
great evolution of heat when a mixture of dry lime with
magnesium ])owder is heated to dull redness in a current of
nitrogen ; this affords a convenient method of separating
nitrogen from the indifferent gases of the atmosphere, and
preparing the latter in a state of purity. Boron nitride,
BN, is a white amorphous powder ; it can also be prcxluced
by heating to redness a mixture of boron oxide with ammo-
nium chloride, until excess of the chloride has volatilised.
flydrazoates. — Besides these compounds, which may
be regarded as the analogues of the oxides, a series of
nitrides is known, which correspond in formula with
hydrazoic acid, HN ... The starting-point for these com-
pounds h sodamine, NaNH^, (sec b-clow). This compound
HYDRAZOATES
171
is heated to 300 in a series of small flasks in a current of
nitrous oxide, when the following reaction takes place :
2NaNH., + N..0 = NaN, + NaOH + NH,. The change
which takes pface is more obvious when the reaction is con-
ceived to occur in two stages: NaNH., + 0<( \\ = NaN^ ||
\N '-N
+ H,0; and NaNH, + H,0 = NaOH + NH,,. The
product of the reaction is dissolved in water, acidilied with
dilute sulphuric acid, and distilled : NaN^.Aq + H.,SO ^.Aq
= HNg.Aq + NaHSO^.Aq. The distillate, which is a
dilute solution of hydrazoic acid, has a peculiar odour, and
if its vapour be inhaled, tainting may result ; it is necessary
to take precautions to distil it in a good draught. The
solution has an acid reaction ; salts may be prepared by
neutralisation with the hydroxides or carbonates of the
metals. The ions, -Ng, are colourless, and the salts of
colourless ions are themselves white. Those of lithium,
sodinm, potassiiun, magnesium, calcium, strontium,
barium, and zinc are crystalline ; their formulx are M'N.
and M"(Ng)., respectively. Silver hydrazoate, AgN.,,
closely resembles the chloride in appearance and in in-
solubility ; it is, however, dangerously easy to explode,
and should be prepared dry only in minute quantity, and
treated with the utmost precaution. Titration with a
deci-normal solution of silver nitrate affords a convenient
meihod of deterr.iining the strength of a solution of
hvdrazoic acid, or ot analysing the hydrazoates ; it is easy
to recognise the ])oint when all hydrazoic acid has been
removed as the insoluble silver salt-
Atnines. — Substituted ammonia, in which one atom of
hydrogen is replaced by an element, is the analogue of the
hydroxides. Such bodies are termed amines or amides.
Sodamine, NaNH^, is easily prepared by jjas.Mng a current
of ammonia, dried by j)assing it through a tower filled with
soda-lime, through an iron U-tube containing sodium, and
heated to about 3'^^°' -^l-^ W*^ ''' i^P'^^ly absorbed, while
r
172
MODERN CHEMISTRY
hydrogen is evolved : 2NH3 + zNa = 2NaNH., + H.^.
When the sodium has been all converted into sodamine,
the tube is emptied by pouring out its contents. Sodamine
is a white brittle substance, with crystalline fracture, not
unlike caustic soda, melting at about 100°. So long as it is
kept dry it is quite permanent, but with moisture it at once
reacts, forming ammonia and caustic soda : NaNH., + HOH
= NaOH + NHg. Similar compounds can be made with
lithium, potassium, rubidium, and probably caesium.
The corresponding compound of zinc, Zn(NH.,)2, is a
white powder, insoluble in ether, formed along with ethane
or methane by the action of anmionia on zinc methide or
ethide: Zn(CH3),+ 2NH3 = Zn(NH.,),+ 2CH4.
Quanidine. — An attempt to prod^uce the amine of
carbon, C(NH.,)4, by the action of ammonia on such
a body as carbon tetrachloride or ethyl orthoformate,
C(OCoHr)4, according to the equations CC1^4-4NH3
= C(N"H2) +4HCI, or C(OC,H5), + 4NH3 = C(NH,),
+ 4HOC.,H5, fails, owing to loss of ammonia. For just
as orthocarbonic acid, C(OH)^, loses water, yielding
ordinary carbonic acid, so carbon tetramine loses ammoni.i ;
the jiroduct is named guanidine, and has the formula
HN = C(NH.,)^.; its analogy with 0-C(OH).^is easily
seen. Guanidine is a white crystalline substance, which,
like ammonia, unites with acids to form salts.
