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JOHN WILLIAM DRAPER, M.D., Professor of Chemistry in the University of New Yrk, Member of the America* Philosophical Society, &c. With nearly Three Hundred Illustrations. SIXTH EDITION. HARPER & BROTHERS, PUBLISHERS, 82 CLIFF STREET, NEW YORK. 1850. ^.Da? ^7 Ir+c, Entered, according to Act of Congress, in the year 1846, ' 'ft? 3^PER& BROTHERS, In the Clerk's Office of the Southern District of New York. rf. PREFACE. THIS text-book on Chemistry, intended for the use of colleges and schools, contains the outline of the course of Lectures which I give every year in this University. I do not, therefore, present to teachers an untried work. Its divisions and arrangement are the result of an experience of several years ; an experience which has proved to me that there is required a text- book of small size, so that students can pass through it readily in the time usually devoted to Chemistry. Every instructor in this science must have observ- ed that the ordinary " Treatises" or " Elements" are by no means suited to his wants. When they are employed in the class-room, there are large portions which have to be omitted, and other portions too briefly explained. In fact, to study Chemistry suc- cessfully, the first thing which is wanted is a com- pendious book, which sets forth in plain language the great features of the science, without perplexing the beginner with too much detail. A2 M44441 VI PREFACE. It will be understood, therefore, that this work, with little pretensions to originality, except where directly specified, occupies a different field from that of the larger treatises. It is intended as a manual, arranged in such divisions as practice has shown to be suitable for daily instruction. It is the exposition of what I have found to be a satisfactory method of teaching ; and of its success our annual examinations are the best testimonial. The unsuitableness of large text-books has led to many attempts to reduce their size by abstracts and compendiums ; but the difficulty can never be avoid- ed by that means ; the very structure of such works is faulty. We never want to use all that an author knows or can possibly say on the subject. It has been well' remarked, that " The greatest service which can be rendered to our science, is for some person who has had the management of large classes for several years to sit down and write a book, set- ting forth what he said and what he did every day in his Lectures. That is the thing we want." While, therefore, this book is offered to instructors as a practical work, the object of which is to display the leading features of the science, I have endeavored to make it a representation of the present state of Chemistry. In this respect many of our most popu- lar works are defective. Among them I should not know where to turn for a simple exposition of the PREFACE. Vil Wave theory of Light or of Ohm's theory of Voltaic Currents ; yet the one is the most striking result of physical research, and the other is connected with the fundamental facts of Electro-chemistry. To the treatises of Hare, Kane, Graham, Gregory, Fownes, Dumas, and Millon I must formally state my obligations. In Descriptive Chemistry I have fol- lowed them closely; and in those cases which are much more common than is generally supposed, where there are differences in the imputed proper- ties of bodies, I have consulted, wherever I could, either original memoirs or the annual reports of Ber- zelius. ^ The number of wood-cuts, representing experi- mental arrangements, which have been introduced, will give to a beginner a clearer idea of the practical part of each Lecture, and, in our country colleges, may sometimes supply the place of defective or in- complete apparatus. To each Lecture is appended a set of questions. They enable a young student more quickly to apprehend the doctrines which are before him. JOHN WILLIAM DRAPER. University of New York, \ July 6, 1846. ) CONTENTS. Lecture Page I. Constitution of Matter 1 II. Constitution of Matter (continued) 6 III. Heat 11 IV. Expansion of Gases and Liquids 15 V. Expansion of Liquids and Solids 20 VL Expansion of Solids 24 VII. Capacity of Bodies for Heat . . . . .28 VIII. Capacity for Heat and Latent Heat . . . .32 IX. Latent Heat (continued) 36 X. Vaporization 40 XL Ebullition 44 XII. Vaporization ... 48 XIII. Evaporation and Interstitial Radiation .... 53 XIV. Conduction 59 XV. Radiation 63 XVI. Theory of the Exchanges of Heat 67 XVII. Nature of Light .... * ;.'..!. . 71 XVIII. Constitution of the Solar Spectrum . . * . 75 XIX. Wave Theory of Light ....... 78 XX. Wave Theory of Light (continued) . . . . . 82 XXI. Wave Theory of Light (continued) . , . . .86 XXII. The Tithonic Rays 90 XXIII. Theory of Ideal Coloration .... . . .94 XXIV. Electricity 97 XXV. Theory of Electrical Induction 101 XXVT. Laws of the Distribution of Electricity and General The- ories 105 XXVII. Faraday's Theory of Electrical Polarization . . .110 XXVIII. Voltaic Electricity 115 XXIX. 'Effects of Voltaic Electricity . . . ... .120 XXX. The Electro-chemical Theory 125 XXXI. Ohm's Theory of the Voltaic Pile Magnetism . . 131 XXXII. Electro-dynamics Thermo-electricity . . Ji/ -" 'C' . 137 XXXIII. The Chemical Nomenclature . . . .'". .144 XXXIV. The Symbols . . Y: > . . . .147 XXXV. The Laws of Combination .... .151 XXXVI. Constitution of Bodies Crystallization . .155 XXXVH. Chemical Affinity .164 X CONTENTS. Lecture r* - "\ Page XXXVIII. Pneumatic Chemistry Oxygen Gas . . 169 XXXIX. Oxygen (continued) 174 XL. Hydrogen . . 178 XLI. "Water 183 XLII. Nitrogen Atmospheric Air 188 XL III. Atmospheric Air (continued) . . . . .194 XLIV. Atmospheric Air (continued) 199 XLV. Compounds of Nitrogen and Oxygen .... 205 XL VI. Compounds of Nitrogen and Oxygen . . . 208 XL VII. Sulphur . 212 XL VIII. Compounds of Sulphur and Oxygen . . . 217 XL IX. Sulphur and Phosphorus ... . 220 L. Compounds of Phosphorus and Oxygen . . . 224 LI. Chlorine ... 228 LII. Chlorine (continued) 232 LIEI. Bromine Fluorine Carhon 237 LIV. Carbonic Acid 241 LV. Cyanogen Boron Silicon Ammonium . . . 245 LVI. General Properties of the Metals 252 LVII. Potassium 256 LVIII. Sodium Lithium Barium 260 LIX. Strontium Calcium Magnesium Aluminum . . 266 LX. Manganese Iron 274 LXI. Iron Nickel Cobalt Zinc 278 LXII. Cadmium Tin Chromium Titanium . . . 283 LXIII. Arsenic 287 LXIV. Arsenic Antimony Tellurium Uranium Copper . 291 LXV. Lead Bismuth Silver 297 LXVI. Mercury Gold Platinum, &c 302 LXVII. General Properties of Organic Bodies . . . .307 LXVni. The Non-nitrogenized Bodies 311 LXIX. Action of Agents on the Starch Group .... 315 LXX. The Metamorphosis of the Starch Group by Nitrogen- ized Fermenta 319 LXXI. The Derivatives of Fermentative Processes . . 323 LXXIL The Derivative Bodies of Alcohol . . .327 LXXIII. Oxydation of Alcohol 330 LXXIV. Derivatives of Acetyle the Kakodyle Group . . 334 LXXV. The Wood Spirit Group 338 LXXVI. The Potato Oil Group the Benzyls Group . . .342 L XXVII. The Salicyle and Cinnamyle Groups . . . .345 LXXVIII. The Nitrogenized Principles Ammonia Cyanogen . 349 LXXIX. Bodies allied to Cyanogen 354 LXXX. Mellone Urea 358 LXXXI. The Vegetable Acids 362 CONTENTS. XI Lecture Pago LXXXII. The Vegetable Alkalies 367 LXXXni. The Coloring Principles 371 LXXXIV. The Patty Bodies 375 LXXXV. The Resins, Balsams, and Bodies arising in destructive Distillation 380 L XXXVI. Animal Chemistry Digestion and Nutrition . . 384 LXXXVII. Origin and Deposit of the Fats and Neutral Nitrogen- ized Bodies 387 LXXXVIH. The Transmission of Food through the System . . 392 LXXXIX. Nature of the Processes of Secretion . . . . .395 INTRODUCTION. CONSTITUTION AND GENERAL PROPERTIES OF MATTER. LECTURE >!' ^ ; n;v N a \\ CONSTITUTION OP MATTER. Distinction between Chem- istry and Natural Philosophy. General Division of Chemistry. Active Forces and Ponderable Bodies. Proof of the Atomic Constitution of Matter in the Cases of a Solid and a Gas. Atoms are inconceivably small. They are not in contact. They are unchangeable and indestructible. THE physical sciences are divided into two classes, com- prehended respectively under the titles of NATURAL PHI- LOSOPHY and CHEMISTRY. Natural Philosophy investigates the relations of masses to one another. The movements of tides in the sea un- der the conjoint influence of the sun and moon ; the de- scent of falling bodies- to the earth ; the pressure of the atmosphere ; the various modes of rendering mechanical forces available, by the action of levers, pulleys, wedges, screws; the phenomena of the planetary bodies, which move in elliptic orbits around a central mass : these are all objects- for the consideration of Natural Philosophy. Chemistry considers the relations of particles to each other ; it investigates the properties and qualities of differ- ent kinds of matter, their mutual influence, and the ac- tion of the imponderable principles upon them. It treats of the causes of those invisible movements which the molecules of bodies around us unceasingly undergo. It also includes many of the phenomena of living beings, explains the objects of respiration, digestion, and other such animal functions. Every change taking place in bodies is due to the op- eration of some active force. It is one of the first princi- Into what classes are the physical sciences divided ? Of what phenom- ena tlons natural philosophy treat? What are the objects of chemistry ? A 2 CONSTITUTION OF MATTER. pies in philosophy, that no movement or mutation can oc- cur in any thing spontaneously ; we must always refer it to a disturbing cause. Under the influence of heat, bodies increase in size ; under that of electricity, some are dis- severed into their component elements ; under that of light, vegetables form from inorganic materials their or- ganized structures. The science of chemistry resolves : 'Itself, thereforf;, into two divisions : the first, embracing the consideration of the active forces of chemistry ; the sec- '', r >Ecj; fhe objects on which those forces operate. \These active forces are Heat, Light, and Electricity. By the older chemists, they are designated as imponder- able substances, from the circumstance that they do not affect the most sensitive balances. We can form no idea of the properties of bodies dis- engaged from the influence of these principles. Thus we find all material substances existing under one of three conditions, solid, or liquid, or gaseous; and the majority can assume either of these conditions under the influence of heat. Water, for instance, at low tempera- tures, exists in the solid state as ice ; at higher tempera- tures, it assumes the liquid condition ; and, at still higher, exhibits the gaseous form. We see, therefore, that it is the degree of heat to which it is exposed which deter- mines its physical state. One of the first problems which the chemist has to solve, is that of determining the true constitution of matter ; not of matter in the abstract, but as placed under the influence of these external powers. All the phenomena of chemistry prove that material substances con- sist of indivisible and exceedingly mi- nute portions, called ATOMS, which are placed at certain distances from one another, those distances being variable and determined by the agen- cy of active forces. Thus, if we take a copper ball, a, Fig. 1, an inch in diameter, and provide a ring, b, of such a What are the two leading divisions of chemistry ? What are the act- ive forces of chemistry ? Why are these called imponderable bodies ? What are the three forms of substances 1 What is it that determines ' these forms ? What is the constitution of matter ? Describe the arrange- ment of the instrument Fig. I, and its use. Fig. 1. CONSTITUTION .OF MATTER. 3 size that the ball at common temperatures can readily pass through it, and having suspended the ball by means of a chain to a stand, cl, expose it to the flame of a spirit lamp, c, as it becomes warm it will be found to dilate, so that, in -the course of a few minutes, it can no longer pass read- ily through the ring, but if placed thereon, remains sup ported. While under these circumstances no visible change has, taken place in the general properties of the ball ; itt. weight remains the same as before, its aspect is the same. We conclude, therefore, that its volume has increased be- cause we have raised its temperature. But now, the lamp being removed, the ball still resting on its ring, begins to cool. In the course of a few min utes it spontaneously drops through the ring. It has, therefore, become less than it was while hot, and, in poinl of fact, when its original temperature is reached, it has re- covered its original size. From this simple, but beautiful experiment, very im portant conclusions may be drawn. The copper ball, in cooling, becomes less : a fact which at once suggests the idea that its constituent particles have approached each other. In its warm and dilated state, although it exhibit- ed no appearance of transparency, or of interstitial spaces, or pores through which light might pass, its particles were not touching one another, for had they been in actual con- tact they could not have more closely approached one an^ other, and contraction could not have taken place. As all bodies contract during the act of cooling, we in- fer that the particles of which they are composed are separated from each other by intervening spaces, and experiments such as that we have been considering suggest two im- portant observations : 1st. That all mate- rial substances are made up of small par- ticles which do not touch each other; and, 2d. That the intervening spaces maybe va- ried at the pleasure of the experimenter. Let us consider a second illustration which will lead us to the same conclusion ; selecting,. as Why, in this experiment, does the ball finally drop through the ring ? Could contraction take place if its particles wejre already in contact ? What two conclusions do these facts suggest ? 4 CONSTITUTION OF MATTER. the object of our experiment, atmospheric air, a substance differing in all its physical and chemical relations from the copper ball. Let us take a tube of glass half an inch in diameter, and bent in the form exhibited in Fig. 2, a, c, d. The tube is closed at its upper end, a ; it is bent at c, and over its open extremity, at d, a bag of India rub- ber is tied, air tight. In the tube there has been previ- ously inclosed a sufficient quantity of water to fill all the portion b, c, d, but the space from a to b is occupied by atmospheric air. It is to the volume of this atmospheric air that our attention is directed. If we compress the India rubber bag in our hand, the Volume of the air instantly becomes less, the diminution being greater in proportion as the pressure is greater. Now, it is inconceivable that this phenomenon should en- sue, unless the aerial particles approached each other ; but such an approach would be impossible if they were already in contact. Two particles could not occupy the same space at the same time. We conclude, therefore, that for atmospheric air, a gaseous body, as well as for copper, a solid, the same law holds good, and that both these forms of matter are constructed upon the same type ; that they are made up of particles set at distances from one another, and that we can change those distances at pleasure, by resorting to changes of temperature, or to mechanical forces. Fig 3. It ls worthy of" observation, that by proper means these interstitial spaces may be greatly increased or diminished, and in very many in- stances without any striking apparent change occurring in the substance under experiment. Thus, if we take a globe of glass two or three inches in diameter, a, Fig. 3, with a neck or tube, &, proceeding from it, and fill the globe full of water, with the exception of a small bubble of air which occupies its upper part, while the open extremity of the tube, b, dips beneath some water contained in a glass jar, c, then, covering the whole with an air-pump receiver, d, proceed to exhaust, we shall find that the little Describe the instrument represented in Fig: 2. What is the use of this instrument ? With an increase of pressure, what happens to the in- cluded air? Can two particles occupy the same space at the same time ? What, then, is the deduction from this experiment ? What is the exper- iment given in Fig: 3 intended to illustrate ? SIZE OF ATOMS. 5 bubble, a, dilates as the machine is worked, and may be rendered a hundred-fold greater than at first. In this ex- panded condition, its particles must have greatly reced- ed from each other, and yet no remarkable physical change is to be observed. There are no dark or vacuous spaces; but, in this attenuated condition, it possesses the aspect which it had when at the common density. With these preliminary facts, we may now direct our attention, 1st, to the properties of atoms ; and, 2d, to the interstitial spaces which part them from each other. That the atoms of which bodies are composed are ex- ceedingly small, we possess abundant proof. By dissolv- ing substances in liquid media, and then greatly diluting the solution, we can effect a subdivision to an incredible extent. A single drop of a solution of sulphate of indigo will communicate a blue color to one thousand cubic inch- es of water, so that every drop of that diluted solution contains a portion of the coloring matter. In the same manner, by resorting to proper tests, we can show that a grain of copper, or silver, or gold, may be divided into many millions of smaller parts, each of which may be readily recognized. Nor is it alone by these chemical processes that such a minute subdivision may be effected : by th.e mechanical process of beating with a hammer, gold may be extended into leaves which are less than the ___i___ part of an inch thick, a dimension far less than the human eye, unassisted by microscopes, can discover, for the smallest spherical object visible to it is about Y oVir P art f an mcn * n diameter. By other processes, it has been estimated that this metal may be divided to such an extent, that a single grain will yield 80 millions of millions of visible parts. The world of organization fur- nishes us with still more striking proofs. There exist animalcules of which it would require many millions to make up the bulk of a common grain of sand, yet these are furnished with digestive and respiratory organs, with circulating juices, and with contrivances as elaborate as the mechanism of the highest orders of life. How minute, then, must the constituent particles be ! To what extent can the constituent atoms be removed ? To what ex- tent can sulphate of indigo be divided? Can similar results be obtained from metalline bodies ? What evidence have we on this point from me- chanical processes? What argument may be drawn from the construe tion of animalcules ? A 2 4 CONSTITUTION OF MATTER. the object of our experiment, atmospheric air, a substance differing in all its physical and chemical relations from the copper ball. Let us take a tube of glass half an inch in diameter, and bent in the form exhibited in Fig. 2, #, c, d. The tube is closed at its upper end, a ; it is bent at c, and over its open extremity, at d, a bag of India rub- ber is tied, air tight. In the tube there has been previ- ously inclosed a sufficient quantity of water to fill all the portion b, c, d, but the space from a to b is occupied by atmospheric air. It is to the volume of this atmospheric air that our attention is directed. If we compress the India rubber bag in our hand, the Volume of the air instantly becomes less, the diminution being greater in proportion as the pressure is greater. Now, it is inconceivable that this phenomenon should en- sue, unless the aerial particles approached each other ; but such an approach would be impossible if they were already in contact. Two particles could not occupy the same space at the same time. We conclude, therefore, that for atmospheric air, a gaseous body, as well as for copper, a solid, the same law holds good, and that both these forms of matter are constructed upon the same type ; that they are made up of particles set at distances from one another, and that we can change those distances at pleasure, by resorting to changes of temperature, or to mechanical forces. F( 3 It is worthy of" observation, that by proper means these interstitial spaces may be greatly increased or diminished, and in very many in- stances without any striking apparent change occurring in the substance under experiment. Thus, if we take a globe of glass two or three inches in diameter, a, Fig. 3, with a neck or tube, &, proceeding from it, and fill the globe full of water, with the exception of a small bubble of air which occupies its upper part, while the open extremity of the tube, b, dips beneath some water contained in a glass jar, c, then, covering the whole with an air-pump receivjer, d, proceed to exhaust, we shall find that the little Describe the instrument represented in Fig: 2. What is the use of this instrument ? With an increase of pressure, what happens to the in- cluded air? Can two particles occupy the same space at the same time ? What, then, is the deduction from this experiment ? What is the exper- iment given in Fig. 3 intended to illustrate ? SIZE OF ATOMS. 5 bubble, #, dilates as the machine is worked, and may be rendered a hundred-fold greater than at first. In this ex- panded condition, its particles must have greatly reced- ed from each other, and yet no remarkable physical change is to be observed. There are no dark or vacuous spaces; but, in this attenuated condition, it possesses the aspect which it had when at the common density. With these preliminary facts, we may now direct our attention, 1st, to the properties of atoms ; and, 2d, to the interstitial spaces which part them from each other. That the atoms of which bodies are composed are ex- ceedingly small, we possess abundant proof. By dissolv- ing substances in liquid media, and then greatly diluting the solution, we can effect a subdivision to an incredible extent. A single drop of a solution of sulphate of indigo will communicate a blue color to one thousand cubic inch- es of water, so that every drop of that diluted solution contains a portion of the coloring matter. In the same manner, by resorting to proper tests, we can show that a grain of copper, or silver, or gold, may be divided into many millions of smaller parts, each of which may be readily recognized. Nor is it alone by these chemical processes that such a minute subdivision may be effected : by the mechanical process of beating with a. hammer, gold may be extended into leaves which are less than the ^o-oViTo- -part of an inch thick, a dimension far less than the human eye, unassisted by microscopes, can discover, for the smallest spherical object visible to it is about __L._ part of an inch in diameter. By other processes, it has been estimated that this metal may be divided to such an extent, that a single grain will yield 80 millions of millions of visible parts. The world t)f organization fur- nishes us with still more striking proofs. There exist animalcules of which it would require many millions to make up the bulk of a common grain of sand, yet these are furnished with digestive and respiratory organs, with circulating juices, and with contrivances as elaborate as the mechanism of the highest orders of life. How minute, then, must the constituent particles be ! To what extent can the constituent atoms be removed ? To what ex- tent can sulphate of indigo be divided 1 Can similar results be obtained from metalline bodies ? What evidence have we on this point from me- chanical processes? What argument may be drawn from the construe tion of animalcules ? A 2 8 SIZE OF INTERSTITIAL SPACES, force of the earth, the force of gravitation, is of a certain intensity on the surface of our planet, but it diminishes as the distances become greater. The forces which connect together the bodies of the solar system, and, indeed, one planetary system with another, act through great intervals of space ; thus the attractive force of the sun, operating through many millions of miles, retains the earth in her orbit. But the attractive and repulsive forces which de- termine the position of the constituent atoms of bodies are limited to a very minute space. If we take two leaden bullets,'and having pared a small portion from the surface of each, so as to expose a brilliant metallic spot, bring them within an inch of one another, they exert no percep- tible attraction, and may be drawn apart with the utmost facility ; we may diminish the distance between them to the tenth, the hundredth, the thousandth part of an inch, and still the same observation may be made ; we may even bring them in apparent contact, and the attractive influence of the particles of '-the one upon those of the other is still undiscoverable ; but, on pressing them together, we can finally bring them within the range of each other's influence, and then they cohere together as though they were a single mass, and require a considerable effort to separate them. The apparatus figured in the margin serves to illustrate F - 5 the same result. Suspend a cir- cular piece of plate glass, a, Fig. 5, an inch in diameter, to one of the arms of a balance, Z>, c, counter- poising it on the opposite arm by weights placed in the scale pan, d. Beneath the plate of glass place a cup, e, containing some quicksilver, and it can be proved that so long as the glass is at a sen- sible distance from the surface of the quicksilver, no at- traction between them is exhibited, for were such the case, the arm of the balance should incline, and the glass descend. As long as the smallest perceptible space inter- venes, no attractive action is developed ; but on bringing the two surfaces in contact, they cohere ; and now it re- Through what spaces can these forces operate ? How can this be proved l>y leaden ballets ? Describe the apparatus, Fig. 5. What is its use ? What the fact which is proved by it ? CONSTITUTION OF MATTER. 9 quires the addition of a considerable weight in the scale pan to draw them asunder. This result does not depend on the pressure of the air, for it equally takes place in a vacuum. From experiments of this kind, therefore, we gather that the spaces through which molecular attractions and repulsions can act are very limited, and it follows of ne- cessity that the interstices which separate the atoms of bodies are exceedingly minute, for through those spaces the action of these forces extends. If the limiting distance through which molecular attraction and repulsion can reach is* as there is reason to believe, from some of the experiments of Newton, less than the millionth of an inch, we are entitled to conclude that the interstitial spaces are much smaller. To what, then, do these results finally point in regard to the constitution of matter, if, as we have seen, the con- stituent atoms themselves are inconceivably minute, and the spaces that separate them as small as we have reason tc conclude 1 We may look upon the universe as represent- ing on a grand scale the constitution of matter on a minute .one. The planetary bodies which compose the solar sys- tem, and which are held in their orbits by the attraction of a central mass, are separated from one another by enor- mous spaces, to which their own magnitudes bear but an insignificant proportion. About thirty such bodies, great and small, compose the group or family to which our earth belongs. But as there are systems of opaque plan- etary bodies, so also there are systems of self-luminous suns, which compose together colonies of stars. In the universe myriads of such systems exist, separated from one another by spaces so great that the mind can form no just idea of them. A planet, such as Jupiter with its at- tendant satellites ; a self-luminous star, like our sun with its surrounding bodies ; a group of shining stars, such as are scattered over our skies ; a collection of such groups as form the nebular masses ; these, in succession, furnish us with a series of illustrations on a scale continually in- creasing in dimensions of the constitution of matter, which is made up of isolated atoms placed at variable distances Does the experiment depend on the pressure of the air ? What are the limiting distances through which molecular forces can act ? State the analogy between the constitution of the universe and the constitution of matter ? 10 CONSTITUTION OF MATTER. from each other, the size of these atoms bearing an insig- nificant proportion to the spaces intervening between them. The human mind is so constituted that it is unable to appreciate whatever is exceedingly great or exceedingly small. We can neither attach a precise idea to the mag- nitudes and grander relations of the universe, nor to the atomic constitution of a grain of dust. Hereafter, when we come to speak of the phenomena of light, we shall see that by following the same philosophical methods which have been cultivated with such success in astronomy, and which have furnished us with a general view of the con- stitution of the universe, we also can obtain a general view of the scale which has been used in the constitution of material bodies, a scale which brings'before us new ideas of time and space. When we are told that in the mill- ionth part of a second a wave of violet light pulsates or trembles seven hundred and twenty-seven millions of times, and that, if we divide a single inch into ten millions of equal parts, this violet wave is only one hundred and sixty-seven of such parts in length, we obtain a glimpse of the scale on which material bodies are composed, and must confess the inability of the human imagination to form a proper conception of such results, though we may feel a just pride in the intellectual power which has ascer- tained them. '* PART I. THE FORCES OF CHEMISTRY. LECTURE III. HEAT. Preliminary Ideas of the Nature of Heat. In- fluence of Heat in the inorganic and organic Worlds, Modes of Transference. Illustrations of Expansion. Heat determines the Magnitude and Form of Bodies Affects our Measures of Time and Space Determines the Distribution of Animals and Plants. WRITERS on chemistry signify by the term Caloric, the agent which excites in our bodies the sensation of heat. By some, however, heat and caloric are used synonymous- ly. Those who look upon this force as if it were a ma- terial and imponderable substance, ascribe to the particles of caloric a self-repulsive power, and an attraction for the particles of ponderable bodies. So great is the control which caloric exercises over all kinds of chemical changes, that few experiments can be made in which transformations of substances take place without contemporaneous disturbances of temperature. In some, heat is evolved ; in others, cold is produced. To this agent, moreover, we so constantly resort for the pro- motion of molecular changes, that the chemist has been not inaptly designated the Philosopher by Fire. It is not alone in the inorganic world that the influences of caloric are traced. Life can not take place except within certain limits of temperature ; limits which are comprehended between the freezing and the boiling points of water, that is, within one hundred and eighty degrees of our thermometer ; and, in point of fact, within a nar- rower range than that. It is, therefore, not alone in chemistry, but also in physiology, that the relations of this agent are of interest. "What is caloric ? What is heat ? On the hypothesis that caloric is an imponderable substance, what are its properties ? Why is it that the study of caloric is of such great importance in chemistry ? Within what limits of temperature can living things exist? 12 HEAT PRODUCES EXPANSION. When an ignited mass, as a red-hot ball, is placed in the middle of a room, common observation satisfies us that it rapidly loses its heat ; its temperature descending until it becomes the same as that of surrounding walls and other bodies. This loss is due to several causes. A part of the heat is carried away by contact with the body which supports the ball, a part by certain motions estab- lished in the surrounding air, and a part by radiation. This removal passes under the name of transference, and as soon as the temperature has declined to that of the ad- jacent bodies, an equilibrium is said to have been attained. There are two methods by which caloric can be trans- ferred : 1st. By radiation ; 2d. By convection. Of the former we have two varieties general radiation, and in- terstitial radiatyon. Fig. 6. Under the influence of an increasing tempera- ture substances expand. This takes place, what- ever their form may be, whether solid, liquid, or gaseous. The experiment which is illustrated by Fig. 1, establishes this fact in the case of a copper ball ; and that the same law holds good for liquids, may be proved by taking a glass tube, a, b, Fig. 6, open at the extremity, movement at once ensues in the liquid column from c toward d. Movement of the index, therefore, takes place when the bulbs are at differ- ent temperatures, and hence the instrument is called a differential thermometer. It was formerly of considera- ble use in researches connected with radiant heat. Different liquids expand different- ly for the same thermometric dis- turbance. This is easily shown by an apparatus, as Fig. 12, in which we have three tubes, a, b, c, with bulbs on their ends, dipping into a trough, f, of tin plate. The tubes and bulbs should be all of the same size, and filled with the liquids to be tried to the "same height. To each a scale is annexed. Let a be filled with quicksilver, b with water, and c with alcohol ; on pouring hot water into the trough, two phe- nomena are witnessed: 1st. All the liquids expand; 2d. They expand unequally when compared together, the mercury expanding least, the .water intermediately, and the alcohol most. Unlike gases, all liquids expand irregularly as their temperature rises, a given amount of heat producing a much greater effect at a high than at a low temperature. Ten degrees of heat, applied to a given liquid at 200, will produce a greater expansion than if applied at 100. The reason appears to be, that as a liquid dilates its co- if this instrument be carried into a warm and then into a cold room, does its index move ? Why is it called differential thermometer ? How can it be shown that different liquids expand differently ? Of mercury, water, and alcohol, what is the order of expansion? Do liquids, like gas es, expand with regularity ? What is the cause of the difference ? 6. u , THE MERCURIAL THERMOMETER. 19 Fig. 13. hesive force becomes less, because its particles are being removed farther from each other ; and, as the cohesive force weakens, its antagonistic power, the heat, produces a greater effect. Advantage is taken of the properties of liquids in the making of thermometers. For these pur- poses, alcohol and mercury are the fluids selected. The mercurial thermometer consists of a fine cap- illary tube, Fig. 13, with a bulb blown on one end ; the bulb and part of the tube are to be fill- ed with quicksilver, and the air expelled from the rest of the tube by warming the bulb until the metal rises by expansion to the top of the tube, and at that moment hermetically sealing the glass by melting the end of it with a blow-pipe. As the thermometer cools, the quicksilver retreats from the top of the tube, and leaves a vacuum above it. It remains now to annex such a scale to the instrument as may make its indications compar- able with other instruments. To effect this, the thermometer is plunged into a vessel con- taining melting ice or snow, and opposite the point at- which the quicksilver stands is marked 32. It is then transferred to another vessel in which water is rapidly boiling, and the point op- posite which it then stands is marked 212. The inter- vening space is divided into 180 equal parts; these are degrees, and similar divisions are made on the scale for all points above 212, and below 32. The zero point, or cipher of the scale, is therefore 32 degrees below the freezing point of water. The melting of ice and the boiling of water are the fix- ed thermometric points. They have been selected for the purpose of rendering thermometers comparable with each other. The numbers which are attached to these points are arbitrary, and accordingly three different scales have been introduced in different countries. That which is commonly used in America and England is the Fahren- For making thermometers, what liquids are selected ? How is the mer- curial thermometer made ? Is there a vacuum above the mercury in the tube ? How is the scale adjusted ? "What is the freezing and what the boiling point ? "What is meant by the zero ? What are the fixed points ? Why are these fixed points employed ? What three scales have been introduced ? 20 THE MERCURIAL THERMOMETER. heit scale, which, *as we have just seen, makes the melting point of ice 32, and the boiling of water 212. In France, the Centigrade scale is employed ; this has for the melting of ice 0, and for the boiling of water 100. In some parts of Europe, Reaumur's scale is used, the points of which are respectively and 80. Chemical authors always specify the thermometer they use by a letter attached to the numbers ; thus, 212 F, 100 C, 80 R, refer to the boiling of water on Fahrenheit's, the Centi- grade, and Reaumur's scales. It is obvious that these de- grees are readily convertible into each other by a simple arithmetical process. LECTURE V. EXPANSION OP LIQUIDS AND SOLIDS. Importance of the Thermometer. Alcohol Thermometer. Point of Max- imum Density of Liquids. Maximum Density of Wa- ter connected with Duration of the Seasons. Expansion of Solids. FROM the considerations advanced in Lecture III., we can perceive the importance of the thermometer. As all our measures of space and time are affected by variations of temperature, the thermometer, which measures those variations, must necessarily be one of the fundamental instruments of physical science. If we state that' a given object is a foot long, we must specify the temperature at which the measure was taken, for at a Tower temperature it will be less than a foot, and at a higher it will be more. There are several peculiarities which quicksilver pos- sesses that eminently fit it to be a thermometric fluid. 1st. It can always be obtained in a state of uniform purity. 2d. It expands with greater regularity than most liquids, as its temperature rises, and when included in a bulb of glass, as in the common instrument, the irregularity of expansion of the glass almost exactly compensates the ir- regular expansion of the quicksilver, and hence the true What is the Centigrade scale ? What is Reaumur's ? Can these be converted into each other ? Why is the thermometer such an important instrument ? What are the qualities which quicksilver possesses which fit it for these uses ? MAXIMUM DENSITY OP WATER. 21 temperature is very accurately marked. 3d. The range of temperature between the points of solidification and boiling is great, the former being 39 Fahrenheit, and the latter at 662 Fahrenheit ; that is, about seven hundred degrees. 4th. It does not soil or moisten the tube in which it is contained, nor does it adhere thereto, but moves up and down with facility. 5th. It is affected much more readily than water or spirits of wine by a given amount of heat, as we shall see when we come to speak of the capacity of bodies for caloric. When very low temperatures have to be measured, such as approach or are below the freezing point of quick- silver, we resort to thermometers filled with alcohol, tinged with some coloring matter to make its movements vis- ible. This fluid requires a diminution of temperature of more than 180 below the zero of our scale before it solidifies, and hence is adapted to the measurement of low temperatures. If we take some water at 100 Fahrenheit, and, placing it in a vessel in which we can observe its volume, reduce its temperature, we shall find, agreeably to the general law heretofore given, that as it cools it contracts. As it successively passes through 80, 60, 50 degrees, it exhibits a continuous diminution ; but as soon as it has fallen be- low 39, although it may still be cooling, it begins to ex- pand, and continues to do so until it reaches 32, when it freezes. If we take some water at 32 and warm it, instead of expanding, it contracts, until it reaches 39 ; but from that point, any farther elevation of temperature causes it to obey the general law, and it expands. It is obvious, therefore, that if we take water at 39, it is immaterial whether we warm it or cool it, it will ex- pand. At that temperature, therefore, this liquid occu- pies the smallest bulk, and is at its greatest density, for neither by cooling nor warming can we reduce it to small- er dimensions. The particular thermometric point at which this takes place is designated " the point of maxi- mum density of water" and very exact experiments show that it is about 39-^ Fahrenheit. Under what circumstances are alcohol thermometers used ? Does water contract regularly when cooled from 100 to 32 1 Does it regularly ex- pand when wanned from 32 ? At what thermometric point does* that change take place ? What is the designation given to that point? Why js that designation appropriate ? 22 POINTS OF MAXIMUM DENSITY. There are many liquids which thus have points of max- imum density, and which expand previous to assuming the solid form. In the act of solidifying, water undergoes a very great dilatation, amounting to about th of its vol- ume ; this is the reason that ice floats upon it. Several melted metals exhibit the same phenomenon, and advan- tage is taken of the fact in the arts. The alloy of which printers' types are formed, or stereotype plates cast, in the act of solidifying, expands, and hence forces itself into every part of a mould in which it may be poured, and copies it perfectly ; the same is the case with melted cast iron. But it is impossible to obtain good castings with such a metal as lead, which contracts as it cools, and there- fore tends to separate from the surface of the mould, or to leave vacant spaces in it. The fact that water possesses a point of maximum den- sity is connected, to a great extent, with several remark- able natural phenomena ; the freezing of water on its surface is one of these results. If the water contracted as it cooled, the colder portions would descend, and rivers or ponds would commence to freeze at the bottom first, the solidification advancing steadily upward. Such col- lections of this liquid would, during the course of a win- ter, become solid masses of ice, and they would greatly prolong that season of the year, from the length of time required to thaw them. But with things as they at pres- ent exist, the coldest water is the lightest ; it floats on the warm water below ; solidification takes place on the sur- face, and a veil or screen is soon formed which protects the liquid beneath. When the warm weather of spring comes on, the ice on the surface is in the most favorable posi- tion for melting, and thus the point of maximum density of water comes to be connected with the duration of the seasons. Fig. 14. We have already proved by the i p^_^^_^g jffl instrument represented in Fig. 1, that solid substances dilate as their * b temperature rises. The same results may be made very apparent by the apparatus, Fig. 14. Are there other liquids which have points of maximum density ? What advantage is taken of this fact in the arts ? Why does water freeze first on its surface ? How is it that these facts are connected with the dura- tion of the seasons ? EXPANSION OF SOLIDS. 23 Upon a strong basis or wooden board, a b, let there be fastened two brass uprights, c d, with notches cut in them, so as to receive the ends of the metallic bar, e. This bar should be very slightly shorter than the distance between the two uprights, that when it is placed resting in their grooves, if we take hold of it and move it, it will make a rattling sound as we push it backward and forward. If now we pour hot water upon the bar, it dilates, as is proved on restoring it to its position between the uprights ; it will no longer rattle, for it occupies the whole distance between them, and perhaps there may even be a difficulty in forcing it into the grooves. For the determination of very small spaces, the sense of hearing may often be far more effectually employed than the sense of sight. The pyrometer, F ^- 15 - of which we have several varieties, is represented in Fig. 15. It may serve to illustrate the fact that solid substan- ces expand by heat. It consists essen- tially of a metallic bar, a a, resting at one end against an immovable prop, e, the other end bearing upon a lever, b. The extremity of this lever presses upon a second lever, c, which also serves as an index. Upon the index-lever a spring acts so as to oppose the lever b, and the point of the index ranges over a graduated scale. If now lamps be applied to the bar, it expands, and the pressure taking effect on the lever, puts it in motion, the index traversing over the scale. On removing the lamp the bar contracts, and the spring pressing the lever in the opposite direction as soon as the bar is cold, brings the index back to its original point. How does the instrument, Fig: 14, prove that a metallic bar expands when heated ? Describe the pyrometer and the mode of using it. 24 CONTRACTION AND DILATATION OF SOLIDS. LECTURE VI. EXPANSION OF SOLIDS. Contraction of Solids. They expand irregularly. Different Solids expand different- ly. Points of Maximum Density. Metallic Thermom- eters. Nature of Tliermometric Indications. IT is a popular error, that when solid bodies have been heated, they do not return, on cooling, to their original size. Without resorting to any experimental proof, a few sim- ple considerations will satisfy us on this point. If a bar of metal be exposed for a length of time in the open air, it will of course be subjected to continual changes of tem- perature ; whenever the sun shines on it it will expand, and during the cold night it will contract. If now, on cooling, it did not rigorously come back to its original size, but remained a little elongated, we should observe it increasing from day to day, and no matter how minute the difference might be, in the course of time it would become perceptible. Public edifices in cities are often surround- ed by railings of cast iron, which are constantly exposed for years to variations of heat and cold, but did any person ever observe them to grow or increase in size? We conclude, therefore, that soHd bodies, on cooling to their original temperature, regain their original bulk. By linear dilatation we mean increase in one dimension, as in length; by cubic dilatation, increase in all dimensions, length, breadth, and thickness. Knowing the amount of linear dilatation of a given solid, we can easily ascertain its cubic dilatation, by multiplying the former by 3. This result is near enough for practical purposes. Solids expand increasingly as their temperature rises, a phenonemon already observed in the case of liquids, and due to the same cause a diminution of the cohesive force of the particles, because of their increased distance. Compared with one another, different solid substances "What decisive proof can be eiven that solids, on cooling 1 to their ori, by means of an air-tight cork, the mouth, c, of the bottle is to be .carefully stopped. When the whole apparatus has reached the ordinary temperature of the air, the stopper at c is withdrawn, and solidification at once takes place, or, if it should at first fail, the introduc- tion of a crystal of sulphate of soda will bring it on. At that moment it will be perceived, that not only does the thermometer indicate a rise of temperature, but if the bot- tle be grasped, it will be found to be sensibly warm. With care, water may be cooled to a point far below that of freezing without assuming the solid form. If, un- der these unusual circumstances, it be agitated, solidifica- tion ensues, and heat is evolved, the temperature rising to 32. On these principles depends the action of freezing mix- tures, of which the following is an example : If we take eight parts of crystallized sulphate of soda, and mix it in a thin tumbler with five parts of hydrochloric acid, the sul- phate of soda, from being a solid, assumes the liquid form ; and taking, in order to effect that change of form, caloric from surrounding bodies, it reduces their temperature. This may be shown by placing four parts of water in a thin glass test tube, and stirring it about in the mixture ; the water speedily freezes, even though the experiment may be made on a warm summer day. In the treatises on chemistry tables of freezing mixtures are inserted. All these mixtures depend essentially on the principle under consideration that latent heat must be furnished to a substance passing from the solid to the liquid state. They consist of various solid substances, the liquefaction of which is brought about by the action of other bodies; thus, in the instance we have seen, the sul- phate of soda is brought from the solid to the liquid state by muriatic acid, and heat is necessarily absorbed. Into the composition of many of the most effective of these freezing mixtures ice or snow enters. Thus, a mixture of snow and common salt will bring the thermometer be- Can water be cooled below 32 without freezing ? Give an example of a freezing mixture. What are the principles on which freezing mix tures act ? D 38 SOLIDIFICATION OF WATER. low the zero point, and when nitric acid is poured on gnow, the temperature falls as low as thirty degrees be- low zero. Many substances, when solidifying, expand. This is the case with water, in which the amount of expansion is about ^th of the bulk. The force which is exerted under these circumstances is very great, and capable to tearing open the strongest vessels. On a small scale, this may be easily shown by filling a bottle full of water, and, having intro- duced the cork, fastening it tightly down with a piece of wire. On putting such a bottle into a freezing mixture, for example, snow moistened with nitric acid, congelation promptly takes place, and the bottle is burst. The freezing point of water is usually spoken of as a fixed point, and is marked as such upon the scales of our thermometers ; but if water be cooled without allowing any movement or agitation of its parts, it may be brought as low as 15. It is then in the same condition as the saturated solution of sulphate of soda just alluded to. The slightest motion is sufficient to solidify it. But though water will retain its liquid form far below its freezing point, ice can not be brought above 32 without melting. The melting of ice, k and not the freezing of water, is there- fore the fixed thermometric point. We have seen that the possession of a point of maxi- mum density by water exerts a great effect upon the du- ration of the seasons : a similar observation might be made as respects its latent heat. If ice, by the absorption of a single degree of heat, when it passes from 32, could turn into water, the great deposits of winter would sud- denly melt, and inundations be frequent ; or, if water, by losing a single degree of heat, turned into ice, freezing would go on with great rapidity. To the melting of ice, or the freezing of water, time is necessary ; the 140 of latent heat have to be disposed of; this, therefore, serves to procrastinate the approach of winter, and causes the spring to come forward with more measured steps. In autumn the water has 140 degrees of heat to give out to What is the amount of the expansion of water in the act of freezing? How may the force with which this expansion takes place be illustrated ? Is the freezing point of water a fixed thermometric point ? How low can water be cooled without freezing? -Is the melting of ice, or the freezing of water, the fixed thermometric point ? What connection has the latent heat of water with the duration of the seasons ? PROPERTIES OF VAPORS. 39 surrounding bodies before it solidifies; in spring it must receive the same amount before it will melt. This, there- fore, serves as a check upon sudden changes in the seasons. Having thus discussed the leading facts observed in the change from the solid to the liquid condition, let us now ;urn our attention to the second change of form, the pass- age from the liquid to the gaseous state. A technical distinction is made between a gas and a vapor ; by the latter, we understand a gas which will readily take on the liquid form. . Some of the leading peculiarities in the constitution of vapors may be exhibited by the following pig. 24. experiment : Take a glass tube, a a, Fig. 24:, with a bulb, b, blown on its upper ex- tremity ; pour water into the bulb, filling the tube to within an inch or two of the end ; this vacant space fill with sulphuric ether ; and now, closing the end of the tube with the finger, invert it in a glass of wa- ter, as is represented in the figure. The ether, being much lighter than water, at once rises to the upper part of the bulb, as is shown by the light space, the bulb being of course full of ether and water conjointly. On the application of a spirit lamp the ether vaporizes, and presses the water out of the bulb into the glass cup. Three important facts may now be established. 1st. Vapors occupy more space than the liquids from which they arise. 2d. They have not a misty or fog-like appearance, but are perfectly transparent. 3d. When their temperature is reduced, they collapse to the liquid state. That the first of these observations is true, is at once seen on comparing the quantity of ether with the volume of vfypor which has risen from it ; the ether occupying but a small space at the top of the bulb, the vapor fills it en- tirely. We perceive, moreover, that ethereal vapor does not possess that cloudy appearance which is popularly at- tached to the term vapor, but that it is as transparent as What is the distinction between a gas and a vapor ? Describe the ex- periment represented in Fig. 24. What is the difference between a va- por and the liquid which forms it, as to volume ? Have vapors necessari- ly a cloudy appearance ? 40 VAPORIZATION. atmospheric air. And, on removing the lamp, so that the temperature may fall, the liquid rushes up violently into the bulb, exhibiting the ready collapse of the ether vapor into the condition of a liquid. We have already proved that a large amount of heat becomes latent, constituting the caloric of elasticity of va- pors. The temperature of steam is 212, as is that of the water from which it rises ; but it contains about 1000 of latent heat, which gives to it its new form. Different vapors possess different quantities of latent heat ; thus, for ether the number is 163, for alcohol 376, and, as we have said, for water 1000; that is enough, were it a solid, to make it visibly red hot in the daylight. / LECTURE X. VAPORIZATION. Vapors form at all Temperatures. Form instantly in a Void. Effects of removing Pres- sure. Measure of Elastic Force of Vapors. Cumula- tive Pressure. Failure of ' Marriotte 's Law. Elasticity increases with Temperature^ Maximum Density of Va- pors. VAPORIZATION goes on at all temperatures. It is not Fig. 25. necessary that the boiling point should be reached ; even ice will evaporate away. The thin films of this substance often seen incrust- ing glass windows may disappear without un- dergoing the intermediate process of fusion, and a mass of ice freely exposed to the air on a dry, frosty day, loses weight. Steam, there- fore, rises from water at all temperatures, but with more rapidity and a higher elastic force as the temperature is higher. In a vacuum vapors form instantaneously. If we take a barometer, a a, Fig. 25, and pass into the Torricellian vacuum which ex On reduction of the temperature, what phenomenon do they exhibit? How are these three facts proved ? What is the amount of caloric of elasticity of steam ? Mention it also in the case of ether and alcohol. How can it be proved that vaporization goes on at all temperatures ? "What is the effect which ensues when a vaporizable liquid is passed into a Torricellian vacuum ? EFFECTS OF CHANGE OF PRESSURE. 41 ists at its upper part, a small quantity of sulphuric ether, even before it has reached the void space, vapor forms, and the mercury is instantly depressed. Under ordinary circumstances, when the instrument, as at b b, is standing at 30 inches, the column at once falls to 15 or 16, the space being now filled with the vapor of ether ; and if in succession other liquids are tried, the same general result is obtained instantaneous vaporization ; but the amount of vapor set free is different in the different cases. Diminution of atmospheric pressure is, therefore, favor- able to vaporization, and were the pressure of the air en- tirely removed, there are many liquids which would as- sume a permanently aerial form. Let a, Fig. 26, be a glass bottle, into the neck of which a funnel, Fig _ 26 b b, is ground air-tight ; the bottle is to be filled with quicksilver, except a small space at its upper part, which is occupied by sul- phuric ether. If this instrument be placed beneath the receiver of an air pump, as soon as exhaustion is made, the mercury will be seen rising into the funnel, and its place tak- en by the transparent vapor of ether. As long as the reduction of pressure continues, the ether keeps the gaseous form, but on re- admitting the air, it returns to the liquid state. By increase of pressure, as well as by diminution of temperature, vapors may be reduced to the liquid con- dition. Though the law that vapors occupy more space than the liquids from which they come is of universal applica- tion, the increase of volume is by no means the same in all cases. Under ordinary circumstances of pressure, a cubic inch of water at its boiling point produces nearly a cubic foot of steam, or 1696 cubic inches, more accurate- ly. The same quantity of alcohol produces 519 cubic inches, and of oil of turpentine 192 cubic inches. The elastic force exerted by vapors under certain lim- its can be measured by the apparatus given in Fig. 25. The theory of the process is very simple. The height at What substances exist commonly in the liquid state, in consequence of the pressure of the air ? "What is the effect of an increased pressure on vapors ? Do all liquids expand equally in assuming the vaporous state ? How can the elastic force of vapors be measured by the barometer ? D 2 42 CUMULATIVE PRESSURES. Fig. 27. which the barometer stands is determined by the pressure of the air. In the experiment there described, as long as there is nothing to counterbalance that pressure, the mer- cury is forced up by it in the tube to a height of 30 inch- es ; but on introducing some ether, the vapor which forms, exerting an elastic forge in the opposite direction, tends to push the mercury out of the tube. On the one hand, we have the pressure of the air ; on the other, the elastic force of the ethereal vapor; they press in opposite directions, and the resulting altitude at which the mercury stands expresses, and, indeed, measures the elastic force of the vapor. Thus, at a temperature of eighty degrees, water will depress the mercurial column about 1 inch, al- cohol about 2 inches, and sulphuric ether about 20. These numbers, therefore, represent the elastic force of the va- pors evolved. In close vessels, from which there is no escape, or where the escape is greatly re- tarded, a constantly accumulating force is generated, when the temperature is raised. Thus, if we place some water in a flask, a, Fig. 27, into which a tube, b b, is in- serted air-tight by means of a cork, and bent in the form exhibited in the figure, and dipping nearly to the bottom of the flask ; on the application of a spirit lamp, the vapor .generated, having no passage of escape, accumulates in the upper part of the flask, and, exerting its elastic force, presses the liquid through the tube in a continu- ous stream. The mechanical force which thus arises, when every avenue of escape is stopped, is strikingly ex- hibited by the little glass bulbs called candle bombs ; these are small glob- ules of glass, about as large as a pea, with a neck an inch long ; into the in- terior a drop of water is introduced, and the termination of the neck hermetically sealed by melting the glass. When one of these is stuck in the wick of a candle or What is the principle involved ? "When -water is heated in a vessel from which the steam can not escape, what is the effect ? How may this fr * illustrated ? Fig. 28. RELATION OF VAPORS TO PRESSURE. 43 0p,mp, as in Fig. 28, the heat vaporizes f a portion of the water, and there being no passage through which the steam can escape, the bulb is burst to pieces with a loud explo- sion ; a mechanical force which is wonderful when we consider the amount of water employed. It is a minia- ture representation of what takes place on the large scale in the bursting of high-pressure steam-boilers. MARRIOTTE'S law, the law which assigns the volume of a gas under variations of pressure, applies, under certain restrictions, to the case of vapors. A permanently elas- tic gas, when the pressure is doubled, contracts to one half of its former volume ; if the pressure be tripled, to one third, and so on, but not so with vapors; if, upon steam, as it rises from water at 212, any increase of pressure be exerted, this vapor at once loses its elastic form, and instantly condenses into water. But vapors, like atmo- spheric air, if the pressure upon them is diminished, fol- low Marriotte's law ; thus, if the pressure be reduced to one half, steam at once doubles its volume. For vapors, therefore, Marriotte's law holds for diminutions of press- ure, but in other instances, when the pressures are in- creased, it apparently fails, the vapors relapsing into the liquid form. That the elasticity of a vapor increases with its temper- ature, may be readily proved by taking a tube one Ft -. 2 9. third of an inch in diameter and 12 inches long, closed at one end and open at the other, a a, Fig. 29, with a jar, b, an inch or more in diameter and 12 inches deep. Let the tube be filled with quicksil- ver, so as to leave a space of half an inch, into which ether may be poured ; invert the tube in the deep jar, also containing quicksilver; the ether of course rises to the upper closed extremity. If now the tube be lifted in the jar as high as possible without admitting external air, a certain portion of the ether will vaporize, and, depressing the quicksilver, its elastic force may be measured by the length of the resulting column. If now the end of the tube be grasped in the hand, or if it be slightly warmed by the application of a "What is Marriotte's law ? Does it apply in the case of vapors under a diminution of pressure? Does it apply under an increase? What rela- tion is there between elasticity and temperature ? How can the increase of elastic force under these circumstances be shown? 44 MEASURE OF ELASTIC FORCE. lamp, the mercurial column is at once depressed, proving^ that the elastic force of the vapor is increasing. As soon as the tube is warmed to the boiling point of the ether, the column of mercury is depressed exactly to the level on the outside of the tube. At this point, therefore, it bal- ances, or is equal to the pressure of the air. Now let the tube be depressed in the jar; it will be seen with what facility the vapor reassumes the liquid condition. As the tube descends, the vapor condenses, and the mercury keeps constantly at the same level. Under these circumstances, it follows that the vapor is at its maximum density. We can not increase that density by bringing pressure to bear upon it by depress- ing the tube, for the moment the attempt is made the vapor liquefies. LECTURE XL EBULLITION. Theory of Boiling. In Papin's Digester Water never Boils. Instantaneous Condensation of Va- pors. Effect of Variations of Pressure. Effect of Na- ture of the Vessel. Boiling on Mountains. Effect of Red-hot Surfaces. BY introducing different liquids into a tube, arranged as that represented in Fig. .29, we can prove that the ob- servation holds good in every case, that, as soon as the boiling point of a liquid is reached, the elastic force of the vapor rising from it is equal to the pressure of the air. We have said that at a temperature of 80 the vapor of water will depress the mercurial column of a barometer about one inch, but if the temperature be raised to 212, the mercury is at once depressed to the level in the cistern ; at that temperature, therefore, the elastic force of the vapor is equal to the pressure of the air. Upon these principles, the phenomena of boiling or ebullition are easily explained. When the temperature of a liquid is raised sufficiently high, vapor is rapidly gen- At the boiling point of a liquid, what is the elastic force of its vapor equal to ? What is meant by the maximum density of a vapor ? How can it be shown that vapors thus in a Torricellian void are at the maxi- mum density ? At the boiling point of water, what is the elastic force of its steam ? Explain the phenomena of boiling. BOILING. 45 crated from those portions of the mass which are hottest, and the violent motion characterized by the term "boiling" is the result. This is due to the fact that the elastic force of the generated vapor at that point is equal to the at- mospheric pressure, and the vapor bubbles expanding, can maintain themselves in the liquid without being crush- ed in ; they rise to the surface, and there burst. But, just before ebullition takes place, a singing sound is often heard, due to the partial formation of bubbles, which, so long as they are in the neighborhood of the hottest part, have elasticity enough to maintain their form ; but the moment they attempt to rise through the cooler portion of the liquid just above, their elasticity is diminished by their decline of temperature, and the atmospheric pressure crushing them in, they resume the liquid condition; for a few moments, therefore, while the vapor has not gath- ered elastic force enough to maintain its condition per- fectly, these bubbles are transiently formed and disappear, and the liquid is thrown into a vibratory movement which gives rise to the singing sound. Water, when heated in a vessel from which the steam can not escape, never boils. This takes place in the inte- rior of Papin's digester, which is a strong metallic vessel, in which water is enclosed, and the orifice through which it was introduced fastened up. As the steam can not es- cape, the water can not boil, no matter what the tempera- ture may be. But the vapor which accumulates in the in- terior of the vessel exerts an enormous pressure. It is under the same conditions as .were considered in the case of the candle bombs. Papin's digest- er is used to effect the solution of bod- ies by water which are not acted on readily by that liquid at its common boiling point. As a vapor, rising from a vaporizing liquid, will bear no increase of press- ure, so neither will it bear any reduc- tion of temperature without instanta- neously condensing. This may be strikingly shown by an arrangement Fg. 30. What is the cause of the singing sound ? Why does water heated in a close vessel never boil ? Describe Papin's digester. What is its use? Can the steam of boiling water be cooled without condensation ? 46 RAPIDITY OP CONDENSATION. such as is represented in Fig. 30. Into the mouth of a flask, , let there be fitted a tube, b, half an inch in diam- eter, and bent, as shown in the figure. Having introduced a little water into the flask, cause it to boil rapidly by the application of a spirit lamp : the steam which forms soon drives out the atmospheric air from the flask and the tube, and when this is entirely completed, and the vapor issuing abundantly from the mouth of the tube, plunge the end of the tube beneath some cold water contained in the jar, c, and take away the lamp. As soon as this is done, the cold water, condensing the steam in the tube, rises to occupy its place ; and presently passing over the bend, introduces itself with surprising violence into the interior of the flask, filling it entirely full, or, which more commonly takes place, breaking it to pieces with the force of the shock. The low-pressure steam-engine depends on this fact of the rapid condensibility of vapor, the high- pressure engine on its elastic force. Fig. si. The principle involved in the action of the low-pressure engine, and more espe- cially that form of it which was the inven- tion of Newcomen, is well illustrated by the instrument represented in Fig. 31. It consists of a glass tube, blown into a bulb at its lower extremity. In the bulb some water is placed, and a piston slides, with- out leakage, in the tube. On holding the bulb in the flame of a spirit lamp, steam is generated, and the piston forced upward. On dipping it into a basin of cold water, the steam condenses and the piston is de- pressed ; and this action may be repeated at pleasure. As the pressure of the atmosphere determines the boil- ing point of a liquid, and as that pressure is variable, the "boiling point is not a fixed, but a variable point. There are many experiments which might be introduced as proofa of this fact. If a glass of warm water be placed beneath the receiver of an air pump, as in Fig. 32, when the Give an example of the rapidity of its condensation. On what proper ty of vapor does the low-pressure steam-engine depend ? On what, the h'igh-pressure ? How may it be proved that the boiling point depends on the pressure ? BOILING IN VACUO. 47 Fig. 32. rarefaction has reached a certain point, ebul- lition sets in, and the water continues to boil at a lower temperature as the exhaustion is more perfect. In a vacuum, water can be made to boil at 67. On this principle, that the boiling point de- pends on the existing pressure, we give an explanation of a curious experiment, in which ebullition is apparently brought about by the application of cold : Take a Flor- ence flask, a, Fig. 33, and, having filled it half full of water, cause the water to b boil violently, so as to expel all the atmos- pheric air; introduce a cork which will fit the mouth of the flask air-tight, a mo- ment after it is moved from the lamp, and before any atmospheric air has been introduced. If the flask be now dipped into a jar, b, of cold water, its water be- gins to boil, and will continue to do so until its tempera- ture is reduced quite low. The cause of this phenomenon is due to the fact, that the cold water condenses the steam in the flask , and a partial vacuum is the result. In this partial vacuum the water boils, as in the experiment il- lustrated by Fig. 32; and the steam, as fast as it is gen- erated, is condensed by the cold sides of the flask. Besides this variation of the boiling point under varia- tion of pressure, the nature of the vessel in which the pro- cess is carried forward exerts a certain action ; thus, in a polished glass vessel the boiling point is 214, but, in a rough metal vessel it is 212. Some travellers report, that in certain mountainous re- gions meat can not be cooked by the ordinary process of boiling. As we ascend to elevated regions in the air? the atmospheric pressure becomes less, because the column of air above is shorter, and therefore there is less air to press. Under such circumstances, the boiling point of water of course descends, and may possibly become so low as to be unable to bring about the specific change re- quired in the cooking of meat. An ascent through 530 At what temperature will water boil in vacuo ? Explain the process by which warm water may be made to boil by the application of cold ? How does the nature of the vessel affect the boiling' point ? Why is it probable that meat can not be cooked on high mountains ? 