UC-NRLF 
 
 B 3 1EM D2E 
 
 

 J. WlCKSON. 
 

 
 
ANIMAL CHEMISTRY. 
 
LONDON 
 
 PRINTED BY SPOTTI8WOODE AND CO 
 NEW-STREET SQUARE 
 
LECTURES 
 
 ON 
 
 ANIMAL CHEMISTRY 
 
 DELIVERED AT 
 
 THE EOYAL COLLEGE OF PHYSICIANS. 
 
 BY 
 
 WILLIAM ODIING, M.B., F.E.S. 
 
 FELLOW OP THE COLLEGE : 
 LECTURER ON CHEMISTRY AT SAINT BARTHOLOMEW'S HOSPITAL. 
 
 LONDON : 
 LONGMANS, GREEN, AND CO. 
 
 1866. 
 
of 
 
 BIOLOGY 
 !RA 
 
 S 
 
 Main Lib. 
 
 
TO 
 
 THOMAS WATSON, M.D., F.RS. 
 
 PRESIDENT OF THE ROYAL COLLEGE OF PHYSICIANS 
 
 THESE LECTURES 
 
 HONOURED AT THE TIME OF THEIR DELIVERY 
 
 BY HIS 
 FRIENDLY EXPRESSIONS OF INTEREST AND APPROVAL 
 
 ARE NOW 
 WITH HIS KIND PERMISSION 
 
 RESPECTFULLY AND GRATEFULLY DEDICATED 
 
 BY 
 HIS OBLIGED SERVANT 
 
 THE AUTHOR 
 
 256336 
 
VI PREFACE. 
 
 manuscript, and further revising the published reports of 
 the s Chemical News,' I have made it my constant object 
 to give such an account of modern Organic Chemistry as 
 should, with a moderate amount of attention, be profit- 
 able and even interesting to those who are not chemists. 
 In other words, I have striven throughout, whether or not 
 successfully, to render my subject popular in the legi- 
 timate sense, by making it generally intelligible. 
 
 I need scarcely say that these lectures are not meant to 
 exert any direct influence upon points of medical practice. 
 I hope, however, they may assist in convincing the pro- 
 fession at large of the necessity for regarding vital pheno- 
 mena from a chemical point of view ; and in promoting 
 among students, especially those about to graduate, the 
 knowledge of a highly important though much neglected 
 branch of natural science. 
 
 ST. BARTHOLOMEW'S HOSPITAL : 
 March i, 1866. 
 
CONTENTS. 
 
 LECTUKE I. 
 
 PAOK 
 PROVINCE OP CHEMISTRY. TYPES OF CONSTITUTION AND RELATIONSHIP. 
 
 AMIDATED ORGANIC COMPOUNDS I 
 
 LECTURE II. 
 
 DOCTRINE OF RESIDUES. APLONE AND POLYMERONE BODIES. ORGANIC- 
 GROUPS AND SERIES. . . 21 
 
 LECTURE III. 
 
 DESTRUCTION AND CONSTRUCTION OF COMPLEX MOLECULES. NATURE OF 
 
 NITROGENOUS COMPOUNDS. OXIDES OF HYDROGEN AND CARBON. . 46 
 
 LECTURE IV. 
 
 FORCES CONCERNED IN VITAL ACTIONS. ACTUAL AND POTENTIAL ENERGY. 
 
 ARTIFICIAL SYNTHESIS OF ORGANIC BODIES 66 
 
 LECTURE V. 
 
 DYNAMIC VALUE OF MUSCLE OXIDATION. INTERMEDIATE PRODUCTS OF 
 
 TISSUE-METAMORPHOSIS. 97 
 
 LECTURE VI. 
 
 URIC ACID AND ITS CONGENERS. CHEMICAL ACTION OF ALTEBATIVB 
 
 MEDICINES. . . 126 
 
Errata. 
 
 Acetic Acetic 
 
 Page 83, hue 5 from foot, /or C 3 H 4 2 read C 2 H 4 2 . 
 
 Page 92, line 19 from top, for (C 3 H 5 )H.CNS read (C 3 H 5 )CNS. 
 
ANIMAL CHEMISTRY. 
 
 LECTUEE I. 
 
 Introductory remarks on recently established general principles in che- 
 mistry Statical chemistry concerned only with the composition of parts ; 
 with the different kinds of matter of which all the tissues and fluids of 
 the body are composed Dynamical chemistry concerned with the changes 
 of composition undergone by various parts from time to time Physical 
 changes, as of a piece of iron, contrasted with its chemical changes 
 Special reference of chemistry to past and future states of bodies Every 
 action of living body attended by changes of chemical composition 
 Eecent advances in chemistry of tissue-products Leucine a result of the 
 natural metamorphosis of glandular tissue Its artificial formation, de- 
 structively and constructively Taurine a constituent of bile, &c. Its 
 artificial production from carbon, hydrogen, nitrogen, oxygen, and sulphur 
 Chemical types of construction and double decomposition Compounds 
 of hydrogen with other three gaseous elements Establishment of mole- 
 cular formulae for hydrochloric acid HC1, water H a O, and ammonia H 3 N 
 Existence in two volumes of gaseous hydrochloric acid, water, and ammonia, 
 of one, two, and three volumes of hydrogen respectively, in addition to 
 one volume of chlorine, or oxygen, or nitrogen Monhydrides, dihydrides, 
 and trihydrides in general, and their derived chlorides Existence of 
 analogous mono-, di-, and tri-chlorides of metals deduced from specific 
 heats of respective metals, &c. Mutual relations of chlorides, hydrates, 
 and amides, both of elements and groupings Interchangeability of com- 
 parable residues (Cl from HC1, HO from H.HO, and H 2 N from H.H Z N) 
 in great variety of compounds Chlorinated, hydrated, and ammoniated 
 forms of the same primitive bodies Many complex nitrogenous tissue- 
 products only the ammoniated forms of comparatively simple bodies 
 Urea, glycocine, and taurine the ammoniated forms of the carbonic, acetic 
 or glycolic, and isethionic acids respectively Mixed hydrate-amides. 
 
' CHEMISTRY LECTURE I. 
 
 (i.) MR. PRESIDENT and GENTLEMEN, It has been, I am well 
 aware, the traditional policy of this College, in its character of a 
 learned body, to foster the cultivation of natural science for its own 
 sake, irrespective of any immediate advantage accruing to medical 
 practice, and regardless even of the ultimate advantage which, 
 sooner or later, must accrue from every addition to our knowledge 
 of the phenomena of life. I therefore make no apology, Sir, for 
 directing your attention to topics of which the present interest, at 
 any rate, is more scientific than practical, relying upon the favour 
 ever extended to pure science within these walls relying still 
 more confidently upon the prospective ability of science to repay 
 your favour many fold. 
 
 I feel, however, that I ought to apologise for venturing to dis- 
 cuss in this presence some of the more rudimentary principles of 
 chemical philosophy ; but the circumstance that these principles, 
 despite their rudimentary character, are yet of very recent intro- 
 duction must furnish my excuse. Indeed, it is only within the last 
 fifteen years or so that chemical facts have been in any large mea- 
 sure subordinated to chemical principles, and only within a very 
 few years past that these principles have been consistently de- 
 veloped and generally acknowledged. But the result of this 
 development and recognition is already apparent: for we find 
 that, notwithstanding the continuous accumulation of recorded 
 experiment, and the continuous discovery of new and complex 
 bodies with a rapidity at which even the most impassive are 
 amazed, chemistry is daily becoming less and less a science of 
 detail, more and more a science of generality, to such an extent 
 indeed, that, in my opinion, a student beginning the study of 
 chemistry now, with a view to make himself acquainted with the 
 knowledge of his own day, has a far less difficult task before him 
 than had his predecessor of twenty years ago, despite the then 
 limited range of chemical inquiry. To some extent, therefore, I 
 am forced, especially in this introductory lecture, to devote .a con- 
 siderable proportion of my allotted time to an enunciation of 
 certain general truths of more or less recent establishment. But, 
 in order that we may set out from the same standpoint, I must 
 
COMPOSITION OF BODIES. 3 
 
 beg still further to trespass upon your attention by reminding 
 you briefly of the special province of chemical science, and the 
 special character of chemical phenomena. 
 
 (2.) If we examine any ordinary plant or animal, we find in it 
 a great number of parts or organs root and stem, and bark and 
 leaves, and flowers and fruit, or bones and ligaments, and muscles 
 and viscera, and nerves and vessels. If we examine any one of 
 these parts more minutely, we find that it also is made up of 
 parts differing from one another, and so disposed towards one 
 another as to present evidence of arrangement or organisation. 
 Proceeding a little further, we find that each of these parts has a 
 definite composition, and that the composition of the different 
 parts is, to some extent, at any rate, independent both of their 
 individual structure and mutual co-ordination. We find, for in- 
 stance, very differently characterised tissues composed mainly of 
 fibrin or albumen, others of gelatin or chondrin, others of fat, 
 and others, again, of phosphate of lime. Now, chemistry does 
 not concern itself at all with the structure and arrangement oi 
 parts, but treats only of their composition. It distinguishes 
 between the different kinds of matter of which all bodies whatso- 
 ever are composed, whether living or dead, structural or structure- 
 less, mineral or organic. In particular, it teaches us as physicians 
 the composition of every tissue and fluid of the human body, 
 and of every external agent by which that body is affected the 
 air we breathe, the water we drink, the food by which we are 
 nourished, the medicines by which we are healed, and the 
 poisons by which we are destroyed. 
 
 (3.) But a knowledge of the composition of bodies is, after all, 
 only the statical or secondary object of chemical inquiry ; for, in 
 common with physics, chemistry has primary reference to the 
 varied existence of matter in time, and to the series of changes 
 which it manifests. We have regard to a body not only as it now 
 is, but as it has been, as it may hereafter be, the changes it has 
 undergone in time past, the changes which it may undergo in 
 time to come. Confining our attention to a single object this 
 
 u2 
 
4 ANIMAL CHEMISTRY LECTURE I. 
 
 piece of iron, for instance let us consider how varied have been 
 the states of its existence at different times. We know that it 
 has been at rest and in motion ; it has been silent and sonorous ; 
 it has been luminous and obscure, hot and cold, liquid and solid, 
 magnetic and non-magnetic, electrical and non-electric. But 
 throughout all these changes of rest and motion, sound and 
 silence, heat and cold, &c., the individual piece of metal has con- 
 tinued one and the same ; it has been composed throughout of 
 identically the same matter. Now, so long as a body continues to 
 be one and the same body so long, in fact, as its composition re- 
 mains unaltered so long do all the changes which it manifests 
 belong to the province of physics, and not to the province of 
 chemistry. For this piece of iron to undergo a chemical change, 
 it must cease to be a piece of iron, and become some other body 
 rust of iron, or vitriol of iron, or tincture of iron, or Prussian 
 blue, or clot of blood, or some one of many hundred different 
 combinations. Looking, then, to the chemistry of this piece of 
 iron, we have regard to the state of ironstone in which it existed 
 before it became metallic iron, and to the many different non- 
 metallic states in which it may hereafter exist. The dynamical 
 interest of a body has reference to its existence in time, to its past 
 and future variations of state, even more than to its present con- 
 dition. I venture to impress this point particularly on your at- 
 tention, that while chemistry treats of the composition of bodies, 
 it has special reference to their changes in composition. Now, 
 when we consider that every action of the living body, every 
 growth, every waste, every secretion, every movement, and even 
 every thought is attended by, and consequent upon, a change of 
 chemical composition, we perceive, in an instant, how much the 
 future of physiology must depend on the progress of chemical 
 research how only the iatro-chemist, if I may so call him, can 
 ever hope to understand the varied series of actions, healthy and 
 morbid, which are continually taking place in the living organism. 
 The chemistry, then, of any animal tissue of a piece of muscle, 
 for instance, no less than a piece of iron has reference to its 
 origin and metamorphoses. The chemist looks equally to its 
 
EXAMPLES OF TISSUE-PRODUCTS. 5 
 
 past and its future to the pabulum from which it was formed, 
 and to the products into which it is ever changing. 
 
 (4.) Of late years the chemistry of animal products has made 
 very great advances. In the table before you are written up the 
 names and somewhat complicated formula of a few of these 
 compounds, most of which occur in the animal body, as results 
 of the natural metamorphosis of its several tissues. Now, de- 
 spite the complexity of many of these bodies, the intimate con- 
 stitution of even the most complicated of them is fairly well 
 understood, and in many cases so well understood that the bodies 
 themselves can be actually built up by the chemist in his 
 laboratory without having any recourse whatever to organic 
 nature. 
 
 Anima 1 Products 
 C H s N Methylamine 
 
 CH 4 N a O 
 
 Urea 
 
 C 2 H 5 N O a 
 
 Glycocine 
 
 C a H 7 NSC, 
 
 Taurine 
 
 C 3 H 6 N 6 
 
 Melamine 
 
 C,H 7 N.O, 
 
 Sarcosine 
 
 C 4 H 9 N 3 0, 
 
 Kreatine 
 
 C 6 H I3 N 0, 
 
 Leucine 
 
 CgHjjN (X 
 
 Tyrosine 
 
 Let me direct your attention to one or two of these more par- 
 ticularly. Here, for instance, is leucine, a white crystalline 
 body, consisting of 6 atoms of carbon, 1 3 of hydrogen, i of ni- 
 trogen, and 2 of oxygen. Now, leucine is a product of the use, 
 and consequent waste or metamorphosis, of glandular tissue. It 
 is found in decoctions of glandular tissue, more particularly of 
 the spleen and pancreas; and also occurs occasionally as an 
 abnormal constituent of urine. It may be made artificially in the 
 flask or crucible by the breaking up of muscle, ligament, skin, 
 horn, hair, feathers, and a variety of other animal substances ; 
 but so well is the constitution of this complex tissue-product 
 understood, that leucine can now be formed, not only destructively 
 by the breaking up of more complex bodies, but constructively 
 by a synthesis of less complex organic bodies quite independently 
 
6 ANIMAL CHEMISTRY LECTttRE I. 
 
 of animal life. It may be produced, for example, by the com- 
 bination with one another of water, valerianic aldehyd,* and 
 prussic acid, as shown in the table ; and in several other ways. 
 
 H a Water 
 
 C 5 H IO Valer-aldehyd 
 
 CH N Prussic acid 
 
 C 6 H I3 N0 8 Leucine 
 
 (5.) The case of taurine, C 2 H 7 NS0 3 , is even more striking. 
 Like leucine, it has been found in glandular tissue, more par- 
 ticularly of the lung ; but its chief source is the bile, where it 
 exists conjugated with cholic acid, to form what is known as 
 tauro-cholic acid ; though whether the constituent taurine of this 
 acid is really formed by the liver, or merely extracted by the 
 liver from the blood of the portal vein, is not, I believe, satisfac- 
 torily ascertained. But the constitution of this highly complex 
 organic body, containing, as you see, carbon, hydrogen, nitrogen, 
 sulphur, and oxygen, is so exactly understood that it can easily be 
 put together in the laboratory, and from such well-known bodies 
 as sulphuric acid, alcohol, and ammonia, each of which again is 
 capable of being produced from its constituent elements ; so that 
 we may actually form this most interesting organic product, 
 taurine, out of sulphur, charcoal, oxygen, hydrogen, and nitrogen, 
 by processes which I hope to bring under your notice more par- 
 ticularly in a subsequent lecture. I might make similar remarks 
 with regard to the greater number of the other products included 
 in the table. Instead, however, of entering at once upon the 
 consideration of these and similar compounds, I propose to occupy 
 the remainder of this lecture with an account of certain bodies 
 of a much simpler character. I mean those fundamental com- 
 binations that serve as types to which the above class of bodies 
 and the great majority of organic as well as mineral compounds 
 are more or less directly referrible. The recognition of these 
 types, with the establishment of their nature and mutual relation- 
 
 . * Obtainable from essential oil of valerian, fermented potato-oil, &c. 
 
HYDROCHLORIC ACID TYPE. 7 
 
 ship, constitutes the great chemical advance of the last dozen 
 years or so ; and, at the present time, a proper understanding of 
 these types enables us to give at once a more or less satisfactory 
 interpretation of even the most recondite discoveries of modern 
 organic chemistry. 
 
 (6.) I need scarcely remind you that among the infinite 
 number of bodies known to chemists, some of them, so far as 
 our present knowledge goes, appear to consist of one kind of 
 matter only. For instance, while cinnabar may be proved to consist 
 of two different kinds of matter, known as sulphur and mercury 
 respectively, out of mercury we can obtain nothing but mercury, 
 and out of sulphur nothing but sulphur. Bodies of this de- 
 scription, therefore, which the chemist has not succeeded in re- 
 solving into two or more different kinds of matter, are assumed 
 to consist of one kind of matter only, and are accordingly termed 
 simple bodies or elements. These elements amount to about sixty 
 in number, and are possessed of very diverse properties. About 
 four-fifths of them are metallic, as mercury, and silver, and gold, 
 and copper, and lead, and iron. The remainder are non-metallic, 
 as oxygen, and chlorine, and bromine, and sulphur, and phos- 
 phorus, and charcoal. The great majority of them exist natu- 
 rally in the solid state. Only two are liquid, namely, bromine 
 and mercury ; while four of them are gaseous, namely, hydrogen, 
 chlorine, oxygen, and nitrogen. Now it is the combinations of 
 these four gaseous elements with one another, or rathtr, I should 
 say, the combinations of hydrogen with the other three gaseous 
 elements, which constitute our primary chemical types chloride 
 of hydrogen or hydrochloric acid, oxide of hydrogen or water, 
 and nitride of hydrogen or ammonia which we will now con- 
 sider seriatim. 
 
 (7.) If we expose a mixture of chlorine and hydrogen gases to 
 diffused daylight, they gradually combine with each other to pro- 
 duce a compound gas called hydrochloric acid the gas which 
 is contained in this sealed tube, and which I dare say I shall 
 be able to render evident to you by breaking off the point of 
 tube under water. The existence of hydrochloric acid gas within 
 
8 ANIMAL CHEMISTRY LECTURE I. 
 
 the tube is now manifested to you by its complete solution in the 
 water, and by its action upon colouring matter. But, if instead 
 of allowing the two gases to act upon one another slowly in 
 diffused daylight, we expose them to direct sunlight, or if we 
 bring them into contact with flame, their combination then takes 
 place, as you see, instantaneously and with explosion. Now, it 
 has been shown over and over again, that when chlorine and hy- 
 drogen gases unite with one another to form hydrochloric acid, it 
 is always in the ratio of equal volumes. If we take one volume 
 of hydrogen and one volume and a quarter of chlorine, the one 
 volume of hydrogen unites with one volume of chlorine, and leaves 
 the extra quarter volume of chlorine unacted upon. In the same 
 way, if we mix together one volume of chlorine and one volume 
 and a quarter of hydrogen, the one volume of chlorine unites 
 with exactly one volume of hydrogen to form hydrochloric acid, 
 leaving the extra quarter volume of hydrogen unacted upon. Try 
 the experiment how we please, we come to the same conclusion, 
 that chlorine and hydrogen gases will unite only in the proportion 
 of volume to volume. But chlorine is exactly 35-5 times heavier 
 than hydrogen ; or, taking the specific gravity of hydrogen as 
 unity, the specific gravity of chlorine will be 35*5 ; or, if we call 
 the weight of a litre of hydrogen i crith, the weight of a litre of 
 chlorine will be 35*5 criths. Accordingly, in hydrochloric acid 
 gas we have one volume of hydrogen united with one volume of 
 chlorine, or I part by weight of hydrogen united with 35-5 parts 
 by weight of chlorine, thus : 
 
 Hydrochloric acid 
 
 Moreover, when hydrogen and chlorine gases unite with one 
 another to form hydrochloric acid gas, they undergo no alteration 
 whatever in bulk. If we take, for instance, a litre of hydrogen 
 and a litre of chlorine, we obtain exactly two litres of hydrochloric 
 acid. This persistence in bulk is capable of being shown by 
 direct experiment, but may be inferred with equal certainty by 
 merely taking the specific gravity of hydrochloric acid gas. The 
 
WATER TYPE. 9 
 
 weight of two litres of hydrochloric acid gas, for instance, proving 
 to be identical with the weight of one litre of chlorine, plus that 
 of one litre of hydrogen, it is evident that mixed hydrogen and 
 chlorine on becoming combined hydrogen and chlorine occupy 
 precisely the same bulk before and after combination. 
 
 (8.) Turning our attention next to the combination of hy- 
 drogen with oxygen, we find that when oxygen and hydrogen 
 gases unite with one another to form water, it is always in the 
 proportion of one volume of oxygen to two volumes of hydrogen ; 
 and, conversely, when we decompose water electrolytically into 
 its constituent gases, we find that for every single volume of 
 oxygen liberated at the one pole, we have two volumes of hy- 
 drogen liberated at the other. Experiment has proved over and 
 over again that just as chlorine and hydrogen will unite with 
 one another only in the proportion of volume to volume, oxygen 
 and hydrogen will unite with one another only in the proportion 
 of one volume of the former to two volumes of the latter gas. 
 But oxygen is found to be exactly 16 times heavier than hy- 
 drogen ; or, taking the specific gravity of hydrogen as unity, the 
 specific gravity of oxygen will be 1 6 ; or, calling the weight of a 
 litre of hydrogen I crith, the weight of a litre of oxygen will be 
 1 6 criths. Hence, in water we have two volumes of hydrogen 
 united with one volume of oxygen, or 2 parts by weight of 
 hydrogen united with 16 parts by weight of oxygen, thus: 
 
 Water 
 
 When, however, two volumes of hydrogen unite with one 
 volume of oxygen, they do not form three volumes, but only 
 two volumes of gaseous water or steam. That is to say, the 
 three volumes of mixed hydrogen and oxygen form only two 
 volumes of combined hydrogen and oxygen. This condensation 
 is capable of being shown by direct experiment, but really we 
 do not require any such experiment, since the result may be 
 demonstrated with equal certainty by observing the specific 
 gravity of steam. We find, for instance, that the weight of two 
 
IO ANIMAL CHEMISTRY LECTURE I. 
 
 litres of steam is identical with the conjoint weight of one litre 
 of oxygen and of two litres of hydrogen ; so that while from 
 two litres of hydrochloric acid gas we can extract only one litre 
 of hydrogen in addition to the one litre of chlorine, from the 
 same bulk of steam or gaseous water we can extract two litres of 
 hydrogen in addition to the one litre of oxygen. In the experi- 
 ment taking place on the table of the electrolytic decomposition 
 of water, you see we have roughly, for the single volume of 
 oxygen, a double volume of hydrogen ; and by performing the 
 experiment with certain precautions, we should obtain exactly 
 twice as much hydrogen in the one tube as we obtained oxygen 
 in the other. 
 
 (9.) Let us now direct our attention to the third typical 
 hydride, namely, hydride of nitrogen or ammonia. The com- 
 bination of hydrogen with nitrogen to form ammonia can be 
 effected by indirect methods only ; but it may be shown by a 
 variety of processes, with which I will not trouble you, that 
 these two gases always unite with each other in the ratio of one 
 volume of nitrogen to three volumes of hydrogen. But nitrogen 
 is found to be exactly 14 times heavier than hydrogen; and, 
 accordingly, taking the specific gravity of hydrogen as unity, the 
 specific gravity of nitrogen will be 14; or, calling the weight of 
 a litre of hydrogen I crith, the weight of a litre of nitrogen will 
 be 14 criths. Hence we have in ammonia three volumes of 
 hydrogen combined with one volume of nitrogen, or 3 parts by 
 weight of hydrogen combined with 14 parts by weight of 
 nitrogen, thus : 
 
 Ammonia 
 
 Further, when one volume of nitrogen combines with three 
 volumes of hydrogen to form ammonia, the four volumes become 
 condensed into exactly two volumes. I cannot show you this 
 conversion of four volumes of mixed nitrogen and hydrogen into 
 two volumes of combined nitrogen and hydrogen, but the reverse 
 experiment is of very easy performance. Thus, if we submit 
 
AMMONIA TYPE. 
 
 II 
 
 ammonia gas to the action of the electric spark, it undergoes de- 
 composition into its elementary constituents, as you perceive. 
 We have here two volumes of ammonia gas, which, by the con- 
 tinued action of the electric spark is decomposed into its con- 
 stituent nitrogen and hydrogen and the two volumes of ammonia 
 become gradually increased into four volumes of hydrogen and 
 nitrogen, mixed in the proportion of three volumes of the former 
 to one volume of the latter gas. But in this case, as in the 
 previous two, the information afforded by a determination of the 
 specific gravity of ammonia renders a direct experiment of any 
 kind unnecessary. We find that the weight of two litres of am- 
 monia gas, for instance, is identical with the conjoint weight of 
 one litre of nitrogen and of three litres of hydrogen ; so that 
 while from two litres of hydrochloric acid gas we can extract 
 one litre of hydrogen, and from two litres of steam we can 
 extract two litres of hydrogen, so from two litres of ammonia we 
 can extract three litres of hydrogen, in addition to the one litre 
 of chlorine, oxygen, and nitrogen respectively. Or from double 
 volumes of chloride of hydrogen, oxide of hydrogen, and nitride 
 of hydrogen, we may obtain one volume of hydrogen, two 
 volumes of hydrogen, and three volumes of hydrogen respectively, 
 in addition, in each case, to the one volume of chlorine, the one 
 volume of oxygen, and the one volume of nitrogen, as illustrated 
 by these models. 
 
 Ammonia 
 
 Hydrochloric acid 
 
 Steam 
 
 (10.) You will observe that all I have hitherto said with 
 regard to these three hydrides is simply a matter of experiment 
 or observation, uncontrolled by any theory whatever. It is a 
 matter of fact that if we take equal volumes of hydrochloric acid, 
 steam, and ammonia gases, we can extract from the ammonia 
 
12 ANIMAL CHEMISTRY LECTURE I. 
 
 three times as much hydrogen, and from the steam twice as 
 much hydrogen, as can be got from the hydrochloric acid ; 
 whereas the amount of nitrogen we can extract from the ammonia 
 is exactly equal in bulk to the amount of oxygen we can extract 
 from the steam, and to the amount of chlorine, and, consequently, 
 of hydrogen, we can extract from the hydrochloric acid. It is 
 also a matter of fact that taking equal volumes of hydrogen, 
 chlorine, oxygen, and nitrogen, the weights of these equal 
 volumes are in the proportion of 
 
 i : 35'5 : 16 : 14 
 as shown more fully in the table before you. 
 
 Specific gravities or weights Molecules or weights of 
 
 of one volume two volumes 
 
 Hi H, 2 
 
 Cl 35-5 Cl, 71 
 
 16 0, 32 
 
 N 14 N a 28 
 
 IHCI 18-25 HCI 36-5 
 
 |H 3 O 9 H a O 1 8 
 
 IH 3 N 8-5 H 3 N 17 
 
 {H 4 C 8 H 4 C 1 6 
 
 (i I .) Now we come to a matter of interpretation. From these, 
 in addition to many other considerations, we accord to hydrogen, 
 chlorine, oxygen, and nitrogen the atomic weights i, 35*5, 16, 
 and 14, and we express the comparable molecules of hydrochloric 
 acid, water, and ammonia by the formulae HCI, H 2 O, and H 3 N 
 respectively, each of which represents the same gaseous bulk, or 
 2-volumes of its particular compound. This formula for water 
 is warranted by a host of considerations. It may suffice here to 
 remark that in composition, condensation, and properties, water 
 H 2 O, is strictly intermediate between the acid monhydride of 
 chlorine HCI, and the alkaline trihydride of nitrogen H 3 N. 
 Further, what is true of hydrochloric acid is also true of hydro- 
 fluoric acid, hydrobromic acid, and hydriodic acid. From 
 2-volumes of each of these gases we are able to extract a single 
 volume of hydrogen; while from equal bulks of sulphuretted, 
 
HYDRIDES AND CHLORIDES. 13 
 
 selenetted, and telluretted hydrogen, we are able to extract twice 
 the volume of hydrogen, and from equal bulks of phosphoretted, 
 arsenetted, and antimonetted hydrogen we are able to extract 
 three times the volume of hydrogen that can be got from the 
 same bulk of hydrochloric acid, as indicated in the table. 
 
 Monhydrides Dihydrides Trihydrides 
 
 HF H a O H 3 tf 
 
 HC1 H,S H 3 P 
 
 HBr H a Se H 3 As 
 
 HI H,Te H 3 Sb 
 
 (12.) We find, moreover, that chlorine is capable not only of 
 uniting with hydrogen in the proportion of volume to volume, 
 but also of replacing hydrogen in the same ratio in a great 
 variety of compounds. Indeed, we may consider the comparable 
 molecules of free chlorine C1C1, and of hydrochloric acid HC1, to 
 be derived from the molecule of free hydrogen HH, by a dis- 
 placement of two atoms, and of one atom, of hydrogen respec- 
 tively, by equivalent quantities of chlorine. Accordingly we are 
 acquainted with chlorides corresponding to all the pre- considered 
 hydrides, C1C1 and C1I corresponding to HC1 and HI ; C1 2 O and 
 C1 2 S corresponding to H 2 O and H 2 S ; and C1 3 N and C1 3 P corre- 
 sponding to H 3 N and H 3 P, &c.; and these chlorides when in the 
 gaseous state are found to have exactly the same bulk as their 
 corresponding hydrides. Thus, from two litres of oxide of chlorine 
 C1 2 O, we are able to extract one litre of oxygen and two litres of 
 chlorine, just as from two litres of oxide of hydrogen H 2 O, we 
 are able to extract one litre of oxygen and two litres of hydrogen. 
 
 Monochlorides Bichlorides Trichlorides 
 
 C1C1 Cl a O C1 3 N 
 
 C1I C1 3 S C1 3 P 
 
 CINa Cl a Zn C1 3 A1 
 
 C1K Cl.Ca Cl 3 Au 
 
 ClAg Cl,Hg Cl 3 Bi 
 
 (13.) The metals do not, as a rule, combine with hydrogen, 
 ^<ut their chlorides, as shown in the above table, may be divided 
 
14 ANIMAL CHEMISTRY LECTURE I. 
 
 into three classes, corresponding to the chlorides of the non- 
 metals, by having regard to such considerations as the following : 
 We find that the proportions of the solid non-metals, iodine, 
 sulphur, and phosphorus, which unite with one, two, and three 
 volumes of hydrogen respectively, and with one, two, and three 
 volumes of chlorine, as shown in the previous tables, and which 
 we have agreed to regard as atomic proportions, have their several 
 specific heats expressed approximately by the number 6-3. Now, 
 if we take for the atomic proportions of the different metals those 
 quantities of each of them w'hich have substantially the same 
 specific heat as one another and as the atomic proportions of the 
 solid non-metals, then we find that the chlorides of the metals, like 
 those of the non-metals, must also be divided into monochlorides, 
 di-chlorides, and trichlorides, &c. Accordingly, we have in the 
 opposite table a list of chlorides of metallic and hydrides of non- 
 metallic elements corresponding, you perceive, with one another. 
 (14.) Only a few of these metallic chlorides can be vaporised 
 at manageable temperatures ; but with regard to such of them as 
 are moderately volatile, it is found that two litres of their several 
 vapours contain as many litres of chlorine as are indicated by their 
 respective formulae, deduced from the specific heats of their con- 
 stituent metals. With regard to corrosive sublimate vapour, for 
 instance, we find that from two litres of gaseous chloride of mercury 
 01 2 Hg, we can extract two litres of chlorine, just as we can from the 
 same bulk of chloride of oxygen C1 2 ; whereas, if we take two 
 litres of chloride of bismuth Cl 3 Bi, we can extract therefrom 
 three litres of chlorine, just as we can also extract three litres of 
 chlorine from two litres of chloride of phosphorus C1 3 P. We 
 find, then, that in the case of those metallic chlorides which are 
 volatilisable, we can get from 2 -volumes of their respective 
 vapours, quantities of chlorine identical with the quantities 
 obtainable from similarly formulated non-metallic chlorides. I 
 may take the opportunity of saying that from considerations of 
 this sort, together with others of almost equal cogency, it is de- 
 monstrable that the formula for corrosive sublimate, HgC] 2 , in 
 the old * London Pharmacopoeia ' is right, while that in the new 
 
FOEMULJ5 OF METALLIC CHLORIDES. 
 