On comparing the formulae of carlwnic acid and guani-
dine, it is evident that several intermediate compounds
should be capable of existence. The series is : —
0=.C(OH), HN-C(OH),, 0-C-/
\
OH
(0
(2)
(3)
/OH
0-C(NH.,), HN = C< HN =C(NH..),.
NH.
(4; ^5) " (^>)
1
CARBAMATES 173
Oi these, the best known are the ammonium salt of (3),
which is termed carbamic acid, and (4), the important
compound urea or carbamide.
Carbamates,— Ammomvaa. carbamate, known by
the famihar name of " smelling salts," is formed by mixing
ammonia and carbon dioxide gases: C0., + 2NH =
^r^t" ^^ ^^^4- It '« a white crvstalline" compound,
soluble m water and smelling of ammonia. Its solution,
when fresh, contains the compound of which the formula
18 given above; but after standing, it is converted by
absorption of water into ammonium carbonate. This has
been ascertained by treating the freshly prepared solution
with sodium hypochlorite, when only half the nitrogen
which the substance contains is evolved :
2H N-CO-ONH,.Aq + 3NaOCl.Aq =
2H2N-CO-OH.Aq + sH.O + 3NaCl + N, ;
on the other hand, with a hypobromite, all the nitrogen
IS evolved :
H,N-CO-ONH,.Aq + 3NaOBr.Aq = CO +
3H,0 + N, + 3NaBr.Aq.
N..W, ammonium salts yield up their nitrogen when
mixed with a solution of a hypochlorite ; hence it is con-
cluded that the compound contained in a fresh solution
IS ammonium carbamate. But on standing, the solution
changes, and after some time it yields all its nitrogen
on treatment with hypochlorite ; hence the assumption of
the elements of water and a change into ammonium car-
bonate may he inferred: H,N-CO-ONH^.Aq + H,.0 =
^^^T^,T^^~^NH4-AS- " liutammoniun/carbamatemav
conceivably possess the formula HO-C(NH)-ONH '•
and It nKry be that it is the .. NH group which resist^
attack. 1 his last supposition is confirmed by the behaviour
ot urea with hypochlorite ; for with it, too', only half the
nitrogen is evolved.
Carbamide. -Vrea. or carbamide, to whicli the tor-
174 MODERN CHEMISTRY
mula 0-=C(NH.,).. is generally ascribed, is the form in
which by far the' largest i)art of the nitrogen is evolved
which is consumed as food by animals. It may be directly
prepared from urine by evaporation to one-third of its bulk,
and addition of nitric or of oxalic acid; the sparingly
soluble nitrate or oxalate is precipitated ; the salt is purified
by recrystallisation from water, and is then mixed with
caustic soda and evaporated to dryness. On treatment
with alcohol, the urea alone dissolves, and deposits m
crystals from a concentrated solution. It is a white, easily
soluble 'substance, with a saline taste. It unites with acids,
forming salts; but as the carbonyl group, CO, has the
property of conferring acidity on neighbouring atoms of
hydrogen, the basic qualities of only one of the two
amido-groups, -NH.„ can display itself; hence the for-
mula of the hydrochloride is CO(NH.)..HCl, and not
CO(NH.,)...2HCI, as might be expected. It is therefore
a mono-acid base.
Urea can also lie produced from inorganic sources, and
it was the discovery of its synthesis from potassium cyanide
by Wehler in 1827 which caused the abandonment of the
old view that compounds containing carbon, with the ex-
ception of its oxides, belonged to a si^ecial class, and could
be produced only by the intervention of " life-power." Its
production is as follows: Potassium cyanide is heated to
tedness with lead oxide; KCN + PbO =. KCNO + Pb.