48 LIQUIDS ON RED-HOT SURFACES. feet lowers the boiling point one degree. Upon this prin- ciple we can determine the altitude of accessible eleva- tions, by determining the thermometric point at which water boils upon them. A peculiar thermometer, called the hypsometer, has been invented for this purpose. When a drop of water is placed on a red-hot polished surface of platinum, it does not, as might be expected, commence to boil rapidly, but remains perfectly quiescent, gathering itself up into a globule. If the platinum be now allowed to cool, as soon as its temperature has reach- ed a point at which it ceases to be visibly hot, the drop of water is suddenly dissipated in a burst of steam. The explanation given of this phenomenon is, that at the high temperature the drop is not fairly in contact with the red-hot surface, but a stratum of steam intervenes ; this, being a bad conductor, prevents ebullition from occurring, but as soon as the temperature declines, and this steam no longer props up the drop, an explosive ebullition en- sues, because of the contact which has taken place. LECTURE XII. VAPORIZATION. The Boiling Point rises with the Press- ure. Relation between sensible and insensible Heat. The Cryophorus. Leslie's Process for freezing Water. Variability of Moisture in the Air. Hygrometers. Method of the Dew Point. UNDER an increase of pressure, the boiling point rises, and the elastic force of the steam evolved becomes corre- spondingly greater. As we have seen, the elastic force of steam from water boiling at 212 is equal to the press- ure of one atmosphere; but if the pressure be doubled, the "boiling point rises to 250 ; if quadrupled, to 294 ; and under a pressure of fifty atmospheres, it is more than 500. How high must we ascend to bring the boiling point to 21 1 ? How may the altitude of mountains be determined by the thermometer? "What are the phenomena exhibited by water in contact with red-hot platinum? What is the supposed explanation? .How is the boiling point affected by an increased pressure ? LATENT HEAT OF VAPORS. 49 These results may be established by the Fi s- 24 - aid of the boiler, represented in Fig. 34, has inserted into its corners four needtes, all pointing in one direction backward ; if this instrument be set upon a floor or flat table, in the course of time it will crawl a considerable distance. During dry Describe Leslie's process for freezing water in vacuo ? Why does a drop of prussic acid held in the air solidify ? How can it be proved that the amount of moisture in the air is variable ? What is the hygrometer ? Describe the hair hygrometer. Describe the instrument, Fig. 37- THE DEW POINT. weather the thin board contracts, and the two fore legs taking hold of the table, the hind ones are drawn up a little space ; when the weather turns damp, the board ex- pands, and now the hind legs pressing against the table, cause the fore ones to advance. Every change from dry to, damp, or the reverse, produces a walking motion in a continuous direction, and the distance passed over is a register of the sum total of these changes. But of all these hygrometric methods, the process known as " the determination of the dew point" is by far the most philosophical. This method consists in cooling the air until it begins to deposit moisture. When there is much moisture in the air, it obviously requires but a slight diminution of temperature to cause a portion of the vapor to deposit as a dew ; but when the air is dryer, the cool- ing must be carried to a greater extent. The precise thermometric point .at which the moisture begins to de- posit is called the dew point. Thus, if we take a thin metallic vessel containing water, and cool it gradually by the addition of a mixture of nitrate of potash and sal ammoniac, or any of the cooling mixtures, continually stirring with the bulb of a small thermometer, as soon as the temperature has reached a Fig. 38. certain point a dew is deposited on the outside of the metallic vessel ; that temperature is the dew point for the time being. Knowing the tem- perature of the air, the dew point, and the baro- metric pressure, the abso- lute amount of vapor can be determined by a sim- ple calculation. Daniell's hygrometer affords a ready and beau- tiful method of determin- ing the dew point. It consists of a cryophorus, a c I, Fig. 38, the bulb What is meant by the " dew point ?'' "What is the process for ascer- taining it ? Describe Daniel! 's hygrometer and the mode of using it. SPECIFIC GRAVITY OF VAPORS. 53 b being made of black glass, and a covered over with muslin. The bulb b contains ether instead of water, and into it there dips a very delicate thermometer, d. Usually, another thermometer is affixed to the stand of the instru- ment. When a little ether is poured on a, by its evapo- ration it cools that bulb, and ether distils over from b, which, of course, also becomes cold. After a time, the temperature of b sinks to the dew point, and that bulb becomes covered with a mist. The thermometer, d, then shows at what temperature this takes place, and of course gives the dew point. LECTURE XIII. EVAPORATION AND INTERSTITIAL RADIATION. Methods of Gay-Lussac and Dumas for ascertaining the Specific Gravity of Vapors. Phenomena of Evaporation. Control of Temperature. Effect of Dryness, Stillness, Pressure, and Surface. Evaporation a Cooling Pro- cess. Conduction of Solids. Difference among different Metals. Rumford's Experiments. THE specific gravity of vapors may be de- Fig. 39. termined in several ways. The following is the method of Gay-Lussac : A graduated jar, a, is inverted in a basin of mercury, c, which rests upon a small furnace. A glass bulb is to be filled quite full with the liquid under ex- amination, and the quantity introduced is accu- rately weighed. The bulb is now slipped into the jar, a, and rises to its top. A cylinder, b, open at both ends, but the lower pressed down into the mercury, is next placed round a, and the interval filled with clear oil. The furnace is now lighted ; the oil and the mercury be- come warm ; the bulb at last bursts, and, as its vapor depresses the mercury in the graduated jar, its vol- ume may be determined. Thus, knowing the weight of the liquid, the volume of its vapor, and the temperature Describe Gay-Lussac's method of determining the specific gravity of a vapor. 54 SPECIFIC GRAVITY OF VAPORS. of the oil, we can easily calculate the volume at 32, and from that deduce the specific gravity. The method of Dumas consists in weighing a glass globe Fig. 40. filled with the vapor to be tried. A por- tion of the sub- stance is to be introduced in- to the globe, the weight of which is first determined, and this is then held, as shown in the figure, in a bath of fusi- ble metal pla- ced over a small furnace. The heat of the melted metal vaporizes the substance, drives out the air, and occupies the whole cavity in a state of purity. When no more vapor escapes from the end of the tube it is sealed by the blow-pipe, and the temperature of the bath ascertained. The globe is now to be carefully weighed, when cold, a second time, and the point of the tube is then broken un- der quicksilver, which rises and fills it completely, and this being subsequently emptied into a graduated jar, the volume of the globe is ascertained. Knowing the vol- ume of the globe, we know the weight of the air it con- tains, and this, subtracted from the first weight, is the weight of the glass when empty. Subtracting this again from the second weighing, gives us the weight of the va- por, and as the air and the vapor occupied the same vol- ume, their densities are as their weights. But, as their temperature was different, a farther calculation is required to bring them to the same standard. There are several conditions which exert a control over the lapidity of evaporation. The amount of vapor which can exist in a given space depends entirely on the temperature. Thus the air included in a glass jar which is standing over water contains, at 32, a certain quantity Describe the method of Dumas. What is it that regulates the quantity of vapor in a given space ? CAUSES CONTROLLING EVAPORATION. 55 of vapor ; but if the temperature rises to 60, it contains more, and still more if it rises to 90. Should the tem- perature descend, a part of the vapor is deposited as a mist. The quantity that remains in suspension is determ- ined by the temperature alone. It is the application of this principle which constitutes the most beautiful part of Watts's great invention, the low-pressure steam-engine. Taking advantage of the fact that the quantity of vapor which can exist in a given space is determined by the lowness of temperature of any portion of it, he arranged a vessel, maintained uniformly at a low temperature, in connection with the cylinder of the engine, and thus reached the apparently paradoxical result of condensing the steam without cooling the cyl- inder. Among other causes exerting a control over evapora- tion in the air is the dry or damp state of that medium. As is well known, evaporation goes on with rapidity when the weather is dry, and is greatly retarded when the weather is damp. So, too, a movement or current exerts a great effect. When the wind is blowing, water will evaporate much more quickly than when the air is quite calm ; this obviously depends on a constant renewal of surfaces, so that as fast as one portion of air becomes moist it is removed, and a dryer portion takes its place. Extent of surface operates in the same way ; the same quantity of water will evaporate much more rapidly if exposed in a plate than if exposed in a cup. Pressure also exerts a great control ; for, as we have seen, evap- oration takes place instantaneously in a vacuum. While, therefore, there are several circumstances which can control the rate of evaporation, it is temperature alone which regulates the absolute and final amount. As we have just seen, a fixed quantity of vapor can exist in a certain space at a given temperature ; and it matters not whether that space is full of atmospheric air or is a vacu- um, the absolute quantity will be precisely the same. At one time it was supposed that evaporation was due lo a solvent power in the air a kind of attraction be- tween that medium and the water with which it is in con- On what principle does the steam-engine condenser depend? What effect have dryness or dampness over evaporation ? "What is the effect of a current ? What of extent of surface ? What of pressure ? What of temperature ? 56 EVAPORATION IS A COOLING PROCESS. tact ; but it is clear that such an opinion is wholly untena ble, for the process goes forward with the greatest rapid- ity in a vacuum, when the air is totally removed. Although the evaporation of liquids, such as water, will take place at very low temperatures, there is reason to be- lieve that the process has a limit; thus, a minute quantity of vapor will rise from quicksilver at a temperature of 60, but at 40 not a trace can be discovered. All processes of evaporation are cooling processes, be- cause the vapor developed requires latent heat to give it the elastic form. For this reason, when any vaporizable liquid, as ether, is poured on the bulb of an air thermom- eter, or on the hand, cold is produced. Fig. 41. The pulse glass ig an instru- ment which may serve as an illustration : it consists of $ glass tube, bent twice at right angles, and terminated by bulbs, as in Fig. 41. It is partially filled with spirit of wine, the rest being occupied by the vapor of that sub- stance. On grasping one of the bulbs in the hand, the warmth is sufficient to boil the liquid ; and as it distills over into the other bulb, an impression of cold is felt. We now come to the consideration of the mode by which heat is transmitted through bodies, or interstitial radiation, called by many writers conduction ; a term in- volving the idea that the particles of bodies are in actual contact, whereas it has been abundantly proved that they are separated from each other by interstices. The pass- age of the heat across these spaces is what is meant by in- terstitial radiation. From the currency which it has ob- tained, and the convenience of the expression, I shall con- tinue to use the word conduction. Different solids conduct heat with different degrees of facility. If we take a cylindrical mass of metal, and hold tightly against its surface a piece of white writing paper, the paper may be placed in the flame of a spirit lamp for a considerable time without scorching ; but if we take a cylindrical piece of wood of the same dimensions, and, Does evaporation arise from a solvent power in the air ? Is there any limit to evaporation? Why are processes of evaporation cooling pro- cesses ? Describe the pulse glass. What is interstitial radiation ? What is conduction? How may it be proved that wood and metals conduct with different degrees of facility ? CONDUCTION OF KEAT. 57 wrapping the paper round it, expose it to the flame, it rapidly scorches. The metal, therefore, keeps the paper cool by carrying off its heat, but the wood, being a bad conductor, suffers the paper to burn. By the aid of the apparatus of Ingenhouse, Fig. 42, the same fact may be proved in a more gen- Fig.vz. oral way. It consists of a trough of brass, six inches or more long, three wide, and three deep ; from the front of it project cylinders of metallic and other substances of the same length and character ; they may be of silver, copper, brass, iron, porcelain, wood, &c., in succession ; the surface of each cylinder is smeared with bees' wax. On pouring boiling water into the trough, the heat passes along these cylinders with a rapidity cor- responding to their conducting power, and the wax cor- respondingly melts. On the silver bar the wax melts most rapidly, and on the wood most slowly : on the others intermediately ; thus affording a clear proof that different solids conduct heat with different degrees of facility. Even among metallic substances, great differences in this respect exist, as may be strikingly Fig . 43. shown by the instrument, Fig. 43. Into a solid ball of copper, a, three wires of equal length and equal diameter are screwed they may be copper, brass, and iron, respectively : they are flattened at their farther extremities, b, c, d, so as to af- ford a place on which pieces of phospho- rus may be put. A lighted spirit lamp is now set beneath the central ball, the temperature of which soon rises, and the heat passes with different degrees of speed along the metals; very soon the piece of phosphorus at the end of the copper takes fire ; then, some time after, follows that on the brass ; and last, that on the iron ; en- abling us to prove to persons at a distance the fact that these different metals conduct heat with different degrees of facility. If a piece of wire gauze be held over the flame of a candle or gas jet, Fig. 44, the flame fails to pass through ; but the Describe the apparatus of Ingenhouse ? "What does it prove ? Are there differences in the conducting powers of metals ? How may that bo paoved 1 58 CONDUCTING POWER OF METALS. . 45. Fig. 44. gaseous matter of which the flame consists freely escapes through the meshes of the gauze, for it may be set on fire, as shown in the figure. Flame is gaseous matter, or solid matter in a state of excessive sub- division, temporarily suspended in gas, brought to a very high temperature. It can not, therefore, pass through a piece of wire gauze, because the metallic threads, exerting a high conducting power, ab- stract its heat from the incandescent gas, and bring its temperature down to a point at which it ceas- es to be luminous. The safety-lamp of Davy is an appli cation of this principle ; by it combustion is prevent- e d from spreading through masses of explo- sive gas, by calling into action the conduct- ing power of a metallic gauze, with which the lamp flame i.s surrounded, as in Fig. 45. The safety-tube of Hemmings, used to prevent ex- plosions in the oxyhydrogen blow-pipe, acts on the same principle. Count Rumford made several experiments to determine the conducting power of those vari- ous materials which are used for the purpose of clothing. He placed the bulb of a thermometer in the center of a spherical glass globe of lar- ger diameter, and filled the interspace with the substances to be tried. Having immersed the apparatus iri boih'ng water until it was at 212, he transferred it to melting snow, and ascertain- ed how long it took to fall a given number of degrees. Linen and cotton were found to be better conductors than wool and the various furs, and hence the reason that they are preferred as articles of summer clothing ; but he also found that much depended on the tightness with which the substances were packed, for the conduct- ing power apparently rose when they were closely com- pressed. These bodies act, therefore, as will hereafter Can the flame of a candle pass through a piece of wire gauze ? is the reason of this ? What is the construction and principle of Davy's safety-lamp ? On what method did Rumford proceed to determine the conducting power of clothing? What was the effect of compression? How are these results connected with the non-conducting power of air ? CONDUCTION OF LIQUIDS. 50 l>e more distinctly seen, not so much by their own badly- conducting power, as by calling into action the non-con- ducting quality of atmospheric air. LECTURE XIV. CONDUCTION. Conduction of Liquids. Transference of Heat by Circulation. Conduction of Gases. Conduct - ing Power of Clothing. THE conducting power of most liquids, such Fig. 40. as water, is very low; a thin stratum is sufficient almost entirely to cut off the passage of heat. This may be shown by an apparatus such as Fig. 46, consisting of a jar, a, nearly filled with water, with an air thermometer included in such a man- ner that the bulb, , is within a short distance of the surface, a depth of a quarter of an inch or less intervening. The tube of the thermometer may be passed through the lower mouth of the jar, c, water-tight by means of a cork, and the position at which the index-liquid stands having been marked, some ether is poured on the surface of the water, upon which it readily floats^ and then set on fire. A very volu- minous flame is the result, and a great deal of heat is evolved ; and, since the bulb of the thermometer is appa- rently separated from the burning ether by a thin film of water only, if the heat traversed that film the thermome- ter should rapidly move ; but the experiment proves it does not; and we therefore conclude that water is a very bad conductor of caloric. While this conclusion is true, a little consideration will show that this experiment presents the facts in a very de- ceptive way ; and though, from its imposing character, it is generally relied on as a complete proof, yet were wa- ter a much better conductor than what it actually is, the same results would be obtained. All flames, as we shall hereafter see, are hollow ; they are merely incandescent on the surface. A great distance, in reality, intervenes be- How does the conducting power of liquids compare with that of solids ? How may water be proved to be a bad conductor ? What deceptive cir- cumstances arc there in this experiment ? 60 CURRENT ACTION IN WATER. tween tHe thermometer bulb and the points of high tem- perature, and in addition, the ether is rapidly evaporating away to feed the flame, and all evaporations are cooling processes. To a certain extent, all liquids conduct heat : thus, mer- cury is a very good conductor ; but in those liquids of which water is the type the dissemination of heat is chief- ly determined by the mobility of their particles, a process which passes under the name of convection or circulation. Fig. 47. The apparatus, Fig. 47, illustrates the na- ture of this process ; it consists of a wide tube into which water may be poured ; the lower portion, as high as a, being colored blue by the addition of some coloring sub- stance, the intermediate portion, from a to b, being colorless, and the upper portion, from b to c. being tinged yellow. Now, by the application of a red-hot iron ring, <7, of such a diameter that it can surround the jar, a space of an inch or more intervening all round, the upper, yellow portion may be made even to boil : it shows no disposition to intermix with the portions beneath. But if the red- hot ring is lowered down so as to surround the blue por- tion, as it becomes warm it will be found to ascend, first through the colorless stratum, and finally through that tinged yellow, on the top. When the lower portion of a liquid is warmed, currents are established, which, rising through the strata above, bring about a rapid dissemina- tion of the heat. This may also be shown by taking a jar, Fig. 48, velocity with which these waves advance, is 195,000 miles in a second. We are not, however, to understand by this that the ethereal particles rush forward in a rectilinear course at that rate : those particles, far from advancing, remain stationary. If we take a long cord, a b, Fig. 60, and having fast- ened it by the extrem- ity, b, to a fixed obsta- cle, commence agita- ting the end, 0, up and down, the cord will be thrown into wave-like motions passing rapidly from one end to the other. This may afford us a rude idea of the nature of the ethereal movements. The particles of which the cord is composed do not advance or retreat, though the undulations are rapidly passing. So, too, if in the center, c, of a surface of water, Fig. Fig. 61. 61, we make a tapping motion with the finger, circular waves are propagated, which, expanding as they go, soon reach the sides of the vessel which holds the water. A light object placed on the suiface is not violently drifted forward by the waves, but remains entirely mo- tionless. We see, therefore, that there is a wide distinction between the mo- tion of a wave and the motions of the particles among which it is passing. They retain their places, but the wave flows rapidly forward. A distinction is to be made between the words vibra- tion and undulation. In the case of the cord, Fig. 60, the vibration is represented by the movement exerted by the hand at the free extremity, a ; the undulation is the wave like motion that passes along the cord. In the case of the water, Fig. 61, the vibration was represented by the tapping motion of the finger, the undulation by the result- ing wave. We, therefore, see that these stand in the re- lation of cause and effect : the vibration is the cause, and the undulation the effect. Throughout the ethereal medi- Do the ethereal particles move forward at that rate ? How may the movements of ethereal waves be represented by a cord ? How may they be represented on the surface of water ? Do the vibrating particles move forward with the wave ? What is the distinction between vibrationi and undulations ? THEORY OF TRANSVERSE VIBRATIONS. 81 urn, each particle vibrates and transmits the undulatory effect to the particles next beyond it. In the same way as a vibrating cord agitates the sur- rounding air, and makes waves of sound pass through it, so does an incandescent or shining particle, vibrating with prodigious rapidity, impress a wave-like movement on the ether, and the movement eventually impinging on the eye is what we call light. To refer again to the simple illustration given in Fig. 60 : it is obvious that there are an infinite variety of di- rections in which we may vibrate that cord or throw it into undulations. We may move it up and down, or horizontally right and left, and also in an infinite number of intermediate directions, every one of which is trans- verse, or at right an- Fig. 62. gles to the length of the cord, as a a, b b, c c, &c., Fig. 62. This is the peculiari- ty of the movement of light. Its vibrations are transverse to the course of the ray; and in this it differs from the movement of sound, in which the vibrations are normal, that is to say, executed in the direction of the resulting wave, and not at right angles to it. This great discovery of the transverse vibrations of light was made by M. Fresnel. It is the foundation of the whole theory of optics, and offers a simple but brill- iant explanation of so many of the phenomena of light, that the undulatory theory is by many writers designated the THEORY OP TRANSVERSE VIBRATIONS. It may, however, be remarked, that though light con- sists of rays originating in these transverse motions, it is not impossible that there may be other phenomena which correspond to movements in other directions. To those movements our eyes are totally blind, and hence we can not speak of them as light. In the same way there may be motions in the air, due to transverse vibrations, but to them our ear is perfectly deaf. But it is not improbable that God has formed organs of vision and organs of hear- How does each ethereal particle propagate the wave to those beyond ? Is there any analogy between sound and lig" __iay a cord be vibrated ? What is implied by verse vibrations ? Are other motions possible ? it? Is there any analogy between sound and light? In how many ways may a cord be vibrated ? What is implied by the term theory of trails- 82 COLORS DEPEND ON WAVE-LENGTH. ing in the case of other animals upon a different type ; eyes that can perceive normal vibrations in the ether, and ears that can distinguish transverse sounds in the air. Lights differ from each other in two striking particulars brilliancy and color. These are determined by certain affections or qualities in the waves. On the surface of water we may have a wave not an inch in altitude, or a wave, as the phrase is, " mountains high." Under these circumstances, waves are said to differ in amplitude ; and, transferring this illustration to the case of light, a wave, the amplitude of which is great, impresses us with a sense of intensity or brilliancy, but a wave, the amplitude of which is little, is less bright. The brilliancy of light de- pends on the magnitude of the excursions of the vibrating particle. LECTURE XX. WAVE THEORY OP LIGHT. Colors of Light depend upon W^ave Lengths. Interference of Sounds. Young's Theory of Interference of Light. Condition of Inter- ference. Explanation of Lights and Shades in Shad- ows. BY the length of a wave upon water, we mean the dis- tance that intervenes from the crest 5 of one wave to that of the next, or from depression to depression. c~ ~d Thus, in Fig. 63, from a to , or, what is the same, from c to d, constitutes the wave length. In the ether the length of the waves determines the phenomenon of color; this may be rigorously proved, as we shall soon see, when we come to the methods by which philosophers have determined the absolute lengths of un- dulations. It has been found that the longer waves give rise to red light, the shorter ones to violet, and those of intermediate magnitudes the other colors in the order of their refrangibility. Two rays of light, no matter how brilliant they are sep- What is meant by the amplitude of waves ? On what does the brillian. cy of light depend ? What is meant by the length of a wave 1 What is the connection between color and wave length ? TWO SOUNDS PRODUCE SILENCE. 83 arately, may be brought under such relations to one another as to destroy each others effect and produce dark- ness. Light added to light may produce darkness. Two sounds may bear such a relation to each other that they shall produce silence ; and two waves, on the surface of water, may so interfere with one another that the water shall retain its horizontal position. Take two tuning forks of the same note, and fasten by a little sealing wax on one prong of each a disc of card-board, half an inch in diameter, as seen Fig. 64, a. Make one of the forks a little heavier than the other, by putting on the end of it a drop of the wax. Then take a glass jar, b, about two inches in diameter and eight or ten long, and having made one of the forks vibrate, hold it over the mouth of the jar, as seen at d, its piece of card-board being downward ; commence pouring water into the jar, and the sound will be greatly re-enforced. It is the column of air in the jar vibrating in unison with the fork, and we adjust its length by pouring in the water; when the sound is loudest, we cease to pour in any more water, the jar is adjusted, and we can now prove that two sounds added together may produce silence. It matters not which fork is taken, whether it be the light or the loaded, on making it vibrate and holding it over the mouth of the resonant jar, we hear a uniform and clear sound, without any pause, stop, or cessation. But if we make both vibrate over the jar together, a re- markable phenomenon arises, a series of sounds alterna- ting with a series of silences ; for a moment the sound in- creases, then dies away and ceases, then swells forth again, and again declines, and so it continues until the forks cease vibrating. The length of these pauses may be varied by putting more or less wax on the loaded fork ; and as we can see that even during the periods of silence both forks are rapidly vibrating, the experiment proves that two sounds taken together may produce silence. Under these circumstances, waves of sound are said to \Vhat is meant by the interference of lights or of sounds ? Give an il- lustration of the interference of sounds. What is the character of the Bound which the resonant jar emits ? Why are there pauses in it ? At the time of these pauses, are the forks vibrating ? 84 LAWS OF INTERFERENCE. Fig. 65. interfere with each other, and in like manner interference takes place among the waves of light. We can gather an idea of the mechanism by considering this case in waves upon water, in which, if two undulations encounter under such circumstances that the concavity of the one corre- sponds with the convexity of the other, they mutually de- stroy each other's effect. If two systems of waves of the same length encounter each other after having come through paths of equal length, they will not interfere. Nor will they interfere even though there be a difference in the length of these paths, provided that difference be equal to one whole wave, or two, or three, &c. But if two systems of waves of equal length encounter each other after having come through paths of unequal length, they will interfere, and that interference will be complete when the difference of the paths through which they have come is half a wave, or 1-*-, 2, 3^-, c. These cases are respectively shown at a I, and c d, Fig. 65, at the point of encounter, x ; in the first instance, the two sets of waves are in the same phase, that is, their concavities and convexities respectively correspond, and there is no interference ; but in the second case, at the point of en- counter, x, the two systems are in opposite phases, the convexity of the one corresponding with the concavity oi the other, and interference takes place. Upon these principles, we can account for the remark- Fig. 66. able results of the following experi- ment : From a lucid point, s, Fig. 66, which may be formed by the rays of the sun converged by a dou- ble convex lens of short focus, or by passing a sunbeam through a pin- hole, let rays emanate, and in them place the opaque obstacle, a Z>, which we will suppose to be a cylindrical When two waves upon water encounter each other, under what cir- cumstances will they interfere ? When systems of waves of equal length encounter one another, when do they, and when do they not, interfere 7 Describe the experiment represented in Fig. 66. INTERFERENCE OF LIGHT. 85 body, seen endwise in the figure; at some distance beyond place a screen of white paper, c d, to receive the shadow. It might be supposed that this shadow should be of a magnitude included between x y^ because the rays, s a, s Z>, which pass tfte sides of the obstacle impinge Fig G7 on the paper at those points. It might farther be supposed, that within the space x y the shadow should be uniformly dusky or dark ; but, on exam- ining it, such will not be found to be the case. The shadow will be found to consist of* a series of light and dark stripes, as represented in Fig. 67. In its middle, at e, Figs. 66 and 67, there is a white stripe ; this is succeeded on each side by a dark one ; this, again, by a bright one, and so on alternately. Upon the undulatory theory, all this is readily explain- ed. Sounds easily double round a corner, and are heard though an obstacle intervenes. Waves upon water pass round to the back of an object on which they impinge, and the undulations of light in the same manner flow round at the back of the piece of wire, a b, Fig. 66 ; and now it is plain that two series of waves which have passed from the sides of the obstacle to the middle of its shadow, that is, along the lines a e, b e, have gone through paths of equal length, and, therefore, when they encounter at the point e, they will not interfere, but exalt each other's effect. But, leaving this central point, e, and passing to^ it is plain that the systems of waves which have come through the paths af, bf, have come through different distances, for bfis longer than a f; and if this difference be equal to the length of half a wave, they will, when they encoun- ter at the pointy, interfere and destroy each other, and a dark stripe results. Beyond this, at the point g, the waves from each side of the obstacles, ft g, b g, again have come through une- qual paths ; but, if the difference is equal to the length of one whole wave, they will not interfere, and a white stripe results. Reasoning in this manner, we can see that the interioi Is the resulting shadow uniformly dark ? At the central point of the shadow, is it dark or light ? Explain the cause of this central light space, and of the alternate dark and light ones on each side of it ? "What is the length of the paths of the waves which go to the illuminated spaces, and of those which go to the dark ones ? H 86 LENGTH OF WAVES. of such a shadow consists of illuminated and dark spaces alternately : illuminated spaces, when the light has come through paths that are equal, or that differ from each oth- er by 1, 2, 3, 4, . . &c., waves; and dark, when the dif- ference between them is equal to ^, 1^, 2|, 3^, . . &c., waves. That it is the interference of the light coming from the opposite sides of the opaque object which is the cause of these phenomena, is proved by the circumstance that if we place an opaque screen on one side of the obstacle, so as to prevent the light passing, the fringes all disappear. LECTURE XXL WAVE THEORY OF LIGHT. Measurement of the Length of a Wave of Light.- Length differs for different Colors. Measurement of the Period of Vibrations. Nature of Polarized Light. Plane, Circular, and Elliptical Polarized Light. Reflection, Refraction, and Absorp- tion of Light. THE experiment, Fig. 66, may enable us to determine the length of a wave of light. This may be readily done by measuring the distances af and bf, or from the sides of the obstacle to the first bright stripe from the central one, for at that point the difference between those two lines, a f and b f, is equal to the length of one wave. We might employ the second bright stripe ; the differ- ence then would be equal to two waves. Farther, if, instead of using ordinary white light, radia- ting from the lucid point, s, we use colored lights, such as red, yellow, blue, &c., in succession, we shall find that the wave length determined by the process just explained differs in each case ; that it is greatest in red, and small- est in violet light. By exact experiments made upon methods more complicated than the elementary one here given, it has been found that the different colored rays of light have waves of the following length : How can it be proved that the waves from the opposite sides of the ob- stacle interfere ? How, by this arrangement, might we measure the length of a wave of light? When different colors oflight are used, are the waves found to be of equal length ? FREQUENCY OF WAVE-VIBRATION. 87 WAVE LENGTHS OF THE DIFFERENT COLORS OF LIGHT. The English inch is supposed to be divided into ten millions of equal parts, and of those parts the wave lengths are : For red light . " orange . " yellow . " green . . In this manner, it 256 240 227 211 For blue 196 " indigo 185 " violet . . . 174 is proved that the different colors of light arise in the ether, from its being thrown into waves of different lengths. Knowing the rate at which light is propagated in a second, and the wave length for a particular color, we can readily tell the number of vibrations executed in a second, for they plainly are obtained by dividing 195,000 miles, the rate of propagation by the wave length. From this it appears, that if a single second of time be divided into one million of equal parts, a wave of red light trembles or pul- sates 458 millions of times in that inconceivably short in- terval, and a wave of violet light 727 millions of times. In speaking of the constitution of matter, in Lectures I. and II., I had occasion to allude to the amazingly minute scale on which it is constructed. The remarkable facts we are now considering are a monument to the genius of Newton and his successors, for they give us a just idea of the scale of space and time upon which Nature carries on her works among the molecules of matter. Common light, as has been said, originates in vibratory motions taking place in every direction transverse to the ray. With polarized light it is different; to gather an idea of the nature of polarized light, we must refer once more to the cord, Fig. 62, which, as has been said, serves to imitate common light when its extremity is vibrated vertically, horizontally, and in all intermediate positions in rapid succession. But if we simply vibrate it up and down, or right and left, then it imitates polarized light; polarized light is, therefore, caused by vibrations trans- verse to the ray, but which are executed in one direction only. What is the length of a wave of red and of violet light respectively? How can we ascertain the number of vibrations in a second ? On the un- dulatory theory, in what directions do the ethereal particles vibrate in the case of common light ? What is the case in polarized light ? 88 POLARIZATION OF LIGHT. There is a certain gem, the tourmaline, which serves to Fig. 68. exhibit the properties of polar- ized light. If we take a thin plate of this substance, c d, prop- erly cut and polished, and allow a ray of light, a b, Fig. 68, to fall upon it, that ray will be freely transmitted through a second plate if it be held symmetrically to the first, as shown at ef; Hut if we turn the second plate a quarter round, as seen at g k, then the light can not pass through. The rays of the meridian sun can not pass through a pair of crossed tourmalines. Fi 69 The cause of this is obvious: if we take a thin lath or strip of pasteboard, c d, Fig. 69, and hold it before a cage, or grate, a b, it will readily slip through when its plane coincides with the bars ; but if we turn it a quarter round, as at e f, then of course it can not pass the bars. Now the plate of tourmaline, Fig. 68, c d, polarizes the light, a b, which falls upon it ; that is, the waves that pass through it are vibrating all in one plane. They pass, therefore, readily through a second plate of the same kind, so long as it is held in such a way that its structure coin- cides with that motion, but if it be turned round so as to cross the waves, then they are unable to pass through it. There are many ways in which light can be polarized : by reflection, refraction, double refraction, &c. The re- sulting motion impressed on the ether is the same in all cases. Light modified as just described is designated plane polarized light ; but there are other varieties of polariza- tion. If the end of the rope, Fig. 62, be moved in a cir- cle, circular waves will be produced, imitating circularly polarized light; and if it be moved in an ellipse, elliptical polarized light. The undul&tory theory of light gives a clear account of the ordinary phenomena of optics. The general law under which light is reflected from polished surfaces is a Describe the optical properties of the tourmaline. Give an illustration of the phenomenon. What is the cause of the action of the second tour maline plate ? Mention some of the methods by which light may be po- larized. What is circularly polarized light ? What is ellipticaliy polar ized lisrht ? LAWS OF REFLECTION AND REFRACTION. 89 direct consequence of it ; that law is : that the angle, d c b, Fig. 70, made by the reflected V* ray, d c, with a perpendicular, c b, drawn to \ the point c, at which the light impinges, is equal to the angle, a c b, which the incident ray makes with the same perpendicular, or, as it is briefly expressed, " the angles of inci- dence and reflection are equal to each other, and on op- posite sides of the perpendicular." By the aid of this law, we can show the action of re- flecting surfaces of any kind, and discover the properties of plane and curved mirrors, whether they be concave or convex, spherical, elliptical, paraboloidal, or any other figures. From the undulatory theory, the law of the refraction of light also follows as a necessary consequence. It is : in every transparent substance, " the sines of 'the angles of incidence and refraction are to each other in a constant ratio ;" and by the aid of this law we can determine the action of media bounded by surfaces of any kind, plane or spherical, concave or convex. It explains the action of lenses, and the construction of refracting telescopes and microscopes. Sir Isaac Newton's discovery, that white light arises from the mixture of the different colored rays in certain proportions, explains the cause of the colors which trans- parent media often exhibit; thus, if glass be stained with the oxide of cobalt, it allows a blue light to pass it, and upon such principles the art of painting on glass depends ; different colors being communicated by different metallic oxides. The cause of this effect is readily discovered ; for, if we make the light which enters a dark room, as in Fig. 56, pass through such a piece of stained glass before it goes through the prism, and examine the resulting spec- trum, we find that several rays are wanting in it ; that the glass has absorbed or detained some, and allowed others to traverse it. A piece of blue glass thus suffers most of the blue light to pass, but stops the green, the yellow, &c. But it is also to be observed, that the light which is trans- mitted by any of these colored media is not pure, it is "What is the general Taw of reflection? What is the law of the refrac- tion of light ? What is the cause of the colors of transparent media ? If the light transmitted through these colored media pure ? 90 THE TITHQNIC RAYS. contaminated with other tints ; the blue glass, for instance, does not stop all the rays except the blue ; it allows a large portion of the red to pass, and hence the light it transmits is more or less compound. LECTURE XXII. THE TITHONIC RAYS. Peculiarities of ike Tithonic Rays. Their Physical Independence of Heat and Light. Analogies with Light. Found in Moonlight, Lamp- light^ Sfc. Preliminary Absorption and definite Action. In producing a Chemical Effect, tlic Ray changes. Daguerreotype. Application to taking Portraits. Na- ture of the Daguerreotype. Other Photogenic Processes. IT has been already observed, that when a solar spec- trum falls upon paper covered over with chloride of sil- ver, the chloride turns black in the more refrangible re- gions, and from this and similar experiments we have been led to the knowledge that there exists in the sunbeam a principle which can bring about chemical changes. This fact has been received from the beginning of the present century; but, of late, much attention has been given to these rays, and from a consideration of the phe- nomena they exhibit, I have endeavored to prove that they constitute a fourth imponderable principle of the same rank as heat, light, and electricity ; and, for the purpose of giving precision to this view, have proposed that they should be called Tithonic rays, from the circumstance that they are always associated with light ; drawing the allusion from the classical fable of Tithonus and Aurora. This name is, however, to be regarded as a provisional one. Every thing seems to indicate that sooner or later all these principles will be reduced to one of a more gen- eral nature, or that they are all modifications of move- ments taking place in the ether. The evidence of the physical independence of the Ti- thonic rays is very much of the same character as the evi- dence of the difference between heat and light. These What reason have we to suppose that there exists another principle besides heat and light in the solar rays ? Why is the name Tithonic rays suggested for this principle ? PROPERTIES OF THE TITHONIC RAYS. 91 rays are invisible to the eye, and therefore are not light ; they do not affect a thermometer, and therefore are not heat. Media which are transparent to heat are not trans- parent to them, and media through which light readily passes are perfectly opaque to them. The Tithonic rays are emitted, and undergo reflection, refraction, and polarization, precisely in the manner of light and heat. Unlike the latter principle, they exhibit no phenomenon of conduction ; the effect which they pro- duce does not pass from particle to particle, but is limited to that on which the light has impinged ; nor is it, as yet, distinctly established that they exhibit. any phenomenon analogous to secondary radiation. An object upon which rays of heat fall, as it becomes warm, radiates back again, but a substance on which Tithonic rays are impinging does not radiate in like manner. In the sunbeams Tithonic rays exist abundantly; 1 have also found them in the moonlight, in sufficient quantity to give copies of that satellite on sensitive surfaces. In lamplight and other artificial light, they also occur to a much greater extent than is commonly supposed. They do not effect a thermometer, because, except under pe- culiar circumstances, they can not produce expansion ; their office appears to be to arrange and group the mole- cules of bodies, and to bring about the substitution of one element for another. When the Tithonic rays fall upon a sensitive medium for a brief space of time, no change takes place in it ; during this time the rays are actively absorbed, but as soon as that preliminary absorption is over they act in a manner which is perfectly definite : if, for instance, it be a decomposition they are bringing about, the amount of decomposing effect will be precisely proportional to the quantity of rays absorbed. When a beam from any shining source causes a de- composing effect, it is uniformly observed that it is itself disturbed ; the medium which is changing impresses a change on the ray. Thus, a mixture of chlorine and hy- Are these rays visible ? Do they affect a thermometer? Can they he conducted like heat? Do they exhibit secondary radiation? Are they found in the moonbeams and artificial lights ? Do they affect the ther- mometer ? The mode of action of these rays on bodies is divided into two stages, what are they ? Does the ray itself change in bringing about these 92 THE DAGUERREOTYPE. drogen unites under the influence of a ray, but that por- tion of the ray which passes through the mixture has lost the quality of ever bringing about a like change again ; the mixture is tithonized and the light detithonized. When a beam from any shining source falls on a changeable medium, a portion of it is absorbed for the purpose of effecting the change, and the residue is either reflected or transmitted, and is perfectly inert as respects the medium itself. No chemical effect can, therefore, be produced by such rays except they be absorbed. It is for this reason that water is never decomposed by the sunshine, nor oxygen and hydrogen made to unite ; for these substances are all transparent, and allow the rays to pass without any ab- sorption, and absorption is absolutely necessary before chemical action can ensue. But with chlorine the case is very different. This sub- stance exerts a powerful absorbent action on light ; the effect takes place on the more refrangible rays; when mixed with hydrogen and*set in the light, it unites with a violent explosion. The process of the Daguerreotype depends on the action of the Tithonic rays. It is conducted as follows : A piece of silver plate is brought to a high polish by rubbing it with powders, such as Tripoli and rotten-stone, every care being taken that the surface shall be absolutely pure and clean, a condition obtained in various ways by different artists, as by the aid of alcohol, dilute nitric acid, &c. This plate is next exposed in a box to the vapor which rises from iodine at common temperatures, until it has ac- quired a golden yellow tarnish ; it is next exposed, in the camera obscura, to the images of the objects it is designed to copy, for a suitable space of time. On being removed from the instrument, nothing is visible upon it ; but on ex- posing it to the fumes of mercury, the images slowly evolve themselves. To prevent any farther change, the tarnished aspect of the plate is removed by washing the plate in a solution of hyposulphite of soda, and finishing the washing with wa- ter ; it can then be kept for any length of time. Does the ray undergo absorption ? "Why can not water be decomposed in the sunshine ? Why do chlorine and hydrogen explode ? Describe the process of the Daguerreotype. Are the images visible at first ? By what means are they brought out ? How is the picture preserved from farther change ? PHOTOGENIC PORTRAITS. 93 Several important improvements on the original process have been made: 1st, by exposing the plate, after it has been iodized, to the vapor of bromine, or chloride of iodine, which gives it a wonderful sensibility ; 2d, by gilding the plate, after the other operations are complete, by the aid of a mixture of hyposulphite of soda and chloride of gold ; this acts like a varnish, fastening the picture and giving it a more agreeable yellow tone. The art of taking portraits from the life, which has now become a branch of industry, was invented by me soon after the Daguerreotype was known in America ; at that time, this, which is by far the most valuable application of the chemical agencies of light, was looked upon in Eu- rope as entirely beyond the powers of this process ; but subsequently great improvements in it have been made. My memoir descriptive of the art may be seen in the Lon- don and Edinburgh Philosophical Magazine (September, 1840), and the facts are also specified in the Edinburgh Review (January, 1843), in which the discovery is attrib- uted to its proper source, the author of this book. When a beam falls upon the surface of a Daguerreotype plate, it communicates to the iodide of silver a tendency to decomposition, but iodine is never set free because of the metallic silver behind. On exposing a surface dis- turbed in this manner to the vapors of mercury, entire decomposition of the iodide ensues, its silver unites with the mercury, forming a white amalgam, and the iodine corrodes the metallic silver behind. The utmost care must be taken in all Daguerreotype processes to have no vapors of iodine, or bromine, or chlorine about the camera or other apparatus ; they possess the quality of effacing the effects of light, and the most common source of failure among Daguerreotype artists is due to neglecting this precaution. There are some important difficulties to which the Da- guerreotype is liable. For taking landscapes it is not available. Green and red colors impress no change upon it. The order of colors and light and shadow is not, there- fore, strictly observed. Mention some of the later improvements of the process ? In this pro- cess is iodine set free from the plate ? With what does the iodine unite under the influence of the mercurial vapor? \Vliy is not the Daguerreo type applicable to landscapes ? 94 IDEAL COLORATION. There are many other photogenic processes now known : several have been invented by Mr. Talbot ; among them may be mentioned the calotype. Sir J. Herschel, also, has discovered very beautiful ones, and these possess the great advantage over Daguerre's that they yield pictures upon paper. In minuteness of effect they can not. howev- er, be compared to the Daguerreotype. LECTURE XXIII. THEORY OF IDEAL COLORATION. Imaginary Coloration. Variation in the Colors of radiant Heat as the Temper- ature changes. Ideal Coloration of natural Objects. Fixed Lines in the Spectrum. Phosphorogenic Rays. Relations of tJie radiant Principles to the Vegetable World. Spectral Impressions. IN explaining the discoveries made by M. Melloni in relation to radiant heat (Lecture XV.), we had occasion to observe the difference between the action of glass and rock salt in their quality of transparency, and it was stated that the phenomenon is due to differences in the nature of the heat analogous to the different colors of light. As these modifications are found also in the Tithonic rays, and as neither these nor the rays of heat are visible to the eye, I have suggested the use of the term ideal or imaginary coloration, as expressing the facts we have now under consideration. By the theory of ideal coloration we mean, that as there are modifications of light constituting the seven primitive colors, red, orange, yellow, green, blue, indigo, and violet, so, too, there are similar modifications of the other invisible principles of the spectrum, differing from each other by the length of the waves which constitute them ; and also, that as natural bodies exhibit to our eyes a variety of colors, so, in the same manner, they are colored as respects these invisible principles, but the col- oration under these circumstances is different from their colorations for light. What is meant by ideal coloration? Do natural bodies possess cplora tion for tbe other principles of the sunbeam as well as light ? Is their ool or the same in these cases ? IMAGINARY COLORS OF BODIES. 95 To make this plain, let us take an illustration : glass is colorless and transparent to light, and allows any kind of light-ray to traverse it with facility ; but to heat, com- ing from sources of a low temperature, it is wholly opaque. And this arises from the circumstance that the rays of heat which come from such a source are constituted of short waves, and therefore bear an analogy to violet light, while glass acts toward the heat as a ruddy or orange-col- ored medium. The reason, therefore, that this heat of low temperature can not go through glass is because it is of a violet color, while the glass is red. But as the tem- perature rises, calorific rays of other tints begin to be emitted, yellow and red successively, and these easily find passage through the medium. To the rays of heat, rock salt is a white body, glass orange, and alum deep red. The color of these bodies for heat is not the same as their color for light ; and as the eye can not detect the phenomenon directly, we speak of it as imaginary or ideal coloration. Radiant heat undergoes polarization after the manner of light ; the wave mechanism is the same in both cases. The Tithonic rays, also, exhibit all the phenomena due to imaginary coloration, and they may therefore be spoken of as violet, yellow, green, blue Tithonic rays. To them the various objects of nature have a peculiar coloration. The bromide of silver is yellowish- white as respects light, but black to these rays. As respects the fixed lines discovered in the luminous spectrum, as represented in Fig. 59, they also occur in the impressions left upon sensitive surfaces on which the spectrum is received, as was discovered by M. Bequerel and myself about the same time (1842). In this instance, however, they are far more numerous, and occur in groups of many hundreds beyond the visible limits of the violet ray. It has already been mentioned that there is associated with the light derived from shining sources an invisible principle, which causes the phosphorescence of many bodies. Thus, if oyster-shells be calcined with sulphur Why does glass change its transparency for radiant heat ? What is the color of rock salt, alum, and glass for heat ? Can radiant heat be po- larized? What is the color of bromide of silver for light rays and Ti- thonic rays respectively ? Can the fixed lines be obtained on sensitive (surfaces ? Give some instances of phosphorescent bodies- 96 PHOSPHORESCENCE. and exposed to the sun, they shine for a considerable time after in the dark. Nor does it require that the time of exposure should be protracted ; the flash of an electric spark is sufficient. But, what is very remarkable in this case, the rays which excite the phosphorescence can not pass through a piece of colorless glass ; to them it is quite^ opaque. The experiments of Mr. Wilson show that a great number of bodies not commonly supposed to be phosphorescent are so*in reality ; that for a few moments after they have been exposed to the sun, they emit a phos- phorescent light. Thus, a sheet of writing paper, on which a key had been laid, having been exposed for a few mo- ments to the sun, on being suddenly removed to a dark room emitted a pale light, the shadow of the key being perfectly visible. Even the hand, after being dipped in the sunshine, emitted subsequently light enough to be visible in a dark place. The various principles of which we have been speak- in.g exert no ordinary control over the phenomena of the natural world. Thus it is to the influence of light that the vegetable world owes its existence ; for plants can only obtain carbon from the air while the sun is shining on them, and it is of that carbon that their solid structures are chiefly formed. It has been a question to which prin- ciple this effect is due"; but, in 1843, I proved that it is the yellow light which is involved. Dr. Priestley discov- ered that the leaves of plants will effect the decomposi- tion of carbonic acid gas under water ; and on immersing tubes filled with water holding this gas in solution, and containing a few green leaves, I found that at the blue extremity of the spectrum no effect whatever took place, while decomposition went on rapidly in the yellow ray. It is light, in contradistinction to other principles, which is the agent producing this result, and of its colored modifi- cations the yellow ray is the most active. As connected with the minute changes of surface which are effected when the different radiant principles fall upon bodies, as in the instance of the Daguerreotype, we may here allude to the formation of spectral impressions, which, though invisible, may be brought out by proper processes. What is the relation of light to the vegetable world ? "What color forms the active ray ? What was Dr. Priestley's discover}' ? What is meant by spectral impressions ? ELECTRICITY. 97 One of these I described several years ago. Take a piece of polished metal, glass, or japanned tin, the temperature of which is low, and having laid upon it a wafer, coin, or any other such object, breathe upon the surface ; allow the breath entirely to disappear ; then toss the object oft' the surface and examine it minutely ; no trace of any thing is visible, yet a spectral impression exists on that surface, which may be evoked by breathing upon it. A form resembling the object at once appears, and, what is very remarkable, it may be called forth many times in succession, and even at the end of many months. Other instances of the kind have subsequently been described by M. Moser. LECTURE XXIV. ELECTRICITY. First Observations in Electricity. De- scription of Electrical Machines. TJic Spark a Test of Electrical Excitement. Repulsion of Electrified Bodies. Simple Means of Excitement. Conductors and Non- conductors . Insulation. Electric Effects take place through Glass. Medicated Tubes. IT was observed, six hundred years before Christ, that a piece of amber, when rubbed, acquired the quality of attracting light bodies. This fact remained without value for more than two thousand years, a striking memorial of the barren nature of the philosophy of those times. With- in the last two hundred years it has given birth to an en- tire group of sciences, and established the existence of a great imponderable principle, which, from the Greek word 7/Ae/crpov, signifying amber, has taken the name ELECTRICITY. The catalogue of substances in which electric develop- ment can be produced was greatly increased by Gilbert, who showed that glass, resin, wax, and many other bodies, are equally effective as amber. To his successors we owe the electrical machine, an instrument which enables us readily to demonstrate the properties of electricity. Give an example. What was the first obsei-vation made in electricity ? From what does the agent derive its name ? 98 ELECTRICAL MACHINES. fig. 71, Electrical machines are of dif- ferent kinds. They may, how- ever, be divided into plate and cylinder machines. These instru- ments are respectively represent- ed in Fig. 71 and Fig. 72. In each of them there are three dis- tinct portions. First, a piece of glass, the shape of which differs in different cases ; in Fig. 71 it is a circular plate, in Fig. 72 a cylinder ; and from these the in- struments take their name. Sec- ond, the rubbers, made of silk or leather, stuffed with hair : the office of these is to press lightly on the glass as it turns round, and pro- duce friction. Third, a brass body, of a cylindri- cal or rounded shape, but with points on that portion of it which looks toward the glass. It is support- ed on glass props, and is termed the prime conduct- or. Some mechanism, such as a winch, is required to turn the glass on its axis ; and when it is desired to bring the machine into activity, all the parts of it having been made thoroughly clean and dry by rubbing with a piece of warm silk or flannel, a little Mosaic gold or amalgam of zinc being spread on the rubber, as soon as the winch is turned the instrument becomes excited. One of the most striking manifestations of electrical development is the spark ; this, which must have been often seen when the back of the domestic cat is rubbed on a frosty night, was first discovered in the case of glass or sulphur, by Otto Guericke, and by him referred to its proper source, electric excitement. On presenting a brass ball or the finger to the prime conductor of the machine, the spark passes, attended with a slight report. It may be 'What varieties of electrical machines have we ? What are the three essential parts of these machines ? What is the rubber ? What is the prime conductor? How is the machine excited? ELECTRICAL LIGHT AND REPULSION. 99 very beautifully shown by pasting Fi s- 73 - small pieces of tin foil round a glass tube in a spiral form, as shown in a b c Fig. 73, a b c, distances of the twentieth of an inch inter- vening between each piece, and the ends of the tube ter- minated by balls. On presenting one of these balls to the prime conductor, and holding the other in the hand, as the spark passes, it has to leap over each interstice be- tween the spangles of tin foil, and exhibits a beautiful spiral line of light. By pasting the tin foil 011 a pane of glass in such a way as to direct the spark F 74 properly, words may be written in electric light, as shown in Fig. 74, As the electric spark can scarcely be confounded with any other physical phenom- enon whatever, its presence is always indubitable evi- dence of electric excitement. Thus, we can prove that electricity may be transferred to the human body from the machine, by placing a man on a Fig. 75. stool supported by glass pillars, Fig. 75. If he touches the prime conductor with one hand, sparks may be drawn from any part of his clothing or body. To Otto Guericke, who was also the inventor of the air pump, we owe another of the most im- portant discoveries in electricity : that bodies pig.16. which have touched an excited substance are subsequently repelled by it ; thus, if we rub a glass tube, Fig. 76, a, until it becomes elec- trified, and then present it to a feather, b, Fig 77 suspended by a silk thread to a stand, c, the feather is at first at- tracted, and then immediately re- pelled. V On this principle, that under certain circum- stances repulsion takes place, are founded dif- ferent methods for ascertaining the existence How may the electric spark be exhibited ? Why may it be used as a test for electric excitement? Can electricity be transferred from the machine to the body ? What discovery did Otto Guericke make in elec. tricity ? How may this property of repulsion be illustrated ? 100 CONDUCTORS AND NON-CONDUCTORS. of electric excitement, when too feeble to cause a spark. Thus, two light balls of cork, Fig. 77 (p. 99), a b, sus- pended by linen threads so as to hang side by side, as soon as they are electrified repel each other. It does not, however, require an electrical machine to demonstrate the principles of this agent. A piece of stout brown paper three inches wide, and a foot long, if held before the fire until it is quite dry and smokes, and then drawn between the knee and the sleeve, becomes highly excited, especially if the person wears woollen clothing. It will yield sparks more than an inch long. Let a, Fig. 78, be the termination of the prime conduct- Fig-. 78. or, and in a hole in it place the long brass rod b, terminated by the brass ball c. If the finger is approached to the ball, sparks freely pass, showing that along brass elec- tricity is conducted ; but if a glass rod of the same diam- eter and length, and terminated by a brass ball, be em- ployed, not a solitary spark can be obtained, proving that glass is a non-conductor of electricity. The important fact that substances may be divided into two classes, conductors and non-conductors, was first ac- cidentally discovered by Dr. Grey, who found that all metals and moist bodies are conductors, and that glass, resins, wax, sulphur, atmospheric air, are non-conductors. In the treatises on chemistry, tables may be found exhibit- ing the relations of bodies in this respect. The conduct- ing power of the same substance differs with circumstan- ces ; thus, ice and glass are.non-conductors, but water and melted glass are conductors. We see, from these facts, the explanation of the struc- ture of the prime conductor ; the electricity derived from the glass by friction passes easily along the brass portion, but can not escape into the earth, owing to the glass sup- ports, which refuse it a passage. When a body is thus placed upon glass, it is said to be electrically insulated, and the process is called insulation. Although electricity can not pass through glass, Sir Isaac Newton found that this substance is no impediment By what simple means may electrical experiments be made ? How may it be proved that brass is a conductor and glass a. non-conductor ? Mention some of the leading substances belonging to each of these classes. Explain the structure of the prime conductor. Can electric influences pass through glass ? TWO SPECIES OF to the exertion of its influences. . Thus, in Fig. 79, if a be the brass ball f the prime conductor, any light objects, such as bits of paper or fragments of cork, placed on a metal stand, b, beneath will be attracted ; and though a pane of glass, c, be placed between a and b, still the same phenomenon takes place. Soon after electricity became a subject of popular at- tention, it was currently believed, that if medicines of va- rious kinds were sealed up in glass tubes, and the tubes electrically excited, their peculiar virtues would be exhal- ed in such a manner as to impress the operator with their specific purgative, emetic, or other powers. Like many of the popular delusions of our times, this imposture was supported by the most cogent evidence, and maladies cur- ed publicly all over Europe. Like them, these " medica- ted tubes" have served to prove the worthlessness of hu- man testimony when derived from the prejudiced and ignorant. LECTURE XXV. THEORY OF ELECTRICAL INDUCTION. Two Species of Electricity. Their Names. General Law of Attraction and Repulsion. Theory of Induction. Permanent Ex- citement by Induction. Takes place through Glass. Illustrative Experiments. A VERY celebrated French electrician, Dufay, having caused a light, downy feather to be repelled by an excit- ed glass tube, intended to amuse himself by chasing it round the room with a piece of excited sealing-wax. To his surprise, instead of being repelled, the feather was at once attracted. On examining the cause of this more mi- nutely, he arrived at the conclusion that there are two species of electricity, the one originating when glass is excited, and the other from resin or wax. To these he gave the names of vitreous and resinous electricity, thus What was formerly meant by medicated tabes 1 How was it first dis- covered that there are two species of electricity 1 What names have been given to these electricities 1 I 2 INDUCTION. .pgiptmg; put tljeir origin ;, they are also called, for reasons \\vh5tjfc J"p3V be giy en? b&ce after, positive and negative elec- tricities'. ' He found that these different electricities possess the same general physical qualities ; they are self-repulsive, but the one is attractive of the other. This is readily proved by hanging a feather by a linen thread to the prime conductor of the machine, and, when it is excited, bringing near to it an excited glass tube. The feather is already vitreously electrified, and the tube, being in the same con- dition, at once repels it ; but a stick of excited sealing- wax being resinously electrified, that is to say, in the opposite condition to the feather, at once attracts it. Two cork balls, as in Fig. 77, suspended by conducting threads, always repel one another when both are excited either vitreously or resinously ; but if one be vitreous arid the other resinous, they attract. These various results may all be grouped under the following general law, which includes the explanation of a great many electrical phenomena. Bodies electrified dis- similarly attract, and bodies electrified similarly repel ; or, more briefly, like electricities repel, and unlike ones attract. There are many ways in which electrical excitement can be developed : in the common machine it is by fric- tion ; in the tourmaline, a crystallized gem, by heat ; and in other cases by chemical action and by conduction. Elec- trical disturbance also very often arises from induction. By the term electrical induction we mean that a body which is already excited tends to disturb the condition of others in its neighborhood, inducing in them an electric condition. Thus, let a, Fig. 80, be the terminal ball of the prime Fig. 80. conductor, and a few inches \ fK off let there be placed a seo ct *\l _ d ondary conductor, b c, of brass D supported on a glass stand, and at each extremity, b and c, of the conductor, let there be ar- ranged a pair of cork balls I What are their physical qualities ? How may this self-repulsion and toutual attraction be proved ? "What is the general law of electric attrac- tions and repulsions ? In what ways may electric excitements be devel- oped ? What is the meaning of electric induction ? Give an illustration. ELECTRICAL INDUCTION. 