 Elements 
 
 Atomic weights 
 
 Specific heats of 
 atomic weights 
 
 Formulas of 
 chlorides, &c. 
 
 Monads 
 
 
 
 
 
 Bromine 
 
 80 
 
 674 
 
 HBr 
 
 Iodine 
 
 I2 7 
 
 6-87 
 
 HI 
 
 Lithium 
 
 7 
 
 6-58 
 
 C1L 
 
 Sodium 
 
 *3 
 
 675 
 
 CINa 
 
 Potassium 
 
 39 
 
 6-61 
 
 C1K 
 
 Silver 
 
 Ml 
 
 6-15 
 
 ClAg 
 
 Dyads 
 
 
 
 
 Sulphur 
 
 3 2 
 
 5-68 
 
 H 2 S 
 
 Selenium 
 
 79'5 
 
 6-65 
 
 H,Se 
 
 Tellurium 
 
 129 
 
 6-1 1 
 
 H 3 Te 
 
 Manganese 
 
 55 
 
 6-69 
 
 Cl a Mn 
 
 Iron 
 
 56 
 
 6-37 
 
 Cl a Fe 
 
 Cobalt 
 
 59 
 
 6-31 
 
 Cl a Co 
 
 Nickel 
 
 59 
 
 6-41 
 
 Cl.Ni 
 
 Copper 
 
 63-5 
 
 6-04 
 
 Cl a Cu 
 
 Magnesium 
 
 24 
 
 5'99 
 
 Cl a Mg 
 
 Zinc 
 
 65 
 
 6-26 
 
 Cl 3 Zn 
 
 Cadmium 
 
 112 
 
 6-35 
 
 Cl 3 Cd 
 
 Mercury 
 
 200 
 
 6-38 
 
 Cl 3 Hg 
 
 Triads- 
 
 
 
 
 Phosphorus 
 
 31 
 
 5-85 
 
 H 3 P 
 
 Arsenic 
 
 75 
 
 6-io 
 
 H 3 As 
 
 Antimony 
 
 122 
 
 6-19 
 
 H 3 Sb 
 
 Bismuth 
 
 210 
 
 6-47 
 
 Cl 3 Bi 
 
 Aluminum 
 
 27-5 
 
 5^7 
 
 C1 3 A1 
 
 Thallium 
 
 20 3 
 
 6-81 
 
 C1 3 T1 
 
 Gold 
 
 J 9 6 '5 
 
 6-37 
 
 Cl 3 Au 
 
 Tetrads- 
 
 
 
 
 Tin 
 
 118 
 
 6-63 
 
 Cl 4 Sn 
 
 Lead 
 
 207 
 
 6-50 
 
 Et 4 Pb 
 
 Palladium 
 
 106-5 
 
 6-31 
 
 Cl 4 Pd 
 
 Platinum 
 
 197 
 
 6 '39 
 
 Cl 4 Pt 
 
1 6 ANIMAL CHEMISTRY LECTURE I. 
 
 4 British Pharmacopoeia,' HgCl,* is indisputably wrong. In the 
 present state of knowledge, the matter no longer admits of any 
 question whatever. 
 
 (15.) Having thus considered our primary hydrides of chlorine, 
 oxygen, and nitrogen, as typical of monad, dyad, and triad com- 
 binations in general, I now wish to direct your attention, lastly, 
 to their mutual relationship. Here we have them written up in 
 a convenient form : 
 
 Chlorides Hydrates Amides 
 
 HC1 H(HO) H(H 3 N) 
 
 KC1 K(HO) K(H 2 N) 
 
 ZnCl, Zn(HO), Zn(EL,N) 2 
 
 PC1 3 P(HO) 3 P(H Z N) 3 
 
 If under suitable conditions we act upon hydrochloric acid 
 HC1, water H.HO, and ammonia H.H 2 N, by a metal say by 
 potassium we obtain in each instance the same reaction. The 
 one atom of potassium turns out one atom of hydrogen; and 
 from each of the three molecules, instead of chloride, oxide, and 
 nitride of hydrogen, we get the chloride, hydrate, and amide of 
 potassium, which may be regarded as compounds of potassium K, 
 with the residues or radicles chlorine Cl, eurhyzen HO, and 
 amidogen H 2 N. Hence, caustic potash and potassamide may be 
 regarded as the hydrated and ammoniated forms of chloride of po- 
 tassium ; and in a similar manner, to nearly every chloride, mineral 
 or organic, simple or compound, there exists a corresponding 
 hydrate and amide bearing to it the same relation that caustic 
 potash and potassamide respectively bear to chloride of potassium. 
 If we consider chloride of potassium, for instance, as a com- 
 pound of metallic potassium, with the residue from hydrochloric 
 
 * Hg; atomic weight, 200; atomic heat, 6-38: Hg ; atomic weight, 
 100 ; atomic heat, 3-19, or half that of the other elements. So that in un- 
 dergoing an equal increment or decrement of temperature, 200 parts of 
 mercury absorb or evolve the same, and 100 parts of mercury only half the 
 amount of heat absorbed or evolved by 23 parts of sodium, 65 parts of zinc, 
 108 parts of silver, 210 parts of bismuth, &c. 
 
AMIDATED COMPOUNDS. 17 
 
 acid, we can in the same way consider caustic potash as a 
 compound of the metal with the residue from water, and potass- 
 amide as a compound of the metal with the residue from ammonia ; 
 and hereafter it will appear that some of the most complicated 
 products of tissue metamorphosis are but the ammoniated forms 
 of comparatively simple bodies, just as potassamide is the ammo- 
 niated form, and caustic potash the hydrated form, of chloride of 
 potassium. Again, if in chloride of zinc ZnCl 2 , we replace the 
 two atoms of chlorine by eurhyzen or peroxide of hydrogen, we 
 obtain hydrate of zinc ; whereas if we replace them by amidogen 
 we obtain zincamide, as also shown in the above table. Similarly 
 if in chloride of phosphorus PC1 3 , we replace the three atoms of 
 chlorine by peroxide of hydrogen, we obtain phosphorous acid ; 
 whereas if we replace them by amidogen we obtain phosphor- 
 amide; these three bodies being, so to speak, the phosphorus 
 representatives of hydrochloric acid, water, and ammonia, or of 
 chloride of potassium, caustic potash and potassamide. 
 
 (16.) Passing on to organic compounds, marsh gas is found to 
 consist of one atom of carbon united with four atoms of hydrogen, 
 so as to constitute the fourth or tetrad term of our series of 
 typical hydrides. Now, if we take the chlorine derivative of 
 this marsh gas that is, if instead of CH 4 we take CH ? C1. an'1 
 replace the atom of chlorine by an atom of peroxide of hydrogen, 
 we obtain ordinary wood-spirit, whereas if we replace it by 
 amidogen, we obtain methylamine, a very common product of 
 the putrefactive decomposition of animal matter, as formulated in 
 the first line of the next table : 
 
 Chlorides Hydrates Amides 
 
 C H 3 C1 C H 3 (HO) C H 3 (H 2 N) 
 
 C Cl a CO (HO), C (H a N\ 
 
 C 3 N 3 C1 3 C 3 N 3 (HO) 3 C 3 N 3 (H,N) 3 
 
 C a H 3 C10, C a H 3 (HO)O a C,H 3 (H 2 N)O a 
 
 C a H 5 ClS0 3 C a H 5 (HO)S0 3 C a H 5 (H a N)S0 3 
 
 Again, if in phosgene gas COC1 2 , we replace the two atoms of 
 chlorine by peroxide of hydrogen, we obtain carbonic acid ; 
 
 c 
 
1 8 ANIMAL CHEMISTRY LECTURE I. 
 
 whereas if we replace them by amidogen we get urea, as shown 
 in the second line of the table. Physiologists regard urea as 
 a complex organic body altogether sui generis. The chemist 
 regards it merely as the ammoniated form of one of the sim- 
 plest mineral acids; for the relation of phosgene and carbonic 
 acid to urea is identical with that of hydrochloric acid and 
 water to ammonia, and with that of chloride of potassium and 
 caustic potash to potassamide. Proceeding a little further, if in 
 cyanuric chloride C 3 N 3 C1 3 , we replace the three atoms of chlorine 
 by three atoms of peroxide of hydrogen, we get cyanuric or pyro- 
 uric acid; whereas if we replace them by amidogen, we get 
 melamine, a product of the action of heat upon urea. Passing 
 qn to chloracetic acid C 2 H 3 C10 2 a derivative of common acetic 
 acid C 2 H 4 2 , by the substitution of an atom of chlorine for hydro- 
 gen if in this body we replace the chlorine by peroxide of 
 hydrogen, we obtain glycolic acid ; whereas if we replace it by 
 amidogen, we obtain glycocine, or sugar of gelatin, glycocine 
 being only an ammoniated form of the glycolic and chlor- 
 acetic acids. 
 
 The next formula, C 2 H 5 C1S0 3 , represents chlorethyl-sulphur- 
 ous acid, and if in this body we replace the atom of chlorine by 
 an atom of peroxide of hydrogen, we obtain isethionic acid; 
 whilst if we replace it by amidogen, we obtain a compound of 
 which I have already spoken, namely, ta urine, taurine, isethi- 
 onic acid, and chlorethyl-sulphurous acid being respectively the 
 amidated, hydrated, and chlorinated forms of one and the same 
 body, being, in fact, ethyl-sulphurous varieties of hydrochloric 
 acid, water, and ammonia. 
 
 (17.) You perceive that this establishment between most com- 
 plicated and diverse bodies of relations similar to those subsisting 
 between hydrochloric acid, water, and ammonia between chlo- 
 ride of potassium, caustic potash, and potassamide furnishes us 
 with a key to the composition and metamorphoses of a whole 
 host of organic compounds ; but the generalisation is capable of 
 being pushed much farther. In bodies with two atoms of 
 chlorine, we may replace either one or both of them by eurhyzen, 
 
MIXED HYDRATE-AMIDES. 19 
 
 or by amidogen ; or we may replace one of them by eurhyzen 
 and the other by amidogen ; whilst in bodies containing three or 
 four atoms of chlorine, the possible number of derived bodies 
 increases in a very rapid manner, according to the ordinary 
 algebraic rule of combinations. I have here written down the 
 names of a few well-known double chloro-hydrates, chloro- 
 amides, and hydrate -amides, by way of illustration. 
 
 Mixed Hydrate-Amides, &c. 
 
 CuF a Cupric difluoride 
 
 CuF.HO Cupric fluorhydrate 
 
 HgCl a Mercuric dichloride 
 
 HgCl.H,N Mercuric chloramide 
 
 C 3 N 3 .C1 3 Cyanuric trichloride 
 
 C 3 N 3 .Cl(H a N), Cyanuric chloro-diamide 
 
 C 3 N 3 (HO) 3 Cyanurie trihydrate 
 
 C 3 N 3 (HO) a (H 2 N) Cyanuric dihydrate-amide 
 
 C 3 N 3 (HO) (H,N) a Cyanuric hydrate-diamide 
 
 C 3 N 3 (H,N) 3 Cyanuric triamide 
 
 First of all we have difluoride of copper, or cupric difluoride, 
 followed by cupric fluorhydrate. Next we have mercuric di- 
 chloride or corrosive sublimate, and then mercuric chloramide, 
 or white precipitate, a body in which one of the original chlorine 
 atoms is replaced by amidogen. Next we come to cyanuric tri- 
 chloride and its numerous derivatives, in the first of which, 
 namely, cyanuric chloro-diamide, two of the original chlorine 
 atoms are replaced by amidogen. Then we have in succession 
 cyanuric trihydrate or ordinary pyro-uric acid, cyanuric dihy- 
 drate-amide or melanuric acid, cyanuric hydrate-diamide or 
 ammeline, and lastly cyanuric triamide or melamine, a body 
 produced, as I have already said, by the action of heat upon 
 urea. 
 
 (18.) Let me give you one more illustration of this relation- 
 ship. I have said that urea CH 4 N 2 0, is an ammoniated form of 
 carbonic acid ; but we are acquainted with another urinary 
 product, namely, guanidine CH 5 N 3 , which is an ammoniated 
 
 c2 
 
2O ANIMAL CHEMISTKT LECTURE I. 
 
 form of urea, and accordingly bears to urea much the same 
 relation that urea itself bears to carbonic acid, thus : 
 
 CN a H 3 (HO) Urea 
 
 CN 8 H 3 (H a N) Guanidine 
 
 I refrain, for the present, from entering into further details 
 upon this subject. I have shown the wide applicability of the 
 generalisation, and that by its means we are capable of associating 
 with one another the most diverse bodies, and of establishing 
 between them the same simple relations which subsist between 
 hydrochloric acid, water, and ammonia ; and in particular I have 
 pointed out that some of the best known products of tissue meta- 
 morphosis are in reality only the ammoniated forms of compara- 
 tively simple bodies. In my next lecture I shall endeavour to 
 satisfy you that the complex character of many organic bodies 
 is more apparent than real, and that most of them may be re- 
 solved into comparatively simple molecules, which are capable of 
 being distributed into certain well denned groups and series ; and 
 I shall take, as concrete illustrations of the point I wish to esta- 
 blish, the composition of salicin among vegetable, and that of 
 hippuric acid among animal products. 
 
21 
 
 LECTUEE II. 
 
 Proximate animal and vegetable principles included in the class of organic 
 compounds, together with various bodies resulting from their natural 
 and artificial metamorphoses Carbon the characteristic element of 
 organic compounds Number, variety, and complexity of its combina- 
 tions with hydrogen and oxygen Highly complex organic bodies built 
 up of less complex molecules Salicin formed of saligenin and glucose ; 
 populin of benzoic acid, saligenin, and glucose Occurrence of con- 
 stituent molecules in an incomplete state Doctrine of residues Exist- 
 ence of minute residues of acetic acid and ammonia in aceto-nitrile, and 
 of oxalic acid and ammonia in cyanogen Eesidues of constituent 
 molecules ever ready to regenerate complete and separate molecules by 
 an absorption of water Aplone molecules either possessed of simple 
 constitution, or associated with bodies of simple constitution as members 
 of the same family Distribution of aplone molecules into series of 
 similarly constituted compounds Also into groups of dissimilarly con- 
 stituted compounds susceptible of mutual metamorphosis Series of 
 primary fatty acids Propionic and butyric groups Relations of alcohols 
 and glycols to mono- and di-basic acids Nature of homologous series 
 Differences and resemblances between the fatty acids Series of 
 aromatic acids and hydrocarbons Other groups and series Every aplone 
 molecule referrible to a definite position in some homologous series and 
 heterologous grouping Hippuric acid formed of three constituent resi- 
 dues, convertible into complete molecules by an absorption of water 
 Assignment of these molecules to appropriate positions in groups and 
 series Possibility of obtaining any two residues in combination, by 
 destruction or removal of third Assumed pre-existence of benzamide, 
 benzoglycolic acid, and glycocine in hippuric acid Probable internal 
 arrangement of the acid Illustrative animal products formed of two 
 constituent residues Urea, glycocine, leucine Analogy of spermaceti 
 and myricin to acetic ether The true fats Illustrative animal products 
 formed of more than two residues Taurine, sarcosine, alloxan, and the 
 biliary acids Scheme of the constitution of kreatine. 
 
22 ANIMAL CHEMISTRY LECTURE II. 
 
 (19.) CHEMISTS have ascertained that the various tissues of plants 
 and animals are composed of, or contain, a great number of dis- 
 tinct chemical compounds, capable, for the most part, of being sepa- 
 rated from one another by what may be regarded as physical pro- 
 cesses that is to say, by processes dependent on differences of 
 volatility, fusibility, solubility in different menstrua, &c. These 
 several compounds have either been built up in the living plant 
 or animal, or been formed spontaneously in the dead plant or 
 animal out of ancestral substances which were themselves built 
 up in the living plant or animal. Somehow or other these proxi- 
 mate animal and vegetable principles, as they are termed, have 
 been produced through the agency of vitality. They have been 
 formed through the intervention of living organisms, and are 
 hence called organic compounds, in contradistinction to such 
 substances as quartz and feldspar and haematite, which pre-exist 
 in the mineral kingdom, and from such substances as copperas 
 and alum and carbonate of soda, which are produced artificially 
 by human ingenuity out of the pre-existing compounds of the 
 mineral kingdom. 
 
 (20.) When the chemist gets hold of these different tissue pro- 
 ducts and components he submits them to a variety of experi- 
 ments, and subjects them to the most strange transformations ; he 
 performs a simple subtraction, by taking away certain constituent 
 atoms and leaving the remainder ; or he performs a simple addi- 
 tion, by affixing other constituent atoms, whether of the same 
 or a different nature ; or he performs a substitution, taking away 
 certain constituent atoms and introducing fresh ones in their 
 places ; or he effects a more or less complete decomposition, by 
 breaking up the original substance into a variety of less complex 
 bodies. Now, all these products into which the chemist trans- 
 forms the proximate vegetable and animal principles, of which 
 we have spoken, belong to the class of organic compounds. As 
 a rule, they do not pre-exist in living organisms, they are not 
 formed spontaneously in dead organisms, but they result from 
 the skill of the chemist operating upon compounds which were 
 
ORGANIC OR CARBON COMPOUNDS. 2J 
 
 formed at some time or other through the agency of living organ- 
 isms. Just as alum and carbonate of soda, which the chemist 
 manufactures out of native minerals, belong to the class of mineral 
 compounds, so do such substances as chloroform and aniline and 
 cyanuric acid, which the chemist manufactures out of the proxi- 
 mate principles of plants and animals, belong to the class of 
 organic compounds. 
 
 (21.) It is found that all organic compounds, whether of na- 
 tural or artificial production, contain carbon as an essential 
 constituent ; nearly all of them contain hydrogen also ; while the 
 great majority consist of carbon, hydrogen, and oxygen. In my 
 last lecture I brought under your notice certain nitrogenous pro- 
 ducts of tissue metamorphosis, but confining our present attention 
 to such organic bodies as consist of carbon, hydrogen, and oxygen, 
 or of carbon and hydrogen only, I would speak to you, in the 
 first place, of their immense number and variety. If we take 
 any three elements whatsoever, exclusive of carbon, we shall find 
 that by their mutual combination they very rarely indeed form 
 more than half-a-dozen definite and distinct compounds ; but we 
 are acquainted with some thousands of compounds composed 
 solely of carbon, hydrogen, and oxygen united with one another 
 in different quantities and proportions ; which thousands of com- 
 pounds differ most strikingly in their properties, but were all 
 produced originally in living organisms, or made artificially by a 
 transformation of antecedent compounds produced originally in 
 living organisms. 
 
 (22.) In addition to their number and variety, organic or 
 carbon compounds are characterised by the complexity of their 
 constitution ; that is, by the number of constituent atoms of 
 which their respective molecules are composed. If we take, any 
 definite mineral substance containing only three different kinds of 
 elementary matter, corresponding to the carbon, hydrogen, and 
 oxygen of the bodies now under consideration, we shall find that 
 the number of constituent atoms in such mineral substance very 
 rarely indeed exceeds ten or twelve, never perhaps reaches 
 
24 ANIMAL CHEMISTRY LECTURE II. 
 
 twenty; whereas, among organic or carbon compounds, bodies 
 containing scores of constituent atoms are very frequently met 
 with, a few of which, by way of illustration, are written up on 
 the table before you. 
 
 Formulae Proximate Organic Principles Atoms 
 
 C 6 H IO 5 Starch 21 
 
 C 6 H I4 6 Mannite 26 
 
 C I3 H I8 7 Salicin 38 
 
 C 20 H M Og Populin 50 
 
 C 27 H a3 I7 Tannin 66 
 
 C z6 R M Cholesterin 71 
 
 C 3a H 64 0^ Spermaceti 98 
 
 C 46 H 9Z 0,5 Myricin 140 
 
 C 57 H JI0 06 Stearin 173 
 
 First of all we have starch, a compound consisting of 6 atoms 
 of carbon, 10 of hydrogen, and 5 of oxygen, making altogether 
 2 1 atoms. Next we have mannite, the crystallisable principle of 
 ordinary manna, of which it forms, I believe, as much as 60 or 
 70 per cent. It contains, as shown by its formula, 6 atoms of 
 carbon, 14 of hydrogen, and 6 of oxygen, making altogether 26 
 atoms. Next we come to the crystallisable bitter principle of 
 willow bark, namely, salicin, which, I am informed by manu- 
 facturers, is still largely produced and used as a substitute for 
 quinine. It is characterised, as you see, by the red colouration 
 it experiences when acted upon by sulphuric acid, and consists, 
 as shown by its formula, of 38 constituent atoms. Next we 
 come to populin, a similar crystallisable principle, less generally 
 known and less widely distributed. It is found in the bark and 
 leaves of the poplar, and contains 50 constituent atoms ; while 
 tannin contains 66 atoms, and cholesterin 71. I may take this 
 opportunity of observing that cholesterin, heretofore regarded as 
 an exclusively animal product, is now known to enjoy an exten- 
 sive distribution in the vegetable kingdom, having been extracted 
 from peas, wheat, almond oil, olive oil, &c. We pass on to 
 spermaceti, with its 98 atoms ; to myricin, or purified beeswax, 
 with its 140 atoms; and, lastly, to stearin, with its 173 atoms of 
 carbon, hydrogen, and oxygen. Comparing tri-elementary bodies 
 
CONSTITUTION OF COMPLEX MOLECULES. 25 
 
 of this kind with tri-elementary mineral substances in which the 
 number of atoms seldom exceeds 10 or 12, you perceive that the 
 compounds presented for our consideration appear at the first 
 glance to be possessed of a highly complicated nature. 
 
 (23.) But in the majority of instances a minute chemical ex- 
 amination of these apparently complex organic bodies has led to 
 the conclusion that they are formed, if I may so say, by the 
 agglomeration of certain less complex molecules. Taking salicin 
 and populin as illustrations, we find that salicin readily breaks 
 up into the less complex molecules known as saligenin and glu- 
 cose or grape sugar, while populin breaks up into a molecule 
 of saligenin, a molecule of grape-sugar, and a molecule of ben- 
 zoic acid. I have here a specimen of saligenin or salicylic 
 alcohol, a beautiful crystalline body, which even when in very 
 weak solution is capable of being recognised by its action on 
 perchloride of iron. Thus, on adding tincture of iron to a dilute 
 solution of saligenin, we get a deep purple colour developed by 
 the mutual reaction of the two bodies, as you observe. Salicin, 
 then, by an absorption of water, breaks up into the less complex 
 bodies saligenin and glucose, as shown in this equation, 
 
 Salicin Water Saligenin Glucose 
 
 C I3 H I8 7 + H,0 = C 7 H 8 Z + C 6 H I2 6 ; 
 
 while, under similar circumstances, populin, with its 50 consti- 
 tuent atoms, breaks up into saligenin, glucose, and benzoic acid, 
 thus : 
 
 Populin Water Saligenin Glucose Benzoic acid 
 
 + aH 3 = C 7 H 8 O a + C 6 H IS! 6 + C 7 H 6 O a 
 
 (24.) Confining our attention to salicin, the point I wish to 
 impress upon you in relation to this body is, that it does not 
 really contain either saligenin or glucose in the state of a com- 
 plete molecule. Adding together the number of atoms of carbon, 
 hydrogen, and oxygen in saligenin, and the number of atoms of 
 the same elements in glucose, we find they are in excess of the 
 
26 ANIMAL CHEMISTRY LECTURE II. 
 
 number of atoms contained in the molecule of salicin, as shown 
 in this table. 
 
 x Saligenin . . C 7 H 8 O a 
 i Glucose C 6 HT,0 6 
 
 i Salicin . . < 
 
 i Water . . H a 
 
 C I3 H ao 8 
 
 Hence the necessity for the atom of water, which has to be 
 incorporated by the salicin before it can split up into its consti- 
 tuents. We may say, then, that salicin does not contain either 
 saligenin or glucose as such, but that it contains, in a state of 
 combination, a residue of saligenin and a residue of glucose, 
 which are, as it were, ever on the alert to take up water, and so 
 produce the separate and distinct molecules, saligenin and glucose 
 respectively. If we attempted to represent the composition of 
 salicin graphically, we should not place two complete circles in 
 apposition side by side, thus, 
 
 Saligenin Glucose 
 
 OO 
 
 but we should place two incomplete circles, or the residues of two 
 circles, in conjunction, thus : 
 
 Salicin 
 
 CD 
 
 (25.) Similarly, with regard to populin, it does not actually 
 contain saligenin, glucose, and benzoic acid, but is made up of 
 the residues of these three bodies, which can only be obtained 
 in their complete and separate state by an incorporation of the 
 elements of water with the populin, thus : 
 
i Saligenin 
 
 i Glucose 
 
 i Benzole acid 
 
 CONSTITUENT RESIDUES. 
 C 7 H 8 0, 
 C, H*ol 
 
 27 
 
 1 Populin 
 
 2 Water 
 
 Accordingly, we should not represent populin graphically by 
 three complete circles in apposition, but by the residues of three 
 circles conjoined with one another, as in one or other of these 
 figures : 
 
 Populin 
 
 (26.) The constituent residues existing in salicin and popu- 
 lin form very considerable proportions of the original molecules 
 but in many instances the residues become extremely small. For 
 instance, by combining acetic acid with ammonia we obtain ace- 
 tate of ammonia, a salt produced by the direct union of the two 
 complete molecules, acetic acid and ammonia. Under certain 
 circumstances an atom of water may be eliminated from this 
 acetate of ammonia, whereby it becomes converted into aceta- 
 mide, which by further loss of an atom of water becomes aceto- 
 nitrile, as shown in the following diagrams. 
 
 Thus, in acetamide the residues of acetic acid and ammonia con- 
 stitute but 59 out of 77 parts, while in aceto-nitrile they amount 
 to only 41 parts, or little more than half the weight of the original 
 molecule. Nevertheless, in aceto-nitrile the two small residues 
 stand apart from one another as perfect representatives of, or 
 proxies for, the entire molecules, ready without a moment's no- 
 tice to regenerate them on the concurrence of suitable conditions. 
 
ANIMAL CHEMISTRY LECTURE II. 
 
 Under a variety of circumstances both acetamide and aceto- 
 nitrile absorb the elements of water, with reconversion into acetate 
 of ammonia, a body containing the complete antagonistic mole- 
 cules, to which the constituent residues of the amide and nitrile 
 alike appertain. 
 
 Acetat-ammonia 
 
 60 
 
 o = 
 
 77 
 
 CO 
 
 Acet-amide 
 
 60 
 
 17 
 
 - H 2 
 
 - 18 
 
 = C,H 5 NO 
 59 
 
 Aceto -nitrile 
 
 60 
 
 H 3 N - 2H 2 
 
 17 - 36 
 
 C,H 3 N 
 
 (27). Let me give you one additional illustration of this doc- 
 trine of residues. Upon applying a gentle heat to certain metallic 
 cyanides we obtain cyanogen gas, which is recognisable by the 
 beautiful violet-coloured flame with which it burns, as you see, 
 at the mouth of the tube. In this experiment the cyanogen is 
 being made by heating cyanide of silver, but it is capable of 
 being produced in an entirely different manner. For if, instead of 
 combining ammonia with acetic acid, we combine it with oxalic 
 acid, and if from the resulting oxalate of ammonia we abstract 
 water, we thereby obtain cyanogen, as shown in this table : 
 
CONSTITUENT EESIDUES. 2Q 
 
 Formulae At. Weights 
 
 1 Oxalic acid C a H a 4 90 
 
 2 Ammonia (H 3 N) HeN a 34 
 
 C a H 8 N a 4 124 
 
 4 Water (H a O) H 8 4 72 
 
 i Cyanogen C a N a 52 
 
 The formula for oxalic acid is C 2 H 2 O 4 , and its atomic weight 
 90. With this we combine 2 atoms, or 34 parts by weight, of 
 ammonia, H6N 2 . Adding these together, we get 124 for the 
 atomic weight of oxalate of ammonia. When from this we sub- 
 tract 4 atoms or 72 parts by weight of water, we have left only 
 2 atoms of carbon from the oxalic acid, and 2 atoms of nitrogen 
 from the ammonia, which exist united with one another to form 
 a double atom, or single molecule, of cyanogen gas, and amount 
 to only 52 parts out of 124, or to considerably less than half 
 the weight of the original compound. In cyanogen, then, the 
 only evidence of the original oxalic acid is carbon, and the only 
 evidence of the original ammonia is nitrogen. Nevertheless, the 
 constituent carbon and nitrogen of this remarkable gas, which in 
 so many of its properties resembles certain of the elementary 
 bodies, are not incorporated with one another, but remain apart, 
 in the same way as do the residues of saligenin and glucose in 
 salicin, and the residues of acetic acid and ammonia in aceto- 
 nitrile, thus : 
 
 Cyanogen 
 
 Accordingly we find that cyanogen gas, when dissolved in 
 water, gradually absorbs the water necessary to re-form oxalic 
 acid and ammonia, the entire molecules, of which the small resi- 
 dues of carbon and nitrogen are but the representatives. In 
 cyanogen gas, no matter how produced, there is a something, 
 however small, pertaining to oxalic acid, a something, however 
 
3O ANIMAL CHEMISTRY LECTURE II. 
 
 small, pertaining to ammonia. The residues are not intermingled 
 promiscuously, but remain apart, ever mindful of their distinct 
 individualities, ever longing to re-form the complete and separate 
 molecules from which they sprung. 
 
 (28.) The progress of organic chemistry, then, has led to the 
 conclusion that highly complex molecules are built up of the 
 residues of less complex molecules, which constituent residues, 
 by a direct or indirect absorption of water, are capable of sepa- 
 ration from one another, and reproduction in their isolated and 
 perfect state. Accordingly, we regard highly complex or poly- 
 merone bodies as compounds formed by the union of less complex 
 or aplone bodies with one another, the union being attended by 
 an elimination of water. Now, these aplone molecules, of which 
 our constituent residues represent greater or less portions, are 
 found either to have a very simple constitution, or to be asso- 
 ciated with bodies of a very simple constitution, as members of 
 one and the same organic family. Despite their enormous 
 number, the great majority of them have been already referred 
 to certain definite positions in certain very simple groups and 
 series ; and we have every reason to believe that, with increase 
 of knowledge, they will all be referred in a similar manner to 
 groups and series, such as these to which I am pointing. Organic 
 chemistry, then, has achieved this great analytic success. The 
 compounds so elaborately built up by living organisms, it has 
 taken to pieces, and the pieces themselves it has arranged into 
 natural series and groups of associated bodies into series of 
 bodies of similar constitution and similar properties that are 
 not susceptible of mutual metamorphosis, and into groups of 
 bodies of dissimilar constitution and dissimilar properties that 
 are susceptible of mutual metamorphosis. 
 
 (29.) Here, for example, we have a series of bodies, namely, 
 the primary monobasic fatty acids, beginning with formic acid 
 CH 2 O 2 , and ending for the present, at any rate, with melissic 
 acid, C 30 Il6o0 2 . Some of these acids have, as you perceive, a 
 very simple, others a somewhat complex constitution, but all of 
 them present an .obvious similarity of constitution, manifest the 
 
FATTY GROUPS AND SERIES. 
 
 same general reactions, and are related to one another by a 
 regular gradation, both of properties and composition. 
 
 Monatomic Fatty Acid Series 
 
 C H a O a 
 
 Formic 
 
 C a H 4 0, 
 
 Acetic 
 
 C 3 H 6 O a 
 
 Propionic 
 
 C 4 H 8 O a 
 
 Butyric 
 
 C 5 H I0 O a 
 
 Valeric 
 
 C 6 H la O a 
 
 Caproic 
 
 C 7 H I4 O a 
 
 CEnanthic 
 
 C 8 H, A 
 
 Thetic 
 
 C 9 H l8 a 
 
 Pelargic 
 
 C IO H ao O a 
 
 Butic 
 
 c u H aa o a 
 
 Enodic 
 
 C Ia H a4 O a 
 
 Laurie 
 
 C I3 H a6 O a 
 
 Cocinic 
 
 C I4 H a8 0, 
 
 Myristic 
 
 C I5 H 30 O a 
 
 Benic 
 
 C l6 H 3a O, 
 
 Palmitic 
 
 C^H^O, 
 
 Margaric 
 
 C l8 H 36 O a 
 
 Stearic 
 
 C I9 H 38 O a 
 
 Balenic 
 
 C ao H 40 0, 
 
 Arachidic 
 
 C aI H 4a O a 
 
 Nardic 
 
 C, 7 H 54 O a 
 
 Cerotic 
 
 C H 6 
 
 Melissic 
 
 (30.) But in the succeeding tables we have two of our primary 
 monobasic fatty acids namely, the third or propionic acid, 
 and the fourth or butyric acid associated each with a set of 
 bodies dissimilar to the acid, and dissimilar to one another ; but 
 all containing the same number of carbon atoms as the particular 
 acid, and correlated with it and with one another by a suscepti- 
 bility of mutual metamorphosis, to such an extent indeed, that 
 they may almost be looked upon as varieties of one and the same 
 primitive body. 
 