The cyanate, KCNO, is next dissolved and mixed with a
solution of ammonium sulphate, and the mixture is evapo-
rated to dryness. It may be supposed that potassium
sulphate and ammonium cyanate are first formed: 2 KCNO
+ (NHJ..SO, = K.,SO, + (NHJCNO. But the latter
compound" is unstable, and undergoes change into its
isomeride, urea : (NHJCNO ^ O C(NH,),. On treat-
ment with alcohol, insoluble potassium sulphate remains
undissolved, while the soluble urea crystallises fiom the
alcohol on evaporation. Urea is alr^o 'prodiiced when carbonyl
chloride or when ethyl carbonate is treated with aqueous
AMIDES OF PHOSPHORUS 175
ammonia : O CCI., + 2NH, = 0^C(NH.,)...HC1 +
HCI; 0=-C(OC aj, 4 2NH3 ^ O C(NH,),. +
iC^HjOH. Lastly, carbamate of ammonium, when heated
in a sealed tube, loses water with formation of urea :
H,N-CO-ONH4 ^- 0=C(NH,), + H,0.
Biuret. — When urea is heated, a body named biuret is
formed, with loss of one molecule of ammonia. We are here
reminded of the relation between an acid and an anhydro-
acid ; this is evident on inspection of the formula; : —
H,N-CO-NH, HO-SO,-OH
Urea. Sulphuric acid.
H.N-CO-NH-CO-NH, HO-SO,-0- SO,-OH
Biuret. Anhydrosulphuricacid.
Amides of Acids of Piiospliorus. — Many com-
pounds analogous to urea are known, where the hydroxy!
groups of acids are replaced by amido-groups, -NH.,. By
the action of ammonia gas on phosphorus oxyc'hloride
ortho-phosphamide is formed : O PCl^ + 3HNH., =
0=P(NH^,)y + 3HCI. The ammonium chloride formed by
the combination of the hydrochloric acid with excess of
ammonia is removed by washing, and an insoluble white
powder remains. When phosphamide is heated, ammonia
is lost, and phosphoryl-amide-imide (the group =NH
is termed the " imido-group"), HN=PO(NH.,), and at
a higher temperature, N=P=0 or phosphoryl nitride are
left. They are also white insoluble powders. By analogy
with carbamic acid and urea, there should exist compounds
in which both hydroxyl and the amido-group are present.
Some such compounds are known. Thiophosphainic
acid, S-P(NH.,)(OH).^, is the product of the action of
ammonia on thiophosphoryl chloride ; and phosphoric
anhydride, when dry ammonia s^as is passed over it, yields
phosphimic acid, thus : pp. + aNH. P OH
176
+ H..O
O
MODERN CHEMISTRY
It is analogous to mctaphosphoric acid,
\p_OH, and forms crystalline salts. Pyrophos-
phamic acids are also known. The addition of phos-
phorvl chloride to a cold saturated solution of ammoma
results in the formation of pyrophospho-diamic acid
H N yOH
" \(P0)— O— (PO)/ , analogous to pyrophos-
phoric acid,
HO. /OH
\(PO)-0-(PO)<;
HO/ OH
and on
heating the solution of this body, one hydroxyl group
replaces one amido-group, yielding pyropliospliajnic acid,
H N /^^ . c
- \/po)_0— (PO)/ . Lastly, the action ot
Hq/ ^OH
ammonia on phosphoric chloride gives a compound named
phospham, HN=P -N, a siiecies of anhydride, but pro-
duced by loss of ammonia, not of water, from the unknown
compound P(NH.,)-,. ^
Analogues of p'hosphorous acid are less well known ; it
ammonia be passed over phosphorous chloride, a white mass
is formed, which has not Wxn separated trom ammonium
chloride, but which is sui^om J to possess the tormula
P/NH ) ' it may be named phosphorosamide.
Amides of Sulphur Ac/c/s. - Similarly amido-
derivatives can be obtained from sulphur trioxide. i he
action of ammonia on that comi)ound yields ammonium
sulphamate. H,N-0 (SO,) NH or, .t less ammonia
Soused, sulphamic acid, HO-(SO,)-NH,; they are
both crystalline, soluble compounds.