103 suspended by linen threads, as shown in the figure. As soon as the ball, a, is electrified by turning the machine, and without any spark passing from it to the secondary conductor, the balls will begin to diverge, showing that the condition of that conductor is disturbed by the neigh- borhood of the excited ball, a. It will farther be found, on presenting an excited piece of sealing wax to the pairs of cork balls, that one set is attracted, and the other repelled. They are, therefore, in opposite electrical states. The disturbing ball is vitre- ously electrified, and that end of the secondary conductor nearest it is resinous, the farther end being vitreous. If the disturbing ball, #, be now removed, the electric dis- turbance ceases, and the corks no longer diverge. These phenomena of electric induction are not depend- ent on the shape of bodies. Let there be two flat circular plates, a b, Fig. 81, sup- ported on glass stands, and set a few inches apart, looking face to face. Let one of them, , be electrified positively by contact with the prime conductor, as indicated by the sign + ; it immediately induces a change in the opposite plate, the nearest face of which becomes negative , and the more distant, positive. It is evident that this disturbance is a consequence of the law, that "like electricities repel, and unlike ones attract." In the plate &, both species of electricity exist, and a be- ing made positive, even though at a distance, exerts its attractive and repulsive agencies on the electric fluid of b, the negative electricity of which it attracts, and draws near to it ; the positive it repels and drives to the farthest side ; so that the disturbed condition of the body b is a result of the fact, that a being electrified positively, will repel positive electricity and attract negative. Now let the plate b be touched by the finger, or a channel of communication opened with the earth; the positive electricity of a still exerting its repulsive agency on that of b, will drive it into the ground, and b will now become negative all over. Lot b be once more insulated, by breaking its commu- In a secondary conductor disturbed by an electrified body, what are the conditions of its ends ? What is the cause of this disturbance ? How- may wo by induction permanently electrify a body ? 104 MISCELLANEOUS EXPERIMENTS. nication with the ground, and let a be removed; A \v\i\ now be found that b is permanently electrified, and in the Dpposite condition to a. By manipulating in this manner, we can, therefore, ef- Fig. 82. feet a permanent disturbance in the condition of an insulated body, by bringing an excited one in its neighborhood. In these changes, the intervention of a piece of glass makes no difference. Let a circulai plate of glass, a, Fig. 82, be set so as to inter vene between the metallic plates, a and b, and still all the phenomena occur as before. Elec trie induction, therefore, can take place through glass. Fig 83 n ^ G principles of induction, and of electric attraction and repulsion, many very interesting experiments may be explained. The following may serve as examples : To the ball of the prime conductor, Fig. 83, let there be suspended a cir- cular plate of "brass, a, six inches in diameter, horizontally, and beneath it another plate, b, supported on a conducting foot, parallel and at a distance of three "or four inches. On the lower plate, b, place slips of paper or of other light substance, cut into the figure of men or animals. On set- ting the machine in motion, so as to electrify the upper plate, the objects move up and down with a dancing mo- tion ; and the cause is obvious : the plate a being posi- tive, repels by induction the positive electricity of the figures through the conducting stand into the earth, and thus, they being rendered negative, are attracted by the upper plate ; on touching it, they become electrified posi- tively like it, and then are repelled, and fall down to dis- Fi 84 charge their electricity into the ground, and this motion is continually repeated. Upon a horizontal brass bar, a b, Fig. m84, three bells are suspended, the outer ones at a and b by chains, the middle I 1 one at c by a silk thread. Between the ^^KwwwKoeaj bells, the metallic clappers, d e, are sus- *^ pended by silk, and from the center bell Can electrical induction take place through glass ? Describe the ex- periment of the dancing figures, and explain the principles involved in it. Describe the experiment of the bells, and the cause of their ringing. MISCELLANEOUS EXPERIMENTS. 105 Fig. 85. the chain f extends to the table. On hanging the ar- rangement by the hook at g to the prime conductor, the bells ring ; the clappers moving from the outer to the cen- tral bell and back, alternately striking them. On a pivot, a, Fig. 85, suspend a bell jar having four pieces of tin foil pasted on its sides, b c d; connect the jar, by means of the insulated wire y, with the prime conductor, so that the pieces of tin foil may receive sparks. On the opposite side ar- range a conductor, #, in connection with the ground by a chain. On putting the machine into activity, the jar will commence rotating on its pivot. Take a cake of sealing wax or gum lac, eight or ten inches in diameter, and receive on its surface a few sparks from the prime conductor by bringing it near the ball. Then blow upon its surface from a small pair of bellows, a mixture of flowers of sulphur and red-lead, which have been intimately ground together in a moitar. This mix- ture is of an orange color, but the moment it impinges on the cake it is, as it were, decomposed ; the yellow sulphui settling on one portion, and the red-led on another, giv ing rise to very curious and fantastical figures. LECTURE XXVI. LAWS OP THE DISTRIBUTION OF ELECTRICITY, AND THE GENERAL THEORIES. Distribution of Electricity. On a Sphere. Ellipsoid. Action of Points. Franklin's Discovery of the Identity of Electricity and Lightning The Leyden Jar. The discharging Rod. The Elec trie Battery. WHEN electricity is communicated to a conducting body, it does not distribute itself uniformly through the whole mass, but exclusively upon the surface ; thus, if to the Explain the arrangement and cause of movement of the rotatory jar. How may powder of sulphur and red-lead mixed together be separated ? Does electricity distribute itself on the surface or in the interior of bodies ? 106 DISTRIBUTION OF ELECTRICITY". spherical ball a, Fig. 86, supported on an insulating foot, b, there be adjusted two hemispherical caps, c c, also on insulating handles, it may be proved that any electricity communicated to a distributes itself entirely on its surface ; for if we place upon a the caps e c, and then remove them, it will be found that every trace of electricity has disappeared from a, and has accumulated on the caps, which, while they were upon the ball, formed its superficies. Fi 87 Again, if we take a large brass ball, bring a secondary ~~ conductor, b, supported on an insu- lating stem, c, and on putting the electrical machine in activity, two or three sparks will pass from a to b, but after that no more. The cause of the refusal, on the part of the secondary conductor, to receive any farther charge is obviously due to the fact that the electricity which is already communicated to it repels that upon the ball, a, and prevents the passage of any more. If now we take a Leyden jar, &, Fig. 94, and having insulated it on a stand, bring it within a Figf 94 . short distance of the ball, a, of the prime conductor, it in the same manner will only receive a few sparks. But if we place a conductor, c, which is connected with the ground, near to the outside coat- ing, it will be found that for every spark that passes between a and b one passes between the outside coating and c, and the sparks follow each other in rapid suc- cession, until the jar becomes fully charged. From this, therefore, we gather, that while positive electricity is Why must the outer coating be in connection with the ground ? Why ia the charge of the jar limited? What is the reason that a secondary insu- lated conductor refuses to receive more than two or three sparks ? When the Leyden jar is insulated, can it be charged ? On bringing a conduct- or in connection with the ground, near the outer coating, what is the result? 112 ELECTROMETERS. passing into the interior of the jar, it is escaping from the exterior, and that the reason the jar condenses is because its sides are in opposite conditions, the positive electrici- ty of the interior being nearly neutralized by the nega- tive electricity of the exterior. Fig. 95. Electrometers are instruments for measuring the intensity of electric excitement. The cork balls, which were represented in Fig. 77, are one of the most simple of these contrivances. The distance to which they will diverge is a rough measure of the intensity of the electric force. The quadrant electrometer depends essentially on the same principles. It consists of an up- right stem of wood, Fig. 95, to which is affixed a semicircular piece of ivory, from the center of which there hangs a light cork ball playing upon a pivot. When this instrument is placed on the prime conductor or other electrified body, the stem par- ticipates in the electricity, and repelling the cork ball which hangs in contact with it, the amount of repulsion may be read off on the graduated semicircle ; but it is obvious that the number of degrees is not expressive of the true electrical intensity, and that no force, no matter what its intensity may be, can ever repel the ball beyond ninety degrees. The gold-leaf electrometer, Fig. 96, consists of a glass cylinder, a, in which two gold leaves are suspended from a conducting rod terminated by a ball or plate b. On the glass opposite the leaves pieces of tin foil are pasted, so that when the leaves diverge fully they may dis- charge their electricity into the ground. This is a very delicate instrument for discovering the presence of electricity, but the torsion electrometer of Coulomb is to be preferred when it is re- quired to have exact measures of the quantity. Coulomb's electrometer consists of a glass cylinder, a, Fig. 97, upon the top of which there is fixed a tube, b, in the axis of which hangs a glass thread, b a, to the Describe the cork b'all electrometer. Describe the quadrant electronic ter. Why does the quadrant electrometer give inaccurate indications ? De- scribe the gold-leaf electrometer. Describe Coulomb's torsion electrometer THE TORSION ELECTROMETER. 113 lower end of which a small bar of gum lac, c, with a gilt pith ball at each extremity, is fasten- ed. Through an aperture in the top of the glass cylinder, another gum lac rod, d, with gilt balls, may be introduced. This goes under the name of the carrier rod. If, now, the lower ball of the carrier rod be charged with the electricity to be measured, and introduced into the inte- rior of the cylinder, as seen in the figure, it will repel the movable ball. By taking hold of - the button &, to which the upper end of the glass thread, a, is attached, we may, by twisting the glass thread for- cibly, bring the carrier ball and the mova- ble ball in contact. The number of degrees through which the thread require-s to be twisted represents the amount of electricity. To the button, Z>, an index and scale are attach- ed, not shown in the figure. By this we can tell the num- ber of degrees of twist or torsion which have been given to the thread. These angles of torsion are exactly pro- portional to the quantities of electricity.- Many of the fundamental phenomena of electricity have been explained by Dr. Faraday upon the hypothesis that induction is an action of polarization, taking place in the contiguous molecules of non-conducting media, and prop- agated in curved lines. Whatever may be the form or constitution of bodies, an electric charge can not be given to them without at the same time giving a charge of the opposite kind, but of the same amount, to them or other bodies in their vicini- ty. This charge is not confined upon their surfaces by the pressure of the atmosphere, but through the polariza- tion of the aerial or solid particles of the surrounding dielectrics, producing in them a charge of the same amount, but of an opposite kind. Thus, if a positively electrified ball be placed in the center of a hollow metal- lic sphere, the intervening space being filled with atmos- pheric air, the charge is not retained upon the ball by the What is the basis of Faraday's theory of induction? On this theory, are charges confined by pressure of the air ? Describe the action of an electrified ball in the interior of a sphere. K2 114 pressure of the air, but because each aerial particle as- sumes by induction a polarity of the opposite kind on the side nearest to the ball, and of the same kind on the side farthest off. This state of force is therefore communica- ted to the interior of the hollow sphere, which is electrified to the same amount, but of an opposite kind to the ball. That this polarization of the particles takes place, is shown by the position which small silk fibres or spangles of gold assume when placed in oil of turpentine, through which induction is established. Each particle disturbs not merely that which is before it or behind it, but it is in an active relation with all surrounding it, and hence the polarity can be propagated in curved lines, and induction take place round corners and behind obstacles. On these principles, w r e can easily account for the dis- tribution of electricity on spherical or ellipsoidal conduct- ors, the repulsion of bodies similarly electrified, the con- densing action of the Leyden vial, and many other similar phenomena. By a variety of experiments, Dr. Faraday has proved that inductive action takes place in curved lines, the di- rections of which can be varied by the approach of bodies. He has also shown that the particles of solids, as gum lac, glass, &c., assume this character of polarity. Non-con- ducting bodies, through which the action of induction takes place, are called dielectrics, and each of them has a specific inductive capacity. Thus, if three metallic plates, a b c, Fig. 98, be insulated parallel to each other, at- mospheric air intervening between a and b, and a plate of gum lac between b and e, the inductive action of the gum lac will be found to exceed that of the air. The fol- lowing table gives some of these results : Inductive capacity of air roo glass 1-76 lac 2-00 sulphur 2'24 All the gases have the same inductive capacity, whatever Does induction take place in straight or curved lines ? Can the parti- cles of solid bodies be polarized ? What are dielectrics ? What is meant by the specific inductive capacity of dielectrics ? Of air, glass, and sulphur, what are the inductive capacities ? What is the case with gas ecus bodies ? THE ELECTROPHORUS. 115 their density, elasticity, temperature, or hygrometric con- dition may be. The electrophorus is an instrument which depends for its action on induction, and is of frequent use in chemis- try. It consists of a cake of gum lac or Fig. 99. sealing wax, b, Fig. 99, on which is placed a flat metallic plate, a, with an insulating handle, c. On exciting b with a piece of warm flannel, it becomes negatively elec- tric, and a being placed on it, and the finger brought near, a negative spark, driven from a by the repulsive influence of b, is received. On lifting a by its insulating handle, a positive spark is obtained ; on putting it down on b, a negative one. And in this manner we may obtain an unlimited number of sparks; positive ones when a is lifted, and negative ones when it is down. A little reflection will show that none of this electricity comes from the excited cake b, but is merely the effect of its inductive influence on the electric condition of the metallic plate, a. The electrophorus may be used when the weather is too damp for the common machine to work. LECTURE XXVIII. VOLTAIC ELECTRICITY. Of Electricity in Motion. Sul- zer's Experiment. Galvanfs Discovery. Volta's The- ory. Water is a compound Body. Description of a simple Voltaic Circle and its Properties. Direction of the Current . Different Kinds of Combinations. Use of Sulphuric Acid. Origin of the Electricity. DURING the last century, a German author of the name of Sulzer observed, that when two pieces of metal of dif- ferent kinds, as silver and zinc, are placed one above and the other beneath the tongue, as often as their projecting ends are brought in contact a remarkable metallic taste is perceived. To explain this result, he supposed that some kind of vibratory movement was excited in the nerves of the tongue. It is the first recorded pnenomenon attributa- ble to Voltaic electricity. Describe the electrophorus ? What fact was first described in Voltaic; electricity ? 116 GALVANIC EXPERIMENTS. In the year 1790, Galvani, an Italian anatomist, observ- ed the contractions which ensue when a metallic commu- nication is made between the nerves and muscles of a dead frog; he found, that if a single metal is employed as the line of communication, contractions of the muscle take place whenever the metal reaches from the nerve to the Fig. 100. muscle ; but that if two pieces of different kinds are used, the contractions are much more energetic. Thus, if we take the skinned hind legs of a frog, Fig. 100, hanging together by a piece of the spine, around which tin foil has been twist- ed, every time that we simul- taneously touch the tin foil and tlie muscle with a bent copper wire, or with a copper and zinc wire, C Z, conjointly, a convulsive contraction takes place. To explain this effect, Galvani supposed that the mus- cular system of animals is constantly in a positively elec- trical state, while the nervous system is negative. In the same manner, therefore, that a discharge takes place in the case of a Leyden vial, when a line of communication is opened between the two coatings, the muscular con- tractions in this case are to be accounted for. For some time these phenomena went under the name of animal electricity ; they subsequently have received the designa- tions of Galvanism and Voltaic electricity. But Vplta, another Italian philosopher, was led to sup- pose that the cause of this remarkable result is not due to any peculiarity of the animal system, but to the contact of the pieces of metal employed. This led to the inven- tion of the Voltaic pile, an instrument which has achieved a complete revolution in chemistry. It is interesting to remark what great results may, in the hands of a true philosopher, spring from the most in- significant observations. The convulsive spasms of a frog's leg have ended in showing that the entire crust of the earth is mae up of metallic oxides, have revealed the What was the fact discovered by Galvani ? In what manner did ht explain it ? Under what names did these phenomena successively pass ^ What was Volta's supposition ? THE SIMPLE CIRCLE. 117 mystery why the magnetic needle points to the north, and revolutionized the science o chemistry. What we have already said in the foregoing Lectures respecting electricity refers chiefly to that agent in a mo- tionless or stagnant state, as the mode of its distribution on conductors, the action of the Leyden vial, &c. The phenomena of Voltaic electricity are those which arise from electricity in a state of motion. From the great advances which these sciences have re- cently made, we are able to present the various topics in- volved in a much clearer way than by merely tracing them in a historical sketch. I shall not, therefore, pur- sue the order in which these facts were successively dis- covered, but present them in what now appears the sim- plest manner. It is to be admitted, though of that abundant proof will soon be given, that water is not a simple, but a com- pound body ; that it consists of two elements, oxygen and hydrogen gases. It is also to be understood that metallic 2inc may be amalgamated or united with quicksilver, by putting it in contact with that fluid metal, under the sur- face of dilute sulphuric acid. Strips of zinc thus amalga- mated exhibit a pure metallic brilliancy. If, now, we take a strip of amalgamated zinc, an inch wide and three or four inches long, and a piece Fis 101 of clean copper of similar size, z and c, Fig. 101, and placing them side by side in a glass, f^ containing water slightly acidulated with sul- phuric acid, we have one of the forms of a sim- ple Voltaic circle. In this, it is to be observed, that so long as the metallic plates remain with- out touching each other, no remarkable phe- nomenon appears ; but if we take a metallic rod, d, and let it connect the top of the zinc and copper together, a series of new facts arises. First, from the surface of the copper, bubbles of gas are evolved ; they are minute, but so numerous as to make the water turbid ; if collected, they are found to be hydro- gen gas. ^ "What is the difference between common and Voltaic electricity? la water a simple or a compound body ? What is meant by amalgamated zinc ? Describe a simple Voltaic circle. As long as the plates are not in contact, does any phenomenon take place ? On communicating by a me- tallic rod, what gas is evolved from the copper ? 118 PHENOMENA OF A SIMPLE CIRCLE. Secondly, the plate of zinc rapidly wastes away, as is easily proved by weighing it from time to time ; and on examining the liquid in the cup, we discover the cause of this waste, for that liquid contains oxide of zinc ; coupling this fact with the former, we infer that, so long as the me- tallic rod, d, is in its place, water is decomposed, its oxy- genuniting with the zinc, its hydrogen escaping from the copper. On removing the rod, d, all these phenomena at once cease. Thirdly, if, instead of a metallic rod, d, a rod of glass, or other non-conductor of electricity, be employed, no de- composition takes place. This, therefore, indicates that the agent which is in operation is electricity. Fourthly, if for the line of communication, d, a piece of metal be employed, and we cautiously lift it from the zinc or copper plate, the moment the contact is broken, in a dark room we see a minute electric spark. It has been already observed that the electric spark can not be confounded With any other natural phenomenon. Fifthly, if the line of communication be a very slender platinum wire, as long as it remains in its position, its tem- perature rises so high that it becomes red hot, and may be kept so for hours together. Now, recollecting that the ignition and fusion of metals take place when they are made to intervene between the coatings of a Leyden vial, and considering all the facts which have just been set forth, we see that the following conclusion may be drawn : that in an active simple Voltaic circle water is decom- posed, its oxygen going to the zinc and its hydrogen to the copper, and that a continuous current of electricity accompanies this decomposition, running from one metal to the other, through the connecting rod. The direction of this current may be determined by several processes; it is as follows: the electricity, leaving the surface of the zinc, passes through the liquid to the copper, then moves through the connecting wire back again to the zinc, performing a complete circuit ; hence the term Voltaic circle. Simple Voltaic circles are of several kinds ; that which What happens to the zinc ? Why do we infer that water is decom- posed 1 If a glass rod is used instead of a metallic one, what is the result ? How can a spark be mads visible ? Can a platinum wire be ignited ? From these facts, what conclusions may be drawn ? What is the course of the current ? ELECTROMOTIVE SOURCE. 119 we have been considering consists of two different metals with one intervening liquid, but similar results can be ob- tained with one piece of metal and two different liquids. In the foregoing experiment, we have used dilute sul- phuric acid: this acid discharges a subsidiary duty. Zinc, when it oxidizes, is covered with a coating impermeable to water and air ; it is this grayish oxide which protects the common sheet zinc of commerce from farther change. When, therefore, a Voltaic pair gives rise to a current by the oxidation of its zinc, that current would speedily stop were not the oxide removed as fast as it forms ; this is done by the sulphuric acid, which forms with it a sul- phate of zinc, a substance very soluble in water, and the metal thus continually presents a clear surface to the water. As to the immediate cause which gives rise to the Vol- taic current, there has been a difference of opinion among chemical authors. Volta believed that the mere contact of the metals was the electromotive source, and endeav- ored to prove, by direct experiment, that if a piece of copper and zinc are brought in contact and then sepa- rated, they become excited, the one positively, and the other negatively ; upon these principles, he was led to the discovery of the Voltaic battery. But many facts have now indisputably shown that the origin of the current is to be sought in the chemical changes going on ; and in the instance we have had under consideration, it is due to the decomposition of water. That the electromotive action does not depend on the contact of the metals, seems to be proved by the fact that, by changing the nature of the liquid intervening between them, we can change the current both in direction and force. What other kinds of Voltaic circles are there ? What is the use of sulphuric acid in these combinations ? What was Volta's opinion as to the electromotive source ? What is the view now taken ? What argu- ments may be adduced for its correctness ? 120 THE VOLTAIC PILE. LECTURE XXIX. EFFECTS OF VOLTAIC ELECTRICITY. Invention of the Vol- taic Pile. Cruickskank's Trough. Hare's Battery. Smee's Simple and Compound Battery. Grove's Batte- ry.* Voltaic Effects, the Spark, Deflagration of Metals. Ignition of Wires. Arc of Flame. Decomposition of Water. Nature of the Gases evolved. IT has been already observed that, in the discussions which arose respecting animal electricity, Volta attributed the action entirely to the metals employed ; and reasoning on this principle, he concluded that the effect ought to in- crease, if, instead of using a single pair of metals, a great number of alternations were employed. Accordingly, on taking thirty or forty silver coins and discs of zinc, and pieces of cloth moistened with acidulated water, of the Fig. 102. same size, and arranging them in a pile or " column, carefully observing to place them in the same order, silver, cloth, . zinc silver, cloth, zinc, &c., he found his expectation ver- ified. On touching, with moistened hands, the ends of the pile, a shock was at once re- ceived, and on making them communicate by a piece of wire, an electric spark passed. This instru- ment, Fig. 102, is the Voltaic pile. From the important uses to which the pile was soon devoted, it became necessary to have it under a more con- venient form. There are several inconveniences attend- ing the original construction : it is liable to overset, is troublesome to put in action, and requires to be taken to pieces and carefully cleaned every time it is used ; its maximum effect lasts but a short time, owing to the weight of the superincumbent column pressing out the moisture from the lower pieces of cloth ; and as soon as they become dry, all action ceases. These difficulties were avoided, to a great extent, in the trough battery, which soon replaced the former instru- ment. It consists of a box, or trough, Fig. 103, three or How was Volta led to the invention of the pile ? Describe the Voltaic pile ? What are its effects ? What inconveniences are there in the original form ? CRUIKSHANKS, HARE*S, AND DANIELI/S BATTERIES. 121 Fig. 103. four inches square at the ends, and a foot or more long ; grooves are made in the sides and bottom of this box, and into them pieces of zinc and cop- ^ - per, soldered face to face, are fastened, water tight, by cement. These grooves are about half an inch apart, and into their interstices acidulated water is poured, care be- ing taken that the metals are arranged in the same direc- tion, so that if the series begins with a copper plate it ends with a zinc. The apparatus is obviously equivalent to Volta's pile laid on its side, and the facility for charg- ing it, and removing the acid when the experiments are over, is very great. From the extremities two flexible copper wires pass; they are called the polar wires, or elec- trodes of the battery. Some very convenient form-s of Voltaic battery have been invented by Dr. Hare. In one of these, the liquid is poured off and on the plates by a quarter revolution of a handle ; in others, the trough is made movable, so that it lifts up -when all the arrangements are ready, ami the plates are immersed. When it is required to have a current, the intensity of which remains constant for a length of time, Daniell's battery is to be preferred. It consists of a copper cylinder, C, Fig. 104, in which a solution of sulphate of copper is poured ; within this is a second cylinder, P, of porous earthen-ware, filled with dilute sul- phuric acid, A, into which an amalgamated zinc rod, Z, dips. From the copper and zinc, rods project, terminated by binding ^Sljews, with which the polar wires may be connected. Smee's battery is also a very valuable rom- bination; it consists of a plate of platinized silver, or platinized platinum, S, Fig. 10/5, on each side of which are placed parallel plates of amalgamated zinc, Z ; these plates are held tightly against a piece of wood, Describe the trough battery. Describe some of the improvements in the battery. What are the forms introduced by Hare, Duniell. Smee, and Grove respectively? L Fig. 104. 122 SMEE 3 AND GROVES BATTERIES. Fig. 105. w, by means of a clamp, b, to which, and also to the silver plate, binding screws, for the purpose of 'fastening polar wires, are affixed. The whole is suspended, by means of a cross piece of wood, in a jar containing dilute sulphuric acid. Smee's compound battery, represent- ed in Fig. 106, is nothing more than a series of the foregoing simple circles. The figure shows one containing six cells ; the position of the platinized sil- ver and zinc plates of one of the pairs is seen at S and Z. It is to be charged with dilute sulphuric acid. Fig. 106. Probably the most powerful of all Voltaic combina- Fig. 107. tions is the instrument invented by Mr. Grove. It consists of two metals and two liquids, amal- gamated zinc and platina, dilute sulphuric acid and strong nitric'acid. A jar, P, Fig. 107, three quarters of an inch in diameter, and made of porous or unglazed earthen-ware, is to be filled with strong nitric acid, N, and in it a slip of pla- tina is placed ; this porous earthen-ware cup is then set in a glass cup, A, nearly three inches in diameter; in this is placed a plate of zinc, Z, one eighth ^of an inch thick, and of such a size, as respects its other dimensions, that it will readily pass between the porous cup, P, and the glass. In the glass, A, is placed dilute sulphuric acid. In this manner several cups are to be provided, the ar- rangement being, zinc in contact with dilute sulphuric acid, and platina in contact with strong nitric acid, with a porous cup intervening between. The workman also DEFLAGRATION OF METALS. 123 previously connects each zinc cylinder with the slip OT platina, which is in the next cup, by soldering between them a strip of copper. Grove's battery owes its force to the decomposition of water by zinc. But the hydrogen is not evolved from the surface of the platina, as it would be in a single circle ; it is here taken up by the nitric acid, which undergoes rapid deoxidation, and therefore, during the use of this battery, volumes of deutoxide of nitrogen are evolved. A battery of fifty cups gives rise to very striking effects ; but five or ten are quite sufficient to repeat all the follow- ing experiments. On separating the polar wires of such a battery from each other, a brilliant spark passes, and, if the separation be gradual, a flame constantly proceeds from one to the other ; the light of which, when the wires are of copper, is of a beautiful green color. If, on the surface of some quicksilver Fig. 108. contained in a glass, Fig. 108, we low- er a thin piece of steel, or iron wire, connected with one of the poles of the battery, the mercury being kept in con- tact with the other, the steel takes fire and deflagrates beautifully, emitting bright sparks, arid the mercury is rap- idly volatilized. When thin metal leaves are made to intervene between the polar wires, they are at once dissipated, the flames they emit being of different colors in the case of different metals. If a piece of platinum wire is made the channel of communication from one pole to the other, if it does not fuse at once, it becomes incandescent, and remains so as long as the instrument is in activity. "When the polar wires are terminated by pieces of well- burned charcoal, or that variety of carbon which is formed in the interior of gas retorts, the light which passes between them when they are removed from contact is one of the What are the chemical effects taking- place in Grove's hattery ? On separating the polar wires of a battery, what phenomenon arises ? How may iron wire be deflagrated ? What phenomenon is seen during the deflagration of metallic leaves ? When a thin platinum wire communicates between the poles, what is the result ? How is the arc of light formed, and what are its properties ? 124 DECOMPOSITION OF WATER. most brilliant that can be obtained by any artificial means. With powerful batteries, the pieces of charcoal may be sep- Fig. 109. arated several inches apart without the ^^^^&S^^^ light ceasing, and then it moves from ^^^^B one to the other pole in an arched form, Fig. 109, the convexity of the arc being upward. This form is due to the current of hot air which rises from the ignited space between the poles, and the light may be blown out by the mouth, just in the same manner that we blow out a candle. But, in a scientific point of view, by far the most inter- esting experiment to be made with the Voltaic battery is Fig. no. the decomposition of water. Through the bottom of a glass vase, or dish, at the point a Z>, Fig. 110, two platinum wires are introduced, water-tight ; they pass into the vase, as a c, b d, parallel to each other, but not touching. Over each of these wires a tube is to be in- verted ; the tube e over c, andy over d, the vase and the tubes being previous- ly filled with water acidulated slightly, to improve its conducting power. Now let the wire a c be connected with the positive pole of the Voltaic battery, and& d with the negative ; bubbles of gas in a torrent arise from their extremities, and pass upward in the tubes, displacing the water. The quantity of gas thus collecting in th.e two tubes is unequal, and whenever we stop the decomposi- tion there will be found iny double the quantity which is in e. When a sufficient amount is collected, let the tube e t containing the smaller portion of gas, be cautiously re- moved, preventing any atmospheric air from getting into its interior, by closing it with the finger, and then, turning the tube upside down, let a stick of wood, with a spark of fire on its extremity, be immersed in the gas. In a moment the wood bursts into a flame, proving that this is oxygen gas. Then take the other tube, and allow to pass into it a quantity of atmospheric air equal to the volume of gas it already holds ; remove the finger and apply a light, and there is an explosion. But this is the property Describe the process for the decomposition of water. What is the rel- ative proportion of the gases collected? How can it be proved that the less quantity is oxygen and tbe larger hydrogen? POLAR DECOMPOSITION. 125 of hydrogen gas. We therefore conclude that in this ex- periment water has been decomposed and resolved into its constituent ingredients, oxygen and hydrogen; and, farther, that in water there is, by vol- Fig ume, twice as much hydrogen as there is oxygen gas. The separation of the two, is perfect, so much so that the de- composition may be conducted in differ- ent vessels. Thus, let N and P be tubes, through the closed upper ends of which platinum wires pass ; invert them in glasses of water, with a siphon of large bore connecting them. On making N communicate with the negative, and P with the positive pole, decomposition ensues, hydrogen gas accumulating in N, and oxygen in P. LECTURE XXX. THE ELECTRO-CHEMICAL THEORY. Theory of the Decom- position of Water. Decomposition of Metallic and other Salts. BecquereVs Illustration of the Formation of Min- erals. Davy's Discoveries. Electro-chemical Theory. 'Electrolytes. Faraday's Theory of definite Action. The Electrotype. THE prominent fact connected with the decomposition of water is the total separation of the constituent elements on the opposite polar wires or electrodes. From the positive wire oxygen alone escapes, and from the nega- tive hydrogen; there is ,no partial admixture, but the separation is perfect and complete. Though the polar wires may be separated from each other by a considerable distance, the same result is uni- formly obtained, and it is to be remarked that the evolu- tion of gas takes place on the wires alone ; no intervening bubbles make their appearance in the intermediate space. The principle on which this is effected may be easily under- What is the constitution of water by volume ? Do these polar decom- positions effect a total separation of the bodies ? In the decomposition of water, do any gas bubbles appear in the intervening space ? L 2 126 VOLTAIC DECOMPOSITIONS. stood, by supposing H H and O O, Fig. 112, to represent Fig. 112. atoms of hydrogen and oxygen respect- ively; each pair of them, therefore, rep- resents a particle of water. Now, if we slide the upper row of atoms upon the lower, as shown at h k, o o, it is obvious that a hydrogen atom will be set free at one extremity of the line, and an oxygen atom at the oth- er, and that, as respects all the intermediate pairs of atoms, though they have changed their places, yet every particle of hydrogen is still associated with a particle of oxygen, constituting, therefore, a particle of water ; and it is at the extremes of the line alone that the gases are set free. So in the polar decomposition by the pile, all the liquid in- tervening between the poles is affected, decompositions and recombinations successively taking place, the hydro- gen atoms moving in one direction, the oxygen in the other, finally to be set free on the surface of the polar wires. This capital discovery of the decomposition of water by Voltaic electricity was originally made by Nicholson and Carlyle. It is by far the most satisfactory method ot demonstrating the constitution of that liquid. After it was made known, any lingering doubts which still remain- ed on the minds of some chemists in relation to the com- posite nature of water were speedily removed. In the same manner that water is decomposed by the Voltaic battery, so, also, many metallic and other salts yield to its influence. Thus, if into ajar containing a solution of blue vitriol, the sulphate of copper, two metallic plates are introduced parallel to each other, and one of them brought in connection with the negative and the other with the positive pole of the battery, decomposition of the salt takes place ; the sulphate of copper being resolred into its constituents, sulphuric acid and the oxide of cop- per, and the latter reduced to the condition of metallic copper by hydrogen simultaneously evolved with it, arising from the decomposition of a part of the water. In this manner the copper may be deposited, with a little care, under the fdrm of a tough metallic mass. How is this explained ? How is it, if decompositions are going on in the intervening space, that the gases are not there seen 1 Can metallic salts be in like manner decomposed ? BECdUERELS EXPERIMENTS. 127 Fig. 114. If in a cubical glass vessel Fig. 113, divided into two par- titions by a diaphragm, a, Fig. 113. and both partitions filled with a solution of iodide of potassium, mixed with a solution of starch, and the positive and negative wires of the battery intro- duced, decomposition of the iodide takes place, its iodine being evolved at the positive wire, and giving with the starch a deep blue color, the blue iodide of starch, while the liquid in the other partition remains colorless. M. Becquerel obtained some very beautiful results by the aid of weak but long-continued electric currents, illus- trating the probable mode of formation of mineral sub- stances by such currents traversing the crust of the earth. If we take a glass tube bent into the form of a U, and close the bended part with a plug of plaster of Paris, putting in one of the branches a solution of carbonate of soda, and in the other of sulphate of cop- per, immersing in one of the solutions a zinc plate, and in the other a copper, connected together by a piece of bent wire, the liquids communicate through the porous plug, and crystals of the dou- ble carbonate of copper and soda form on the plate im mersed in the copper liquid. In the same Fig. 115. manner, other compound salts and mineral bodies may be produced. Or if we take ajar, A, and fill it with a so- lution of nitrate of copper to a, and then with dilute nitric acid to B, and immerse in it a slip of copper, C D, presenting equal surfaces to the two liquids, an electric current is genera- ted, the copper is dissolved in the upper solu- tion, and is deposited in crystals at D in the lower. As in this manner water and various saline bodies un- Describe the polar decomposition of iodide of potassium. Can decom- positions be produced by very feeble Voltaic currents ? Describe some of the arrangements of M. Becquerel for illustrating the probable mode of formation of minerals. 128 ELECTRO-CHEMICAL THEORY. dergo decomposition by the action of the pile, it occurred to Sir H. Davy that probably other substances, at that time supposed to be simple, might also be decomposed. He accordingly subjected the alkaline and earthy bodies, then reputed to be elementary, to the influence of a powerful battery, and found that his supposition was verified. On placing a fragment of caustic potash between the poles, it immediately melted ; from the positive oxygen gas es- caped in bubbles, and from the negative, small metallic globules, having the appearance of quicksilver, emerged ; these were characterized, however, by the singular qual- ities of an intense affinity for oxygen, so that they would take fire on being touched by water, or even ice, and were so light as to swim upon the surface of that liquid. The result of Davy's experiments proved that the al- kaline substances and all the earths are oxidized bodies, and in most instances oxides of metals. On these principles, Davy established a division of ele- mentary bodies into electro-positive and electro- negative substances. The former are those which, during a polar decomposition, go to the negative pole, and the latter those that go to the positive. The electro-chemical theory as- sumes that all bodies have a natural appetency for the as- sumption of the positive or negative states respectively, and that all the phenomena of chemical combination are mere- ly cases of the operation of the common law of electrical attraction ; for between particles in opposite states at- traction ought to take place, and when in a compound body, such as water, which consists of particles of nega- tive oxygen and positive hydrogen, the poles of an active Voltaic battery are immersed, they will effect its decom- position, the negative oxygen going to the positive pole and the positive hydrogen to the negative pole. Davy's theory thus not only accounts for the decom- posing agencies of the battery, but also for all common cases of chemical combination, referring both to the fun- damental law of electric attraction. With all its simplic- ity, it would be very easy to show, however, that it is founded on a groundless assumption, and can not account for a great number of well-known facts. What were the discoveries of Davy respecting the alkaline and earthy bodies ? What is meant by the electro-chemical theory ? Does this the- ory also account for chemical combination ? THE ELECTROTYPE. 129 The Voltaic pile can not decompose all bodies indis* criminately. An electrolyte for so a decomposable sub- stance is termed must always be a fluid body. It also appears that all electrolytes must have a binary constitu- tion, or contain one atom of each of their two constituent ingredients. Mr. Faraday discovered that the action of an electric current in effecting the decomposition of various bodies is perfectly definite : thus, if we make the same current pass through a series of vessels containing water, iodide of potassium, melted chloride of lead, they will all be de- composed, but in very different quantities. If of the wa- ter there be decomposed 9 parts, there will be 165 of iodide of potassium, and 139 of chloride of lead ; but these numbers represent what will be hereafter given as the atomic weights of the bodies in question. A current which can set free one grain of hydrogen will evolve 108 of silver, 104 of lead, 39 of potassium, 31*6 of copper, &c., these being the atomic weights of those substances respect- ively. A very beautiful application of electro-chemical decom- position has, of late, been introduced into the arts. It passes under the name of the electrotype. It consists in the precipitation of metallic copper, gold, silver, platina, &c., on different surfaces, by the aid of a Voltaic current. Thus, suppose it were required to obtain a perfect copy in copper of one of the faces of Fig. lie. a medal ; let a glass trough, N C, Fig. 116, be filled with a solution of the sulphate of copper, and to the negative wire, Z, of a Smee's Voltaic battery, let the medal N be at- tached, all those portions, ex- cept the face designed to be copied, being varnished over, or covered with wax, to pro- tect them from contact with the liquid. To the positive wire, S, let there be attached a mass of copper, C. As soon as the battery is in action, decomposition of the sul- To what bodies is the decomposing influence of the Voltaic battery lim- ited ? Can substances other than binary compounds be thus decomposed ? Explain Faraday's law of the definite action of a Voltaic current. De. scribe the electrotype. 130 THE VOLTAMETER. phate takes place, metallic copper is precipitated on the face of the medal, copying it with surprising accuracy. This copper is, of course, withdrawn from the sulphate in the solution ; but while this is going on, sulphuric acid and oxygen are being evolved on the mass of copper, C. They therefore unite with it ; and thus, as fast as copper is precipitated on N by oxydation, new quantities are ob- tained from C, and the liquid keeps up its strength unim- paired. In the course of a day the medal may be re- moved. It will be found incrusted with a tough, red coat of copper, which may be readily split off from it. It is a perfect copy of the surface on which the deposition took place, and, in turn, it may be used as a mould for obtaining a great number of casts. Gilding, silver- plating, and platinizing are now performed on the same principles, the electrotype being one of the most beauti- ful contributions which science has of late given to the arts. An instrument, the Voltameter, has been invented by Mr. Faraday for measuring quantities of Voltaic electricity. It is represented in Fig. 117. It consists of a glass jar, b, filled to the height d with water, and through its cover, c, a graduated tube, a, passes. In the lower part of the tube at g, two pieces of platina foil, which form the terminations of the polar wires of the battery, the current of which is to be measured, are introduced, the connection with those wirea being made by the aid of the mercury cups, ef. The tube, , having been filled with water, as soon as the cur- rent passes decomposition takes place, the gases' collecting in the graduated tube, and measuring the amount of the current. Fig. 117. Describe the Voltameter. DIFFERENT VOLTAIC BATTERIES. 131 LECTURE XXXI. OHM'S THEORY OF THE VOLTAIC PILE. MAGNETISM AND ELECTRO-MAGNETISM.^ Yalta's Pile. Hare's Calorimo- tor. Zamboni's Pile. Ohm's Theory. Electro-motive Force. Resistance. General Law for the Force of the Current. Laws and Phenomena of Magnetism. Elec- tro-magnetism, Oersteds Discoveries in. The Galvan- ometer. Electric Rotations. Tangential Force. Elec- tro-magnets. WITH a given amount of metallic surface we can pro- duce Voltaic batteries having different qualities. Thus, if we take a square foot of copper and a square foot of zinc, and place between them a piece of wet cloth, we shall have a battery which can not give shocks, nor effect the decomposition of water, but which will cause a fine metallic wire to become white hot, or even to fuse. If, again, we take a square foot of copper and a square foot of zinc, and cut each into 144 plates, an inch square, and arrange them with similar pieces of cloth as a Voltaic pile, the instrument will give shocks, and decompose wa- ter rapidly. From the same quantity of metal two differ- ent species of battery may be made ; one consisting of a few plates of large surface, or one of a great number of alternations of smaller plates. Of these varieties of battery, the calorimotor of Dr. Hare is an example of the first. It consists of a series of zinc plates, all connected together, and one of copper, also similarly connected, constituting therefore, in reality, a single pair of very large surface. The great amount of heat evolved by this apparatus is its peculiarity. The electric pile of Zamboni is an example of the other kind. It consists of a series of ten or twenty thousand discs of gilt paper, alternating with similar pieces of very thin zinc foil. These are arranged in a tube, and kept in contact by the pressure of screws at each end. In Fig. 118 (p. 132), the pile is laid on a pair of gold What are the two principal forms of battery ? What do the oalorimo- tor and Zamboni's pile illustrate ? What is the effect produced by a bat tery of large plates ? What by one of many alternations ? 132 OHM'S THEORY Of VOLTAIC CURRENTS. Fig us. leaf electroscopes, both of -which diverge, the one being positive and the other negative, the cen- tral parts of the pile being neutral. This instrument exhibits no calorific ef- fects; its phenomena are those of electricity of high tension. These, and, indeed, " - =-=*' ..--3gf=- * m any of the phenomena of the electric current, are clearly accounted for by the aid of Ohm's theory of the Voltaic pile, of which the fol- lowing is an exposition : 1st. By ELECTRO-MOTIVE FORCE we understand the causes which give rise tp the electric current; this, as we have explained in the simple circle, is the oxidation of the zinc. 2d. By RESISTANCE we mean the obstacles which the current has to encounter in the bodies through which it passes. When we affect the electric current in any portion of its path, either by varying the electro-motive force, or changing the resistances, we simultaneously affect it throughout the whole circuit; so that, in a given space of time, the same quantity of electricity passes through each transverse section of the circuit. In any Voltaic circle, simple or compound, the force ot the current is directly proportional to the sum of all the electro-motive forces which are in activity, and inversely proportional to the sum of all the resistances ; that is to say, the force of any Voltaic current is equal to the sum of all the electro-motive forces, divided by the sum of all the resistances. The resistance to conduction of a metal wire is directly as its length, and inversely as its section ; that is to say, the longer the wire is, the greater its resistance, and the thicker it is, the .ess its resistance. If we augment or diminish, in the same proportion, the What is meant by electro-motive force ? In a simple circle, what is its origin? What is meant by resistance ? On affecting one part of a cur- rent, is the rest affected? What conclusion is drawn from that fact? What is the fprce of the current equal to ? In a wire, what is the law of resistance ? 133 electro-motive forces and the resistances of a Voltaic cir- cuit, the force of the current will remain the same ; if -we increase the electro-motive force, the force of the current increases ; if we increase the resistance, the force of the current diminishes. If, in two Voltaic circles of equal force, the same re- sistance is introduced, the forces of the currents may be enfeebled in very different proportions ; for the newly-in- troduced resistance may, in one of the circles, bear a very great proportion to the resistances already existing, and, in the other, a very insignificant proportion. The following, therefore, is the general law which de- termines the force of a Voltaic circuit. 1st. The electro-motive force varies with the number of the elements, the nature of the metals, and of the liquids which constitute each element; but it does not in any manner depend on the dimensions of their parts. 2d. The resistance of each element of a Voltaic circuit is directly proportional to the distance between the plates, as occupied by the liquid, the resistance of the liquid it- self, and the length of the polar wire connecting the ends of the circuit ; and inversely proportional to the surface of the plates in contact with the liquid, and to the section of the connecting wire. 3d. The force of the current is equal to the electro- motive force divided by the resistance. From the circumstance that lightning has been repeat- edly known to render implements of steel magnetic, and from a general analogy which exists between the phenom- ena of magnetism and those of electricity, it was long ago believed that these phenomena were due to one common cause; but it was not until 1819 that their true relation- ship was first established by CErsted. The phenomena of the magnet itself were discovered more than 2000 years ago. The natural magnet, or load- stone, which is an iron ore, possesses the quality of at- tracting pieces of iron or steel, but upon almost all other substances it is without action. To hardened steel it com* How does the force of the current change with changes in the electro- motive force and the resistance ? When a new resistance is introduced into two circles, does it follow that both will be affected alike ? Give the general law which determines the force of the Voltaic current. What are the properties of a magnet 1 What is the difference of its action on iron and steel ? M 134 MAGNETISM. municates its own properties in a permanent manner; but soft iron is only transiently magnetic, and as soon as it i removed from the influence of the magnet it loses its power. Bars of steel-which have been magnetized can communicate their activity to other bars ; they are, there- fore, of constant use in physical investigations, and are of two forms, straight bars and horseshoe magnets. Fig, n9. If a magnetic bar have iron ities, d d, few orthem being found in the middle. If a piece Fig. 120. of card-board is laid over a magnet, and K-V the filings dusted on it, they arrange them- selves in curves, call- ed magnetic curves ; there being in this, as in the former in- stance, centers of ac- tion, P P, toward the extremities of the bars, around which the curves are arranged. The ap- pear*nce is show in Fig. 120. A light magnetic bar, S N so arranged that it can be pois- Fig.^i. ed on a pivot, C, with free- dom of motion, is a magnetic -U needle. It was discovered by the Chinese that such a needle, Fig. 121, possesses polarity, or points north and south, a fact of the utmost importance in navigation. When to a needle the poles of a bar are approached, it exhibits attractive and repuls- ive movements. The law under which these take place is, " Like poles repel, and unlike ones attract;" two north or two south poles repel, but a north and a south attract. What are the forms of artificial magnets ? How may the existence of poles be shown bv iron filings ? Describe a magnetic needle. What is meant by its polarity? What is the law of magnetic attractions and re- pulsions ? ELECTRO-MAGNETISM. 135 Either pole of a magnet is attracted by a piece of unmag- netized soft iron. The intensity of magnetic action is in- versely proportional to the square of the distances. If a magnetic needle be brought into the neighborhood of a wire, along which an electric current is passing, the needle is at once disturbed from its position, and tends to set itself at right angles to the wire. The direction in which the transverse movement takes place depends on the relative position of thevneedle and the wire ; thus, 1st, if the wire be above the needle and parallel to it, that pole next the negative end of the battery moves west- ward ; 2d, if the wire be beneath the needle, it will move eastward ; 3d, if the wire be on the east side of the needle, the pole is elevated ; 4th, if on the west, it is depressed ; in all these various positions, the tendency being to bring the needle at right angles, or transverse to the wire. It follows, from these facts, that if a magnet- ic needle be placed in the interior of a rectan- gle of wire, Fig. 122, through which a cur- rent is made to flow, all the portions of the wire conspire to move the needle in the same direction. The effect, therefore, becomes much greater than in the case of a single con- tinuous wire. On the same principle, if, instead of a single turn, the Fig. 122. Fig. 123. wire is repeatedly coiled upon it- self, so as to make a great many turns, the effect upon the needle may be greatly increased; and when the needle is made nearly astatic, that is to say, its tendency to point north nearly destroyed by arranging it upon an axis with another needle, similar to it in all respects, but with its poles reversed, as N S, S N, Figure 123, the directive tendency of the one needle neutralizing How does the intensity of magnetic action vary ? In what does CEr- Bted's discovery consist ? What is the direction which the needle moves in the four positions round the wire ? What is the effect on a needle in the interior of a rectangle ? What is the principle of the galvanometer ? 136 ELECTRO-MAGNETIC ROTATION. the other, but both tending to turn in the same direction by the current in the coil of wire, inasmuch as one is with- in the coil and the other above it, the arrangement forms a most delicate means of discovering and measuring an electric current. It is called a galvanometer. As action and reaction are always equal and contrary, it is obvious that, if a conducting wire be movable and the magnet stationary, the latter can be made to impress motions on the former. Conducting wires can be made to revolve round the r. 124. poles of a magnet, or the pole of a mag- net round a conducting wire ; thus, in a glass cup, Fig. 124, let a magnet, , be fixed vertically, and the cup filled with mercury ; by means of a loop, , let a conducting wire, , be suspended, having perfect freedom of motion. If an electric current is made to pass down this wire through the mercury, and escape by the path d, the wire rotates round the pole n as long as the current passes. From this and similar experiments, it therefore ap- pears that the force exerted between a conducting wire and a magnet is not a direct attractive or repulsive power, but one continually tending to turn the movable body round the stationary one, deflecting it continually, and acting in a tangential direction. Hence it is sometimes spoken of as a tangential force. If round a bar of soft iron a conducting wire, covered over with silk, be spirally twisted, as in Fig. 125, whenever an electric current is passed, the iron becomes intensely magnetic, and loses its magnetism as oon as the current stops. A bar an inch in diameter, bent so as to represent a horseshoe, Fig. 126, with a wire cov- ered with silk for the purpose of sepa- rating its successive strands from each Fig. 125 On the same principles, can the wire be made to move ? Describe a method of showing the rotation of a wire round the pole of a magnet. What is the nature of the force exerted between a conducting wire and a magnet ? Describe the construction and properties of a straight electro- magnet. ELECTRO-MAGNETS. 137 other, may be made to give rise to very striking results. Prof. Henry, by a modi- fication of the conducting wire, succeeded in imparting so intense a degree of mag- netism to a piece of soft iron that it could support more than a ton weight. If under one of these ELECTRO-MAGNETS a dishful of small iron nails be held, the moment the current passes, the nails are all attracted, and, while they are held by its poles, may be moulded, as it were, by the hand in various shapes, but as soon as the current stops they fall off. It is upon this principle of producing temporary magnetism by an electric cur- rent that Morse's electric telegraph depends. Fig. 126 LECTURE XXXII. ELECTRO-tftNAMICS THERMO-ELECTRICITY, &C. Am- pere's Discovery. Properties of a Helix. Nature of the Magnet. Faraday's Discovery of Magnetic Electricity. Magnetic Machines. Faradian Currents. Thermo- electricity. Production of Heat and Cold by Electric Currents. Thermo-electric Pairs. Peculiarity of these Currents. Electro-motive Power of Heat. Melloni's Pile and Thermometer. Improvements in Thermo-elec- tric Pairs. Animal Electricity. Steam Electricity. SOON after the relation between electricity and magnet- ism was established, M. Ampere discovered that there are reactions between electric currents themselves. Two electric currents flowing in the same direction at- tract each other, but two electric currents flowing in op- posite directions repel ; or, more briefly, " Like currents attract, and unlike ones repel." If a conducting wire be bent in the form of a helix, its terminations returning toward its middle, as shown in Fig. 127, it exhibits all the properties of an ordinary mag- netized bar ; for as soon as the current passes, it points Describe the Lorseshoe electro-magnet, between electric currents ? M2 What is the law of reaction 138 PROPERTIES OF A HELIX. Fig. 127. north and south, and is attracted and re- pelled by the poles of a magnet, just as though it were a magnet itself. A very neat arrangement for illustrating these results is seen in Fig. 128. A small sim- ple circle, consisting of a zinc and copper plate, connect- Fig . jgs. ed together by means of a wire bent so as to form a flat coil, is floated by means of a cork in acidulated water. The current runs round the coil in the direction of the aiTows, and the arrangement, obeying the magnetic influence of the earth, turns, with its plane pointing north and south, just as a magnet would do if introduced into the interior of the coil, in the position shown in the figure by the dark line. Ampere infers, from the analogy of these instruments, that the magnet owes its qualities to electric currents cir- culating in it in a transverse direction. The directive action of the magnetic needle or the electric helix depends on the reaction of electric currents circulating in the earth, due to the unequal heating of its surface by the rays of the sun. We have seen that an electric current can develop magnetism in a bar of iron or steel ; in the former, tran- sient, in the latter, perma- nent magnetism. Thus, if the iron bar, n s, Fig. 129, \n be placed in the axis of a helix of copper wire, along which a current is flowing, the current develops magnetism in the bar. It was dis- covered by Faraday that the converse also holds good, and that a magnet can give rise to an electric current. Thus, in Fig, 129, let the terminations a b of the helix c Describe the phenomena of the electro-dynamic helix, Fig. 127. De- scribe those of the flat coil. "What is Ampere's theory of the nature of the magnet ? Can a magnetized bar be made to develop electric currents ? Fig. 129. MAGNETO-ELECTRIC CURRENTS. 139 be brought in contact, and having placed a soft iron bar, n s, within it, let the bar be made magnetic by the ap- proach of a strong magnet. As n s assumes the magnetic condition, it generates a current, which runs through the helix c; and if at this moment the wires a b are drawn apart, a bright spark, sometimes called the magnetic spark, passes. It does not come, however, from the mag- net itself, but is due to the electric current established in the helix by the disturbing action of the magnet. If be- tween the terminations a b a slender wire is placed, it may be made red hot, or water may be decomposed, or any of the phenomena of a Voltaic battery may-be exhib- : ted by the aid of this magneto-electric current. On this principle are constructed the magneto-electric machines, of which different forms have of late been so generally introduced for the purpose of the medicinal application of electricity. They all depend essentially on the principle, that if we coil round a piece of soft iron a conducting wire, as often as the iron is magnetized, a wave of elec- tricity flows through the wire. If two conducting wires be placed parallel and near to each other, when an electric current is passed through one of them a wave of electricity flows in the opposite di- rection through the other ; and on the first current stop- ping, another wave, coinciding with it, passes through the second wire. These momentary currents are all called, from the name of their discoverer, Faradian currents. If we take a bar of antimony, it unites with great energy with the oxygen of the included air, producing white flakes, which, as the combustion is ceasing, descend in the jar, giving a min- iature representation of a fall of snow. On collecting some of this phosphoric snow, its properties will be found to be in striking contrast with the phosphorus which produced it ; for instance, far from being unacted on by water, it has such an intense affinity for that substance, that it hisses like a red-hot iron when brought in contact with it. It reddens litmus solution, and possesses the quali- ties of a powerful acid. Nor is the change confined to the phosphorus ; if we examine the air in which it was burned, we find it has lost its quality of supporting com- bustion. Changes of volume, and, consequently, changes of dens- ity, constantly attend chemical action ; a pint of water and a pint of sulphuric acid, mixed together, form less than two pints ; and the same may be observed of alcohol and water. When to two substances already in union, a third, hav- ing a stronger affinity for one of the other two, is present- ed, decomposition ensues- Thus, if to the carbonate cf soda nitric acid be presented, the soda and nitric acid com- bine, and the carbonic acid is driven off in the form of a What are the changes which phosphorus undergoes when burned in the air? Give an example of change of volume and of density Under what circumstances does decomposition take place 1 MEASURE OF CHEMICAL AFFINITY. 167 gas. And, again, if upon the nitrate of soda so produced sulphuric acid is poured, the nitric acid is driven off, and sulphate of soda results. It was at one time thought that, by examining a number of such cases, we might discover the order of affinity of bodies for one another and arrange them in tables ; these are sometimes called the Tables of Geoffroy. Thus, the table Soda. Sulphuric acid, Nitric *'.' Muriatic " Acetic " Carbonic " presents us with the order in which a number of acids stand in relation to soda, the most powerful being the first on the list, and the salt which results from the union of any one of those acids with the soda can be decomposed by the use of any other acid standing higher on the list. . But it is now known that these tables are far from rep- resenting the order of affinities ; a weaker affinity often overcomes a stronger by reason of the intervention of disturbing extraneous causes ; and tables so constructed lead, therefore, to contradictory conclusions. Some very simple considerations may illustrate this. Potassium can take oxygen from carbon at low temperatures, or, in other words, decompose carbonic acid gas, but it by no means follows that the affinity of potassium for oxygen is great- er than that of carbon, and accordingly we find that at higher temperatures carbon can take oxygen from potas- sium. Indeed, under the influence of heat, light, and electricity, we find all kinds of chemical changes going on, and in the same manner the condition of form exerts a remarkable influence in these respects, so that cohesion and elasticity may be placed among the predisposing caus- es producing chemical results. If a number of bodies 6xist in a solution together, they will at once arrange themselves hi such a way under the influence of cohesion as to produce insoluble precipitates, if that be possible ; or, under the influence of elasticity, to determine the evo- What are the tables of Geoffrey ? How may it be shown that these are not tables of affinity ? What may be enumerated among these dis- turbing causes ? What is the influence of cohesion ? What is the influ- ence of elasticity ? Give examples of the action of the?-Q disturbing agents 168 TABLES OF GEOFFROY. lution of a gas ; if the carbonate of soda is decomposed by acetic acid, it by no means follows that the latter has the stronger affinity for soda, the decomposition being probably determined by the fact that the carbonic acid can take on the elastic form and escape away as a gas. The sulphate of soda may be decomposed by baryta, the cause of the decomposition being probably due to cohe- sion, for the sulphate of baryta which results is a very in- Boluble body. We have, therefore, no true measure of affinity, for the relation of bodies in this respect changes with external conditions, and the tables of Geoffroy are only tables of the order of decompositions, but not of the order of affinity. What do the tables of Geoffroy, in reality, express ? PART III, INORGANIC CHEMISTRY, LECTURE XXXVIII. PNEUMATIC CHEMISTRY. Ancient Opinions on the Con- stitution of the Gases. Doctrine of the Unity of Air. OXYGEN GAS. Modes of Preparation. Properties. Ori- gin of its Name. Relations to Atmospheric Air and Combustion.- Burning of Metals. IN the catalogue of the elementary bodies of the an- cients four substances were included, earth, air, fire, and water. The progress of knowledge has shown that three out of the four are compound bodies. For a length of time it was supposed that the various exhalations and vapors were nothing more than vitiated forms of atmospheric air ; and though from time to time first one and then another of the gaseous bodies was dis- covered, chemists were slow to admit that they were any thing more than modifications of one common principle. Thus, Roger Bacon, in the thirteenth century, discovered one of the carburets of hydrogen, and Van Helmont, in the sixteenth, carbonic acid. The invisibility of these bodies, their remarkable chemical relations in extinguish- ing flame and producing death, the great mechanical force to which they often gave rise when generated in pent-up vessels, their occurrence in mines, the bottom of wells, in church-yards, and lonely places, suggested to a supersti- tious mind a supernatural origin, and Van Helmont gave them the name of gas, corrupted from gahst (or geist), which signifies a ghost or spirit. But it is to the researches on the properties of fixed air, which Black made about 1750, that pneumatic chemistry owes its origin. These were soon followed by the dis- coveries of Priestley, Scheele, and others. That of oxygen "What opinions were formerly held respecting the different gases ? What was the original signification of the terra gas ? By whom was tho doctrine of the plurality of airs established ? P 170 PREPARATION OF OXYGEN. gas, by the former of these philosophers, in 1784, forever destroyed the ancient notion of vitiated airs ; for this gas can support combustion arid respiration far better than the atmosphere. It may be said with justice that modern chemistry dates its origin from the discovery of oxygen gas. OXYGEN. O = 8-013. Oxygen gas is probably the most abundant of the ele- ments. It constitutes about one third of the weight of the solid mass of the earth, eight ninths of that of the waters of the sea, and one fifth the volume of the air. A simple mode of preparing oxygen is to place in a re tort, a, Fig. 148, some red oxide of mercury, connecting with the retort a receiver, b, from which there passes a bent tube, c, which dips beneath the water of a pneumatic trough, g. On raising the temperature of the oxide by the flame of a spirit lamp, it is resolved into metallic mer- cury and oxygen gas ; the former distills into the receiver b, and the latter collects in the inverted jar of the trough. Another process is to place the peroxide of manganese (Mn. O 2 ) in an iron bottle, from which a tube, b, Fig. 149, projects; this tube may be connected with another, f, by means of a cork and an India-rubber tube, e. The bot- tle is to be arranged in a small furnace, and made red hot; the manganese loses one third of its oxygen, which may be collected in a gas-holder, as shown in the figure. The most convenient mode of preparing it is to place in a flask, a, Fig. 150, a mixture of chlorate of potash and peroxide of manganese ; to the mouth of the flask a tube, ft, is adapted by means of a tight cork, the lower end of the In what bodies does oxygen occur ? Describe its preparation from red oxide of mercury, from peroxide of manganese, and from chlorate of potash. PREPARATION OP OXYGEN. 