 C 3 H 8 
 
 C 3 H 8 O a 
 
 a H o, 
 
 C 3 H 6 O a 
 C 3 H 6 3 
 C H 
 
 C 3 H 4 5 
 
 Propionic Group 
 
 Propene 
 Propyl-alcohol 
 Propyl-glycol 
 Glycerin 
 
 C 3 H 6 6 
 
 Propiou-aldehyd 
 Propionic acid 
 Lactic acid 
 Glyceric acid 
 
 C 3 H 4 
 C 3 H 4 O a 
 C 3 H 4 3 
 
 Malonic acid 
 Tartronic acid 
 
 C 3 H a 5 
 
 Propylene 
 AUyl-alcohol 
 
 Acrolic aldehyd 
 Acrolic acid 
 Pyruvic acid 
 
 Mesoxalic acid 
 
32 ANIMAL CHEMISTRY LECTURE II. 
 
 Butyric Group 
 
 C 4 H IO Butene C 4 H 8 Butylene 
 
 C 4 H I0 Butyl-alcohol 
 
 C 4 H 10 O a Butyl-glycol 
 
 C 4 H 8 Butyr-aldehyd 
 
 C 4 H 8 O z Butyric acid C 4 Hg 0, Crotonic acid 
 
 C 4 H 8 '0 3 Bulatic acid 
 
 C 4 He 4 Succinic acid C 4 H 4 4 Fumaric acid 
 
 C 4 H 6 5 Malic acid C 4 H 4 5 Metatartric acid 
 
 C 4 H 6 6 Tartaric acid 
 
 (31.) Of the correlated bodies comprised in groups of this 
 description, chemists attach far greater importance to those occu- 
 pying certain particular positions, than to the remainder. Thus, 
 the principal terms of every well represented organic group such 
 as the propionic, and butyric, to which I have just directed your 
 attention are, I st, the monatomic alcohol ; 2nd, the monobasic 
 acid corresponding thereto ; 3rd, the diatomic alcohol or glycol ; 
 and 4th, the dibasic acid corresponding thereto, as shown below in 
 the case of the 2-carbon and 3 -carbon groups, for instance : 
 
 Principal Group-Terms 
 
 (C a H 6 Alcohol (C 3 H 8 Propyl-alcohol 
 
 ( C a H 4 0, Acetic acid \ C 3 H 6 O z Propionic acid 
 
 C a H 6 0, Glycol (C 3 H 8 3 Propyl-glycol 
 
 C.,H 3 4 Oxalic acid (C 3 H 4 4 Malonic acid 
 
 The monobasic acid, you observe, differs in composition from 
 its correlated alcohol by containing one additional atom of oxygen 
 in place of two subtracted atoms of hydrogen ; while the dibasic 
 acid differs from its correlated glycol by containing two additional 
 atoms of oxygen in place of four subtracted atoms of hydrogen. 
 But even of these four principal members of every complete 
 organic group, by far the most importance is attached to the 
 monobasic acid, which is accordingly selected in preference to the 
 alcohol, glycol, or dibasic acid as the characteristic term or pivot 
 of the group. As a rule, the series of monobasic acids is more 
 
FATTY ACID SERIES. 33 
 
 complete than that of the other terms ; the bodies themselves enjoy 
 an extensive natural distribution, either in the isolated condition 
 or in the form of constituent residues ; they can be obtained in a 
 comparatively pure state, many of them occurring as commercial 
 products; and their properties, both as individuals and as a class, 
 have been very carefully investigated. 
 
 (32.) Nearly all of these primary monobasic acids are capable 
 of being distributed into one or other of two principal series, 
 known as the fatty and aromatic series respectively. To the 
 fatty acid series, beginning with the formic, acetic, and pro- 
 pionic acids, I have already directed your attention. You observe 
 that each successive member of the series differs in composition 
 from its predecessor by an increment of I atom of carbon and 2 
 atoms of hydrogen. Bodies in which this difference of CH 2 pre- 
 vails are said to be homologous, and the series of fatty acids is 
 accordingly spoken of as a homologous series. It is noticeable 
 (vide preceding table of monatomic fatty acids series) that from 
 the first to the twenty-first term, the series is complete, while 
 between the twenty-first and thirtieth terms only one intermediate 
 acid is known, namely, cerotic acid, an important constituent of 
 ordinary beeswax, and especially of the so-called Chinese wax, 
 secreted by an insect of the coccus tribe. Now, while the differ- 
 .ence in composition and properties between the acids at either 
 extremity of this series is very great, that between any two or 
 three consecutive acids, more especially of those low down 
 in the list, is so slight as to be scarcely appreciable. Thus the 
 formic and acetic acids when in a state of purity are perfectly 
 mobile, strongly corrosive liquids; the butyric, valeric, and ca- 
 proic acids are thin oils ; while the palmitic, margaric, and stearic 
 acids are mild inactive solids. In comparing formic with palmitic 
 acid, which is only two-thirds of the way down the list, we 
 scarcely perceive a single point of resemblance ; but in comparing 
 formic with acetic acid, or still more decidedly in comparing pal- 
 mitic acid with the margaric and stearic acids, the difficulty is 
 rather to see the difference than the resemblance between them. 
 Moreover, between even the upper and lower members of the 
 series there is a latent similarity, and indeed certain well-marked 
 
 D 
 
34 ANIMAL CHEMISTRY LECTURE II. 
 
 properties are common to all the acids under consideration. They 
 are all volatile, inflammable, saponifiable, monobasic, and decom- 
 posible in a similar manner under the influence of the same 
 reagents. We are not in the habit of regarding vinegar in any 
 form as an inflammable material, but in reality strong acetic acid 
 is almost as inflammable as alcohol. It only requires to be heated 
 externally for a few minutes, wken it burns as you observe with 
 a large, lambent, feebly luminous flame. Neither are we in the 
 habit of regarding the acetates as soaps, yet solutions of acetates 
 possess the property of forming a persistent froth or lather to such 
 an extent as to be highly characteristic ; so that by searching out 
 for latent resemblances we can perceive that the different members 
 of the series, from the top to the bottom, are associated with one 
 another in a very intimate manner. 
 
 (33-) ^he P r i mar y aromatic acids at present known are far less 
 numerous, and the series consequently is far more limited, as 
 shown in this table : 
 
 Monatomic Aromatic Acid Series 
 
 C 6 H 4 0, Collie ? 
 
 C 7 H 6 2 Benzaic 
 
 C 8 H 8 O a Toluic 
 
 C 9 H I0 3 Picic 
 
 C IO H ia O a Cuminic 
 
 These acids correspond generally with the previously considered 
 fatty acids, in the reactions of which they are susceptible, and in 
 their mutual relationship. The first on the list, or collie acid, is 
 said to result from the artificial oxidation of albuminous matter, 
 but its existence is at any rate open to question. Next we have 
 benzoic acid, which is usually regarded as the representative in the 
 aromatic, of acetic acid in the fatty series. This is followed by 
 two acids of which at present comparatively little is known, 
 namely, the toluic and picic ; while the list is terminated by cu- 
 minic acid, a product formed by the spontaneous oxidation of the 
 chief constituent of oil of cumin. Now, just as the acetic, pro- 
 pionic, and butyric acids are associated each with their respective 
 hydrocarbons, alcohols, aldehydes, and more highly oxidised acids, 
 
ORGANIC GROUPS AND SERIES. 35 
 
 as shown in the group-tables to which I have already adverted, so 
 is every other primary monobasic acid, both of the fatty and 
 aromatic series, associated with a more or less complete set of 
 congeners, having to it the same relations of composition, pro- 
 perties, and mutual metamorphosis, that the various members of 
 the acetic, propionic, and butyric families have to the acetic, pro- 
 pionic, and butyric acids respectively. Here, for example, we 
 have tabulated the principal compounds which are associated in 
 this manner with benzoic acid : 
 
 Benzole Group 
 
 C 7 H 8 Benzoene 
 
 C 7 H 8 Benzyl-alcohol 
 
 C 7 H 8 O z Benzyl-glycol 
 
 C 7 H 6 '0 Benz-aldehyd 
 
 C 7 H 6 'o a Benzoic acid 
 
 Cj H 6 3 Ampelic acid, &c. 
 
 (34.) Conversely, we may select any set of compounds occu- 
 pying analogous positions in the different groups, and arrange 
 them in series corresponding to those of the monobasic acids. 
 Here, for instance, we have the series of aromatic hydrocarbons : 
 
 Aromatic Hydrocarbon Series 
 C 6 H 6 Phenene 
 
 C 7 H 8 Benzoene 
 
 C 8 H IO Xylene 
 
 C 9 H I2 Ketinene 
 
 C IO H I4 Cymene 
 
 Again, in the next table we have the two series of primary fatty 
 alcohols and of aldehydes resulting from their dehydrogenation : 
 
 Fatty Alcohol Series Fatty Aldehyd Series 
 
 C H 4 Methylie C a, O Chloroformic 
 
 C a H 6 Ethylie C a H 4 O Acetic 
 
 C 3 H 8 Propylic C s H 6 Propionic 
 
 C 4 H I0 Butylic C 4 H 8 Butyric 
 
 C 5 H IZ Amylic C 5 H I0 Valeric 
 
 C 6 H I4 Caprylic C 6 H I3 Caproic 
 
 C 7 H I6 Anthylic C 7 H I4 (Enanthic 
 &c. &c. 
 
 D2 
 
36 ANIMAL CHEMISTRY LECTURE II. 
 
 Lastly, we have the carbonic and oxalic series of acids apper- 
 taining to the primary monobasic acids, and to the above tabulated 
 alcohols and aldehydes : 
 
 Diatomic Fatty Acid Series 
 
 C H a 3 Carbonic 
 
 C a H 4 3 Glycolic C a H a 4 Oxalic 
 
 C 3 H 6 3 Lactic C 3 H 4 4 Malonic 
 
 C 4 H 8 3 Bulatic C 4 H 6 4 Succinic 
 
 C 5 H I0 3 Phocic C 5 H 8 4 Pyrotartric; 
 
 C 6 H la 3 Leucic C 6 H I0 4 Adipic 
 
 C 7 H I4 3 ^j C 7 H IZ 4 Pimelic 
 
 C 8 H I6 3 I C 8 H I4 4 Suberic 
 
 C 9 H I8 3 [ Banting C 9 H l6 4 Anchoic 
 
 C IO H, 3 J C IO H I8 4 Sebacic 
 
 Accordingly, when we break up any complex animal product 
 into its simpler constituent molecules, by an absorption of water, 
 we are always, or nearly always, able to refer each of the com- 
 pleted molecules to its appropriate position in some homologous 
 series and in some heterologous grouping ; just as we accord to 
 common ethylic alcohol its proper place both in the series of 
 alcohols and in the group of acetic compounds. 
 
 (35.) Now, let us apply these several considerations to unravel 
 the composition and relationship of some particular animal pro- 
 duct, say hippuric acid, of which a very beautiful specimen, 
 kindly lent me for the occasion by Messrs. Hopkins and Williams, 
 stands on the table before you. This acid is represented by the 
 very complex formula C g HgNO 3 , and is composed, therefore, of 
 22 constituent atoms. It is now known to consist of a residue of 
 benzoic acid, a residue of oxiacetic or gly colic acid, and a residue 
 of ammonia, united with one another in a particular manner. 
 The positions of the benzoic and gly colic acids in the groups 
 and series' to which they belong have been already referred to 
 the benzoic being the second term of the primary aromatic 
 acid series, and the glycolic the second term of the carbonic 
 acid series the former being the pivot of the benzoic, the latter 
 a well known member of the acetic group. 
 
CONSTITUTION OF HIPPURIC ACID. 37 
 
 a. Benzole acid C 7 H 6 O a 
 
 /3. Oxiacetic acid C,H 4 3 
 
 7. Ammonia H 3 N 
 
 C 9 H I3 N0 5 
 - i. Water H 4 0, 
 
 Hippuric acid C^Hg N0 3 
 
 (36.) You observe that by subtracting two atoms of water from 
 the sum of the atoms of carbon, hydrogen, nitrogen, and oxygen 
 contained in the three molecules of benzoic acid, oxiacetic acid, 
 and ammonia, there is left a compound having the formula of 
 hippuric acid. Now there are few bodies about whose intimate 
 constitution greater varieties of opinion have been maintained than 
 with regard to this acid. Each successive chemist who has sub- 
 mitted it to examination has acted upon it with a different reagent, 
 and accordingly as the special reagent employed has attacked one or 
 other of the different residues entering into its constitution, so has 
 a different hypothetical formula been accorded to the unfortunate 
 body. Of the three constituent residues, the oxiacetic is the 
 most easily oxidisable, and accordingly when hippuric acid is 
 acted upon by oxidising agents, peroxide of lead for instance, the 
 acetic residue is destroyed, while the benzoic and ammonia residues 
 remain combined with one another in the form of benz amide. 
 Hence hippuric acid was represented as a compound of some form 
 of acetic acid with benzamide, which is. itself resolvable into ben- 
 zoic acid and ammonia. (Fehling.) 
 
 o. Benzoic acid 
 7, Ammonia 
 
 - Water H a O 
 
 Benzamide C 7 H 7 NO 
 
 (37.) Ammonia undergoes a very remarkable decomposition 
 when acted upon by nitrous acid, its hydrogen being transformed 
 
3 ANIMAL CHEMISTRY LECTURE II. 
 
 into water and its nitrogen liberated in the gaseous state, together 
 with the nitrogen of the nitrous acid, thus : 
 
 Ammonia Nitrous acid Water Nitrogen 
 
 H 3 N + HN0 4 = aH 3 + N, 
 
 Accordingly, when hippuric acid is treated with nitrous acid, 
 its ammoniacal residue is similarly destroyed by the nitrous acid, 
 while the two other residues are left combined with one another 
 in the form of benzoglycolic acid. Hence, hippuric acid has 
 been represented as a combination of ammonia, with benzoglycolic 
 acid, which is itself susceptible of decomposition into its constituent 
 benzoic and glycolic acids. (Strecker.) 
 
 a. Benzoic acid C 7 H 6 0^ 
 
 -0. Glycolie acid C a H 4 3 
 
 C 9 H I0 5 
 - Water H z 
 
 Benzoglycolic acid C 9 H 8 4 
 
 (38.) I am not aware of any reagents capable of destroying the 
 benzoic residue, and so leaving the glycolic and ammoniacal resi- 
 dues in combination with one another ; but on boiling hippuric 
 acid with acids or alkalies, the benzoic may be separated from 
 the other two residues, which are thus obtained in the form of 
 glycocine, or sugar of gelatin. Hence hippuric has been, 
 and is now, commonly regarded as a compound of benzoic acid 
 with glycocine, which is itself resolvable into glycolic acid and 
 ammonia. (Dessaignes.) 
 
 j8. Glycolic acid C a H 4 3 
 
 7. Ammonia H 3 N 
 
 C a H 7 N0 3 
 - Water H z 
 
 Glycocine C 3 H 5 N0 3 
 
CONSTITUTION OP HIPPURIC ACID. 39 
 
 (39.) Our actual knowledge, then, of the constitution of hip- 
 puric acid amounts to this, that it contains the residues of three 
 distinct molecules, which by an absorption of water are capable 
 of being obtained separate from one another. When any one of 
 these residues is destroyed or removed, the other two residues are 
 left in combination ; and accordingly by treating hippuric acid 
 with different reagents, we may obtain the benzoic and ammoniacal 
 residues in the form of benzamide, or the benzoic and glycolic 
 residues in the form of benzogly colic acid, or the glycolic and 
 ammoniacal residues in the form of sugar of gelatin. To this 
 much, which is certain, a something may be added which is pro- 
 bable. From many considerations into which I cannot at present 
 enter, it seems, at any rate, that the ammoniacal constituent of hip- 
 puric acid is actually in more intimate association with the gly- 
 colic than with the benzoic residue, so that the composition of 
 hippuric acid would be better represented by a chain of three 
 circles than by a trefoil, as contrasted in the diagram below ; 
 although, as I have said, the benzoic and ammoniacal residues 
 may be left in combination with one another by the excision, so 
 to speak, of the glycolic or oxiacetic residue. 
 
 Hippuric Acid 
 
 Be this as it may, I shall assume that hippuric acid consists of 
 a residue of benzoic acid and a residue of glycocine, which last 
 consists of a residue of glycolic or oxiacetic acid combined with a 
 residue of ammonia ; and similarly in the case of many other 
 
4O ANIMAL CHEMISTKY LECTUKE II. 
 
 bodies composed of more than two ultimate residues, I shall 
 assume, with greater or less warrant, that we can ascertain the 
 mode in which the residues are successively appended to one 
 another, as in the second list of bodies which I shall presently 
 bring under your notice. 
 
 (40.) The compounds whose names are written up in the third 
 column of the two following tables occur either as natural pro- 
 ducts of the animal body, or as constituent residues of such 
 natural products. In the first and second columns are given 
 the names of the simpler molecules, by the mutual combination 
 of which, with elimination of water, the corresponding bodies 
 named in the third column are produced. I think I may venture 
 to say that in every instance the bodies in this column have 
 been proved to consist of the residues which they are here re- 
 presented to contain, although, as I have said, in those bodies 
 which are composed of more than two ultimate residues, the 
 order in which the residues are successively combined, or the 
 relation in which any two of them stand to the remainder, may 
 be to some extent a matter of assumption. The word ' acid ' is 
 omitted from the columns for the sake of space : 
 
 Kesiduea Diamerones 
 
 Alcohol Sulphuric Isethionic 
 
 Wood-spirit Ammonia Methylamine 
 
 Carbonic Ammonia Urea 
 
 Glycolic Ammonia Glycocine 
 
 Leucic Ammonia Leucine 
 
 Palmitic Cetal Spermaceti 
 
 Palmitic Melyssal Myricin 
 
 Palmitic Glycerin Palmitin 
 
 Stearic Glycerin Stearin 
 
 Oleic Glycerin Olein 
 
 (41.) The first of these bodies, namely, isethionic acid, is 
 a constituent of taurine, and is formed by the union of alcohol 
 and sulphuric acid with elimination of water, or, in other words, 
 it contains a residue of each of these two bodies. Next on the 
 list is methylainine, a frequent product of the putrefactive 
 
CONSTITUTION OF UREA, ETC. 4! 
 
 decomposition of animal matter. It contains a residue of wood- 
 spirit and a residue of ammonia. 
 
 Then we come to urea, which contains a residue of carbonic 
 acid and a residue of ammonia. In my first lecture I spoke of 
 urea as being the ammoniated form of carbonic acid as bearing 
 to carbonic acid the same relation that ammonia bears to water 
 whereas I now represent it as a compound of carbonic acid and 
 ammonia with elimination of water ; but a little consideration 
 will show that the two modes of regarding this and similar 
 bodies are substantially the same. The empirical formula for 
 carbonic acid by which I mean hydrated carbonic acid is 
 CH 2 3 , while that for urea is CH 4 N 2 O. But regarding the two 
 bodies as derivatives of the double atoms of water and ammonia 
 respectively, or as the hydrate and amide of carbonyl, these 
 formulae become (CO) // H 2 O 2 , corresponding to H 4 O 2 , and 
 (CO)"H 4 N 2 corresponding to H6N 2 respectively. Accordingly, 
 the representation of urea as a compound of carbonic acid and 
 ammonia with elimination of water, or as a variety of carbonic 
 acid in which certain elements of water are replaced by the cor- 
 responding elements of ammonia, is shown in these almost 
 identical equations : 
 
 Carbonic acid z-Ammonia z-Water Urea 
 
 CH a 3 + H 6 N 8 - H 4 a = 
 
 (CO)H a O, + (H 3 )H 4 N a = (H a )H a O a + (CO)H 4 N, 
 
 Glycocine, or sugar of gelatin, the next compound on the 
 list, contains, as I have already observed, a residue of ammonia and 
 a residue of gly colic or oxiacetic acid. Leucine, a body upon 
 which I shall offer some observations in a future lecture, is a homo- 
 logue of glycocine, and contains a residue of ammonia and a residue 
 of leucic acid. We now come to spermaceti, which contains a 
 residue of palmitic acid, an important member of our primary 
 series of fatty acids, united with the residue of a solid alcohol, the 
 cetylic, which bears to palmitic acid precisely the same relation that 
 common ethylic alcohol bears to acetic acid, so that spermaceti is 
 a true homologue of acetic ether, as shown in these equations : 
 
42 ANIMA.L CHEMISTRY LECTURE II. 
 
 Acetic Ethylic Water Acetic ether 
 
 C 2 H 4 2 + C 3 H 6 - H 2 = C 4 H 8 4 
 
 Palmitic Cetylic Water Spermaceti 
 
 C l6 H 3a O, + C I6 H 34 - H a O = C 3Z H 64 Z 
 
 Next, we have myricin, which forms from 60 to 80 per cent, 
 of ordinary beeswax, and is composed of a residue of palmitic 
 acid united with a residue of another solid alcohol, the melyssic, 
 having the formula C 30 H6 2 0. Myricin is formed according to 
 the same typical equation as spermaceti and acetic ether, 
 namely, A + B H 2 O = X ; but the constituent palmitic acid, 
 instead of being combined with the alcohol of its own group, is 
 combined with the alcohol containing a double number of carbon 
 atoms. 
 
 The three following bodies are selected as examples of the 
 true fats. The first of them, namely, palm it in, is an impor- 
 tant constituent of palm oil or butter, and also exists in human 
 and other soft fats to a considerable extent. They are all 
 three produced in accordance with the same typical equation, 
 3A + B 3H 2 = X, as shown below : 
 
 Fatty acid Glycerin Water 
 
 3C l6 H 3a O z + C 3 H 8 3 - 3H 2 = Palmitin 
 
 3C I8 H 36 Z + C 3 H 8 3 - 3H Z = Stearin 
 
 3C I8 H 34 Z + C 3 H 8 3 - sH a O = Olein 
 
 You observe that stearic acid is a homologue of palmitic acid, 
 to which it stands next but one on the series; but oleic acid, 
 which differs in composition from stearic acid by a deficiency of 
 two hydrogen atoms, belongs to another set of compounds alto- 
 gether, namely, the secondary series of fatty acids. The simplest 
 known acid of this series is the acrolic, which is a member of the 
 propionic group, and, as you may perceive by referring to the 
 previous table of propionic compounds, bears to propionic acid 
 the same relation that oleic bears to stearic acid. 
 
COMPLEX ANIMAL PRODUCTS. 43 
 
 (42.) All the bodies in the table we have just considered con- 
 tain the residues of what may be regarded as primary, or aplone, 
 molecules; but one or other of the residues contained in the 
 several compounds included in the next table is itself a complex 
 body built up by the union of two or more simple molecules. 
 
 Residues Polymerones 
 
 Isethionic Ammonia Taurine 
 
 G-lycolic Methylamine Sarcosine 
 
 Carbonic Urea Allophan 
 
 Oxalic Urea Paraban 
 
 Mesoxalic Urea Alloxan 
 
 Benzoic Glycocine Hippuric 
 
 Cholic Glycocine Bile acid a 
 
 Cholic Taurine Bile acidjS 
 
 Urea Sarcosine Kreatine 
 
 Urea Methylamine Methyluramine 
 
 Thus taurine, of which I am able, through the kindness of 
 Mr. Lloyd Bullock, to exhibit an extremely handsome specimen, 
 contains a residue of ammonia united with a residue of isethionic 
 acid, which already contains a residue of alcohol and a residue of 
 sulphuric acid. Sarcosine, which is a constituent of kreatine, 
 contains a residue of gly colic acid and a residue of methylamine, 
 which itself contains a residue of wood-spirit and a residue of 
 ammonia. Allophan is a purely artificial compound, closely re- 
 lated to paraban and alloxan, which are products of the 
 oxidation of uric acid. These three bodies contain respectively 
 a residue of carbonic acid CH 2 O 3 , of oxalic acid C 2 H 2 4 , and of 
 mesoxalic acid C 3 H 2 O 5 , combined with a residue of urea, which 
 itself contains a residue of carbonic acid and a residue of am- 
 monia. The constitution of all three bodies is expressed by the 
 same typical equation A + B 2H 2 O = X, as exemplified below 
 in the case of alloxan : 
 
 Urea Mesoxalic Water Alloxan 
 
44 ANIMAL CHEMISTRY LECTURE II. 
 
 We next come to hippuric acid, which, as I have already 
 said, contains a residue of benzoic acid and a residue of glyco- 
 cine, which itself contains residues of glycolic acid and ammonia. 
 This is succeeded by the two principal acids of the bile, the first 
 of which, or glyco-cholic acid, contains a residue of cholic 
 acid and a residue of glycocine, and consequently differs only 
 from hippuric acid in containing a residue of cholic acid C 24 H 40 5 , 
 instead of a residue of benzoic acid C 7 H6O 2 . The other bile acid, 
 known astauro-cholic acid, contains a residue of cholic acid 
 and a residue of taurine, which already contains residues of 
 ammonia and isethionic acid, the latter body further containing a 
 residue of alcohol and a residue of sulphuric acid, thus : 
 
 Cholic 
 Tauro-cholic 
 
 Taurine -I ( Alcohol 
 
 (Ammonia 
 Isethionic -I 
 
 Sulphuric 
 
 (43.) The last compound which I propose to bring under your 
 notice to-day is kreatine, a beautiful crystalline body, as you 
 may perceive, from the unusually fine specimen lent me by Dr. 
 Hugo Miiller. This body, which exists largely in the juice of 
 flesh, and also, though to much less amount, in human urine, is 
 represented by the formula C 4 H 9 N 3 O 2 . Under the influence of 
 caustic baryta it absorbs water, with transformation into sar- 
 cosine and urea, the residues of which pre-exist in the kreatine, 
 thus : 
 
 Urea Sarcosine Water Kreatine 
 
 CH 4 N a O + C 3 H 7 NO a - H a O = C 4 H 9 N 3 O a 
 
 The urea, as I have already observed, contains residues of 
 carbonic acid and ammonia, and the sarcosine residues of glycolic 
 acid and methylamine, which last body further contains a re- 
 sidue of ammonia and a residue of wood-spirit, as shown in this 
 diagram : 
 
CONSTITUTION OF KREATINE. 45 
 
 Urea j arbonic 
 
 Ammonia 
 
 Kreatine 
 
 We have seen that the glycolic residue of hippuric acid may 
 be got rid of by oxidation, so as to leave the benzoic and ammonia 
 residues combined with one another in the form of benzamide. 
 Similarly the glycolic residue of kreatine may be got rid of by 
 oxidation, so as to leave the urea and methylamine residues 
 combined with one another in the form of methyluramine or 
 methyl-guanidine, thus : 
 
 Urea Methylamine Water Methyluramine 
 
 CH 4 N 2 -f CH 5 N - H a O = C a H 7 N 3 
 
 Concluding with these extremely complex animal products, I 
 trust I have satisfied you of the main position with which we 
 started, that highly complex molecules are built up of the re- 
 sidues of comparatively simple molecules, which are capable for 
 the most part of being referred to definite positions in certain 
 natural series or groups of associated bodies in such series as 
 those of the aromatic and fatty acids, aldehydes, alcohols, &c., 
 and in such groups as the benzoic, acetic, propionic, and butyric 
 groups for instance. 
 
46 ANIMAL CHEMISTRY LECTURE III. 
 
 LECTURE III. 
 
 Recapitulation Statical and dynamical aspects of organic chemistry 
 Destruction and construction of constituent molecules Tendency of 
 oxidation to produce molecules with fewer and fewer carbon and 
 hydrogen atoms Final production of carb-anhydride C0 1} and water 
 H,0 Destructive or analytic phase of organic chemistry Natural 
 synthesis of organic compounds attended by deoxidation Liberation of 
 oxygen by growing vegetables Tendency of deoxidation to combine 
 separate carbon and hydrogen atoms into complex molecules Vege- 
 table tissue and secretion formed by deoxidation of carbonic anhy- 
 dride and water Imperfect knowledge of intermediate products 
 Formation of nitrogenised tissues Ammonia in its relation to plant 
 life Correlations of ammonia, nitrous acid, and nitrogen Deoxidation 
 of nitrous acid by plants Manurial equivalency of nitrous acid and 
 ammonia Existence of nitrogen in natural organic products as a 
 residue of ammonia Artificial synthesis of organic bodies Combina- 
 tion of constituent molecules with one another Elementary formation 
 of constituent molecules Historical remarks on organic synthesis 
 Alleged incompetency of chemical, and necessity for vital action 
 Artificial production of all organic compounds by purely chemical 
 means Kolbe's indirect formation of acetic acid from carbon, hy- 
 drogen, and oxygen, in 1845 Subsequent advances by Berthelot and 
 others Oxidation of hydrogen into water, and of carbon into carbonic 
 anhydride Evolution of light and heat Deoxidation of water and 
 carbonic anhydride into hydrogen and carbon Similar separations of 
 oxygen from hydrogen and carbon effected by living plant and by 
 artificial processes Comparison of deoxidising vegetal and oxidising 
 animal functions Nature of forces concerned in respective actions. 
 
 (44.) I STATED in my last lecture that chemists were acquainted 
 with a great number of monobasic organic acids, containing two 
 atoms of oxygen in their respective molecules, and that these 
 acids were capable of being arranged in two principal classes, 
 
ORGANIC GROUPS AND SERIES. 47 
 
 known as the aromatic class and the fatty class, and exemplified in 
 the accompanying lists : 
 
 Fatty Acids Aromatic Acids 
 
 Formic C H 3 O z Collie ? C 6 H 4 O a 
 
 Acetic C a H 4 O z Benzoic C 7 H 6 O a 
 
 Propionic C 3 H 6 O a Toluic C 8 H 8 0, 
 
 Butyric C 4 H 8 O a Picic C 9 H I0 8 
 
 Valeric C 5 H I0 2 Cuminic C IO H Ia O a 
 
 Melissic C 30 H 6o O a 
 
 The acids of these two series presented, I told you, a marked 
 parallelism in their constitution, seriation, and properties ; and, 
 moreover, when submitted to the action of the same chemical 
 reagents, underwent precisely analogous metamorphoses. I dwelt 
 still more upon the mutual resemblance manifested by consecu- 
 tive members of the same series, and pointed out that even the 
 most remote members were distinguished from one another by 
 gradational differences only. I observed, also, that each one of 
 these primary monobasic acids> fatty or aromatic, was associated 
 with a more or less complete set of congeners, which differed 
 from it in constitution and properties, but were correlated with it 
 by the circumstance of their containing the same number of 
 carbon atoms, and still more markedly by their derivation from, 
 and convertibility into it and one another that acetic acid 
 C 2 H 4 2 , for instance, was associated with the less oxidised bodies, 
 olefiant gas C 2 H 4 , alcohol C 2 H6O, and aldehyd C 2 H 4 0, as well as 
 with the more highly oxidised glycolic and oxalic acids, C 2 H 4 3 
 and C 2 H 2 4 , respectively to such an extent, indeed, that they 
 might all be regarded as varieties of one and the same primitive 
 molecule. I further went on to say that the complex tissue pro- 
 ducts of the animal and vegetable kingdoms were built up of the 
 residues of these fatty and aromatic acids, and of their respective 
 congeners ; so that, upon breaking up such tissue products into 
 their constituent molecules, we were, in the great majority of 
 instances, able, even at the present time, to refer the constituent 
 
48 ANIMAL CHEMISTRY LECTURE III. 
 
 molecules to their appropriate positions in certain definite series 
 and groups ; and had every reason to believe that with increasing 
 knowledge we should be able to make the assignment in every 
 instance. 
 