The action of sulphur dioxide on ammonia is accompanied
bv the production of the analogous compounds, ammomum
sulphurosamate and sulphurosamic acid, the latter ot
which has the formula HO -(SO) NH.^.
K.v.iiX«:?
COMPLEX AMINES
177
These comiHJunds may Ik taken as instances of bcxiies
analogous to acids in which the hydroxyl is rephiced by
the aniido-group. They arc, as a rule, stable in presence
of water, and they do not generally unite with acids, the
acid nature of the oxygen which they contain counteracting
the basic nature of the aniido-group. Many compounds
are however known, in which the amido-group replaces
hydroxyl, and which, having no acidic oxygen present, are
known onK as salt^ in combination with acids. Some of
these will now lie described.
Salts of Complex Am/nes. — Calcium chloride,
exijosed to a stream of :mimonia gas, rapiilly absorbs it,
and forms the compound CaCl,.8NH.5. It would api^ar
that this compound is one of calcamine, Ca(NH.) „ with
2HCI, with which six molecules of ammonia are associated
in some manner resembling that in which water of crystal-
lisation is associated in salts containing it. Thus we have
CaCI.,.6H..O ; and Ca(NH,,).C1.^.6NH3 has an analogous
formula. Zinc and cadmium form similar compounds,
and other salts may be obtained from the ai)propriate salts
of the metals; thus, by saturating zinc sulphate with
ammonia, the compound Zn(NH3).,S0,.H.,0 separates
in crystals. Again, with aluminium, Al(N"H„).jCl3 has
been prepared ; and dyad iron, manganese, and nickel
yield somewhat similar compounds. Such bodies must
be regarded as salts of ammonium, in which a met d
has taken the place of one atom of hydrogen in eat "
molecule of ammonium ; a dyad metal reijlacins ':\
probable that the compound of ammonia with calcium
VOL. II.
178
MODERN CHEMISTRY
f
I
f
+ - +
chloride in solution contains as ions Ca, CI, NH^, nnd
OH, together with non-ionised NH^H and molecular
NH3, the fact that zinc hydroxide, precipitated by addition
of ammonium hydroxide to a solution of the chloride, is
re-dissolved by furtht-r addition of ammonia, is doubtless
to be explained by tiie formation of the complex ion
Znf NHol „ which is soluble in water. But this does not
exclude the presence of the usual ions, Zn, CI, NH^, and
OH, which doubtless co-exist with those already mentioned.
In some cases, the stability of the complex ions is much
greater than in that mentioned, and of this some instances
will be given.
C/tromam/nes.— Chromium hydroxide,when digested
with exce.^s of ammonia and anmionium chloride, forms a
deep red solution; and on exi)OMng it to air, a \^)let
powder separates, of the formula Cr^i.,.4NH3.H.O. This
powder, heated to ioo% loses its water of cr_, stallisation,
and the residue has the formula CrCl3.4NH3. The
ammonia is not expelled until the temperature 200' is
reached. It would appear, therefore, that this comixjund
is not Cr(NH,)3.Cl8.NH3, t.ie fourth molecule of ammonia
being regarded as of the same nature as water of crystallisa-
tion ; it must rather be supposed that a complex ammonium
group,-NH.,--NH3, is capable of existence ; whence the
compound would have the formula Cr^NHg— NH^ — CI.
Salts containing chromium have lieen prepared, in which
^, 4» 5. 6, and 7 molecules of ammonia are associated with
the original chromium salt. They find their explanation
by a hypothesis like the one given.
Cobaltamines. — Similar compounds are known with
triad cobalt. On adding a solution of ammonia to cobalt
sulphate, the nrecipiiate at first formed (a basic sulphate)
AMINES
«79
dissolves ; exposure to air causes the oxidation of the cobalt
from dyad to triad, and a black jHiwder is dejKJsited. On
careful addition of hydrochloric acid, kecpinj^ the mixture
cold, the colour of the |H)wdi'r chanj;es to red ; the com-
/XH.,-CI
pound has the formula Co( NH".— XH^— Cl.H.O, and is
\NH;.— CI
analogous to the chromium compound mentioned alxwe.