171 Fig. 149. tube dipping beneath a jar upon Fig.iso. the pneumatic trough, c. On rais- ing the temperature of the flask by a spirit lamp, oxygen gas is freely evolved. The peroxide of manga- nese takes no part in the change, out it causes the decomposition to go on at a low temperature, and the gas is more rapidly set free. The change, being confined to the chlorate of potash, is therefore expressed as follows : that is, the chlorate of potash, at the temperature in ques- tion, has its atoms disarranged, resolving itself into ona atom of chloride of potassium and six atoms of oxygen gas. It may also be prepared by exposing a mixture of bi chromate of potash and sulphuric acid, or peroxide of manganese and sulphuric acid, to heat. Oxygen gas is a colorless body, having no odor no\ taste. It is a non-conductor of electricity, and a bad re fractor of light. It is a powerfully electro-negative ele- ment. In specific gravity it is heavier than atmospheric air; for the air being 1*000, oxygen is 1*1026, or, accord- ing to some chemists, I'll 11. One hundred cubic inches weigh about 34 grains. Its atomic weight, is 8*013, hy- What are its leading physical properties ? What is its specific gravity ? 172 PROPERTIES OF O drogen being taken as I'OOO. It has never been con- densed into the liquid state. To a certain extent it is soluble in water, one hundred volumes of that liquid dissolving about four of the gas, a fact of considerable importance in physiology, as it is upon the oxygen so found in water that aquatic animals depend for their respiratory process. On litmus water, or any blue vegetable solution, oxy- Fig. 151. gen exerts no action, as is easily shown by agita- ting it with such a solution in Hope's eudiometer (Fig. 151) ; but though it is not acid itself, when it unites with a great variety of bodies it gives rise to powerful acids, and from this circumstance its name was derived. Oxygen, o%v$, acid, and yevveLv, to generate. The most important qualities of atmospheric air are due to the presence of oxygen gas. It is for this reas- on that the air supports combustion and respiration. The powers of oxygen, in this respect, may be illustrated by many striking experiments ; thus, if into a jar filled with Fig. 152. it, a stick of wood, with a spark of fire on its ex- tremity, be immersed, it bursts out at once into a flame, burning brilliantly. On immersing a lighted taper in a jar of oxygen (Fig. 152), the light becomes of a dazzling white- ness, the taper wasting rapidly away ; but it is to be observed that after a time the combustion de- clines, and finally the light is extinguished. If a piece of charcoal of bark in an ignited state be placed in a bottle of oxygen, the combustion goes on with great activity, a multitude of sparks being thrown off. When the char- coal is extinguished, if a little lime-water be poured into the bottle and agitated in it, the lime-water at once becomes of a milky white- ness ; for the carbon, during the combustion, uniting with the oxygen, produces carbonic acid gas, and this forms with lime a white insoluble precipitate, the carbonate of lime. Can it be liquefied ? Is it soluble in water ? From what circumstance is its name derived ? What are its relations in the ordinary processes of combustion ? Describe its effect on a liehted taper, and on isrnited char- coal . COMBUSTION IN OXYGEN. 173 A piece of India-rubber set on fire, and immersed in oxygen gas, burns with the emission of a daz- Fig. 154. zling light. And if, upon a small stand, some burning sulphur is placed, and a jar of oxygen inverted over it, as shown in Fig. 154, the light which is emitted is of a splendid blue color, and the smoke ascending up the middle of the jar, and falling in curious rings down its sides, affords an illustration of the manner in which currents are excited in gases. But it is not alone such substances as wood, char- coal, or sulphur which will burn in oxygen gas ; Fig. 155. many bodies commonly regarded as incombustible give rise to the same result. If a piece of steel wire be rolled round into a spiral, and the ex- tremity of it be dipped in melted sulphur, or wrapped round with cotton, so as to afford the means of introducing it in an ignited condition Fig. 156. into oxygen gas, the combustion is at once commu- nicated to the steel, which burns in a very brilliant man- ner, emitting scintillations. A stream of oxygen from a gas-holder, being thrown upoiv an iron nail made red hot in the flame of a spirit lamp, or placed in an ignited cavity in a piece of charcoal, causes the iron to burn with rapidity, emitting a shower of sparks. What is its effect on ignited sulphur ? What is its effect on an ignited metal, as iron or steel ? P2 174 COMBUSTION IN OXYGEN. LECTURE XXXIX. OXYGEN CONTINUED. Drummond's Light. Combustion of Phosphorus. Double Change arising in Combustion. The Lavoisierian Doctrine. Basic, Indifferent, and Acid Oxides. Physiological Relations of Oxygen. Supporters of Combustion. Nature of Flame. Con- stancy of Heat evolved. Vegetable Origin of Oxygen in the Air. IF a piece of lime the size of a peppercorn be placed in the flame of a spirit lamp, through which oxygen gas is directed by a blowpipe, the lime phosphoresces pow- erfully, emitting a light so bright that the eye can scarcely bear it. This is the original form of what is called Drum- mond's light. The light, however, is still brighter when the oxyhydrogen blowpipe is employed. Fie-. 157. '^^ e combustion of phosphorus in oxy- gen gas constitutes one of the most brill- iant experiments. A piece of lighted phos- phorus immersed in an atmosphere of this gas, burns with the evolution of a prodig- ious amount of light and heat, Fig. 157. Notwithstanding the production of dense flakes of phosphoric acid intervening be- tween the eye and the burning mass, the light is very brilliant. When any combustible substance is burned in oxygen gas, two striking phenomena are exhibited : a change in the combustible, and a change Ifethe oxygen. A fragment of ignited charcoal rapidly wastes away, and the surround- ing gas loses its power of supporting combustion. Until the time of Lavoisier, it was generally supposed that burn- ing was due to the escape of a certain principle, called phlogiston, from bodies, but he showed that in all these cases there is no loss of weight, and that, in reality, the What is the original form of the Drummond light ? What are the phe- nomena of the combustion of phosphorus in oxygen ? In these combus- tions, what changes take place in the oxygen and in the burning body ? THE OXIDES. 175 combustion is due to the oxygen uniting with the burning body ; and if care be taken to collect all the products of the action, their united weight will be exactly that of the oxygen and combustible conjointly. Lavoisier was dis- posed to believe, that in all cases of true burning the pres- ence of oxygen is indispensable, an idea now known to be erroneous ; for light and heat are evolved in all cases where chemical action is going on with great intensity, no matter what may be the substances which happen to be present. In the Lavoisierian system of chemistry, oxygen was regarded as being the essential supporter of combustion ; and as, in many instances, it gives rise to the production of acids, it was also regarded as the essential principle of acidity ; and from this circumstance its name was derived, as has been already said. But so far from every acid containing oxygen gas, it is now well known that there are many from which this principle is wholly absent. If any substance in particular deserves the name of " the acid former," it is hydrogen, for it is doubtful whether any powerful acid exists which does not contain hydro- gen. Basic substances, on the contrary, are characterized by containing oxygen. To the compounds which arise from the unien of oxy- gen with other bodies the generic designation of oxides is given ; and of them we have three classes. 1st. Basic oxides. 2d. Indifferent oxides. 3d. Acids. If M repre- sents an electro-positive body, the basic oxides are con- stituted as follows : MO . . . Protoxide, usually the most powerful base. M z 03 . . Sesquioxide, a weaker base. MO, . . Deutoxide, a still weaker base. M 2 . . . Suboxide, The oxides of manganese furnish a good example of the three classes : Protoxide of manganese Sesquioxide Deutoxide . Manganic acid . Hypermanganic acid . What was Lavoisier's theory of combustion? What is the relation of oxygen to acid and basic bodies ? What is the generic designation for its compounds ? What are the three classes of compounds which it yields ? In the basic, the indifferent, and the acid group, what is the general rela- tion of the ox vaen ? MnO t Indifferent oxide. 176 PHYSIOLOGICAL RELATIONS OF OXYGEN. From which it may be inferred that, in a family of ox- ides of an electro-positive body, the most powerful base i that containing one atom of oxygen, and that, as the quaa- tity of this element increases, indifferent bodies may be formed ; that is to say, those in which neither the basic nor acid qualities are well marked, and on a still farther increase acids are produced. In this respect, therefore, the original idea of Lavoisier respecting the character of oxygen is to some extent substantiated. In its physiological relations oxygen is a most interest- ing body. It is for the purpose of introducing this ele- ment to the interior of the system that the respiratory mechanism of animals is devoted a mechanism which differs according to their mode of life, the gills of a fish and the lungs of a man having the same ulterior object. If two jars are taken, one full of atmospheric air, and one of oxygen gas, and small animals placed beneath each, it will be found that in the latter those animals survive much longer than in the former. The gas introduced into the system arterializes the blood, and, eventually unit- ing with carbon and hydrogen, keeps up the temperature to a standard point, which, in the human mechanism, is about 98 F. Oxygen gas, therefore, is emphatically the supporter pf respiration. The terms, supporter of combustion and combustible body, formerly much used by chemical writers, are ex- pressive of an erroneous idea. No substance is in itself a supporter of combustion, nor is any one intrinsically a combustible body. If a jet of hydrogen burns in an at- mosphere of oxygen, so, also, will a jet of oxygen burn in an atmosphere of hydrogen gas. In fact, both bodies are equally engaged in producing the result, combustion only taking place upon their mutual surface of contact. Th* division in question has arisen from the circumstance that the most familiar instances of combustion we witnesf take place in the atmosphere, which owes all its active qualities to the presence of oxygen. Combustion takes place only at those points where th* uniting substances are in contact. The flame of a can- For what purpose is oxygen introduced into the system ? Why is it to be regarded as the supporter of respiration ? Is the division of bodies inet combustibles and supporters of combustion a correct one ? What i nature of flame? STRUCTURE OF FLAME. 177 die is not incandescent throughout, but is a Fig. 158. mere superficies or luminous shell, with a dark interior. In such a flame several distinct parts may be traced. Around the wick, a, Fig. 158, at the points i i, the light is of a blue color ; for here the air being in excess, the combustion is perfect. From this toward c the combustible matter predominates, and the light is most in- tense. A faint exterior cone, e e, surrounds the more luminous portion, but the interior at b is totally dark, as may be proved by placing a piece of mica or glass upon the flame. It is prob- able that the light arises chiefly from the ignition of solid matter, for incandescent gases are only faintly luminous. The hydrogen of the flame is first burned, and for a mo- ment carbon is set free in the solid form at a very high temperature, its oxydation instantly ensuing. A given weight of a combustible body, when burned, will always furnish a constant amount of heat. If an ounce of carbon be burned in a few moments in pure oxygen gas, the amount of heat disengaged appears to be very great ; though, in reality, it is the same that would finally be yield- ed by a slower combustion in atmospheric air. So, too, me- tallic iron becomes white hot when burned in oxygen, be- cause the combination goes forward with great rapidity ; but precisely the same amount would be yielded in the slow oxydation of rusting, though in the latter instance it might take years for the completion of the process. This is a fact of great physiological importance. We have just said that atmospheric air owes all its ac- tivity to the presence of oxygen, and as there are inces- santly combustive processes going on, the tendency of which is to remove oxygen from the air and generally re- place it with carbonic acid a result, also, which ensues from respiration, in every part of the earth where animals are found it would appear a necessary consequence that the constitution of the air should incessantly change, the amount of oxygen declining and that of carbonic acid in creasing. But in this respect the vegetable world exerts Why do the different regions of a lamp flame differ in luminous power? Is there any difference in the amount of heat evolved in rapid and in slow combustions ? What are the causes which tend to diminish the amount of oxygen in the air ? 178 ORIGIN OF OXYGEN IN NATURE. an opposite tendency to the animal ; for, under the influ ence of the light of the sun, plants decompose carbonic acid gas, setting free its oxygen, and appropriating the carbon to their own uses. This beautiful fact was origin- ally discovei ed by Priestley, who found, that if some green Fig. 159. leaves were placed in a bottle, as in Fig. 159, con- taining carbonic acid gas, or, what is more conven- ient, water holding that substance in solution, so long as the sun does not shine on them no action is perceived ; but if the bottle be set in the sun, bub- bles of gas are rapidly disengaged from the leaves, and, rising up through the water, collect in the upper part of the bottle, and, if examined, prove to be very rich in oxygen. A question has arisen as to what principle the remark- able decomposition is due. I have proved, by causing it to take place in the prismatic spectrum, that it is due to the yellow ray of light. (Phil. Mag., Sept., 1843.) LECTURE XL. HYDROGEN. Preparation and Properties of Hydrogen. Relations to Respiration. Combustibility .Its Light- ness. Explosive Combustion. Production of Water. Oxyhydrogen Blow-pipe. HYDROGEN. #"=]. IF a piece of potassium be wrapped in paper and rap- idly immersed beneath an inverted jar at the water-trough, violent reaction soon sets in, a gas collects in the upper part of the jar, and the potassium, oxydizing, dissolves in the water. The gas so produced is hydrogen, and the decomposition is very simple, as shown in the following symbols : that is, water acted upon by metallic potassium yields ox- ide of potassium and hydrogen gas. In practice more economical processes are resorted to. Like potassium, metallic zinc can decompose water. at or- dinary temperatures, but there is this difference between By what agency is this tendency compensated ? What is the principle of the decomposition of water by potassium ? HYDROGEN GAS. 179 them, that while the oxide of potassium is very soluble in water, the oxide of zinc is nearly insoluble. A plate of polished zinc immersed in water does not, therefore, give rise to a stream of gas, for the moment the incipient ac- tion has set in it ceases, the zinc becoming covered with an impervious pellicle of oxide, which cuts off farther contact with the water. If, however, we add any acid substance which can form with the oxide a salt soluble in water, the action will go on continuously, because the zinc can now expose a clear metallic contact. Such a substance is sulphuric acid. To make hydrogen, therefore, we take a bottle, Fig. 160. a, Fig. 160, and having placed in it some strips of zinc, add sufficient water to cover them entirely, and then adjust to the mouth of the bottle a cork, through which two tubes, b and c, pass. Through b sulphuric acid is poured in such a quantity as to excite a brisk but not too violent effervescence, and the gas, as it generates, passes out through c. It is absolutely nec- essary 'to allow a quantity of the gas to escape before at- tempting to collect it, because the first portions form, with the air in the. upper part of the bottle, an explosive mix- ture ; but as soon as it is judged that the air is all expelled, we may proceed to collect the gas ; and whenever the pro- duction slackens, if more acid be added through the fun- nel tube, b, the supply may be kept up. Hydrogen gas is a transparent and colorless body, which exerts a powerful refracting action on light. When pure, it has neither taste nor smell, but, as thus obtained, it has a peculiar odor. It is the lightest body in nature, its specific gravity being 0-0694. One hundred cubic inches of it weigh 2'1 grains. The weight of its atom is taken as the standard of comparison of other atomic weights in this book; it is therefore = 1. It exerts no action on vegetable colors, and is very sparingly soluble in water, one hundred cubic inches of that liquid dissolving about one and a half of hydrogen gas. Hydrogen has never been liquefied. As respects the animal economy, hydrogen gas does What is the reason that zinc can not decompose water alone ? How may hydrogen gas be made by the aid of zinc ? What are the properties of this gas? 180 PROPERTIES OF HYDROGEN. not exert any directly deleterious effect ; and although it can not, of course, carry on the functions of respiration, which are acts of oxydation, yet it can, for a short space, be introduced into the lungs with impunity. If a person whose lungs are inflated with it attempts to speak, his voice resembles the feeble and shrill voice of a child. This arises from the small density of hydrogen ; a bell rung in this gas emits almost as feeble a sound as if rung in a vacuum. One of the most striking peculiarities of hydrogen is its great inflammability in contact with ox- Fig. iei. ygen. If a jar, Fig. 161, with a stop- cock at its upper extremity, be filled with hydrogen, and then, being depress- ed in the water of the trough, the cock opened and a light brought near the hydrogen as it escapes, it takes fire at once, burning with a pale yellow flame. Or if to the mouth of a bottle containing the mate- rials for generating hydrogen, a, Fig. 162, a cork, through which a glass tube, &, is passed, be adjust- ed, and after allowing the air in the bottle to be dis- placed, a light be applied to the issuing gas, it takes fire and burns in the same manner; an experiment com- monly described as the philosophical candle. The following experiment proves three facts at the Fig. 163. same time: 1. The great lightness of hydro- gen; 2. Its inflammability; 3. That it is not a supporter of combustion. A jar, a, Fig. 163, is to be filled with hydrogen at the water-trough, and then/ being lifted in the air with its mouth downward, a taper, placed on a bent wire, is car- ried into its interior. As the taper passes the mouth of the jar there is a feeble explosion, and the hy- drogen taking fire, burns with a pale flame ; but as soon as it is immersed in the atmosphere of the gas the taper is extinguished. It may, however, be relighted as it is brought out of the jar at the burning hydrogen, and this may be repeated several times in succession. The com- What are its relations to respiration ? How may its combustibility be demonstrated 1 How may its inflammability, its non-supporting power and its lightness be simultaneously illustrated ? COMBUSTION OF HYDROGEN. 1$1 bustibility of the gas and its quality of not supporting combustion are obvious enough, and its lightness is proved by the fact that it does not flow out of the open mouth of the jar, which it would do at onee if it were heavier than atmospheric air. The application of hydrogen to aerostatic purposes is founded upon its small specific gravity. This property is very distinctly illustrated by filling an India rubber gas- bag with hydrogen, and having attached to the stop-cock, a, Fig. 164, which closes it, a common earth- Fig. 164. en-ware tobacco-pipe, &, by dipping the pipe in a solution of soap, bubbles may be blown. These rise through the air with rapidity ; and if a lighted taper is brought near them as they are ascending, the hydrogen takes fire and burns with a yellowish flame. If, in a strong brass vessel, a, Fig. 165, we place a mixtui e of hydrogen and atmospheric air in equal Fig. 165. volumes, and, having inserted the cork, c, tightly, pass, by the aid of the ball and wire, b, an electric spark through the gas, Si. violent explosion takes place, the hydrogen burning in- stantaneously with the atmospheric oxygen, and giving rise to the production of water. Musical sounds originate in vibratory movements com- municated to the air. If the flame of a philosophical can- , for example, Ffe dle is covered by a wide glass tube, as, the neck of a broken retort, an intensely powerful sound is emitted. This arises from the circum- stance that the hydrogen burns in the tube, giving rise to a series of small explosions, which follow each other with rapidity, and these explosions throw the air in the tube into a vibratory state. Accord- ing as the tube is raised or lowered, these explo- sions occur with different degrees of rapidity, some- times producing a clattering sound, and then a pure mu- sical note. Whatever may be the circumstances under which hy- To what purpose is hydrogen applied in consequence of its lightness ? How may this be illustrated on a small scale ? When mixed with oxygen r air, and an electric spark passed through it, what is the result ? Under irhat circumstances will the flame of hydrogen emit a musical sound ? 182 OXYHYDROGEN BLOW-PIPE. drogen burns, whether quietly, as in the philosophical candle,. or with trivial explosions, as in this tube, or with a violent detonation, as in the preceding experiment, the uniform product of the combustion is water. During the combination of these elementary bodies with each other a very great amount of heat is given out, for hydrogen combines with eight times its own weight of oxygen, a greater proportion than is met with in the case of any substance whatever. Advantage is taken of this in the construction of the oxyhydrogen blow-pipe, an instrument invented by Dr. Hare, which furnishes us with the most efficient means of obtaining a high temperature. There Fig. 167. are several different forms of this blow- pipe ; in some the gases are mixed in the proper proportions in a strong receiver, and set on fire after passing through a Hemming's safety tube. But it is better to keep them in separate reservoirs, and conduct them to a common jet, where they may simultaneously mix and be burned, as is shown in Fig. 167, where O is the oxygen reservoir, H the hydrogen, a b the flexible lead pipes, leading to a common jet, c, at which the gases are set on fire. By this instrument substances perfectly infusible in a common furnace melt at once. The intensity of the heat of this blow-pipe depends, to a great extent, on the fact that, unlike ordinary flames, the oxyhydrogen flame is, as it were, solid j that is, incandescent throughout all its parts. In its general relations, hydrogen possesses so many of the properties of the metallic class, that there is every reason to believe it is, in reality, a metal. The facts of its aerial form and transparency can scarcely be regard- ed as of any weight against this conclusion, for the vapor of mercury possesses a similar aspect. What is the uniform production of its combustion 1 Why is so much heat evolved in the burning of a mixture of oxygen and hydrogen ? De- scribe Hare's compound blow -pipe. What is the peculiarity of the flame ? To what class of bodies does hydrogen probably belong ? WATER. 183 LECTURE XLI. WATER. Hydrogen Acids. Water. Its Properties. Compressibility. Constitution of Water. Syntheses of Water. By Spongy Platinum. Determination of its Composition by Weight. Analysis of Water. Chemi- cal Relations of W^ater. Water of Crystallization and Saline Water. Acts as a basic, indifferent, and acid Body. Purification. Deufoxide of Hydrogen. WATER. HO = 9-013. HYDROGEN unites with all the electro-negative substan- ces, and, with many of the more prominent ones, forms strong acids. The hydrogen acids of chlorine, bromine, iodine, and fluorine are all constituted upon the same type, in which, if the electro-negative radical be repre- sented by R, we have HR. But with oxygen, instead of an acid, a neutral body re- sults. This body is common water. Water, as will be presently proved, results from the union of oxygen and hydrogen, one atom of each of these elements combining to form one atom of water. It is. therefore, a binary compound. Its symbol is HO. By volume, it consists of two of hydrogen united with one of oxygen; by weight, one part of hydrogen united with eight of oxygen. These statements correspond with the first, because the hydrogen atom is twice the volume of that of oxygen ; and the weight of an atom of oxygen is eight times that of hydrogen. Water is a colorless and tasteless body. It freezes at 32 F., and boils at 212 F. Its specific gravity is 1-000, being the standard of comparison of all other liquid and solid bodies. The specific gravity of its vapor, steam, compared with atmospheric air, is 0-6201. It is a com- pressible and elastic substance. One cubic inch of it at 62 weighs 252-45 grains. When hydrogen unites with electro-negative substances, what class of bodies arise ? What is the constitution of water ? What are the proper- ties of water ? 184 COMPRESSIBILITY OF WATER. Fig. 168. The compressibility of water is at once dem- onstrated and measured by an instrument in- vented by GErsted, and represented in Fig. 168. It consists essentially of a strong glass cylinder, a a, filled with water, upon which a powerful pressure can be exerted by means of a piston driven by a screw, b. In this cylinder of water a gage, represented on a larger scale by Fig. 169, is placed. The gage consists of a reservoir, e, prolonged into a fine tube, f ; there is also a scale annexed. The reservoir and part Fi 169 of the tube are filled with water, and a small column of quicksilver, x, indicates the point on the tube to which the water The pressure exerted is measured by an d. reaches, air-gagej If, now, this instrument be placed in the strong glass cylinder, as seen in Fig. 168, and pressure exerted by turning the screw, the air in the gage, cZ, contracts and indicates the amount of that press- ure ; at the same time, the small column of mercury, x, descends in the tube, showing that the water con- tracts, and measuring its amount. On turning the _screw the other way, so as to relieve the apparatus of pressure, the air-gage comes back to its original point, and the mercury in the fine tube ascends again. It is obvious, therefore, that by this instrument we meas- ure the compressibility of the water contained in the res- ervoir, e, due allowance being made, for the minute amount of contraction which the glass of which e is made, and ^.170. which is pressed equally on its inside and outside, undergoes; and also for variations of temperature. CErsted's instrument shows that water is compress- ed 2-s-^J'o P art f i ts volume for each atmosphere of pressure. The constitution of water was first clearly proved by Mr. Cavendish. It can be illustrated in a vari- ety of ways. Thus, if over a jet of burning hydro- gen a cold glass bell be suspended, as in Fig. 170, it becomes soon covered with a misty dew, and, Describe CErsted's instrument for proving its compressibility. What is the amount of its compressibility ? How may its composition be synthet- ically illustrated ? SYNTHESIS OP WATER. 185 if the experiment be prolonged, drops of liquid finally trickle down the sides, and may be caught in a vessel placed to receive them. When . examined, this liquid is found to be water. It has arisen from the union of the hydrogen with atmospheric oxygen. If in a vessel over the mercurial trough twenty meas- ures of pure hydrogen are added to ten measures of pure oxygen, and a small pellet of spongy platinum passed up through the quicksilver, union between the two gases rapidly takes place, so that it is usual, in order to moder- ate its action, to mix the spongy platina previously with a little pipe clay. As the gases unite, the mercury rises, until at last they have totally disappeared. This beauti- ful experiment shows that the constitution of water by volume is 2 hydrogen to 1 oxygen, as has already been said. The composition of water by weight was determined by Berzelius as follows : Let a flask, a, Fig. 171, con- Fig-. 171. taining zinc and dilute sulphuric acid, be connected by a bent tube, Z>, with another tube, d, containing chloride of calcium ; the hydrogen which is consequently evolved from the flask deposits any small quantity of water it may be contaminated with in the bulbs c c, and then passing through the chloride of calcium tube, J, is made perfectly dry. The tube d is connected with a tube of hard glass, on which a bulb, e, is blown. This bulb is filled with a known weight of oxide of copper, which can be raised tt a red heat by means of a spirit lamp, h ; and as the dry hydrogen passes over the ignited oxide it reduces it, form- How may the constitution of water be proved synthetically by spongy platinum ? Describe the method of Berzelius for determining the compo- sition of water by weight. Q2 186 ANALYSIS OF WATER. ing with its oxygen water, and leaving pure metallic cop- per. The water thus produced is partially collected in the bulby) and the rest of it is detained by a second chlo- ride of calcium tube, g. If, therefore, we weigh the tube e before and after the experiment, in the latter instance its weight will be less than the former, the difference being due to the amount of oxygen which has been removed. If, also, we weigh the tubes f and g before and after the experiment, in the latter case they weigh more than in the former, the differ- ence being the weight of the water produced. Thus, it will be found that for every eight grains that the oxide of copper has lost nine grains of water have been pro- duced, showing that the constitution of water is by weight 8 of oxygen to 1 of hydrogen. Fig. 172. The composition of water may also be proved analytically as well as synthetically. It has been already stated that this can be done by the 1 Voltaic battery in a very sat- isfactory manner. An apparatus suited for this purpose is shown in Fig. 172. The polar wires of the battery enter the sides of a globular glass vessel full of water, and over their terminations tubes are inverted in which to receive the gases. The hy- drogen is double the volume of the ox- yg en - Another form of the same apparatus is seen in Fig. 173. In a bent tube full of water, the platina wires, N P, are introduced by means of corks. On the current passing, oxygen is collected in one of the branches of the tube and hydrogen in the other. Lavoisier determined the composition of water by passing its vapor over pieces of iron made red hot in a tube. Thus, if from the retort, a, Fig. 174, containing boiling water, steam is- passed through a red-hot iron tube, c c, filled with turnings of iron, or iron wire, decomposition takes place, black oxide of iron forming, and hydrogen gas escaping by the tube,jf, into the gas-holder, m n. How may the analysis of water be effected ? Describe the principle of Lavoisier's analysis of water. DECOMPOSITION OF WATER. 187 The chemical relations of water are of the utmost im- portance. It exerts a more general solvent action than any other liquid known, holding in solution gaseous and solid substances, acids, alkalies, and salts. As respects gaseous bodies, the quantity which water will take up is to a considerable extent dependent on pressure, and in the case of salts, an increase of temperature very fre- quently increases its solvent powers. Salt-crystals some- times contain a very considerable quantity of it, as is shown in the case of common alum, of which, if a Fig. 175. mass be put upon a red-hot brick, Fig. 175, it melts in its own water of crystallization, and, after a great quantity of steam is thrown off, a dry residue remains. Crystals often con- tain water in two different states, one portion known under the name of water of crystallization, which may generally be expelled by a moderate heat ; another portion known as saline water, which is with much more difficulty driven off. In the works on chemistry, the for- mulae are constructed so as to indicate these different con- ditions of the water : Aq (aqua.) being the symbol for the water of crystallization, and HO for the saline water; thus, FeO + SO S + HO + 6Aq, How does water compare with other bodies as respects solvent power? What is meant by water of crystallization, and saline water? How is this difference indicated in formulae ? 188 DEUTOXIDE OF HYDROGEN. is the symbol for green vitriol, which is therefore a sul- phate of the protoxide of iron, with one atom of saline water and six of water of crystallization. The latter is easily driven off by heat, but the former only at high tem- peratures, or by l>eing replaced by some other body. Water unites with many acids with great energy. If mixed with sulphuric acid, and a thermometer immersed, the temperature will run up rapidly to above 212. With basic bodies, the same results may be obtained as when quicklime is sprinkled with water, or potash and soda dissolved in it : toward acids water acts as a base ; toward bases it acts as an acid ; and toward salts as an indifferent body. As found in nature, water is always impure. Rain- water and melted snow contain the various soluble gases which are in the air; spring, river, well, and mineral waters the soluble bodies of the strata through which they have flowed ; from these it can only b<5 purified by the process of distillation. DEUTOXIDE OF HYDROGEN. HO 2 = 17-013. There is another compound of hydrogen and oxygen, the deutoxide of hydrogen. It contains twice the amount of oxygen found in water, and is characterized by a remark- able facility of decomposition. It is a liquid substance, possesses bleaching powers, and is heavier than water LECTURE XLII. NITROGEN. Preparation of Nitrogen. Properties. Its Indifferent Nature. Its Oxygen Compounds. Atmos- pheric Air. Constitution of. Dimensions of. Rela- tions to Organization. Density and Temperature. Fix- ed and Variable Constituents. Experimental Proofs of its Pressure. NITROGEN. N= 14-19. NITROGEN gas is most readily procured from the atmos- pheric air by burning phosphorus in a bell jar over the "What is the relation of water to acids, bases, and salts ? By what pro- cess is water purified ? "What is the constitution and properties of the deutoxide of hydrogen ? What is the process for preparing nitrogen by phosphorus ? NITROGEN GAS. 189 pneumatic trough. If a piece Fig. 176. of phosphorus be laid in a cup (Fig. 176) and set on fire, all the oxygen in the air of the jar, a, will be consumed, white flakes of phosphoric acid forming, and these, being finally dissolved in the water of the trough, d, there is left behind nitrogen, contami- nated to a small extent by the vapor of phosphorus. If nitrate of ammonia be placed in a retort, and the tem- perature raised until it emits protoxide of nitrogen, and at that moment, by means of a wire passing through a cork in the tubulure, a piece of zinc is lowered down upon the melted mass, oxide of zinc is produced, and nitrogen gas escapes. The decomposition is very simple, NO . . Zn = Zn O . . N. Nitrogen gas is a colorless, tasteless, and inodorous body, very sparingly soluble in water, that liquid dissolv- ing but 1^ per cent, of its volume. It is lighter than at- mospheric air, its specific gravity being 0-976. Its atomic weight is 14'19. It does not support combustion nor respi- ration, and from the latter circumstance obtained formerly the name of azote ; but it does not exert any directly pois- onous agency on the animal system. Nitrogen gas is little disposed to unite with other bod- ies, except when either it or they are in the nascent state. Its compounds, too, are prone to decompose from trivial causes ; hence it is among them that we find some of the most remarkably detonating bodies. Many animal and vegetable substances, into the composition of which it enters, are characterized by the facility with which they tend to undergo putrefactive changes, and, as we shall here- after find, ferments owe their remarkable powers to the presence of this element. Nitrogen unites with oxygen, and forms five different bodies, NO . . . NO Z . . . NO 3 . . . NO, . . . NO 5 . How may it be made from nitrate of ammonia ? What are the proper- ties of this gas ? Why does it give rise to so many explosive bodies ? To what is the property of ferments due ? How many compounds of oxygen and nitrogen are there ? 190 THE ATMOSPHERIC AIR. Their names are Protoxide of nitrogen. Nitrous acid. Deutoxide of nitrogen. Nitric acid. Hypohitrous acid. With oxygen, also, it forms atmospheric air; "but this is a mixture, and not a compound. ATMOSPHERIC AIR. The mechanical properties and constitution of the at- mosphere are so important, that I shall here introduce the consideration of them before passing to the description of the oxides of nitrogen. The atmosphere consists chiefly of oxygen and nitrogen gases, in the proportion of about 21 volumes of the former to 79 of the latter. It also contains a minute but essential quantity of carbonic acid, which, however, varies at dif- ferent times, 10,000 parts of air containing, on an average, about five parts of this gas. Besides these, there are found in it variable quantities of the vapor of water, and traces of ammonia, sulphureted hydrogen, and carbureted hy- drogen. It is a colorless, invisible, elastic substance, 815 times lighter than water, and is taken as the standard of comparison for the specific gravity of gases. Its specific gravity is, therefore, = TOGO. One hundred cubic inch- es of it weigh, at the mean temperature, and pressure very nearly 31 grains. There are many methods by which the analysis of the air can be effected. lire's eudiom- eter, Fig. 177, which consists of a siphon tube, closed at one end and open at the other, may be used for this purpose. Into the closed branch of the instrument, which is also grad- uated, a measured quantity of air is introduced, and to it is added an equal volume of hydrogen. The bend of the tube is occupied by wa- ter, as shown in the figure, a column of air intervening between this water and the open ex tremity of the tube. On this the thumb is closely pressed, Of what is the atmospheric air composed? "What is its specific grav. ity 1 What is the weight of 100 cubic inches of it 1 How may it be an. alyzed by Ure's eudiometer? Fig. r ANALYSIS OF THE AIR. 191 as represented, and an electric spark passed through the instrument by the aid of its platina wires. This sets the gases on fire ; the column of air beneath the thumb acting like a spring to repress the movement at the time of the explosion. The amount of gas then left is ascertained on the divisions, and one third of the deficit represents the quantity of oxygen originally present. To enable the experimenter to operate on larger quan- tities of gas, Brunner's instrument may Fif 17g be used. It consists of a tube, a be, with three bulbs blown upon it ; these bulbs are filled with cotton which has been im- pregnated with melted phosphorus. The tube is attached, by means of a cork, to a glass vessel, d, filled with mercury. On opening the stop-cock, e, the mercury flows out, atmospheric air introducing itself by a b c, and its oxygen being re- moved by means of the extensive surface of phosphorus which the cotton presents. Consequently, by measuring the mercury which has flowed out we ascertain the quantity of nitrogen introduced into the vessel d, and the increased weight of the tube a b c determines the amount of oxygen. The result of such experiments shows that the atmos- pheric air is composed of from 20-79 to 21-08 parts of oxygen in 100 volumes. By weight, its constitution is about, Oxygen . . Nitrogen . . The earth's atmosphere does not extend indefinitely into space, but terminates at an altitude of about fifty miles. It forms, therefore, a mere film on the face of the earth, for the diameter of the globe is nearly 8000 miles. If a representation of it were placed on a common twelve-inch globe, it would scarcely be one eighth of an inch thick. Its relations to the world of organization are full of in- terest. All plants come from it and all animals return to How by Brunner's instrument ? What is its constitution by volume and by weight ? To what distance does it extend ? 192 DENSITY OF THE AIR. it, so that it stands as the bond of connection between these orders of life. As we ascend to more elevated regions the air becomes less dense, for the obvious reason that, as it is a very com- pressible body, those portions of it nearest the ground have to sustain the weight of the superincumbent mass, and are therefore more dense ; but in the higher regions, where the superincumbent pressure is less, the air is more rare, as is shown in the following table : Height in Miles. Volume of Air. Barometric Inches. o- 1 30- 2-705 2 15' 5-41 4 7.5 8-115 8 3-75 10-82 16 1-875 13-525 32 9375 16-23 64 46875 which also shows that the great mass of the atmosphere is comprehended within a very short distance of the earth's surface. At different altitudes it is of very different tem- peratures, being colder as the altitude is greater. Of the constituents of the air, the oxygen and nitrogen are usually spoken of as fixed, the carbonic acid, ammo- nia, and water as variable. There are causes in operation which tend continually to impress changes in the amount of all these bodies. Every process of combustion, and the respiration of every animal, remove oxygen and replace it by carbonic acid. But the growth of plants has the re- verse action, removing carbonic acid and replacing it by oxygen, so that for many centuries in succession the con- stitution of the atmosphere is unchanged. Of the mechanical properties of the air, the first to 179 which we have to direct our attention is its press- ure, which takes effect equally in all directions, up- ward, downward, and laterally. Thus, if we take \a a gl ass tu ^ e several feet long, a, Fig. 179, closed at one end uud open at the other, and having filled it full of water, place over the mouth of it a piece of card, b, and turn it upside down, the card will not fall off, nor the water flow out ; they remain, as it were, suspended on nothing, but in reality sus- What are its relations to animals and plants ? Why does its density decrease with the altitude ? How does its temperature vary ? Which are the fixed, and which the variable constituents of the air ? Give sonwe illustrations of the upward pressure of the air. '. * & PRESSURE OF THE AIR. 193 tained by the upward pressure of the air. Or if we take a bottle, a, Fig. ISO, with a hole, b, half an inch in diameter in the bottom of it, and having filled it with water, close the mouth of it with the fin- ger, it may be held up in the air without the wa- ter flowing out, although the aperture b is wide open. In this instance, again, it is the upward pressure of the air which sustains the liquid. Let the glass globe a, Fig. 181, with its neck 5, be inverted in some water contained in ajar, c, and the whole covered by an air-pump re- ceiver. As the receiver is exhausted, bubbles of air pass through the water and escape away, but as soon as the pressure is restored the water is forced out of the jar upward into the globe. The air-pump enables us to exhibit in a very striking manner many of the chief mechanical properties of the at- mosphere. Thus, if upon the plate of it there Fi be placed a glass receiver, a, Fig. 182, as soon as the air is exhausted from its interior, the su- perincumbent pressure retains the glass so firm- ly in contact that it is impossible to lift it off, Fig. 184. but as soon as the air is readmit- ted it can be easily removed. If within the receiver a a smaller one, b, be placed, and exhaustion made, while a is fixed b can be easily moved by shaking the pump, but on letting in the air, a becomes loose and b firmly pressed in contact with the plate. If over the mouth of a Fig. 183. jar, Fig. 183, placed upon the pump, the palm of cu the hand be laid, as the air is exhausted it is pressed in close contact with the jar, and can only be removed by the exertion of a very con- siderable force. On a small plate, a, Fig. 184, furnish- ed with a stop-cock, b, terminating in a fine Give an illustration of its downward pressure. Describe the experi- ment represented in Fi?. 183. 194 PRESSURE OF THE AIR. jet, c, let there be placed a tall glass receiver. The stop- cock being now screwed into the pump and opened, the air may be exhausted from the interior of the receiver and the stop-cock closed. But being now opened under the surface of some water in a cup, the water passes through the jet and rises to the top of the jar, forming a fountain in vacuo. LECTURE XLIII. ATMOSPHERIC AIR. Pressure of the Air. Simple Means of Exhaustion. Determination of the Weight of Air. Amount of Pressure. Elasticity of Air. Exists in the Pores of Bodies. Respiration of Fishes. Measure of Elastic Force. THE Magdeburg hemispheres, invented by Otto Guerick, who also invented the air pump, illustrate in a very striking manner atmospheric pressure. They con- Fig. 185. sist of a pair of brass hemispheres, a b, Fig. 185, with handles ; they fit, without leakage, to each other by a flange, so as to form a perfect sphere. One of them has a stop-cock, through which the air may be exhausted, and on this being done, it will be found almost impossible to pull them apart, though as soon as the air is readmitted, and its pressure restored to the in- terior, they will fall asunder by their own weight. If over the mouth of an open receiver, a, Fig. 186, a Fig. 186. piece of bladder be tightly tied with a waxed thread, when the air is exhausted the bladder becomes deeply depressed into a spherical con- cavity by the superincumbent pressure, and finally bursts inward with a loud explosion. It is upon the principle of atmospheric press- ure that the various instruments used by surgeons for cup- ping act. One of the most simple methods of performing this operation is to place the cupping glass for a moment over the flame of a spirit lamp, and then transfer it rapid- Describe the fountain in vacuo. What are the Magdehurg hemispheres ? What is the principle illustrated in these various experiments ? How is the process of cupping performed ? WEIGHT OF AIR. 195 ly to the skin. Spirits of wine, when burning, forms a very large quantity of steam, which, of course, fills the in- terior of the glass in a rarefied state by reason of the hicrh temperature of the flame. As soon as this steam con- denses a vacuum is formed, and the soft surface on which the cup is placed is pressed into its interior. For mahy of these experiments, an air pump is not nec- essarily required, but simple contrivances will answer in its stead. Thus, if we take an eight-ounce rial, a, Fig. 187, and fit to the mouth of it a cork, b, through which there passes a piece of glass tube, c, drawn into a narrow jet at one extremity, but open at the other, by pla- cing the finger over the opening and intro- ducing it into the mouth, the air, by the ac- tion of the tongue and the muscles of the mouth, may be sucked out to a great extent ; and when the exhaustion has been carried, by this means, as far as possible, by pressing the finger over the opening, it will close ft, act- ing, therefore, as a valve. And now, if the bottle be turned upside down, as at e, the tube dipping beneath some wa- ter in a cup, as soon as the fin- ger is removed the water is press- ed upward, and forms a fountain in vacuo. The pressure of the air depends primarily on the fact that it is a heavy body, as may be proved by the direct experiment of weighing it. For this purpose, let a light glass flask, a, Fig. 188, fitted with a stop-cock, be counterpoised at the balance ; then let the air be exhausted from it, and its weight determined again. It will now be found lighter than before ; but upon opening the stop-cock it will regain its original weight. Experiments made in this man- ner show that a flask contain- ing 100 cubic inches will, when Describe a simple method by which partial exhaustion may be pro- duced by the mouth. How may the weight of air be directly ascertained 1 Fig. 188. 196 SPECIFIC GBAVITY OF GASE3. Fig. 189. exhausted, weigh about thirty-one grains less, and there- fore we infer that that is the weight of 100 cubic inches of atmospheric air. Atmospheric air is used as the standard of comparison of the specific gravities of other gaseous bodies. The process for the determination is very simple. A glass globe, g, Fig. 189, holding 20 or 30 cu- bic inches, is exhausted of air, and by means of the stop- cocks, e d, attached to the jar, c, containing the gas to be tried. This gas, which is con- fined by mercury, has been passed through the drying tube, , by the delivering tube, b, into the jar, which should be graduated. On opening the cocks, e d, the gas flows into the exhausted globe ; the quantity introduced may be determined on the graduation, and its weight ascertained by the balance. There are several different methods of stating the amount of the mean pressure of the air ; thus, we say that it is equal to 15 pounds on the square inch, or to a col- umn of mercury 30 inches long, or to a column of water 30 feet long. That air is a highly elastic substance, can be readily ^ J90 shown. Under a receiver (Fig. 190) let there be placed a half-blown bladder, the neck of which is tightly tied ; as the air is removed from the receiver the bladder distends, Fig. IQI. but, on restoring the pressure, it becomes as flaccid as it was be- fore, showing that the air included in it expands and contracts as the pressure upon it is made to vary. This may be still better shown by taking a small India-rubber bag (Fig. 191), the mouth of which is closed tightly, and using In what manner may the relative weight of other gases be determined ? What is the pressure of the air on a square inch equal to ? What is nearly the equivalent length of a mercurial and water column*? How may the elasticity of air be illustrated ? ELASTICITY OF AIR. 197 Fig. 192. it instead of the bladder in the last experiment. On rare- fying the air in the receiver, the bag begins to dilate, and may be extended to several times its original dimensions, as shown in the dotted line ; but as soon as the pressure is restored, it returns to its original size. Nor does this expansion take place with an inconsiderable force. If a flaccid bladder be placed, as in Fig. 192, with several heavy lead- en weights put upon it, as soon as it is caus- ed to dilate by removing the pressure, it will push up the weights. Nor does it-lose its elastic force or spring by being long pent up in close vessels. Some of the old chem- ists kept air compressed in copper globes for months, and found that, as soon as an opening was made for it, it expanded to its original dimensions. Let there be taken a glass bulb, a (Fig. 193), the open neck of which, , dips beneath some water in Fig. 193. a jar, e, and let the bulb and tube be full of water, with the exception of a small space oc- cupied by atmospheric air. On covering the apparatus with an air-pump receiver, d, and exhausting, the bubble of air, a, gradually ex- pands, and after a time, as the action of the machine is continued, fills the entire glass, both bulb and tube ; but as the pressure is restored, it con- tracts again, and goes back to its original size. By taking advantage of the expansibility of air under Fig. 194. reduction of pressure, we are able to dem- p igi 195< onstrate its existence in the pores of many bodies ; thus, if we place in glasses of water an egg (Fig. 194), an apple (Fig. 195), or other such pb^ects, and, covering them with a receiver, exhaust, we shall see innumerable bubbles of air escaping through the water. The same observa- tion may be made in the case of many liquids which hold gaseous substances dis- solved. A glass of ale placed in an exhausted receiver How may the elasticity of air be shown by an India-rubber bag ? Give an illustration of the amount of this force. How may the presence of air be detected in the pores of solid bodies ? How may air be shown to exist dissolved in liquids R2 193 RESPIRATION OF FISHES. Fig. 198. Fig. 196. (Fig. 196) foams from the escape of carbonic acid gas, and even clear spring or river water, examined in the same manner (Fig. Fig. 197. 197), is found to contain a large quantity of air in solution. This last fact is of considerable importance, for it is by the aid of this air that the respiratory function of fishes is carried forward. On examination, however, it is found that this is not true atmospheric air, but a mixture, which is richer in oxy- gen. The atmosphere contains 21 per cent, of oxygen, but this gas contains 33. The cause of the difference is the unequal solubility of oxygen and nitro- gen ; for the former gas, being much the more soluble, the water takes up relatively a greater portion of it from the air. Fishes, therefore, respire this gas, its richness in oxygen making up. for its inferior amount; and when they are placed in, water which has been in an exhausted receiver, they die. Their move- ments, also, are, to a certain extent, regulated by the air contained in a receptacle, or bladder, in their bodies ; by the compression of it they can descend, and by its expan- sion rise. If they be placed in water in a partially ex- hausted receiver, they float on the, surface, or can only descend to the bottom for a moment by violent muscular exertion. The necessity of air to the support of com- bustion may be illustrated by comparing the length of time a candle will burn in a large receiver full of air, and in the same exhaust- ed, Fig. 199. In the latter case it speedily dies out, the smoke descending to the bottom of the jar in the rarefied medium around. Substances prone to decay, such as meats and fruits, may be preserved for a length of time in vessels void of air. The process is Of what use is the air dissolved in water ? What is its composition 7 How may the necessity of air to the support of combustion be proved'? Fig. 199. PRESERVATION OF FRUITS. 199 illustrated in Fig. 200. The F^.aoo. fruits are placed in a large jar closed by a sound cork, covered with sealing-wax. A small hole is made through the cork, and the jar covered by an air-pump receiver. On exhausting, the air passes out through the hole, and when the vacuum is per- fect the hole is closed by melt- ing the wax by the sunbeams converged by a convex lens, the access of the air being thus cut off. From the foregoing experiments and considerations, it appears that the primary fact in pneumatics is, that the air has weight ; from this, by a necessary consequence, arises its pressure and the inequality of density of the at- mosphere at different altitudes. It also follows that the elastic force of the air must be precisely equal to the pressure upon it. In any given stratum of air, as, for in- stance, that which rests upon the surface of the earth, the pressure of the superincumbent mass is equipoised by the elastic force ; if the elastic force were less, compression would ensue ; if greater, dilatation. The pressure and the elastic force must, therefore, be equal to each other. LECTURE XLIV. ATMOSPHERIC AIR. The Barometer. Description of it. Cause of the Phenomenon. Proof that it is the Pressure of the Air. History of the Invention. PaschaVs Ex- periment. Illustrations of the Nature of Pressure. Variability of Pressure. Point of Perpetual Congela- tion. Local Disturbances in the Constitution of the Air. Diffusion of Gases. The Air is a Mixture. Mar- riotte's Law. Gay-Lussac's and Rudberg's Law. IF we take a tube of glass, a b, Fig. 201, page 200, more By what means may objects be preserved from its influence ? What is the relation between the pressure and the elastic force of the air ? 200 Tfi BAROMUTER. Fig. 201. ^an thirty inches long, closed at one end and open at the other end, and, having filled it with quick- & silver, invert it in a cup, c, filled with that metal, the mercury will not flow out of the tube, but will remain suspended at a height of twenty-eight or thirty inches. If there be placed beside Fig. 202 the tube a scale, d, divided into inches and decimal parts, the zero of the division coinciding with the level of the mercury in the cup, such an instrument forms the ' c barometer; The cause of the suspension of the mercury in the tube is the pressure of the air. This may be demonstrated by placing over the barometer a tall air-pump receiver, and exhausting. It will be found that, as the pressure in the interior of the receiver is reduced, the column of mercury in the barometer falls, and on restoring the press- ure it rises to its original point. Fi e . 203. The same fact may be proved in another manner If a tube, upward of thirty inches long, the upper extremity of which is closed by a piece of bladder, be filled with mercury and inverted in a cup, as shown in Fig. 203, the bladder will be found deep- ly depressed, the pressure of the air in that di- rection being borne by it ; but if now a minute pin- hole is made in the bladder, so as to allow the air to press upon the top of the mercury, the column >rapidly descends, flowing out of the tube. The barometer was originally invented by Torricelli. Some plumbers, working for the Duke of Florence, found that it was impossible to make a pump which should raise water more than about thirty feet. This fact eventually com- ing to the knowledge of Torricelli, he suspected that the water rose in those machines in consequence of the pressure of the air, and not through Nature's abhorrence of a vac- uum, as was at that time supposed. But if the limit to which water can be raised by a pump is reached when the pressure of the column of liquid equilibrates the pressure of the air, it follows that if a heavier fluid than water be Describe the barometer. What is it which supports the mercurial col umn ? How may this be proved ? By whom was the barometer invent ed? What were the circumstances of the invention? PRINCIPLE OF THE BAROMETER. 201 used, the height to which it can be raised is less. A pump ought, therefore, to lift quicksilver only about as many inches as it can lift water feet ; for the weight of these liquids is about as one to thirteen and a half, and, accord- ingly, Torricelli found, by means of a small pump fixed to a long glass tube, that such, in reality, is the case. The barometer is a simplification of the same apparatus. That it is the pressure of the air which sustains the mer- curial column was satisfactorily proved by Paschal, who reasoned that, if this were the case, the barometric column ought to be shorter on the top of a mountain than in a valley, because in the former position that pressure must necessarily be less. On the experiment being made, hia reasoning was found to be true. The principle of the barometer may be illustrated by substituting for the pressure of air the pressure of a col- umn of water. Thus, if we pour some quicksilver into the bottom of a deep glass jar, a, Fig. 204, and plunge into it a long tube, b, open at both ends, the quicksilver will rise in this tube, so that its level on the inside will be coincident with that on the outside. But if now we begin to fill the jar with water, r, for every thirteen and a half inches in depth poured in, the quicksilver, d, will rise one inch, the mercurial column counterpoising the column of water. And, on the same princi- ple, the column of quicksilver in the barometer counter- poises that of the air to the top of the atmosphere. Mr. Boyle discovered that the pressure of the air is not always the same, but it undergoes many variations, the mercurial column sometimes falling near to 27 inches, or rising above 30. The range is commonly estimated at 2'5 inches. It is considerably less in the tropics. These changes of pressure are exceedingly irregular, and are connected with meteorological phenomena. There are also diurnal variations, the column rising twice in the twenty-four hours. In winter the first maximum is about nine A.M., and the minimum at three P.M., the second maximum being about nine P.M. What was Paschal's experiment ? What did it prove ? How may the phenomena of the barometer be illustrated by the pressure of a water column ? What is the extent of the irregular variations of pressure ? What are the diurnal variations ? At what times do the maxima and minima occur ? 202 DIFFUSION OF GASES. It has already been observed that the mean pressure of the air is estimated at 15 pounds upon a square inch, or equal to a column 30 inches long. A man of average size sustains a pressure on the surface of his body of nearly thirty thousand pounds. The temperature of the atmosphere is lower as we as- cend to more elevated regions. A point, therefore, can always be reached over any place of which the tempera- ture never rises over 32 F., and where water is always frozen. This point is known under the name of the point of perpetual congelation. Its altitude differs very much in different places, being highest at the equator, and low- er as we go toward the poles. It is at The Equator. . . . 15,000 feet. Latitude 40 .... 9000 " " 75 .... 1000 " 85 .... 117 " Many causes conspire to give rise to local disturbances in the constitution of the air. In its lower strata combus- tion and respiration are actively going on ; they tend to diminish the oxygen and increase the carbonic acid. At the equator the effect of a constantly brilliant sunshine on the leaves of plants is to diminish the carbonic acid and increase the oxygen. But notwithstanding these local dis- turbances, and also the fact that the constituents of the air are of very different specific gravities, the constitution of the atmosphere is nearly the same in all places. This Pig. 205. commixture is partly effected by the mechanical action of winds, and partly by the property which gases have of diffusing into each other. Thus, if two vials, a and e, Fig. 205, communicate with each other by means of stop-cocks, b c d, and if, in a, a light gas, such as hydrogen, is placed, and in e a heavy gas, as carbonic acid, in a few min- utes after the stop-cocks are opened the gases will diffuse into each other, the light one descend- ing and the heavy one ascending, until they are perfectly commixed. And this effect will take place even though a barrier should intervene. Thus, Dr. Mitchell found that gases would read- ily pass through the close texture of India-rub- What is the point of perpetual congelation ? How does it vary with the latitude ? What are the causes which tend to change the composi- tion of the air ? What is meant by the diffusion -of gaaes ? , MARRIOTTE'S LAW. 203 ber to mingle with each other ; and I have observed the same in the case of films of water. Thus, if a Fi 206 bottle, a, Fig. 206, full of atmospheric air, have its mouth closed by a film of soap-water spread over it by the finger, and then be placed under a bell jar containing protoxide of nitrogen, this latter gas passes rapidly through the film, and distends it into a bubble by forcing its way into the bottle. The force with which gases will thus pass into each other is sometimes very great. I have proved that sulphureted hydrogen will diffuse into atmospheric air, though resist- ed by a pressure of more than fifty atmospheres. That the atmospheric air is a mixture, and not a com- pound, is proved by its easy decomposibility, its refract- ive power, and by the fact that its constituents retain their properties unchanged. The amount of its oxygen may be determined by the combustion of phosphorus, or detona- tion with hydrogen ; the amount of its carbonic acid, which varies in damp or dry seasons, being dissolved out by showers of rain, may be determined by potash or lime- water, and its aqueous vapor by the process for the dew- point already described. Atmospheric air being thus an elastic and compressi- ble body, it remains to explain the law which de- Fig. 207 termines its volume under changes of pressure. This is known under the name of the law of Mar- riotte, and, applying to many other gases besides atmospheric air, is to the effect that the tolume of a gas is inversely as the pressure upon it. This law is of the utmost importance in gaseous chpmistry. It may be illustrated by the instrument (Fig. 207), where a b is a bent tube, open at the end #, and closed at b. The branch a may be several feet long, and b six inches. A small quantity of mercury is poured into the tube, so as to occupy the bend and shut up a column of air between d and b. Now, if the tube ia filled with quicksilver to the height of 30 inches, as to a, the pressure of this column is exerted on the air in the closed branch, b ; and as there are now the weight of two atmospheres, that of the ordinary atmosphere and that of Does this take place through intervening barriers ? How is this con- nected with the constitution of the air ? What proofs are there that the atmosphere is a mixture, and not a compound ? What is Marriotte's law f How may its truth be proved ? Giv examples of Marriotte's law. 204 DILATATION OF ATMOSPHERIC AIR. the mercurial column, it is compressed into half its former volume, c. If we bring upon it three atmospheres, it will be compressed into one third ; if four, to one fourth, &c. And the law holds good, also, for diminutions of pressure. If, on a given volume of gas, the pressure is reduced to one half, the volume doubles ; if to one third, it triples ; to one fourth, it quadruples ; in all cases the volume being inversely as the pressure. The exact amount of dilatation of atmospheric air for elevations of temperature was determined by G-ay-Lussac as follows : In a tin box, A, containing water, there is in- Fig. 208. troduced through a perforation at o' a bulb, g, with a tube, g', containing the air, the dilatation of which is to be measured. This air has been previously introduced in a state of dryness by the chloride of calcium tube, li h 1 . At m is a globule of mercury, which acts as an index, and confines the air. On the opposite side of the tin box, at o, a thermometer, s t b, is introduced, and another one, v, passing through the top of the box, occupies the center. The bcx is first filled with water containing fragments of ice, and when the thermometers are at 32, the position of the index, m, is marked. The furnace is then lighted, and when the water boils, and the thermometers are at 212, the index, m, is again observed. The difference indicates the dilatation of the air for 180 ; and in this manner Gay-Lussac found that 1000 volumes of air be- come 1375. These results have been of late carefully ex- amined by Rudberg, who fixes the amount of expansion of air at T ij of its volume, at 32, for every degree of Fahrenheit's scale. What is the law of Gay-Lussac ? What is the absolute dilatation of air determined by Rudberg ? PROTOXIDE OF NITROGEN. 205 LECTURE XL\. COMPOUNDS OP NITROGEN AND OXYGEN. Protoxide oj Nitrogen. Preparation and Properties of. Constitu- tion. Supports Combustion. Produces Intoxication. Deutoxide of Nitrogen. Preparation and Properties of. Constitution. Relations to free Oxygen. Hyponitric Acid. Preparation and Properties of. PROTOXIDE OP NITROGEN. NO = 22-203 IF the nitrate of ammonia be exposed to a temperature of about 350 degrees in a retort, Fig. 209. Fig. 209, it undergoes decompo- sition, being resolved into water and the protoxide of nitrogen ; the former condensing in the neck of the retort, and the latter rising into the pneumatic jar. If whitish fumes are evolved, they indicate that the process is going on too fast, and the heat must then be moderated. The change taking place is very simple. It is a mere rearrange- ment of the constituent atoms of the nitrate of ammonia. NO, + NH 3 ... = ... 2(NO) + 3(HO). One atom of that salt, therefore, yields two atoms of protoxide of nitrogen and three of water. The protoxide of nitrogen is a colorless gas, transpa- rent, like atmospheric air ; it has a sweetish taste, and is soluble in water, that liquid taking up about three fourths of its volume of the gas when cold, but the solvent power being greatly diminished by warming the water. Its specific gravity is 1-527. It may be liquefied at Fi g _2W 45 by a pressure of fifty atmospheres, and has even been solidified. It is composed, by atom, of one of nitrogen and one of oxygen, and by vol- ume, of two volumes of nitrogen united to one of oxygen, condensed into two volumes, a constitution like that of water. It therefore contains half its bulk of oxygen gas, and supports combustion with How may protoxide of nitrogen be made ? "What are its properties * What is its constitution ? Does it support combustion ? S 200 DEUTOXIDE OF NITROGEN. activity. A lighted taper immersed in it burns brightly, and, as in oxygen, if there be merely a spark on the wick, it kindles into a flame. Phosphorus burns in it with great, brilliancy. Sir H. Davy discovered that not only does this gas sup- port respiration, but that it exerts a remarkable physio- logical action when breathed, producing a transient in- toxication, which wears off after two or three minutes. These effects are undoubtedly due to the oxydizing ac- tion which the protoxide establishes in the system. In this respect it is far more active than even pure oxygen gas, and the reason is obvious : oxygen is but slightly ab- sorbable by watery fluids, but this gas is taken up by them to a very great extent. When it is introduced into the lungs, it is rapidly dissolved in the blood, and carried by the circulation to every part of the body, oxydizing whatever is in its path, and producing a febrile warmth and an unusual mental disturbance. The protoxide of nitrogen shows but little disposition to unite with other bodies. It may be regarded as an in- different substance. DEUTOXIDE OF NITROGEN. NO 2 = 30-216. The deutoxide or binoxide of nitrogen may be made by the action of nitric acid moderately diluted upon me- tallic copper. If these substances are introduced into a flask together, and, when the action mod- erates, fresh portions of nitric acid be added through the funnel (Fig. 211), a colorless gas is evolved, which may be collected over wa- ter, in which it is only sparingly soluble, one hundred volumes of that liquid dissolving about five of the gas. It is composed of equal volumes of nitrogen and oxygen united, without condensation. Its specific grav- ity is, therefore, 1"0416. It does not support combustion ; a lighted taper immersed in it is at once extinguished ; but if phosphorus, burning violently, be introduced in it, the combustion goes on with increased activity. Iron and several other metals withdraw from it one half of its oxygen, converting it into the protoxide. What are its relations to respiration ? How long does this intoxicating effect last ? What is the cause of it ? Why is the protoxide of nitrogen au indifferent substance ? How is the deutoxide obtained ? What is it constitution ? Does it support combustion ? HYPONITBOU3 ACID. 20? The most remarkable quality of the deutoxide of nitro- gen is its action on mixtures containing oxygen gas, as, for example, atmospheric air ; with these it at once pro- duces red fumes of nitrous acid, which are soon removed if water be present, the deutoxide taking up two atoms of oxygen to change into nitrous acid. On this principle it has been used for the purpose of effecting the analysis of atmospheric air, but, unless several precautions are ob- served, the results are incorrect. The deutoxide should be added in a small and steady stream to the air ; red fumes are at once produced ; these are soon removed by the water, and the residue is less in volume than the air and deutoxide taken together. One fourth of the deficit is equal to the volume of the oxygen originally present. By operating in this manner, as I have had many occa- sions to observe, correct results may be obtained. The general process may be illustrated by taking a tall jar and placing in it a certain volume of atmospheric air, to which- is to be added an equal volume of the deutoxide. Though both gases are colorless at first, a deep copper- colored vapor is the result ; this is removed after a time by the action of the water, which, rising in the jar, ex- hibits a deficit in the amount of the gases. A solution of the protosulpbate of iron dissolves this gas abundantly ; and if a small quantity of the sulphuret of carbon be poured into it, and a light applied, the mix ture burns with a blue flame. HYPONITllOUS ACID. NO 3 38'229. This substance' may be made by mixing four volumes of dry deutoxide of nitrogen with one of dry oxygen, and exposing the mixture to cold. The gases condense into a liquid of a greenish color, which gives forth an orange vapor. Hyponitrous acid is decomposed by the contact of water, deutoxide of nitrogen escaping with an effer- vescence, and nitric acid being produced, three atoms of hyponitrous acid yielding one of nitric acid and two of the deutoxide. What is its action on gaseous mixtures containing oxygen ? - Under what circumstances may it be used to determine the amount of oxygen ? How may its action on oxygen mixtures be illustrated ? What is its re- lation with the protosulphate of iron? And what with the vapor of sul- phuret of carbon ? How may hypoiiitrous acid be procured ? What is the action of water on it ? 