 (45.) Moreover, in my first lecture I pointed out to you that 
 organic chemistry had a statical aspect which related to the com- 
 position of bodies, and a dynamical aspect which related to their 
 changes of composition. But in all that I have hitherto ob- 
 served I have had regard principally to the statical aspect of 
 the question. I have glanced, indeed, at the mutual metamor- 
 phosis by oxidation and deoxidation of compounds belonging to 
 the same natural group ; and have referred more fully to the 
 combination of their several residues with one another in forming 
 complex tissue products, and to the separation of the completed 
 residues from one another in the breaking up of these products ; 
 but I have not yet considered the mode in which the primary con- 
 stituent molecules are themselves produced, or yet the mode in 
 which, when once produced, it is possible for us to destroy them, 
 and to these points I will now direct your attention. 
 
 (46.) If we treat the more complex members of our series of 
 fatty acids, for instance, with powerful oxidising agents, we 
 obtain bodies in which the number of the constituent atoms of 
 hydrogen and carbon becomes progressively less and less, until 
 we arrive at bodies containing only two, and finally at bodies 
 containing only one carbon-atom. In some cases these succes- 
 sive oxidation products are found to contain the same number of 
 atoms of oxygen as the bodies from which they were produced, 
 though in the majority of instances they contain a greater 
 number, and consequently belong to more oxygenised series. 
 But whether they contain the same or a greater number of 
 oxygen atoms, we find the number of their atoms of carbon and 
 hydrogen become gradually less and less, their molecules pertain- 
 ing to simpler and simpler groupings. For example, the follow- 
 ing intermediate compounds, among many others, have been 
 successively obtained by oxidising stearic acid CigH^Oa, with 
 nitric acid of moderate strength : 
 
DESTRUCTIVE BESULTS OF OXIDATION* 49 
 
 Oxidation Products 
 
 Kutic acid 
 
 C IO H 
 
 zo0 2 
 
 Suberic 
 
 
 
 (Enanthic 
 
 C 7 H 
 
 .A 
 
 Pimelic 
 
 
 
 Caproic 
 
 C 6 H 
 
 1,0, 
 
 Adipic 
 
 
 
 Butyric 
 
 C 4 H< 
 
 5 o a 
 
 Succinic 
 
 
 
 Hi 4 
 
 (47.) The tendency of oxidation, then, is to separate the con- 
 stituent carbon and hydrogen atoms from one another, until at 
 last there is left only the most stable mono-carbon compound 
 known to chemists, namely, carbonic anhydride, or, as it is fre- 
 quently called, carbonic acid. No matter what the complexity of 
 the original molecule, the chemist eventually succeeds in trans- 
 forming it by oxidation, though a series of less and less complex 
 molecules, into carb-anhydride, or oxide of carbon, on the 
 one hand, and water, or oxide of hydrogen, on the other the 
 identical bodies out of which the vegetable organism directly, and 
 the animal organism indirectly, builds up those complex bodies 
 which we have designated proximate organic principles. As was 
 observed by Gerhardt some twenty years ago, 'one of the two 
 extremities of the scale of organic compounds is occupied by al- 
 bumin, and gelatin, and fat, and cerebral matter ; the other ex- 
 tremity by carbonic acid, and water, and ammonia ; while an 
 infinity of bodies are included in the interval. The chemist r by 
 treating the superior substances with oxidising agents, gradually 
 descends the scale of complexity, converting these substances into 
 more and more simple products, by successively burning off a 
 portion of their carbon and hydrogen.' 
 
 (48.) Thus, then, we have presented to us one important aspect 
 of organic chemistry, namely, its analytic or destructive aspect ; 
 that aspect upon which, until of late years, the attention of 
 chemists was almost exclusively directed ; that aspect, indeed, 
 which was at one time considered to be the only possible aspect 
 that could ever be presented. To quote again from the same dis- 
 tinguished chemist, of whom I am always proud to avow myself 
 
5O ANIMAL CHEMISTRT LECTURE III. 
 
 a pupil: 'I show,' said Gerhardt, writing in 1842, ' how the 
 chemist does everything that is contrary to living nature that 
 he burns, destroys, works by analysis the vital force alone 
 operates by synthesis and reconstructs the edifice destroyed by 
 chemical forces.' But, in reality, there is another side to the 
 shield ; there is a constructive as well as a destructive, a synthetic 
 as well as an analytic organic chemistry ; and to this view of 
 the subject I will now direct your attention. 
 
 (49.) I need scarcely remind you of the mode in which vege- 
 table structures are built up. The minute seed grows into the 
 gigantic tree, the great mass of which is made up of carbon, hy- 
 drogen, and oxygen, that the living organism has stored up 
 from the carbonic acid and water with which it has been sup- 
 plied throughout the period of its existence, and which it has 
 inter- combined into the various forms of vegetable tissue. Now, 
 this storing up of carbon, hydrogen, and oxygen this formation of 
 vegetable compounds is attended throughout by an evolution of 
 oxygen. The proportion of oxygen contained in carbonic acid 
 and water being greatly in excess of the proportion contained in 
 vegetable tissue and secretion, we have throughout the growth of 
 every plant a constant deoxidation of carbonic acid and water 
 the carbon, hydrogen, and necessary oxygen being retained in the 
 substance of the plant, the oxygen in excess of the requirements 
 of the plant being discharged into the atmosphere. Let me re- 
 call to your recollection one of the original experiments of 
 Priestley upon this subject. He showed, for example, that under 
 exposure to sunlight, a quickly-growing leafy plant, immersed in 
 an atmosphere which by the combustion of fuel had been freed 
 from oxygen and charged with carbonic acid, gradually restored 
 that atmosphere to its pristine condition, by an absorption and 
 subsequent decomposition of its carbonic acid into oxygen gas 
 evolved from the leaves, and carbon retained within the vegetable 
 structure. Here we have an imitation of the experiment. A 
 bunch of fresh mint has been thrust into this narrow cylinder of 
 dilute carbonic acid water standing in the small pneumatic 
 trough, and the whole exposed to sunlight. You perceive that 
 
CONSTRUCTIVE KESULTS OF DEOXIDATION. 51 
 
 the leaves are now covered all over with minute beads of gas, and 
 that a small but appreciable quantity of gas has collected at the 
 top of the cylinder. By pulling the attached thread I am able to 
 withdraw the bunch of mint, and on now passing up a few 
 bubbles of nitric oxide, a dark-brown vapour is produced at the 
 top of the cylinder, proving the contained gas to be oxygen ; 
 which oxygen, gradually evolved by the growing plant, has been 
 separated by the plant from the carbonic acid, or hydrated oxide 
 of carbon, wherewith it was surrounded. 
 
 (50.) Now, just as oxidation tends to break up the constituent 
 carbon and hydrogen atoms of a complex organic molecule 
 into simpler and simpler bodies, so, on the other hand, do 
 we find that deoxidation tends to combine the separated carbon 
 and hydrogen atoms into more and more complex bodies. 
 The organism of a plant, for instance, operating upon mono- 
 carbon molecules only, effects simultaneously their deoxidation 
 and inter-combination. It deoxidates them with evolution of 
 oxygen into the atmosphere, and combines the residual less 
 oxygenated carbon and hydrogen into the various forms of vege- 
 table tissue and secretion. What the intermediate stages are 
 between water and carbonic acid, on the ono hand, and some 
 vegetable principle such as mannite or sugar on 'the other, we can- 
 not positively say, though our knowledge upon the subject is re- 
 ceiving daily accessions. But be our acquaintance with the 
 intermediate stages ever so imperfect, the final result is perfectly 
 intelligible. We know, for instance, that in the production of this 
 body, mannite, there has been a deoxidation of six molecules of 
 carbonic anhydride and seven molecules of water, and that in the 
 course of the deoxidation, the thirteen separate molecules have 
 been conjoined into one single molecule, thus : 
 
 Carb-anhydride Water- Oxygen Mannite 
 
 6 CO, + 7 H a O - 130 = i CsH^Oe 
 
 (51.) This, then, is the point which I wish to bring promi- 
 nently under your notice that while oxidation tends to the sepa- 
 ration of atoms, and the formation of simple out of complex 
 
 E2 
 
52 ANIMAL CHEMISTRY LECTURE III. 
 
 bodies, deoxidation, as manifested in the vegetable kingdom, 
 tends to the combination of atoms, or to the formation of complex 
 bodies out of simple ones. Now, the chemist in his laboratory 
 can imitate, however crudely, this synthesis of nature. We find 
 in the laboratory, as in the organism, that deoxidation, actual or 
 potential, leads to the conjunction of atoms, and to the building 
 up of complex molecules. In broad antagonism to the doctrines 
 which only a few years back were regarded as indisputable, we 
 now find that the chemist, like the plant, is capable of producing 
 from carbonic acid and water a whole host of organic bodies, 
 and we see no reason to question his ultimate ability to reproduce 
 all animal and vegetable principles whatsoever. 
 
 (52.) But for the production of certain organic principles, 
 whether by natural or artificial means, something more than car- 
 bonic acid and water is required. The albuminoid bodies, in 
 particular, cannot be formed without nitrogen, and plants, in 
 general, cannot grow without a supply of ammonia or some 
 transformable compound. You will observe, however, that 
 ammonia, considered as a pabulum for plants, differs in this 
 important respect from both carbonic anhydride and water, that 
 it is not susceptible of deoxidation, or amenable, in other words, 
 to the characteristic chemical action of plant-life. On the con- 
 trary, ammonia is the most thoroughly deoxidised, or rather 
 hydrogenetted, compound of nitrogen with which chemists are 
 acquainted. Even nitrogen itself may be looked upon as less de- 
 oxidised than ammonia, being intermediate between ammonia 
 and nitrous acid, thus : 
 
 Nitrogen Molecules 
 
 H N 3 Nitric acid 
 
 H N O a Nitrous acid 
 
 N N Nitrogen 
 
 H 3 N Ammonia 
 
 The nitric and nitrous acids being regarded as oxidised forms 
 of nitrogen, ammonia must be regarded as a deoxidised form, the 
 element quoad its state of oxidation being strictly intermediate 
 
REDUCTION OF NITROUS ACID. 53 
 
 between ammonia and nitrous acid, as I hope to render experi- 
 mentally evident to you. 
 
 (53.) Thus, on passing a series of electric sparks from the 
 Kiihmkorff machine through the moist air contained in this 
 apparently empty glass cylinder, a portion of the nitrogen of the 
 contained air becomes gradually oxidised, and after a short time 
 we shall see brown nitrous fumes make their appearance, in 
 accordance with this reaction : 
 
 Nitrogen Oxygen Water Nitrous acid 
 
 N 3 + 3 + H a O = 2HNO a 
 
 By allowing the experiment to continue, the depth of colour 
 in the cylinder will go on increasing so as to be visible from every 
 part of the theatre. But I dare say I shall be able to render the 
 nitrous acid already produced abundantly manifest, by allowing it 
 to act upon a piece of paper stencilled with starch and iodide of 
 potassium solution. That we have really obtained a consider- 
 able amount of nitrous acid, by the few sparks which have as yet 
 passed through the air in the cylinder, is shown by the speedy 
 liberation of iodine from the iodide of potassium, and consequent 
 appearance of the word NITROUS in purple characters upon the 
 prepared paper. 
 
 (54.) Now for the reverse experiment. In this flask is a mix- 
 ture of materials for generating hydrogen, namely, a little granu- 
 lated zinc, some iron borings, and warm solution of potash. 
 Active effervescence quickly takes place, aud the evolved gas, 
 which is without action on turmeric paper, as you perceive, 
 bums with the characteristic flame of hydrogen. If we now 
 absorb the brown nitrous fumes contained in this gas-bottle, 
 by agitation with aqueous potash, and pour the solution so 
 produced of nitrite and nitrate of potassium into our hydrogen 
 flask, you observe that the effervescence becomes more rapid, 
 and that the evolved gas is now decidedly ammoniacal, as shown 
 by its browning the turmeric paper and fuming with the hydro- 
 chloric acid vapour I bring into its neighbourhood. The re- 
 action taking place in the flask is represented in this equation, 
 
54 ANIMAL CHEMISTRY LECTURE III. 
 
 Nitrous acid Hydrogen Water Ammonia 
 
 HNO a + H 6 2H 2 + H 3 N; 
 
 so that not only is oxygen taken away from, but hydrogen is 
 added to the nitrogen of our original nitrous acid. 
 
 (55.) By combining the oxidised form of nitrogen, or nitrous 
 acid HNO 2 , with the hydrogenetted form of nitrogen, or ammonia 
 H 3 N, we obtain nitrite of ammonia NH 3 HN0 2 , a neutral crystal- 
 lisable salt, whose somewhat concentrated solution is contained in 
 this flask-retort. Now, on applying heat to the retort, observe 
 what takes place. There is, you see, a copious evolution of gas, 
 some of which we will collect over the pneumatic trough ; and, in 
 order to save time, will content ourselves with only a small 
 cylinder full. The gas, produced in this manner from the nitrite 
 of ammonia solution in the retort, is nitrogen, recognisable at 
 once by its property of extinguishing flame. In this decomposi- 
 tion then the hydrogen of the ammonia exactly suffices to remove 
 the excess of oxygen from the nitrous acid, whereby the nitrogen 
 of both constituents of the salt is simultaneously liberated, 
 thus:- 
 
 Ammonia nitrite Water Nitrogen 
 
 NH 3 HNO Z = zH a O + N, 
 
 Hence nitrogen may be looked upon as exactly intermediate in 
 its state of oxidation between nitrous acid on the one hand, and 
 ammonia on the other ; whilst ammonia must be considered the 
 extreme product of deoxidation. Accordingly, it lias been found 
 as a general result both of laboratory and field experiments, the 
 latter conducted more especially by Messrs. Lawes and 'Gilbert in 
 this country, that cereals and other plants thrive equally well 
 upon salts of nitrous or nitric acid as upon salts of ammonia ; 
 and that when a plant is supplied with water, carbonic acid, and 
 nitrous acid, it exerts upon the nitrous acid the same sort of re- 
 ducing action that it does upon the water and carbonic acid, 
 whereby not only amylaceous, but ammoniated or nitrogenised 
 principles are abundantly produced. Indeed some chemists have 
 maintained that nitrous acid, rather than ammonia, forms the 
 
NITROGENOUS ORGANIC COMPOUNDS. 55 
 
 normal nitrogenous food of plants, and that the ammonia of cul- 
 tivated soil is habitually converted into nitrous acid before its 
 absorption by their rootlets. 
 
 (56.) Be this as it may, in all animal and vegetable nitro- 
 genised products of which the constitution is understood we 
 know, and in all other such principles have good reason to 
 believe, that the constituent nitrogen exists as a group apart as 
 a residue of, or proxy for, ammonia ready on the occurrence of 
 suitable conditions to regenerate that ammonia. As was observed 
 by Laurent some ten years ago, * nitrogen does not enter into the 
 constitution of organic substances on the same footing, so to 
 speak, as do the other bodies. Organic compounds seem to con- 
 sist of carbon, hydrogen, and oxygen only ; whilst nitrogen exists 
 therein but as the representative of ammonia on the one hand, or 
 of nitric acid on the other.' In organic compounds of natural 
 origin, nitrogen occurs only as a residue of ammonia ; whilst in 
 organic compounds of artificial origin, it occurs sometimes as a 
 residue of ammonia, as in cyanogen C 2 N 2 , sometimes as a residue 
 of nitric acid, as in azobenzide C 12 H 10 N 2 . 
 
 (57.) In the artificial formation of organic compounds, then, there 
 are two distinct points for our consideration, namely, the building 
 up of the primary oxihydrocarbon molecules, and the combination 
 of the residues of these molecules with one another, and with am- 
 monia, to form complex organic principles. Now, the power of 
 combining the residues of aplone molecules with one another, so 
 as to form more or less complex bodies, has been in the possession 
 of chemists from almost the earliest days of organic chemistry, 
 and has been fully recognised to be in their possession. But, 
 somewhat strangely, it is only of late years that this well-known 
 power has been applied to the construction of some of themost 
 familiar components of animal and vegetable bodies. It is only 
 of late years, for instance, that chemists have produced stearin, 
 by putting together the residues of glycerin and the fatty acid ; 
 or sarcosine, by putting together the residues of acetic acid and 
 methylamine ; or hippuric acid, by putting together the residues 
 of benzoic acid and glycocine ; or taurine, by putting together 
 
5 ANIMAL CHEMISTRY LECTURE III. 
 
 the residues of isethionic acid and ammonia, &c., as referred to in 
 my last lecture. It must be observed, however, that the neglect 
 of these syntheses did not arise so much from want of interest in 
 the production of the bodies, as from want of knowledge of their 
 intimate constitution. No sooner, for instance, was the constitu- 
 tion of the above four compounds satisfactorily made out than they 
 were obtained artificially by Berthelot, Volhard, Dessaignes, and 
 Strecker and Kolbe respectively ; and as it has been with these, 
 so doubtless will it be with many other complex tissue products, 
 with the constitution of which we are as yet imperfectly ac- 
 quainted. 
 
 (58.) The first stage of the process of organic synthesis, how- 
 ever, or the building up of the primary oxihydrocarbon mole- 
 cules, was considered until very recently as altogether beyond the 
 art of the chemist. It used to be thought that chemistry was 
 essentially incompetent to the production not only of organised, 
 but of organic bodies. For the production of these bodies, the 
 intervention of some living organism, the expenditure of some 
 vital force whatever that might be was considered absolutely 
 necessary. While the constituent atoms of a piece of alum, for 
 instance, were admittedly held together by mere mechanical and 
 chemical forces, the atoms of a piece of sugar, on the other hand, 
 or of a piece of fat, were conceived to be put together in some 
 ; mysterious way by vital forces. These opinions were originally 
 \ propounded by Berzelius at a time when the then state of know- 
 | ledge may possibly have justified their enunciation. They re- 
 [ mained almost unchallenged for a long series of years, and are 
 I still asserted in some recent text-books with a degree of dog- 
 matism altogether opposed to the present advanced state of know- 
 ledge* on the subject. 
 
 (59.) The great progress recently made in the constructive art 
 of the chemist is, I think, a topic of sufficient interest to war- 
 rant me in entering into further detail upon the heretofore 
 accepted opinions, which I find expressed very well in the last 
 edition but one of Liebig's Chemical Letters the last edition that 
 was translated by Dr. Gregory, who, writing in 1851, says: 
 
REPUTED ACTIONS OF VITAL FORCE. 57 
 
 ' We are able to construct a crystal of alum from its elements, 
 namely, sulphur, oxygen, hydrogen, potassium, and aluminum, 
 inasmuch as heat as well as chemical affinity are, within a certain 
 limit, at our free disposal, and thus we can determine the manner 
 of arrangement of the simple and compound elements. But we 
 cannot make an atom of sugar from the elements of sugar, be- 
 cause in their aggregation into the characteristic form of a sugar 
 atom, the vital force co-operates, which is not within the reach of 
 our control, as heat, light, the force of gravity, &c., are to a cer- 
 tain extent We may produce atoms of a higher 
 
 order by combining two, three, four, or more compound organic 
 atoms ; we can decompose the more complex into less complex 
 compound atoms ; we can produce sugar from wood or starch, 
 and from sugar we can produce oxalic acid, lactic acid, butyric 
 acid, acetic acid, aldehyd, alcohol, formic acid, &c., although we 
 are altogether incapable of producing any of these compounds by 
 a direct combination of their elements.' 
 
 (60.) I might further refer you to Dr. Gregory's deservedly- 
 popular Handbook, of which the last edition appeared in 1857, 
 and to many other works, as showing the general prevalence of 
 these opinions, but content myself with extracting the following 
 series of passages from the most recent of all our chemical 
 manuals. You will see that in this work, published only two 
 years ago, the statements made by Liebig in 1851, and by older 
 chemists long before then, are substantially reiterated. * Organic 
 chemistry,' say the authors, ' is that branch of the science which 
 refers to the properties and composition of organised products, or 
 of substances which have been formed in vegetables and animals 
 under the influence of life. . . , The products, or those sub- 
 stances which result from artificial processes, are far more nume- 
 rous than the educts, or proximate principles of which organic 
 compounds are considered to be formed. These educts, which, 
 as their name implies, may be extracted in an unaltered state, are 
 the immediate or proximate principles of the vegetable or animal 
 structure. . . . Some bodies which exist naturally in the 
 vegetable structure, and are regarded as educts, may be arti- 
 
5 ANIMAL CHEMISTRY LECTURE III. 
 
 ficially produced by a reaction of mineral on organic substances. 
 In all cases, however, either an organic substance or a body 
 derived from the organic kingdom is indispensable to this conver- 
 sion. . . . The principal sources of hydrocyanic acid are 
 certain metallic cyanides. But these compounds have an organic 
 origin ; they are the products of a reaction of organic upon inor- 
 ganic substances ; hence the production of hydrocyanic acid by 
 their decomposition furnishes no exception to the remark above 
 made. Under this point of view, the production of artificial 
 urea from hydrated cyanate of ammonia is simply a conversion 
 of cyanic acid (a derivative of an organic substance) into an- 
 other organic compound. By no processes yet known can gum, 
 starch, or sugar be produced from their elementary constituents 
 C, H, O ; and by the production of alcohol from a mixture of 
 sulphuric acid, olefiant gas, and water, Berthelot has merely 
 proved that a hydrocarbon of organic origin or one derived from 
 organic matter is capable of being converted into another organic 
 product.' Thus the view very generally entertained but a few 
 years back was substantially this that the chemist could not 
 produce organic out of mineral matter ; he might transform one 
 kind of organic matter into some allied kind of organic matter 
 starch into sugar, and olefiant gas into alcohol, for instance ; he 
 might produce certain simple organic principles by the breaking 
 up of more complex molecules oil of spiraea, for instance, from 
 salicin, alcohol from sugar, and glycerin from fat ; and he 
 might even produce highly complex principles, by a conjunction 
 of two or more simple principles oil of wintergreen by com- 
 bining salicic acid with wood spirit, and fat by combining stearic 
 acid, for instance, with glycerin ; but this was the limit of his 
 powers he might shuffle about the residues of existing organic 
 compounds in a variety of ways, but was utterly unable to 
 produce even the simplest of them by elemental synthesis. 
 
 (6 1.) Our present knowledge, however, assures that these 
 opinions are altogether without foundation. Already hundreds 
 of organic principles have been built up from their constituent 
 elements, and as I have previously said, there is now no reason 
 
SYNTHESIS OF ACETIC ACID. 59 
 
 to doubt our capability of producing all organic principles what- 
 soever in a similar manner. Wohler's artificial production of 
 urea from cyanate of ammonia in 1828, and Pelouze's artificial 
 production of formic from hydrocyanic acid in 1831, were in 
 reality very important pioneering achievements, although cyano- 
 gen and its compounds were at that time known only as products 
 of the decomposition of organic bodies. But in 1845, Kolbe 
 produced acetic acid from carbon by a series of strictly inor- 
 ganic reactions, and thereby laid the foundation of modern syn- 
 thetic chemistry. The successive steps of his process are shown 
 in the following table : 
 
 Acetic Acid Synthesis 
 C S, Carbon disulphide 
 
 C C1 4 Carbon tetrachloride 
 
 C a Cl 4 Tetrachlor-ethylene 
 
 C Z HC1 3 Z Trichlor-acetic acid 
 
 C a H 4 O a Acetic acid 
 
 Disulphide of carbon CS 2 , was first obtained by the combustion 
 of charcoal in sulphur vapour. This compound was next acted 
 upon by chlorine at a high temperature, whereby it was converted 
 into chloride of sulphur and chloride of carbon CC1 4 . Then by 
 transmission through red-hot tubes, this last product was trans- 
 formed, with evolution of chlorine, into the so-called sesqui- 
 chloride of carbon, 2CC] 4 =C1 2 + C 2 C16, and eventually into the 
 so-called bichloride of carbon or tetrachlor-ethylene, C 2 Cl6= 
 C1 2 -f C 2 C1 4 . In the course of his examination of this tetrachlor- 
 ethylene, Kolbe observed that by exposure to chlorine in presence 
 of water, it was decomposed into a mixture of hydrochloric and 
 trichlor-acetie acids, thus : 
 
 Chlor-ethylene Water Chlorine Chlorhydric Chlor-acetic 
 
 C Z C1 4 + 2H,0 + Cl a = 3HC1 + C Z HC1 3 0, 
 
 Then by subjecting this trichlor-acetie acid to the action of 
 nascent hydrogen, he successively converted it into dichlor-acetic 
 
60 ANIMAL CHEMISTRY LECTURE III. 
 
 acid C 2 H 2 C1 2 2 , monochlor-acetic acid C 2 H 3 C10 2 , and finally into 
 normal acetic acid C 2 H 4 O ?> . In concluding his account of these 
 singular transformations, Kolbe remarked with great prescience : 
 ' From the foregoing observations we deduce the interesting 
 fact that acetic acid, hitherto known only as a product of the 
 oxidation of organic materials, can be built up by almost direct 
 synthesis from its elements. . . . If we could but trans- 
 form acetic acid into alcohol, and out of the latter could obtain 
 sugar and starch, we should then be enabled to build up these 
 common vegetable principles, by the so-called artificial method, 
 from their most ultimate elements.' 
 
 (62.) Kelying upon these results, Laurent in his ' Methode de 
 Chimie,' 1853, and Hofmann in a course of lectures l On Organic 
 Chemistry,' delivered the same year at the Royal Institution, the 
 latter, with very great detail, showed how impossible it was to 
 draw the line of demarcation between carbon compounds of or- 
 ganic, and carbon compounds of mineral origin. They both 
 referred to Kolbe's formation from mineral elements of acetic 
 acid or vinegar, and of certain highly complex bodies procurable 
 from vinegar, such as mesidine C 9 Hj 3 N, and nitro-mesidine 
 C 9 H 12 N 2 O 2 . It must be admitted, however, that to .the labours 
 of Berthelot, prosecuted unintermittingly for the last ten years, 
 is due that full recognition of synthetic organic chemistry which 
 now obtains, and the very great advances recently made therein 
 both by himself and by others, which I purpose hereafter to 
 bring under your more especial consideration. 
 
 Before proceeding, however, to exemplify the powers of organic 
 synthesis in the artificial formation of animal and vegetable pro- 
 ducts from carbon, hydrogen, and oxygen, I must beg leave to 
 make a rather long digression. I propose, firstly, to bring before 
 you some elementary experiments connected with the production 
 and decomposition of the oxides of carbon and hydrogen, or car- 
 bonic anhydride CO 2 , and water H 2 O, respectively ; and then to 
 consider with you what bearing these experiments have upon the 
 forces exerted in animal and vegetable life, or, in other words, 
 upon the so-called vital forces. 
 
OXIDATION OF HYDROGEN AND CARBON. 6 1 
 
 (63.) I have here an ordinary form of apparatus in which 
 hydrogen gas is being generated in the usual manner from zinc 
 and dilute sulphuric acid, and dried by transmission through oil 
 of vitriol. On burning the jet of dried hydrogen under this cold 
 bell jar, we observe that the interior of the jar becomes quickly 
 covered with a film of condensed steam or water, produced by 
 the direct combination of the hydrogen gas with the oxygen of 
 the air ; and, by properly contrived experiments, I might show 
 that the weight of water produced in this way is exactly equal 
 to the weight of oxygen and hydrogen' consumed in the burning. 
 But during the combustion of the gases there is a production not 
 only of water, but of heat ; which I may exhibit to you in a 
 more striking manner. We have here a piece of clean platinum 
 foil, which is now maintained in a state of ignition by the hydro- 
 gen flame. I turn off the supply of hydrogen for a minute or so, 
 and before the platinum has become quite cold, turn it on again, 
 when you observe that the metal becomes and continues feebly 
 red-hot without inflaming the gas. The mixed hydrogen and 
 air on the surface of the foil combine with one another to form 
 water, and at the same time produce an amount of heat sufficient 
 to maintain the metal in a state of visible ignition. But where 
 does this heat come from ? We have a production of heat and a 
 production of water; ought we not to account for the one as 
 intelligibly as we do for the other ? 
 
 (64.) I now take a piece of charcoal, and make it red-hot in 
 the Bunsen gas flame. Having first poured a little lime-water 
 into the bottle of oxygen, to show the result of the action, I 
 next introduce the glowing charcoal, when combination between 
 the gas and charcoal takes place, you perceive, with vivid com- 
 bustion. In this experiment, then, we have carbonic anhydride 
 or di-oxide of carbon formed, the source of which is perfectly 
 evident ; and upon shaking up the resulting gas with the clear 
 lime-water we previously poured into the bottle, that which was 
 soluble hydrate of calcium becomes insoluble carbonate of cal- 
 cium or chalk, whereby we have as you see, a considerable 
 white turbidity produced, thus : 
 
62 ANIMAL CHEMISTRY LECTURE III. 
 
 Carb-anhyd. Lime . Water Chalk 
 
 ro , H a Ca"O a or w n ( CCa"0 3 or 
 
 iCaO.H 2 
 
 If instead of absorbing it by lime-water in this manner, we were 
 directly or indirectly to weigh the resulting carb-anhydride, we 
 should find that its weight was exactly equal to that of the carbon 
 burnt, plus that of the oxygen which served to burn it. But, in 
 addition to carbonic anhydride, there was during the combination 
 an abundant production of light and heat. Now the axiom, that 
 out of nothing comes nothing, is just as true of light and heat 
 as of water and carbonic anhydride. We have no difficulty in 
 understanding the production of the carbonic anhydride ; what, 
 however, is the origin of the light and heat ? 
 
 (65.) So much, then, for the formation of oxide of hydrogen 
 or water, and oxide of carbon or carbonic anhydride ; now for 
 their decompositions. By a variety of means we are able to 
 separate hydrogen and carbon from their respective combinations 
 with oxygen one of the most suitable materials for the pur- 
 pose being metallic sodium. If, for instance, we introduce under 
 this inverted jar of water a piece of metallic sodium, which, for 
 the sake of convenience, I have diluted with a little mercury, so 
 that the reaction may take place more slowly than it otherwise 
 would, we get, you perceive, a regular evolution of hydrogen 
 gas. The sodium combines with the oxygen of the water, whilst 
 its hydrogen is set at liberty ; and in a similar manner we may 
 liberate carbon from carbonic anhydride, as I will now endeavour 
 to show you. The carbonic anhydride that we produced by the 
 combustion of a piece of charcoal in oxygen was absorbed, you 
 will remember, by means of lime, whereby we obtained this pre- 
 cipitate of chalk, from which by treatment with hydrochloric acid 
 we may easily re-obtain the carbonic anhydride. Thus, if I transfer 
 our mixture of chalk and water into the narrow cylinder standing 
 over this mercurial trough, and then pass up a little hydrochloric 
 acid, you see that the chalk disappears with effervescence, while a 
 quantity of gas collects at the top of the cylinder, which is the 
 
DEOXIDATION OF CARE-ANHYDRIDE. 63 
 
 carbonic anhydride we lately produced in this large gas-bottle 
 by the direct combination of charcoal and oxygen : 
 
 Chalk Chlorhydric Chlor-calcium Water Carb-anhyd. 
 
 CaO.CO, + zHCl = CaCl, + H a O + C0 3 
 
 In the arrangement on the table before you, we are producing 
 a current of carbonic anhydride in a similar manner, by acting 
 upon chalk or, rather, marble, with dilute hydrochloric acid. 
 The gas evolved in the Woulfe's bottle is transmitted over pumice 
 and oil of vitriol to render it dry, and then conveyed to the 
 bottom of an ordinary Florence flask, into which I have dropped 
 a piece of clean metallic sodium. We now apply a large blow- 
 pipe flame to the bottom of the flask so as to heat the contained 
 sodium. There is a little practical difficulty in starting the reac- 
 tion, and perhaps the experiment may not succeed at the first 
 trial, but it is sure to succeed sooner or later. The action is now 
 beginning, and you observe the piece of sodium glowing in the 
 flask. The glowing is soon succeeded by a brilliant combustion, 
 attended by the formation of copious white fumes. The sodium 
 has effected a decomposition of some of the carbonic anhydride, 
 united with its oxygen to form soda, and liberated its carbon in 
 the form of a black mass, which remains, as you see, at the 
 bottom of the flask. 
 