Other salts ot this base have lx?en made ; they are termed
roseo cobaltamines. If temjierature be allowed to rise,
during the addition of hydrochloric acid to the oxidised
solution of cobalt sulphate in ammonia, an isomeric substance
is produced, containing no water of crystallisation, and
having a jmrple colour. Other salts arc known ; they are
termed salts of purpureo-cobaltamine. It is jjossible to
represent the formula of such compounds as follows : —
Diamines: CI Co(XH,)Xl,.
Triamines : Co(XH.,).,Cl3.
Tetramines : Cl-Co(XH.,-XH,).,Cl.,.
Pentamines : NH.,-Co(X"H -„XH,,)_(C1,.
Hexamincs : Ct)(XH..-NHy)3Cl.{.
Other Amines. — Many compounds of copper, mer-
cury, silver, gold, and the metals of the platinum group
arc known, which admit of rcjjresentation in a similar
manner. They differ, however, inasmuch as the metal
must be considered to have replaced more than one atom of
livdrogen in one molecule of runmonium. Thus we have :
Cu'2 =NH.,C1, di-cuprosammonium cMoride, a black
powder produced by the action of ammonia gas on warmed
cuprous chloride :
Cu'-XH.^Cl, cuprosammonium chloride, formed by
dissolving cuprous chloride in ammonia ; it is a well-known
absorbent for carbon monoxide and tor acetylene.
Cu' (XH.J..C1 ,, cuprammonium chloride, and cupri-
diammonium sulphate. Cu' (XH.r-XH.J.SO^, the
former .1 green substance, the latter a deep blue compound ;
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I So
MODERN CHEMISTRY
! ii
both produced by the action of ammonia on the respective
cupric salt. The formation of the latter is a well-known
test for copper.
With silver there are: Argentamine, a black ex-
plosive powder, probably of the formula AgNH.,, produced
by adding ammonia to silver hydroxide ; and numerous
compounds of formulae like Ag(NH3)Cl, produced by
dissolving the respective silver salts in ammonia. With
gold: Auric chloride, digested with ammonia, yields
"fulminating gold," an explosive black substance, which is
a mixtufe of HN= AuCl and HN=Au-NH.,.
A familiar test for mercurous mercury is to add ammonia,
when the compound turns black. This is due to the
formation of di-mercurosammonium chloride, or some
similar compound, of the formula Hg'2=NH^Cl, where two
atoms of hydrogen in ammonium chloride are replaced by
two atoms of monad mercury. It has long been known,
too, that mercuric salts produce a white precipitate on treat-
ment with ammonia. This is chiefly due to the formation of
chloro-mercuramine, CI -Hg" -NH., ; here, the presence
of electro-negative chlorine deprives the amido-group of
basic properties. On boiling this compound with ammo-
nium chloride, mercuraminonium chloride is produced:
Cl-Hg-NH^ + NH.Cl = Hg(NH3)2Cl,.
With platinum, and the other members of that group,
similar compounds are produced ; but their constitution can
be inferred sufficiently from what has preceded.
These compounds are derivatives of ammonia ; there are
few similar compounds of phosphine ; one, however, is
produced when phosphoretted hydrogen is passed over
aluminium chloride; its formula is PH3.3AICI3. And
arsine, passed through a solution of mercuric chloride, yields
HgoAsCl.HgCl.^ ; it is somewhat analogous to the black
precipitate, Hg,NH.HCl.
Phosphides, Arsenides, and Antimonides.—A
few compounds of phosphorus, arsenic, and antimony with
metals have been made. They are generally obtained by
PHOSPHIDES, ETC. i8i
direct union between the heated metal and the element.
Thus, if sodium and phosphorus be heated together under
xylene, a hydrocarbon boiling about 130% a black com-
pound is formed, Na.jP, from which excess of phosphorus
can be dissolved out by treatment with carbon disulphide.