208 NITROUS ACID. LECTURE XL VI. COMPOUNDS OP NITROGEN AND OXYGEN. Nitrous Acid. Preparation and Properties of. Remarkable Changes of Color. Nitric Acid. Discovery of. Cavendish's Experiments. Sources from which it is Derived. Com,' mercial Preparation. Its Properties. Is a Hypothet- ical Body. Purification. Detection . NITROUS ACID. NO 4 = 46-242. NITROUS acid may be made by mixing together one volume of dry oxygen with two of the dry deutoxide of nitrogen, and exposing the mixture to a very low tem- perature ; but it is much more easily procured by distill- " ing, in a porcelain or hard glass Fig. 212. retort, a, Fig. 212, dry nitrate of lead, and receiving the gases in a tube, I, artificially cooled by a freezing mixture, c. The nitrous acid condenses as a colorless liquid, which becomes yellow as its temperature rises. Its spe- cific gravity, in the liquid form, is 1/42. It solidifies at 40 F., and boils at 82 F. Its vapor possesses remark- able optical qualities. When its temperature is very low, it is nearly colorless ; it takes on an orange tint as the degree of heat increases, and finally becomes almost black. The peculiarity of the phenomenon is, that if the gas be examined while undergoing these changes, by passing a ray of light through it and analyzing it by means of a prism, as explained in Lecture XIX., a great number of fixed lines are found in the resulting spectrum ; and as the temperature rises these increase so much in number and in breadth that the light becomes finally obliterated. The vapor of nitrous acid, when once mixed with atmos- pheric air, is condensed into the liquid form with great difficulty. It is wholly irrespirable, and, even when di- luted, of a very unpleasant odor. Nitrous acid is, for the most part, decomposed by water, ) 4 ... = ... 2NO & + NO t , How may nitrous acid be made ? What are its properties ? How does the color of its vapor change by heat ? What is the cause of the fina. blackness ? What are the%elations of nitrous acid and water? NITRIC ACID. 209 three atoms of it yielding to two of nitric acid and one of the deutoxide of nitrogen, as seen in the formula ; but the nitric acid produced protects a portion of the nitrous acid, which thus escapes decomposition. Its vapor is ab- sorbed by nitric acid. The production of this acid by the process with nitrate of lead is of considerable philosoph ical interest ; PbO + NO, ... = ... PbO + NO, + O, one atom of the nitrate of lead yielding one atom of ox ide of lead, which remains in the retort, one of nitrous acid, and one of oxygen gas, which escape. It might be expected that, in such a distillation, we should obtain oxide of lead and nitric acid. The cause of the non-ap- pearance of the latter body will, however, be presently understood. NITRIC ACID. NOs 54-255. Nitric acid, the* most important of the compounds of oxygen and nitrogen, and one of the most important of the acid bodies, was first discovered during the ninth century. The discovery of this and some of the other powerful acids form one of the epochs in chemistry. The science can scarcely be said to have existed until that time, the Egyptians, Greeks, and Romans having no knowledge of these bodies, nor, indeed, of any more pow- erful than vinegar. The constitution of nitric acid was determined by Mr. Cavendish, who formed it synthetically, by passing electric sparks through atmospheric air in contact with a solution of potash. The nitrate of potash was obtained. Nitric acid also occurs to a small extent in rain water, especially after thunder storms, and by some supposed to originate upon the same principles as in Cavendish's ex- periments ; but probably it is due to the oxydation of ammonia, which always exists in the air. The chief sup- ply is derived indirectly from the decay of vegetable or animal matter, in the presence of oxygen gas, and in con- tact with basic bodies. Collections of such refuse pass under the name of nitre beds, and, in France and Ger- What is the decomposition whtfch takes place when nitrate of lead is distilled? When was nitric acid discovered? How was its composition determined by Cavendish ? What is the source of the nitric acid in rain water? S2 210 NITRIC ACID. many, furnish the saltpetre which is used for the manu- facture of gunpowder. In the East Indies, nitrate of potash is obtained by lixiviation from the soil in which earthy nitrates naturally occur. From South America the nitrate of soda is exported ; it is found as an efflo- rescence on sails in which common salt probably exists. In most of these cases the nitric acid arises from the oxydation of ammonia produced during putrefactive fer- mentation. NH 3 + 8 ... = ... NO, + 3HO. The formula shows the probable nature of the action ; one atom of ammonia, under the influence of eight of oxygen, will yield one of nitric acid and three of water. The nitric acid of commerce is made by distilling equal weights of sulphuric acid and nitrate of potash. The process may be conducted in a small way in a glass re- tort, A, Fig. 213 ; and it is found advantageous to use Fig. 213. the quantity of sulphuric acid here stated, because a solu- ble bisulphate of potash is formed, which may be easily removed without breaking the retort. Half as much sul- phuric acid would effect the decomposition, but it would require a higher temperature, and the neutral sulphate which forms could with difficulty be removed. The change which takes place is thus exhibited : (KO, M) 5 ) + 2(HO, SO,} ... = .. ..(KO, HO, 2SO 3 ) From what sources is nitrate of potash produced ? How may nitric acid ise from the oxydation of ammonia ? How may nitric acid be made 1 PROPERTIES OF NITRIC ACID. 211 that is, one atom of nitrate of potash and two of sulphuric acid furnish one atom of bisulphate of potash, and one of hydrated nitric acid distills over into the receiver, B, which is kept cool by a stream of water flowing from i into a vessel, c c, the waste water passing through led. A net is wrapped over the receiver to distribute the water evenly. In this process nitrate of soda may be advanta- geously substituted for nitrate of potash. Hydrated nitric acid thus produced is a colorless liquid, which boils at 248 F., though this point changes with the amount of water in the acid. It freezes at 40 ; is decomposed into oxygen and nitrogen by being passed through a red-hot glass tube. It turns yellow in the sun- shine, owing to a portion being decomposed and nitrous acid set free, which dissolves in the residue, and gives it an orange tint. The nitric acid of the shops (aqua fortis) commonly possesses this color, from which it may be freed by boiling in a glass vessel. It stains the skin and other organic matters yellow, and hence is used in the arts of dyeing. Its action on many metalline and other combustible bodies is exceedingly violent, ow- Fig. 214. ing to the great amount of oxygen it contains. Poured upon some pieces of copper in a wine- glass, over which a bell jar may be inverted (Fig. 214), an effervescence takes place, and the red fumes of nitrous acid abundantly form. Though it is one of the most powerful oxydizing agents we possess, it often happens that, in a state of great concentration, it will scarcely act on a metal, but the addition of a little water causes the action to set in. Nitric acid (iVO 5 ) is a hypothetical or imaginary body which has never yet been isolated ; the nearest approach to it that we know is the strongest aqua fortis. This has a specific gravity of 1-521, and consists of one atom of hypothetical nitric acid and one of water. Its formula, therefore, is NO. + HO. Its molecular constitution probably is What are its properties ? When passed through a red-hot tube, what happens to it 1 Why is commercial nitric acid often yellow ? -What is the action of this acid on the skin and on metallic bodies ? What is the near- est approach to hypothetical nitric acid ? 212 SULPHUR. It is, as we shall find hereafter, a hydrogen acid. From this we see the reason of the circumstance that in the de- composition of dry nitrate of lead, described in this Lecture, nitric acid does not make its appearance, but nitrous acid and oxygen ; for, being a hypothetical body, its atom is dissevered in the act of being set free. Nitric acid of commerce can be purified by distillation, rejecting the first portions which come over, as they con tain chlorine, and leaving a portion in the retort contain- ing sulphuric acid and fixed impurities. If twelve parts are distilled, the first three may be cast aside, and one left in the retort; the intermediate eight are pure. When it is in a solution, nitric acid may be detected by the addition of sulphuric acid, and a drop or two of pro- tosulphate of iron ; a brownish color is produced where the two liquids meet. When in a concentrated state, the evolution of red fumes, by the action of copper, detects it. It also gives a blood-red color with morphia. The nitrates deflagrate when ignited with combustible matter, a result which may be well shown by grinding together a few ounces of nitrate of potash and common sugar, and set- ting fire to the mixture. Owing to the solubility of all its compounds, nitric acid can not be precipitated. LECTURE XL VII. SULPHUR. Natural and Artificial Forms. Preparation of Flowers. Properties of Sulphur. Its Vapor. Ox- ygen Compounds of Sulphur. Sulphurous Acid. Prep' aration. Properties. Bleaching Effects. Condensa~ tion to the Liquid State. Its Compounds. SULPHUR. 5 = 16-12. MUCH of the sulphur in commerce is derived from vol- canic countries, in which it occurs often in a pure and crystallized state. It is one of the most common element- ary substances, being found abundantly united with va- rious metals, such as iron, copper, lead. In combination with lime, baryta, &c., it occurs as sulphuric acid, and is Why can not it be isolated ? How may it be purified ? How may it be detected ? Why can not nitric acid be detected by precipitation ? Un- der what forms does sulphur naturally occur ' FLOWERS OF SULPHUR. 218 also an ingredient of many animal and vegetable prod- ucts. Sulphur is met with under three different forms : roll sulphur, flowers of sulphur, and lac sulphuris. Roll sul- phur is an impure variety, which receives its form from being cast into cylindrical molds ; the flowers of sulphur are formed from the impure brimstone by sublimation ; lac sulphuris differs from the foregoing in being of a white color. It is prepared by precipitation from the persulphu- ret of potassium by hydrochloric acid. The preparation of flowers of sulphur is conducted in an apparatus, such as Fig. 215. A is a room, or chamber, of 2000 feet capacity ; c is a pan containing sulphur, which is melted by the furnace, o s ; the vapor passes along i d b, and, entering the chamber, is there condensed. The re- sulting flowers are removed through the door p. If an explosion occurs, when the process commences, it lifts the valve e, and the gases escape through the chimney, t t M M is a shed under which the apparatus is constructed. As the iron pan becomes exhausted, new quantities of brimstone can be introduced through the door n. Sulphur commonly exists as a solid of a yellow col- or, and of a specific gravity of 1'99, having neither taste nor smell. It melts at 226 F. into a pale yellow-colored liquid ; but what is very curious, if the heat be raised to about 450 F., it changes to the color of molasses, and be comes so thick and tenacious that the capsule in which the fusion is carried on may be turned upside down with- out the sulphur flowing out. At 600 F. it boils, and, as What are its artificial forms ? How are the flowers of sulphur made ? "What are the properties of sulphur ? What changes may be observed in it when melting' ? PROPERTIES OF SULPHUR. the heat approaches that point, it again becomes fluid ; and, as it cools, runs through the same changes again in a reverse order. If suddenly quenched in cold water at the low temperature, before it thickens, it solidifies into ordi- nary sulphur ; but if heated for a time to near 600, and then quenched, it becomes, on cooling, elastic, like India- rubber, and may be drawn into long threads ; and in this state is sometimes used for taking casts of coins, for by keeping a few days it slowly returns to the condition of ordinary sulphur. When rubbed 'on a piece of flannel it becomes highly electric, assuming the negative state, and at one time was used in the making of electrical machines, before the pow- ers of glass were discovered. A roll of it held in the warm hand emits a crackling sound, the crystals of which it is composed separating from one another. It is -a bad conductor of heat and electricity, crystallizes under two different systems, and is, therefore, a dimorphous body, one of its forms being an acute rhombic octahedron, and the other an oblique rhombic prism. When heated to about 300 F. in the open air, it takes fire, and burns witfi a blue flame, emitting a suffocating odor, fumes of sulphurous acid gas. It is wholly insoluble in water ; its proper solvent fe the bisulphuret of carbon. The vapor of sulphur is of a deep yellow color, and has the high specific gravity of 6*648. In it metallic bodies will burn precisely as they do Fig. 216. ^ rf^ * n oxv g en g as - Dr. Hare has shown that if a gun barrel be heated red hot at the breech, and a piece of sulphur drop- ped into it, the muzzle being closed with a cork, an ignited jet of sulphur vapor issues from the touch-hole, in which, if a bunch of iron wire be held, it takes fire and burns brill- iantly. . Sulphur has a very extensive range of affinities, uniting with most metallic substances in several different propor- tions, with hydrogen and also with oxygen. With the latter substance it furnishes the following compounds : "What electrical condition does it assume by friction ? What are its conducting; powers ? Why is it called a dimorphous body ? At what tem- perature does it take fire, and what is the product of its combustion? What is the specific gravity of its vapor? Docs it support combustion? What are the oxygen compounds of sulphur? SULPHUROUS ACID. 215 SO 3 . . SO 3 . . S Z O 5 . O 6 ; Fig. 217. their designations are, respectively, Sulphurous acid. Sulphuric acid. Hyposulphurous acid. Hyposulphuric acid. Sulphureted hyposulphuric acid (acid of Langlois). Bisulphureted hyposulphuric acid (acid of Fordos and Gelis). SULPHUROUS ACID. SO* = 32-146. This acid may be formed by burning sul- phur in oxygen gas or in atmospheric air ; in the latter instance the resulting gas is, ojf course, contaminated with nitrogen. The pro- cess may be conducted under a bell jar, the burning sulphur being placed on a capsule or stand. But a much better process is to effect the partial deoxydation of sulphuric acid by heat- ing oil of vitriol with mercury, which deprives it of one atom of oxygen, forming an oxide of mercury, which unites with one atom of the excess of .sulphuric acid pres- ent to form a sulphate. For many of the ordinary purpo- ses to which sulphurous acid is applied, it may be pro- cured by the action of fragments of charcoal heated with sulphuric acid. In this case, however, carbonic acid is also evolved. When* a solution in water is required, the gas may be passed directly into that liquid, but if it be nec- essary to retain it in a gaseous state, it must be received in jars at the mercurial trough, or collected by the meth- od of displacement. It is, under ordinary circumstances, a transparent and colorless gas, having an un- pleasant taste, and the smell characteristic of burning sul- phur. It is wholly irrespira- ble, and promptly extinguish- es a lighted taper. Its specific gravity is 2'222, and, therefore, if a stream of it which has been cooled by flowing from the How may sulphurous acid be made ? What is the principle of the pro- cess when sulphuric acid acts on mercury or charcoal? What are tha products in each case ? Why must the gas be collected over mercury ? What are its properties ? Fig. 218. 216 SULPHUROUS ACID. generating flask a, Fig. 218, through a bent tube, b, immers- ed in a jar of cold water, be conducted to the bottom of an- other jar, c, the gas, as it collects, displaces the atmospheric air, floating it out of the vessel. This process is of very general application in the collection of gases which are absorbable by water, and is known under the name of the method by displacement. In a jar of sulphurous acid thus collected, if a lighted 219 - taper be immersed, it is at once extinguished. If the jar be inverted over water, the gas is speedily dissolved, that liquid taking up about thirty-seven times its volume of the gas. If veg- etable colors are submitted to its influence, they are bleached, but the color is not destroyed as in bleaching by chlorine, since it can be restored by the action of a stronger acid. Sulphurous acid is among the gases one that most read- ily takes the liquid form. If there be connected with the flask from which this gas is being evolved a bent tube pass- ing through iced water in ajar, and the gas, after traversing this tube, be conducted into a bottle placed in a freezing mixture of snow and dilute nitric acid, it condenses into a colorless fluid of the specific gravity 1'45, which boils at 14 F. This fluid is sometimes used to produce in- tense cold by its evaporation. With bases, this acid forms a complete series of salts, the sulphites, which are readily decomposed by the stron- ger acids, and are occasionally employed as deoxydizing agents, from the circumstance that metallic oxides maybe reduced by them, their sulphurous passing into the con- dition of sulphuric acid* What is the method by displacement ? To what extent is this acid sol- uble in water ? Are its bleaching effects permanent ? How may it bo condensed ? What are the properties of this liquid ? For what purposes are the sulphites employed 1 SULPHURIC ACID. 217 LECTURE XLVIII. COMPOUNDS OF SULPHUR AND OXYGEN. Sulphuric Acid. The Anhydrous Acid. Its Affinity for Water. Ger- man Oil of Vitriol. Its Constitution and Uses. Com- mon Sulphuric Acid. Preparation on the Large Scale. Its C/iemical Relations. Purification. Detection. Other Sulphur Acids. SULPHURIC ACID. SO 3 = 40-159. THIS compound is not alone the most important of the acids of sulphur, but also the most important of all acids. By the aid of it, nitric, hydrochloric, and many other strong acids are made for commercial purposes. In the production of carbonate of soda and chloride of lime, im- mense quantities of it are consumed. Of sulphuric acid we have several varieties, differing from each other in the amount of water they contain. 1st. There is anhydrous sulphuric acid, the formula for which has already been given as containing one atom of sulphur and three of oxygen. This substance may be prepared by submitting the fuming oil of vitriol of Nord- hausen to a temperature of about 290 Fahr., when there distills over a white substance of a crystalline aspect. It fumes in the air, melts at 77 Fahr., is converted into va- por at 160, has an intense affinity for water, in which, if it be placed, it hisses like a red-hot iron. It is to be par- ticularly remarked, however, that the acid powers of this substance are very feebly marked ; it shows little tenden- cy to unite with other bodies, and when such combina- tions are effected, the resulting substances are different from the true sulphates. 2d. German, or Nordhausen oil of vitriol, HO, SO 3 -{- SO.. This substance is prepared by taking green vitriol, and, by exposure to heat, driving off its water of crystalliza- tion (six atoms), and also a portion of its saline water. If the dried powder be placed in a stone- ware retort and exposed to a high temperature, there distills over a dark What are the properties of anhydrous sulphuric acid, and how is it pre- pared ? W hat is the process for preparing the German oil of vitriol ? What is its appearance 1 218 OIL OF VITRIOL. oily liquid ; hence the term oil of vitriol : this is the sub- stance in question. Its formula shows that it is composed of two atoms of anhydrous acid united to one of water. A considerable quantity of it is used in the arts /or dis- solving indigo. 3d. Common sulphuric acid, HO, SO 3 . This is the substance which passes in commerce as common oil of vitriol. It is made on the large scale by burning sulphur with nitrate of potash or soda, and con- ducting the sulphurous and nitrous acids which result into large chambers lined with lead, in which steam is thrown, the bottom of the chamber being covered with water. The sulphurous acid takes oxygen from the ni- trous acid, reducing it to the condition of deutoxide ; but this being done in the presence of atmospheric air, which fills the chamber, the deutoxide instantly reassumes the condition of nitrous acid. The deutoxide, therefore, con- tinually transfers oxygen from the atmospheric air to the sulphurous acid, and brings it to the condition of sulphuric acid. After a time the water at the bottom of the chamber becomes charged with sulphuric acid ; it is then concen- trated by drawing off the excess of water in platina or glass boilers, and finally assumes the specific gravity 1'845. It is a dense, oily liquid, freezes at 45 and boils at 620. The attraction of common sulphuric acid for water is F*-.220. very intense. If a tube, containing some ether, be stirred in a glass (Fig. 220) in which sulphur- ic acid and water are being mixed, the tem- perature rises so high that in a few moments the \a ether boils. On the same principle, it will re- move from most gases which are passed over it any water they may contain; and, as we have seen in Lect. XII., water may be frozen by taking advantage of the rapidity with which sulphuric acid will absorb its vapor. Organic substances may also be charred by the action of this acid ; for example, woody fibre is a com- pound of carbon with the elements of water, and when acted upon by sulphuric acid, the carbon is set free, the acid taking from it a portion of its water. For what purpose is it used ? What is the process for preparing com- mercial sulphuric acid? What are its properties? What illustration* may be given of its intense affinity for water ? AC1D3 OF SULPHUR. 219 Sulphuric acid of commerce is never pure ; it contains sulphate of lead, derived in the process of its manufacture, and also, sometimes, arsenic, selenium, and nitrous acid. From the first it may be purified by dilution with water, in which sulphate of lead is insoluble ; but when required entirely pure, it must be distilled, the first portions being rejected. The presence of sulphuric acid may be detected by any of the soluble salts of barium, such as the chloride of barium, or the nitrate of baryta, the white sulphate of baryta precipitating insoluble in water and acids. To black woolen clothing this acid communicates a 1 eddish stain, removable by being touched with ammonia. Besides the compounds just described, we have other definite hydrates of sulphuric acid, thus : (4) S0 3 + 2HO. (5) SO, + 3HO. The fourth of these has a specific gravity of 1'78, and crystallizes at 39 Fahrenheit in large and beautiful crys- tals. The fifth has a specific gravity of T632. HYPO-SULPHUROUS ACID, S a O 2 = 48-266, has not yet been isolated ; one of its salts, the hyposul- phite of soda, is extensively used in the Daguerreotype process for removing the sensitive coating on the plates. HYPOSULPHUBIC ACID, S 2 O 5 = 72-355, is a sirupy liquid of a very acid taste, and is not applied to any use. Besides these, we have two other acids of sulphur : Sulphureted hyposulphuric acid, S 3 O5= 88-475, discovered by Langloia. Bisulphureted hyposulphuric acid, S*Oo = 104-595, discovered by Fordos and G-elis. Chemists are now very generally agreed that all these compounds are to be regarded as hydrogen acids a striking departure from the Lavoisierian doctrines. They have been led to this view by the consideration that no well-marked acid exists in which hydrogen is not found ; that all these sulphur acids possess the same neutralizing By -what substances is it usually rendered impure ? How may it be purified? How may it be detected? How may sulphuric acid stains on clothing be removed? What other hydrates of this body are there? What are the uses of hyposulphurous acid ? What other sulphur acida are there ? What is the nature of the views now held in relation to the acida of sulphur, and acids generally. 220 SULPHURETED HYDROGEN. power, though the quantity of oxygen they contain is so different. They regard them all as being formed by the union of one atom of hydrogen with a series of different compound radicals, as the following table shows : Sulphurous acid H4- SO 3 . Sulphuric acid . H+ SO 3 -f- O. Hyposulphurous acid H~{~ &O 3 -- S. Hyposulphuric acid //-}- SO 3 4- SO 3 . Acid of Langlois H-\- SO 3 -- SO 3 -4-S. Acid of Fordos and Gelis . . . H+ SO 3 -f SO 3 + S 2 . Chlorosulphuric acid J7-f- SO 3 4- Cl. Nitrosulphuric acid H-\- SO 3 -- NO 2 . lodosulphuric acid H--SO 3 -\-I; and, extending these views to the constitution of othei acids generally, an acid is defined to be " a compound of hydrogen with a simple or compound radical, in which the hydrogen may be replaced by any other metal." LECTURE XLIX. SULPHUR AND PHOSPHORUS. Sulphureted Hydrogen. Mode of Preparing it. Its Odor, Acid Relations, and other Properties. Extensively used as a Test. Occurs in Nature. Relations to the Animal System. Bisul- phureted Hydrogen. SELENIUM. PHOSPHORUS. Pre- pared from Bones. Shines in the Dark. Action of Light. Combustibility. Compounds with Oxygen SULPHURETED HYDROGEX. #=17-12. Fig. 221. THIS gas may be easily prepared by the ac- tion of hot hydrochloric acid on the native sulphtiret of antimony pulverized, and may be collected over a saturated solution of salt or warm water. The action of the materials being Sb 2 S 3 + 3(HCZ) ... = ...Sb. 2 Cl 3 + 3(HS) ; that is, one atom of the sesquisulphuret of antimony and three of hydrochloric acid yield one of the esquichloride of antimony and three of sulphureted hy- drogen. Sulphureted hydrogen is a colorless and transparent gas, having the odor of rotten eggs. It is absorbed by Describe the process for preparing sulphureted hydrogen. What are its distinctive properties ? SULPHURETED HYDROGEN. 221 water readily, that liquid taking up two or three times its volume. Its specific gravity is 1-177. It is combustible, and may readily, be burned from a jet placed in the flask in which it is being evolved, the products of its combustion being sulphurous acid and water ; but if the air in which it is burn- ed be limited in quantity, water alone is produced and sulphur deposited. Its solution in water decom- poses gradually by contact with the air, the hydrogen un- dergoing oxydation, and the sulphur being set free. It has the properties of a weak acid, reddening litmus fee- bly, and yields with metallic bases water and sulphurets : MS. many of these sulphurets being insoluble and highly col ored : antimony gives an orange precipitate ; arsenic and cadmium, yellow; lead, brown; and manganese, flesh- colored. On this principle, the presence of sulphureted hydrogen may be always detected : the carbonate of lead, for example, is blackened; and hence, white paint ex- posed in places in which sulphureted hydrogen is being evolved turns dark, and metallic silver tarnishes, and finally becomes black. By a pressure of about seventeen atmospheres the gas may be liquefied. The action of sulphureted hydrogen on metallic bod- ies may be illustrated in a very interesting manner by writing on a sheet of paper with a solution of acetate of lead, the letters being invisible until exposed to a stream of this gas, when they turn black. Its action in producing precipitates may be shown by conducting a stream of it through a solution of tartar emetic, arsenious acid, or acetate of lead. Sulphureted hydrogen is sometimes naturally dissolved in spring water, constituting the mineral waters of various places, as the Virginia Springs. It is also said to be con tained in the brackish water of the mouths of large rivers, due, perhaps, 'to the action of the organic matter they contain upon the sulphates existing in the sea. It has been thought by some authors that the existence of this gas in the air of those places is connected with the fevers What are the results of its combustion ? What is the nature of the precipitates it gives with metallic oxides ? How may this action be il- lustrated ? Is this gas soluble in water ? What is the probable cause of its occurrence at the mouths of large rivers ? T 2 222 SELENIUM. PHOSPHORUS. which there prevail. Sulphureted hydrogen is exceed- ingly poisonous when respired. There is another compound of sulphur and hydrogen, the constitution of which is not precisely known, though it is usually described as bisulphureted hydrogen, and its formula is therefore jH~ 2 . In its properties it is said to have several analogies with the deutoxide of hydrogen. 'SELENIUM. s e = 39-6. This element was discovered by Berzelius in certain varieties of pyrites. It is a rare substance, analogous, in many respects, to sulphur. It burns in the air, forming an oxide which exhales the odor of decaying horseradish. PHOSPHOEUS. P=l5-7. A remarkable substance, first discovered by Brandt, and now extensively procured from burned bones, in which it occurs as a phosphate of lime. It is found, also, in other animal products, being an essential ingredient in fibrin and albumen, and also in the brain and nervous matter. Fig. 223. To procure it, burned bones are reduced to pow- der, and digested with di- lute sulphuric acid ; the li- quid is strained, mixed with powdered charcoal, and, when dry, introduced into a stone-ware retort, #, Fig. 223, to the neck of which a bent copper tube, b, is at- tached, the mouth of which dips beneath water. The retort being now exposed in a furnace to a white heat, half the phosphoric acid in the mixture is deoxydized by the charcoal, carbonic oxide gas escaping, and phospho- rus distilling over. Phosphorus is commonly transparent and colorless. When exposed to the light it turns of a deep red, and this takes place in a vacuum, or in gases which have no action on the phosphorus. In lustre and general appearance it What other compound of sulphur and hydrogen is there ? What is se- lenium ? From what source is phosphorus derived ? PROPERTIES OF PHOSPHORUS. 223 has a waxy aspect. Exposed to the air it smokes, and in a dark place shines a property from which its name is derived. During this slow oxydation it exhales an odor much resembling that experienced when an electrical ma- chine is in high activity. At 32 it is brittle, at 113 it melts, at 572 it boils, distilling over unchanged, if oxy- gen be absent. But in the air it takes fire and burns at about 120, with evolution of flakes of anhydrous phos- phoric acid. Its specific gravity is 1*77. From the intense affinity which phospl'orus has for oxy- gen, it requires to be kept under the surface of water. It is met with in commerce in the form of small sticks, a form given to it by melting it in glass tubes under warm water, and pushing the resulting cylinders out as soon as they have set. If kept in an opaque bottle it is white, but it slowly turns more or less red on exposure to the day- light. From the facility with which it takes fire, it is necessary to handle it very carefully, and to avoid keeping it in con- tact with the warm hand too long. A few particles of dry phosphorus placed between two pieces of brown pa- per and rubbed with a hard body, take fire and burn fu- riously as soon as the papers are separated. It is upon this principle that it will readily inflame by the heat of friction, that its useful application in the manufacture of friction matches depends. In chlorine, or the vapor of bromine and iodine, it takes fire spontaneously. There are several compounds of phosphorus and oxy- gen, as follows : P S O . . P 2 O . . P 2 O 3 . . P 3 O 5 . These are respectively Oxide of phosphorus. Phosphorous acid. Hypophosphorous acid. Phosphoric acid. What remarkable property does this body possess ? Why is phosphorus to be kept under the surface of water ? What is the action of light upon it 1 What useful application is made of its ready combustibility ? How many compound of phosphorus and oxygen are were ? 224 PHOSPHORUS AND OXYGEN. LECTURE L. COMPOUNDS OF PHOSPHORUS AND OXYGEN. Oxide of Phosphorus. Preparation of. Hypophosphorous and Phosphorous Acids. Phosphoric Acid. Three States of Hydra ( -ion. Properties of these three Acids. Their Salts. Phosphureted Hydrogen. Spontaneously In- flammable and Non-inflammable Varieties. CHLORINE. Preparation of. Its Relations to Combustion and Respiration. OXIDE OF PHOSPHORUS. P 3 O = 55-113. Fig. 224. THIS oxide may be formed by causing a stream of oxygerf gas, from the tube a, Fig. 224, to be directed upon phospho- rus under hot water in a glass, I. A brilliant combustion under the water is the result, with the production of phos- phoric acid and of a red powder, which is the substance in question. HYPOPHOSPHOROUS ACID, P 2 O= 39-413, is very little known ; it is formed when phosphorus is boiled in alkaline solutions. PHOSPHOROUS ACID, P 2 O a = 55-439, is formed during the slow combustion of phosphorus in the air ; it may also be produced by acting on the sesquichlo- ride of phosphorus with water. The solution of this acid is sometimes used as a deoxydizing agent. PHOSPHORIC ACID. P 2 O 5 = 71-465. Anhydrous phosphoric acid is formed when phosphorus burns in dry air or ox- ygen gas (Fig. 225). It condenses m white flakes of a snowy appearance, and possesses an intense affinity for water, in which, if placed, it hisses like a red-hot iron. It can scarcely be said to possess acid properties. Until it has united with water, those properties are very feebly developed. How is oxide of phosphorus made ? What is its appearance ? How are hypophosphorous and phosphorous acids produced 1 Under what *ur- cumstances is anhydrous phosphoric acid produced 7 ACIDS OF PHOSPHORUS. 225 With water, phosphoric acid unites in three propor tions, producing Monobasic phosphoric acid . . P 2 O 5 + HO, or H -f- P 2 O$. Bihasic " . . PaOs-f- 2//O, or 2#-f- PiO 7 Tribasic " . . P 3 O5 + 3#U or 3^-f- P*O d . These acids also have the names of metaphosphoric, pyro phosphoric, and common phosphoric acids respectively Either of them may exist in solution with water. Metaphosphoric, or the monobasic phosphoric acid, may be obtained by dissolving phosphorus in dilute nitric acid, evaporating, and exposing the residue to a red heat. It may also be obtained by dissolving the anhydrous acid in water, evaporating and igniting it. In both these cases a transparent body, like ice or glass, is produced ; hence called glacial phosphoric acid. It contains one atom of water, which can not be removed from it by heat. Monobasic phosphoric acid is characterized by giving a white granular precipitate with nitrate of silver ; it also coagulates albumen, producing white curds. If kept in a solution of water, or boiled with it, it passes into the tribasic state. Pyrophosphoric, or bibasic phosphoric acid, may be obtained by heating the common phosphoric acid to 417 F. for some time. In solution it neither precipi- tates silver nor coagulates albumen, but its salts yield, with silver, a flaky white precipitate. Like the former, this turns into the tribasic acid by boiling with water. Common, or the tribasic phosphoric acid, may be ob- tained from bone earth by the action of oil of vitriol, which yields a precipitate of sulphate of lime ; or, more easily, by boiling a solution of the anhydrous phosphoric acid. In solution it neither precipitates silver nor coagu- lates albumen, but its salts yield a Canary-yellow precip- itate with the nitrate of silver. By exposure to a low heat it becomes bibasic, and to a red heat, monobasic. These hydrogen acids of phosphorus give rise to a very extensive and complex class of salts, according to the extent to which their hydrogen is replaced by metal- lic bodies. Thus, the monobasic phosphoric acid can yield only one series of salts, in which all its hydrogen is How many compounds does it yield with water ? How is metaphos- phoric acid made ? What is glacial phosphoric acid ? What are the properties characteristic of monobasic, bibasic, and tribasic phosphoric acids respectively ? How many series of salts can each yield 1 226 PHOSPHURETED HYDROGEN. replaced by a metal; but the bibasic can yield two differ- ent series, according as the metal replaces one or both atoms of base ; and the tribasic can yield three different series, according as one or two or all three of its hydro- gen atoms are replaced. PHOSPHURETED HYDROGEN, P i H a = 34-4, may be made by boiling phosphorus in a strong solution of lime or potash in a retort, a, Fig. 226, the neck of Fig. 226. which dips beneath the surface of water, a few drops of ether being previously put into the retort. As the bub- bles of gas break on the water, they take fire, burning with a bright yellow light, and there ascends through the air a ring of gray smoke, which dilates as it rises, and exhibits a curious rotatory movement of its parts. This gas, also, may be made by bringing the phosphuret of cal- cium in contact with water. Phosphureted hydrogen is a colorless gas, exhaling a peculiar odor, like garlic, and, when burning, produces phosphoric acid and water. It exists under two forms : 1st. Spontaneously inflammable; 2d. Not spontaneously inflammable. It is said that the first may be changed into the second by small quantities of the vapor of ether, oil of turpentine, &c., and the second into the first by the addi- tion of a minute quantity of nitrous acid. CHLORINE. Cl^= 35-47. Chlorine is found abundantly in nature in union with so- dium, forming common salt, a substance which, for the most part, gives to the sea water its salinity, and consti- Describe the preparation of phosphureted hydrogen. What are the properties of phosphureted hydrogen ? How may its two forms be con- verted into each other 1 In what substances does chlorine chiefly occur ? PREPARATION OF CHLORINE. 227 tutes the deposits of rock salt. It is, therefore, an abund- ant substance. Chlorine is best made by the action of hydrochloric acid on peroxide of manganese : MnO, + 2HCI... = ...MnCl + 2HO + Cl; that is, one atom of peroxide of manganese and two of hydrochloric acid yield one atom of the chloride of man- ganese, two of water, and one of chlorine. Half the chlo- rine is, therefore, given off as chlorine gas, and the other half remains as chloride of manganese. Chlorine gas being very soluble in cold water, and act- ing with great energy on mercury, it can Fig. 227. neither be collected at the water nor mercu- rial trough ; but, having a specific gravity of 2-470, we are able to collect it by the meth- od of displacement, as shown in Fig. 227. It may, however, also be collected over warm water or a saturated solution of common salt. When chlorine is required in a state of dryness, it may be obtained by an apparatus like that represented in Fig. a is the retort containing the hydrochloric acid and 228. Fig. 22a manganese. It is connected with a small receiver, t>, which retains part of the water which the gas may bring over ; this, again, is connected with a chloride of calcium tube, c, which effects the perfect drying of the gas. Chlorine is a gas of a pale, yellowish green color. It may How may it be formed? What are its properties? How is it pro- cured in a state of dryness ? 228 PROPERTIES OF CHLQIUXE. be liquefied by a pressure of four atmospheres. A taper immersed in it burns for a few minutes with a dull red flame, emitting volumes of smoke, due to the fact that the Fig. 229. hydrogen of the flame continues to burn or unite with the chlorine, forming hydrochloric acid ; but the carbon, having little affinity for chlorine, is set free in an uncombined state, as lampblack. Powdered antimony, or thin brass leaf, plunged in this gas, becomes incandescent, and burns, pro- ducing a chloride. A piece of phosphorus im- mersed in it takes fire at common temperatures, and burns with a pale flame. The smell of chlo- rine is disagreeable, and its effect, even in a diluted state, suffocating. It irritates the air passages of the lungs, producing hiccough and an unpleasant expectoration LECTURE LI. CHLORINE, CONTINUED. Bleaching Properties. Combus- tion of Hydrocarbons. Disinfecting Qualities. Com- pounds with Oxygen. Properties of Hypochlorous, Chlorous, and Chloric Acids. Quadrochloride of Nitro- gen. Hydrochloric Acid. Preparation in the Gaseous and Liquid States. THE most valuable property of chlorine is its power of discharging vegetable colors, on which is founded its ap- plication in the arts of bleaching arid calico printing. This Fig. 230. property may be illustrated in many ways. By pouring a solution of litmus or indigo through a funnel, a, Fig. 230, into a flask, b, containing chlo- rine gas, the decoloration takes place instantly, or, , "b if the color is not completely discharged, it will be found, in a short time, to disappear. The same takes place when a solution of chlorine in water is used. The peculiarities of chlorine in supporting combustion are remarkable, when compared with those of oxygen What are its relations in the combustion of a taper, and how does it act on certain metals and phosphorus? What is its effect on the animal system ? Of the properties of chlorine, which is the most valuable ? How may it be illustrated ? PROPERTIES OF CHLORINE. 229 gas. A piece of paper, Fig. 231, dipped in oil Figm 231 of turpentine, takes fire in a moment at com- mon temperatures, when placed in a jar of chlo- rin-e, arid, as we have seen, phosphorus and sev- eral of the metals undergo spontaneous ignition in the same manner. These phenomena depend on the intense affinity which chlorine has for elec- tro-positive bodies, but it is very remarkable that it seems to have little disposition to unite with carbon. As in the burning of a taper, so in this exper- iment with turpentine, it is the hydrogen which burns, and the carbon is evolved in clouds of smoke. Chlorine is also used by physicians for the purpose of destroying miasmata, and the effluvia of sickrooms or oth- er places. It is necessary, from its irrespirable qualities, to disengage it slowly and with caution where patients are present. The chlorides of soda and lime are common- ly used. Free chlorine may be detected by its smell, its bleach- ing action on indigo solution, and giving a white, curdy precipitate with the nitrate of silver. Its solution in water is readily made by introducing a small quantity of water into a bottle full of chlorine, agitating it, and Opening the mouth of the bottle from time to time under water ; the gas being gradually absorbed, the bottle becomes full of water, which, of course, contains its own volume of chlo- rine. This solution decomposes in the sunshine, evolving oxygen gas, the water being decomposed. With oxygen chlorine unites in several proportions, producing, CIO . . CIO. . . CIO, . . CIO,. They are designated Hypochlorous acid. Chloric acid Chlorous acid. Perchloric acid. HYPOCHLOROUS ACID. CIO = 43-483. Hypochlorous acid may be obtained, by agitating the red oxide of mercury, suspended in water, with chlorine. If a strong solution of it be placed in an inverted tube, and pieces of dry nitrate of lime be added, the gas is dis- What is the cause of the clouds of smoke deposited when carburets of hydrogen burn in chlorine gas ? For what purpose is chlorine used by physicians ? How may chlorine be detected ? How may a solution of it be made? What compounds of chlorine and oxygen are known ? How is hypochlorous acid made, and what are its properties ? 230 ACIDS OF CHLORINE. engaged, and rises to the top of the tube. It is of a deep- er color than chlorine, bleaches powerfully, and, by a slight elevation of temperature, explodes, evolving two volumes of chlorine and one of oxygen gas. The bleaching compounds are compounds of chlorides and hypochlorides. They are easily decomposed by acids. Thus, when chloride of lime is to be used for dis- infecting purposes, it ie merely required to expose it with water to the carbonic acid of the air, or to add a little of it, from time to time, to a vessel containing dilute sulphur- ic acid. CHLOROUS ACID, CIO 4 = 67-522, may be made by cautiously acting on small quantities of chlorate of potash with sulphuric acid. It is a yellow gas, which explodes furiously from very slight causes, the warmth of the hand being often sufficient to give rise to a violent action. It contains two volumes of chlorine and four of oxygen, condensed into four volumes. It may be conveniently made by operating on a few grains of the Fig 232 chlorate in a test tube. If into a glass, a, Fig. 232, containing water, a small quantity of chlo- rate of potash is placed, and upon it a few frag- ments of phosphorus, and sulphuric acid be poured through a funnel, b, so as to act on the chlorate, chlorous acid is set free ; it communi- cates a golden yellow color to the water, and as each bubble passes by the phosphorus it sets it on fire, furnishing a beautiful instance of combustion under water. CHLORIC ACID, CIO* = 75-535, may be made by decomposing the chlorate of baryta by sulphuric acid, and evaporating the solution. It is a yel- low, viscid acid : a piece of paper dipped in it is set on fire. It does not bleach. It forms salts, one of which, the chlorate of potash, is of considerable importance, and is used for the preparation of oxygen. A few grains of the chlorate of potash, ground in a mortar with a pinch of flowers of sulphur, explodes incessantly during the tritu- ration. PERCHLORIC ACID. ClOt = 91-561. The perch (.orate of potash forms along with the chloride What are the properties of chloric acid? How may the combustion of phosphorus under water be produced by it ? How is chloric acid made ? HYDROCHLORIC ACID. 231 of potassium when one third of its oxygen is expelled from chlorate of potash ; the two salts may be separated from each other by boiling in water, the perchlorate crys- tallizing on cooling. From this perchloric acid may be obtained by distillation with an equal weight of oil of vit- riol, mixed with half as much water. It may be obtained in the form of a white crystalline mass, very deliquescent, and its solution is sometimes used as a test for potash, with which it gives a sparingly soluble salt. The solu- tion fumes in the air, has a specific gravity of 1*65, and does not posse-ss bleaching properties. CHLORINE AND NITROGEN. These substances unite, forming an oily liquid, when a warm solution of sal ammoniac is exposed to chlorine gas. The resulting body is regarded as a quadrichloride of nitrogen (NC1 4 ). By its violent explosions, several emi- nent chemists have been seriously injured. The mere contact of oily matter produces a detonation. CHLORINE AND ^HYDROGEN. HYDROCHLORIC ACID. HCl = 36-47. This acid, called also muriatic acid, is easily prepared by placing in a flask six parts of common salt and ten parts by weight of oil of vitriol, mixed with four of water, the mixture being suffered to cool before it is introduced. On heating the mixture, hydrochloric acid is evolved, which passes along a bent tube into a bottle containing six parts (by weight) of water. The end of the tube dips but a very short distance beneath the surface of this wa- ter, so that if the liquid should rise it may be received into a ball blown upon the tube, and the extremity of the tube becoming uncovered, atmospheric air may pass into the interior of the flask. At the close of the process, the liquid in the bottle, which should be constantly surrounded by ice water in a small tank, more than doubles its volume, and is a pure solution of hydrochloric acid. The action is NaCl + 2(HO, S0 3 ). .. = ... HCl + (NaO,HO,2SO 3 ); that is, one atom of chloride of sodium and two of sul- phuric acid yield one atom of hydrochloric acid and one of the bisulphate of soda. How is perchloric acid prepared, and for what purpose is it used? What are the properties of the chloride of nitrogen ? How is hydrochloric acid made ? 232 IIYDROCHLOIIIC ACID. From the liquid thus produced, or from the commercial muriatic acid, by heating in a flask, pure hydrochloric acid gas may be obtained ; it may also be less advanta- geously procured by the direct action of strong oil of vit- riol on common salt, the reaction in this case being NaCl + HO, SO 3 ... = ... HCl + NaO, SO,. Pure hydrochloric acid is a transparent, colorless gas, possessing powerful acid qualities, very absorbable by wa- ter, which liquid takes up several hundred times its own. volume of the gas ; it fumes in moist air, and has a pungent odor. If a dry Florence flask (Fig. 233) be filled with it by the process of displacement, and the mouth of it opened under the surface of cold water, the water rushes up into the flask, absorbing the gas with great violence. The specific gravity of hydrochloric acid is 1'284. It contains equal volumes of its constituents, uni- ted without condensation. LECTURE LII. CHLORINE, CONTINUED. Production of Hydrochloric Acid by Light. Action of Hydrochloric Acid on Metallic Protoxides. Muriatic Acid Solution. Detection of Hy- drochloric Acid. Nitromuriatic Acid. IODINE. Sour- ces of. Preparations and Properties. Tests for Iodine. Its Action on Starch. Hydriodic Acid. Oxygen Compounds of Iodine. PURE hydrochloric acid gas is also obtained when a mixture of chlorine and hydrogen, in equal proportions, is exposed to the light. In the dark these gases appear to have no disposition to unite, but if they be placed in a flask covered over with a wire screen, and a beam of the sunlight reflected upon them from a looking-glass, a vio- lent explosion ensues and hydrochloric acid is formed. I have found that, in this remarkable experiment, the action is chiefly due to the chlorine, which, from being in How may the gas be procured ? What are the properties of hydro- chloric acid gas ? How may its affinity for water be proved ? What is its constitution ? What is the action of sunlight on a mixture of chlorine and hydrogen ? To which of these bodies is this action due ? PROPERTIES OF HYDROCHLORIC ACID. 233 a passive, assumes an active state by exposure to rays of an indigo color. It may be thrown into the same condi- tion in many other ways ; for example, by the contact of spongy platina. Moreover, when chlorine by itself has been exposed to the sun, it gains the quality of uniting more easily with hydrogen than chlorine which has been made and kept in the dark. When hydrochloric acid is brought in contact with metallic oxides, decomposition of both ensues, and metallic chlorides are formed, thus : MO + HCl ... = ... MCI + HO. or, M. 2 3 + 3(HCI)... = ...M,C1 3 +3HO; that is, one atom of a metallic protoxide with one atom of hydrochloric acid yields one atom of a protochloride of the metal and one of water. But, in the case of a sesqui- oxide, one atom of it with three of hydrochloric acid yield one atom of the metallic sesquichloride and three of water. The constitution of hydrochloric acid, and its Fig. 234. action on metallic oxides, may be strikingly illus- trated by taking a flask, b (Fig. 234), filled with it, in a perfectly dry state, and allowing the perox- ide of mercury, in fine powder, to fall through it. The bichloride of mercury, corrosive sublimate, instantly forms, and drops of water make their ap- pearance on the sides of the flask. It is under the form of a solution in water, as liquid muriatic acid, or spirit of salt, that hydrochloric acid is chiefly used. The mode of obtaining it has been described in the last Lecture. This liquid, when concentrated, has a specific gravity of 1*21, and contains 42 percent, of acid. It smokes in the air, and reddens blue litmus powerfully. The commercial acid is usually of a yellow color ; it con- tains chloride of iron, derived from the iron vessels from which it is distilled. It also often contains sulphuric acid, chlorine, sulphurous acid, tin, or arsenic, and is, therefore, best prepared by the process described, which yields it in perfect purity. Hydrochloric acid may be detected by yielding, when What is the action of hydrochloric acid on metallic oxides ? What are the products of the action of hydrochloric acid on peroxide of mercury ? What are the properties of liquid muriatic acid ? What are its ioa purities ? U2 234 NITROMURIATIC ACID. in a free state with ammonia, dense white clouds of sal ammoniac. If two glasses, one filled with this acid, and the other with ammonia, be brought near each other, a white cloud forms be- tween them. A glass rod, a (Fig. 236), dipped in ammonia may be used for the same Fig 236> purpose. With nitrate of silver hydrochloric /g&fc acid yields a white chloride of silver, which SaPg, turns black in the light, being the same pre- cipitate given under the same circumstances by free chlorine. From this latter substance it maybe distinguished by litmus water, which is bleached by chlorine, and reddened by hydrochloric acid. Nitromuriatic acid, or aqua regia, is formed by adding to hydrochloric acid one half or a third of its volume of nitric acid. The nitric acid, furnishing oxygen to the hy- drochloric acid, forms water, and chlorine, with nitrous acid, is set free in the solution. Aqua regia is used as a solvent for platina and gold, a result which may be illus- trated by placing a sheet of gold leaf in the mixture. IODINE. 7=126-57. Iodine chiefly occurs in the products of the sea, being found in sea-weed, sponge, &c. ; also in certain brine springs, and in some ores of silver and zinc. It may be obtained by lixiviating the ashes of sea- weeds, and evaporating the solution until no more crystals are de- posited. The residual liquor is then acted upon by sul- phuric acid, and subsequently heated with peroxide of manganese, in a leaden retort, a b c (Fig. 237, page 235), the iodine distills over into the receivers, d. It is a solid substance, of a deep blue or black appear- ance, with a semi-metallic lustre, communicates to the skin a fugitive yellow stain, and exhales an odor like that of sea beaches. It crystallizes in rhomboidal plates, is brittle, and has a specific gravity of 4*948. At 225 it melts, and boils at 347, exhaling, even at moderate tempera- tures, a splendid purple vapor, from which its name is de- rived. The specific gravity of this vapor is 8*707 ; it is, therefore, one of the heaviest gaseous bodies known. How may hydrochloric acid be detected? "What is the preparation and property of nitromuriatic acid ? From what source is iodine procured ? What is the method of its preparation ? What is its appearance ? "What is the color of its vapor ? From what circumstance is its name derived? 235 Iodine supports combustion much in the Fig. 238. same manner as chlorine. A jar, a (Fig. 238), containing a few grains of it, placed in a small sand bath, b, and warmed by a spirit lamp, c, may be easily filled with its dense vapor, the atmospheric air floating out before it. In this vapor if a lighted taper is plunged, it exhibits a retarded combustion ; but a piece of phos- phorus, introduced on a spoon, takes fire and burns. In the same manner, if a quantity of iodine Fig , 23 g be placed in a small capsule, and upon it a fragment of dry phosphorus (Fig. 239), spontaneous ignition ensues, with the ev- olution of phosphoric acid, and the vapor of iodine, iodide of phosphorus remaining in the capsule. In water, iodine is but slightly soluble, that liquid taking up r^Vf P art of i ts weight and assuming a brown color. Alcohol dissolves it freely, forming tincture of iodine. In solutions of the iodides iodine may be dissolved. With many substances iodine gives characteristic reac- tions. The iodide of potassium, with the acetate of lead, What are its relations as respects combustion ? Is it soluble in water and alcohol? 236 HYDRIODIC ACID. yields a golden yellow precipitate ; with the bichloride of mercury, a fine scarlet-colored biniodide. This substance possesses the singular quality that, if dried and sublimed in a tube, it yields crystals of a brilliant yellow aspect, which become red on being simply touched with a hard body. With a solution of starch free iodine yields a deep blue color, the solution becoming colorless if heated, but the blue color returning on cooling, provided the temper- ature has not been carried to the boiling point. If a po- tato be cut in two, and a little tincture of iodine poured on the surface, innumerable blue specks make their ap- pearance, each corresponding to the position of a granule of starch. Starch and free iodine will, therefore, mutually detect the presence of each other. HYDRIODIC ACID. HI= 127-57 Hydriodic acid gas may be obtained by dissolving in a solution of iodide of potassium as much iodine as it will hold, adding small pieces of phosphorus, and warming the mixture. A colorless transparent gas is evolved, which fumes in the air, and may be collected over mercury. Its specific gravity is 4*384. It has the general relations of hydrochloric acid, and, like it, is very soluble in water. Fig. 240. A solution of hydriodic acid in water may be made by passing a stream of sulphureted hydrogen from a flask, a (Fig. 240), through L water, b, in which that substance is suspend- ed. The acid forms and sulphur is deposited : I+HS... = ...S + HI. With nitrate of silver this acid yields a pale yellow pre- cipitate, the iodide of silver. This is the substance which forms the basis of the remarkable compound used in the Daguerreotype. In that case it is formed by holding a plate of pure, polished silver in the vapor of iodine ; the plate tarnishes and turns yellow, and, if set in the sun- shine, turns promptly of a deep olive black. Iodine yields two oxygen acids, iodic (1O 5 ) and peri- odic acid (IO 7 ). With nitrogen, also, it gives NI 4 , char- acterized, like the analogous compound of chlorine, by the facility with which it explodes. How may it be detected? In what manner is hydriodic acid made? What is the simplest method of obtaining a solution of it ? "What is the precipitate it yields with nitrate of silver ? What are the oxygen com pounds of iodine ? BROMINE. 287 LECTURE LIII. BROMINE FLUORINE. Bromine. Sources of. Proper- ties . Compounds of. FLUORINE. Hydrofluoric Acid. Its Properties and Action on Glass. CARBON. Allo- tropic Forms of. Preparation of some of those Forms. Diamond. Oxygen Compounds of Carbon. Carbon- ic Oxide. BROMINE. Er 78-39. BROMINE occurs in sea water, and also to a more consid- erable extent in certain brine springs both in America and Europe. From these it may be obtained by evaporating the water until the salt solution is concentrated, and after the chloride of sodium has crystallized from the liquor, passing through it a current of chlorine gas, the solution turning yellow as the bromine is set free. It is next agita- ted with sulphuric ether, which carries to the surface all the bromine. This is then acted on by potash, which gives a mixture of bromate of potash and bromide of potassium. On ignition, oxygen is expelled, and the whole converted into the latter salt, from which the bromine may be distilled by the aid of peroxide of manganese and sulphuric acid. It is a liquid of a deep blood-red appearance, solidify- ing at 4 F., and boiling at 113 F. Its specific gravity is 2-99. It exhales an orange vapor, and is commonly kept beneath the surface of water. Its smell is very dis agreeable, a circumstance from which its name is derived Like chlorine, it bleaches, and in all its relations possesses a general resemblance to that substance. A lighted taper burns for a short time in its vapor with a greenish flame Phosphorus burns spontaneously in it. Bromine yields a hydrogen acid (HBr], hydrobromic acid, and with oxygen, bromic acid (BrO^). In their gen- eral properties these bodies resemble the corresponding compounds of chlorine. The bromide of silver is much more sensitive to light than either the chloride or iodide. . FLUORINE, F= 18-74, is found in combination with calcium, as the fluoride of From what si urce is bromine obtained ? What are the properties of bromine, and to what bodies has it a close analogy ? 238 FLUORINE. calcium, or fluor spar. It occurs also in the topaz and other minerals. In the enamel of teeth and in bones it has been detected, especially in fossil bones, which sometimes contain as much as ten per cent, of fluoride of calcium. The special properties of fluorine are as yet unknown, for it has not been isolated. Various attempts have been made at different times, but without satisfactory results. It possesses an intense affinity for electro-positive bodies, and gives rise to a series of compounds resembling those of chlorine, iodine, &c. It does not unite with oxygen. HYDROFLUORIC ACID. HF= 19-74. This energetic acid may be obtained by decomposing fluoride of calcium by sulphuric acid in a vessel of platina or lead, the vapors being conducted into a metallic re- ceiver kept at a low temperature. The action is CaF + HO, 80,... = .. . CaO, SO 3 + HF. It is a smoking liquid, which acts powerfully on the skin, boils at a temperature of a little above 60 J F., and possesses the remarkable quality of corroding glass. If a piece of glass be coated over with a thin film of bees' wax, and letters or other marks made through the wax to the glass with a pointed implement, on setting it over a vessel of lead or tin in which, from a mixture of fluor spar and sulphuric acid, hydrofluoric acid is escaping in vapor, the glass is deeply etched on all those parts which have been uncovered, as is seen when the wax is removed. Liquid hydrofluoric acid may be employed for the same purpose, but the letters are not so visible as when the vapor is used. . CARBON. C = 6-04. This, which is one of the most interesting and import- ant of the elementary bodies, occurs under many differ- ent natural forms. It is an essential ingredient in the structure of all animal and vegetable beings ; it is found in various states in the air, the sea, and the crust of the earth. The striking peculiarity of carbon, which at once arrests our attention, is the different allotropic conditions under which it is presented. This substance may be said to yield Are the special properties of fluorine known ? How is hydrofluoric acid made ? What remarkable quality does it possess ? From what sources may carbon be procured ? What is its most striking property ? FORMS OF CARBON. 239 in itself a whole group of elementary bodies. Among these might be enumerated, (1.) Diamond, which crys- tallizes in octahedrons, is transparent, incombustible, ex- cept in oxygen gas, and the hardest body known ; hence its use in cutting glass. (2.) Gas-carbon, which, unlike diamond, is a good conductor of electricity, and is opaque. (3.) The various forms of charcoal, anthracite coal, and coke. (4.) Plumbago, which has a metallic lustre, is opaque, and so soft and unctuous that it is used to relieve the friction of machinery. (5.) Lampblack, a powerful absorbent of light and heat, and possessing such strong affinity for oxygen that it can take fire spontaneously in the air. Other forms of carbon might be cited ; these, however, are enough to establish the fact that this single body fur- nishes varieties which differ more strikingly from each other than many different metallic bodies. Charcoal is made by the ignition of wood in close ves sels, the volatile materials being dissipated and the carbon left. The nature of the process may be il- lustrated by taking a slip of wood, b, Fig. 241, and placing its burning extremity in a test tube, a. This retards the access of the surrounding air, and, as the combustion proceedsj a cylinder of charcoal is left. Fig- 242. Lampblack is formed on a similar principle. In the iron pot, a, Fig. 242, some pitch or tar is made to boil, a small quantity of air being ad- mitted through apertures in the brickwork. Imperfect combustion takes place, the hydrogen alone burning, the carbon being carried as a dense cloud of smoke into the chamber b c by the draft. In this there is a hood, or cone, of coarse cloth, d, which may be raised or lowered by a pulley. The sides of the chamber are covered with leather, and on these the lampblack collects. Diamond is the purest form of carbon. Its specific Mention some of its allotropic forms. How are charcoal and lampblack n;adf> .' 240 CARBONIC OXIDE. gravity is 3'5 : it exhibits a high refractive and dispersive action upon light. Charcoal possesses, in consequence of its porous structure, the quality of absorbing many times its own volume of different gases. Ivory black, which is made by the ignition of bones in close vessels, has the val- uable quality of removing organic coloring matters from their solutions : a property which may be shown by filter- ing a solution of indigo through it. In all its forms, car- bon-seems to be infusible, but when burned in air or an excess of oxygen, they all give rise to carbonic acid gas. It combines directly with several of the metals, yielding carburets. With oxygen it gives two compounds, CO ... CO 2 , de^jg&ated respectively as carbonic oxide and carbonic acid. CARBONIC OXIDE, CO = 14-053, is produced when carbon is burned in a limited supply of oxygen, or when carbonic acid is passed over red-hot iron, or over red-hot carbon. In these cases the actions are: * C0 3 +C ...... . 2(CO). COz+Fe ... ... CO + FeO. In the first the carbonic acid unites with one atom of carbon, and yields two of carbonic oxide ; in the second, it loses one atom of oxygen to the iron and yields one of carbonic oxide. . It may also be prepared by heating ox- r. 243. alic acid with oil of vitriol in a flask, a, Fig. 243, the decomposition giving equal volumes of carbonic acid and carbonic oxide, as is explained under oxalic acid. The acid may be sepa- rated by passing the mixture through a bottle, b, containing potash water, and the oxide collected over water. But the best process /or procuring it is to heat one part of prussiate of potash with ten of oil of vitriol in a retort : the carbonic oxide comes over in a state of purity. As obtained by any of these processes, it is a colorless What are the properties of diamond? What are those of ivory black? What are the oxygen compounds of carbon ? What is the action of car- bon and of metallic iron on carbonic acid at a red heat? How is carbonic txide produced from oxalic acid ? From what other substance may it be procured ? >.. :. : CARBONIC ACID. 241 gas, which may be kept over water, in Fig. 244. which it is only sparingly soluble. It is without odor, and is irrespirable. A jet of it burns in the air with a beauti- ful blue flame, combining with oxygen and yielding carbonic acid. Its specific gravity is 0*9722 : it has never been liquefied. It is the combustion of this gas which produces the blue flame oft- en seen in a coal fire. Carbonic oxide is a compound radical, giving origin to a series of bodies. LECTURE LIV. CARBONIC ACID. Methods of Preparation by Decomposi- tion and Combustion. General Properties, and Relation to Combustion and Respiration. Its Solution in Water. Exists in the Breath. Its Liquid and Solid Forms. Light Carbureted Hydrogen. Marsh Gas. Natu- ral and Artificial Production. Olefiant Gas. Action with Chlorine. CARBONIC ACID. CO* = 23-066. CARBONIC acid is commonly prepared by the action of dilute hydrochloric acid on chalk, or any carbonate of lime, the action being CaO, CO,i-HCl ... = ... CaCl,HO+CO,; that is, one atom of carbonate of lime and Fig. 245. one of hydrochloric acid yield one atom of chloride of calcium and one of water, and one atom of carbonic acid gas is set fred. The process may be conducted in a flask, as in the figure, the gas being evolved so rapidly that it may be collected over water, though that liquid absorbs it very freely. Carbonic acid is abundantly formed in many process- es. It is the result of the complete combustion of carbon- aceous bodies, is evolved during the respiration of ani- What are the properties of this gas ? How is carbonic acid gas made ? Tinder what circumstances is carbonic acid formed daring combustion 7 In what other processes does it appear? -A. 242 CARBONIC ACID. mals, arid in alcoholic fermentation. It is t\ie fixed air of the older chemists. It is a colorless and transparent gas at common tem- peratures, with a faint smell and slightly acid taste. It is irrespirable, and acts in a diluted state as a narcotic pois- on ; even air, containing one tenth of its volume of this Fig. 246. gas, produces a marked effect. Its specific gravity is 1-527, and it may, therefore, be collected by displacement (Fig. 246). For the same reason, it collects in the bottom of wells and pits, and often suffocates work- men who descend into such places. It does not support combustion ; a lighted taper lowered into a * 247 J ar partly filled with it is extinguished the mo- merit it reaches the gas (Fig. 247). It may be poured from one vessel to another, and if a jar of it is poured upon the flame of a candle, the light is at once extinguished. Its density and other qualities may be well illustrated when it is formed by the action of fuming nitric acid on carbonate of ammonia, a smoky cloud marking its position and movements. Carbonic acid reddens litmus water, but the blue col- or is restored on boiling, the acid being driven off by the heat. It is soluble in water, which, under in- creased pressure, takes up several times its volume of it, constituting the soda water of the shops. Its solubility may be established by agitating it with water in Hope's eudiometer, Fig. 248, or by passing it through Nooth's soda-water machine, Fig. 249. A common test for the presence of car- bonic acid in wells is to lower a lighted candle, and if its flame be extinguished, it is inferred that the gas is present ; but it does not fol- low that a man may safely descend into such places though a candle will continue to burn. What are its properties? What are its relations to combustion? What is its specific gravity ? What is soda water ? How may carbonic acid be detected ? CARBON AND HYDROGEN. 243 If, through a tube, the breath be made to pass into lime-water, a deposit of carbonate of lime renders the water milky ; or, if the breath be conducted through lit- mus water, the color changes to red ; the air thus expired from the lungs contains three or four per cent, of carbonic acid. Under a pressure of thirty-six atmospheres, carbonic acid condenses into a liquid characterized by the extraordinary quality that it is four times more expansible by heat than even atmospheric air. This liquid, when allowed to es- cape through a jet, evaporates so rapidly, and produces so much cold, that a portion of it instantly solidifies. Solid carbonic acid is a substance not unlike snow ; mixed with alcohol or ether, it produces a degree of cold equal to 180 Fahr. Although carbonic acid has the name of an acid, it pos sesses the properties indicated by that term in a feeble degree. The gas contains its own volume of oxygen. The common test for its presence is lime-water, which is rendered turbid by it. CARBON AND HYDROGEN. These substances unite, producing many compounds, some of which are solid, some liquid, and others gaseous* . They are of course all combustible bodies, and the de"" scription of nearly all of them belongs to organic chem istry. LIGHT CARBURETED HYDROGEN, CH 2 = 8-04, occurs abundantly in coal mines, and forms with their atmospheric air explosive mixtures ; it is also found dur- ing the putrefaction of vegetable matter under wate:r ; on stirring the mud of ponds, bubbles of this gas escape; hence the name marsh gas. It may be obtained artificially by heating acetate of potash with hydrate of baryta. (KO) + (C!uimu of cuuntio biiiyiu niiiy bo nhluinod by boiling with llm oxiduit of loud or rn|>|>fi. iiinl ;.i'|i,ii .il III", lln- HulphlirotH "I tllONO lllOtlllN by lillnilion, By acting upon it with hydrochloric. or nitric acid, ill-- . iil.'M.I. or mi i .id- of burytu luuy ! prepared. :-, \|/|',l in- 1 1'imTUXIhK OK Ii Mill M ('/' Ihtrt/fd IN ibtind imtivo, UN ilu> ininnrul WitheHtt* mid iniiy bd prepared by prdolpitating iiNolu bio null of biirytu with mi iilknlino (Mirbonuto. It IN NO!II- blo iu 4!)()U timM iti Wpiglit of cold wutor, und XJ.'HX) of boiling vvutor. tiuijiJutfr ttf Haryta, ibund nutivo iibuiuliiiitly a hrany fi/>in , und iVoin it mi.,-, i of tho OOtOttOUndl of Curium uro tH'wpurod, It in cullod huiivy npur, HH douNity lining 4 f -17. It cryHtnlli/oN gonomlly in tubular pluton, und in wholly in wutor. IJOCJTUllK LIX. STUONTHTM. U*c in P-yrotroJiny. Malta of Protoxide. , CALCIUM. Protoxide vj\ Sourcct in Naturr* 2V#/ j\ trt Unfold Cofkpounii, CMondv t Wuoridc t /ilnitf. Aiii/MiNi'M. SuyuitwicUt'UMt in the Aft*. 7V.\7.v. Salt* of the *SV,v;//V>.nWr, ])oul*le tfuljt/iatv, Alum. Alttnu/iti'tttrt of Porcelain and (flitM.Ot/trr Mr.tals. HTJIONTITIM. /?* 43-, f l'n IN inotul inuy b ubtuinod by tho wainn jirocoHHOK \vhirh hiivo IHMMI unod for obtutnitig buriuiri, with \vhich it him u oonfidePlble urrulo^y, It M nuini -il conipoundn uro tho Hul|ihiito und ourbonuto, from which its otltmr prvpurn- tiotlM ni.ty bo oblninctl, Strontiuin yiohln n protoxide, which 'in tho IMIIUH of u of Hulls, dillri in!- from burytu Htilta in not being How inny tlio mili'luii.' nl ImrvU'H l I'Onvorlwd Into tl' ul|iliurt (( iwrlum? Wlml MW tUi< |ini|inril(Hl nl 1 tlio Il< f TIIK J'KOTOMDIC OK HTIIONTIH M ( \iiln>nl'^tn>ntiti in llm .\ht>n(ittuil<- <>!' tniiu i .il"- i i i^ul nltdtt* of tftt'otitid. in llm n'/i'n/i/K 1 o!' iiiuuM'iilo^iHlM. It in not N IK M\ \ .IM milpliiiln of liiirylu, niul in Miiio! to Im Hollllllo ill llhoill IIMIII linn ||;l \Vi