 (66.) The piece of charcoal in this flask then has been ex- 
 tracted from carbonic anhydride, which is itself producible, as I 
 have shown you, by the direct combustion of charcoal in air or 
 oxygen. So that when we act upon oxide of hydrogen with 
 sodium, we separate the oxygen and obtain the hydrogen ; and 
 when we act upon oxide of carbon with sodium we separate the 
 oxygen and obtain the carbon. Now the living plant effects a 
 similar decomposition of these two compounds, but in a gradual 
 manner, which we shall hereafter endeavour to imitate. The 
 plant absorbs oxide of hydrogen or water, and oxide of carbon or 
 carbonic anhydride ; deoxidises both compounds to a more or less 
 complete extent ; evolves the separated oxygen into the atmo- 
 sphere ; and retains the united carbon and hydrogen, with or 
 
64 ANIMAL CHEMISTRY LECTURE III. 
 
 without some oxygen, in the form of vegetable tissue or secretion. 
 When the tissue or secretion is subjected to a full red heat, it 
 yields, among other products, free carbon, free hydrogen, and 
 various compounds of carbon with hydrogen. The piece of 
 wood-charcoal now in my hand, for instance, has resulted indi- 
 rectly from a gradual deoxidation of carbonic anhydride by the 
 living plant, just as this other piece of charcoal in the flask has 
 resulted directly from a violent deoxidation of carbonic anhydride 
 by the metallic sodium. 
 
 (67.) Thus, then, we have presented to our notice the most 
 important terrene, or rather cosmical function of plant life. The 
 living plant effects a decomposition of carbonic anhydride and 
 water, evolves the liberated oxygen, and retains within its organ- 
 ism the united carbon and hydrogen, which becoming the food of 
 animals, are simultaneously disunited and re-oxidised once more 
 into carbonic anhydride and water. Now, I wish to consider 
 with you I was going to say more minutely, but I should rather 
 say more broadly what is the essence of these complementary 
 actions in their relation to the first principles of that dynamical 
 philosophy which is often spoken of as the science of energetics. 
 It formed part of my original plan to give merely a passing glance 
 at this subject, and I certainly should not have ventured to dis- 
 cuss it in the elementary form in which I now propose to bring it 
 under your notice, had it not recently come to my knowledge 
 that certain principles of mechanical philosophy admitted by that 
 class of naturalists who are called physicists, to be as fundamental 
 even as the laws of gravitation, are not generally acknowledged 
 by that other class of naturalists who are called physicians. Now, 
 in order to contrast with one another the great antagonistic func- 
 tion of plants and animals the decomposition of carbonic anhy- 
 dride and water by the one class, and recomposition of carbonic 
 anhydride and water by the other it would not conduce to my 
 object, even if it were within my competency, to discuss with 
 you the simplest functions of organic life, as manifested by the 
 most minute and simple organisms, in some of which it is scarcely 
 possible for us to distinguish between the animal or vegetable 
 
CORRELATIVE VEGETABLE AND ANIMAL PROCESSES. 65 
 
 character. Feeling that every phase of life deserves our attentive 
 examination, I am far from insensible to the advantages attending 
 the study of its most elementary forms. But this study cannot, 
 I maintain, teach us the whole truth. There are principles ol 
 the highest importance which can only be learned by having 
 regard to the directions in which animal and vegetable life re- 
 spectively tend by comparing with another the highly differen- 
 tiated forms of animal and vegetable life, not in their minute 
 details, but in their broad general features. In my next lecture, 
 then, we shall have to consider more especially what is the nature 
 of the force exerted in the characteristic actions of vegetable and 
 animal life whether we have to do with some peculiar internal 
 vital force, or only with the ordinary external forces of nature, 
 working in a manner strictly parallel to that in which they are 
 habitually exerted in the inorganic world. 
 
66 ANIMAL CHEMISTRY LECTURE IT. 
 
 LECTURE IV. 
 
 % 
 
 External relations of vegetable and animal processes Nature of cosmical 
 forces Mutual convertibility of heat and motion Their quantitative 
 equivalency with one another Illustrations of motion resulting from 
 muscular effort Force rendered latent in mechanical separation of 
 attracting bodies Actual and potential energy Chemical separation 
 of attracting bodies Theory of electrolysis Force of galvanic battery 
 derived from combustion of zinc Heat of dissolving zinc manifested 
 externally in ignition of platinum wire The same heat stored up in 
 electrolytic oxygen and hydrogen Its reproduction by explosion of 
 mixed gases Solar heat rendered latent in separated oxygen and 
 vegetable tissue Its liberation by combustion of vegetable tissue in 
 air All terrestrial force traceable to ( the sun Accumulation of solar 
 force by vegetable organisms Its dissipation by animal organisms 
 Reverse subsidiary actions Baseless hypothesis of vital force Artifi- 
 cial performance of alleged vital syntheses Stages of constructive 
 vegetal and destructive animal action Occurrence of same intermediate 
 products in both kingdoms General processes of synthetic chemistry 
 Passage from one organic group to next in complexity Continuous 
 series of synthetic operations Production of urea, formic acid, prussic 
 acid, trimethylamine, and chloroform from mineral elements Syn- 
 thesis of di-carbon compounds, including alcohol, taurine, acetic acid, 
 glycocine, and oxalic acid Of tri-, tetra-, and penta-compounds, in- 
 cluding glycerine, the lactic, butyric, succinic, malic, tartaric, and 
 valeric acids, and fousel oil Of hexa-compounds, including caproic 
 acid, leucine, and grape sugar? Of hepta-compounds, including oil 
 of bitter almonds, and the benzoic, salicic, and gallic acids Possible 
 artificial manufacture of food. 
 
 (68.) AT the conclusion of my last lecture I was insisting upon 
 the importance of viewing the phenomena of animal and vege- 
 table life in relation to the external forces of the universe. I 
 observed that, however valuable might be the study of the more 
 minute and elementary forms of life, and I was far from wishing 
 
EXTERNAL ORIGIN OF FORCE. 67 
 
 to decry its value in any way, there were, on the other hand 
 some great truths which could only be appreciated by comparing 
 the most highly specialised forms of life with one another, not 
 in their minute details, but in their broad general features. I 
 also observed, that while the chief eosmical function of highly- 
 developed vegetable life was deoxidation, or the separation of 
 oxygen from carbon and hydrogen, the leading function of highly 
 developed animal life was oxidation the recombination of the 
 separated oxygen and carbo-hydrogen with one another ; and 
 we agreed to consider upon this occasion the essential nature of 
 these two correlative processes. I said, further, that I was in- 
 duced to bring this subject under your notice in a more ele- 
 mentary and detailed manner than I originally contemplated, 
 from finding that certain principles believed by physicists to be 
 as fundamental as the laws of gravitation were not heartily and 
 unreservedly admitted by physicians. 
 
 (69.) First of all, then, we have to inquire into the character 
 and import of that deoxidation of carbonic anhydride and water, 
 which takes place in vegetable organisms, and the origin of the 
 forces by which it is brought about. Now, in entering upon the 
 discussion of this question, I must direct your attention for a 
 short time to topics which at first sight seem but very remotely 
 connected either with chemistry or physiology. To paraphrase 
 in sober earnest the expressions used in sarcasm by a very dis- 
 tinguished Fellow of this College, the value of whose contribu- 
 tions to physiological science no one can be more ready than 
 myself to acknowledge, I shall preface my remarks by a few ob- 
 servations upon force and the constancy of its amount in the 
 universe. Then, by a reference to systems and suns, and worlds, 
 and steam-engines, and mills, and telegraphs, I shall endeavour 
 to satisfy you that the same forces are at work in living plants 
 and animals as in the inorganic world ; and that the study of the 
 indestructibility and correlation of force will teach us much, 
 though far indeed from all, concerning the nature of life. 
 
 (70.) Let us begin, then, by considering the correlation that 
 exists between the forces of heat and motion their equivalency 
 
 p2 
 
68 ANIMAL CHEMISTRY LECTURE IV. 
 
 with, and convertibility into, one another of which no better 
 illustration perhaps can be chosen than a steam-engine ; and the 
 philosophical toy upon the table, known as Hero's celipile, will 
 answer our purpose perfectly well. On lighting a fire under the 
 boiler of a steam-engine, some of the heat liberated in the 
 furnace gradually passes into the water ; and as each successive 
 increment of heat is absorbed from the furnace, the temperature 
 of the water rises until it arrives at a certain point. During the 
 time the water takes in rising from its original temperature up to 
 the boiling point, heat is being conveyed into it, at what may be 
 regarded as an uniform rate. When, however, a certain degree 
 of heat is reached, the temperature of the water no longer rises, 
 although the heat of the furnace continues passing into it at the 
 same rate as before ; but now some of the heat absorbed, instead 
 of being manifested in the form of heat, appears in the form of 
 motion, and the steam-engine begins to work. Just as in the 
 oelipile before you, the heat of the spirit -flame was passing into 
 the water for several minutes with no other effect than that 
 of raising its temperature; whereas^ after the lapse of several 
 minutes, the heat of the flame still passing into the water ceased 
 to increase its temperature in the slightest degree, but caused 
 instead a rapid rotatory motion of the instrument. Thus, we 
 perceive generally that the development of motion is consequent 
 upon an absorption of heat, and conversely, we shall find that an 
 arrest of motion is tantamount to the liberation of heat. For 
 example, if we employ our steam power in drilling a piece of 
 metal, the motion of the engine is lessened by the friction of the 
 drill, and a certain amount of heat is thereby generated. The 
 original heat of the furnace, absorbed by the boiling water with- 
 out any increase of its temperature, produces a less amount of 
 motion than formerly, but the diminution of motion is supple- 
 mented by a remote increase of heat less of the heat which 
 passes into the water being now manifested in the form of mo- 
 tion, but the difference reappearing at a distance in its primi- 
 tive form of heat. 
 
 (7 1 .) Similarly when a bullet strikes upon an iron target, its 
 
CORRELATION OF HEAT AND MOTION. 69 
 
 motion is suddenly arrested, and its temperature as suddenly 
 raised. That which was motion has become heat, and the quan- 
 tity of heat shared between the bullet and the target is exactly 
 proportional to the previous velocity of the bullet, or to the 
 quantity of its motion that has been arrested. Again, in exact 
 proportion to the diminution of motion in the working parts of the 
 steam-engine, so is the amount of heat developed by the friction 
 of the drill upon the piece of metal. For not only are heat and 
 motion convertible into one another in a general way, but they 
 are convertible in a manner which admits of accurate measure- 
 ment. By suitably contrived experiments it may be shown, in 
 every instance, that so much heat developed is equivalent to so 
 much motion arrested, and conversely that so much motion 
 generated is equivalent to so much heat absorbed. It has been 
 ascertained for instance, more particularly by Mr. Joule, that the 
 force of a pound weight falling through 772 feet is exactly equal 
 to the amount of heat which a pound of water will give out in 
 cooling one degree Fahrenheit ; or, in other words, that the heat 
 developed by the arrest of the motion of a pound weight falling 
 through 772 feet would raise the temperature of a pound of 
 water one degree, and that the heat given out by the cooling of a 
 pound of water one degree would lift a pound weight to the height 
 of 772 feet. Heat and motion, therefore, are in every case inter- 
 changeable for one another according to a definite standard of 
 equivalency. > * -" 
 
 (72.) Now, let me direct your attention to some simple illus- 
 trations of motion ; and, first of all, to the direct motion of a 
 projectile hurled from the arm of a man. Upon seeing the rapid 
 flight of a dart or javelin through the air, we recognise imme- 
 diately that the motion of the javelin did not originate in itself, 
 but was impressed upon it by some external force. We never 
 think of attributing its motion to the exercise of any peculiar 
 javelin force, but to the action of the muscular force by which it 
 was originally projected. We know that the momentum of the 
 javelin is exactly proportionate to the amount of force exerted in 
 hurling it, and that when it strikes some distant object, the blow 
 
70 ANIMA.L CHEMISTRY LECTURE IT. 
 
 which that object receives is as surely struck by the man as if he 
 had delivered it directly with his fist. Let us now take an illus- 
 tration in which motion is transmitted through the intervention 
 of some simple instrument, as in the case of a bow and arrow, 
 for example. Here, also, the motion of the arrow through the 
 air does not take place in virtue of any force originating in the 
 bow, but is consequent on the muscular force exerted in drawing 
 the bow and cord asunder ; and, limited only by the suscep- 
 tibility of the bow, the momentum of the arrow depends en- 
 tirely upon the amount of force exerted by the archer in 
 pulling the bow-string. 
 
 (73.) Again, in discharging a cross-bow, the cord is first 
 drawn over the catch by a muscular effort, and the arrow after- 
 wards projected by the release of the cord. Now, although the 
 susceptibility of this kind of bow is far more limited than that of 
 a long bow, still it is evident that the force with which the arrow 
 is eventually projected does not originate in the bow, but is only 
 a transformation of the muscular force exerted in separating the 
 bow and cord from one another. Moreover, if instead of pulling 
 the trigger of the cross-bow immediately after the cord is 
 drawn over the catch, we allow the bow to remain in its bent 
 state for weeks, or months, or years, and then release the cord ; 
 still the force with which the arrow is at last projected will 
 be the original muscular force exerted at the moment of 
 pulling the bow and cord asunder. Suppose, for instance, that I 
 were to draw the cord of a cross-bow over the catch to-day, and 
 a century hence some one were to release it by touching the 
 * trigger, still the force of the projected arrow would not be his 
 force, but my force, exerted by me to-day, lodged in the bow for a 
 hundred years, then manifested in the motion of the arrow, and 
 finally transformed into heat upon the cessation of its flight. 
 
 (74.) Similarly, the force with which a cannon-ball falling from 
 the top of the Monument would strike the pavement beneath, would 
 be the exact expression of the force exerted in lifting it to the 
 top that is to say, in separating the cannon-ball and the pave- 
 ment a certain distance from each other, no matter how many 
 
ACTUAL AND POTENTIAL AGENCY. 71 
 
 years before. We may thus render muscular force latent in a 
 stretched bowstring, raised cannon-ball, or other instrument, for 
 any length of time. This latent force is generally spoken of as 
 potential energy, while the active force exertable at any moment 
 by the flying arrow or falling ball constitutes its actual or dynamic 
 energy. Thus the actual energy of my arm becomes the potential 
 energy of the crossbow, reappears as the actual energy of the 
 projectile, and is finally not lost, but dissipated in the form of 
 heat. The point, then, I wish particularly to impress upon you 
 is, that the actual mechanical energy manifested in the falling 
 together, or springing together, of two separated bodies, the ball 
 and the earth, the cord and the bow, is only a liberation of the 
 potential energy stored up in them at the moment they were 
 pulled apart from one another. 
 
 (75.) Let us now turn our attention to an altogether different 
 kind of pulling apart, namely, the pulling apart of oxygen and 
 hydrogen from their state of chemical combination. I am here 
 repeating the well-known experiment of the electrolytic decom- 
 position of water. By means of a galvanic battery I am tearing 
 asunder the previously combined oxygen and hydrogen, and col- 
 lecting the two gases in separate cylinders. Now, what is the 
 nature of this separation, and how is it brought about ? Seizing 
 one link in the chain of actions as a starting-point, let us consider 
 first of all the combustion of zinc in the battery-cell ; for in all 
 ordinary batteries the direct or indirect oxidation of zinc is the 
 source of the power obtained. Upon holding this bundle of 
 loose zinc shavings in the blowpipe flame, you see that the 
 metal takes fire from time to time and burns with very great 
 brilliancy, being converted into the white flocculi of oxide of 
 zinc which are now floating about the room. If we introduce 
 the ignited zinc into a vessel of chlorine, it continues to burn, 
 you observe, with even greater intensity than before, producing 
 abundant fumes of chloride of zinc. But we may obtain chloride 
 of zinc more readily by dissolving the metal in hydrochloric 
 acid; and in this case, also, the combination of zinc with chlorine 
 is attended by an evolution of heat. Thus, the solution of 
 
72 ANIMAL CHEMISTRY LECTURE IV. 
 
 granulated zinc in hydrochloric acid, now taking place in this 
 gas-generating flask, is being accompanied by a considerable 
 elevation of temperature in the liquid, as well as by an evolution 
 of hydrogen, according to the equation 
 
 Zinc Hydrochloric Zinc chloride Hydrogen 
 
 Zn" + 2HC1 = Zn"Cl z + H a . 
 
 (76.) Now, equivalent for equivalent, the quantity of heat 
 liberated by the combination of zinc with oxygen or chlorine is 
 much greater than that evolved by the similar combination of 
 hydrogen ; and accordingly, when we burn zinc at the expense 
 of hydrogen, as in this experiment, we obtain in the flask just so 
 much of the heat produced by the burning of the zinc as is in 
 excess of the heat absorbed in the unburning, so to speak, of the 
 hydrogen.* Hence, leaving out of consideration certain sub- 
 sidiary phenomena, the heat produced by the solution of a given 
 quantity of zinc in hydrochloric acid, and the heat producible by 
 burning the thereby liberated hydrogen in an atmosphere of 
 chlorine, added together, would exactly equal the amount of heat 
 producible by burning the same quantity of zinc directly in 
 chlorine gas, as we did a minute or two ago. Thus, by the 
 solution of zinc in hydrochloric or sulphuric acid, we have a 
 certain proportion of the combination-heat of the metal set free. 
 The intensity of this heat is not great, in, consequence of its 
 being associated with so large a mass of matter in the flask, but 
 
 * Vide Professor Williamson's lecture On the Dynamics of the Galvanic 
 Battery.' Phil. Mag. xxvi. 452. Taking as our unit of heat the quantity 
 of heat necessary to raise the temperature of a kilogramme of water i C. 
 that is to say, from o C. to i C. it is found that 65 grammes of zinc 
 Zn", in combining with twice 35-5 grammes of chlorine Cl a , to form 136 
 grammes of chloride of zinc Zn"Cl 2 , evolve 101-31 units of heat; whereas 
 2 grammes of hydrogen H z , in combining with twice 35-5 grammes of 
 chlorine Cl ? , to form 73 grammes of hydrochloric acid 2HC1, evolve only 
 47-56 units of heat. Hence in decomposing 73 grammes of hydrochloric 
 acid by 65 grammes of zinc, according to the equation Zn" + 2HCl = Zn"Cl 2 
 + H a , we should have 101-31 47-56 = 53-75 units of heat liberated as 
 initial battery power. 
 
DERIVATION OF GALVANIC FORCE, 73 
 
 its quantity is very considerable, and constitutes, indeed, the 
 entire dynamic energy we have at our disposal in the galvanic 
 battery. 
 
 (77.) When the zinc and platinum plates of the battery 
 communicate freely with each other, the combination-heat of the 
 attacked zinc is manifested solely by a rise of temperature in the 
 contents of the cell, precisely as in. the case we have just consi- 
 dered of the simple solution of granulated zinc in hydrochloric 
 acid. But the battery is a machine for enabling us to apply and 
 transform this combination-heat of the zinc in a variety of ways. 
 For instance, if I complete the communication between the zinc 
 and platinum plates by means of a platinum wire, you observe 
 that the small coil of wire assumes an intense state of ignition. 
 Now, the heat of this platinum wire is nothing more than a por- 
 tion of the translated heat of the zinc burning in the cell ; which, 
 instead of being manifested at the point of action in the cell, is 
 manifested at a distance in the wire ; much as a portion of the 
 furnace heat absorbed in the evaporation of water may be mani- 
 fested at a distance by the friction of a drill. The heat exhibited 
 by the platinum wire does not originate in the wire, but in the cell, 
 and so much of the heat of the burning zinc as appears in the 
 wire is lost to the cell. Just as the contracting muscle strikes 
 its blow at a distance of many yards by means of the conducting 
 javelin, so does the burning zinc strike its blow at the spot whereto 
 it is conducted by the copper strands. 
 
 (78.) In electro-motive machines, the heat of the burning 
 zinc is employed in doing mechanical work, just as the heat of 
 burning coal is employed, though with far greater economy, in a 
 steam-engine. But in the decomposition of water taking place 
 upon the table, the heat of the burning zinc is employed in the 
 chemical work of pulling oxygen and hydrogen apart from one 
 another. Of the heat producible by the combustion of a given 
 weight of zinc, the proportion manifested externally in the 
 ignition of platinum wire, or employed externally in the separa- 
 tion of oxygen and hydrogen, is supplemental to the quantity 
 absorbed in heating the cell ; so that in the electrolysis of water, 
 
74 ANIMAL CHEMISTRY LECTURE IV. 
 
 as in the heating of platinum wire, so much the more external 
 work done, so much the less internal heat developed. By the 
 electrolytic decomposition of water, the heat of the burning zinc, 
 which does not appear internally in the cell, and which might be 
 manifested externally in the ignition of platinum wire, lies dor- 
 mant in the separated oxygen and hydrogen ; but it is not lost. 
 On the contrary, I can render it evident to you with the greatest 
 ease. Now that we have collected a sufficient quantity of our 
 electrolytic gases, I have only to mix them together and explode 
 them, when you observe a considerable evolution of light and 
 heat resulting from their combination ; which light and heat are 
 nothing more than the light and heat of the burning zinc, not 
 manifested in the cell, but retained for a time in the separated 
 gases, so as to constitute their potential energy. The explosion 
 of the gases at once or a hundred years hence would make no 
 difference. The heat and light resulting from their eventual 
 explosion would still be the heat and light of the burning zinc 
 stored up in them, so to speak, at the moment of their electro- 
 lysis. In my last lecture I showed you the formation of water 
 by the combustion of hydrogen in the oxygen of the air, and 
 called your attention specially to the heat developed by the com- 
 bination. The heat so developed did not originate in the oxygen 
 and hydrogen, but was simply a liberation of the heat force, 
 which, directly or indirectly, at some time or other, had been 
 employed in pulling them apart, and been rendered latent in 
 them so long as they continued apart just as the force of a 
 stretched cross-bow does not originate in the bow, but is merely 
 latent muscular force stored up in the separated bow and cord. 
 Similarly in the brilliant combustion of carbon in oxygen gas to 
 form carbonic anhydride, there was no generation of heat, but 
 only a liberation of the heat previously stored up in the two 
 separated elements. 
 
 (79.) At length, then, we are in a position to understand the 
 nature of the action taking place in the vegetable kingdom, by 
 which carbonic anhydride and water are decomposed to con- 
 sider what is the external force employed in the pulling apart of 
 
ABSOKPTION OF SOLAR ENERGY BY PLANTS. 75 
 
 oxygen from hydrogen and carbon, and what becomes of it. 
 This force is no other than the light and heat force emanating 
 from the sun, rendered latent in the oxygen on the one hand, and 
 the carbo -hydrogen of vegetable tissue or secretion on the other, 
 and reproducible by the act of their recombination or combus- 
 tion. The sun's rays, for instance, falling upon the leaves of 
 the sugar-beet or sugar-cane effect an eventual decomposition of 
 carbonic acid into oxygen and sugar, thus : 
 
 Garb-anhydride Water Sugar Oxygen " 
 
 But the heat and light of the sun absorbed in this pulling apart 
 of oxygen and carbon, the one discharged into the atmosphere, 
 the other retained in the vegetable juices, are not lost, but ren- 
 dered latent in the oxygen and sugar respectively. Here I have 
 a mixture of sugar with a compound in which the oxygen of the 
 air has been accumulated, namely, chlorate of potassium, and on 
 touching the mixture with a drop of sulphuric acid on pulling 
 the trigger of the cross-bow, so to speak there is produced a 
 violent deflagration, in which the light and heat of the sun, 
 stored up in the separated sugar and oxygerT, are again manifested 
 to you by the combination of the two bodies with one another to 
 reproduce carbonic acid. The light and heat of this combus- 
 tion, and, indeed, of every combustion, are nothing more than the 
 light and heat of the sun, originally absorbed by the living plant, 
 and rendered latent in the tissue of the plant, and oxygen 
 of the air respectively. Even the heat evolved by the direct or 
 indirect combustion of zinc is no exception ; it is only the heat 
 stored up in the metal at the moment of its deoxidation by 
 means of the coal or charcoal in which the sun's force was in- 
 termediately retained. 
 
 (80.) We see, then, in this way, that the vegetable organism is 
 a machine in which the sun's energy is absorbed in the pulling 
 apart of carbon and hydrogen from oxygen. The light and heat 
 force emanating from the sun is rendered latent in the separated 
 oxygen and carbo-hydrogen, just as human muscular force is 
 
j6 ANIMAL CHEMISTRY LECTURE IV. 
 
 rendered latent in the stretched cross-bow. "When the separated 
 carbo-hydrogen, in the form of some vegetable product, is recom- 
 bined with the evolved oxygen, as in burning coal and wood 
 upon the fire, or in consuming bread and oil and wine in the 
 animal frame, the heat liberated in both instances is nothing 
 more than the heat of the sun which had been stored up in the 
 carbo-hydrate and oxygen respectively. Conversely, the animal 
 frame is a machine in which the sun's energy is set free by the 
 recombination of that oxygen and carbo-hydrate, in the pulling 
 apart of which it had been absorbed or rendered latent. The 
 plant may be regarded as a miser, or hoarder up ; the animal, on 
 the other hand, as a spendthrift, or dissipator, of the sun's force ; but 
 just as the miser is not a producer, or the spendthrift a destroyer 
 of gold, so neither is the vegetable a producer, nor the animal a 
 destroyer of force. All modern philosophy combines to prove 
 that force, like matter, is indestructible. It may be accumulated, 
 but not created ; be dissipated, but not destroyed. The force of 
 every kind, active or latent, existing in the earth, at any given 
 moment, is only the sum of the force received by the earth 
 
 from the sun in excess of the force radiated back from the earth 
 
 
 into space. 
 
 (8 1.) Hitherto, in contrasting the functions of animal and 
 vegetable life with one another, I have had regard to their broad 
 general features, looking at each description of life as a whole. 
 A more detailed examination, however, shows us that oxidising 
 and deoxidising processes are common to both kingdoms of 
 nature. For instance, the germination of seeds and maturation of 
 fruits are strictly oxidising, while the conversions of starch and 
 sugar into fat in the animal organism, are strictly deoxidising 
 or vegetative acts. It would seem, indeed, that in all purely 
 nutritive processes, whether of vegetable or animal life, there is an 
 absorption or rendering latent of force, and consequent necessity 
 for its extraneous supply. In highly-developed vegetable life this 
 force is derived directly from the sun. In highly-developed 
 animal life it is obtained by a liberation, within the body, of the 
 sun's force which had been rendered latent in the food we eat 
 
LIBERATION OF SOLAR ENERGY BY ANIMALS. JJ 
 
 and air we breathe respectively. But whilst nutritjpn, or the 
 storing up of force, constitutes the chief action of vegetable life, 
 in animal life it occupies an altogether subordinate position. 
 For the prime characteristic of animality is activity, the employ- 
 ment of pent-up force in the production of external acts. 
 Hence, while in the vegetable and animal organism, deoxidising 
 and oxidising processes, constructive and destructive actions 
 alike take place, in the vegetable the destructive are subordinate 
 to the constructive, whilst in animals the constructive are subor- 
 dinate to the destructive acts. * The contraction, for instance, of 
 a man's muscle depends entirely upon the oxidation or destruc- 
 tion of the substance of that muscle, and the equivalent of motion 
 produced upon the amount of muscle destroyed. 
 
 (82.) Thus we perceive that all actions of the animal body are 
 traceable to cosmical force ; that in living as in dead matter there 
 is no creation of force ; and that any explanation of the pheno- 
 nojnena of life which recognises the agency of vital force is 
 simply no explanation at all. Applying the word force as we 
 now do to certain transferable states of actual or potential ac- 
 tivity having quantitative metamorphic correlations, I much 
 question whether the expression chemical force is a correct one, 
 though it is one of which the meaning is perfectly definite and 
 intelligible. By the chemical force of so much oxygen and 
 hydrogen, for instance, we mean the potential energy stored up 
 in them at the moment of their separation, and reproducible 
 from them in the act of their combination. Similarly, we might 
 apply the phrase vital force to the potential energy of so much 
 fat .or muscle, capable by oxidation of being manifested in the 
 form of external heat or motion. But what the physiologist 
 means by vital force I have never been able to understand. So 
 far as I can make out, it seems to be a sort of internal, intrans- 
 ferable, immeasurable, self-originating power, which performs 
 nutritive acts by its absolute will and pleasure ; as if it were not 
 abundantly manifest that the growth of a plant and incubation of 
 an egg cannot be performed without a direct supply, and the 
 development of animal organisms without an indirect supply of 
 
78 ANIMAL CHEMISTRY LECTURE IV. 
 
 external 4> rce ' Speaking of the progress of natural science, 
 Mr. Mill has very pertinently observed that for a long time 
 ' fictitious entities continued to be imagined as means of account- 
 ing for the more mysterious phenomena; above all, in phy- 
 siology f where under great varieties of phrase, mysterious forces 
 and principles were the explanation, or substitute for explanation, 
 of the phenomena of organised beings.' 
 
 (83.) Seeing, then, that the enormous number and variety of 
 animal and vegetable compounds are produced out of carbonic 
 acid, water, and ammonia, not by any peculiar vital force, but 
 merely by the light and heat force of the sun acting through 
 organic machinery, the question naturally arises whether the 
 chemist may not effect in his laboratory-machinery a similar 
 intercombination of deoxidised carbonic acid and water, either by 
 a direct application of sun-force, or, indirectly, by the aid of 
 those terrestrial transformations of sun-force which are so abun- 
 dantly at his disposal. This question, decided absolutely* in 
 the negative BO long as the fiction of vital force tyrannised 
 over men's minds, has of late years received a rapid suc- 
 cession of brilliant affirmative replies. Already hundreds of 
 vegetable compounds heretofore produced only in living or- 
 ganisms, and, as was supposed, put together and held together 
 by vital force, have been formed by the chemist in his laboratory 
 out of carbonic acid, water, and ammonia, or, in other words, 
 out of charcoal, hydrogen, oxygen, and nitrogen. That a still 
 greater number of compounds have not been so formed is due 
 more to a deficiency of knowledge than of power ; for as our 
 acquaintance with the constitution of bodies, and with synthetic 
 processes, is daily advancing, so is the unlimited constructive 
 power of chemical art becoming daily more and more apparent. 
 
 (84.) Before proceeding, however, to exemplify this power of 
 forming organic compounds artificially, I will first make one or 
 two further remarks upon the order of their natural production. 
 At present we are unable to trace the series of changes, undergone 
 by carbonic acid and water, which result in the formation of tar- 
 taric acid, or sugar, or fat, or other complex vegetable product. 
 