Arsenide and antimonide of sodium are also obtained by
heating the elements together. The formula; of these
compounds are of the type AsNag ; and with dilute acid,
the corresponding hydride of phosphorus, arsenic or antimony
is evolved : AsNaa + 3HCl.Aq = ASH3 + 3NaC l.Aq.
A mixture of calcium phosphide, Ca.jP^, with calcium
pyrophosphate is produced on throwing phosphorus into a
crucible containing red-hot lime ; on treatment with water,
spontaneously inflammable phosphine is evolved. The
spontaneous ignition is due to its containing P.,H^, a liquid,
very unstable compound.
The phosphides, arsenides, and antimonides of the
other metals are usually dark-coloured substances, with
more or less metallic lustre, and therefore conductors of
electricity. Some of them occur native; for example,
smaltine, CoAso, a common ore of cobalt, J")rming silver-
white crystals ; copper-nickel, NiAs, red lustrous crystals,
and one of the chief nicki.l ores ; speiss, a deposit formed
in the pots in which smaltine and copper-nickel are fused
with potassium carbonate and silica, in the preparation of
smalt, a blue glass containing cobalt ; its formula appears to
be NigAs^,. Mispickel, or arsenical pyrites, is a white
lustrous substance, of the formula FeSAs.
Cyanides. — The elements carbon and nitrogen form a
very stable group, of which the compounds have been well
investigated, termed cyanogen. Carbon and nitrogen do
not unite directly ; but if a mixture of finely divided carbon
with carbonate of potassium or sodium, or, better, of barium,
be heated to about 1 200° in a current of nitrogen, combina-
tion ensues, and a cyanide is formed, KCN, NaCN, or
Ba(CN),; BaC03 + 4C + N2 = Ba(CN)2 + 3CO. Potas-
sium cyanide is also produced when a mixture of animal
I82
MODERN CHEMISTRY
refuse (horns, hides, hair, dried entrails, &c., ot animals)
with potassium carbonate and iron filings is heated. The
nitrogen of the animal matter and the carbon unite with the
potajsium of the carbonate, forming cyanide. On addition
of water, this cyanide reacts with salts of iron, forming a
double cyanide of iron and potassium, termed "yellow
prussiate of potash," or ferrocyanide of potassium, of the
formula K^Fe(CN)o. When this compound is heated to
dull redness, it fuses ; a black mixture or compound of iron
and carbon remains, and melted potassium cyanide can be
poured out of tl.e crucible. Potassium cyanide, KCN, is a
very soluble salt ; it crystallises well from alcoho.. Its
solution smells of hydrocyanic acid ; this is because it is
hydrolysed by water. The acid, HCN, is so very weak
that the number of hydrogen ions present in its solution are
comparable in number with those of ionised water ; hence
the change : H-OH + K-CN.Aq=HCN + KOH.Aq.