  • lll . . I I .. . 1 1 1 MI{ Wllttll'. filtrate ttf tftrtmttti ionim DM iiigrudicint of tint rod firo ii < .1 in ihcni i I'M ; ii < i \ ,i ,i Ih .< in ortiilmdroiiN, mid in H.illlhln in liv IIIIM-M i! . \\ i p-lil iif . ..I.I \\ .il. i .iii.l Ii ill il ( wtMghi !' lioiling wttttir. ALOIUM, Ca m OO'fl. ( ' \i rii \i li.n n< \. i lin< Mini M lull <\ .limn. ii i< I ii^ pi'oiMirl icirt. It. oxydi- zt)H with rapidity, yielding u protoxido, known ulno UK lull I. hum or lima. Limn ... . in UN a cnrlwnntn in tlm vnrioun liuoitonpl, miirl)l . , h ilkn, &c,, whirli lorm in miiiiy countrUn ox toilMivr ill. MM, I. nil rilli-v Il "lli, i .ill .,i. \i y .il.im.l mil l''rom thn rurboiiiifn, jmrn or oiiiflJiiim nmy Im nit. tfiiimd liy nxpoHiiro to u liri^lit rod ntntt. 1 1' llm IIIIK^IOIIO contHiiiN Hilicrt, it may, liowovor, bo <;w/7>w/v//, n, wilic-nio nfTmin liii'iuiii^, which jirovtuitH tlio product from h, I u, II |M. ( .-.-I ;i rilroni' ulliiiily I'm \V(ilT, nn.l iiiiih-M Him,' \\iili \\iili .1 "i.-.ii rlnviitiuii of tdinporiUuro, IIH nxliiliilnd in tho prociiHN l< .1 |. , , !' :i 1 1 u I 1.1 1 1 \ .in I i. l.i I. . in nl i .ih /. .i.i.l |.< i |',c| |y, I'M, :.| > IM i , -,l, I, -I if, I III mir-. Hi M Mf (Mil Of, 1 1 IM llMnd UN Ii Irrtl. lor ciulMHiic, acid, vvilli \\ In. 1 1 1 1 fivi 1 1 if u liiif rnr. Wlml. IM thn itiliir H ttiN ! HuiiinT Whtil, im Mitt iiiluniliK- I. nl Illllll. 'M nf l ; I nl. Mill! Nlllj.l. .1. '.I Mil? VVlllll, ir, In,.. ' Uli,|,U' wliul. I'linnn l... .1 ' I.IIPI ' I 1 i. .... ill I i, I,. Unit* l>n | ,1 / \vi.ui HI Hi. ,, ,,| win. 'i on il. I VVIitiL uro tll ,,!,:,,, Mi, ,, ..I Im.. \vnli-rY 268 COMPOUNDS OF CALCIUM. bonate of lime. Cream of lime is nothing but lime-water in which hydrate of lime is mechanically suspended. The hardening of lime mortars depends chiefly on the absorp- tion of carbonic acid. Hydraulic lime possesses the qual- ity of setting under water. It contains oxide of iron, alumina, and silica. Lime is best detected by oxalate of ammonia, with which it gives a white precipitate of oxalate of lime, pro- vided the solution be not acid. Among other compounds of calcium may be mentioned Chloride of Calcium, CaCl=55'97, formed by dissolving carbonate of lime in hydrochloric acid, evaporating the solution to a sirup, and, on cooling, the chloride crystallizes. It is exceedingly deliquescent. Chloride of calcium, dried without crystallization, is used in organic analysis for collecting water, and, generally, in other chemical operations for drying gases. Fluoride of Calcium, CaF=39'24:, called, also, fluor spar, and frequently found as a mineral associated with lead. Crystallizes in cubes, octahedrons, &c., of various colors. It is found in fossil, and, to a smaller extent, in recent bones. It is used for various or- namental purposes, and is the source from which the com- pounds of fluorine are derived. Sulphuret of Calcium, CaS=:36'Q2. obtained by igniting the sulphate of lime with charcoal, and constitutes Canton's phosphorus, commonly made by igniting oyster shells with sulphur ; possesses the curious quality of shining in the dark, after a brief exposure to the sun or to the rays of an electric spark. SALTS OF THE PROTOXIDE OF CALCIUM. Carbonate of Lime is abundantly found in nature, form- ing whole ranges of mountains, the limestones, marbles, &c., of mineralogists. It occurs pure in the form of Ice- land spar, in rhomboidal crystals, possessed of double re- fraction. It is dimorphous, assuming the form of six-sid- ed prisms, as in the mineral called Arragonite. It is an- What is milk of lime ? For what purposes is the chloride of calcium used ? Under what forms does fluoride of calcium occur ? What sinsu- lar quality does the sulphuret of calcium possess ? What are the dimor- phous forms of carbonate of lime ? ^ > MAGNESIUM. 269 hydrous, insoluble in wate*, but in water charged with carbonic acid it is soluble, and is deposited from such a liquid on boiling, or by the diffusion of carbonic acid into the air. The carbonic acid is expelled from this salt by a red heat, and the action of the more powerful acids. Carbonate of lime may be obtained in union with water, by boiling hydrate of lime with a solution of sugar. Sulphate of Lime Gypsum occurs native, both in crystals, the primary form being a rhombic prism, and also in extensive crystalline masses. '.It contains two atoms of water ; there is a variety, however, passing under the name of anhydrite, which contains no water. On calcining the hydrous sulphate of lime at a low red heat, it becomes plas- ter of Paris, and has the property of setting into a hard mass when made into a paste with water. The sulphate of lime is soluble in 500 parts of boiling water, and often occurs in the water of springs, to which it communicates hardness. Phosphate of Lime Bone-ear tJi Phosphate is one of the tribasic phosphates ; it is precipitated when earth of bones is dissolved in muriatic acid, and the solution neu- tralized by ammonia. Chloride of Lime BleacJiing Powder is made b.y ex- posing hydrate of lime to chlorine. It is a white pow- der, exhaling a faint odor of chlorine, and is used exten- sively as a bleaching agent. MAGNESIUM. Mg = 127. MAGNESIUM may be procured by igniting a mixture of chloride of magnesium and sodium in a porcelain cruci- ble ; the chloride of sodium forms, and magnesium is set free. The chloride may be dissolved by water. It is a white, malleable metal, which melts at a red heat, and, with excess of air, oxydizes, forming Protoxide of Magnesium . Mg O = 2 7 1 3 . This substance, called, also, calcined magnesia, or sim- magnesia, may be made by heating the carbonate to w redness ; the carbonic acid is driven off, and the mag- nesia remains as a white powder, insoluble in water, but Under what circumstances is it soluble in water ? Under what forms does sulphate of lime occur, and for what purposes is it used ? In what does the phosphate of lime occur ? What is bleaching powder ? How is magnesium obtained ? "What are the propeities of it ? Under what names does the protoxide pass ? Z 2 ply lo 270 SALTS OF MAGNESIUM. neutralizing acids completely and forming with them a complete series of salts. Magnesia occurs very abundantly in nature, often asso- ciated as a carbonate with carbonate of lime, as in dolo- mitic limestone. It also occurs in fertile soils, and is es- sential to the growth of certain plants. It is well distinguished from all the foregoing alkaline earths by the relation of its sulphate. The sulphates of baryta, strontia, and lime form a series of salts, the solu- bility of which, in water, is constantly increasing ; to these the corresponding magnesia salt may be added ; it is very soluble. Magnesia is precipitated from its sulphate by the caus- tic alkalies, and by the carbonates of potash and soda as a carbonate, but not by the carbonate of ammonia in the cold. It may be detected by adding carbonate of ammo- nia and phosphate of soda in succession, when the phos- phate of magnesia and ammonia is precipitated. Heated before the blow-pipe, after having been moistened with nitrate t)f cobalt, magnesia becomes of a pinkish color. SALTS OF THE PROTOXIDE OF MAGNESIUM. Carbonate of Magnesia is found native, and may be prepared by boiling the sulphate with an alkaline carbon- ate, diffusing the precipitate in water, and passing a stream of carbonic acid through it ; by spontaneous evap- oration the carbonate of magnesia is deposited in crystals The carbonate of magnesia, the magnesia alba of the shops, is prepared by precipitating the sulphate of mag- nesia with the carbonate of potash ; it occurs in light white cubical cakes, or in powder, and is not a true car- bonate, for it does not contain a full equivalent of carbonic acid. It is said to be a compound of one atom of hydrate of magnesia with three atoms of hydrated carbonate of magnesia. It is very slightly soluble in water. Sulphate of Magnesia Epsom Salts of commerce is produced by the action of dilute sulphuric acid on magne- sian limestone. Its crystals are small four-sided prisms, soluble in an equal weight of cold and three fourths their weight of boiling water, the solution having a bitter taste. A. low heat expels six out of the seven equivalents of the combined water. What is dolomitic limestone ? How may magnesia be detected ? How is its carbonate prepared ? Of what is Epsom salt composed ? ALUMINUM. 271 Phosphate of Magnesia and Ammonia, one of the vari- eties of urinary calculus, may be formed artificially when a tribasic phosphate, a salt of ammonia, and a salt of mag- nesia are mixed together. Magnesium is the last of the alkaline earthy metals. Its history completes that of our first group of metallic bodies. At the head of the second group we find aluminum, the first of the earthy metals. ALUMINUM. ^^13-7. Obtained, by Wholer, by the action of sodium on the chloride of aluminum, being the same process as that given for the preceding metal. It is a gray powder, which melts beneath a red heat ; takes fire when heated in air, producing Sesquioxide of Aluminum. AI Z O 3 =51'539. This oxide, called, also, alumina and clay, occurs nat- urally under certain forms, which are highly prized, as the ruby and sapphire. In a more impure condition it yields the various common clays, which also contain silica or metallic oxides, or other extraneous bodies. Alumina may be prepared from the sulphate of alumina and potassa, common alum, by precipitating the sulphuric acid by chloride of barium. The sulphate of baryta goes down, and there is left in the solution chloride of po- tassium and chloride of aluminum. When the mass is dried, water is decomposed ; hydrochloric acid is then ex- pelled, and alumina, mixed with the chloride of potassium, remains behind ; the latter is to be dissolved away by wa- ter, leaving the alumina as a white substance, which, with water, forms a plastic mass, capable of being moulded, and retaining its shape when baked. After ignition, it adheres to the tongue, and during the act of drying it con- tracts considerably in volume, a property which formerly gave rise to the invention of Wedgewood's pyrometer. The presence of alumina gives to the clays those prop- erties which fit them for the purpose of the potter and brickmaker. Alumina is also used as a mordant to fix the colors of certain dyes upon cloth. In what form is the phosphate of magnesia and ammonia sometimes found ? How is aluminum prepared ? What is the constitution of its ox- ide ? Under what natural forms does it occur ? How may alumina be prepared? What principle is involved in Wedgewood's pyrometer? What is meant hy a mordant ? 272 PORCELAIN. EARTHEN-WARE. GLASS. Alumina is precipitated from its solutions by fixed al- kalies, which yield a white hydrate of alumina, soluble in an excess of the precipitant. It is also thrown down by alkaline carbonates ; and, when these precipitations are made in a solution tinged with coloring matter, the alu- mina carries it down with it. Such colored precipitates pass under the name of lakes ; and it is this property of attaching such colors to itself, enabling it to cause their firm adhesion to cloth fibre, which is the principle of its application as a mordant. Among the purposes to which alumina is applied may be mentioned the manufacture of PORCELAIN, and the dif- ferent kinds of earthen-ware. The former substance, first made by the Chinese, is very compact and translucent. It consists essentially of clay mixed with a fusible body, which binds all its parts together, and is covered with a glaze, which does not terminate abruptly on the surface, but pervades the substance of the mass. In this respect it differs from common earthen-ware. Feldspar, or the silicate of lime, are bodies suitable for communicating this glassy structure. In the manufacture of porcelain, great care is taken to select clay free from iron. It is mixed with powdered quartz and feldspar, and the requisite shape given it either by the potter's wheel, or by pressing it into moulds. It is then dried in the air, and more perfectly in a furnace, and, when ignited, forms biscuit. This is dipped in the glaze, suspended in water, and becomes covered over with a uniform coat of it. It now remains to dry it once more, and fuse the glaze upon it. EARTHEN-WARE consists of a white clay mixed with sil- ica. It is glazed with a fusible material containing oxide of lead, and colored of different tints by metallic oxides ; for example, blue by cobalt. Connected with the manufacture of pottery, may also be mentioned the manufacture of GLASS, of which there are several varieties, some consisting of silica, potash or soda, and lime, others containing a large quantity of oxide of lead. If silica be heated with carbonate of potash and lime, or oxide of lead, carbonic acid is expelled, and glass How may the presence of alumina be recognized ? What are lakes ? What substances are used in the preparation of porcelain and earthen ware ? How \ glass made ? SALTS OF ALUMINUM. 273 forms. The mass is kept in a fused condition till it is free from air bubbles, and is then cooled until it becomes plas- tic, so that it may be blown or moulded. Articles of glass, after they are manufactured, require to be annealed or slowly cooled down. This allows their parts to assume a regular structure, and prevents excess- ive brittleness. Soluble glass is formed when silica is heated with twice its weight of carbonate of soda or potash. It derives its name from the fact that it is for the most part soluble in water. SALTS OF THE SESGUJIOXIDE OF ALUMINUM. Sulphate of Alumina is made by dissolving alumina in dilute sulphuric acid. It enters into the composition of the alums. Sulphate of Alumina and Potash Alum. This import- ant salt is prepared from alum slate. It crystallizes in octahedrons, has an astringent taste, reddens litmus paper. It dissolves in about eighteen times its w r eight of cold, and less than its own weight of boiling water. It contains twenty-four atoms of water, and, when exposed to heat, foams up, melting in its own water, which, being evapo- rated away, leaves a white porous mass, commonly called burnt alum. In the same way that the sulphate of potash unites with the sulphate of alumina, so, also, do the sulphates of am- monia and of soda, forming respectively the ammoniacal and soda alums. The alumina in the common alum may be replaced, also, by the sesquioxides of iron, manganese, or chromium, giving iron, manganese, and chrome alums. The following metals, GLUCINUM, THORIUM, YTTRIUM, ZIRCONIUM, LANTHANIUM, and CERIUM, are very rare bod- ies, and, being of little interest, may be passed over with- out farther notice. Why mast it be annealed ? What are the properties of the sulphate of alumina and poUash ? 274 MANGANESE. LECTURE LX. MANGANESE. Its Seven Oxides. The Peroxide and its Applications. Mineral Chameleon. Acids of Manga- nese. Salts of the Protoxide. IRON. Its Natural Forms. Reduction on the Great Scale. Cast Iron. Wrought Iron. Steel. Passive Iron. MANGANESE. jtf = 27-7. MANGANESE may be procured by igniting its oxides with a mixture of lampblack and oil in a powerful furnace, the reduction being somewhat difficult. It is a white metal, specific gravity 8'013, requiring a white heat for its fusion, and oxydrzing readily in the air. It is remarkable for the number of oxygen compounds which it yields ; they are MnO . . . Mn,O z . . . MnO, . . . MnO 8 . . . Mn^O, . . . designated respectively, Protoxide of manganese. Sesquioxide of manganese. Peroxide of manganese. Permanganic acid. Red oxide of manganese. Varvicite. Manganic acid. Of these, the protoxide may "be made by passing hydro- gen gas over red-hot peroxide of manganese. It is of a green color, is a basic body, and forms a series of salts, of which the sulphate is used in dyeing. It is isomorphous with magnesia and zinc. Hydrosulphuret of ammonia yields with it a flesh-colored precipitate, ferrocyanide of potassium a white, and the chloride of soda a dark brown hydrated peroxide. The sesquioxide is made by igniting the peroxide, as will be presently explained. The red oxide and varvicite occur as minerals ; but of the whole series the peroxide is by far the most valuable. Peroxide of Manganese, Mn0 2 =4 c 3'726, is found abundantly as a mineral, and passes in commerce under the name of black oxide of manganese, a name in- dicating its color. It is insoluble in water, and when ex- posed to a red heat gives off one fourth of its oxygen, forming the sesquioxide, as stated above, the action being How may manganese be obtained? What are its properties? How many oxides does it furnish ? How may manganese be detected ? What is the constitution of the peroxide ? COMPOUNDS OF MANGANESE. 275 2(MnO,) ... =r ... Mn. 2 O 3 + O. On this fact is founded one of the processes for obtaining oxygen gas. Heated with hydrochloric acid, it yields chlorine, as has been explained. It was formerly called glassmakers' soap, from the circumstance that it removes, when added to melted glass, the stain of protoxide of iron, by turning it into peroxide, and causes the glass to become colorless ; but if too great a proportion of per- oxide of manganese is used, the glass assumes an ame- thystine color. Peroxide of manganese, when ignited with caustic pot- ash in a platina crucible, yields a substance known as Mineral Chameleon, which is of a green color. Water dissolves from it the Manganate of Potash, which is of a beautiful grass green, the solution speedily passing through a variety of shades of purples, blues, and reds. As yet, manganic acid is a hypothetical compound, and has not been insulated. When mineral chameleon is dissolved in hot water, a red solution is obtained of the Permanganate of Potash ; from the permanganate of ba- ryta a crimson solution of Permanganic Acid may be pro- cured by the aid of sulphuric acid ; but permanganic acid can not be obtained in the solid form. Among other compounds of manganese, the following may be named : Protochloride of manganese MnCl = 63*15. Perchloride " Mn^Cli = 303'19. Perfluoride " " MmFli = 186-46. The protochloride may be made by acting on the per- oxide with muriatic acid, evaporating to dryness, and fusing at a- red heat. On digesting with water, the proto- chloride dissolves, and any impurity of iron is left in the state of oxide. Then, by crystallizing, the chloride can be obtained in pink crystals. The perchloride is pro- duced when permanganate of potash, common salt, and sulphuric acid are heated. It is a dark greenish and volatile liquid. The perfluoride is obtained by distilling sulphuric acid, permanganate of potash, and fluor spar; it is a greenish yellow gas. What color does it give to glass ? How is mineral chameleon made ? What are its properties 1 Can manganic acid be insulated ? How may the chlorides of manganese be formed ? What are the properties of the fluoride ? . 276 IRON. , SALTS OF THE PROTOXIDE OF MANGANESE. Protosulphate of Manganese, formed by dissolving pro- toxide of manganese in sulphuric acid. The figure of its crystals depends on the temperature at which they were formed. They have a rose-colored tint. It is insoluble in alcohol, very soluble in water, and is used by the dyers to produce a fine brown color. There is but one sulphuret of manganese. It is ob- tained as a hydrate when manganese is precipitated by hydrosulphuret of ammonia (MnS, HO). It is of a flesh- red color. IRON. Fe = 28-00. IRON sometimes occurs in a native state and as mete- oric iron, also as oxide, carbonate, sulphuret, &c. It is one of the most abundant of the metals. Much of what is found in commerce is derived from clay iron-stone, which is an impure carbonate containing silica, alumina, magnesia, and other foreign substances. The native per- oxide of iron, red haematite ; the hydrated peroxide, brown haematite ; the black oxide, or magnetic iron ore, furnish some of the finer varieties of the metal. From clay iron-stone metallic iron is procured by the action of carbonaceous matter and lime at a high temper- ature. The ore, having been roasted, is thrown into the furnace with coal and lime. If the iron i-s in the ore as a silicate, the lime decomposes it at those high temperatures, forming a slag of silicate of lime, and the oxide of iron set free is instantly reduced by the carbonaceous matter ; the metal sinking down, protected by the slag, is let off by opening a hole in the bottom of the furnace. The substance thus produced is not pure iron ; it con- tains carbon and other 'impurities, and passes under the ***me of cast or pig iron. It is purified by melting and nudden cooling, which converts it into fine metal ; this tine metal is then melted under exposure to air, which burns off the carbon as carbonic oxide, and the mass, from being perfectly fluid, becomes coherent. It is now subjected to violent mechanical action, such as hammer^ ing or rolling ; this forces out or burns off the impurities, What is the formation and use of the protosulphate of manganese ? What are the forms under which iron chiefly occurs ? How is it obtain- ed from clay iron-stone? What is cast iron? By what processes is it inverted into wrought iron ? IKON. 277 increases its tenacity, and it becomes the wrought iron of commerce. Cast Iron melts readily at a bright red heat, and expands in solidifying . on this depends its valuable application for making castings. Kept under the surface of salt water for a length of time, cast iron becomes converted into a body somewhat like plumbago, due, probably, to the removal of the iron as a chloride ; the carbon which is left behind is sometimes observed, as it dries, to become hot : a phenom- enon to be accounted for by its porous state. These facts have been frequently verified in the case of cannon which have lain for years at the bottom of the sea. There are two forms of cast iron, white and gray ; the former con- tains about five per cent, of carbon, the latter three or four. Pure Iron may be obtained by decomposing precipitated peroxide of iron by hydrogen gas, and melting the result. The metal has a bluish color, is more ductile than mallea- ble, and is the most tenacious of all bodies. It becomes very soft at a red heat, and possesses the welding property ; on this depends the art of forging it. Its specific gravity is 7*7. It is one of the few magnetic bodies, and, when soft, its magnetism is so transient that it may gain and lose that quality a thousand times in a minute. The melting point of iron is very high. In the mode of preparing it from cast iron it does not undergo the process of fusion, but its particles are simply welded together. The fibrous struc- ture which wrought iron possesses is the chief cause of its great tenacity; a wire -^th OI * an mc ^ m diameter will bear a weight of 60 pounds. Steel, which is a valuable preparation of iron, is made by placing alternate strata of iron bars and charcoal pow- der in a close box and keeping them red hot. The pro- cess is known by the name of cementation. The iron gains about 1/5 per cent, of carbon. Steel is much more fusible than iron, and becomes excessively hard and brit- tle by being brought to a red heat and then suddenly quenched in cold water. When allowed to cool slowly, it is quite soft, and various degrees of elasticity and hard- ness may be given to it by the process of tempering. By placing a piece of platina in nitric acid of a specific What are the properties of cast iron? What changes does it undergo under water? How may pure. iron be obtained? What are its proper ties ? What is steel ? How is it made, and what are its properties f A A 278 OXIDES OF IRON. gravity of 1*34, and then bringing an iron wire in contact with it and withdrawing the platina, the iron assumes a passive or allotropic state. It now exhibits no tendency to unite with oxygen, cannot precipitate copper from its solutions, and simulates the properties of platina and gold. LECTURE LXI. IRON. Oxides of. Three Oxides and Ferric Acid. Tests for Iron. Salts of the Protoxide and Peroxide. The Sulphurets. NICKEL* Its Reduction from the Oxalate. COBALT. Smalt. Zaffre. Sympathetic Ink. ZINC. Distillation of. Salts of the Protoxide. - IRON AND OXYGEN. IRON burns with rapidity in oxygen gas, as may be Fig. 263. proved by igniting a piece of it in wire coiled into a spiral form in a jar of that gas (Fig. 263), when it will be found to take fire and burn beau- tifully. In atmospheric air, under favorable cir- cumstances, the combustibility of this metal may be proved. Thus, fine iron filings, sprinkled in the flame of a spirit lamp, burn with scintilla- tions ; exposed to air and moisture, it slowly rusts. Iron yields four oxides : Protoxide .... FeO = 36-013. Black oxide . . . Fe 3 O 4 = 116-052. Peroxide . . . . Fe 2 O 3 = 80;039. Ferric acid .... FeO 3 = 52-039. Protoxide of Iron. FeO=36'Ol 3. This oxide has not yet been insulated, but it exists, united with acids, in an extensive series of salts, from which it is thrown down as a hydrate by alkalies, and is then of a white color, which darkens as it passes into the state of peroxide. Ferrocyanide of potassium gives a white precipitate, and the ferridcyanide a deep blue. Hy- drosulphuret of ammonia gives a black sulphuret of iron. Sulphureted hydrogen and gallic acid give no precipitate. How may iron be rendered passive ? How may the rapid oxydation of iron be illustrated ? How many oxides does this metal yield ? What are the reactions which the protoxide furnishes with tests ? OXIDES OF IROX. 279 Black Oxide of Iron. Fe 3 O, = 116'Q52. This oxide, known also as the magnet or loadstone, is found as a mineral. It is a compound of the protoxide and peroxide. The scales of iron found in blacksmiths' forges mainly consist of it. It may also be produced by decomposing the vapor of water by metallic iron in a red- hot tube. Peroxide of Iron, JPe. 2 O 3 =80'039, is found in nature as oligist iron, or as a hydrate. It may be produced artificially as a hydrate by precipitation from a solution of persulphate of iron by a caustic or carbona- ted alkali, or in a pure state by igniting green vitriol; there is then left a red powder, known as rouge, used for polishing metals^ This oxide is not magnetic ; it is the basis of a series of salts which yield, with alkalies, a brown hydrated peroxide; with ferrocyanide of potassium, Prus- sian blue ; with sulphocyanide of potassium, a blood-red solution ; with tannin a-nd gallic acid, a black. This last is of considerable interest, constituting the basis of ordi- nary ink. The presence of iron can always be determined by passing it into the condition of peroxide, and applying the foregoing tests. Ferric Acid, FeO 3 = 52'Q39, is prepared by heating peroxide of iron with four parts of nitrate of potash. The result is treated with cold water, which yields a red solution of the ferrate of potash. This slowly decomposes in the cold, and very rapidly when the solution is warm. The ferrate of baryta precipitates when the potash solution is acted on by a soluble salt of baryta. It is a permanent body, of a crimson color. Among other compounds of iron, the following may bo named : Protochloride of iron Fed 63'47. Perchloride " Fe 2 Cl 3 162-35. Protiodide " Fel = 153-57. Protosulphnret " FeS 44-12. Sesquisulphuret " Fc*S 3 =104-36. Bisulphuret " . . ; t ,. . Fe~S 2 = 60-24. Under what natural forms does the black oxide occur? How may it be formed artificially ? What are the natural forms of the peroxide ? How may it be prepared 1 For what purposes is it used ? What is its action with reagents ? What is common ink? How may the presence of iron be detected ? What are the properties of feYric acid ? Of the other com- pounds, mention some of interest. 280 SALTS OF IKON. Of these, the protochloride is formed by passing hydro- chloric acid over red-hot iron. It is white, but forms a green solution in water. The perchloride, in solution, by dissolving* peroxide of iron in hydrochloric acid. The protiodide, by boiling an excess of iron filings with idine, and evaporating ; it forms, on cooling, a dark gray mass. Its solution absorbs oxygen from the air. The protosul- phuret of iron, which is much used for forming sulphuret- ed hydrogen, may be made by heating a mass of iron to a white heat, and applying to it roll sulphur, and receiv- ing the melted globules in a bucket of water. It may also be procured by igniting iron filings with sulphur. The bisulphuret occurs abundantly as a mineral of a gold- en yellow color, crystallized in cubes or allied forms, and known as Iron Pyrites. It frequently assumes the form of various organic remains, being one of the common petri- fying agents, but in this state differs essentially from the cubic pyrites, both in color and oxydizability, these fossil remains rapidly decaying under exposure to the air, but the other form being unacted on. Besides these, there is a^ulphuret of iron which is magnetic. SALTS OF THE PROTOXIDE OF IRON. Carbonate of Iron may be obtained from the sulphate by an alkaline carbonate, falling as a whitish precipitate. ' It turns brown, however, from the absorption of oxygen. It occurs as a mineral in spathic iron, and dissolves in water containing carbonic acid, forming chalybeate waters. Protosulphate of Iron Copperas Green Vitriol is prepared largely by the oxydation of iron pyrites, and crystallizes in oblique prisms of a grass green color. It has a styptic taste, dissolves in twice its weight of cold, and three fourths its weight of boiling water. It contains five atoms of water. At a low red heat it becomes anhy- drous. In this state it is used for the manufacture of the Nordhausen sulphuric acid. SALTS OF THE PEROXIDE OF IRON. Persulphate of Iron may be formed by adding to a so lution of the protosulphate of iron half an equivalent of sulphuric acid, and peroxydizing by nitric acid. With water it forms a red solution. What is iron pyrites ? What is the difference of its forms ? How is the carbonate of iron formed ? What is the process for preparing the sul- phate ? How is the persulphate obtained ? NICKEL AND COBALT. 281 NICKEL. A T i = 29'5. NICKEL may be obtained by igniting its oxalate in a cov- ered crucible, carbonic acid escaping, and the metal being reduced. NiO+C 2 O 3 ...=... Ni+2(COJ ; one atom of the oxalate of nickel yielding one of the met- al arid two of carbonic acid gas. Nickel is a white metal, requiring a high temperatura for fusion. It is magnetic, and has a specific gravity of 8'5. .It is c6mmonly associated with. iron in meteorites, and enters into the composition of German silver ; unites with oxygen, forming a protoxide and sesquioxide, the former yielding salts of a green color; the latter is an in different body. SALTS OF THE PROTOXIDE OF NICKEL. Sulphate of Nickel crystallizes from its solutions witk six atoms of water in slender green prisms, which, when exposed to the sun, change into an aggregate of octahe drons, becoming opaque. Nickel is chiefly used in the preparation of German silver, an alloy of copper, zinc, and nickel. It is of a white color, takes a good polish, and is malleable. COBALT, Co = 29-5, is generally associated with iron and nickel, and with them occurs in meteoric iron. Like the preceding metal, it may be obtained by igniting its oxalate in a covered crucible, carbonic acid being disengaged and metallic cobalt left. It is a pinkish white metal, requiring a high temperature for fusion. Its specific gravity is 7*8. ll is magnetic, as recent experiments have proved. It forms a protoxide and a sesquioxide, the former being the basis of a class of salts which are chiefly of a pink or blue col- or. 'Smalt is a silicate of cobalt, and Zaffre an impure oxide ; the former is used to communicate to paper a faint blue tinge, and the blue color which the oxide gives to glass is taken advantage of in coloring the common vari- eties of earthen- ware. Cobalt is easily detected upon this principle. By what process is nickel obtained ? What are its properties ? Under what remarkable circumstances does it occur with iron? What change does the sulphate of nickel undergo in the sunlight? How is cobalt pro- cured? Is it magnetic like nickel ? What is smalt? What is zaffre t What are the uses of cobalt ? A A2 282 ZINC. The chloride of cobalt may be made by dissolving the oxide or the metal in hydrochloric acid. It is a pink solution, which turns blue when dried. It forms a beau- tiful sympathetic ink, for letters written with it, especially on paper which has a pinkish tinge, are entirely invisible, but become of a bright blue color when the paper is warmed, the letters again fading as they become cool and moist. ZINC. Zn = 32-3. ZINC is a very abundant metal, immense quantities of it occurring in the state of New Jersey and in various Fig. 264. other places. From zinc blende, which is a sul- phuret, converted by roasting into an oxide, or from the carbonate brought into the same state by ignition, the metal may be obtained by the process of distillation by descent. The ox- ide, mixed with charcoal, is introduced into a crucible which has an iron tube passing through a hole in its bottom, as seen in Fig. 264, and the lid being luted on, the temperature is raised to a white heat, and the zinc, distilling over, may be condensed in water. Zinc is a bluish- white metal, which melts at about 770 F., and, if exposed at a bright red heat to the air, takes fire and burns with a brilliant pale green flame. Its spe- cific gravity is about 7-00. At common temperatures it is brittle, but it may be rolled into thin sheets at about 300 F., and then retains its malleability when cold. During its combustion there arises from it a great quantity of flocculent oxide, which formerly went under the name of nihil album, or philosopher's wool. Among the com- pounds of zinc may be mentioned Protoxide of zinc ZnO = 40-313. Chloride " ZnCl = 67'75. Sulphuret " ZnS == 48'4. Of these, the oxide is formed, as has been said, during the combustion of zinc. It is also precipitated as a white hydrate from its soluble salts by potash or soda, soluble in excess of the precipitant. The chloride may be made by the action of hydrochloric acid on metallic zinc. It is What property does the chloride possess ? By what process is zinc ob- tained ? Is there any connection between its ductility and temperature ? During combustion, what arises from it? How may it be detected? CADMIUM. TIN. 283 used in the arts for soldering under the name of butter of zinc. The sulphuret occurs as a mineral under the name of zinc blende. SALTS OF THE PROTOXIDE OF ZINC. Sulphate of Zinc White Vitriol. This salt is formed in the process for procuring hydrogen- gas by the action of dilute sulphuric acid on zinc. It crystallizes in color- less prisms with six atoms of water, and is soluble in two and a half parts of cold water. It has a styptic taste, and reddens vegetable blues. There are three different subsulphates of this oxide. Silicate Of Zinc, the electric calamine of mineralogists ; remarkable for becoming electric when heated. LECTURE LXII. CADMIUM. Sources of. Its Volatility. TIN. Block and Grain. Its Properties. Protoxide and Stannic Acid. Chlorides of Tin. Mosaic Gold. Its Uses. CHRO- MIUM. Chromiron. Green Oxide and its Uses. Chromic Acid. Salts of the Scsquioxide. Salts of Chromic Acid. Other Metals. TITANIUM. CADMIUM. Gd = 55-8.' CADMIUM usually occurs associated with zinc as a car- bonate. In the preparation of that metal by distillation, as has been described, the cadmium first comes over. From any impurity of zinc it may be separated by pre- cipitation from an acid solution by sulphureted hydrogen, which throws the cadmium down as a yellow powder, out does not act on the zinc. The sulphuret of cadmium is then dissolved in nitric acid, the oxide precipitated by potash, and, when dry, reduced by charcoal. The com- pounds of cadmium are not important. The metal itself is very volatile. TIN. Sn = 57-9. TIN occurs as an oxide in England, Mexico, Germany, and the East Indies. It may be reduced by the action of charcoal at a high temperature. It is found in corn- How is white vitriol prepared ? What is electric calamine ? Under what circumstances does cadmium occur? What are the native forms of tin? 284 COMPOUNDS OF TIN. merce under two forms, block tin and grain tin. If a bar of tin is heated, the purer parts, being the more fusible, ooze out of it, constituting grain tin, and the mass which is left behind is block tin. Tin is a white metal like silver. It oxydizes in the air superficially, the action ceasing as soon as a thin crust is formed. At a red heat it oxydizes rapidly, forming putty powder, used for polishing metals. It is very malleable, and may be rolled into thin foil. When bent backward and forward it emits a crackling sound. It is very soft ; its specific gravity 7*2. It melts at 442, and burns when raised to a high temperature in the air. Some_of its com- pounds are Protoxide of tin ...... SnO = 65-913. Sesquioxide ....... Sn. 2 O 3 = 129-839 Peroxide ........ SnO t = 73'926. Protochloride ....... SnCL = 93*37. Perchloride . . ..... SnCl 2 =126.74. Protosulphuret ...... SnS = 74' Persulphuret ....... SnS a = 90'1. The protoxide may be made by precipitation from the protochloride by carbonate of potash. It is to be washed with warm water, and its water finally driven off in a cur- rent of carbonic acid gas at a red heat. It is of a black color, is easily set on fire in atmospheric air, passing into the condition of peroxide. Its salts reduce the noble metals to the metallic state, when added to their solutions, and yield with the chloride of gold the Purple ofCassius. The peroxide, called also stannic acid, from exhibiting weak acid properties, may be made by the action of ni- tric acid on tin. It is a hydrate in the form of a white powder, insoluble in acids and water ; but if obtained by precipitation from perchloride of tin, it is soluble both in acids and alkalies. Melted with glass, it forms a white enamel. The protochloride may be made by dissolving tin in warm hydrochloric acid. The solution, when concentra- ted, deposits crystals of the hydrated protochloride. These are decomposed when heated. The anhydrous protochlo- ride may be had by passing hydrochloric acid gas over metallic tin at a red heat. The perchloride is procured What are block and grain tin ? What are the properties of tin ? When a bar of tin is bent backward and forward, what phenomenon arises ? How is the protoxide made, and how do its salts act on those of the noble metals ? How is stannic acid prepared ? What doea it yield with glass ? CHROMIUM. 285 by distilling eight parts of tin with twenty-four of corro- sive sublimate. It is a smoking fluid, and was formerly called the Fuming Liquor of Libavius* A solution of this substance, much used in dyeing, is made by dissolving tin in nitromuriatic acid, or by warming a solution of the protochloride with a little nitric acid. Of the sulphurets, the first may be formed by pouring melted tin on sulphur, and igniting the powdered result with more sulphur in a crucible. It is a*bluish gray com- pound. The persulphuret is obtained when two parts of peroxide of tin, two of snlphur, and one of sal ammoniac are ignited in a retort. It is a body of a golden yellow color, formerly called Aurum Musivum, or Mosaic gold, in small scales of a greasy feel, and is used for exciting electrical machines, being much more energetic than the common amalgam, though less durable in its power. Tin furnishes several valuable metallic combinations ; Tin Plate is sheet iron superficially alloyed with it. The soft solders are alloys of lead and tin. Pewter is an alloy with antimony. CHROMIUM. Cr=28. CHROMIUM occurs abundantly near Baltimore as the chromate of iron (Chrome Iron), more rarely as the red chro- mate of lead. The metal may be obtained by the action of charcoal on the oxide at a high temperature, and is of a yellowish-white color. It takes its name from its tend- ency to produce highly colored compounds. It is very infusible, and has a specific gravity of about G'OO. Its com- pounds, to be here, described, are Sesqaioxide of chromium . . . . Cr 2 O 3 = 80'039. Chromic acid CrO 3 = 52-039. Sesquichloride of chromium . . . Cr 2 Cl 3 = 162-26. The sesquioxide may be prepared by heating the chro- mate of mercury to redness in a crucible. The mercury is driven off, and the chromic acid partially deoxydized, leaving a beautiful grass-green powder, the sesquioxide. It may also be obtained by heating the bichromate of pot- ash red hot, and washing the residue in water ; also as & hydrate, by boiling a solution of bichromate of potash with What is the fuming liquor of Libavius ? How is mosaic gold made, and what is its use ? What alloys does tin furnish ? Under what forms does chromium occur in nature ? How is its sesquioxide prepared, and what is its use ? 286 COMPOUNDS OF CHROMIUM. muriatic acid, and adding alcohol ; the mixture becomes of a green color, and ammonia precipitates the hydrated sesquioxide. It is a weak base, yielding a class of salts of a blue or green color. In the state of hydrate it is sol- uble in acids ; but, on making it red hot, it suddenly be- comes incandescent, passes into another allotropic state, and is now insoluble. This sesquioxide is isomorphous with the sesquioxides of iron and alumina. In its two al- lotropic states, it yields corresponding classes of salts, one of which is green, and the other reddish green. It is used for communicating a green color to porcelain. Chromic Acid may be made by adding one volume of a saturated solution of bichromate of potash to one and a half of oil of vitriol. On cooling, red crystals of chromic acid are deposited. It is isomorphous with sulphuric acid, produces with bases yellow and red ;salts, is a powerful oxydi-zing agent, is decomposed by a red heat into the ses- quioxide, destroys the color of indigo and other dyes, and may be detected by producing with the salts of lead, chrome yellow, and by its ready passage, under the influ- ence of deoxydizing agents, into the sesquioxide. The sesquichloride is procured when chlorine is passed over a mixture of the sesquioxide and charcoal in a red- hot tube. It is a lilac-colored body, which forms a green solution in water. There is also an oxy chloride, which may be distilled as a deep-red liquid from a mixture of chromate of potash, common salt, and oil of vitriol. The fluoride, which is a red gas, is obtained by distilling in a silver retort a mixture of chromate of lead, fhior spar, and oil of vitriol. It is decomposed by the moisture of the air, forming chromic and hydrofluoric acids. SALTS OF THE" SESdUIOXIDE OF CHROMIUM. Sulphate of Chromium and Potash Chrome Alum. When the oxide of chromium is dissolved in sulphuric acid and mixed with the sulphate of potash and a little free sulphuric acid, crystals of chrome alum are deposit- ed in red or blue octahedrons. The sulphate of chromium alone does not crystallize. Chrome Iron, a compound of the sesquioxide of chro- mium and the protoxide of iron, is found native, crystal- How is chromic acid made ? Does it possess bleaching powers ? How are the chloride and fluoride obtained ? What is the form of the latter body ? What is chrome alum ? SALTS QF CHROMIC ACID. 287 lized in octahedrons, and also massive. It furnishes most of the compounds of chromium. SALTS OF CHROMIC ACID. Chromate of Potash may be made by igniting chrome iron with one fifth its weight of nitrate of potash. It crystal- lizes in small, lemon-yellow prisms, and is very soluble in hot water. The crystals are anhydrous. Bichromate of Potash may be prepared from the for- mer by adding an equivalent of acetic acid : it crystal- lizes in prisms of a ruby red. Large quantities are con- sumed by dyers. Chromate of Lead- Chrome Yellow, obtained by pre- cipitation from either of the foregoing salts by a soluble salt of lead. It is used as a paint. Dichromate of Lead is formed by adding chromate of lead to melted nitrate of potash, arid dissolving out the chromate of potash and excess of nitre by water. It is of a beautiful red color. The following metals, VANADIUM, TUNGSTEN, MOLYB- DENUM, OSMIUM, and COLUMBIUM, are not applied to any purposes in the arts, or are so rare as not to be of general interest. TITANIUM might be included in the same obser- vation ; it is, however, deserving of remark as being a red metal like copper, and titanic acid, one of its oxygen com- pounds, is used in the coloring of artificial teeth. LECTURE LXIII. ARSENIC. Preparation of the Metal. Properties of Ar- senious Acid. Two Varieties of it. Two methods of detecting it. Process in Cases of Poisoning, Sulphur- eted Hydrogen Test. Marsh's Test. The Copper Test. Difficulties arising from Antimony^ AUSENIC. As 37-7. ARSENIC is obtained by sublimation in a current of air of the arseni'uret of cobalt and iron, the vapor condensing as a white oxide. This being mixed with powdered char- What is the constitution of the two chromates of potash ? What is chrome yellow ? "What is the color of titanium ? From what substances, and in' what manner, is arsenious acid prepared ? 288 COMPOUNDS OF ARSENIC. Fig. 265 coal,, or black flux, and heated, the metallic arse- nic sublimes. The process may be conducted in a tall vial imbedded in a crucible filled with sand, two thirds of the vial projecting above the heated sand. On this cooler portion the metal condenses. It is also sometimes found in a native state. Arsenic is a metallic body, of an aspect darker than cast iron ; it is very brittle, its specific gravity is 5*88, and, when slowly sublimed, it crystallizes in rhombohedrons. At 356 F. it sublimes without undergoing fusion, its melting point being much higher than that of sublimation. Its va- por has a smell of garlic, as may be readily recognized by throwing a little arsenious acid on a red-hot coal. Arse- nic prepared by black flux tarnishes, it is said, from con- taining a little potassium. Among its compounds, the fol- lowing may be mentioned : Arsenious acid ^ ..... . As^O 3 ^= 99-439. Arsenic acid As 2 O 5 = 115-465. Protosulphuret of arsenic . . . . AsS = 53-8. Sesquisulphuret of arsenic . . . As 2 S 3 = 123-7. Arseniureted hydrogen .... AsH = 38'7. Arsenious Acid is formed when arsenic is sublimed in atmospheric air. It is a white substance, which, when the process is conducted slowly, crystallizes in octahe- drons. Similar octahedral crystals may be obtained by heating arsenious acid itself in a tube to 380 F. When the operation has been recently performed and a large mass sublimed, it is a glassy, transparent body, which in the course of time slowly becomes milk-white. The spe- cific gravity of arsenious acid is 3'7. It is nearly taste- less, of sparing solubility in water, the two varieties dif- fering in this respect. By 100 parts of water, 11*5 of the opaque, but only 9'7 of the transparent, are dissolved. This substance passes currently under the name of arse- nic. It ought not to be forgotten that the arsenic of chem- ical writers and that of commerce are very different bod- ies : the one is black and the other white ; the one is a metal and the other its oxide. Arsenious acid may be detected by several methods. How is the metal ohtained from it ? What are its properties ? What is the odor of its vapor ? Why can not it be melted ? From the metal, MOW may arsenious acid he procured ? What change does the glassy va- riety undergo in time ? Of these varieties, which is most soluble in water ? What is the difference between the arsenic of chemists and the arsenic of commerce ? TESTS FOR ARSENIC. 289 1st. "With ammonia sulphate of copper, it gives an emerald green precipitate ; the arsenite of copper, or Scheele's green. 2d. With the ammonia nitrate of silver, a canary yel- low precipitate ; the arsenite of silver. 3d. With sulphureted hydrogen, a solution, previously acidulated with acetic or muriatic acid, yields a yellow pre- cipitate, the sesquisulphuret of arsenic, orpiment. This, when dried and ignited with black flux (a mixture of charcoal and carbonate of potash, obtained by igniting cream of tartar in a covered crucible), yields a sublimate of metallic arsenic. 4th. With the materials for generating hydrogen gas ; that is, sulphuric acid, zinc, and water*, placed in a bottle ; if arsenious acid be present, arseniureted hydrogen is dis- engaged. When set on fire, it burns with a pale blue flame, emitting a white smoke ; and if a piece of cold glass be held in the flame, there is deposited upon it a black spot of arsenic, surrounded by a white border of arsen- ious acid. This stain is volatilized on heating the glass. Or if the arseniureted hydrogen be conducted through a tube of Bohemian glass, made red hot at one point by a spirit lamp, it is decomposed, and metallic arsenic depos- ited on the cooler portions beyond the ignited space. 5th. If a solution containing arsenious acid be acidu- lated with hydrochloric acid, and boiled with slips of cop- per, the metallic arsenic is deposited upon the copper vis an iron gray crust. In cases of poisoning by this substance, it is unsatisfac- tory to apply, in the first instance, color-giving tests, such as the first, second, and third ; as the liquid obtained from the stomach is itself highly colored and turbid. It is, therefore, desirable to examine that organ and its contents minutely, endeavoring to discover any white granules, or specks, which may be supposed to be arsenious acid, and if such are found, to examine them separately. The contents of the stomach, the larger pieces having been divided, are to be boiled in water, and strained through a linen cloth. A current of chlorine gas passed What is the action of ammonia sulphate of copper on arsenious acid ? What of the ammonia nitrate of silver ? What of sulphureted hydrogen ? What is the process for detecting it by arseniureted hydrogen ? What is that by copper ? In cases of poisoning, why can not color tests be applied 1 How is the liquid obtained from the stomach to be clarified ! BB 290 through this liquid coagulates and separates much of the animal matter ; or, what is more convenient, if the solu- tion be first acidulated with nitric acid, and then nitrate of silver be added, much of the animal matter may be re- moved. By the addition of a solution of common salt, the excess of the silver salt may be precipitated, and the liquor being filtered, is then fit for the third or fourth of the foregoing tests. In the application of sulphureted hydrogen, the liquor having been clarified as just stated, the gas is passed through it until it smells strongly. It is then to be boiled for a short time, to expel the excess of gas, and filtered. The yellow precipitate of sesquisulphuret of arsenic, or orpiment, which is* collected, is to be thoroughly dried, and introduced, with twice its bulk of black flux, into the Fig. 266. bulb, , of a tube, such as Fig. 266, made of hard glass. On the temperature being rais- ed by a lamp, metallic arsenic sublimes, forming an iron black ring round the part, b. By cutting off the bulb of the tube and heating the black crust gradually, it slowly sublimes to- ward the colder part, producing a white deposit of ar- senious acid in octahedral crystals. In the application of Marsh's test, the liquor, having been cleared either by chlorine or by nitrate of silver, as above described, is to be introduced into a bottle con- taining dilute sulphuric acid and zinc, a tube, bent as Fig. 267. represented in Fig. 267, tz, passing lat- erally from the cork; arseniureted hy- drogen now passes off, and may be set on fire as it escapes from the end of the tube, and examined by holding in the flame a piece of cold glass, b. If no spot be produced, then the tube, which for this reason should be made of a hard glass not containing lead, is to be ignit- ed by a spirit lamp at the point c, and the gas will de- posit its arsenic a little beyond that point. In this mari- ner, the tube being kept red hot for hours, the smallest quantity of arsenic may be discovered. If the liquor, notwithstanding the care taken to clear it, Describe the test by sulphureted hydrogen. Describe Marsh's test. How may a small quantity of metal be separated from a large quantity of liquid by this test ? ARSENIC. 291 froths when the hydrogen is disengaged, so as to inter- fere with the results by choking the tube, the gas is best collected under a jar at the pneumatic trough, and may be subsequently examined. The fifth test, by copper, may be sometimes advanta- geously applied to collect the arsenic from solutions ; the crust upon the copper may be subsequently examined, ei- ther by sublimation or otherwise. It is to be remembered that antimony will yield results closely resembling those of arsenic by Marsh's test ; but on heating the glass plate on which the stain has been de- posited, if it be arsenic, it will totally volatilize away; but, if antimony, though the flame of a blow-pipe be thrown upon it, it will not disappear, but only gives rise to a yel- low oxide, which turns white on cooling. In medico-legal investigations, it should also be re- membered that, as sulphuric acid and zinc of commerce sometimes contain arsenic, it is absolutely necessary that the specimens about to be used be -critically examined themselves by being tried alone before the suspected so- lution is added. LECTURE LXIV. ARSENIC. Antiseptic Quality of Arsenious Acid. Anti- dote for Poisoning. Arsenic Acid. Isomorphous with Phosphoric Acid. Realgar and Orpiment. Arseniuret- ed Hydrogen. ANTIMONY. Reduction of. Oxides, Chlorides, and Sulphurets of. Antimoniureted Hydro- gen. Detection of Antimony. TELLURIUM. URANIUM. COPPER. Reduction of. Use of Oxide. Detection of. Salts of Protoxide. ARSENIOUS ACID possesses a remarkable antiseptic qual- ity, and hence often preserves the bodies of persons who have been poisoned by it. Advantage is also taken of this fact by the collectors of objects of natural history in pre- serving their specimens. When the liquid froths, what course is to be pursued ? When may the test of copper be advantageously applied ? What metal closely resembles arsenic in these respects ? Why is it necessary to examine the sulphuric acid and zino employed in these experiments ? Does arsenious acid pos- sess an antiseptic quality ? 292 COMPOUNDS OF ARSENIC. The antidote for poisoning by arsenic is the hydrated eesquioxide of iron. It may be made by adding carbon- ate of soda to the muriate of iron. It should be given in the moist state, mixed with water. After being once dried, it loses much of its power. It produces an inert basic arsenite of the peroxide of iron. Arsenic Acid is found in nature in union with various bases. It may be made by acting on arsenious acid with nitric acid, with the addition of a little hydrochloric acid, and evaporating till the nitric acid is expelled. The re- sulting acid contains three atoms of water, and is isomor- phous with tribasic phosphoric acid. The arseniates yield, with nitrate of silver, a dark-red precipitate of the triba- sic arseniate of silver. The monobasic and bibasic forms of the acid are not known. It should not be forgotten in medico-legal inquiries respecting arsenic, that the arse- niate of lime may naturally replace phosphate of lime in bone earth, and this acid substitute the phosphoric in other parts of the system. The protosulphuret of arsenic may be obtained by melt- ing arsenious acid with sulphur. It occurs as a mineral Realgar, and is a red-colored substance. The sesquisulphuret is deposited when a stream of sul- phureted hydrogen is passed through a solution of arse- nious acid. It is a yellow body, and is used in dyeing ; it is also known under the name of Orpiment. Arseniureted Hydrogen is prepared by acting on an al- loy of zinc and arsenic with dilute sulphuric acid. It is a colorless gas, burns with a blue flame, exhales an odor like garlic. Its specific gr^ity is 2*695. It is decom- posed by chlorine, iodine, and the arsenic is separated by heat and by the rays of the sun. ANTIMONY. Sb = 64-6. This metal occurs commonly as a sesquisulphuret in nature, from which it may be obtained by heating with iron filings, a sulphuret of iron forming, and metallic an- timony subsiding to the bottom of the crucible. It may also be obtained by fusing the sulphuret with black flux, What is the antidote for this poison? How is it prepared? How is arsenic acid prepared ? What fact arises from the isomorphism of arsen- ic and phosphoric acids ? What is realgar ? What is orpiment ? How may arseniureted hydrogen be made ? From what source is antimony ob- tained ? What is the process for its preparation ? COMPOUNDS OF ANTIMONY. 293 which produces a sulphuret of potassium and metallic antimony. Antimony is a blue-white metal, of a very crystalline structure, and so brittle that it may be pulverized. It melts at 810 F. Its specific gravity is 6'7. It possess- es, at high temperatures, an intense affinity for oxygen ; a fragment of it the size of a pea being ignited on a piece of charcoal before the blow-pipe, and then suddenly thrown on the table, takes fire, breaking into a multitude of glob- ules, and filling the air with fumes of the white sc&qui- oxide. Antimony yields the following compounds : Sesquioxide of antimony .... Sb 2 O 3 = 153-239. Antimonious acid & 2 4 =161-252. Antimonic acid Sb 2 Or, = 169'265. Sesquichloride of antimony Sb 2 C1 3 = 235*46. Perchloride " . 6 2 C7 5 -=306'3. Sesquisulphuret Persulphuret Oxysulphuret : 177-5. SB =209-7. t S, + Sb a O,=: The Sesquioxide of Antimony may be made by adding to an acid boiling solution of chloride of antimony car- bonate of soda. It is a gray powder, and is the base of a class of salts, among which tartar-emetic may be men- tioned. These salts give an orange-colored precipitate with sulphureted hydrogen. Antimonious Acid is produced by heating the oxide of antimony, or antimonic acid. It is a white powder, and unites with bases, forming antimonites. Antimonic Acid may be prepared by acting on metallic antimony with nitric acid. Sesquichloride of Antimony is made by dissolving one part of sulphuret of antimony in five of hydrochloric acid, and distilling. As soon as the matter which passes over becomes solid, the receiver is to be changed, and, contin- uing the heat, the sesquichloride is collected. It was for- merly known as butter of antimony. The perchloride may be made by burning antimony in chlorine gas. The oxy chloride is produced when the sesquichloride is placed in contact with water. It was formerly known as pow- der of algaroth. The sesquisulpliuret occurs abundantly as a mineral, as What are its properties ? What color is the precipitate yielded by the salts of the sesquioxide and sulphureted hydrogen ? How is antiinonious acid prepared ? What is the butter of antimony ? What is the powder of algaroth? What is the aspect of the native sesquisulphuret ? B B 2 294 COMPOUNDS OF ANTIMONY. has been said. It is also formed by the action of sulphu- reted hydrogen on the salts of the oxide of antimony. In this case it is of an orange color, in the former it has a metallic aspect. The persulphuret is procured when the sesquisulphuret and sulphur are boiled in a solution of potash, the liquor filtered, and an acid added, a yellow precipitate going down. It was known formerly as the Golden Sulphurel of Antimony. The oxysulphuret occurs native as the red ore of antimony, and may also be made by boiling the sesquisulphuret with a solution of potash. On cooling, precipitation of it takes place. It is stated, however, by Berzelius, that this is not a true compound, but merely a mechanical mixture of the oxide and sulphu- ret in irregular proportions. This precipitate is also known under the name of Kermes Mineral. From the liquor, af- ter the kermes is separated, an acid throws down the gold- en sulphuret of antimony. Antimoniureted Hydrogen. ^When hydrogen is evolved from a solution containing tartar emetic (tartrate of anti- mony and potash), this substance is produced. It is a gas, having a superficial resemblance to arseniureted hydro- gen, and when used as in Marsh's apparatus, gives a stain on glass resembling that of arsenic. From arsenic it may be distinguished by not being volatile. The soluble salts of antimony may be distinguished by giving an orange precipitate with sulphureted hydrogen, soluble in sulphuret of ammonium, but again precipitated by an acid. Antimony furnishes some valuable alloys : printer's type metal, for example, is an alloy of this substance with lead. It expands in the act of solidifying, and, therefore, takes accurate impressions of the interior of a mould. TELLURIUM. Te = 6W. TELLURIUM is a rare metal, of a white color, very fusi- ble and volatile, having several analogies with selenium, and uniting with hydrogen to form tellureted hydrogen, which, with water, yields a claret-colored solution. URANIUM, U= 217, is likewise a very rare metal, of the nature of which there What is the golden sulphuret ? What is Kermes mineral ? How is antimoniureted hydrogen made ? How may the salts of antimony be dis- tinguished? What are the properties of tellurium? COPPER. 295 are considerable doubts, it being supposed that what was formerly regarded as the metal is in reality its protoxide. It may be remarked, if these observations are incorrect, that uranium has the highest equivalent of any of the ele- mentary bodies. It is used to a small extent to give black and yellow colors to porcelain. COPPER. Cu = 31-6. COPPER is often found native, and in certain parts of the United States in masses of very great magnitude. It also occurs as a carbonate and sulphuret. In the latter com- bination, it is found with the sulphuret of iron, as yellow copper ore. This being roasted, the sulphuret of iron changes into oxide, the copper sulphuret remaining un- changed. The mass is then heated with sand, which yields a silicate of iron, the sulphuret of copper separa- ting. This process is repeated until all the iron is parted ; and now the sulphuret of copper begins to change into the oxide, which is finally decomposed by. carbon at a high temperature. Copper is a red metal, requiring a high temperature for fusion. Its specific gravity is 8-617. It has great tenac- ity, and is ductile and malleable. A polished plate of it, heated, exhibits rainbow colors, and is finally coated with the black oxide. It is one of the best conductors of heat and electricity. Among its compounds, the follow- ing may be mentioned : Protoxide of copper CuO =39-613. Suboxide " Cu^O =71-213. Chloride " CuCl =66-02. Bichloride " C 2 C7 = 98-62. Disulphuret " Cu 2 S =79'32. Protoxide of Copper may be made either by igniting me- tallic copper in contact with air, or by calcining the ni- trate. It is a black substance, not decomposable by heat, but yielding oxygen with facility to carbon and hydrogen, and hence extensively used in organic analysis. It is a base, yielding salts of a blue or green color. The sub- oxide, called, also, red oxide, occurs native as ruby cop- per. It is a feeble base. The disulphuret also occurs native, as copper pyrites. What is remarkable as respects the alleged atomic weight of uranium ? Under what forms does copper naturally occur? What is the process for its reduction? What are its properties ? Which of its oxides is used in organic analysis ? 296 SALTS OF COPPER. Copper is easily detected. Caustic potash gives, with its protosalt, a pale-blue hydrate, which turns black on boiling. Ammonia, in excess, yields a beautiful purple solution ; ferrocyanide of potassium, a chocolate brown precipitate ; sulphureted hydrogen, a black*; and metallic iron, as the blade of a knife, precipitates metallic copper. SALTS OF THE PROTOXIDE OF COPPER. Carbonate of Copper. The neutral carbonate of cop- per is not known ; but there are several varieties of di- carbonates. One, which passes under the name of Miner- al Green, is formed by precipitating with -an alkaline car- bonate. It occurs naturally in the form of Malachite. Slue copper ore is another dicarbonate ; the paint called Green Verditer has a similar composition. Sulphate of Copper Blue Vitriol is prepared for com- merce by the oxydation of the sulphuret of copper. It crystallizes in rhomboids of blue color, with four atoms of water. It is 'soluble in four times its weight of cold, and twice its weight of hot water. It is an escharotic, an as- tringent, and has an acid reaction. With ammonia it forms a compound of a splendid blue color, which may be ob- tained in crystals ; with potash, also, it forms a double salt. There are also subsulphates of copper. Nitrate of Copper, formed by the action of nitric acid on metallic copper. It crystallizes in prisms, or in plates. It acts with very great energy on metallic tin. There is a subnitrate of copper. Arsenite of Copper Scheelc's Green produced by add- ing solution of arsenious acid to the solution of ammonia sulphate of copper. Copper yields several valuable alloys. Brass is an al- loy of copper and zinc ; gun metal, bell metal, and spec- ulum metal, of copper and tin. The gold and silver of currency contain portions of this metal ; it communicates to them the requisite degree of hardness. How may copper be detected ? Under what forms do the carbonates of copper occur? What are the method of preparation and properties of the sulphate ? What is Scheele's green ? What are brass, gun metal, and bell metal ? Why is silver and gold coinage alloyed ? LEAD. 297 LECTURE LXV. LEAD. Reduction of Galena. Relations of Lead to Wa- ter. The Oxides of Lead. Detection of Lead. BIS- MUTH. SILVER. Amalgamation. Crystallization.- Cupellation. Properties of Silver. Salts of Silver. LEAD. Pb = 103-6. LEAD occurs under various mineral forms, but the most valuable one is galena, a sulphuret. From this it is read- ily obtained. The galena, by roasting in a reverberatory furnace, becomes partly converted into sulphate of lead ; the contents of the furnace are then mixed, the tempera- ture raised, and the sulphate and sulphuret produce sul- phurous acid and metallic lead, the action being PbO, SO 3 + P1>S ... = ... 2SO a - + Pb,. Lead is a soft metal, of a bluish- white color. Its spe- cific gravity is 11*381. It melts at 612 F., and on the surface of the molten mass an oxide (dross) rapidly forms. At common temperatures it soon tarnishes. In the act of solidifying it contracts, and hence is not fit for castings. It possesses, at common temperatures, the welding prop- erty ; two bullets will cohere if fresh-cut surfaces upon them are brought in contact. Under the conjoint influ- ence of air and water lead is corroded, a white crust of carbonate forming. But when there are contained in the water small quantities of salts, such as sulphates, these form with the lead insoluble bodies, which, coating its surface over, protect it from farther destruction. For this reason, lead pipe can be used for distributing water in cities without danger. Lead is one of the least tena- cious of the metals. The tartrate of lead calcined in a tube yields one of the best pyrophori. On bringing it into the air at common temperatures, it spontaneously ignites. Of the compounds of lead, the following are some of the more important : Under what form does lead chiefly occur? How is galena reduced? Why can not lead be used for castings ? What is the action of pure wa- ter, and water containing salts, upon it? 298 COMPOUNDS OF LEAD. Protoxide of lead PbO =111-613. Sesquioxide " P 2 O 3 = 231-239. Peroxide " PbO 2 = 119-626. Bed oxide " P6 3 O 4 = 342-852. Chloride " PbCl = 139-62. Iodide " Pbl =229-9. Sulphuret " PbS = 119'7. The protoxide is made by heating lead in the air ; it ia u yellow body, which fuses at a bright red heat. In the first state it is called massicot ; in the latter, litharge. It yields a class of salts, being a base. It is slightly soluble in water. The peroxide is made from red lead by di- gesting it with nitric acid, which dissolves out the protox- ide, and leaves the substance as a puce colored powder. The red oxide, or red lead, is made by calcining lead in a current of air at 600 or 700 F. It is used in the manufacture of flint glass. The chloride is made by the action of hot hydrochloric acid on protoxide of lead : on cooling, it is deposited in crystals. The iodide is formed when any soluble iodide is added to a protosalt of lead ; it is a beautiful yellow precipitate, soluble in boiling water, forming a colorless solution, which, on cooling, de- posits golden crystals. The sulphuret is galena ; it crys- tallizes in cubes, and has a high metallic lustre. Lead is easily detected by sulphureted hydrogen, which throws it from its solutions as a deep brown or black pre- cipitate, and by the iodide of potassium or chromate of potash, which gives with it a yellow precipitate. Sul- phuric acid yields with its salts a white insoluble sulphate of lead. SALTS OF THE PROTOXIDE OF LEAD. Carbonate of Lead White Lead Ceruse. This salt forms as a white precipitate when an alkaline carbonate is added to a solution of a salt of lead. Large quantities of it are consumed in the arts as white paint. For com- merce it is procured by mixing litharge with water con- taining a small proportion of acetate of lead ; carbonic acid gas is then sent over it, and the carbonate rapidly forms. It is also made by exposing metallic lead in plates to the action of the vapor of vinegar, air, and moist- ure, the metal becoming oxydized and carbonated. "What is massicot ? How is it prepared ? What is litharge ? How is the peroxide prepared? How is minium made? How may lead be detected ? Mention some of the methods by which white lead may be made. BISMUTH. SILVER. 