FOHMATION OF VEGETABLE PRODUCTS. 79 
 
 It seems probable, however, that the process by which such bodies 
 are constructed does not consist in the simultaneous deoxidation 
 of several atoms of carbonic acid into one complex molecule, as 
 illustrated by the equation used in my last lecture to explain the 
 production of mannite, 
 
 Garb-anhydride Water Oxygen Mannite 
 
 6 CO Z + 7 H a O - 130 = C 6 H I4 6 ; 
 
 but that a series of more and more complex, less and less oxidised, 
 intermediate bodies are successively produced, by the. fixation of 
 deoxidised carbonic acid upon the previously formed compounds. 
 For example, we may conceive mannite to be built up somewhat 
 in this manner. By a simultaneous dehydration and deoxidation 
 of two molecules of carbonic acid, we should first obtain oxalic 
 acid, thus : 
 
 z Carbonic acid i Oxalic acid 
 
 Then by a further deoxidation of oxalic and carbonic acids, we 
 might obtain tartaric acid, thus : 
 
 i Oxalic acid C, H, 4 
 
 a Carbonic acid C a H 4 6 
 
 C 4 H 6 10 
 4 Oxygen 4 
 
 Tartaric acid C 4 H 6 6 
 
 Lastly, by a joint deoxidation of tartaric acid, carbonic acid, and 
 water, we might obtain mannite, thus : 
 
 1 Tartaric acid C 4 H 6 Q 6 
 
 2 Carbonic acid C a H 4 6 
 a Water H 4 O z 
 
 8 Oxygen 
 
 Mannite C 6 H I4 6 
 
80 ANIMAL CHEMISTRY LECTURE IV. 
 
 The actual occurrence of these particular actions is quite un- 
 proven ; but that some such actions take place is rendered highly 
 probable by a variety of considerations. Thus, in the gradual 
 development and ripening of the olive, we find certain vegetable 
 acids replaced by mannite, and at a later stage this mannite itself 
 replaced by the less oxidised and more complex oleine. (De Luca.) 
 (85.) Again, the compounds formed in one organ of a plant are 
 known to be transferred, in a more or less altered form, to other 
 ^ organs, in which they become accumulated ; and it is not im- 
 probable that certain vegetable products of deoxidised carbonic 
 acid and water may have undergone a partial reoxidation, or even 
 several alternate reoxidations and deoxidations, in the course of 
 their history. Similarly in animals, although the ultimate process 
 is one of oxidation, we know that in certain proximate principles 
 of food the oxidation of some of their constituents is effected at the 
 expense of the remainder, which consequently became deoxidised ; 
 and it is possible that some animal products may have undergone 
 an entire deoxidation, or even several alternate deoxidations and 
 reoxidations, before their final discharge from the body. On all 
 these points very much yet remains to be learned ; but still, the 
 general position holds good, that vegetables effect a simultaneous 
 deoxidation and intercombination of carbon molecules, while ani- 
 mals conversely effect their simultaneous reoxidation and separa- 
 tion. In many instances, also, the representatives of certain stages 
 of building up and breaking up, in vegetable and animal life 
 respectively, are closely allied to, or even identical with, one 
 another. Oxalic acid, for instance, the simplest product of 
 vegetable synthesis, and a frequent constituent of both the highest 
 and lowest vegetable organisms, may be formed, as we have just 
 seen,\)y a deoxidation of carbonic acid. But it also occurs abun- 
 dantly in animal juices and secretions, not as a product of the 
 deoxidation of carbonic acid, but as the last intermediate stage in 
 the oxidation or downward transformation of more complex bodies 
 into carbonic acid ; just as the oxalic acid of commerce is ob- 
 tained from sugar by a process of oxidation which, if carried too 
 far, yields little else than carbonic acid. Benzoic acid, again, 
 
GENERAL SYNTHETIC METHODS. 01 
 
 which enjoys a wide distribution in the vegetable kingdom as a 
 product of deoxidation, is also a constant result of the natural and 
 artificial oxidation of animal tissues. The power, then, of pro- 
 ducing such bodies as benzoic acid and oxalic acid out of more 
 complex bodies such as albumin and sugar, by artificial processes 
 of oxidation, more or less similar to the natural processes taking 
 place in the animal body, has for a long time past been in the 
 acknowledged possession of the chemist. Now, I propose to fur- 
 nish you with illustrations of his inverse power, to which I have 
 so often referred, of producing both animal and vegetable com- 
 pounds by deoxidising, or synthetic, or vegetative processes that 
 is to say, of forming organic compounds without having any 
 recourse to living organisms or reputed vital forces. 
 
 (86.) I will first give you an account of the general processes 
 employed for passing from a more simple to a more complex 
 group, and then of the particular processes by which certain indi- 
 vidual substances have been obtained, interspersing occasional 
 remarks upon the nature and relationship of some of the sub- 
 stances themselves. At starting, let me recall to your recollection 
 the associated series of homologous fatty acids and alcohols, as 
 written up on the table before you : 
 
 Alcohols Acids 
 
 C H 4 Methylic C H a 0, Formic 
 
 C 2 H 6 Ethylic C a H 4 O a Acetic 
 
 C 3 H 8 Propylic C 3 H 6 0, Propionic 
 
 C 4 H I0 Butylic C 4 H 8 0, Butyric 
 
 C 5 H Ia O Amylic C 5 H I0 0, Valeric 
 
 C 6 H I4 Caprylic C 6 H I3 O a Caproic 
 
 C 7 H I6 Anthylic C 7 H, 4 0, (Enanthic 
 
 C 8 H I8 Octylic C 8 H l6 0, Thetic 
 
 Now, by a variety of processes, some new, some old, it is, and 
 for a long time past has been, possible for us to fasten on to one 
 or other of these alcohols an additional atom of carbon, in such a 
 way as to produce the acid corresponding to the alcohol next in 
 the series. Thus, by means of prussic acid CHN, or carbonic an- 
 hydride C0 2 , or phosgene COC1 2 , we can convert methyl-alcohol 
 
 G 
 
82 ANIMAL CHEMISTRY LECTURE IY. 
 
 into acetic acid, vinic alcohol into propionic acid, propyl-alcohol 
 into butyric acid, and so on ; but until very lately we could 
 not step from acetic to propionic acid, or from propionic to butyric 
 acid, that is to say, we could obtain butyric acid C 4 H 8 2 , from 
 certain members of the 3 -carbon group, but not from those mem- 
 bers which we had ourselves produced from the 2 -carbon group ; 
 and, similarly, we could produce propionic acid C 3 H6O 2 , from cer- 
 tain members of the 2 -carbon group, but not from those members 
 which we had ourselves produced from the I -carbon group. The 
 series of synthetic operations by which it would be possible to 
 pass from any group not merely to the next, but to the next 
 but one, and so on ad libitum, was incomplete through our 
 ignorance of the metamorphic relation subsisting between the 
 acid and its associated alcohol. The alcohol, and not the acid, 
 being the plastic member of the group, we could convert the 
 I -carbon alcohol into the 2 -carbon acid, and the 2 -carbon alcohol 
 into the 3 -carbon acid, and so on; but being unable to convert 
 the 2 -carbon acid into the 2-carbon alcohol, we could not by any 
 means pass from the I -carbon to the 3 -carbon group. Very 
 recently, however, this difficulty has been overcome by the sepa- 
 rate researches of "Wurtz and Mendius, who have shown us how 
 to transform any acid into its corresponding alcohol ; whereby a 
 continuous series of synthetic processes may now be carried on as 
 far as we please. Without entering into purely chemical details, 
 I may say that the process of Wurtz consists in transforming the 
 aldehyd of the acid into the normal form of the alcohol ; while 
 that of Mendius consists in transforming the nitrile of the acid into 
 the ammoniated form of the alcohol, by means of nascent hydro- 
 gen, as illustrated below in the case of ethylic alcohol, thus: 
 
 Aceto-nitrile Ethyl-amine 
 
 C,H 3 N + H 4 C 3 H 7 N or C,H 5 .H,N 
 
 Acet-aldehyd Ethyl-hydrate 
 
 C a H 4 + H 3 C 3 H 6 or C 2 H 5 .HO 
 
 Ethyl-chloride 
 
 C,H 5 C1 or C 3 H 5 .C1 
 
GENERAL SYNTHETIC METHODS. 
 
 The amine is readily convertible into the hydrate, and the hy- 
 drate into the chloride, bromide, or iodide ; which last bodies, or 
 their metal derivatives such, for example, as sodium-ethylate 
 C 2 H 5 .NaO, and sodium-ethyl C 2 H 5 .Na are the forms of alcohol 
 most usually employed in actual synthetic processes. 
 
 (87.) Prior, then, to this discovery by Wurtz and Mendius, of 
 means for passing from the acid to its alcohol by hydrogenation, 
 although many important syntheses had been effected, there had 
 been no consecutive series of syntheses. The previously known 
 processes would allow us to pass from certain mobile members 01 
 one group to certain immobile members of the next, but would 
 carry us no further. Nowadays, however, by transforming the 
 immobile acid into the mobile alcohol, we can proceed continu- 
 ously through an apparently unlimited series of synthetic opera- 
 tions. Thus, letting CO stand for the transferable part of carbonic 
 anhydride CO 2 , phosgene-gas COC1 2 , and aqueous prussic acid 
 CHN.H 2 0, we have the following series of operations leading to 
 the production of fatty acids and alcohols of any degree of com- 
 plexity, each of them capable of metamorphosis into scores of 
 allied compounds; which, again, are capable of entering into com- 
 bination with one another, as explained in my second lecture, to 
 form still more numerous and complicated polymerone bodies. 
 
 Methylic 
 ( i -Carb. alcohol C H 4 
 
 Acetic 
 U-Carbonacid CHO a 
 
 /"2-Carb. alcohol 
 \3-Carbon acid 
 
 / 3 -Carb. alcohol 
 (,4-Carbon acid 
 
 Ethylic 
 C a H 6 
 Propionic 
 
 Propylic 
 C 3 H 8 
 
 Butyric 
 
 C 4 H 8 0, 
 
 CO = 
 
 H 4 = 
 
 CO = 
 
 Acetic 
 C a H 4 0, 
 
 Propionic 
 
 Ethylic 
 C a H 6 
 
 Propylic 
 C 3 H 8 
 
 Butyric 
 
 CO 
 
 ;. &c. 
 
84 ANIMAL CHEMISTRY LECTURE IV. 
 
 Starting from the I -carbon or methyl-alcohol, we can convert 
 it into the 2-carbon or acetic acid by well-known processes. But 
 in order to proceed from the z-carbon acid, we must first trans- 
 form it into the 2-carbon alcohol the alcohol, in some or other 
 of its forms, being the synthetic starting-point, so to speak and 
 this we have very recently learned to do. Then, by affixing 
 deoxidised carbonic anhydride on to the 2-carbon alcohol, we 
 convert it into the 3 -carbon or propionic acid. Then by acting 
 upon propionic acid by deoxidised water, we transform it into 
 3 -carbon or propyl-alcohol, upon which we again affix deoxidised 
 carbonic- anhydride to convert it into the 4~carbon or butyric 
 acid, and so on continuously, by a series of deoxidising actions 
 with carbonic oxide and hydrogen alternately. 
 
 (88.) Now let us proceed to notice briefly, in the order of their 
 complexity, some of the more interesting organic or carbon com- 
 pounds which have been produced artificially by elementary syn- 
 thesis. Among mono-carbon compounds, we have first carbonic 
 acid CH 2 3 , alike the most important product of animal oxidation 
 and subject of vegetable deoxidation. Associated with carbonic 
 acid or hydrate, we have carbonic amide or urea CH 4 N 2 O, a 
 body standing towards carbonic acid in the same relation that 
 ammonia stands to water, and convertible into carbonic acid by 
 an exchange of certain elements of ammonia for the corresponding 
 elements of water, thus : 
 
 Urea Water Ammonia Carbonic acid 
 
 , + (H,)H,0, = (H a )H 4 tf a + (CO)"H a O a 
 
 Carbonic acid is likewise met with in its dehydrated form as car- 
 bonic anhydride CO 2 , and as the sulphur derivative of that body 
 or carbonic sulphide CS 2 . These compounds are obtainable by 
 burning charcoal in oxygen and sulphur respectively, the last of 
 them, under the name of disulphide of carbon, being now pro- 
 duced on an enormous scale for certain manufacturing uses. 
 Moreover, by the dehydration of carbonic acid, a substance that 
 is known only in the state of solution, we also produce carb- 
 anhydride, as shown in the following equation 
 
SYNTHESIS OF FORMIC ACID. 85 
 
 Carbonic acid Water Carb-anhydride 
 
 CH a 3 - H,0 = CO, 
 
 which is reconvertible into the acid or a salt thereof by actual 
 or potential rehydration, thus : 
 
 Carb-anhyd. Lime Chalk 
 
 CO, + Ca"0 = CCa"0 3 
 
 Carb-anhyd. Potash Potas. bicarb. 
 
 CO, + KHO = CKH0 3 
 
 The deoxidised forms of carbonic acid and anhydride, respec- 
 tively, or formic acid CH 2 2 , and carbonic oxide CO, are readily 
 procurable therefrom by processes of reduction, and are correlated 
 with each other in a similar manner. For example, by the de- 
 hydration of formic acid, we obtain carbonic oxide, 
 
 Formic acid Water Carb. oxide 
 
 CH 3 0, - H,0 = CO; 
 
 convertible into a formiate by means of caustic alkali, thus : 
 
 Carb. oxide Potash Potas. formiate 
 
 CO + KHO = CKHO, 
 
 (89.) The production of formic acid or formiates by the 
 reduction of carbonic acid with sodium (Kolbe), and by the 
 combination of potash with carbonic oxide (Berthelot), being 
 among the early examples of the formation of organic from in- 
 organic compounds, excited on their first announcement a large 
 amount of chemical interest. Formic acid, indeed, is a substance 
 enjoying a very extensive natural distribution. In the vegetable 
 kingdom it occurs in the juice of the stinging nettle, in decaying 
 pine needles, and as a product of the spontaneous oxidation of 
 turpentine. In the animal kingdom it has been occasionally re- 
 cognised in human blood, urine, perspiration, and in the fluids of 
 the spleen and muscles. It also exists largely in the juice of red 
 ants, from which it may be obtained by simple distillation, and 
 
86 ANIMAL CHEMISTRY LECTURE IY. 
 
 in the corrosive fluid of certain caterpillars, &c. Again, by 
 combining formic acid with ammonia, we obtain formiate of am- 
 monia, which yields by dehydration that important organic com- 
 pound met with in cherry-laurel water, bitter almond emulsion, 
 &c., and known as prussic acid, cyanide oi hydrogen, or formio- 
 nitrile, thus : 
 
 Formic acid Ammonia Water Prussic acid 
 
 CH,O a + H 3 N - aH,0 = CHN 
 
 Moreover, this acid, or a corresponding cyanide, may nowadays 
 be procured, not only from formic acid, but by the direct com- 
 bination of carbon, nitrogen, and a metal. 
 
 Further, by oxidising a cyanide that of potassium CKN, for 
 instance we obtain cyanate of potassium CKNO, convertible by 
 double decomposition into cyanate of ammonia, which changes 
 spontaneously into urea, thus : 
 
 Ammonia cyanate Urea 
 
 CHNO.H 3 N = CH 4 N a O 
 
 This is the celebrated reaction by which urea was first produced 
 artificially by Wohler in 1828 ; but, at that time, the cyanogen 
 of the cyanide of potassium employed was known only as a 
 product of organic origin. You observe that by oxidising formic 
 acid CH 2 O 2 , we obtain carbonic acid ; and by oxidising the mon- 
 ammoniated form of formic acid namely, prussic acid CHN, in 
 presence of more ammonia, we obtain the di-ammoniated form 
 of carbonic acid namely, urea ; which has since been produced 
 by several other artificial processes. > 
 
 (90.) The still less oxidised monocarbon compounds belong to 
 the methyl sub-group, and are, principally 
 
 Methyl Compounds 
 
 ( CH 4 or CH 3 .H Methyl-hydride or marsh-gas 
 
 |CH 5 C1 or CH 5 .C1 Methyl-chloride 
 
 CH 4 or CH 3 .HO Methyl-hydrate or wood-spirit 
 
 CH 5 N or CH 3 .H 8 N Methyl-amine 
 
SYNTHESIS OF MARSH-GAS. 87 
 
 These four bodies the methyl varieties of hydrogen, hydro- 
 chloric acid, water, and ammonia are mutually convertible by a 
 variety of processes. Marsh-gas, in addition to its occurrence as 
 the chief constituent of coal-gas, as the fire-damp of coal mines, 
 and as the gas of stagnant ponds or marshes, has recently been 
 recognised by Pettenkofer as a normal ingredient of expired air. 
 Wood- spirit, again, is not only a product of destructive distilla- 
 tion, but occurs in nature as a constituent residue of the essential 
 oil of wintergreen, thus : 
 
 Wintergreen-oil Water Salicicacid Wood-spirit 
 
 C 8 H 8 3 -f H a O C 7 H 6 3 + CH 4 
 
 Among other well-known methyl-compounds may be men- 
 tioned sarcosine, kreatine, caffeine or theine, theobromine, coniine, 
 narcotine, &c. &c. Methylamine I have already referred to on 
 several occasions. Associated with it we have trimethylamine 
 (CH 3 ) 3 N, a frequent constituent of stale brine in which herrings 
 and other fish have been pickled. 
 
 (91.) The production of methylic from carbonic or formic 
 compounds may be effected in a variety of ways. Thus, prussic 
 acid, by hydrogenation, yields methylamine : 
 
 Pruesio acid Hydrogen Methylamine 
 
 CHK + H 4 CH 5 N 
 
 Formiate of barium is decomposed by heat with production of 
 marsh-gas, thus : 
 
 Barium formiate Barium carb. Carb-anhyd. Marsh-gas 
 
 a] cH Ba O* = 2CBa"0 3 + CO, + CH 4 
 
 Marsh-gas also results from passing a mixture of carbonic sul- 
 phide and sulphuretted hydrogen over metallic copper heated to 
 redness, thus : 
 
 Carb. sulph. Hyd.sulph. Copper Cupr.sulph. Marsh-gas 
 
 CS a + 2H,S + Cu 8 = 4Cu a S + CH 4 
 
88 ANIMAL CHEMISTRY LECTURE IV. 
 
 Perhaps a still more interesting mode of obtaining methyl- 
 compounds consists in submitting disulphide of carbon to pro- 
 longed treatment with chlorine gas, whereby it is converted into 
 perchloride of carbon, which by the continuous action of nascent 
 hydrogen yields the following series of compounds : 
 
 Marsh-gas Derivatives 
 C C1 4 Perchloride of carbon 
 CH C1 3 Chloroform 
 CH 3 Cl a Dichloromethene 
 CH 3 C1 Chloride of methyl 
 CH 4 Methene, or marsh-gas 
 
 Thus, among monocarbon compounds of purely artificial pro- 
 duction, we have the following interesting bodies, of which all 
 save the last occur naturally in the vegetable or animal kingdom, 
 namely, urea, formic acid> prussic acid, trimethylamine, and 
 chloroform. 
 
 (92.) The principal members of the dicarbon group, namely, 
 alcohol and acetic acid, together with their respective congeners, 
 are procurable from monocarbon compounds by a variety of 
 processes. Thus, according to some observations of my own, on 
 submitting a mixture of marsh-gas and carbonic oxide to a full 
 red heat, acetylene or klumene is produced, thus, 
 
 Marsh-gas Carb. oxide Water Klumene 
 
 CH 4 + CO = H 2 + C 3 H 3 ; 
 
 and this klumene, when acted upon by nascent hydrogen, yields 
 olefiant gas, or ethylene, thus : 
 
 Klumene Hydrogen Ethylene 
 
 C a H a + H a = C a H 4 
 
 Now, olefiant gas, as pointed out by Faraday and Hennel 
 nearly fifty years ago, and as rediscovered and established beyorid 
 question by Berthelot within the last few years, is absorbed by 
 
SYNTHESIS OF ALCOHOL. 89 
 
 oil of vitriol, and upon distilling the diluted acid, is liberated 
 therefrom in the form of alcohol or spirit of wine, thus : 
 
 Ethylene Water Alcohol 
 
 C a H 4 + H,0 = C a H 6 
 
 This production of alcohol from olefiant gas, or ethylene, an 
 important constituent of ordinary coal gas, is undoubtedly, in 
 many points of view, a result of very great interest, but as a 
 step in organic synthe'sis I think its importance has been some- 
 what over estimated alcohol and olefiant gas being closely allied 
 members of the same carbon group. However, Berthelot's dis- 
 covery of a process for obtaining alcohol by purely inorganic 
 means naturally achieved considerable notoriety, and gave a 
 great impetus to the general prosecution of synthetic methods. 
 
 (93.) You observe that artificial alcohol is produced from 
 olefiant gas, which is itself produced from acetylene or klumene, 
 which is itself produced from monocarbon compounds of strictly 
 mineral origin. But a still more interesting way of obtaining 
 acetylene has also been rediscovered and established by Berthelot, 
 namely, the combustion, so to speak, of carbon in hydrogen gas. 
 When charcoal is burnt in oxygen, the heat evolved by the 
 initial combination is more than sufficient to maintain the com- 
 bustion, and accordingly the piece of charcoal when once ignited 
 continues to burn. But in the combustion of charcoal in 
 hydrogen, if it may so be called, the piece of charcoal has to be 
 maintained throughout in an intense state of ignition by means 
 of the electric arc. "When, for instance, the charcoal terminals 
 of a moderately powerful battery, enclosed in a globe through 
 which a current of dry hydrogen is passing, are approximated to 
 each other so as to become ignited, as in the ordinary electric 
 lamp, the hydrogen and ignited carbon combine with one another 
 to form hydride of carbon or acetylene, much in the same 
 way that oxygen and ignited carbon combine with one another 
 to form oxide of carbon or carb-anhydride. But oxidation tends 
 to the separation, hydrogenation to the conjunction of carbon 
 atoms ; and accordingly, while by the combustion of charcoal in 
 
9 ANIMAL CHEMISTRY LECTURE IV. 
 
 oxygen we obtain only the monocarbon compound C0 2 , by its 
 combustion in hydrogen we obtain the dicarbon compound C 2 H 2 , 
 which is separated from the excess of hydrogen by transmission 
 through an ammoniacal solution of the white or inferior chloride 
 of copper, whereby it is retained in the form of cuprous acetylide 
 C 2 HCu. This compound is thrown down as an abundant bright 
 red precipitate, and, by treatment with warm hydrochloric acid, 
 is decomposed with liberation of acetylene gas, thus : 
 
 Cupr-acetylide Chlorhyd. acid Cuprous chlor. Acetylene 
 
 C 8 HCu + HC1 = CuCl + C s H a 
 
 Acetylene is characterised by the extreme luminosity with which 
 it burns. You observe the great opacity and whiteness of its 
 flame, and the large amount of light afforded by it in proportion 
 to its bulk, when compared, for instance, with the flame of 
 ordinary coal gas, of which, indeed, acetylene is a constituent, 
 though only to a small extent. By hydrogenising his cuprous 
 acetylide with a mixture of zinc and ammonia, instead of treating 
 it with hydrochloric acid, Berthelot produced olefiant gas or 
 ethylene, from which, by indirect hydration with sulphuric 
 acid, he afterwards obtained alcohol, as I have already de- 
 scribed. 
 
 (94.) Now, among other animal products, alcohol occurs as a 
 residue of tyrosine, a compound to which I shall refer more par- 
 ticularly in my next lecture ; and, as I have before observed, 
 of taurine, which is producible in the following manner: 
 Under certain circumstances, the residues of alcohol and sul- 
 phuric acid combine with one another to form isethionic acid, 
 easily convertible into chlorethyl-sulphurous acid C 2 H 5 C1SO 3 , 
 by means of pentachloride of phosphorus. This chloride is re- 
 transformable into its hydrate or isethionic acid C 2 H 5 (HO)SO 3 , 
 by the action of water, while both the chloride and the hydrate 
 are transformable into the amide or taurine C 2 H 5 (H 2 N)S0 3 ,* by 
 
 * These formulae are not meant to express the assumed internal mole- 
 cular arrangement of the three bodies, but only their positively ascertained 
 mutual relationship. 
 
SYNTHESIS OF GLYCOCINE, ETC. 9 1 
 
 means of ammonia, according to the following reactions, the first 
 of them due to Kolbe, the second, which is earliest in point of 
 time, to Strecker : 
 
 Chloride and Hydrate Taurine or Amide 
 
 C a H 5 (Cl)S0 3 + H(H a N) = HC1 + C,H 5 (H 4 N)S0 3 
 C,H 5 (HO)S0 3 + H(H a N) = H a O + C,H 5 (H,N)S0 3 
 
 (95.) Alcohol is also procurable from acetic acid by the 
 hydrogenising processes of Wurtz and Mendius, already de- 
 scribed ; while acetic acid is reprocurable from alcohol by oxi- 
 dation, as in the ordinary manufacture of vinegar. Moreover, 
 acetic acid C 2 H 4 2 , may be obtained synthetically from methyl- 
 alcohol CH 4 0, by fixation of carbonic oxide CO, according to 
 the previously mentioned general methods ; and also from di- 
 sulphide of carbon by Kolbe's historic process, referred to in my 
 last lecture. The successive stages of this, the earliest unim- 
 peachable process for obtaining an organic compound by strictly 
 mineral means, are indicated in the table before you 
 
 Acetic Acid Synthesis 
 C S a Carbon disulphide 
 
 C C1 4 Carbon tetrachloride 
 
 C 2 C1 4 Tetrachlor-ethylene 
 
 C 3 HC1 3 0, Trichlor-acetic acid 
 C,H 4 0, Acetic acid 
 
 The disulphide of carbon, produced by the direct combination 
 of sulphur and carbon, is converted, by treatment with chlorine, 
 into tetrachloride of carbon; this, by heating to redness, into 
 tetrachlor-ethylene ; this, by the action of moist chlorine, into 
 trichlor-acetic acid ; and this, by means of nascent hydrogen, 
 into ordinary acetic acid. By arresting the hydrogenation at a 
 certain point, and treating the so formed monochlor -acetic acid 
 C 2 H 3 C10 2 , with ammonia, we obtain glycocine, whereas by 
 treating it with methylamine we obtain sarcosine, which, in com- 
 bination with urea, constitutes kreatine, a compound, however, 
 that has not yet been prepared artificially. 
 
92 ANIMAL CHEMISTRY LECTURE IV. 
 
 Thus, among 2 -carbon products of the animal and vegetable 
 kingdom, that have been obtained by strictly mineral processes, 
 may be mentioned alcohol, taurine, acetic acid, glycocine, and 
 last, though not least important, oxalic acid; which results 
 from the oxidation of alcohol, acetic acid, and glycolic acid, &c., 
 and is producible synthetically from the mono-carbon formic and 
 carbonic acids. 
 
 (96.) By means of the general processes to which I directed 
 your attention some time back, as well as by certain special 
 processes, it is easy to pass from the 2-carbon to the 3 -carbon 
 group, upon which, however, we must rest satisfied with be- 
 stowing a very cursory glance. It comprises among its members 
 glycerin C 3 H8O 3 , the basic principle of the true fats, whether 
 of vegetable or animal origin. Also lactic acid C 3 H6O 3 , an 
 important constituent of the juice of flesh, and a product of that 
 fermentation of grape-sugar and milk-sugar which is set up by 
 putrefying curd. We have also the chief constituents of essential 
 oil of garlic, or allyl-sulphide (C 3 H 5 ) 2 S, and of essential oil of 
 mustard, or allyl-sulphocyanate (0 3 H 5 )H.CNS, to be included in 
 the list of artificially produced members of the propionic family. 
 
 (97.) Passing on to the 4-carbon group, we have first butyric 
 acid C 4 H8O 2 , a product of the destructive metamorphosis of 
 sugar, mannite, &c. Combined with alcohol it forms butyric 
 ether or essential oil of pine-apple, while combined with glycerin 
 it forms that constituent of ordinary butter which is known as 
 butyrin. Succinic acid C 4 H60 4 , is readily procurable from 
 butyric acid, and bears to it the same relation that oxalic bears 
 to acetic acid. It is probably the most frequent artificial product 
 of the oxidation of fatty matters, and has also been met with 
 naturally in the cystic fluids of hydatids, hydrocele, &c. From suc- 
 cinic acid it is easy to procure in succession the well-known vege- 
 table products, malic acid C 4 H6O 5 , and tartaric acid C 4 H6O6, 
 which, again, are reconvertible into succinic acid. The malic and 
 succinic acids, in particular, are very intimately associated with, 
 and readily convertible into, one another. Thus, asparagine 
 C 4 H8N 2 O 3 , the crystalline principle of asparagus and other 
 
SYNTHESIS OF GRAPE SUGAR? 93 
 
 etiolated plants, yields one or other of these acids, according to 
 the treatment to which it is subjected. 
 
 (98.) The 5 -carbon compounds of artificial origin are of less 
 general interest. I may mention fousel oil or amyl-alcohol 
 C 5 Hi 2 O, and valerianic or valeric acid C 5 H 10 O 2 , a product 
 originally obtained from essential oil of valerian. By combining 
 amyl-alcohol with acetic acid we procure the pear flavour, and 
 by combining it with valeric acid, the apple or quince flavour 
 used in confectionery, which are probably identical with the 
 essential oils existing naturally in the ripe fruits. Again, by 
 combining valeric acid with glycerin we produce valerin, a 
 constituent of whale oil. 
 
 (99.) Of the 6-carbon fatty compounds which have been 
 artificially obtained, the most interesting are caproic acid C6H 12 O 2 , 
 and leucic acid C6H 12 O 3 . Caproic acid is met with as a glyce- 
 ride in goat's butter, while amido-caproic acid or leu cine is an 
 occasional constituent of human urine, and a constant product of 
 the metamorphosis of glandular tissue. Starch C6H 10 O 5 , grape 
 sugar C6Hi 2 C>6, mannite C6Hi 4 06, and a host of allied alimentary 
 substances are also included in this group, though their exact 
 relationship to the typical members is not as yet clearly es- 
 tablished. Now, grape sugar has been obtained by Berthelot 
 from glycerin, which is itself, as I have said, obtainable by 
 purely inorganic means ; so that, in one sense, sugar may be 
 added to the list of artificially produced organic compounds. 
 Still the means employed for effecting the conversion of the 
 glycerin namely, the action of putrefying animal tissue must 
 prevent our regarding the resultant sugar as being strictly of 
 inorganic origin ; although formed exclusively out of the glyce- 
 rin, the animal tissue not having contributed any actual material 
 to its formation. However, if sugar has not yet been obtained 
 by a satisfactory process, the recent production of strictly allied 
 bodies, such as the propyl-phycite of Carius, together with our 
 increasing knowledge of the metamorphic relations of sugar itself, 
 assures us that an unexceptionable means for building up this 
 important alimentary principle cannot much longer escape us. 
 
94 ANIMAL CHEMISTRY LECTURE IV. 
 
 Hitherto the transformation of fatty into aromatic compounds 
 has not been accomplished according to any definite reaction; 
 but both phenene C6H6, and phenol or carbolic acid CeH^O, are 
 producible by transmitting the vapour of alcohol or fousel oil 
 through red-hot tubes. From the former of these bodies we 
 readily obtain aniline or phenylamine CgH-rN, which is recon- 
 vertible into both phenene and phenol. 
 
 (100.) The 7-carbon fatty acid and alcohol are usually ob- 
 tained from castor oil. So far as I know, they have not yet been 
 produced artificially from inorganic materials, but undoubtedly 
 could be so produced at any moment. With the 7-carbon 
 aromatic compounds the case is different. By the general pro- 
 cesses already referred to, phenene has been converted into 
 benzoic acid C 7 H6O 2 , by Harnitzky and Kekule, and phenol into 
 salicic acid C 7 H6O 3 , by Kolbe. Benzoic acid readily yields 
 benzoic aldehyd or essential oil of bitter almonds, and also glyco- 
 benzoic or hippuric acid. Salicic acid, again, is readily oxidi- 
 sable into gallic acid, of which tannin constitutes the natural 
 glucoside, as shown by the following decomposition : 
 
 Tannin Water Glucose Gallic acid 
 
 C, 7 H W I7 + 4 H a O = C 6 H X ,0 6 + 
 
 From salicic acid we may also obtain methyl-salicate or essential 
 oil of wintergreen, salicic aldehyd or essential oil of spirasa, and 
 saligenin or salicylic alcohol, a compound frequently mentioned 
 in my second lecture as a constituent residue of salicin and 
 populin salicin being, indeed, a glucoside of saligenin, much 
 in the same way that tannin is a glucoside of gallic acid, thus : 
 
 Salicin Water Glucose Saligenin 
 
 C I3 H I8 7 + H a O = C 6 H Ja 6 + C 7 HA 
 
 Moreover, tyrosine a very remarkable product of tissue 
 metamorphosis though not yet produced from salicic acid, has 
 much the same relation thereto that leucine has to caproic, and 
 
SYNTHESIS OF ALIMENTARY SUBSTANCES? 95 
 
 sarcosine and glycocine have to acetic acid it being, indeed, the 
 ethyl-ammoniated form of salicic acid. 
 
 Another /-carbon compound of artificial production, and of 
 great interest in an industrial point of view, is benzoene, or toluol 
 C 7 H8, which Fittig and Tollens have recently obtained from 
 phenene or benzol C6H6. Starting from these two bodies, we 
 may procure all the so called coal-tar colours, with the brilliancy 
 and variety of which most of us are now familiar. The red 
 base or rosaniline C 20 Hi 9 N 3 , the violet base or triethyl-rosaniline 
 C 2 6H 31 N 3 , and the blue base or triphenyl-rosaniline C 3 8H 31 N 3 , 
 being producible in this way from their constituent elements, 
 furnish us with admirable illustrations of the constructive powers 
 of modern organic chemistry. 
 