The ionised portion of the hydrocyanic acid is as usual non-
volatile ; but the non-ionised portion has a vapour-pressure,
and can be detected by its smell (cf. p. hO*
Hydrocyanic >4c/pounds, 91
Ions, co'our of, 64
Iridium, 12
Iron, 16, i8, 19
,, halides, 63
,, hydride, 31
,, hydroxides, 78
Krypton, 5
LANTHANtM. t6
,, hydroxide, 77
Lead, 16, 18, 25
,, chlorides, 62
., hydroxide, 77
Lithium. 8, 11
hydride, 31
,, hydroxide, 74
Magnesium, 8, 16
,, hydroxide, 'jj
Manganates, 152
Manganese, 18
,, dioxide, 102
,. halides, 63
,, hydi oxides, 78
Manganicyanides, 187
Marsh's test, 39
Mass-action. 14, ^12
Mercuramines, 180
M»'»'curic iodide, 56
MvTcury, 12, 22
Meteoric iron, 31
Methane, 32, 36
Mixtures, 1
Molybdates, 154
Molybdenum halides, 63
Nasc K.NT state, 39, 42
Neon, s
Neutral oxides, 98
Neutralisation, 75
Nickel, 10, 16, 18
,, halides, 63
,, hydride. 31
hydroxide, 78, 79
Niobium, 16
Nitrates, 127
Nitric acid, action on metals, 95
,, oxidation with, 97
,, oxidj. 97
,, peroxide, 98
Nitrides, 37, 169
Nitrites, 134
Nitrogen, 22
iodide, 59
,, oxygen compounds of,
132
chloride, 58
Nitrous oxide, 95
OSMIRIDIUM, 197
Osmium, 12
Osmocyanides, 187
Osmosis, 116
Oxalic acid. 113
Oxidation, 64
Oxides, 69
,, formation of, 80, 81
Oxygen. 13, 15
Ozone, 23
Palladium. 12
,, halides, 64
202
INDEX
I'iilladiiim hydride, 31
Parke's process, 195
Pattison's prtKfss, n/i
Pfrl)orates, 168
PercirlKjnates, 168
I'erchlorati'S, 142
Percliromic acid, 167
Pcriodatus, 134
Permanganates, 152
Peroxides, 192
Persiilpliat-'s, 168
Pewter, 196
Phosphamidos, 176
Phosphates, 126
Phosphides, 37, 181
Phosphincs, 89,
Phosphonitim hahdrs, 65, 66
Phosphorus, 18
acids, 133
,, halidcs, 64
hydride, 36, 37
Platinum, 12
,, halides, 64
hydride, 31
Polymerisation, 48
Potassium, 8, 17
,, hy<' oxide, 74
,, teti oxide, 92
Potential, electric, 23
Rkduction. 25, 64
Rhodium, 12
Rubidium, 8, 17
,, hydroxide, 74
Ruthenium, 12
Ruthenocyanides, 187
Scandium, 16, 25
,, hydroxide, 77
Selenates, 159
Selenic acids, 159
Selcnides, 69
Selenious acid, 146, 149
Selenium, 12, 22
,, haiides, 60
hydride, 39
Silicates, 115
Silicides, 191
Silicon, 16, 17
,, Huoiide, 59
Silver, lo, 12, 16, 23
,, hydroxide, 77, 78
,, oxide, 79
Sodium, 8, 17, 18
,, dioxi(le, 92
,, hydride. 31
,, hydroxide, 74
Solder, 196
Solubility-product, 83, 84, 85
Solution of K^ses, 3
Spinels, I'X)
Stcol, 21
Strontium, 8, 16
,, oxide, 76
Sulpliamides, 177
Sulphates, 159
Sulphides, 69, 81
Sulphites, 147, 148
Sulphon.ites, 148
Sulphur, 12, 22
,, ethers, 90
,, halides, 60
hydride, 33. 39
„ trioxide, 155
Sulphuric acid, 155
Sulphurous acid, 146, 149
Sulphuryl chloride, 149
Tantalim, 16
Tellurates, 159
Telluric acid, 159
Tellurides, 69
Tellurium, 12, 22
,, halides, 60
hydride, 39
Tellurous add, 149
Thallium, 16, 18
,, hyciroxide, 77
Thermal data, 145
Thio-acids, 130
Thiocarbonates, 106, no
Thionates, 166
Tiiiosulphates, 164
Thorium, 16
,, hydroxide, 77
Tin, 16, 18, 24,
,, chlorides, 62
INDEX
ao3
Tin, JivHroxidfs, 77
Tinni'd iron, ms
Titiinium, I'i, 17
,, hydro.vjile, 77
TunRstaips. 154
'luiijjsten (,;i'ii(l(S, fi 5
Type-metal, 196
Uranatis, 154
Uraiiiiini halidcs, 63
Urea, 174
VAI-KNTY. '■"T
Vanadates. 129
Vanadium, 16
Watkr. .43. 35, 36
of crystallisation, 53
Xknon, t,
YiTi-: JM, 16
Yttrium, 17
,, liydroxiilf, 77
/r.( , 17, If)
,, hydroxide, 77
/incates, 78
/irconium hydroxide, 77
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