299 Nitrate of Lead may be formed by dissolving litharge in dilute nitric acid ; it crystallizes in opaque white octa- hedrons, which dissolve in seven or eight times their weight of cold water. They contain no water of crystal- lization, and are decomposed at a red heat, as stated in the description of nitrous acid. By the action of ammo- nia, three other nitrates of lead may be obtained. Among the alloys of lead are the soft solders. Two parts of lead and one of tin constitute plumber's solder ; one of lead and two of tin, fine solder. BISMUTH. Bi =71-07. BISMUTH is found both native and as a sulphuret. It is of a reddish color, melts at 497, and may be obtained in beautiful cubic crystals by cooling a quantity of it until solidification commences, then breaking the surface crust and pouring out the fluid portion. When bismuth is dissolved in nitric acid, and the solu- tion poured into water, the white subnitrate is deposited, once used as a cosmetic ; when this is washed, and sub- sequently heated, the protoxide is left. There is also a peroxide. Fusible metal is an alloy of eight parts of bismuth, five of lead, and three of tin ; it melts below the boiling point of water, and may be obtained in crystals. SILVER. ^ = 108-31. SILVER is found native, and as a'sulphuret and a chlo- ride, occurring, also, with a variety of other metals, and in small proportion with galena. When disseminated as a metal through ores, it may be collected from them by amalgamation with quicksilver, and, on distilling, the quicksilver is driven off. When it is obtained from the sulphuret, that ore is roasted with common salt, which changes it into a chlo- ride. This, with the impurities with which it may be associated, is put into barrels, which revolve on an axis, along with water, pieces of iron, and metallic mercury ; j;he iron reduces the chloride to the metallic state, and the silver amalgamates with the mercury. This is washed from the impurities, strained through a bag to separate "What change does the nitrate undergo at a red heat ? Of what are the common solders composed ? What are the properties of bismuth ? What is fusible metal? Under what forms does silver commonly occur ? How is it reduced from the sulphuret I 300 CRYSTALLIZATION. CUPELLATION. the excess of mercury, and the residue is driven off' by distillation. The extraction of silver, when it occurs in small quan- tity with lead, has been recently much improved by the introduction of the process of crystallization. It depends upon the fact that an alloy of lead and silver is more fusi ble than lead. A large quantity of argentiferous lead is melted and allowed to cool. As the setting goes on, the first portions which solidify are pure lead ; they may be removed by iron colanders, and by continuing the process there is finally left a portion containing all the silver. This is exposed to a red heat, and a stream of air direct- ed over it ; oxydation of the lead takes place, and the litharge is removed by the blast, the process being finally completed by cupellation. A cupel is a shallow dish made of bone ashes, and is very porous. In this, if an alloy of lead and silver be heat- ed with access of air, the lead oxydizes, and, melting into a glass, soaks into the cupel, or may be driven from the surface by a blast of air directed from a bellows. At the same time, any copper or other base metal oxydizes and is removed along with the lead. The completion of the process is indicated by the silver .assuming a certain brill- iancy, or flashing, as the workmen term it. Silver is a white metal capable of receiving a brilliant polish. It is malleable and ductile, an excellent conduct- or of heat and electricity. Its specific gravity is 10-5. It melts at 1873 F., and when melted absorbs a large quan- tity of oxygen, giving it out again as soon as it solidifies, and assuming a frosted or porous appearance. The pres- ence of a minute quantity of copper prevents this effect. Silver is so soft that, for making plate or coins, it requires to be alloyed with a portion of copper ; from this it may be purified by dissolving it in nitric acid, and precipitating the silver as chloride by a solution of common salt. Sil- ver shows little disposition to unite with oxygen, though it tarnishes readily by the action of sulphureted hydrogen. It yields three oxides, but of its compounds the following* are the most important : What is the process of amalgamation ? What is the process of crystal- lization ? What is the process of cupellation ? What are the properties of silver ? Why does it frequently require to be alloyed with copper ? What remarkable relation does it possess to oxygen ? COMPOUNDS OF SILVER. 301 Protoxide of silver . . . . AgO = 116-323. Chloride " .... AgCl = 143'78. Iodide " .... Agl =234-48. Sulphuret " .... AgS =124-43. The protoxide may be made by the action of caustic potash on a solution of nitrate of silver, or by boiling re- cently-prepared chloride in potash. It is a dark powder, which may be reduced by heat alone. The chloride is sometimes found native, as horn-silver, and may be made by precipitation from the nitrate by hydrochloric acid, or a soluble chloride. Like the iodide, it turns dark 011 exposure to the indigo rays, and hence is used in photo- genic drawing. The sulphuret is produced whenever sul- phureted hydrogen acts on oxide of silver, or even metal- lic silver ; it is a black compound. Silver is easily detected by precipitation as a chloride : a curdy, white precipitate, insoluble in water, but soluble in ammonia. It turns dark on exposure to the sun. SALTS OF THE PROTOXIDE OF SILVER. Nitrate of Silver Lunar Caustic procured by dissolv- ing silver in .nitric acid, diluted with twice its weight of wa- ter. It crystallizes in tables which are not deliquescent and contain no water of crystallization. It enters into fusion at 426 F., but at higher temperatures undergoes decom- position. It is frequently cast into small sticks and used by surgeons as a cautery. It is soluble in its own weight of cold and half its weight of hot water, and, when in contact with organic matter, turns black in the rays of the sun. Ammoniuret of Silver Berthollet' } s Fulminating Silver is formed by digesting precipitated oxide of silver in am- monia. It explodes with the utmost violence under the feeblest friction, with the evolution of nitrogen and the vapor of water. How may the protoxide be prepared ? What changes do the chloride and iodide exhibit under the influence of light ? How may silver be de- tected ? How is lunar caustic made ? C c 302 MERCURY. LECTURE LXVI. MERCURY. Process of Reduction. The Liquid State of. Its Oxides. Calomel and Corrosive Sublimate. De- tection of Mercury. Its Salts. Amalgams. GOLD. Chloride of. Purple of Cassius. PALLADIUM. PLA- TINUM. Its Catalytic Effects. Platinum Black. IRID- IUM. RHODIUM. MERCURY. fl = 202. MERCURY may be obtained from the bisulphuret (cin nabar) by distillation with iron filings. It is also, to a certain extent, found native. The striking characteristic of mercury is its liquid condi- tion. Its melting point is the lowest of that of any of the metals, being 39 F. Its specific gravity at 47 F. is 13-545. It boils at 662 F. Kept at that temperature in the air for a length of time, it produces red oxide ; but at common temperatures it is not acted on by the air. It may be freed from impurities for the purposes of the lab- oratory, by being kept in contact with dilute nitric acid. It gives the following compounds of interest : Protoxide of mercury Peroxide " Protochloride " Bichloride " Protosiilphuiret " Bisulphuret " . HgO =210-013 . Ego* = 218-026. . HgCl 237-42. . HgCl* = HgS = 218-1. = 234-2. The protoxide may be made by triturating calomel with potash water in a mortar. It is a black powder, "which is decomposed by light or any of the reducing agents. The peroxide may be formed, as stated above, by the ac- tion of air on hot mercury, but more easily by dissolving mercury in nitric acid and evaporating and heating the salt until no more fumes of nitrous acid are evolved. It is a red powder, and when warmed becomes almost black, the color returning as the temperature descends. Like the former, it is a base, and yields a class of salts. The Protochloride, or Calomel, may be made by adding hydrochloric acid to the protonitrate of mercury, or by sub- Under what forms does mercury commonly occur? What is the most striking property of this metal ? How may it be purified ? What are the properties of the protoxide and peroxide ? What is calomel ? COMPOUNDS OF MERCURY. 303 liming a mixture of bichloride of mercury and mercury. It is a white powder, insoluble in water, and darkens slowly by exposure to sunshine. The bichloride (or Cor- rosive Sublimate) is formed when mercury burns in chlo- rine gas, but more economically by sublimation from a mixture of persulphate of mercury and common salt. It is a heavy, white, crystalline body, soluble in water, has a metallic taste, and is poisonous. The antidote for it is albumen (the white of an egg). Of the sulphurets of mercury, the protosulphuret is black, and the bisulphuret commonly red ; in this case it passes in commerce under the name of vermilion, and is used as a paint. It can be obtained, however, quite black, a peculiarity already observed in the case of' the perox- ide, and still more strikingly in the biniodide, which may be sublimed in beautiful yellow crystals, which become of a splendid scarlet color by merely being touched. Mercury may be detected by being precipitated from its soluble combinations by metallic copper as a metal. Its salts, either alone or with carbonate of soda, heated in a tube, yield metallic mercury, which volatilizes. SALTS OF THE OXIDES OF MERCURY. Nitrates of the Oxides of Mercury. When cold dilute nitric acid acts on mercury it gives rise to neutral or basic protosalts, as the acid or mercury is in excess ; if the acid be hot, a pernitrate forms ; these salts are decomposed by an excess of water, giving rise to basic compounds. The neutral pernitrate exists in solution only. Persulphate of Mercury is formed by boiling sulphuric acid and mercury, and evaporating to dryness. It occurs in the form of a white granular mass, and is decomposed by water, giving a yellow precipitate, a subsulphate call- ed Turpeth Mineral. The alloys of mercury are called amalgams ; the amal- gam of tin is used for silvering looking-glasses, and that of zinc for exciting electrical machines. GOLD. Au = 199-2. Gold is found native, and may be obtained by washing What is corrosive sublimate ? What is the antidote to it 1 For what purpose is the bisulphuret employed? What change occurs to the yel- low biniodide when it is touched ? How may mercury be detected ? How- are the protonitrate and the persulphate prepared ? Under what forma does gold occur ? 304 GOLD. or by amalgamation with mercury. It may be purified from silver by quartation ; that is, fusing it with three times its weight of silver, and then acting on the mass with nitric acid. The gold is left as a dark powder. From all other metals gold is distinguished by its yel- low color. Its specific gravity is 19-3. It melts at 2016 F. It is the most malleable of all the metals, as is proved by gold-leaf, which may be obtained ^^^Viro mcn i* 1 thick- ness ; is not acted upon by the air or oxygen. Objects of art covered with it have retained their brilliancy for thousands of years. No acid alone dissolves it; but it is soluble in aqua regia, and also by chlorine. It can, however, be made to yield two oxides, a pro- toxide and a teroxide ; and two chlorides having the same constitution ; the terchloride is formed by the action of nitromuriatic acid (aqua regia) on gold. When evapora- ted, it yields red, deliquescent crystals. Deoxydizing agents, such as protosulphate of iron, reduce it to the me- tallic state ; this is probably due to their decomposing water and presenting hydrogen to the chloride. Hydro- gen gas decomposes the terchloride, and, by heating it, it first changes into the protochloride and then into metallic gold. "With a solution of tin it forms the Purple of Cas- sius. This and the action of protosulphate of iron serve as a test for it. PALLADIUM. Pd = 53-s. Palladium is found associated with platinum, and is best obtained from the cyanide of palladium by ignition. It is a white metal, requiring a high temperature for fu- sion ; specific gravity 11-5. It does not tarnish in the air, is dissolved by nitric acid and aqua regia, is one of the welding metals, and, when heated, acquires a purple oxy- dation like watch spring. It is used to some extent by dentists. Its compounds are not of importance. PLATINUM. Ft = 98-84. Platinum is found native, but always associated with other metals. It is obtained by first forming a chloride of platinum and ammonium ; this, when ignited, leaves What is quartation ? "What are the properties of this metal ? How many oxides does it yield? How is the terchloride prepared ? What is the purple of Cassius ? With what metal is palladium generally associ- ated ? What are its properties ? What superficial effect takes place when it is heated in the air ? How is platinum obtained from its ores ? PLATINUM. 305 pure spongy platinum, which being, exposed to powerful pressure, and then alternately made white hot and ham- mered, becomes a solid mass. Platinum is a white metal. Its specific gravity is very high, being 21 '5. It can not be melted in a furnace, but fuses before the oxyhydrogen blow-pipe. It is a welding metal, and on this fact its preparation depends. It is very malleable and ductile, is not acted upon by oxygen, air, or any acid alone, but dissolves in aqua regia. It pos- sesses the extraordinary property of causing hydrogen and oxygen to unite at common temperatures, an effect which takes place with remarkable energy when the metal is in a spongy state. A jet of hydrogen falling upon spongy platina in the air makes it red hot, and pres- ently after the gas takes fire. It also brings about the rapid transformation of alcohol into acetic acid, and va- rious other chemical changes. If a quantity of ether be poured into Ft z- 268 - a glass jar, Fig. 268, and a coil of pla- tinum wire, recently ignited, be intro- duced, the metal continues to glow so long as any ether is present. Platinum is invaluable to the chem- ist. It fumishes a variety of imple- ments of great value, and is met with under the forms of crucibles, tubes, wire, foil, &c. Platinum Slack is prepared by slow- >n^ ly heating to 212 a solution of chlo- ride of platinum, to which an excess of carbonate of soda and some sugar have been added. It is a dark powder, and possesses the property of determining a variety of chemical changes with much more energy than platinum in mass. Platinum can be caused to yield two oxides, which are not of any importance ; and two analogous chlorides, of which the bichloride, which is the common platinum salt, is made by dissolving the metal in nitromuriatic acid, What is the specific gravity of this metal ? By what acid may it be dissolved ? What remarkable relations does it possess to hydrogen gas ? Under its influence, what is alcohol transmuted into ? What is platinum black ? Cc2 306 IR1D1UM. - RHODIUM. and evaporating to a. sirup. It is soluble in water and alcohol, and is used ibr detecting the salts of potash. IBIDIUM. Jr Iridium is associated with platinum. It is said to have been found of specific gravity 26*00. Dr. Hare has ob- tained it 21-8 ; it is, therefore, the heaviest of the metals. Its name is derived from the different colors (iris) of its compounds. RHODIUM. = 52-2. Like the former metal, rhodium is associated with the platina ores. It is a hard white metal ; its specific grav- ity is ll'OO, and is sometimes used to form tips to metal- lic pens. What are the properties of iridium? What are those of rhodium? PART IV. ORGANIC CHEMISTRY. LECTURE LXVII. Peculiarities of Organic Bodies. Their Constituent Ele- ments. Prone to Decomposition. Carbon always Pres- ent. Compound Radicals. Doctrine of Substitution. Types. Action of Heat. Eremacausis. Propagation of Decay. Action of Acids and Alkalies. THE theory of molecular arrangement, which has been already given, forms the foundation of organic chemistry. It asserts that the characters of compound bodies do not alone depend on the nature of their constituent elements, nor even on the relative amount of those elements ; but that variation of physical forms may result from atoms of the same name and of the same number arranging them- selves in subordinate groups, which groups then unite with each other. The leading ultimate elements of organized bodies are carbon, hydrogen, .nitrogen, and oxygen. Almost all or- ganic bodies arise from variations in the number and grouping of identical elements. Now a partial consideration of the conditions under which the theory of molecular arrangement acts, exhibits to us a most striking difference in the nature of the com- pounds formed upon its principles and the compounds heretofore described as examples of inorganic chemistry. In the one, peculiarity of grouping is the grand feature ; in the other, the character of the combining elements. Urea differs from the cyanate of ammonia in the arrange- ment of its constituents only ; but the leading mark of dis- tinction between sulphuric and phosphoric acids is, that the one contains sulphur and the other phosphorus. The number of substances which, besides the four men- On what do the characters of compound bodies depend ? Of what four leading elementary bodies are organic substances chiefly composed ? In what striking respect do these substances differ from inorganic ones ? 308 CHARACTERS OF ORGANIC BODIES. tioned above, enter into the composition of organic bodies is very limited. Among such may be mentioned potash, soda, lime, magnesia, oxide of iron, chlorine, fluorine, sul- phur, phosphorus, and silica. Some of those bodies, such as alumina, which appear to take the lead in inorganic productions, are here scarcely seen. While the laws of inorganic chemistry appear to be fully in operation as respects the bodies ori the study of which we are now entering, there are some peculiarities which deserve to be pointed out. The remarkable insta- bility, or proneness to decomposition, which so many of them exhibit, generally tends to the production of second- ary compounds of a much more stable nature. At a red heat all organized bodies are decomposed ; and as the ele- ments of which they consist are endowed with the most energetic affinities, any extensive elevation of tempera- ture tends to impress upon them a change. "With but few exceptions, the attempts which have hitherto been made to produce them artificially have been abortive ; but this rs, probably, rather due to our want of knowledge than any intrinsic impossibility in effecting such combinations. With the exception of a few bodies, such as ammonia, which, in point of fact, belong rather to inorganic chem- istry, all organized bodies contain carbon. Of late, by in- direct processes, chemists have succeeded in obtaining pseudo- organized compounds, into the constitution of which such bodies as platinum and arsenic enter. In inorganic chemistry we see a constant disposition to the binary form of union : a disposition which is well rep- resented by the electro-chemical theory. Thus, potassi- um unites with oxygen, two bodies together, to form pot- ash ; and this, again, with sulphuric acid, two bodies to- gether, to form sulphate of potash. In very many instan- ces, the same thing can be traced in organic chemistry ; only here, instead of having such bodies as chlorine or iodine, potassium or sodium to deal with, we find com- pound bodies which discharge analogous functions. These bodies go under the name of compound radicals. They may be divided into distinct groups, some discharging the What other elements are found among organic bodies ? In their de- composition, what do they generally produce ? Can any of them with- stand a red heat? Can they be formed by artificial means? What is meant by compound radicals ? COMPOUND RADICALS. 309 duty of electro-negative, some of electro-positive, and some of indifferent bodies. In several cases they have been insulated, but in others they remain as yet as ideal or hypothetical bodies. Table of Compound Radicals. Amidogen. Oxalyle. Cyanogen. F errocy anogen. Ferridcyanogen. Cobaltocyanogen. Chromocy anogen. Platiuocy anogen. Iridiocyanogen. Sulphocyanogen. Mellone. Uryle. Benzyle. Salicyle. Cinnaniyle. Ethyle. Acetyle. Kakodyle. Methyle. Formyle. Cetyle. Amyle. Glyceryle. The qualities of bodies depending as much on the mode of arrangement of their constituent particles as on the chemical nature of those particles, it has been found con- venient to arrange them in groups, according to their type of structure ; thus, for instance, in the former de- partment of chemistry, such bodies as hydrochloric, hy- driodic, hydrobromic acids may be arranged together as belonging to one type ; and from the first of these all the rest may be conceived as arising, by substituting an atom of iodine, bromine, fluorine, &c., for the atom of chlorine which it contains. The bodies which can thus be substituted for each other appear to have certain relationships ; for the sub- stitution of a given substance can not take place indiscrim- inately by all other bodies. As a general rule, in inor- ganic combinations, electro-negative bodies can only be substituted by electro-negative, and electro-positive by electro-positive. But many of the most prominent cases in organic chemistry are precisely the reverse. In them, for example, we find chlorine, a powerful electro-nega- tive, taking the place of hydrogen, an equally powerful electro-positive body, and, in the compound, discharging all its functions. For these reasons, it has been supposed that the electro-chemical theory fails to furnish any ex- planation ; but I have proved that chlorine, like many other bodies, can assume different allotropic states ; at one time being an active electro-negative body, and at an- other quite passive. Moreover, it ought not to be for- What compound radicals are known ? Under what circumstances can bodies be substituted for each other? Is there any difference in this re- bpect between inorganic and organic bodies ? 310 DESTRUCTION OF ORGANIC COMPOUNDS. gotten that hydrogen, in relation to carbon, is as much an electro-negative body as chlorine itself. A chemical type is, therefore, a system, or group of atoms of a certain number, arranged in a certain relation- ship with each other. From this each atom may be dis- placed, and one of another kind substituted in its stead; and this may be carried forward until not one of the orig- inal atoms is left, the new group officiating in all respecta like its predecessor. But should one of the atoms be displaced, and no new one substituted for it, then, the re- maining atoms changing their position, the type is broken up and a new one is the result. Organic compounds, being for the most part composed of carbon, hydrogen, nitrogen, and oxygen, exhibit a con- stant tendency to break up into subordinate groups, and eventually to give rise to the production of the simpler binary bodies, carbonic acid, water, and ammonia. The carbon constantly inclines to unite with oxygen to form carbonic acid, the hydrogen, in the same manner, to form water, or, with the nitrogen, to produce ammonia ; and these tendencies may be satisfied in a variety of ways. Elevations of temperature in the open air at once give rise to carbonic acid, water, and free nitrogen; or if in close vessels out of the contact of air, to an extensive se- ries of compounds, differing in each case with the sub- stance exposed, and of a less complex constitution. Even in the air, at common temperatures, a slow action often goes on, as in the decay of wood or the souring of wine ; hence called eremacausis (slow combustion). When a combustible substance is ignited in the air at one point, the burning presently spreads throughout the whole mass; and in the slow combustion, eremacausis, the same takes place. A substance undergoing such a change, if placed in contact with another capable of un- dergoing it, propagates its effect throughout the whole mass. For this reason, the decay of yeast, a ferment, im- presses a metamorphosis on sugar, compelling it to give off carbonic acid gas ; and putrefaction of fresh meat is eas- ily brought on by the contact of putrid animal matter. What is a chemical type ? Under what circumstances do new types result ? "What are the binary bodies eventually produced ? What is the result of elevation of temperature in the open air ? What in close vessels 1 What is meant by eremacausis ? In what respect does -eremacausis re- semble common combustion ? THE NON-NITHOGENIZED BODIES. 311 Nitric, sulphuric, and other strong acids impress striking changes when heated with organic matters ; thus, when the former acts on starch, oxalic acid is formed; when sulphuric acid acts on oxalic, it totally destroys it, resolv- ing it into carbonic acid, carbonic oxide, and water. In the same manner, also, basic bodies produce striking chang- es, generally giving rise to the production of acids, and the evolution of hydrogen and ammonia. In the present state of organic chemistry, it is impos- sible to present a perfect system of arrangement, as in in- organic chemistry, or one approaching to the finish of that department. The course, therefore, which I shall now take is recommended rather for its usefulness in facilita- ting study than for the propriety of its classification. LECTURE LXVIII. THE NON-NITROGENIZED BODIES. The Starch Group. Starch. Action of Iodine. Various Forms of Starch. Production of Dextrine. Action of Diastase. Leio- come. Can e Sugar. Glucose. Distinction between Cane and Grape Sugar. Milk Sugar. Gum. Lig nine. THE non-nitrogenized bodies, which we shall first con- sider, are characterized by the peculiarity that they form a group, each member containing twelve atoms of carbon, united with hydrogen and oxygen in the proportions to form water. They are for the most part indifferent bod- ies. The Starch Group. Starch Cane sugar (crystallized) . . Grape sugar Milk sugar Gum Ci2//uOu. Lignine CizH% Os. Sec. &.c. Starch Fecula (C 13 H lo Oi ) is found abundantly in the vegetable kingdom, and may be obtained from potatoes What is the effect of strong acids and alkalies on organic bodies ? How many carbon atoms does each member of the amyle group contain? In what proportion are their oxygen and hydrogen? Mention some of the chief bodies of this group. From what sources, and in what manner, w starch obtained ? 312 VARIETIES OF STARCH. by rasping and washing the mass upon a sieve, the starch being carried off by the water. It may also be obtained from flour by making it into a paste with water and then washing it. The starch separates, and gluten is left be- hind. It is a white substance, commonly met with in irregu- lar prismatic masses, which shape it assumes while drying. It is insoluble in cold water, and also in alcohol, and con- sists of granules of different sizes, as it is derived from different plants, those of the potato being about the two hundred and fiftieth of an inch in diameter. When starch is heated in water, the covering mem- brane of each granule bursts open, and the interior matter dissolves out. If the proportion of starch be considerable, the whole forms a jelly-like mass, which may be dried in a yellowish body, having the same constitution as starch itself. Gelatinous starch passes under the name of Ami- dine. With free iodine, starch strikes a deep blue color. When water containing this compound is heated to 212 F., the color totally disappears, and is not restored on cool- ing ; but if the source of heat be removed as soon as the color disappears, and before the temperature reaches 212 F., the color returns. Starch and iodine constitute an ex- ceedingly delicate test for each other. In commerce, starch is found under various modifica- tions, such as Arrow-root, Tapioca, Cassava, Sago. It forms an important article of respiratory food. Inuline, which is derived from the dahlia and other plants, is a sub- stance approaching starch in many respects. When starch is boiled in water with a small quantity of sulphuric acid, it changes into Dextrine, a substance of the same composition ; the acid being subsequently removed by carbonate of lime and filtration, that body is procured on evaporation as a gummy mass. But if the ebullition be continued for a longer time, the dextrine disappears and grape sugar comes in its stead. Starch may also be converted into grape sugar by the action of a peculiar ferment, Diastase, which is contained in an infusion of What is the size of its granules ? What is the effect of hot water on it ? What is amidine ? What is the action of iodine on starch ? Mention gome other varieties of starch. How is it converted into dextrine ? How into grape sugar? What is diastase ? CANE SUGAR. 313 malt. Gelatinous starch may, in the course of a few min- utes, at 160 F., be converted into dextrine by this sub- stance, and soon after into sugar. In either of these cases the presence of atmospheric air is not required ; the final action being that the starch simply assumes three atoms of water, and becomes converted into grape sugar. When baked at a temperature of about 400 F., starch becomes soluble in water, and passes in commerce under the name of British Gum, or Leiocome. Cane Sugar (C^H^O^-}-2HO) is found abundantly in the juices of many plants, and is chiefly extracted for com- mercial purposes from the sugar-cane, which, being crushed between rollers, yields a juice, which is mixed with lime and boiled ; a coagulum having been removed from it, it is rapidly evaporated at as low a temperature as possible, and then crystallized. In tliis state, after a brownish sir- up, molasses, has drained from it, it passes in commerce un- der the name of Muscovado, or brown sugar. This is pu- rified by boiling in water with albumen, which, coagulat- ing, separates many of the impurities ; the solution is then decolorized by animal charcoal, evaporated, solidified in conical vessels, and, being washed with a little clean sirup, is thrown into commerce as loaf-sugar. Sugar is also ob- tained from the sap of the maple-tree, and from beet-root. From a strong solution Sugar crystallizes in rhombic prisms, which are colorless; they pass under the name of Sugar Candy. It is soluble in one third its weight of cold water, and in any quantity of hot. It has a sweet and proverbially characteristic taste.- When heated, it melts, and gives rise to a yellowish, transparent body, called Barley Sugar. But if kept at a temperature of 630 F., it turns of a reddish-brown color, constituting Caramel. Sugar unites with various bodies, such as lime and oxide of lead, and with common salt yields a crystallized prod- uct. By caseine it is transformed into lactic acid. Grape Sugar Fruit Sugar Glucose Starch Sugar Diabetic Sugar (C 12 H 14: O 14 } is the substance just de- scribed as arising from the transmutation of starch under the influence of acids. It occurs naturally in many vege- table juices and in honey. What is its action on starch? How is British ^um formed? .From what sources, and by what means, is cane sugar derived ? What are its properties? By what means is caramel formed? D D 314 GHAPE AND MILK SUGAR. Compared with cane sugar, it is much less soluble in water, and less disposed to crystallize. It requires l parts of water for solution. It may be distinguished by its action with caustic alkalies and sulphuric acid, the form- er turning it brown and the latter dissolving it without blackening, while cane sugar is little acted on in the form- er instance, and blackened in the latter. The two vari- eties may also be distinguished by being mixed with a so- lution of sulphate of copper, to which, if caustic potash be added, blue liquids are obtained, and these being heated, the grape sugar throws down a green precipitate, which turns deep red, the solution being left colorless : the cane sugar alters very slowly, a red precipitate gradually form- ing, and the liquid remaining blue. Grape sugar, like cane sugar, gives with common salt a crystallized com- pound. When heated to 212 F. it loses two atoms of water, and becomes C^H^O^.- Milk Sugar Lactine (C 12 jr i2 O l2 ) ;may be obtained by evaporating whey to a sirup, and the crystals which then form are to be purified by animal charcoal. It is sparingly soluble, requiring five or six times its weight of water. The crystals are gritty^ between the teeth. It is through the alcoholic fermentation of this body that the Tartars procure intoxicating milk. Besides the foregoing, there are several subordinate varieties of sugar, among which may be cited Ergot sugar * . . C^H^O^ ; Eucalyptus sugar ...... CuHuOu; and others, as liquorice sugar, mushroom sugar, or man- nite, &c. GrUM . Gum Arabic is obtained from several species of the mimosa or acacia, from the bark of which it exudes ; is obtained in white or yellowish tears, of a vitreous as- pect. It dissolves in cold water, forming mucilage, from which it may be precipitated pure, as Arabine, by alcohol. Bassorine is the principle of Gum Tragacanth ; it does not dissolve in water, but merely forms a jelly-like. mass. With this substance should be classed Pectine, the jelly obtained from currants and other fruits. This substance furnishes Pectic acid by the action of bases. What is the difference between cane and grape sugar ? By what test may they be distinguished? What are the properties of milk sugar? Mention some other varieties of sugar. From what source is gum de- rived ? What are arabine, bassorine, and pectine ? LIGNINE. #15 LIGNINE. This substance, with Cellulose and other bod- ies, forms the woody fibre or ligneous tissue of plants. It occurs in a state of purity in the fibres of fine linen and cotton, and, as is well known, is of perfect whiteness, in- soluble in water and alcohol, and tasteless. Strong and cold sulphuric acid converts it into a dextrine, as may be shown by adding to that substance pieces oJf linen, taking care that the temperature does not rise ^so as to blacken the mixture, which is to be well stirred, and suffered to stand for a time. On dissolving it then in water, and neutralizing by the addition of chalk, dextrine is obtained ; or if, before neutralizing, the solution is well boiled, grape sugar is produced. LECTURE LXIX. ACTION OF AGENTS ON THE STARCH GROUP. Action of Sulphuric Acid on Sugar. Glucic Acid produced by Lime. Melassic Acid. Action of Nitric Acid. Pro- duction of Oxalic Acid. Constitution of Oxalic Acid. Its Salts. Oxamide. Saccharic Acid. Rhodizonic and Croconic Acids. Mucic Acid. Xyloidine. Its Properties, IN the preceding Lecture we have already explained the change of starch into sugar, and of lignine into dex- trine, under the influence of sulphuric acid ; and in the vegetable world there can be no doubt that these and other similar modifications arise from the action of many causes. On inspecting the constitution of the group, it will be seen that, in theory, this is to be done by the ad- dition or abstraction of water. When melted grape sugar is mixed with strong sul- phuric acid, and the diluted solution neutralized with car- bonate of baryta, the sulphosaccharate of baryta is found in the solution. The Sulphosaccharic acid is a sweetish liquid, readily decomposing into sugar and sulphuric acid. When, in the process of converting cane sugar into How may lignine be prepared? When pure, what is its color, and what its relation to water ? How may it be converted into dextrine and grape sugar ? In this change, what is the action impressed on the lignine ? How is sulphosaccharic acid made ? 315 OXALIC ACID. grape sugar by boiling with sulphuric acid, the action is long continued, a dark-colored substance is formed, con- sisting of two different bodies, Ulmine and Ulmic Acid, or, as they are termed by Liebig, Sacchulmine and Sacchulmic Acid. The latter is converted into the former by contin- ued boiling in water. When a solution of grape sugar containing lime is kept for some time, the alkaline reaction of the lime finally disappears through the formation of Glucic Acid, the con- stitution of which is C & H h O b . It is soluble, deliquescent, of a sour taste, and yielding, for the most part, soluble salts. If grape sugar be boiled with potash water until it becomes black, a dark substance may be precipitated by an acid. This is Melasinic Acid, its constitution being CwJSeCk These are some of the less important results of the action of acid and alkaline bodies on the starch group ; there are others of far more interest. OXALIC ACID (C 2 O 3 , HO -\-2Aq). Oxalic acid is formed by the action of nitric acid on starch or sugar, or any other of the starch group, except gum and sugar of milk. One part of sugar is to be mixed with five of nitric acid, di- luted with twice its weight of water, and the acid finally distilled off until the residue will deposit crystals on cool- ing. These, being collected, are to be purified by redis- solving and crystallizing. They are oblique rhombic prisms, more soluble in liot than cold water, of an in- tensely acid taste, and poisonous to the animal economy, chalk or magnesia being the antidote. Oxalic acid also occurs naturally in several plants, in union with potash or lime. As the foregoing formula shows, the crystals of oxalic acid contain one equivalent of saline water and two of water of crystallization. The latter may be removed by exposure to a low heat, the crystals then becoming a white powder, and subliming without difficulty. Any at- tempt to remove the saline water and isolate the oxalic acid (as C 3 O 3 ) leads to its decomposition. Thus, when the acid is heated with oil of vitriol, total decomposition What are sacchulmine and sacchulmic acid? What is the constitution of glucic acid ? What is the action of potash on grape sugar ? Describe the preparation of oxalic acid. What is the antidote to it ? What is the action of oil of vitriol on oxalic acid ? BALTS OF OXALIC ACID. 317 results ; equal volumes of carbonic oxide and carbonic acid are set free : for the constitution of oxalic acid is such, that we may regard it as composed of an atom of each of those bodies : C,0 3 ... = ...CO a + CO; and upon this is founded one of the methods of preparing carbonic oxide gas. The gaseous mixture which results from the action of the oil of vitriol is passed, as in Fig. 243, through a bottle containing potash water, which ab- sorbs the carbonic acid, and the carbonic oxide may be collected at the water trough. The production of oxalic acid from sugar by nitric acid is due to the replacement of hydrogen by an equivalent quantity of oxygen. C 12 H 9 9 .. + 18 ... = ... C 12 18 . . + H 9 9 ; that is, one atom of dry sugar with eighteen of oxygen yields six atoms of oxalic acid and nine of water. Salts of Oxalic Acid. There are three potash salts : 1st. Neutral Oxalate of Potash, made by neutralizing oxalic acid with carbonate of potash ; crystallizes in rhombic prisms, soluble in three times its weight of water. 2d. Binoxalate of Potash, made by dividing a solution of oxalic acid into two parts ; neu- tralize one with carbonate of potash, and then add the other. It crystallizes in rhombic prisms, has a sour taste, and dissolves in forty parts of water. It occurs naturally in several plants, as the Oxalis Acetosella. 3d. Quadroxalate of Potash. Divide a solution of oxalic acid into four parts ; neutralize one and add the rest. It crystallizes in octa- hedrons ; less soluble than either of the foregoing. These salts are sometimes used for the removal of ink stains from linen. Oxalate of Ammonia, prepared by neutralizing a hot solution of oxalic acid with carbonate of ammonia. It crys- tallizes in rhombic prisms, which are efflorescent. Its so- lution is used, as has been already stated, as a test and precipitant of lime. When exposed to heat in a retort, it is, for the most part, decomposed into water, ammonia, How is this acid produced from sugar ? How many oxalates of potash are there ? How are they prepared ? For what purpose are these salt* sometimes used ? DD2 318 SACCHARIC MUCIC ACIDS. carbonic acid, cyanogen, and other compounds ; but a sub- stance of the name of Oxamide also sublimes, the consti- tution of which is C& NO,.. . = ...NH 2 + 2(CO), that is, containing the constituents of one atom of amido- gen and two of carbonic oxide. This remarkable sub- stance, when boiled with potash, yields, through the de- composition of water, oxalate of potash and ammoniacal gas. Oxalate of Lime occurs naturally, forming the skeleton of many lichens, and is obtained, as has just been said, by precipitating a lime salt. It is soluble in nitric acid, and, ignited in a covered crucible, is converted into carbonate of lime. SACCHARIC ACID (C^H^On + dlfO) Oxalhydric Acid, -made by the action of dilute nitric acid on sugar. It is a pentabasic acid. RHODIZONIC ACID (C 7 O 7 -\-3HO), obtained by the action of potassium on carbonic oxide at a red heat. When boiled, it changes into Croconic Acid, a yellow body hav- ing the constitution C 5 O 4 -\-HO. MUCIC ACID (CuH a O 4 +2HO), obtained by the action of dilute nitric acid on gum or sugar of milk, as in the preparation of oxalic acid by other members of the starch group. It requires sixty times its weight of water for so- lution. Decomposed by heat, it yields pyromucic acid. XYLOIDINE (C 6 H 4 O 4 , NO b \ made by the action of nitric 'acid, sp. gr. 1*5, on starch, which is converted into a gelati- nous body, and yields this substance as a white precipi- tate when acted on by water. Its origin is apparent from a comparison of its formula with that of starch. Xyloid- ine is insoluble in boiling water, but by the continued ac- tion of nitric acid changes into oxalic acid. 100 parts of starch yield 128 of xyloidine. GUN COTTON. Pyroxyline. A remarkable compound, proposed as a substitute for gunpowder by Schonbein, whose process for preparing it has not yet been divulged. It may be made by the action of monohydrated nitric acid Under what circumstances does oxamide form? What is its constitu- tion? How is saccharic acid made? Under what circumstances can glass be silvered with it? How is the rhodizonate of potash formed? What is its composition ? How is it changed into croconic acid ? Under what circumstances does mucic acid form ? FERMENTATION. 319 on cotton, paper, or sawdust; and still more conveniently by a mixture of nitric and sulphuric acids on those substances. The cheapest and best process for its preparation is that discovered by Prof. Ellet, of South Carolina College. It consists in soaking carded cotton for a few minutes in a mixture of pulverized nitrate of potash and oil of vitriol, washing the result in hot water to free the cotton from the potash salt, and finishing the washing by a weak so- lution of ammonia. Gun cotton appears white, like or- dinary cotton, the fibre being little changed ; it is some- what harsh to the touch ; when perfectly dry, it explodes when heated to about 300 F., or by the blow of a ham- mer. It is estimated as having about three times the me- chanical force of gunpowder. 100 parts of cotton yield about 165 of gun cotton. It contains twice as much nitric acid as xyloidine. LECTURE LXX. ON THE METAMORPHOSIS OF THE STARCH GROUP BY Ni- TROGENIZED FERMENTS. Action of Leaven. Bread. Fermentation of Sugar. Fermentation of Grape Juice. Primary Action on the Ferment. Activity of Ferments due to Nitrogen. Effects of Temperature. Production oj Butyric Acid. Ferments of different Properties. Pro- duction of Wine and intoxicating Liquids. IN the preceding Lecture we have traced the action of the more powerful inorganic agents on the amyles, and seen how a variety of bodies of different characters arise, some of which, as oxalic acid, are of very considerable importance. But there is another system of changes which can be impressed on this group of bodies, far more curious in its nature, and leading to far more important results. When flour, made into a paste with water, is brought in contact with Leaven, that is to say, a similar dough, un- dergoing an incipient putrefactive fermentation, at a tem- perature of 60 or 70 F., bubbles of gas are disengaged, Decomposed by heat, what does mucic acid yield ? How is xyloidine prepared, and what are its properties ? What is the action of leaven on 320 ACTION OF FERMENTS. the paste swells up, and, when baked, forms leavened bread. This ancient process, which is now in use all over the world, depends on the action of the changing leaven being propagated to the sugar which the flour contains. The sugar is resolved into alcohol and carbonic acid gas, the former of which may be obtained by distilling the dough j and the bubbles of the latter, entrapped in the yielding mass, gives to the bread the lightness for which it is prized. But this process may be better traced by observing the phenomena of alcoholic fermentation in the case of pure sugar. If we take a solution of sugar in water, it may be kept for a length of time without undergoing any change ; but if nitrogenized matters, such as blood, albu- men, leaven, in a state of putrescent decay, are mixed with it, then, at a temperature of 70 F., the sugar rapidly disappears, carbonic acid is given off, and alcohol is found in the solution. The change is obvious. ' C lz H l2 Ou ... = ... 2(C ACTION OF FERMENTS. 321 yeast itself is exhausted, and then any excess of sugar re- mains unacted upon. It is obvious that the primary action is an oxydation of the ferment, and the moment its particles are set in motion the motion is propagated to the adjacent body, the particles of which submit in succession ; and there- fore the fermentation is not a sudden action, but one re- quiring time. Moreover, it is plain that the action is lim- ited ; a given quantity of yeast will transmute only a defi- nite quantity of sugar. The ferments, or bodies which possess this singular quality, are nitrogenized bodies ; and, inasmuch as non- nitrogenized bodies never spontaneously ferment while oxydizing, it is to the nitrogen that we are to impute the qualities in question. Temperature has a remarkable control over ferment action. The juice of carrots or beets, fermenting at 50 Fahr., will yield alcohol, carbonic acid, and yeast; but the same juices, fermenting at 120 Fahr., produce lactic acid, gum, and mannite. Under these circumstances, therefore, alcohol is the product of fermentation at low, and lactic acid at high temperatures. But when milk ferments at 50 Fahr., lactic acid is the chief product, while at 80 Fahr. the casein acts like a yeast ferment, the milk sugar becoming transformed into grape sugar, and then resolving itself into alcohol and carbonic acid. In this instance the action is the reverse of the former, lactic acid being the product of a low, and. alcohol of a high temperature. A very remarkable decomposition takes place when casein ferment acts on sugar at 80 Fahr. in presence of carbonate of lime. Under these circumstances, carbonic acid gas and hydrogen are evolved, and Butyric Acid ap- pears. On comparing the constitution of butyric acid with alcohol, it will be seen that the latter contains the elements of the former, with an excess of hydrogen ; so that, during this fermentation, the alcohol atom is divided. All ferments possess certain properties in common, but each has its specific powers ; and the products which are What is the primary action in these cases ? Is the action of the fer- ment definite ? To what element in the yeast is the action due 1 What is the effect of temperature on fermentation? Describe the causes of the fermentation of vegetable juices and of milk ? Under what circumstances does butyric acid form ? 322 PREPARATION OP WINES. evolved differ in different cases. Most commonly the ac- tivity of these bodies is excited by an incipient oxyda- tion, the result of whkh would be to bring the ferment itself to a simpler constitution. In this respect, therefore, the first stage of fermentation is a combustion at common temperatures, or an eremacausis of the ferment itself; but this action is speedily propagated to the surrounding mass, which becomes involved in the change. What- ever, therefore, prevents the incipient oxydation of the ferment puts a stop to the whole process. By raising their temperature to 212, and then cutting off the access of air, substances which would otherwise undergo a very rapid change may be kept for any length of time without alteration. On this principle, meats, milk, and other viands may be preserved. We have now pointed out the peculiarities of ferment action, showing that two successive stages may be traced in the process ; the first arising in the oxydation of the ferment, by which its molecules are decomposed ; and the second, which consists in the propagation of this move- ment to the surrounding particles, upon which changes are impressed, the nature of which differs with the tem- perature and the specific action of the ferment itself. Wine is made from the expressed juice of grapes, which, containing a nitrogenized body, albumen, when exposed to the air undergoes spontaneous fermentation ; the course of the action being, 1st. The oxydation of the vegetable albumen ; 2d. The propagation of its action to the grape sugar. If the sugar is in excess, the wine remains sweet ; if the albumen is in excess, the wine is dry. The vrine, as soon as the first action is over, is removed into casks. During these changes, the bitartrate of potash, which exists naturally in grape juice, and which, though sparing- ly soluble in water, is much less so in alcohol, is deposit- ed. It goes under the name of Argol. Most other fruit juices contain free acid, such as malic or citric ; and hence good wine can not be made from them, because, if all the sugar is removed, they possess a sharp taste ; and if, as is What is the change which the ferment itself undergoes ? What is the effect of cutting off the access of air ? What are the two stages of fer- ment action ? What is the process for the making of wine ? When is the wine sweet, and when dry ? What*s argol ? Why are other fruit juice* less proper for making wine than grape juice ? ALCOHOL. 323 commonly the case, a portion is left to correct the acid- ity, it is liable to run into a second fermentation. Inferior liquids, such as cider, perry, &c., are made from other vegetable juices, as those of apples, pears, &c. Beer, porter, and ale are made from an infusion of malt, which is barley, a portion of the starch of which is trans- posed into sugar by partial germination. The principles of the fermentation are, in all these instances, the same. LECTURE LXXJ. ON THE DERIVATIVES OF FERMENTATIVE PROCESSES.- Alpohol. Its Properties. Exists in Wines. Lactic Add. Production and Properties. Sulphuric Ether. Its Distillation. The Ethyh Series. Chloride. Bromide.-r-Nitrate, fyc. CEnanthic Ether. ALCOHOL (Hydrated Oxide of E thy k) C A H 6 O 2 . BY the distillation of wine, or any other fermented sac- charine juice, spirits of wine maybe obtained. As first pre- pared, it contains a large quantity of water, which comes over with it. This product being rectified, and the first por- tion preserved, yields a spirit containing twelve to fifteen per cent, of water. By putting this into a retort with half its weight of quicklime, keeping the mixture a few days, and then distilling at 'a low temperature, absolute or an- hydrous alcohol is obtained. Anhydrous alcohol is a colorless liquid of .a burning taste and pleasant odor. Its specific gravity, at 60 F., is 0-795. It boils at 123 F., and at a still lower point if slight- ly diluted with water, though the boiling point rises if the water be in greater proportion. It has not been yet fro- zen. The specific gravity, also, varies with the amount of water present; and hence the purity of spirits of wine may be determined by ascertaining its density. Alcohol is very inflammable, burns with a pale blue flame, with the producton of carbonic acid gas and water. It is much used in chemical investigations as furnishing a lamp flame free from smoke, and as possessing an extensive range of How is alcohol procured ? How may it be obtained anhydrous ? What are its properties 1 How may the strength of spirits of wine be deter- mined ? For what purposes is it used in chemistry ? 324 LACTIC ACID. solvent powers, acting upon resins, oils, and other bodies, which are not acted upon by water. The strong wines, such as port and sherry, contain from nineteen to twenty-five per cent, of alcohol ; the light wines from twelve per cent, upward ; and beer, porter, &c., from five to ten per cent. Lactic Acid Fermentation. We have already seen that vegetable juices as well as milk will, under certain cir- cumstances of temperature, yield, during fermentation, lactic acid instead of alcohol. This acid may, therefore, be made by dissolving a quantity of sugar of milk in milk, putting it in a warm place, and allowing it to turn sour spontaneously. A part of the caseine of the milk here acts as the ferment, and as lactic acid is set free, it coagulates the rest and makes it insoluble. By the addition of car- bonate of soda, to neutralize the acid, this is prevented, and the ferment resuming its activity, produces more lactic acid. When, by this process, all the sugar is exhausted, the liquid is boiled, filtered, evaporated to dryness, and the lactate of soda dissolved out by hot alcohol. From this alcoholic solution the acid may be obtained by pre- cipitating the soda by sulphuric acid. Lactic Acid ( C 6 H 5 O r ,-\-HO) is obtained as a sirupy solu- tion by concentrating in a vacuum over oil of vitriol. It is colorless, has a specific gravity of 1'215, is very sour, and soluble in water and alcohol. It yields a complete series of salts, most of which are soluble. Among these salts, the most interesting are those of lime and of zinc. ETHER Sulphuric Ether Oxide of Ethyle (C 4 H 5 O). Ether is prepared by distilling equal weights of alcohol and oil of vitriol, receiving the resulting vapor in a Lie- big's condenser, a d Ti c, as in Fig. 269, the condenser be- ing cooled by water from the reservoir, ?', flowing into the funnel, c, the waste passing into the vessel, b, and the ether distilling into the bottle, e. The process is to be stopped as soon as the mixture begins to blacken. The first prod- uct may be rectified by redistillation from caustic potash. '" Ether is a colorless and limpid liquid, of a peculiai odor and hot taste. It boils at t)6 F., and has not yet How much alcohol per cent, is contained in port, sherry, beer and ale ? What is the process for obtaining lactic acid ? What is its constitution ? What are its properties ? How is ether made ? What are the proper- ties of ether? COMPOUNDS OF ETHYLE. 325 been frozen. Its specific gravity, at 60 F., is -720. It volatilizes with rapidity, and therefore produces cold. It is combustible, and burns with the evolution of much more light than alcohol. The specific gravity of its vapor is 2-5S6. With oxygen or atmospheric air it forms an ex- plosive mixture, and, kept in contact with air, it becomes acid from the production of acetic acid. It dissolves in alcohol in all proportions, but ten parts of water are re- quired to dissolve one of it ; it also dissolves many fatty substances, and hence is of considerable use in organic chemistry. Ether is regarded as the oxide of an ideal compound radical, ethyle, C 4 H 6 , which gives rise to a series of othei bodies. The Ethyle Group. Ethyle, C*H- = Ae. Oxide of ethyle = Ae, O. Hydrated oxide = Ae, O + HO. Chloride of ethyle = Ae, Cl. Bromide " = Ae, B. Nitrate " . : . ' . . = Ae, O 4- NOn. Hyponitrite " = Ae, O -j- NOs. &c. &c. The oxide of ethyle, as has just been stated, is ether it- self. The hydrated oxide is alcohol. Is it soluble in water ? What class of bodies does it dissolve ? Of what substance is it an oxide ? E E 326 COMPOUNDS OP ETHYLE. Chloride ofEthyle Hydrochloric Ether may be made by saturating rectified spirits of wine with dry hydro- chloric acid gas, and distilling the result at a low tempera- ture, conducting the vapor through a bottle of warm Wa- ter, and then condensing in a receiver surrounded by a freezing mixture. It is a colorless, volatile liquid, of a peculiar aromatic smell ; the specific gravity is '874. It boils at 52, and is not decomposed by nitrate of silver. Bromide of Ethyle (Hydrobromic Ether) and Iodide vf Ethyl (Hydriodic Ether) are not of any importance ; and the same remark may be made as respects the sulphuret and the cyanide. Nitrate of Ethyle Nitric Ether may be made on the small scale by distilling equal weights of alcohol and nitric acid with a. small quantity of nitrate of urea. The latter substance is used to prevent the nitric acid deoxydizing, and giving rise to the production of hypoiiitrite instead of nitrate of ethyle. Nitrate of ethyle is insoluble in water, has a density of 1*112, boils at 185, and has a sweet taste. Its vapor explodes when heated. Hyponitrite of Ethyle Nitrous Ether (AcO, iVO a ). This ether may be made by passing the hyponitrous acid, disengaged from one part of starch and ten of nitric acid, through alcohol, diluted with half its weight of water and kept cold. It is a yellowish, aromatic liquid, having the odor of apples. It boils at 62 F. Its density is '967. The sweet spirits of nitre is a solution of this ether with aldehyde and other substances in alcohol. Carbonate of Ethyle Carbonic Ether (AeO, CO 2 ] made by the action of potassium on oxalic ether, and distill- ation of the product with water. It floats on the surface of the distilled liquid, is an aromatic liquid, and boils at 259. Oxalate ofEthyle Oxalic Ether prepared by distill- ing four parts of binoxalate of potash, five of sulphuric acid, and four of alcohol into a warm receiver. The product is washed with water to separate any alcohol or acid, and redistilled. It is an oily liquid, of an aro- matic odor ; it boils at 353 F., and is slightly heavier than water. With an excess of ammonia it yields Oxamide and What is the true name of hydrochloric ether, and how is it prepared ? How is the nitrate of ethyle made ? How is nitrous ether prepared, and what are its properties ? How are carbonic ether, acetic ether, and for- mic ether made ? SULPHOVINIC ACID. 327 alcohol. With a smaller proportion of ammonia and al- cohol it yields Oxamethane, C S H 7 NO C . Acetate of Ethyle Acetic Ether (AeO, C 4 H 3 O^ and Formiate of Ethyle Formic Ether (AeO, C. 2 HO^) are procured in a similar manner with the foregoing, substi- tuting in one case acetate of potash, and in the other formiate of soda. (Enanthic Ether (AeO, C 14 JJ 13 O. 2 ) is prepared from an oily liquid which passes over during the distillation of cer- tain wines. It has a powerful vinous odor, is a colorless liquid, specific gravity -862 ; it boils at 410 F., dissolves readily in alcohol, and gives their peculiar aroma to the wines in which it is found. From it cenanthic acid may be obtained by the successive action of potash and sul- phuric acid. It is an oily body, becoming a soft solid at 550 F. LECTURE LXXII. DERIVATIVE BODIES OF ALCOHOL. Sulphovinic and Phos- phovinic Acids. Products of Sulphovinic Acid at Dif- ferent Boiling Points. The continuous Ether Process. The continuous Olejiant Gas Process. Dutch Li- quid. -^-Successive Substitutions of Chlorine in it. Heavy and Light Oil of Wine. Sulphate of Carbyle and its derivative Acids. SULPHOVINIC Acid^Bisulphate of Ethyle (CH- O .2SO 3 + HO). A mixture of sulphuric acid with an equal weight of alcohol is to be heated to the boiling point, and then allowed to cool. It is then to be diluted with water and neutralized with carbonate of baryta; the sulphate of ba- ryta subsides. The solution is then filtered, evaporated, and, when cold, the sulphovinate of baryta crystallizes. From this the Sulphovinic acid may be obtained by pre- cipitating the baryta with dilute sulphuric acid, and evap- orating the resulting solution in vacuo. It is a sirupy liquid, of a sour taste, giving rise to a series of soluble salts, which decompose at the boiling point, as will be pres- ently seen. From what source is cenanthic ether derived ? What is its relation to vinous bodies ? How is Sulphovinic acid made ? W hat is its composition ? 528 CONTINUOUS ETHER PROCESS. Phosphovinic Acid (C t H- a O, PO 5 +2HO) is made on the same principles as the foregoing, phosphoric acid being substituted for sulphuric, and decomposing the resulting baryta salt in the same way. It is a sirupy liquid, of a sour taste, and dissolves in water, alcohol, and ether very readily. It is decomposed by heat. If sulphovinic acid be diluted so as to bring its boiling point below 260 F., it is resolved at that temperature chiefly into sulphuric acid and alcohol, which distills over. If the boiling point is from 260 F. to 310 F., the dis- tillation results chiefly in the production of hydrated sul- phuric acid and ether. If, by the addition of sulphuric acid, the boiling point is carried above 320 F., the action is more complex, but the chief product which passes over is olefiant gas. The ordinary method of preparing ether is, therefore, obviously very disadvantageous, because it is only within a particular range of temperature that that body is evolved. At first the low temperature yields alcohol, and as the heat rises, the mixture begins to blacken and olefiant gas to be evolved. To obviate these difficulties, a very beautiful process, the continuous process, has been introduced. It consists in taking a mixture of eight parts by weight of sulphuric acid and five of alcohol, specific gravity '834, the boiling point of which is about 300 F. This is brought to that temperature, and alcohol of the same density is allowed slowly to flow into the mixture, the boiling point being steadily kept as near 300 F. as possible, and the mixture maintained in a state of violent ebullition. Water and ether distill over together, and may be passed through a Liebig's condenser; they collect in the receiver in sepa- rate strata, or, if this does not take place at first, the ad- dition of a little water in the receiver insures it. In this manner a very large quantity of alcohol maybe converted into ether and water by the action of a limited amount of sulphuric acid ; and in a similar manner, by ad- justing the boiling point so as to be between 320 and 330 F., olefiant gas may be continuously obtained. All, therefore, that is required, is to convey the alcoholic va- \Vhat is the composition and mode of preparation of phosphovinic acid ? What is the result of the exposure of sulphovinic acid at different boiling points ? Describe the continuous process for the preparation of ether. SUBSTITUTIONS IN DUTCH LIQUID. 329 por through a mixture of oil of vitriol with half its weight of water, which has the required boiling point. In this process the acid does not blacken, and it is therefore much more advantageous than that described for the preparation of olefiant gas in Lecture LI V. Chloride of Olefiant Gas Dutch Liquid (C 4 H 4 C1. 2 ) is prepared by mixing equal volumes of chlorine and ole- fiant gas in a large glass globe. It is a colorless and fra- grant liquid, soluble in alcohol and ether, but less so in water. It boils at 180 F., and when acted on by a so- lution of caustic potash in alcohol, it yields chloride of potassium and a substance C^H^Cl, which, on being cooled by a freezing mixture, condenses into a liquid. This li- quid, brought in contact with chlorine, absorbs that sub- stance, and yields a new compound, CH A Cl r which may again be decomposed by an alcoholic solution of potash into chloride of potassium and a new volatile body, C 4 H,C1 2 . There is an iodide and a bromide of olefiant gas, which possess a constitution analogous to the chloride. When chlorine gas is made to act upon Dutch liquid, three different substances may be successively formed by the gradual abstraction of hydrogen, and its equivalent substitution by chlorine. These substances are as follow : Dutch liquid ....... C 4 H 4 C1 2 . (1.) C 4 H 3 C1 3 . (2.) C 4 H 2 Cl<. (3.) C 4 CI&. The first and second of these products are volatile li- quids, the third is the perchloride of carbon, in which it ap- pears that all the four atoms of hydrogen in the Dutch liquid have been removed, and their places occupied by four atoms of chlorine. This perchloride of carbon is a white, crystalline body, soluble in alcohol and ether. Its melting point is 320 F. By passing its vapor through a red-hot porcelain tube, it is decomposed, yielding C 4 C1 4 , and free chlorine, and this again gives rise to subchloride of carbon, C 4 C/ 2 , by being passed through an ignited por- celain tube at a white heat. The former of these bodies is a colorless liquid, and the latter a silky solid. Heavy Oil of Wine (C; Monochlorureted hydrochloric ether . . 'C 4 H^C1 2 ; Bichlorureted " . " . . C^H^Cl* ; Trichlorureted " " . . C 4 H 2 Cl^; duadrichlorureted " " . . C 4 H Ch; Perchloride of carbon C 4 Ck' r furnishing, therefore, a very striking instance of the doc- trine of substitution. Mercaptan Sulphur-alcohol (C 4 H 6 S 2 ) is prepared by saturating a solution of caustic potash, specific gravity 1*3, with sulphureted hydrogen, and distilling it with an equal volume of sulphovinate of lime -of the same density. It passes over with water, on the surface of which it floats as a colorless liquid, specific gravity '842, soluble in alcohol. It boils at 97, smells like onions, and burns with a blue flame. Mercaptan corresponds to alcohol in which all the oxygen has been replaced by sulphur; but in its action on metallic oxides it answers to the hydruret of a compound radical, C 4 H 5 S. 2 . Thus, with peroxide of mercury, it forms a mercaptide with the production of water; and this may be decomposed by sulphureted hy- drogen, sulphuret of mercury subsiding, and mercaptan being reproduced. Mercaptan derives is name from its strong affinity for mercury (Mercurium Captans). Xantliic Acid'(C 6 H 5 S 4 O + HO}. Hydrate of potash is to be dissolved in twelve parts of ajcohol, specific gravity 800, and bisulphuret of carbon dropped into the solution Describe the successive action of chlorine upon ether. What remark- able qualities does mercaptan possess ? How is it prepared ? From what is its name derived ? What is the process for preparing xanthic acid? KAKODYLE. 337 until it ceases to have an alkaline reaction. On cooling to zero, the xanthate of potash crystallizes : it is to be dried in vacuo. It is soluble in water and alcohol, but not in ether ; and from it xanthic acid may be procured by the action of dilute hydrochloric acid. Xanthic acid is an oily liquid, heavier than water, which first reddens and then bleaches litmus paper. At 75 it is decomposed into alcohol and bisulphuret of carbon. It is also decom- posed by the action of the air. KAKODYLE (C 4 H 6 As = Kd) is a compound radical, which gives rise to an extensive group of bodies, in which it acts the part of a metal. The Kakodyle Group. Kakodyle, CiHsAs =Kd. Oxide of kakodyle = KdO. Chloride " = KdC~ Iodide " = Kdl. Sulphuret " = KdS. &c. &c. Kakodyle may be obtained by decomposing the chlo- ride of kakodyle with metallic zinc in an apparatus filled with carbonic acid gas, and may be purified by re-distil- lation from zinc, similar precautions being taken to -ex- clude atmospheric air. It is a colorless liquid, of a pow- erful odor, taking fire on the contact of air, oxygen gas, or chlorine; boils at 338, crystallizes at 21, and is de- composed by a red heat into olefiant gas, light carbureted hydrogen, and arsenic. Oxide of Kakodyle Alkarsine Cadet's Fuming Liquor is prepared by the distillation of acetate of potash and arsenious acid, receiving the products in an ice-cold vessel the temperature being finally carried to a red heat. The oxide comes over in an impure state, sinking to the bot- tom of the other products. It is to be decanted, washed with water, boiled, and then distilled in a vessel full of hydrogen from hydrate of potash. It is a colorless li- quid, specific gravity 1*462, boils at 300, and solidifies at 9 ; is sparingly soluble in water, but more so in alcohol ; is excessively poisonous, possessing a concentrated smell like garlic. Heated in the air, it burns, producing car- bonic acid, water, and arsenious acid. Chloride of Kakodyle may be procured by the action of What is its action on litmus paper ? What is kakodyle ? How may it be isolated ? What are alkarsine and Cadet's fuming liquor ? How is it prepared, and what are its properties? F F 388 THE WOOD-SPIRIT tiKOUP. a dilute solution of corrosive sublimate on a dilute alco holic solution of oxide of kakodyle ; a white precipitate falls, which, distilled with strong hydrochloric acid, yields corrosive ^ublimate, water, and the chloride of kakodyle passes over. When purified by chloride of calcium, and distilled in an atmosphere of carbonic acid, it is a color- less liquid, of a dreadful odor, heavier than water, and iii- Boluble therein, but soluble in alcohol. It is very poison- ous. It boils at about 212, the vapor taking fire in the air. KaJwdylic Acid Alcargcn (Kd . O 3 ) may be made by the action of oxide of mercury upon oxide of kakodyle un- der the surface of water, at a low temperature. Kakodylic acid forms crystals which deliquesce in the air, are soluble in water and alcohol, but not in ether. It is not acted upon by oxydizing agents, such as nitric acid, but is reduced to oxide of kakodyle by several deoxydizing bodies. It is not poisonous. Kakodyle furnishes a complete series of bodies : the iodide, sulphuret, cyanide, and a substance isomeric with the oxide, which has the name of parakakodylic oxide. LECTURE LXXV. -SriRiT GROUP. Methyle. Its Oxide and Hy- drated Oxide. Salts of Methyle. Formic Acid, natu- ral and artificial Production of. Derivatives of l^Vood Spirit. Substitutions of Chlorine in Oxide of Methyle. Substitutions in Chloride of Methyle. IN the destructive distillation of wood in the prepara- tion of pyroligneous acid, there passes over a body to which the name of wood spirit has been given. This is the hydrated oxide, or alcohol of an ideal compound rad- ical, passing under the name of methyle. The Methyle Group. Methyle, C 2 H 3 = Me. Oxide of methyle . . . . = MeO Hydrated oxide ......