 (101.) Thus have I illustrated to you the mode in which 
 chemists can nowadays, without any recourse to vitality, build 
 up primary molecules containing as many as seven atoms of 
 carbon, either from carbonic acid, water, and ammonia, the 
 materials out of which living organisms construct identical or 
 similar molecules, or else from the elementary substances, carbon, 
 hydrogen, oxygen, and nitrogen, upon which living organisms 
 can exert no plastic action whatever. I might even proceed 
 further, but should then be obliged to depart from the regular 
 sequence I have hitherto followed. Moreover, my object has 
 been rather to illustrate to you the general mode of procedure 
 than to make known to you the utmost limits that have as yet 
 been attained. Of the three great classes of alimentary sub- 
 stances, the oleaginous are quite, and the saccharine almost within 
 our reach. The albuminous, indeed, are still far beyond us; 
 and no wonder, since their very constitution is at present not 
 only unknown, but unsuspected. In their case, however, as in 
 that of many other bodies, so soon as we succeed in unravelling 
 the mystery of their natural composition, so soon may we aspire 
 confidently to the work of their artificial reconstruction. 
 
 (102.) Only a few words more, which I will borrow from my 
 friend Dr. Frankland, who has himself contributed very largely 
 to synthetic methods and results. 'It would be difficult,' said he, 
 
96 ANIMAL CHEMISTRY LECTURE IT. 
 
 to conclude a subject like the present without some notice of 
 the considerations which naturally suggest themselves regarding 
 the possibility of economically replacing natural processes by 
 artificial ones in the formation of organic compounds. At pre- 
 sent,, the possibility of doing this only attains to probability in 
 the case of rare and exceptional products of animal and vegetable 
 life. By no processes at present known could we produce sugar, 
 glycerin, or alcohol from their elements at one hundred times 
 their present cost, as obtained through the agency of vitality. 
 But, although our present prospects of rivalling vital processes in 
 the economic production of staple organic compounds, such as 
 those constituting the food of man, are exceedingly slight, it 
 would be rash to pronounce their ultimate realisation impossible. 
 It must be remembered that this branch of chemistry is as yet in 
 its merest infancy ; that it has hitherto attracted the attention of 
 but few minds ; and further, that many analogous substitutions 
 
 of artificial for natural processes have been achieved 
 
 In such cases where contemporaneous natural agencies have been 
 superseded, we have almost invariably drawn upon that grand 
 store of force collected by the plants of bygone ages and conserved 
 in our coal-fields.' 
 
97 
 
 LECTUEE V. 
 
 Muscular action dependent on muscular metamorphosis Theoretic oxidation 
 of muscle into one proportion of urea and seven of carbonic acid Prac- 
 tical results Dynamic value of muscle oxidation Quantities of heat 
 producible by combustion of hydrogen and carbon Difference between 
 quantity and intensity of heat Unit of heat equivalent to 424 kilo- 
 'grammetres of motion Quantities of motion producible by combustion 
 of hydrogen and carbon Economy of muscle as a motive exponent of 
 combustion Reciprocity of heat and motion in muscular action Solar 
 origin of muscular force Amount of force derivable from muscle pro- 
 portional to degree of its oxidation Imperfect knowledge of natural 
 process of oxidation Artificial oxidation of muscle Nature of inter- 
 mediate products Relation of aldehydes and nitriles to acids Simple 
 constitution of acids obtained by muscle oxidation Production of both 
 fatty and aromatic compounds General distribution of leucine and tyro- 
 sine Their formation by indirect oxidation of nitrogenous tissue 
 Leucine the most elaborate of fatty, and tyrosine of aromatic animal 
 products Constitution and analogies of leucine or amido-caproic acid 
 Probable constitution of tyrosine, or ethylamido-salicic acid Natural 
 history of salicic compounds, including indigo Occurrence in human 
 urine of indigo, salisuric acid, and phenol Relationship of tyrosine to 
 hippuric acid. 
 
 (103.) THAT muscular exertion is dependent on muscular me- 
 tamorphosis or oxidation is a subject rather for the physiologist 
 than the chemist to dilate upon. Perhaps, however, I may be 
 permitted to remind you of such observations as the following 
 that a free supply of thoroughly oxygenated arterial blood is 
 essential for complete well-developed muscular action ; that the 
 volume of oxygen contained in blood which has circulated 
 through a contracting muscle is less than one-fourth of that con- 
 tained in blood which has traversed the same muscle at rest, 
 
 H 
 
9 ANIMAL CHEMISTRY LECTURE Y. 
 
 \vbile there is a corresponding increase, not of course an equal 
 increase, in the volume of its carbonic acid ; that the irritability 
 of muscular fibre out of the body is arrested by its removal from 
 oxygen, and again manifested on its re-exposure thereto ; and 
 lastly, that other things being equal, the amount of urea excreted 
 by the kidneys, and of carbonic acid excreted by the lungs, is 
 proportionate to the muscular activity of the individual. Seeing, 
 then, that muscular exertion is really dependent upon muscular 
 oxidation, we have to consider what should be the products, and 
 what the value of this oxidation. 
 
 (104.) Unfortunately, the precise molecular formula the ex- 
 act chemical constitution of muscle is at present unknown. 
 But in muscle, as in all the albuminoid class of bodies, we do 
 know the ratio in which the constituent carbon and nitrogen 
 stand to one another. Thus it is established beyond all question 
 that the ratio of the number of atoms of carbon to the number 
 of the atoms of nitrogen in muscle is as nearly as possible, if not 
 quite exactly, four to one. In the most minute fragment of 
 muscle, then, for every single atomic proportion of nitrogen there 
 are four atomic proportions of carbon, thus : 
 
 4 CARBON to i NITROGEN. 
 
 It will be more convenient, however, to express this ratio by the 
 doubles of the above numbers, so that, instead of four to one, we 
 will adopt eight to two, as our expression of the atomic ratio of 
 carbon to nitrogen in every particle of muscle : 
 
 8 CARBON to 2, NITROGEN. 
 
 Admitting, further, as a result of its ultimate metamorphosis, 
 that the whole of the nitrogen of muscle is converted into urea, let 
 us first consider what proportion of its carbon must be associated 
 with thisnitrogen to produce urea, and what proportion be thereby 
 left for excretion in the form of carbonic acid. Now, although the 
 molecular constitution of muscle is undetermined, that of urea is 
 
RESULTS OF MUSCLE OXIDATION. 99 
 
 perfectly definite.* As shown by its formula, CN 2 H 4 0, the mole- 
 cule of urea consists of one atom of carbon, two atoms of nitro- 
 gen, four atoms of hydrogen, and one atom of oxygen. In other 
 words, leaving out of consideration its hydrogen and oxygen, the 
 atomic ratio of nitrogen to carbon in urea is as two to one. 
 Accordingly, every two atoms of nitrogen in urea have one atom 
 of carbon associated with them ; so that if we take the two pro- 
 portions of nitrogen existing in muscle and add to them the one 
 proportion of carbon necessary to form urea, we shall have seven 
 proportions of carbon left for conversion into carbonic acid, 
 thus : 
 
 a NITROGEN 
 
 The theoretical result, then, of the complete oxidation of 
 muscle is the appearance of one-eighth of its carbon in the form 
 of urea, and of seven- eighths of its carbon in the form of carbonic 
 acid. 
 
 (105.) Now, let us see what is the actual result. We have two 
 series of experiments made by Bischof and Voit, and Pettenkofer 
 and Voit respectively, in which lean dogs were fed exclusively 
 upon a moderate diet of flesh. In the first series of experiments 
 a small proportion of fat left in the flesh was duly allowed for ; 
 while in the second series the fat was entirely removed. The 
 general results of the two series of experiments are shown 
 below : 
 
 C. of Garb, acid C. of Urea 
 
 7*29 to I Bischof and Voit 
 6-85 to i Pettenkofer and Voit 
 7 '07 to i Mean 
 
 Thus the ratio of carbon excreted in the form of carbonic acid 
 to carbon excreted in the form of urea was as 7-29 to i in the 
 
 * This mode of viewing the relationship of muscle to urea and carbonic 
 acid was suggested by Dr. Lyon Play fair's essay ' On the Food of Man in 
 relation to his Useful Work,' to which I am otherwise much indebted in the 
 early part of this lecture. 
 
 H2 
 
100 ANIMAL CHEMISTRY LECTURE V. 
 
 first series of experiments, as 6*85 to I in the second series, and 
 as 7 '07 to i in the mean of the two. Theoretically, then, the 
 ratio of carbon in carbonic acid to carbon in urea is as 7 to I ; 
 experimentally it is found to be as 7 '07 to i a striking mutual 
 corroboration of the two methods of calculation and research. 
 
 (106.) With regard to the dynamic value of muscle oxidation, 
 I told you in my last lecture that, by the separation of oxygen 
 from carbon and hydrogen, a certain amount of heat-force was 
 absorbed and rendered latent in the separated bodies, which, by 
 their re-combination, was again liberated and rendered sensible. 
 Confining our attention to hydrogen, and speaking in round 
 numbers, we may say that the heat evolved by burning a cubic 
 foot of hydrogen that is, by combining a cubic foot of hydrogen 
 with half a cubic foot of oxygen will raise the temperature of 
 5 \ cubic feet of water one degree Fahrenheit ; or that the heat 
 of burning hydrogen is capable of raising the temperature of 5 \ 
 times its bulk of water one degree. But, seeing that the 
 quantity of matter in a body is proportionate to its weight, 
 we get a much better idea of the amount of heat developed, 
 by comparing the items gravimetrically instead of volumetri- 
 cally. We thus find that the combustion of one part by 
 weight of hydrogen will evolve an amount of heat sufficient 
 to raise the temperature of more than 61,000 parts of water one 
 degree Fahrenheit, or 34,000 parts of water one degree centi- 
 grade. Now, in comparing the amounts of heat given out by the 
 combustion of different substances, it is convenient to have some 
 definite standard of comparison ; and the usual continental stand- 
 ard is altogether, perhaps, the most convenient. According to 
 this standard, the amount of heat given out by one kilogramme 
 of water in cooling one degree centigrade, or, conversely, the 
 amount of heat absorbed by one kilogramme of water in rising 
 one degree centigrade, is called the unit of heat. We find, then, 
 ihat when one gramme of hydrogen gas is burned into water, it 
 gives out 34 units of heat ; or it will raise the temperature of 34 
 kilogrammes that is, 34,000 times its own weight of water 
 one degree ; while, turning our attention to carbon, we find that 
 
QUANTITY DISTINCT FRO&' "iNTEttfeTlY oV HEAT/ J 10 1 
 
 one gramme of carbon, in being oxidised or burned into carbonic 
 anhydride, gives out 8 units of heat, or will raise the temperature 
 of 8 kilogrammes that is to say, 8000 times its own weight of 
 water one degree. 
 
 (107.) It must be remembered, of course, that the quantity of 
 heat evolved during the oxidation of a given weight of hydrogen, 
 carbon, or other combustible, is perfectly independent of the 
 rapidity or slowness of the action. Provided only that the same 
 products are formed, the same amount of heat is liberated in 
 their formation, whether it takes place rapidly or slowly, vio- 
 lently or gradually. It is only the intensity of the heat, and not 
 its quantity, which varies with the rapidity of the combination. 
 When a stout piece of iron rusts in the air, we get oxide of iron 
 produced as the result of the slow burning of the metal, but there 
 is no obvious rise of temperature. On the other hand, when a 
 piece of iron wire is burned in oxygen gas, we have a brilliant 
 combustion, and an intense development of heat. In reality, the 
 products formed in these two cases are not identical, but only 
 allied. Assuming them, however, to be identical, the amount of 
 heat given out in the rapid burning of the metal would be iden- 
 tical with that given out during its slow rusting. The difference 
 is merely that in the one case all the heat is given out in the 
 course of a few seconds that there is a great quantity of heat 
 produced in a short time while in the other case this same 
 quantity of heat is developed only during a long series of years. 
 As a matter of fact, the quantity of heat evolved by the slow 
 rusting of a given weight of iron is considerably greater than 
 that evolved by its rapid combustion in oxygen, the resulting 
 compound being not only more highly oxidised, but in a state of 
 hydration, or combination with solid water. 
 
 (108.) A very ordinary experiment will serve, perhaps, to 
 illustrate more strikingly the point now under consideration. 
 Upon immersing this plate of copper in a jar of chlorine gas, for 
 instance, the chlorine combines gradually with the metal, and 
 there is no evident rise of temperature ; but when very thin 
 copper leaf is immersed in chlorine gas, the combination takes 
 
1O2 ANIMAL CHEMISTRY LECTURE Y. 
 
 place instantaneously, with evolution of sufficient heat to render 
 the leaf luminous with vivid combustion, in fact as you per- 
 ceive. Now, the amount of heat given out under these opposite 
 circumstances is identical ; the only difference is in its intensity 
 in the quantity of heat associated with a given quantity of 
 matter at a given moment. In the last case, the action being 
 instantaneous, and the quantity of matter to be heated very 
 small, we have what we call an intense heat that is, the mo- 
 mentary association of a large quantity of heat with a small 
 quantity of matter ; whereas in the other case, the action being 
 gradual, the development of heat is likewise gradual, spread over 
 a long period of time, and associated with a large quantity of 
 matter, the increased temperature of which is, therefore, at no 
 one moment very perceptible. The terms quantity and intensity 
 of heat are strictly analogous to the terms quantity and velocity 
 of motion. In a pound weight of iron raised to 1000 the 
 melting point of silver, or ten pounds weight raised to 100 
 the boiling point of water, the quantity of heat capable of being 
 imparted say, to a gallon of ice-cold water is substantially the 
 same, though the intensity of the heat is ten times as great in the 
 one case as the other ; just as the quantity of motion is the same 
 in a pound weight moving at the rate of I ooo feet, or a ten-pound 
 weight moving at the rate of 100 feet per second, although the 
 velocity of motion is ten times as great in the one case as the 
 other. We come, then, to this conclusion that chemical action, 
 whether rapid or slow, provided only that the same substances 
 react and the same products result, always furnishes the same 
 amount of heat. 
 
 (109.) Now, let us apply this fundamental law of combination 
 to the fuel-constituents of our tissues. If we inflame a mixture 
 of hydrogen and oxygen gases, the combination and consequent 
 evolution of heat being instantaneous, we obtain, indeed, the 
 highest degree of temperature capable of being produced by 
 direct chemical action. On the other hand, if we take the same 
 mixture of oxygen and hydrogen gases, and cause them to unite 
 slowly by means of spongy platinum, the oxidation and develop- 
 
QUANTIVALENCY OF HEAT AND MOTION. 103 
 
 ment of heat being spread over a period of many minutes, 
 there is no great manifestation of temperature at any one 
 instant. The quantity of heat is, however, the same in both 
 cases. One gramme of hydrogen in combining with oxygen, 
 whether quickly or slowly, will always evolve 34 units of 
 heat; and one gramme of carbon in combining with oxygen, 
 whether quickly or slowly, will always evolve 8 units of 
 heat, The slow oxidation of so much carbon and hydrogen 
 in the human body, therefore, will always produce its due 
 amount of heat, or an equivalent in some other form of 
 energy ; for while the latent force liberated by the combustion of 
 the carbon and hydrogen of fat is expressed solely in the form of 
 heat, the combustion of an equal quantity of the carbon and 
 hydrogen of voluntary muscle is expressed chiefly in the form of 
 motion. You may remember that I referred in my last lecture 
 to the equivalency subsisting between heat and motion to the 
 circumstance that so much heat was convertible into so much 
 motion. Accordingly, when we burn or oxidise the carbo-hydro- 
 gen of animal tissue, instead of getting the heat-force which was 
 exerted in separating this carbo -hydrogen from oxygen remani- 
 fested in the form of heat, we have it, under certain circumstances, 
 manifested in the form of motion. 
 
 (no.) Let us then proceed to consider what are the quanti- 
 tative relations subsisting between heat and motion. We have 
 taken as our unit of heat the quantity of heat absorbed or 
 evolved by one gramme of water in rising or falling through one 
 centigrade degree of temperature. Now, this is found by experi- 
 ment to be the exact quantity of heat generated by collision with 
 the earth of a kilogramme weight falling from a height of 424 
 metres. So that the mechanical force of a kilogramme weight 
 which has fallen through 424 metres, or, in other words, the 
 mechanical force necessary to lift a kilogramme weight to the 
 height of 424 metres, is equal to, interchangeable for, and con- 
 vertible into the heat-force evolved or absorbed by a kilogramme 
 of water in changing its temperature one degree. Or the arrest 
 of a unit of motion would raise the temperature* of a kilogramme 
 
104 ANIMAL CHEMISTRY LECTUEE T. 
 
 of water at zero one degree, and conversely, the absorption of a 
 unit of heat would lift I kilogramme weight to the height of 
 424 metres. Of course, the force necessary to lift I kilogramme 
 through 424 metres, or 10 kilogrammes through 42-4 metres, or 
 424 kilogrammes through I metre, is the same ; whence it is 
 convenient to apply the expression kilogram -metre to the product 
 of the kilogrammes lifted into the metres of height, and to say 
 that the heat evolved by the cooling of a kilogramme of water 
 one degree centigrade is equal to 424 kilogrammetres of motion, 
 and vice versa. Or we may adopt Mr. Joule's original standard, 
 and say that the heat evolved by the cooling of a pound of water 
 one degree Fahrenheit is equal to 772 foot-pounds of motion. 
 
 (in.) The applicability of these considerations to the combus- 
 tions of hydrogen and carbon taking place in the animal body is 
 obvious. We have said that the combustion of I gramme of 
 hydrogen evolves 34 units of heat, and that a unit of heat is 
 equal to 424 kilogrammetres of motion ; so that the combustion 
 of i gramme of hydrogen will produce 34x424=14,416 kilo- 
 grammetres of motion ; or will serve to lift I kilogramme weight 
 through 14.416 metres of height, or 14,416 kilogrammes through 
 I metre of height, &c. &c. Similarly, the combustion of I 
 gramme of carbon will suffice to produce 3392 kilogrammetres 
 of motion, thus : 
 
 One gramme Kilogrammetres 
 
 burnt of motion 
 
 HYDROGEN 34 x 424 = 14.416 
 CAEBON 8 x 424 = 3, 392 
 
 In this way, then, we can form some idea of the mechanical 
 power generated, or quantity of motion producible, by the com- 
 bustion of the hydrogen and carbon of our muscles into water, 
 and carbonic acid or urea respectively.* Our knowledge of the 
 
 * The heat produced by the conversion of carbon into urea is doubtless 
 that producible by its complete burning into carbonic anhydride C0 2 , and 
 not merely that producible by its half burning into carbonic oxide CO, as 
 sometimes represented. 
 
ECONOMY OF MUSCLE COMBUSTION. 105 
 
 intimate constitution of muscle is, however, too imperfect to allow 
 of our estimating the amount of motion producible by its oxida- 
 tion with any degree of exactitude ; but, as the result of a rough 
 calculation, it may be taken that the combustion of the unburnt 
 carbo-hydrogen of one gramme of dry muscle, free from fat, is 
 capable of furnishing 1923 kilogrammetres of motion, or will 
 suffice to lift 1923 kilogrammes to the height of I metre.* 
 
 (112.) Now, although the ratio of the [amount of motion 
 actually produced to that theoretically producible by the com- 
 bustion of a given weight of muscle, has not. I believe, been 
 satisfactorily ascertained, this much is. certain, that muscular 
 tissue is, without exception, by far the most perfect of machines 
 for manifesting the force liberated by chemical action in the form 
 of motion. No artificial contrivance with which we are ac- 
 quainted is at all comparable to it in economy that is to say, in 
 the proportion of mechanical work performed to the total force 
 liberated. The steam-engine, for instance, is an artificial ma- 
 chine, expressly intended for the conversion of chemical force 
 into motion. Heat is generated in the boiler-furnace by a com- 
 bination of the carbo-hydrogen of the coal with the oxygen of 
 the air, but only a certain amount of this heat is absorbed in the 
 evaporated water, and then only a certain amount of the heat so 
 absorbed is translated into motion. According to Sir W. Arm- 
 
 * Assuming for muscle the formula C Ia H I9 N 3 4 x 6, and subtracting all 
 the oxygen and nitrogen, with the necessary hydrogen, in the forms of water 
 and ammonia, so as to leave a residue of C^H., x 6, then 269 grammes of 
 muscle would leave 144 grammes of carbon and 2 grammes of hydrogen for 
 oxidation, which should furnish 517,280 kilogrammetres of motion, thus: 
 
 Grammes Kilogrammetres Kilogrammetres 
 
 CABBON 144 x 3,39^ = 488,448 
 
 HYDROGEN 2 x 14,416 = 28,832 
 
 517,280 
 
 Hence one gramme of muscle should furnish 517,280-4-269 = 1923 kilogram- 
 metres of motion ; but from the imperfection of the data on which the * 
 calculation is based, particularly as regards the heat absorbed in the sepa- 
 ration and volatilisation of carbon, this result can only be regarded as ap- 
 proximative. 
 
106 ANIMAL CHEMISTRY LECTURE V. 
 
 strong, indeed, not more than one-tenth of the force liberated by 
 the combustion of the coal used for raising steam is realised as 
 available motion. Be this as it may, it appears that by burning, 
 or consuming, or oxidating a given weight of muscle in our 
 bodies, we obtain a quantity of available motive force which 
 could only be produced by the combustion of at least five or 
 six times its weight of coal in the most perfect steam-engine 
 that ever was constructed. 
 
 (113.) The superior economy of muscle over any artificial con- 
 trivance, as a motive machine, seems to depend in great measure 
 upon the circumstance of the force liberated by its oxidation 
 being expressed directly in motion, instead of first appearing in 
 some intermediate form of energy. Thus, in a steam-engine, the 
 immediate effect of the oxidation is not motion, but heat, some of 
 which eventually or intermediately appears as external motion. 
 In this case, the combination first produces heat, and the heat is 
 afterwards transformed into motion ; whereas, in muscular tissue, 
 the combination first produces motion, which is afterwards, in 
 many cases, transformed into heat. The force liberated by the 
 combustion of the muscular fibre of the heart, for instance, is 
 expressed directly in the contraction of its ventricles, and the 
 consequent propulsion of the blood through the greater and lesser 
 circulations. But by the time the blood gets back to the heart, 
 it has given up all its motion, and requires to be again propelled 
 by another contraction of the ventricles, and so on. Now, what 
 becomes of the motion received by the blood at each contraction ? 
 It appears in the form of heat. The blood circulating through 
 the vessels and capillaries undergoes a certain amount of friction. 
 It is brought to a state of rest gradually by the hindrance to its 
 motion, just as a bullet is brought to rest suddenly by the hin- 
 drance to its motion. In both cases, that which was motion 
 becomes heat, and, in the latter case, the quantity of heat finally 
 produced by the friction of the blood is generated as truly by the 
 combustion of the heart-fibre, as if it had been burnt directly 
 in a furnace. Under certain circumstances, indeed, as in the 
 attempt to lift a heavy weight, the oxidation of muscle within 
 
SOLAR ORIGIN OF MUSCULAR FORCE. IO/ 
 
 our bodies produces a direct liberation of heat instead of motion. 
 In the case of a person actually lifting a weight, the combustion 
 of his tissue is expressed in the motion of the weight ; but sup- 
 posing he only attempts to lift a weight which is too heavy for 
 him, there is then no production of motion, but instead of it a 
 corresponding increase of temperature in the muscle. In tetanus, 
 again, where the violent contraction of the muscles produces no 
 external motion, their temperature has been observed to rise as 
 much as six degrees centigrade or eleven degrees Fahrenheit 
 above the normal state. Conversely, in the case of a man work- 
 ing a treadmill, although the amount of heat evolved from his 
 person is absolutely larger, its proportion, relatively to the 
 amount of tissue burned, is smaller than in the case of a person at 
 rest, by a difference equivalent to the external work performed. 
 But in fever, where there is a rapid destruction of tissue without 
 any corresponding mechanical effect, we have a complementary 
 manifestation of external heat. 
 
 (114.) Thus we return once again to the conclusion which I 
 brought more prominently under your notice in my last lecture. 
 We perceive that muscular exertion does not result from vital 
 force generated within the body, or, indeed, from force of any 
 kind generated within the body, but only from a liberation 
 within the body of pent-up solar force, which at some time or 
 other had been rendered latent in the separated carbo-hydrate of 
 our food on the one hand, and oxygen of our breath on the other. 
 As ingeniously observed by Dr. Tyndall, when speaking of the 
 sun, ' It is at his cost that animal heat is produced, and animal 
 motion accomplished. Not only is the sun chilled, that we may 
 have our fires, but he is likewise chilled that we may have our 
 powers of locomotion.' From the terms in which I lately referred 
 to the fiction of vital force, some physiologists who honoured me 
 by their presence seemed to infer that chemists and physicists 
 were insensible to those important distinctions existing between 
 living and dead matter, which they, on the other hand, profess to 
 explain by declaring the former to be possessed, and the latter 
 dispossessed, of vital force. I believe, however, that chemists 
 
I08 ANIMAL CHEMISTRY LECTURE V. 
 
 appreciate in its fullest extent what may be termed the mystery 
 of life, but they look upon the physiologists 1 explanation as a 
 mere periphrasis, as only another mode of saying that dead 
 matter differs from living matter because it is dead, while living 
 matter differs from dead matter because it is alive. Chemists and 
 physicists are well assured that, be life what it may, it is not a 
 generator, but only a transformer, of external force. In the 
 vegetable kingdom solar force is absorbed in the production of 
 our food ; in the animal kingdom it is liberated by the erema- 
 causis of our fat and glands and muscles. 
 
 (115.) Now, the full realisation of the force derivable from a 
 given weight of muscle depends upon its complete oxidation into 
 water and carbonic acid or urea. Should it be only converted 
 into sugar, or kreatine, or uric acid, these are imperfectly burned 
 substances, which still retain a certain amount of potential energy 
 liberable from them by a further oxidation. They still have 
 associated with them some portion of the latent force put into the 
 original tissue-constituents at the period of their formation ; and 
 accordingly, by their further oxidation, we are capable of getting 
 an additional amount of work out of them. In order, therefore, 
 to obtain the full equivalent of heat-force or motive force to which 
 we are entitled by the waste of our tissues, it is important that 
 this waste should be thorough, that both the hydrogen and carbon 
 should be converted into the most completely oxidised compounds 
 they are susceptible of forming, the whole of the hydrogen into 
 water, and the whole of the carbon into its most stable mono- 
 carbon compound, namely, carbonic acid, or the ammoniated form 
 of that acid, namely, urea. In some cases of imperfect oxidation, 
 however, we get less oxidised, and more complex, dicarbon mole- 
 cules produced, such, for example, as oxalic acid, which occurs 
 either in its normal saline state, or colligated with urea in the 
 forms of allantoine, oxaluric acid, &c. In cases of yet more im- 
 perfect oxidation, we meet with still less oxidised tricarbon mole- 
 cules, such, for example, as the mesoxalic compound which, by its 
 colligation with urea, forms uric acid. We may even have tetra- 
 carbon molecules such as succinic acid, pentacarbon molecules 
 
INTERMEDIATE OXIDATION PRODUCTS. 1 09 
 
 such as amido-valeric acid or phocine, hexacarbon compounds 
 such as amido-caproic acid or leucine, and heptacarbon com- 
 pounds such as the benzoic residue of hippuric acid, and the 
 salicic residue of tyrosine. 
 
 (i 16.) You will remember that by certain processes of artifi- 
 cial oxidation to which I referred in a former lecture, we obtain 
 from any particular substance a series of less and less complex 
 bodies terminating in carbonic acid ; or, to use again the words 
 of Gerhardt, we gradually descend the scale of complexity, con- 
 verting the original substance into more and more simple products 
 by successively burning off a portion of its carbon and hydrogen. 
 In other cases, however, as in some of Gorup-Besanez's experiments 
 upon the oxidation effected by ozone in alkaline liquids, whether or 
 not a series of bodies intermediate between the initial substance 
 and final carbonic acid are really formed, we are quite incapable of 
 detecting them, and consequently, of tracing their metamorphoses. 
 The constituent carbon-atoms of the original substance seem, at 
 any rate, to become at one step completely isolated and oxidised. 
 Whether, therefore, the more complex molecules formed by natural 
 tissue-oxidation are to be regarded as direct, but intermediate, 
 products of the principal oxidation, or as by-products resulting 
 from subsidiary processes, is at present an open question, though 
 the balance of evidence with regard to certain products, at any rate, 
 seems to be in favour of the latter view. In any case, however, the 
 formation and even excretion of some or other of these bodies, in 
 greater or less proportion, according to the nature of the organ- 
 ism, uric acid largely in birds and land-reptiles, hippuric acid 
 largely in herbivora, and both acids sparingly in mankind are 
 obviously normal or healthy actions. By the excretion of such 
 imperfectly burned substances, indeed, a certain amount of 
 force does not become utilised within the animal, but this pro- 
 digality of force in organic nature is far inferior to that which 
 we observe in the inorganic world. Some of these inter- 
 mediate products of tissue metamorphosis, more particularly 
 the hippuric and uric acids, leucine and tyrosine, are of suffi- 
 ciently constant occurrence and general interest to deserve our 
 
IIO ANIMAL CHEMISTRY LECTUEE Y. 
 
 special examination. Hippuric acid we have already discussed 
 somewhat fully, while the consideration of uric acid I must 
 postpone to my next lecture. There remain, then, only leucine 
 and tyrosine ; but, before adverting to the natural occurrence 
 of these bodies in the living and dead body, let me direct your 
 attention for a short time to certain allied products obtainable 
 from nitrogenous tissue by artificial processes. 
 
 (117.) When flesh, for instance, is submitted to the action of 
 the oxidising agent most commonly employed by chemists 
 namely, a mixture of sulphuric acid with either bichromate of 
 potassium, or peroxide of manganese there are produced a con- 
 siderable number of monobasic acids, to which I shall refer more 
 particularly hereafter, together with several of their associated 
 aldehydes and nitriles. Now the relationship of an aldehyd to 
 its corresponding acid and alcohol is very simple, and may be 
 exemplified by common or vinic aldehyd among fatty, and by 
 benzoic aldehyd among aromatic compounds. Thus, when vinic 
 alcohol is submitted td oxidation, it does not simply take up an 
 additional dose of oxygen, but instead gives up a portion of its 
 hydrogen to the oxgenant, being thereby converted into alcohol 
 dehydroffenatus or aldehyd, thus : 
 
 Alcohol Oxygen Water Aldehyd 
 
 C 3 H 6 + = H,0 + C a H 4 
 
 The resulting aldehyd is a much more readily oxidisable substance 
 than the original alcohol, and upon exposure to air, is rapidly con- 
 verted by direct absorption of oxygen into acetic acid, thus : 
 
 Aldehyd Oxygen Acetic acid 
 
 C^H 4 + C 2 H 4 2 
 
 Similarly, benzyl-alcohol is not susceptible of mere oxidation, but, 
 by the action of oxygenants, is dehydrogenised into benz-aldehyd, 
 or essential oil of bitter almonds, 
 
 Benzyl-alcohol Oxygen Water Benz-aldehyd 
 
 C 7 H 8 -f = H a O + C 7 H 6 
 
RELATION OF ALDEHYDES TO ACIDS. Ill 
 
 which, upon exposure to air, quickly changes by a direct absorp- 
 tion of oxygen into benzoic acid, thus : 
 
 Benz-aldehyd Oxygen Benzoic acid 
 
 C 7 H 6 + C 7 H 6 S 
 
 Oxygen, then, which removes hydrogen from the alcohols, attaches 
 itself directly to the aldehydes, and thereby distinguishes the one 
 class of compounds from the other ; even when, as in the case of 
 ally 1-alcohol and propionic aldehyd, the two bodies have the same 
 ultimate composition, represented in their case by the empiric 
 formula C 3 H 6 O. 
 
 (118.) Although, however, the characteristic property of the 
 aldehydes is to absorb oxygen with conversion into acids, they 
 may nevertheless be rehydrogenised into alcohols, as by the 
 method of Wurtz referred to in my last lecture, thus : 
 
 Benz-aldehyd Hydrogen Benzyl- alcohol 
 
 C 7 H 6 + H a C 7 H 8 
 
 Or, still more curiously, one moiety of the reacting aldehyd may 
 be oxidised into the corresponding acid or its salt, and the other 
 moiety simultaneously hydrogenised into the alcohol, as in Can- 
 nizzaro's well-known process : 
 
 Benz-aldehyd Potash Potas. benzoate Benzyl-alcohol 
 
 2C 7 H 6 + KHO = C 7 H 5 K0 3 + C 7 H 8 
 
 Correlated, then, with every alcohol and acid is an intermediate 
 aldehyd, several of which bodies, in addition to benz-aldehyd, are 
 familiarly known to us in the form of essential oils. Thus, the 
 essential oils of chamomile, cinnamon, spiraea, and rue, contain 
 the angelic, cinnamic, salicic, and methyl-rutic aldehydes, con- 
 vertible by oxidation into the angelic, cinnamic, salicic, and rutic 
 acids respectively. The prime characteristic then of the aldehydes 
 is their acidifiability by direct absorption of oxygen ; so that, con- 
 sidered as products of oxidation, they may be looked upon as in- 
 completely formed acids. When, therefore, we find that by treating 
 
112 ANIMAL CHEMISTRY LECTURE V. 
 
 muscle with some oxidising agent we obtain certain aldehydes 
 together with their corresponding acids, it only shows that our 
 oxidising agent is employed in deficiency, or rather that the pro- 
 ducts, being readily volatile, are not left in contact with the heated 
 oxidising mixture sufficiently long to be entirely converted into 
 acids. 
 