= MeO -4- HO. Chloride = MeGL &c. Sec. What is the process for preparing the chloride of kakodyle 1 What are its properties 1 What is the constitution of alcargen ? Under what cir- cumstances is wood spirit produced ? What is its ideal compound radical T COMPOUNDS OF METHYLE. 339 Oxide of Methyle Mcthylic Ether Wood Ether (C. 2 H 3 O). This substance is made from the hydrated ox- ide on the same principle that ether is obtained from al- cohol : one part of wood spirit and four of oil of vitriol being heated in a flask, the vapor is passed through a small quantity of caustic potash solution, and received at the mer- curial trough. It is a permanently elastic gas, colorless, and has a specific gravity of 1*617, burns with a pale flame, is very soluble in water, which takes up thirty-three times its volume of it, and yields it unchanged when heated. Hydrated Oxide of Methyle Wood Spirit Pyroxylic Spirit may be separated from crude wood vinegar by dis- tillation. It passes over with the first portions along with a little acid, which, being neutralized with hydrate of lime, the wood spirit may be separated from the oil which floats on its surface, and redistilled. The product thus obtained may be rectified in the same manner as common alcohol, and rendered anhydrous by quicklime. It is then a color- less liquid, of a hot taste and peculiar smell. It boils at 152, and has a specific gravity of -798 at 68. It is sol- uble in water, dissolves resins and oils, and may be burn- ed like spirit of wine. It then exhales a peculiar odor. . Chloride of Methyle (MeCl) may be made from the re- action of sulphuric acid upon common salt and wood spirit. It is a colorless gas, which may be collected over water; has a density of 1'731. It has a peculiar odor, is inflammable, and may be decomposed by passing through a red-hot tube. Sulphate of Oxide of Methyle (MeO, SO 3 ) may be pre- pared by distilling one part of wood spirit with eight or ten of oil of vitriol ; the product is to be washed with water, and redistilled from caustic baryta. It is an oily, neutral liquid, smelling like garlic ; specific gravity 1-321. It boils at 370. It is not soluble in water, but is decom- posed by that liquid, especially at the boiling temperature, into sulphomethylic acid and hydrated oxide of methyle. It is to be observed, that in the series of wine alcohol there is no compound corresponding to this. Nitrate of Oxide of Methyle (MeO, NO 6 ) is obtained by How is the oxide of methyle prepared, and what is its form ? What is the constitution of pyroxylic spirit? What are its properties, and for what purposes may it be used '? How is the chloride of methyle prepar- ed ? In the wine series, is there any compound analogous to sulphate of oxide of methyle ? 310 FORMIC ACID. the action of a mixture of wood spirit and oil of vitriol upon nitrate of potash. It is a colorless liquid, heavier than water ; boils at 150 ; burns with a yellow flame. Its vapor explodes when heated. In a solution of caustic potash, it decomposes into nitrate of potash and wood spirit. Oxalate of Oxide of'MetJiyle (MeO, C. 2 O 3 ) is made by distilling oxalic acid, wood spirit, and oil of vitriol. The liquid which is collected is allowed to evaporate ; it yields crystals of the oxalate. When pure, it is colorless ; melts at 124, and boils at 322. It is decomposed by hot water into oxalic acid and wood spirit, by solution of ammonia into oxamide and wood spirit. Sulphomethylic Acid (MeO, 2SO 3 + HO), the com- pound corresponding to sulphovinic acid, and prepared in the same way, by substituting wood spirit for alcohol It is thus procured as a sirup or in small crystals, solu- ble in water and alcohol. It is an instable body, and pos- sesses many analogies with sulphovinic acid. Formic Acid (C 2 HO 3 + HO). This acid, in the wood- spirit series, is the analogue of acetic acid in the alcohol series. It maybe procured on principles similar to those involved in the preparation of acetic acid, as by the grad- ual oxydation of the vapor of wood spirit in the air under the influence of black platinum. In a dilute state it may be prepared by distilling one part of sugar, three of per- oxide of manganese, and two of water, with three parts of sulphuric acid, diluted with an equal weight of wa- ter. The liquid which distills is to be neutralized by carbonate of soda, purified by animal charcoal, and redis- tilled along with sulphuric acid. It occurs naturally in the bodies of red ants, and hence has obtained the name of formic acid. From the distillation of those animals it was originally procured. Anhydrous formic acid (C. 2 HO 3 ) obviously contains the elements of two atoms of carbonic oxide and one of water. It yields two hydrates, respectively containing one and two atoms of water. The first, for which the formula has already been given, is procured by the ac- How is the nitrate obtained, and what are its properties ? Describe the preparation of the oxalate and of sulpho-methylic acid. What is the con- stitution of formic acid ? How is it procured 1 From what circumstance is its name derived? What are its properties? DERIVATIVES OF METIIYLE. 341 tion of sulphureted hydrogen on formiate of lead. It is a colorless liquid, of a strong odor; boils at 212, and crys- tallizes below 32. It is inflammable, and has a specific gravity of 1-235. It blisters the skin. Formic acid yields a complete series of salts. Chloroform (C. 2 HC1 3 ) is made by distilling wood spirit w>h a solution of chloride of lime. It is a colorless liquid ; specific gravity 1*48 ; boils at 141. It burns with a green flame, and is decomposed by an alcoholic solution of potash into chloride of potassium and formiate of pot- ash. The relationship between formic acid and chloro- form is obvious : it consists in the substitution of three atoms of chlorine for three of oxygen. There are also two analogous compounds : Bromoform C 2 HBr 3 . lodoform C 2 /// 3 . FormometTiylal (C 3 H 4 O. 2 ) is prepared by distilling wood spirit, oxide of manganese, and dilute sulphuric acid. On saturating the product with potash, formomethylal sepa- rates as a colorless oily liquid : specific gravity '855 ; boils at 107, and soluble in water. Methyle-mercaptan. Formed as the common mercap- tan, by substituting sulphomethylate of potash for sulpho- vinate of lime. It is analogous to common mercaptan. When chlorine is made to act on the oxide of methyle at common temperatures, it removes one of the hydrogen atoms ; and by continuing the action, a second may be taken away, and the process of substitution, as shown in the following series, may be carried so far as to end in the removal of oxygen and the production of chloride of carbon. Oxide of methyle C 2 H 3 O. - 1st substitution C Z H 2 O, Cl. 2d " C Z H O, C7 2 . 3d " C 2 O, C1 3 . 4th (chloride of carbon) . C 2 C7 4 . Other methylic compounds furnish similar series, thus : Chloride of methyle ^ . C 2 H 3 CL 1st substitution C Z H Z C1 2 . 3d " (chloroform) . . . . . . C^H C1 3 . 3d " (chloride of carbon) . . C 2 CZ 4 . How is chloroform obtained ? "What is the process for preparing for- momethylal ? Describe the series of substitutions of chlorine on the oxide of methyle. Describe the analogous substitutions with chloride of methyle ? FF 2 342 FUSEL OIL. LECTURE LXXVI. THE POTATO OIL GROUP. Fusel Oil. Chloride of Amyle. Sulphamylic Acid. Amilen. Relations of Valerianic Acid. THE BENZYLE GROUP. Oil of Bitter Almonds. Benzoic Acid. Sulphobenzoic Acid. Chloride of Benzyle. Benzamide. IN the distillation of brandy from potatoes, a volatile oil passes over. It is regarded as the hydrated oxide of an ideal compound radical, which passes under the name of Amyle, having the constitution C 10 H n . The Potato Oil Group. Amyle, CioHn ......... = Ayl. Amyle ether .......... = AylO. Amyle alcohol (potato oil) ..... = AylO -f- HO. Chloride of amyle ........ = AylCl. &.C. &.C. Amilen ......... CioHio. Valerianic acid Of these, amyle and its oxide, amyle-ether, are ideal. Hydrated Oxide of Amyle Amyle Alcohol Potato Oil Fusel Oil ( C W H U O-}-HO). This substance passes over toward the end of the first distillation of potato spirit, and communicates to it a milky aspect. On standing, it floats on the surface, and may be purified by washing with wa- ter, drying with chloride of calcium, and redistillation. It is a fluid oil of a suffocating odor, which acts power- fully on the animal system. Its specific gravity is '818 ; it boils at 269. Chloride of Amyle (AylCl} is made by distilling equal weights of potato oil and perchloride of phosphorus, wash- ing with potash water, and redistilling from chloride of calcium. It is an aromatic liquid, boils at 215, and burns with a green flame. Under the influence of sun- shine, eight of its hydrogen atoms may be removed, eight chlorine atoms being substituted for them, C lQ H n Cl yield- ing C w H 3 Cl gt forming chlorureted chloride of amyle. What is the imaginary radical of the potato oil group ? What are the nature and relations of fusel oil ? What are the properties of the chloride of amyle ? VALERIANIC ACID. 843 The Iodide and Bromide of Amyle are compounds anal- ogous to the chloride. Acetate of Oxide of Amyle is obtained by distilling ace- tate of potash, potato oil, and sulphuric acid. . It is a col- orless liquid, which boils at 257. Sulphamilic Acid (AylO, 2SO 3 H + O) is generated when sulphuric acid is made to act on an equal weight of potato oil. From this, by the successive action of car- bonate of baryta and sulphuric acid, it may be procured by operating on the same principles as for sulphovinic acid, to which, both in constitution and properties, it is the analogue. It is a sirupy or crystalline body, and is decomposed by ebullition into potato oil and sulphuric acid. Amilen ( C 10 Hi ) is obtained by the action of anhydrous phosphoric acid on potato oil ; it is an oily liquid which boils at 320. In constitution and position it, therefore, occupies, in the amyle series, the same situation that ole- fiant gas does for the wine alcohol series, and, indeed, is isomeric with that body. Valerianic Acid ( C 10 H 9 O 3 ) bears the same relation to the amyle group which acetic acid does to the wine alcohol group, or formic acid to the wood spirit group. It is formed when warm potato oil is dropped on platinum black in contact with the air. It occurs naturally in the root of the Valeriana Officinalis, but is best made by heat- ing potato oil in a flask, with a mixture of quicklime and hydrate of potash, for several hours at a temperature of 400. The white residue is immersed in cold water, and distilled with a slight excess of sulphuric acid, so as to drive off hydrated valerianic acid and water. It is a col- orless oil of an acid taste, combustible, and boiling at 347. When acted upon by chlorine in the dark, and the action aided by heat, it gives rise to Chlorovalerisic Acid ( C W H 6 Cl^O 3 4- HO), in which there has been a removal of three hydrogen atoms and a substitution of three of chlorine. Under the influence of the sunshine, by the same process, another hydrogen atom is removed, and Chlorovalerosic Acid forms, its constitution being C i0 H 5 Cl t O 3 + HO. To what substance is sulphamilic acid analogous ? What relation is there between amilen and olefiant gas 7 What is the relation between acetic and valerianic acids ? From what natural source may the latter be derived ? How is it made artificially ? What id the successive action of chlorine upon it ? 344 THIS BENZYLE GROUP. The Benzyle Group. Benzyle, CuHnOz = Bz. Hydruret of benzyle = Bz -4- II. Oxide of benzyle (benzole acid) . . . . = Bz 4- O. Chloride =Bz + CL Sec. &c. Of this series, benzyle, the radical, is an ideal body. It is a radical which discharges the functions of a metallic body, giving rise to oxides, chlorides, iodides, &c., as the table shows. Hydruret of Benzyle Oil of Bitter Almonds (BzH) is obtained by the distillation of bitter almonds, from which the fixed oil has been expressed, with water, and arises from the action of the water upon Amygdaline contained in the seed. It may be purified by distillation from pro- tochloride of iron with hydrate of lime in excess, and is a colorless liquid of an agreeable odor, slightly heavier than water, and also slightly soluble therein, but very soluble in alcohol and ether. It boils at 356. In the air it pass- es into benzoic acid by absorbing oxygen. Oxide of Benzyle Benzoic Acid (BzO -f HO). This acid is obtained by sublimation from gum benzoin, that substance being placed in a shallow vessel, over the top of which a cover of filtering paper is pasted, and this cov- ered by a taller cylinder of stouter paper. On heating, the vapors pass through the filtering paper, and, condens- ing in feathery crystals in the space above, fall down upon the paper and are retained by it. A better method is to boil a mixture of the gum with hydrate of lime, filter, concentrate the solution, add hydrochloric acid, and the benzoic acid crystalHzes in thin plates on cooling. It may be subsequently sublimed. When pure it has no odor. It melts at 212, and boils at 462. Its vapor excites coughing. It is much more soluble in hot than in cold water. It forms a series of salts, and is sometimes used for the separation of iron from other metals. Sulphobenzoic Acid (C^H 5 O 3 , SO 3 + 2HO), a bibasic acid, formed by the action of anhydrous sulphuric acid upon benzoic acid, the mass being dissolved in water and neutralized by carbonate of baryta. On filtering, and add- What is the radical of the benzyle series ? What is oil of bitter al monds '? From what substance does it arise ? What is benzoic acid ? By what processes may it be prepared ? What is the process for pre paring sulphobenzoic acid ? DERIVATIVES OF BENZYLE. 345 ing hydrochloric acid to the hot solution, on cooling the sulphobenzoate of baryta crystallizes, which may be de- composed by dilute sulphuric acid. It is a white crystal- line mass. Chloride of Benzyle (BzCl). When chlorine gas is passed through oil of bitter almonds, hydrochloric acid is formed, and, after expelling the excess of chlorine by heat, chloride of benzyle remains. . It is a colorless liquid, of a disagreeable odor, heavier than water, combustible, and decomposed by boiling water into benzoic and hydrochlo- ric acids. Benzamide ( C i4 H r NO 3 ) is formed by the action of chlo- ride of benzyle on dry ammonia, the hydrochlorate of am- monia being removed from the resulting white mass by cold water. From a solution in boiling water, the ben- zamide crystallizes. It melts at 239. It corresponds in its chemical relations to oxamide. Hydrobenz amide (C 42 H iS N 2 ), made by the action of pure oil of bitter almonds on solution of ammonia, the product being washed with ether, and from its alcoholic solution this substance crystallizes ; but when impure almond oil is employed, three other compounds may be obtained : they are benzhydramide, azobenzoyle, and nitrobenzoyle. LECTURE LXXVII. THE SALICYLE AND CINNAMYLE GROUPS. Benzoine, Ben- zone, Benzine. Hippuric Acid. THE SALICYLE GROUP. Artificial Formation of Oil of Spircea. Compounds of Salicyle. Melanic Acid. THE CINNAMYLE GROUP. Compounds of Cinnamyle. BENZOINE (C 14 JJ 6 O. 2 ), a body isomeric with bitter al- mond oil. It is found in the residue after purify ing~ that oil from hydrocyanic acid by distillation from lime and oxide of iron, and may be obtained by dissolving out those bodies by hydrochloric acid. It crystallizes from an alco- holic solution, on cooling, in colorless crystals, which melt at 248. It dissolves in an alcoholic solution of caustic How is the chloride of benzyle made ? How are benzamide and hydro- benz amide formed ? What relation does benzoine bear to oil of bitter almonds ? 346 DERIVATIVES OF BENZYLE. potash, which, by boiling until the violet color has disap- peared, furnishes benzilate of potash, a salt from which benzilic acid may be obtained by hydrochloric acid. The constitution of Benzilic Acid is C^H^O*, -f HO. Benzone (C n H b O) is obtained by the distillation of dry benzoate of lime at a high temperature, carbonate of lime remaining behind. The decomposition is interesting, the ben zoic acid atom being divided, and yielding benzone and carbonic acid. C 14 H,0 3 ... = ... CuH b O + CO,. Benzine (CuH & ) arises when crystallized benzoic acid is distilled from hydrate of lime at a red heat. It is an oily liquid, and, after being separated from the water which comes over with it, is to be rectified. It boils at 187, so- lidifies at 32, and is lighter than water. In its formation the hydrated benzoic acid is resolved into benzine and carbonic acid. Sulphobenzide (C n H- SO^) is formed by taking the sub- stance which arises from the union of benzine with anhy- drous sulphuric acid, and acting upon it with an excess of water. The sulphobenzide, which is insoluble in that liquid, may be obtained in crystals from its ethereal solution. It melts at 212 F. From the acid liquid from which it has been separated hyposulphobenzic acid may be obtained. Its constitution is C^H b S z O b -{-HO. Nitrobenzide (C^H b NO 4 ), produced by the action of fuming nitric acid on benzine, with the aid of heat. It is an oily liquid, of a sweet taste, heavier than water, and boiling at 415. From it Azobenzide (C^H^N) may be obtained by distillation with an alcoholic solution of caus- tic potash, in the form of red crystals. Chlorbenzine ( C 1Z H & C1 6 ) is formed by the union of ben- zine and chlorine in the sun-rays. When distilled, the solid yields hydrochloric acid and a liquid, Chlorbenzide Hippuric Acid (C 18 H S NO 5 + HO] is found in the urine What is the result of the distillation of dry benzoate of lime ? What is the nature of the decomposition ? What is the result of the distillation of crystallized benzoic acid and hydrate of lime ? What is the result of the action of anhydrous sulphuric acid and benzine ? What is the action of nitric acid on benzine ? What substance results from the union of ben- zine and chlorine ? From what sources may hippuric acid be obtained 1 THE 8ALICYLE GROUP. 347 ot graminivorous animals, and occurs in the urine of per- sons who have taken benzoic acid. It may be prepared by evaporating the fresh urine of the cow, and acidulating the concentrated liquor with hydrochloric acid ; crystals of hippuric acid are deposited, which may be decolorized by bleaching liquor and hydrochloric acid. It crystallizes in square prisms, sparingly soluble in cold water, of a bit- ter taste and acid reaction. By a high temperature or the action of sulphuric acid, it yields benzoic acid. THE SALICYLE GROUP. There is contained in the bark of the willow and other trees a bitter crystalline principle, SALICINE (C 2l H l3 O n ). This substance may be extracted by boiling the bitter bark . in water, and digesting the concentrated solution with ox- ide of lead to decolorize it, removing any dissolved lead by sulphureted hydrogen, and evaporating until the sali- cine crystallizes. It forms white needles of a bitter taste, much more soluble in hot than cold water. Distilled with bichromate of potash and sulphuric acid, it yields hydro- salicylic acid, or the artificial oil of meadow sweet, a sub- stance containing Salicyle, the ideal compound radical of a series of bodies. The Salicyle Group. Salicyje, CnH.,0^ = SI. Hydrosalicylic acid = SlH. Iodide of salicyle =811. Chloride = SICl. &c. &c. Hydrosalicylic Acid Oil of Spircea Ulmarta,or Mead- ow Sweet (C^H^O^H] is prepared by distilling one part of salicine, one of bichromate of potash, two and a half of sulphuric acid, and twenty of water; the salicine being dissolved in one portion of the water, and the acid mixed with the rest. The yellow oil which comes over is rectified from chloride of calcium. It may also be ob- tained by distilling the flowers of meadow sweet with water. It is transparent, but turns red in the air. It is slightly soluble in water, and very soluble in alcohol. Its specific gravity is T173 ; it boils at 385 F. It contains the same elements as benzoic acid. Salicylic Acid (CnH 4 O 4 -\-O) is obtained by the action Under what circumstances does benzoic acid produce it ? From what is salicine obtained ? "What is the constitution of salicyle ? How may the oil of meadow sweet be made artificially ? 348 COMPOUNDS OF SALICYLE. of hydrate of potash on the foregoing body by the assist- ance of heat. After the disengagement of hydrogen is over, the mass is dissolved in water, and salicylic acid separates in crystals on the addition of hydrochloric acid. It is more soluble in hot than cold water, and is charred by hot oil of vitriol. Chloride of Salicyle (C l4 H 5 O 4 Cl)is made by the action of chlorine on hydrosalicylic acid. Its crystals are insol uble in water, but soluble in solutions of fixed alkalies, from which it separates on the addition of an acid, resist- ing decomposition even when boiled in caustic potash. It unites with caustic potash. Bromide and Iodide of Salicyle also exist, but are not of interest. Chlorosamide (C^H 15 N 6 O d Cl 3 ). Ammoniacal gas is ab- sorbed by the chloride of salicyle, producing a yellow body, which crystallizes from a boiling ethereal solution. It is insoluble in water. When acted upon by hot acids, it yields a salt of ammonia and chloride of salicyle ; an al- kali forms with it ammonia and chloride of salicyle. There is an analogous bromosamide. Salicyluret of Potassium (KSl) is formed by the action of oil of meadow sweet on a solution of caustic potash. It forms in yellow crystals from its alcoholic solution, and has an alkaline reaction. Melanic Acid (C 10 HO 5 ) is produced when the crystals of salicyluret of potassium are exposed in a moist state to the air. They first turn green and then black, and alcohol extracts from them melanic acid. CINNAMYLE. The essential oil of cinnamon is supposed to be the hy- druret of an ideal compound radical, cinnamyle, analo- gous to benzoyle, and yielding a series. The Cinnamyle Group. Cinnamyle, CizHiOz = Ci. Hydruret of cinnamyle (oil of cinnamon) . . . . = CiH. Oxide (cinriamic acid) . . . . = CiO. Chloride " = CiCl. &c. &c. Hydruret of Cinnamyle Oil of Cinnamon ((7 18 .H" 7 3 -f What ia the constitution of salicylic acid ? What is the action of am- monia on chloride of salicyle ? Under what circumstances is melanic acid produced ? What is the essential oil of cinnamon ? What is the consti tutiou of cinnamyle ? AMMONIA. 349 H] is obtained by infusing cinnamon in a solution of salt, and then distilling the whole. It is heavier than water, and may be separated from that liquid by contact with chloride of calcium. Cinnamic Acid (C l& H 7 O 2 + O) is formed when oil of cinnamon is exposed to oxygen gas, the oil becoming a white crystalline mass, hydrated cinnamic acid. It may also be obtained by boiling hard Tolu balsam with hydrate of lime. The cinnamate of lime crystallizes as the solu- tion cools, benzoate of lime remaining in solution. The crystals are decolorized by animal charcoal, and then de- composed by hydrochloric acid ; from the hot solution cinnamic ackl crystallizes. It melts at 248, and boils at 560. It is soluble in boiling water and in alcohol; is decomposed by hot nitric acid, and yields benzoic acid, with oil of vitriol and bichromate of potash. Chlorocinnose (C 18 jEr 4 C7 4 2 ) arises from oil of cinna- mon by the substitution of four atoms of chlorine for four of hydrogen, and is made by the action of chlorine on oil of cinnamon by the aid of heat. It crystallizes from its alcoholic solution in colorless needles. LECTURE LXXVIII. THE NITROGENIZED PRINCIPLES. AMMONIA and its Salts. CYANOGEN. Preparation and Properties of Prussia Acid. Amygdaline and Synaptase. The Cy- anides. Oxygen Acids of Cyanogen. AMMONIA. I have already described, in Lecture LY, the compounds of hydrogen and nitrogen, under the names of amidogen, ammonia, and ammonium, and have also shown the relation there is between the salts of potash and soda and those of the oxide of ammonium. This compound metal is a hypothetical body; its exist- ence may, however, be illustrated by passing a Voltaic current through a globule of mercury in contact with moist chloride of ammonium, or by putting an amalgam of mercury and potassium in a strong solution of that salt. How may cinnamic acid be prepared? What is the constitution of ohlprocinnose, and how is it prepared ? What is ammonium ? G Q 350 COMPOUNDS OF AMMONIA. The mercury rapidly increases in volume, retaining its metallic aspect, becomes of the consistency of butter, with a very trivial increase of weight ; the resulting substance is the Ammoniacal Amalgam. All attempts to insulate ammonium from it have failed. The most important salts of ammonia are the following : Chloride of Ammonium- Sal Ammoniac Muriate of Am- monia was formerly brought from Egypt, but is now made from the ammoniacal liquors resulting from the destructive distillation of animal matters, coal, &c. It is soluble in water, crystallizes in cubes or octahedrons, and sublimes below a red heat unchanged. It is decomposed by lime and potash, and is formed when the vapors of ammonia mingle with those of muriatic acid. Nitrate of Ammonia is formed by neutralizing nitric acid with ammonia. It is deliquescent, and therefore very soluble in water. It melts at 240, and at a higher temperature decomposes into steam and protoxide of ni- trogen, as is explained in Lecture XLV. Carbonates of Ammonia. The neutral carbonate only exists in combination. With the carbonate of water it unites, forming Bicarbonate of Ammonia, which may be prepared by washing the commercial Sesquicarbonate with water or alcohol, which leaves it undissolved. The car- bonate of ammonia of commerce is prepared by sublima- tion from a mixture of sal ammoniac and chalk. Its con- stitution is not uniform, though it is commonly regarded as a sesquicarbonate. Sulphate of Ammonia may be made by neutralizing sulphuric acid with carbonate of ammonia. It is soluble in twice its weight of cold water, and crystallizes in six- sided prisms. Hydrosulphuret of Ammonia is made by passing sul- phureted hydrogen into water of ammonia until no more is absorbed. Though colorless at first, it absorbs oxygen, and, sulphur being liberated, it turns yellow. It is of considerable use as a metallic test. CYANOGEN. Bicarburct of Nitrogen (C 2 N). The mode of preparing this remarkable body, and also its leading How is the ammoniacal amalgam prepared ? From what sources is sal ammoniac derived ? For what purpose is nitrate of ammonia employed ? What is the carbonate of ammonia of commerce ? How is hydrosulphuret of ammonia made, and what is its use ? What is the constitution of cy- anogen ? HYDROCYANIC ACID. 351 properties, have been described in Lecture LV. It is ot great interest in organic chemistry, as being the first dis- tinctly established compound radical, and the best repre- sentative of the electro-negative class of those bodies. We may call to mind that it is easily made by the de- composition of cyanide of mercury at a low red heat, is a gaseous body, soluble in water, and, therefore, must be collected over mercury. It is combustible, and burna v** 1 * - ^urple flame. Tlie Cyanogen Group. Cyanogen, C 2 N = Cy. Hydrocyanic acid = CyH. Cyanic acid = CO. Pulminic acid ^=.Cy^O z - Cyanuric acid = Cty 3 O 3 . &c. &c. Paracyanogen ( C. 2 N). When the cyanide of mercury is decomposed in the process for preparing cyanogen, a brownish substance is set free, which is paracyanogen. It is insoluble in water and alcohol, and is only remarkable in being isomeric with cyanogen. Hydrocyanic Acid Prussic Acid Cyanide of Hydro- gen (C 2 iV-f- jff). Hydrocyanic acid may be obtained in a state of purity by passing dry sulphureted hydrogen gas over dry cyanide of mercury in a tube, and conducting the vapor, which is evolved when the tube is warmed, into a vial immersed in a freezing mixture. The result of the decomposition is sulphuret of mercury and hydrocyanic acid. In a state of aqueous solution, it is best obtained by the action of dilute sulphuric acid on the ferrocyanide of potassium in a retort, and receiving the vapor in a Liebig's condenser. Having ascertained the strength of the prod- uct, it may then be diluted to the proper point. This ex- amination may be conducted by precipitating a known weight of the acid with nitrate of silver in excess, collect- ing the cyanide of silver on a weighed filter, washing, drying, and reweighing, which gives the weight of the cyanide. This, divided by five, is the weight of the pure hydrocyanic acid, nearly. Anhydrous hydrocyanic acid is a colorless and very vol- atile liquid, which exhales a strong odor of peach blooms ; What interesting fact is connected with its discovery ? What are it* properties ? What is paracyanogen ? How may hydrocyanic acid be made ? By what process can its strength be determined ? 352 AMYGDALINE. has a density of -705 ; boils at 79. It mixes with water and alcohol in any proportion. A drop of it held in the air on a glass rod becomes solidified by the rapid evapora- tion from its surface. In the sunlight it decomposes rap- idly, producing a dark-colored substance ; and the same change goes on, though much more slowly, in the dark. It is one of the most insidious and terrible poisons, a few drops producing death in a few seconds ; and even its vapor, largely diluted with air, brings on very unpleasant symptoms. Under the action of strong acids it is decom- posed into ammonia and formic acid, the change being very simple : C>N, H + 3 HO = NH 3 + C. 2 HO S . Under such circumstances, hydrochloric acid yields mu riate of ammonia and hydrated formic acid. Hydrocy anic acid may, to a certain extent, be preserved from spontaneous change by the presence of a minute quantity of any mineral acid. Prussic acid may be detected by its smell, and by yield- ing a precipitate of Prussian blue when acted upon in so- lution successively by sulphate of iron, potash, and an ex- cess of hydrochloric acid. The liquid in which the poison is suspected to exist should be acidulated with sulphuric acid and distilled, and the hydrocyanic acid will be found in the first portions which come over. Amygdaline (C 4() H^NO. 22 ). A crystallizable substance found in bitter almonds, the kernels of peaches, &c. ; is of considerable interest in connection with hydrocyanic acid, inasmuch as these organic bodies yield, when distilled with water, that substance. The change consists in the ac- tion of water upon amygdaline by the aid of an azotized ferment called Synaptase, or Emulsine, which constitutes the larger portion of the pulp of almonds ; the bitter al- mond oil at the same time makes its appearance. Amyg- daline may be abstracted from the paste of bitter almonds, from which the fixed oil has been expressed, by the aid of boiling alcohol, which being subsequently distilled off, the sugar which is contained in the sirupy residue is de- stroyed by fermentation with yeast. The liquid being What are its properties ? What is the action of strong acids upon it ? How may it be partially preserved from spontaneous change ? How may it be detected ? What is amygdaline ? What is tke potion of aynaptase and water upon it ? How may it be obtained ? COMPOUNDS OF CYANOGEN. 353 evaporated again to a sirup, is mixed with alcohol, which precipitates the amygdaline as a white crystalline pow- der, purified by being redissolved in alcohol and left to cool. It is soluble in hot and cold water, but sparingly soluble in cold alcohol. A weak solution of it in water, under the influence of a small quantity of the emulsion of sweet almonds, yields at once oil of bitter almonds and hydrocyanic acid. When amygdaline is boiled with an alkali, it yields Amygdalinic Acid, which forms a salt with the alkali, and ammonia is evolved. Cyanide of Potassium (KCy) may be formed by the di- rect union of cyanogen and potassium, or by the ignition of the ferrocyanide of potassium in a close vessel. For common purposes in the arts it may be formed in a state somewhat impure by mixing eight parts of ferrocyanide of potassium, rendered anhydrous by heat, with three of carbonate of potash, also dry, and fusing the mixture in a crucible, stirring it until the fluid part of the mass is col- orless. The sediment is allowed to settle, and the clear liquid poured off; it is the substance in question. Cyanide of potassium is very soluble in water, yields colorless oc- tahedral crystals, which deliquesce in the air; it melts without change at a red heat, and exhales the odor of prussic acid. It is very poisonous. Cyanide of Mercury may be made by dissolving red oxide of mercury in hydrocyanic acid, or by the action of a solution of ferrocyanide of potassium on sulphate of mercury ; the cyanide crystallizing from the filtered hot solution. It forms fine prismatic crystals, more soluble in hot than cold water. It is poisonous ; and, when decom- posed at a low red heat, yields cyanogen gas. Cyanic Acid(CyO-\-HO) is procured by heating in a re- tort cyanuric acid, deprived of its water of crystallization ; a colorless liquid comes over into the receiver, which is the hydrated cyanic acid ; it has a strong odor like acetic acid, and produces blisters on the skin. It is decomposed by the contact with water into bicarbonate of ammonia. C 2 NO, HO + 2HO ... = ... C 2 O 4 + NH 3 , and is a very instable body, spontaneously changing in a short time into Cyamelide, a body of the same constitu- By what processes may the cyanide of potassium be made ? How may the cyanide of mercury be prepared? Exposed to heat, what does it yield ? What are the constitution and properties^ of cyanic acid ? G o2 364 DERIVATIVES OF CYANOGEN. tion, but a white opaque solid, insoluble in water and al- cohol, and decomposed by hot oil of vitriol into carbonate of ammonia. Fulminic Acid (Ci/ 2 O 2 -\-2HO) has not yet been insula- ted, but some of its salts, presently to be described, are characterized by the violence with which they detonate under very trivial disturbances. It is a bibasic acid. Cyanuric Acid(Cy 3 O s +3HO) may be made by heating urea, which disengages ammonia ; the residue is dissolved in hot sulphuric acid, and nitric acid added until the liquid becomes colorless : on mixing it with water, and allowing it to cool, the cyanuric acid separates. Its crys- tals are efflorescent ; it is sparingly soluble in water, and is a tribasic acid ; and, as has been already stated, at a red heat it may be distilled, and yields cyanic acid without other product. LECTURE LXXIX. BODIES ALLIED TO CYANOGEN. Salts of the Oxycyano- gen Acids. FERROCYANOGEN. Ferrocyanides of Hy- drogen and Potassium. Prussian Blue and Basic Blue. FERRIDCYANOGEN. SULPHOCYANOGEN. Compounds with Hydrog-en and Potassium. Melam, Melamine, Sfc. CYANATE of Potash (KO, CyO] maybe prepared by ox- ydizing cyanide of potassium by oxide of lead in an earth- en crucible ; the result boiled with alcohol yields, on cool- ing, crystals of cyanate of potash, in thin, transparent plates, which undergo no change in dry air, but with moisture become converted into bicarbonate of potash and ammonia. Cyanate of Ammoniac-Urea (C 2 H 4 N 2 O^). The vapor of hydrated cyanic acid, mixed with ammoniacal gas, yields cyanate of ammonia. The solution in water, when heated, gives off ammonia, and the cyanate changes into Urea, from which caustic alkalies can not disengage am- monia. Urea may also be made from the action of sul- phate of ammonia or cyanate of potash. What of fulminic acid ? What of cyanuric acid ? How is the cyanate of potash made ? How may urea be formed artificially ? SALTS OF FULMINIC ACID. 355 Fulminate of Silver (2AgO, C 4 N. 2 O. 2 ) is made by dis- solving silver in warm nitric acid and adding alcohol. It separates from the hot liquid in white grains, which, being washed in water, are dried in small portions on filtering paper. It detonates with wonderful violence when ei- ther struck or rubbed. It is sparingly soluble in hot wa- ter, and crystallizes from that solution on cooling. It yields, by digestion with water and metals, salts, as those of zinc and copper. Fulminate of Mercury (2HgO, C t N 2 O. 2 ) is prepared in the same manner as the foregoing, and, like it, is very ex- plosive. It is used for making percussion caps. Chloride of Cyanogen (CyCl) is prepared by the action of chlorine on moist cyanide of mercury in the dark. It is a colorless gas, soluble in water, congeals at 0, and boils at 11 ; condenses into a liquid under the pressure of four atmospheres. When kept in this condition, in sealed tubes, for a length of time, it assumes the solid state, which form may also be given to it by acting on an- hydrous hydrocyanic acid by chlorine in the sun's rays ; hydrochloric acid is formed, and the solid cyanide crys- tallizes. It exhales a peculiar odor, melts at 284, and is soluble in alcohol and ether. FERROCYANOGEN. Ferrocyanogen (C 6 N 3 Fe = Cfy) is an ideal compound radical. Hydroferrocyanic Acid (Cfy, 2H) may be obtained by decomposing the insoluble ferrocyanide of lead by sul- phureted hydrogen while suspended in water. The so- lution being filtered, is to be evaporated with sulphuric acid in vacuo until the acid is left solid. It may also be prepared by agitating its aqueous solution with ether, or by adding hydrochloric acid to a strong solution of ferro- cyanide of potassium, and then mixing it with ether, which precipitates the acid. It is soluble in water, to which it gives a powerful acid reaction. It decomposes alkaline carbonates with effervescence, and does not dissolve ox- ide of mercury in the cold. In these respects, therefore, it strikingly differs from hydrocyanic acid. What is the process for preparing fulminating silver, and what are ita properties 1 For what purpose is fulminate of mercury used ? What re- sults from the action of chlorine on cyanide of mercury in the dark ? What te ferrocyanogen ? How is hydroferrocyanic acid obtained ? 356 COMPOUNDS OF FERROCYANOGEN. Ferrocyanide of Potassium Prussiate of Potash (2K, Cfy+ 3HO). This salt is made on the large scale by igniting potash, iron filings, and animal matters in an iron vessel; the mass is then acted upon by hot water, which dis- solves out a large quantity of cyanide of potassium, which is converted into the ferrocyanide by the iron, and the filtered solution, on cooling, yields it in lemon-colored crystals, soluble in four parts of cold water. It is not poisonous. At a red heat it decomposes, and yields cy- anide of potassium. It is a very valuable reagent ; with copper it yields a chocolate precipitate ; with protoxide of iron, a white ; and with peroxide of iron, Prussian blue. Common Prussian Blue (3 Cfy + 4 Fe) is prepared by precipitating a persalt of iron by solution of ferrocyanide of potassium ; when dry, it is of a deep blue, with a lustre of coppery-red. It is insoluble in water, is decomposed by alkaline solutions, which yield alkaline ferrocyanides, and precipitate oxide of iron. It is soluble in solution of ox- alic acid, and then constitutes the basis of blue writing inks, which are used for steel pens. It is also much em- ployed as a paint. Basic Prussian Blue (3Cfy, kFe + FeO.j) is formed when the white precipitate, yielded by a protosalt of iron with ferrocyanide of potassium, is exposed to the air. As its formula shows, it is common Prussian blue, with perox- ide of iron. It differs from Prussian blue in the remark- able peculiarity that it is soluble in pure water. FERRIDCYANOGEN. Ferridcyanogen (C 12 N 6 Fe. 2 = Cfdy}. A hypothetical compound radical, which yields some compounds of in- terest. Ferridcyanide of Potassium (3J -f- Cfdy) may be made by passing chlorine through a dilute solution of ferrocy- anide of potassium until it ceases to yield a precipitate with a persalt of iron. The liquid being concentrated, yields, on cooling, deep-red crystals, the solution of which is of a greenish color. It gives no precipitate with perox- ide of iron, but with the protosalts a bright blue, lighter than Prussian blue, and known as Turnbull's Blue. How is the prussiate of potash prepared ? Is it poisonous ? What color does it give with protoxide and peroxide of iron? What is common Prussian blue ? What is its composition ? For what purposes is it use-' 7 In what respect does basic Prussian blue differ from it ? What is the c** SULPHOCYANOGEN. 357 Cobaltocyanogen, a hypothetical radical, yielding com- pounds analogous to the preceding bodies. Sulphocyanogen (C. 2 NS. 2 ) (Csy), a compound radical, not yet insulated with certainty. Its formula shows that it is a bisulphuret of cyanogen. HydrosulpJiocyanic Acid (CsyH] may be obtained by decomposing sulphocyanide of lead by sulphureted hy- drogen in water. The solution is decomposed by ebulli- tion. It has the odor of acetic acid. It yields with per- oxide of iron a blood-red color. Sulphocyanide of Potassium (KCsy) may be made by heating powdered ferrocyanide of potassium with half its weight of sulphur and Dne third of carbonate of potash, and keeping it melted for a short time. The mass is then boiled with water, which dissolves out the sulphocyanide, and the solution being concentrated, yields prismatic crys- tals of the salt. It is soluble in water and alcohol, and deliquesces in the air. It melts at a red heat. Its solu- tion with peroxide of iron yields a blood-red color. Mclam (C^HgNu) is produced when sulphocyanide of ammonium is distilled at a high temperature, or by heating dry sulphocyanide of potassium with twice its weight of sal ammoniac. It is insoluble in water, but dissolves in strong sulphuric acid. When heated, it yields mellone and ammonia. Melamine (C 6 H 6 N e ) is produced when melam is dissolv- ed in a hot solution of potash. It separates on cooling. It is a basic body, uniting with acids. Ammeline (CjfiZ^O.J remains in the solution after the melamine has crystallized. It may be precipitated with acetic acid. Ammelide (C l2J H~ 9 iV 9 6 ) is prepared by dissolving amine- line in sulphuric acid, and precipitating with alcohol. What are cobaltocyanogen and sulphocyanogen? What color does hydrosulphocyanic acid yield with peroxide of iron ? By what process is sulphocyanide of potassium made ? What results from the distillation Df the sulphocyanide of ammonium 1 What are melamine, ammeline, and ammelide ? 358 MELLONE. LECTURE LXXX. MELLONE UREA. Mellone, Preparation of. Mellomdes of Hydrogen and Potassium. Natural and artificial Formation of Urea. Uric Acid. Its Properties. De- rivatives of Uric Acid. Parabanic, Oxaluric, and Thi- onuric Acids. Alloxantine. Purpurate of Ammonia. Xanthic and Cystic Oxides. MELLONE (C 6 N^ =Me). If sulphocyanideof potassium be acted upon by chlorine or nitric acid, a yellow pow- der is deposited ; this, when heated, gives off bisulphuret of carbon and sulphur, and there is left a yellowish pow- der, which is mellone. The relation of its constitution with cyanogen is obvious. It resists a moderate heat with- out change. Hydromellonic Acid ( MeH ). By adding hydrochloric acid to a hot solution of mellonide of potassium, this acid separates as a white powder on cooling. It is partially soluble in hot water, and possesses strong acid powers. Mellonide of "Potassium (KMe) maybe prepared by melt- ing ferrocyanide of potassium with half its weight of sul- phur, and adding, when the fusion is complete, five per cent, of dry carbonate of potash. The resulting mass is acted on by water, and the solution being filtered, is evap- orated, until, on cooling, it forms a mass of crystals, from which the sulphocyanide may be removed by alcohol, and the mellonide left. It is soluble in water, and yields, by double decomposition with the salts of baryta, lime, &c., mellonides of these bodies, for the most part sparingly soluble. Urea (C 2 H t N 2 O^) may be obtained from urine by add- ing to it, when concentrated, a strong solution of oxalic acid. The precipitated oxalate of urea is to be boiled with powdered chalk, arid the filtered solution concentra- ted until the urea crystallizes on cooling. It may also be made artificially by adding to a strong solution of cyanate of potash an equal ^weight of dry sulphate of ammonia ; the solution is evaporated to dryness in a water bath, and How is mellone prepared ? What is the action of hydrochloric acid on the mellonide of potassium 1 How may urea be made artificially ? URIC ACID. 359 the urea dissolved out by alcohol. It crystallizes in prisms, very soluble in water, but permanent in the air. At a high temperature it gives off ammonia and cyanate of^ ammonia, cyanuric acid remaining. Urea contains the ele- ments of cyanate of oxide of ammonium, has neither an acid nor alkaline reaction, is decomposed by hot alkaline solutions, with evolution of ammonia, and, by uniting with two atoms of water, yields carbonate of ammonia, a result which takes place during the putrefaction of urine, the change being brought on by a nitrogenized ferment the mucus of the bladder. Urea unites with acids, and forms, with nitric and oxalic acids, characteristic salts. Uric Acid Lithic Acid ( C IQ H 4 N 4 O 6 ) may be obtained from the solid urine of serpents, which, being boiled in solution of caustic potash and filtered, yields uric acid, by the addition of'hydrochloric acid, as a white, inodorous, and sparingly soluble powder ; soluble without change in sul- phuric acid, from which it is precipitated by water. Uric acid also exists in human urine, and appears to be always a product of the action of the animal economy. Of its salts, the urate of soda is interesting ; it is the chief ingredient of gouty concretions in the joints, called chalk-stones. The urate of ammonia occurs as a urinary calculus, and is often deposited from urine as a reddish cloud or pow- der. Allantoin (C 4 H 3 N 2 O 3 ) is prepared by boiling uric acid with peroxide of lead ; the filtered solution, being con- centrated, deposits prismatic crystals of allantoin on cool- ing. It is soluble in 160 parts of cold water. By a solu- tion of caustic alkali it is decomposed into ammonia and oxalic acid, assuming, during this change, the elements of three atoms of water. Alloxan (C S H 4 N. 2 O 10 ) is made by the action of concen- trated nitric acid on uric acid in the cold. The uric acid is to be added in small portions successively, until about one third the weight of the nitric acid has been used. An effervescence takes place, and there is left a white mass, from which the excess of acid is to be drained. The sub- stance is then to be dissolved in hot water and crystallized. What are its properties ? To what substance does it give rise in fer- mentation ? Under what circumstances does uric acid occur 1 What are jhalk-stones ? Under what form does urate of ammonia occur ? How may allantoin be prepared ? What is the action of cold nitric acid on urio acid ? 360 ' ALLOXANIC ACID. Its solution has an acid reaction and a bitter taste, and stains the skin purple, and, with a protosalt of iron and an Alkali, yields a characteristic blue compound. Alloxanic Acid ( C 4 HNO 4 + HO) may be prepared by decomposing the alloxanate of baryta by dilute sulphuric acid. The alloxanate itself is obtained by the addition of barytic water to a warm solution of alloxan. It is a strong acid, decomposing carbonates, and even water, by the aid of zinc. Mesoxalic Acid (C 3 O 4 -f 2 HO). Mesoxalic acid may be obtained by boiling a solution of alloxan with acetate of lead, the resulting mesoxalate of lead being decom- posed by sulphureted hydrogen. It is a strong acid, re- sists a boiling heat, and is bibasic. Mykomelinic Acid (C s H d N 4 O 5 ) is prepared by boiling a solution of alloxan with an excess of ammonia, and then precipitating by an excess of dilute sulphuric acid. It is a light yellow powder. Parabanic Acid (C 6 N 3 O 4 + 2HO) is formed by the ac- tion of strong nitric acid on alloxan, or uric acid, by the aid of heat. The crystals form on cooling, and may be dried by draining, and then recrystallized. It is soluble in water, reddens litmus, and forms beautiful prismatic crystals. Oxaluric Acid (C 6 H 3 N. 2 O 7 -f HO) may be made by de- composing a hot solution of the oxalurate' of ammonia by dilute sulphuric acid, and cooling rapidly. The ammonia salt is itself procured by boiling a solution of the para- banate of ammonia, when it crystallizes, on cooling, in small needles. Oxaluric acid is a white crystalline pow- der ; it contains the elements of one atom of parabanic acid and three of water, and its solution, by boiling, yields oxalic acid and oxalate of urea. Thionuric Acid (C s H & N&O lt + 2HO), a bibasic acid prepared by decomposing thionurate of lead with sul- phureted hydrogen. It contains the elements of one atom of alloxan, one of ammonia, and two of sulphurous acid. Uramile (C S H 5 N 3 O 6 ). When an excess of a saturated solution of sulphurous acid in water is mixed with a cold How is alloxanic acid prepared ? What substance results from boiling alloxan with acetate of lead ? How is mykomelinic acid prepared ? What substance results from the action of hot nitric acid on ui-ic acid ? What is the relation between oxaluric and parabanic acid? How is uramile prepared ? ALLOXANTINE. MUREXIDE. 361 solution of alloxan, and an excess of carbonate of ammo- nia with caustic ammonia added, and the whole boiled, the thionurate of ammonia is deposited on cooling. From this the lead salt, used in the preparation of the foregoing acid, may be obtained by acetate of lead. The thionurate of ammonia, with a little hydrochloric acid, being boiled in a flask, there separates a white body, which is uramile. It differs from thionuric acid in not containing the ele- ments of two atoms of sulphuric acid. If the thionurate of ammonia is mixed with dilute sulphuric acid and evap- orated in a water bath, Uramilic Acid is deposited ; it is C IG H 10 N,0 15 . Alloxantine (C s H 5 N 2 O m ) is made when sulphureied hydrogen gas is passed through a cold solution of alloxan. The product is filtered, washed, and boiled in water, which deposits the alloxantine, on cooling, in transparent rhombic prisms, which turn red on exposure to ammonia. This substance is alloxan, with one atom of hydrogen. A hot solution of it is decomposed when a stream of sulphur- eted hydrogen is passed through it, and Dialuric Acid forms. Murexide Purpuratc of Ammonia (C^H 6 N b O g ) may be made by the action of dilute nitric acid on uric acid, and then adding ammonia, or by boiling equaj weights of uramile and red oxide of mercury with eighty times their weight of water^ rendered alkaline by ammonia. The liquid turns of a deep purple color, and, when filtered, deposits, on cooling, crystals of murexide in square prisms, which, by reflected light, are of a green metallic lustre, and, by transmitted light, of a purple. It is spar- ingly soluble in cold water, but much more so in hot, and is one of the most splendid compounds known. Murexan Purpuric Acid. Murexide is to be dissolved in a solution of caustic potash, and dilute sulphuric acid added. It forms a yellow powder, and, dissolved in am- monia, gives rise to the foregoing body.- Xantkic Oxide (C 4 HyN 2 O 2 ) occurs as a urinary calculus of a brown color and waxy aspect. The calculus may be dissolved in dilute potash, and xanthic oxide precipi- How is alloxantine prepared ? What is tlie action of dilute nitric acid and ammonia on uric acid '/ What is the color of the crystals of murexjde ? How may murexan be prepared ? Under what circumstances dp xanthjo oxide mid cystic oxide occur ? H H 362 THE VEUETAliLE AClUd. tates as a white powder by carbonic acid. It is a waxy body. Cystic Oxide (C 6 Hf,NS^O 4 ) occurs also as a urinary calculus. LECTURE LXXXI. TIJE VEGETABLE ACIDS. Tartaric Acid, Preparation of. Salts of Tartaric Acid. Acids allied to Tartar- ic. Citric and its allied Acids. -*-Malic and its allied Acids. Tannic Acid. Gallic Acid. Acicts allied to them. OF the vegetable acids several will be described with Jheir associated alkalies. The following are those of which I shall treat in this Lecture : Tartaric. ......... C s H*O W -f- 2HO. Paratartaric ...... . . C% H*Q W -f- '2HO. Pyrotartarie . .... . . . Cn H.,O-> + HO Tartralic ....... 26's H^Oio -f 3HO Tartrelic ........ CsH 4 O 10 -- HO. .Citric ..... ... . jCi 2 H-,O ll --3HO. Aconitrc ....... . . C 4 H O 3 - - HO. Malic .......... Gs H*Os 4- %HO. Maleic .......... CsHiOs --2ffO. Fuiriavk r - . - V . . C4 H Oa -f HO. Tannic ..... . . . . Cis/ftOo -f 3HO. Gallic ......... Ci H O 3 -)- 1HO. Ellagic ....:.... Ci H2O4. Pyrogallic ....... . CQ HzOs. -MetagaUic ....... . CQ HzO*. Besides acids such as these, which constitute a very nu- merous group, there is another class, which pass under the name of Coupled Acids, the peculiarity of which is, that they consist of an acid affixed or coupled to another body, which, without affecting the neutralizing power of the acid, accompanies it in all its combinations. Thus, hypo- sulphuric acid couples with naphthaline to form hyposul- phonaphthalic acid, which neutralizes just as much of any base as hyposulphuric acid itself could do, the naphtha- line not changing its powers. Tartaric Acid (C S H 4 O K + 2HO}. A bibasic acid which occurs, as has been already stated, in the juice of grapes and other fruits as bitartrate of potash. It may be ob- tained by dissolving cream of tartar in boiling water and What are coupled acids ? From what source is tartarie acid derived ? SALTS OF TARTARIC ACID. 363 adding powdered chalk, a tartrate of lime precipitating. The rest of the tartaric acid may be obtained from the so- lution by the addition of chloride of calcium, which yields another portion of tartrate of lime, which may be decom- posed by digesting with an equivalent proportion of dilute sulphuric acid. The concentrated and filtered solution yields crystals acid to the taste, inodorous, and soluble both in water and alcohol ; the solution decomposes by keeping. '* Tartaric acid yields several valuable salts. Tartrate of Potash Soluble Tartar (2KO, C S H 4 O 10 ) may be made by adding carbonate of potash to cream of tartar. It is very soluble. Bitartrate of Potash Cream of Tartar (KO, HO, C.H+Oio). This is the salt which is deposited from the juice of the grape during fermentation, as Argol. It may be purified from the coloring matter it contains by solution in hot water, and the action of animal charcoal. In cold water it is very sparingly soluble. It yields black flux when ignited in a close vessel, the black flux being car- bonate of potash enveloped in carbonaceous matter. Tartrate of Potash and Soda Rochelle Salt Salt oj Seignette (KO, Na O, C,H^ O 10 -f 1 OHO) may be procured by neutralizing a solution of the foregoing salt with car- bonate of soda. On evaporation and cooling it separates in large, prismatic crystals. Tartrate of Antimony and Potash Tartar Emetic (KOSb,O,, C,H,O i0 -\-2HOy.This valuable medicinal agent is made by boiling oxide of antimony with a solu- tion of cream of tartar ; on cooling, the crystals are depos- ited. They are much more soluble in hot than in cold water, and dissolve without decomposition. Racemic Acid Paratartaric Acid. This remarkable acid, which has the same constitution as tartaric acid, and resembles it very closely, is found in the grapes of certain parts of Germany and France. Racemic acid, however, differs from tartaric in yielding a precipitate with a neu- tral salt of lime. Pyrotartaric Acid (C 6 H 3 O 6 + HO) is obtained by the destructive distillation of tartaric acid, coming over with a variety of other products. What is soluble tartar ? From -what source is cream of tartar derived? What is Roehslle salt ? How is tarta>- emetic prepared ? What is the relation between racemic and tartaric acids ? 364 CITRIC ACID. The action of heat on tartaric acid is remarkable. When exposed to a temperature of 400 F., it melts, throws off water, and yields in succession three different acids, tar- tralic, tartrelic, and anhydrous tartaric acid, the constitu- tion of which, compared with tartaric acid, is as follows : Tartaric acid C e H*Oi -\-2HO. Tartralic " 2C 8 # 4 Oio -f 3HO. Tartrelic " C a H^ O w + HO. Anhydrous tartaric CgH^Oio. All these, by the continued contact of water, pass back into the condition of tartaric acid. Citric Acid (C l2 H-,O n -i-3HO), a tribasic acid, occurring abundantly in the juice of lemons and other sour fruits, and separated therefrom by the aid of chalk and sulphur- ic acid. It is clarified by digestion with animal charcoal, and yields prismatic crystals of a pleasant taste, and sol- uble both in hot and cold water. The crystals are of two different forms, according to the conditions of their forma- tion ; those which separate in the cold by spontaneous evaporation contain five atoms of water, three of whicli are basic ; but those which are deposited from a hot solu- tion contain only four. The citrates form a very numerous family of salts, for, as the acid is tribasic, we may have them with three atoms of metallic oxide, or two of oxide and one of water, or one of oxide and two of water, besides subsalts. AconiticAcid EquiseticAcid(C 4 HO s -f- HO) is form- ed by fusing citric acid, and the resulting brown product is dissolved in water, the change being CH S 14 ...="... 3( C, Fig. 272, powdered galls. On pouring on them sulphu- ric ether, a liquid drops through the funnel tube, c, into the bottle, a, spontaneously sepa- rating into two portions ; the lower, which is a solution of tannic acid in water, is to be de- canted and evaporated in presence of sul- phuric acid in vacuo. It yields tannic acid, or tannin, in the form of an uncrystallized mass. This acid is soluble in water, but much less so in ether, has an astringent taste, and reddens litmus paper. With the persalts of iron it yields a characteristic and valuable precipitate of a black color, the basis of common writing ink. It forms insoluble compounds with starch, gelatine, and other or- ganic bodies, that with gelatine being of considerable in- terest. It is the basis of leather. From the characteris- tic precipitate it gives with that metal, it is used as a test for iron, which must, however, be in the state of peroxide, as the protosalts are unacted upon. The gradual dark- ening of pale writing inks is due to the gradual oxydation of the iron they contain. CatecMn (C l6 H ti 6 ). There is a body extracted by hot water from catechu, called catechin. It crystallizes in needles, and does not form an insoluble compound with gelatine, and gives a green color with persalts of iron. By the action of caustic potash in excess, it yields a black and insoluble substance, Japonic Acid. By the action of car- bonate of potash, it yields Rubinic Acid. What two acids are yielded by it under the action of heat ? What is the relation between maleic, fumaric, and aconitic acids ? How is tan- nic acid made ? What color does it yield with persalts of iron ? What is the basis of leather ? From what cause do pale writing inks darken ? What is catechin ? H H 2 3t)8 GALLIC ACID. Gallic Acid (C 7 HO 3 -f 2HO) may be formed by expos- ing a solution of tannic acid J;o the air, or by making powdered- galls into a paste with water, and keeping it exposed in a warm place to the air for some weeks. The mass is then pressed and boiled with water. On cooling, the solution precipitates a quantity of gallic acid, which may be purified by re-crystallization. Like tannic acid, this substance yields no precipitate with a protosalt of iron, but a deep blue-black with a persalt. It does not, however, precipitate gelatine. Its crystals are soluble in one hundred parts of cold and three parts of boiling wa- ter. The solution has an astringent taste. Tannic acid passes into gallic acid by oxydation, carbon- ic acid and water being evolved. 8 ... = ... 2(C 7 H0 3 + 2HO) + 2(HO) that is, one atom of tannic acid and eight of oxygen yield two of gallic acid, two of water, and four of carbonic acid. Ellagic Acid (C 7 H 2 O 4 ) t or gallic acid minus one atom of water, may be extracted after the removal of gallic acid by an alkali, and precipitated as a gray powder by hydro- chloric acid. Pyrogallic Acid (C 6 H 3 O 3 ) sublimes when gallic acid is heated in a retort to 420. It is in the form of white crys- tals, which are soluble in water. It strikes a black color with the protosalts of iron. Metagallic Acid (C 6 Jf^O. 2 } is formed when gallic acid is suddenly heated in a retort to 500. It is a black mass, insoluble in water, but soluble in alkalies, from which it is precipitated as a black powder by acids. How may gallic acid be prepared? How is ellagic acid procured? What is the action of heat on allic acid ? VEGETABLE ALKALIES. 367 LECTURE LXXXII. THE VEGETABLE ALKALIES. General Properties of Veg- etable Alkalies. Morphia. Its Preparation and Prop- erties. Other Alkalies of Opium. Meconic Acid. Alkalies of Bark, Quina, Cinchona, fye. Kinic Acid. Strychnia and Brucia. Table of Alkaloids. Artificial Alkaloids. THE vegetable alkalies constitute an extensive class of bodies, which are, for the most part, the active medicinal agents of the plants in which they occur. They are gen- erally sparingly soluble in water, but more soluble in boiling alcohol, of a bitter taste, and characterized by containing nitrogen. In their natural state they are unit- ed with an acid, and, possessing basic properties in a very marked manner, neutralize acids completely. This qual- ity seems to depend on the nitrogen they contain, and has no reference to their oxygen, for the quantity of this latter element which may be present seems to have no relation to their neutralizing power, and, indeed, in some of them it is not present at all. In many respects they are analogous to ammonia, their salts, unlike those of some of the compound radicals, such as ethyle, &c., un- dergoing decomposition in the same manner as the salts of ammonia. Thus, the chloride of ethyle does not de- compose the nitrate of silver, but the analogous com- pounds of ammonia and the vegetable alkalies do ; and these bodies may, therefore, be separated from the natural combinations in which* they occur precisely as we should separate lime, or potash, or magnesia in their salts. Most of the vegetable alkalies are poisonous bodies, and, indeed, among them we meet with some of the most ter- rific poisons known. There are several recently-discov- ered artificial substances, such as Aniline, and those con- taining arsenic and platinum, which ought to be classed with these basic bodies. What are the vegetable alkalies ? What element do they aH contain ? In what condition are they commonly found ? What are their relations to acid bodies? What are their general properties? Have any of them been made artificially ? 368 MORPHIA. NAKCOT1NE. Of the numerous vegetable alkalies, those which I shall now describe are the most important. Morphia (C^H^NO^ + 2HO). This substance is the active principle of ppium, and was the first discovered of these alkalies. It was insulated by Sertuerner in 1803. It may be prepared by mixing a concentrated infusion of opium with a solution of chloride of calcium in excess ; the mixture, when warmed, deposits a precipitate of me- conate and sulphate of lime, and the hydrochlorate of mor- phia remains m solution. From this it may be crystal- lized by evaporation, and a dark liquor, containing nar- cotine and coloring matter, separated by pressure in a piece of flannel. The impure hydrochlorate may be re- dissolved and re-crystallized, and, by repeating the opera- tion, or resorting to animal charcoal, it may be obtained quite white. The salt may now be dissolved in hot water and acted on by an excess of ammonia, which throws down pure morphia as a white precipitate. It may be obtained in crystals by solution in alcohol. Morphia is almost insoluble in water; it neutralizes acids, and forms cry stalliz able salts. Its solution is bit- ter. It dissolves readily in dilute acids, and yields a deep orange-red color when acted on by strong nitric acid. The most common of its salts are the hydrochlorate, the sulphate, and the acetate. Narcotine (C^H^NO 15 ) is associated with morphia in opium. It may be obtained by digesting the insoluble portion with dilute acetic acid ; the precipitate produced by ammonia is to be dissolved in alcohol, and purified by animal charcoal. It yields prismatic crystals, insoluble in water, and is a weak base. By the action of peroxide of manganese and sulphuric acid, and by bichloride of plati- num, it yields an extensive series of bodies, some of which are acids and others bases. Codeine (C^H W NO 5 }. The hydrochlorate of morphia, prepared as above described, contains this base ; and when the precipitation with ammonia is made it remains in so- lution. When pure, it crystallizes in octahedrons, and is a powerful base. Along with this body, in opium there oc- casionally occur other substances of less importance, as Tkelaine^ Pseudomorphine, Narceine, and Meconine. From what is morphia obtained ? When was it discovered ? Give a process for its preparation. How is narcotine prepared ? What are its properties ? What other alkaline bodies are obtained from opium? Q,U1NA. CINCHONA. 369 Meconic Acid (C^HO^, 3HO). A tribasic acid, asso- ciated with morphia in opium. It may be obtained from the meconate of lime, which precipitates in the prepara- tion of morphia by mixing it with warm dilute hydro- chloric acid, and repeating the operation until all the lime is removed. When purified from coloring matter, it crystallizes in scales, which are soluble in water and al- cohol. When heated, it loses six atoms of water of crys- tallization ; and if its solution be boiled, or the dry acid heated in a retort, Comenic Acid, C n H 2 O^ 2HO, a biba- sic acid forms with the disengagement of water and carbon- ic acid. Meconic acid yields, with the persalts of iron, a blood-red solution. It forms several series of salts, like all tribasic acids. Comenic acid, when heated, yields carbonic acid and a new body, Pyromeconic Acid, with a small quantity of an- other substance, parameconic acid. Pyromeconic acid is composed of C lo H A O a , HO. Quina Quinine (C M H 12 NO^). This, which is one of the most valuable of the vegetable alkalies, is obtained from Cinchona Bark. The decoction of the ground bark in dilute hydrochloric acid is to be boiled in an excess of milk of lime, and the precipitate acted upon by boiling alcohol ; on evaporation Cinchona is deposited in crystals, but the quina remains in solution. It may be precipitated by the addition of water, and obtained in crystals from the spontaneous evaporation of its solution in absolute al- cohol. Quina neutralizes acids perfectly, giving rise to salts, of which the hydrochlorate, phosphate, sulphate, &c., are employed in medicine. It is sparingly soluble in water, but very soluble in alcohol or acids. The basic sulphate of quina, a common preparation, is sparingly sol- uble in water, but the neutral sulphate is much more so. For this reason, sulphate of quina is often dissolved in di- lute sulphuric acid. Cinchona (C^H^NO). This alkali is obtained, as just stated, in the preparation of quina, with which it is asso- ciated in bark, and is found in large quantity both in the gray and red bark. It crystallizes in prisms, is sparing- How is meconic acid procured ? "What is the action of heat upon it ? What color does meconic acid yield with persalts of iron ? When comenio acid is heated, what acids does it yield? From what source is quina de rived ? How is cinchona prepared ? 370 STRYCHNIA. 'BRUC1A. ly soluble in water. Its salts, like those of the foregoing, are very bitter. Two other analogous bodies exist in different species of bark. They are Chinoidine and Aricine. Kinic Acid (C^H n O n , HO) is associated with the fore- going bodies in bark. It is obtained by decomposing the kinate of lime, obtained in the manufacture of sulphate of quina by oxalic acid, filtering the solution from oxalate of lime, and the kinic acid crystallizes on evaporation. It is very soluble in water. Strychnia ( C^H^N^ O 4 ) occurs in Nux Vomica, St. Ig- natius' s Bean, in the poison Upas Tieute, and other vege- table products. It may be extracted from nux vomica seeds by boiling them in dilute sulphuric acid, and then acting with lime and alcohol as described in the case of" quina. Strychnia requires 7000 parts of water for solution, and communicates to it an intensely bitter taste. It is one of the most violent poisons known. Its alkaline powers are well defined, and it produces a complete series of salts. It is soluble in hot alcohol, but not in ether. The anti- dote for an over-dose of it is an infusion of tea. Brucia (C^H i5 N, 2 O 7 ) is associated with strychnia, -and, being very soluble in cold alcohol, is readily separated from it. It is also more soluble in hot water, and pos- sesses the poisonous character of strychnia. These sub- stances are found in union with Igasuric Acid. The following table gives the names of other vegetable alkalies, and bodies analogous to them : Aconitine. Daturine. Picrotoxine. Antearine. Delphinine. Pipeline. Asparagine. Elaterine. Phloridzine. Atropine. Emetine. Popnliuev C affeine Theine. Gentianine. Salicine. Chelidonine. Hesperidine. Solaniae. Chinoidine. Hyosciamine. Stramonine. Colchicine. Meconine. Thebaine. Conine. Narceine. Theobromine. Curarine. Narcotine. Veratrine. Daphnine. Of some of these bodies, as nicotine and conine, it may What other alkalies exist in bark ? With what acids are these bodies associated ? From what sources is strychnia procured ? What are the properties of strychnia? What is the best antidote to its poisonous ef- fects? With what other alkali is it associated? Mention some othei vegetable alkalies. COLORING BODIES. 371 oe remarked that they are volatile oily liquids, which can form crystallizable salts and acids. They both contain nitrogen, and are interesting in their relations to the three following bodies, which may be formed artificially. Aniline ( C^HjN). This substance is formed by the ac- tion of potash on isatine, and is also one of the ingredi- ents of the oil of coal tar. It is an oily liquid, boils at 358, and yields crystalline salts with acids. Leukol (C iS H s N). Formed with the foregoing in oil of coal tar, from which it may be separated by distillation. it is also an oily liquid, and can yield crystallizable salts. Quinoline ( C 19 H S N). Formed by distilling quinine or strychnine with caustic potash. An oily liquid, very bit- ter, strongly alkaline, and yielding crystallizable salts. Besides these bodies there are other artificial bases of an analogous nature, but which differ in the remarkable particular of containing platinum and arsenic ; such, for example, as the platina bases of Reiset and Gros, or the arsenico-platinum radical kakoplatyle. The formation of these organic bases leads us to hope that the vegetable alkalies themselves will hereafter be artificially formed. LECTURE LXXXIH. THE COLORING BODIES. General Properties of Color- ing Principles. Madder. Hcematoxyline. Gartha- mine. Yellow Colors. Chlorophyll. Indigo. Sul- phindigotic Acid. Deoxydized Indigo. Action of Heat and Reagents on Indigo. Litmus. Carmine. THE coloring principles derived from the organic king- dom may be conveniently divided into two classes : the non-nitrogeriized and the nitrogenized. They may also be readily classed into groups, as blue, red, yellow, green. For the most part they are derived from vegetable pro- ductions. For some coloring matters the fibres of those tissues commonly employed for clothing have a sufficient affinity as to hold the color so that it can not be removed by mere What analogous substances have been formed artificially ? What may be remarked as respects the salts of Reiset and Gros ? How may color- ing principles be classified ? 372 NON-NITROGENIZED COLORS, washing, and is permanently dyed. But in other in- stances this is not the case ; the artist then has to avail himself of the qualities possessed by intermediate bodies, such as alumina and the oxide of tin, which at once pos- sess the double quality of an affinity for the coloring mat- ter and an affinity for the cloth fibre. 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