 (119.) But in addition to aldehydes and acids, certain nitriles, 
 more particularly formio-nitrile and valero-nitrile, have been 
 obtained by muscle oxidation. You may remember that I have 
 already, in previous lectures, made mention of prussic acid, cyanide 
 of hydrogen, or formio nitrile ; of cyanide of methyl, or aceto- 
 nitrile ; of cyanogen, or oxalo-nitrile, &c. The majority of these 
 nitriles are procurable either by the action of the simplest organic 
 nitrile, namely, prussic acid, upon the preceding alcohol, or by 
 the action of ammonia upon the co-equal acid, with elimination 
 of water, as shown below in the case of valero-nitrile : 
 
 Water Valero-nitrile 
 
 H 2 = C 5 H 9 N 
 
 Water Valero-nitrile 
 
 Butyl-alcohol 
 
 Prussic acid 
 
 C 4 H I0 H 
 
 h CHN 
 
 Valeric acid 
 
 Ammonia 
 
 C 5 H I0 O a H 
 
 H 3 N 
 
 The first process is a true synthesis, or passage from a lower to 
 a higher carbon group, as explained in my last lecture when 
 speaking of general synthetic methods ; while the second is merely 
 a metamorphosis of the acid into its dehydrated ammonia-salt. 
 Now by treatment with caustic alkalies, the several nitriles or 
 organic cyanides absorb water to reproduce ammonia and a salt 
 of the acid to which they respectively appertain, thus : 
 
 Valero-nitrile Potash Water Ammonia Pot.valerate 
 
 C 5 H 9 N + KHO + H a O = H 3 N + C 5 H 9 KO a 
 
 Prussic acid Potash Water Ammonia Pot. formiate 
 
 CHN -t- KHO + H 2 = H 3 N + C H KO Z 
 
 Accordingly, the occurrence of nitriles, in addition to acids and 
 aldehydes, only shows that certain oxidation -products of the carbo- 
 
ACIDS OF FLESH OXIDATION. 113 
 
 hydrate constituents of muscle exist partly in combination with 
 an ammonia-residue derived from its nitrogenous constituents, 
 whereby, instead of the normal acids, we obtain, in some cases, 
 their dehydrated ammonia salts ; whence it follows that the ni- 
 triles, like the aldehydes, do not call for any separate considera- 
 tion, but may be discussed with their respective acids, of which 
 indeed, they constitute mere varieties. 
 
 ( 1 20.) The following acids, then, in the state of acids, aldehydes, 
 and nitriles, have been obtained by the oxidation of flesh with a 
 mixture of sulphuric acid and peroxide of manganese, as now 
 taking place in the retort upon the table : 
 
 Fatty Acids Aromatic Acids 
 
 Cg H I2 2 Caproic 
 
 C 5 H J0 2 Valeric 
 
 C 4 H 8 2 Butyric 
 
 C 3 H 6 2 Propionic C 8 H 8 2 Toluic ? 
 
 C 2 H 4 2 Acetic C 7 H 6 2 Benzoic 
 
 C H 2 2 Formic C 6 H 4 3 Collie ? 
 
 These several acids, you observe, contain but two atoms of 
 oxygen in their respective molecules, In reality, however, we 
 cannot doubt that corresponding acids with three and four atoms 
 of oxygen are also formed, as in other modes of oxidation ; but 
 such poly-oxygen acids being much less volatile than their di- 
 oxygen congeners, instead of being removed at once from the oxi- 
 dising mixture, remain in contact with it for so great a length of 
 time are subjected in fact to such a prolonged process of oxida- 
 tion that they become more or less completely destroyed, or, 
 in other words, converted into carbonic acid. 
 
 ( 1 2 1 .) Now, there are two special points of interest connected 
 with the above lists of muscle-acids, which are arranged, you 
 observe, in the order of simplicity, instead of complexity, as 
 heretofore. The first point to which I would direct your at- 
 tention is, that even the most complex of them is comprised 
 among the simpler members of its particular series. Thus, while 
 by the direct or indirect oxidation of fat we may obtain acids 
 
 I 
 
114 ANIMAL CHEMISTRY LECTURE V. 
 
 with eight, nine, ten, and even sixteen atoms of carbon, the most 
 complex acids as yet obtained by the artificial oxidation of flesh, 
 are those with five, six, and seven atoms ; for the production of 
 toluic acid is at any rate very doubtful. Now, although this 
 oxidation of flesh has not been performed with sufficient fre- 
 quency, or variety of process, to warrant our laying much stress 
 upon the results obtained, still less of affirming that no more 
 complex aplone molecules than those with seven atoms of carbon 
 are in any case procurable, nevertheless the above observation, 
 taken in conjunction with other facts, has an interest which must 
 not be overlooked. Thus, among all the products of tissue-meta- 
 morphosis occurring in the living body, with the possible excep- 
 tion of indigo, which, like toluic acid, contains eight carbon 
 atoms ; among all the products of the putrefactive decomposition 
 of dead animal tissue ; among all the products obtainable by its 
 direct oxidation as just referred to ; and among all the products 
 obtainable by its indirect oxidation with acids or alkalies, not a 
 single aplone molecule with more than seven atoms of carbon has 
 yet been positively observed. 
 
 (122.) Comparing the ascertained constitution of olein, for 
 instance, with the hypothetical constitution of some protein body, 
 we know that the molecule of olein contains 57 carbon atoms, 
 and that these atoms pertain to the residues of four distinct 
 aplone molecules, namely, three molecules of oleic acid, contain- 
 ing each 1 8 carbon-atoms, and one molecule of glycerin, con- 
 taining 3 carbon-atoms. Accordingly, by the breaking up of 
 olein we may obtain aplone molecules with as many as 18 
 atoms of carbon, and with successively fewer and fewer atoms, 
 according to the degree of oxidation, until finally we get such 
 bodies as succinic acid C 4 H6O 4 , oxalic acid C 2 H 2 O 4 , and carbonic 
 acid CH 2 3 ; while, among intermediate compounds, the palmitic 
 acid with 16, the sebacic and rutic acids with 10, and the suberic 
 acid with 8, are certainly, and other acids with from i to 18 
 carbon-atoms, in all probability, procurable. On the other hand, 
 the composition of the molecule of albumin is at present unde- 
 termined ; but assuming, according to the balance of authority, 
 
AROMATIC ACIDS OF FLESH. 115 
 
 that it contains 72 carbon-atoms, what is the number and what 
 the complexity of the aplone molecules between which these 
 7 2 carbon atoms are divided ? All we can say is that no aplone 
 molecule with more than 7 or 8 carbon atoms has hitherto been 
 produced by its natural or artificial decomposition, so that its 
 constituent residues probably appertain to much simpler mole- 
 cules, than do the residues of ordinary fat. 
 
 (123.) The other point of interest connected with the artificial 
 oxidation of flesh is, that the acids and aldehydes thereby 
 produced belong to both our primary series, namely, the fatty 
 and the aromatic ; so that while the oxidation of muscle in the 
 laboratory yields us certain fatty acids which are producible by the 
 similar oxidation of fat, it yields in addition certain acids of the 
 aromatic series that are not producible by the oxidation of fat. 
 This result acquires additional importance from the consideration 
 that chemists are at present quite unable to transform fatty into 
 aromatic compounds, or vice versa, by any definite reaction. It 
 is true that when various bodies of the fatty class are subjected 
 to a full red heat, some products belonging to the aromatic class 
 are formed; but this transformation is one that we cannot 
 trace. It belongs to the class of changes which are termed 
 destructive or indefinite, in contra-distinction to those easily 
 traceable and definite reactions which we call more especially 
 metamorphic. By no ordinary treatment with reagents, and cer- 
 tainly by none of the modes of treatment to which muscle has 
 been subjected, are we able to pass from the fatty to the aromatic 
 class of bodies ; and accordingly, when we find, by treating 
 flesh, &c., with sulphuric acid and manganese, that both aro- 
 matic and fatty acids are produced, we have a right to infer that, 
 be the exact composition of the flesh what it may , it certainly 
 contains, in addition to its ammonia residues, one or more resi- 
 dues of compounds belonging to the fatty, and one or more 
 residues of compounds belonging to the aromatic class. This 
 conclusion becomes even more irresistible when we consider 
 that not only by the direct oxidation of nitrogenous tissue now 
 taking place on the table, but by its indirect oxidation, through 
 
 i2 
 
Il6 ANIMAL CHEMISTRY LECTURE V. 
 
 the agency of acids and alkalies, as well as by its post-mortem 
 putrefactive decomposition, and its ante-mortem natural trans- 
 formation, compounds belonging to both the aromatic and fatty 
 class simultaneously make their appearance. 
 
 (124.) Among these compounds, leucine and tyrosine de- 
 mand our special attention leucine being an ammoniated term 
 of the 6 -carbon fatty, and tyrosine an ethyl-ammoniated term of 
 the 7 -carbon aromatic acid group. These two bodies occur in 
 association with one another under the following circumstances : 
 In the first place, they result from the putrefaction of flesh, 
 cheese, white of egg, gluten of wheat, &c. They have also been 
 detected in fresh blood, and occur very generally in glandular 
 tissue and secretion leucine, however, in much the larger pro- 
 portion, so that in some cases where it has been recognised, the 
 tyrosine probably accompanying it has been overlooked. Leu- 
 cine, more particularly, has been found in the spleen, thymus, 
 thyroid, and lymphatic glands ; and, indeed, from its occurrence 
 in the two former, received at one time the names of lienine and 
 thymine. Both compounds are met with most abundantly in the 
 pancreas and its secretion, but they also occur in the liver and 
 bile, and in the kidneys and urine, particularly in certain patho- 
 logical conditions. Leucine has also been recognised in the 
 salivary and intestinal glands and their secretions, and is, accord- 
 ing to Boedeker, an ordinary constituent of pus. 
 
 (125.) That leucine and tyrosine pre-exist in the living body, 
 and are not merely post-mortem products, is evident from the 
 circumstance of their having been detected in the urinary, pan- 
 creatic, and, in the case of leucine, purulent and salivary secre- 
 tions of living animals. But more than this. A long time back, 
 De la Rue noticed that tyrosine existed pre-formed in the dried 
 cochineal insect ; and Staedeler, by crushing up various living 
 animals in a mortar with a mixture of powdered glass and alcohol, 
 has recently recognised the presence of both tyrosine and leucine 
 in invertebrata belonging to all the principal non-infusorial 
 classes. Thus it is manifest that leucine and tyrosine are pos- 
 sessed of a very extensive natural distribution. As yet indeed 
 
PRODUCTION OF LEUCINE AND TYROSINE. 1 1/ 
 
 they have not been detected in the juice of flesh, a circumstance 
 which appears the less surprising, however, when we remember 
 that even urea itself, an undoubted product of muscular meta- 
 morphosis, has never been satisfactorily recognised in healthy 
 muscular tissue, probably on account of its rapid removal by the 
 circulation. 
 
 (126.) Artificially, leucine and tyrosine may be produced not 
 only from flesh, but also from blood-albumin, white of egg, gluten, 
 casein or cheese, gelatin, chondrin, elastic tissue, horn, nails, fea- 
 thers, hair, hedgehog-spines, cockchafer- elytra, &c. &c., by one 
 or other of two well-known indirect processes of oxidation, which 
 consist respectively in boiling the above-named substances for 
 many hours with some mineral acid, and in fusing them gently 
 with caustic alkali. Now, these two apparently opposite processes 
 are the same in principle. In each case, the acid or alkali merely 
 enables the protein or gelatinoid substance to react with water 
 H 2 O, whereby one portion of it becomes oxidised into leucine, 
 tyrosine, &c., while another portion is hydrogenised into divers 
 products. The nature of this action is best exposed by consider- 
 ing the case of some tolerably simple well-characterised sub- 
 stance such, for instance, as benz-aldehyd, or essential oil of 
 bitter almonds. When this body is treated with caustic potash, 
 one-half of it becomes oxidised into benzoic acid, which appears 
 in the form of an alkaline benzoate, and the other half is hy- 
 drogenised into benzyl-alcohol, as I mentioned a few minutes 
 ago: 
 
 Benz-aldehyd Water Benzoic acid Benzyl-alcohol 
 
 aC 7 H 6 + H a O = C 7 H 6 O a + C 7 H 8 
 
 When, however, a large excess of alkali is used, and the action 
 allowed to become more violent, the hydrogen does not enter 
 into any combination, but is simply liberated in the gaseous state, 
 thus : 
 
 Benz-aldehyd Water Benzoic acid Hydrogen 
 
 C 7 H 6 + H 3 = C 7 H 6 3 + H 8 
 
Il8 ANIMAL CHEMISTRY LECTURE V. 
 
 Now, in fusing the above-mentioned animal substances with 
 caustic alkali, a greater or less proportion of gaseous hydrogen 
 from the decomposed tissue-water is similarly liberated ; whereas, 
 in boiling them with mineral acids, the same hydrogen, instead 
 of being liberated, effects certain hitherto unexamined combina- 
 tions or reactions ; while, in both cases, the oxygen of the decom- 
 posed water effects the production of leucine and tyrosine. Here 
 are specimens of leucine and tyrosine obtained in this way by the 
 action of sulphuric acid on feathers, and here another fine speci- 
 men of tyrosine, extracted from cochineal, all kindly lent me by 
 Dr. Hugo Miiller. 
 
 (127.) Thus the conclusion that nitrogenous tissue contains a 
 something related to the fatty group and a something related to 
 the aromatic group, suggested by the results of its direct oxida- 
 tion with peroxide of manganese or chromic acid, is confirmed by 
 the results of its indirect oxidation with acids and alkalies. 
 Among fatty compounds, we obtain, in the one case, caproic 
 acid, and, in the other, amido-caproic acid, or leucine; while 
 among aromatic compounds we obtain, in the one case, benzoic 
 acid, and, in the other, ethyl-amido-salicic acid, or tyrosine. 
 Now, let us consider the constitution and respective relationships 
 of these amidated bodies. 
 
 Starting from our primary fatty acids, we may obtain the 
 following series of chlorine derivatives : 
 
 Fatty Acids a-Derivatives 
 
 C H a 0, Formic C H Cl O a Chloro-formic? 
 
 C a H 4 0, Acetic C a H 3 Cl 0, Chlor-acetic 
 
 C 3 H 6 O z Propionic C 3 H 5 Cl 0, Chloro-propionic 
 
 C 4 H 8 O a Butyric C 4 H 7 Cl O z Ckloro-butyric 
 
 C 5 H I0 O a Valeric C 5 H 9 Cl 0, Chloro-valeric 
 
 C 6 H Ia O a Caproic C 6 HnCl O a Chloro-caproic 
 
 Now, if in each of these derived acids we replace the residue 
 of hydrochloric acid, or Cl, by the residue of water, or HO, we 
 obtain a new series of acids ; whereas, if we replace it by the 
 residue of ammonia, orH 2 N, we obtain a series of amides, thus: 
 
NATURE OF GLYCOCINE AND LEUCINE. 119 
 
 0-Acids V-Amides 
 
 C H (H0)0 3 Carbonic C H (H a N)0, Carbamic ? 
 
 C, H 3 (HO) 3 Glycolic C a H 3 (H a N) 0, Glycocine 
 
 C 3 H 5 (HO)0, Lactic C 3 H 5 (H 2 N)O a Alanine 
 
 C 4 H 7 (HO)0, Bulatic C 4 H 7 (H Z N)0, Bulatine 
 
 C 5 H 9 (HO) 0, Phocic C 3 H 9 (H,N) O a Phocine 
 
 C 6 H n (HO)0, Leucic C 6 H XI (H,N)0, Leucine 
 
 Excluding the mono-carbon compounds, whose behaviour in 
 other cases is frequently different from that of their more complex 
 homologues, we find that the /3-acids and y-amides may be obtained 
 from the corresponding fatty acids, through the intervention of 
 their a-chloro-derivatives, as above described. Excluding, again, 
 the mono-carbon compounds, we obtain the /3-acids by acting 
 upon the several y-amides with nitrous acid, whereas by acting on 
 them with an electro-negative chloride and water, we obtain the 
 a-chloro -acids, convertible into the normal acids by treatment 
 with nascent hydrogen. The relation, therefore, of glycocine to 
 the gly colic and chlor-acetic acids, and of leucine to the leucic 
 and chloro-caproic acids, is merely the relation of ammonia 
 H.H 2 N, to water H.HO, and to chlorhydric acid H.C1, as I 
 explained to you more fully in my first lecture. 
 
 (128.) Glycocine I have referred to on several previous 
 occasions. It is produced, together with leucine and tyrosine, by 
 the action of acids or alkalies upon nitrogenous, and more par- 
 ticularly gelatigenous tissues, whence its original name of sugar 
 of gelatin. It exists as a constituent residue of sarcosine and 
 kreatine, as well as of the hippuric and glyco-cholic acids. The 
 next body, alanine, is obtainable from acet-aldehyd by treatment 
 with aqueous prussic acid in the same way that leucine is obtain- 
 able from valer-aldehyd, as mentioned also in my first lecture. 
 By analogy it should be called lactine, were not this appellation 
 otherwise appropriated namely, by milk-sugar CaH^Oe, whose 
 formula, you observe, is exactly twice that of lactic acid C 3 H6O 3 , 
 a compound to which this sugar is in some way or other very 
 closely related. It is curious that while lactic acid exists so 
 largely in flesh-juice, gastric juice, &c., alanine, which is 
 only an ammoniated form of lactic acid, should never have 
 
I2O ANIMAL CHEMISTRY LECTURE V. 
 
 been recognised in any natural or artificial product of animal 
 tissue. I am not aware that bulatine has yet been obtained 
 from any source whatever ; while phocine has been noticed upon 
 one occasion only by Gorup-Besanez in the pancreas of an ox. 
 Leucine, on the other hand, as I have already remarked, exists 
 naturally in, and is producible artificially from, a great variety of 
 animal and vegetable bodies. 
 
 (129.) In commencing the study of the constitution of tyro- 
 sine, we are at once struck by the great resemblance which its 
 formula bears to that of hippuric acid. You observe that the 
 molecule of tyrosine differs in ultimate composition from the 
 molecule of hippuric acid, by an excess of two atoms of hydrogen, 
 thus : 
 
 C 9 H 9 N 3 Hippuric acid 
 C 9 H U N 3 Tyrosine 
 
 Inasmuch, however, as complex molecules of this description 
 are built up of the residues of several simpler molecules, it may 
 happen, and indeed not unfrequentlydoes happen, that the numbers 
 of the atoms of carbon, hydrogen, oxygen, and nitrogen in two or 
 more complex bodies, approximate very closely to, or are even 
 identical with, one another ; whilst the bodies themselves are com- 
 posed of very different residues, and accordingly have no real rela- 
 tionship of proximate constitution. Such, however, is not the 
 case with hippuric acid and tyrosine. Each of these bodies is 
 composed of three constituent residues namely, an ammonia 
 residue, a 2 -carbon residue belonging to the fatty, and a y-carbon 
 residue belonging to the aromatic class. That the aromatic resi- 
 due of tyrosine, however, differs from the residue of hippuric 
 acid in belonging to the salicic instead of the benzoic sub-group, 
 is evident from a variety of considerations pointed out by Schmitt 
 and Nasse, whose recently published views on the constitution of 
 tyrosine, if not demonstrated with absolute certainty, are so pro- 
 bable in themselves, and so supported by collateral testimony, as 
 to leave us in very little doubt as to their substantial correctness. 
 Thus tyrosine agrees with other salicic compounds in the charac- 
 teristic properties of yielding phenol by distillation, and chloranil 
 
INDIGO AND SALICIC COMPOUNDS. 121 
 
 by chlorination, and, after suitable treatment, of striking a purple 
 colour with ferric salts, as you perceive. This last reaction 
 constitutes Piria's well-known test for tyrosine. Now, according 
 to Schmitt and Nasse, the particular member of the salicic sub- 
 group which enters into the constitution of tyrosine is salicic 
 acid, whose formula, you observe, differs from that of benzoic 
 acid by an excess of one atom of oxygen. Moreover, benzoic 
 acid is isomeric with salicic aldehyd, and salicic acid with ampelic 
 or oxi-benzoic acid, thus : 
 
 C 7 H 6 3 Benzoic acid, and salicic aldehyd 
 C 7 H,50 3 Ampelic acid, and salicic acid 
 
 (130.) With regard to the natural history of salicic compounds, 
 salicin is a glucoside of salicylic alcohol, and oil of spiraea con- 
 stitutes salicic aldehyd, while oil of wintergreen is composed 
 largely of methylic salicate, as I have already explained. That 
 some salicic grouping, moreover, occurs as a constituent residue of 
 indigo CgHyTO, is shown by the following considerations. 
 When, for example, indigo experiences decomposition by treatment 
 with reagents, its single atom of nitrogen and one of its eight atoms 
 of carbon are more particularly affected ; and hence, as a convenient 
 representation of its probable molecular constitution, we may as- 
 sociate this mobile carbon and nitrogen with one another, and so 
 write the formula of indigo upon the y-carbon or salicic type, 
 thus : 
 
 C 7 H 5 (CN)0. Indigo or cyan-salicol 
 
 Now, by boiling indigo for a long time with oxidising. agents, 
 and by treating salicic acid with strong nitric acid, we obtain 
 identically the same product, which has received the names of 
 anilic, indigotic, and nitro-salicic acid, thus : 
 
 Indigo Oxygen . Anilic acid Carb-anhyd. 
 
 C 7 H 5 (CN)0 + 6 C 7 H 5 (NO a )0 3 + C0 2 
 
 Salicic acid Nitric acid Nitro-salicic acid Water 
 
 C 7 H 6 3 + (NO^HO = C 7 H 5 (NO a )0 3 + H.HO 
 
122 ANIMAL CHEMISTRY LECTURE V. 
 
 Again, when indigo is gently fused with caustic alkali it under- 
 goes a simultaneous hjdration and oxidation, whereby it is con- 
 verted into anthranilic acid, thus : 
 
 Indigo Water Oxygen Anthranil. acid Carb-anhyd. 
 
 C 7 H 5 (CN)0 + H,0 + 3 = C 7 H 5 (H 2 N)O a + C0 a 
 
 When, however, the reaction takes place more violently, we get 
 salicic acid produced instead, thus : 
 
 Carb- Am- 
 
 Indigo Water Oxygen Salicic acid anhyd. monia 
 
 C 7 H 5 (CN)0 + 2H Z + O z = C 7 H 5 (HO)O a + C0 a + H 3 N 
 
 You observe that the anthranilic and salicic acids furnish us 
 with another instance of that relationship between amidated and 
 hydrated compounds to which I have so often adverted. 
 
 Seeing from the observations and researches of Prout, Heller, 
 Debuyne, Hassall, Scheerer, Schunk, and others, that human urine 
 not unfrequently deposits indigo spontaneously, and contains ha- 
 bitually an indigo-yielding substance known as indican, which is 
 probably a glucoside of white or hydrogenised indigo, we come 
 to the conclusion that while a salicic residue in the form of tyro- 
 sine is a constant product of the natural and artificial oxidation of 
 nitrogenous tissue, another salicic residue in the form of indigo or 
 indican is a usual ingredient of that secretion by which the pro- 
 ducts of disintegrated nitrogenous tissue are principally discharged. 
 Moreover, this occurrence of indigo in urine further exemplifies a 
 point with which we must all, I believe, have been more or less 
 struck, both in this and previous lectures namely, the thorough 
 interdependence of vegetable and animal chemistry, as shown by 
 the frequent relationship and even identity of products formed in 
 vegetable and animal organisms. 
 
 (131.) Another physiological point of interest connected with 
 salicic compounds is their occurrence in the urine in the form of 
 salisuric acid. It is well known that when benzoic aldehyd or 
 acid is taken internally, it makes its appearance in the urine in 
 
CASTOREUM AND PHENYLIC COMPOUNDS. 123 
 
 the form of glyco-benzoic or hippuric acid C 9 H 9 NO 3 ; and, no 
 doubt, some, at any rate, of the hippuric acid excreted both by 
 vegetable and mixed feeders is derived from the ingestion of cer- 
 tain benzo-genetic articles of food. Similarly, the administration 
 of salicin and salicic aldehyd or acid is followed by the appear- 
 ance in the urine of glyco-salicic or salisuric acid C 9 H 9 NO 4 , 
 readily decomposible into glycocine and salicic acid, just as hip- 
 puric acid is decomposible into glycocine and benzoic acid. 
 Hence the salisuric and salicic acids may be regarded as normal 
 constituents of the urine of the beaver, with which willow bark 
 is well known to be a favourite food. The occurrence of 
 salicic compounds in castoreum also is doubtless due in a similar 
 manner to the food of the beaver. Castoreum, moreover, contains 
 phenol, or coal-tar kreosote, which, according to Staedeler and 
 others, is an ordinary constituent of human urine, and an impor- 
 tant contributor to its characteristic odour. Now, the relation of 
 phenol to salicic acid is very simple. Under suitable conditions 
 salicic acid breaks up into phenol and carb -anhydride, which, 
 under other conditions, re-unite to form salicic acid, thus : 
 
 Phenol Carb-anhyd. Salicic acid 
 
 C 6 H 6 + CO, = C 7 H 6 3 
 
 Remembering that urine of a dark brown colour, or becoming 
 of a brown colour by oxidation, contains a pigment which is in 
 some way or other related to indigo, and also that an apparently 
 similar brown urine is occasionally passed after the internal or 
 external administration of phenol, kreasote, tar-oil, &c., this rela- 
 tionship of salicic and phenyl compounds presents a considerable 
 pathological interest. Phenol may indeed be considered as the 
 nucleus not only of salicic acid, but likewise of tyrosine and indigo ; 
 from both of which it is also readily obtainable. Moreover, by 
 treatment with chlorine, all four bodies yield the same 6-carbon 
 ultimate product, namely, chloranil C6C1 4 O 2 , or perchloroquinone. 
 
 (132.) It now only remains for us to consider the ultimate 
 constitution of tyrosine, and its analogy to hippuric acid. Starting 
 
124 ANIMAL CHEMISTRY LECTURE T. 
 
 from water and ammonia, we have the following alcoholic deriva- 
 tives : 
 
 Hydrates Amines 
 
 ^ I Hydric H H 1 ^ 
 
 ^ I Methylic C H 3 H } N Methyl-ainin 
 
 Ethylic N Ethyl-amine 
 
 Now, replacing an atom of hydrogen or the atom of chlorine, 
 in acetic and chloracetic acid respectively, by the residue of water, 
 HO, we obtain glycolic or oxiacetic acid ; replacing it by the resi- 
 due of ammonia, HHN, we obtain amid-acetic acid, or glycocine; 
 replacing it by the residue of methylamine, CH 3 HN, we obtain 
 methyl-amid- acetic acid, or methyl-glycocine, or sarcosine; and, 
 lastly, replacing it by the residue of ethylamiue, C 2 H 5 HN, we 
 obtain ethyl-amid-acetic acid, or ethyl-glycocine, thus: 
 
 Acetic Derivatives 
 
 C 2 H 4 2 Acetic acid 
 
 C 2 H 3 2 (C1) Chlor-acetic acid 
 
 C 2 H 3 2 (HO) Glycolic acid 
 
 C 2 H 3 2 (H 2 N) Glycocine 
 
 CJE 3 2 (C H 4 N) Sarcosine or methyl-glycocine . 
 
 C a H 3 2 (C 2 H 6 N) Ethyl-glycocine 
 
 The constitution and mutual relationship of the above tabulated 
 bodies have been established as well by their recomposition as 
 by their decomposition. In the case of tyrosine, however, we 
 have only a knowledge of its decompositions to fall back upon, 
 from which, however, it would appear, according to Schmitt and 
 Nasse, that it corresponds most nearly in constitution with sarco- 
 sine or methyl-glycocine among natural products, and still more 
 nearly with the artificial ethyl-glycocine of Heintz. Just, indeed, 
 as sarcosine is acetic acid in which an atom of hydrogen is replaced 
 by the residue of methylamine, so is tyrosine salicic acid in which 
 an atom of hydrogen is replaced by the residue of ethylamine, 
 thus: 
 
CONSTITUTION OF TYROSINE. 125 
 
 C 2 H 3 (C H 3 .HN)0, Sarcosine, or methylamid-acetic acid 
 C 7 H 5 (C a H 5 .HN)0 3 Tyrosine, or ethylamid-salieic acid 
 
 (133.) Lastly, Dessaignes having prepared hippuric acid by 
 substituting a residue of glycocine (C 2 H 3 O 2 .HN) for the atom of 
 chlorine in chlorobenzoic aldehyd C 7 H 5 (C1)O, the relationship of 
 hippuric acid and tyrosine to one another and to the benzoic and 
 psrsalicic acids may be shown by the following formulae, the par- 
 entheses of which are merely intended to point out the exchanged 
 portions of the original and derived bodies : 
 
 Benzoic acid Hippuric acid 
 
 C 7 H 5 (HO)0 C 7 H 5 (C 2 H 3 Z .HN)0 
 
 Persalicic acid Tyrosine 
 
 C 7 H 5 (HO)0 3 C 7 H 5 (C 2 H 5 .HN)0 3 
 
 Now, ethylamine is indirectly convertible into glycocine by 
 oxidation, whereas salicic acid is convertible into benzoic acid 
 by deoxidation; or the fatty 2-carbon constituent of hippuric 
 acid is more highly oxidised, whilst its aromatic /-carbon con- 
 stituent is less highly oxidised than are the corresponding residues 
 of tyrosine.* Doubtless, therefore, the natural production of the 
 two bodies by tissue metamorphosis takes place under diiferent 
 conditions. Their joint occurrence in the urine, however, together 
 with that of indigo and phenol, confirms the inference we have 
 already drawn that be the chemical constitution of nitrogenous 
 tissue what it may, there exist 'in its molecule one or more group- 
 ings belonging to the fatty family, and yielding fatty oxidation- 
 products, together with one or more groupings belonging to the 
 aromatic family, and yielding aromatic oxidation-products. In my 
 next lecture we shall consider the intimate constitution of uric 
 acid and its congeners. 
 
 * Since this lecture was delivered, Earth has rendered it probable that 
 the aromatic constituent of tyrosine is not ordinary salicic acid, but the 
 particular variety or isomer of it, which is known as paroxibenzoic acid. 
 
126 ANIMAL CHEMISTRY LECTURE VI. 
 
 LECTURE VI. 
 
 Uric acid Its excretion throughout the animal kingdom History of its 
 chemical examination Its undecomposibility save by oxidation Pro- 
 bable pre-existence in it of urea Classification of uric acid products into 
 an-ureides, mon-ureides, and di-ureides Also into carbonic, oxalic, and 
 mesoxalic compounds Oxidation of mesoxalic into oxalic, and of oxalic 
 into carbonic acid TJreides formed by an elimination of either one or two 
 atoms of water Hydrogenised carbonic, oxalic, and mesoxalic compounds 
 Table of uric acid products Additional intermediate and amidated bodies 
 Oxalic mon-ureides and di-ureides Mesoxalic mon-ureides associated 
 with barbituric acid Mesoxalic di-ureides, including hypoxanthine, xan- 
 thine, and uric acid Their mutual convertibility Eelationship of xan- 
 thine to guanine The pseudo-uric and uroxanic acids Uric acid viewed 
 simply as a compound of carbonic oxide and urea Excretion of urate of 
 ammonia by birds and insects Dynamic values of oxidation into uric 
 acid and urea respectively Function of lungs supplemented by discharge 
 of uric acid from kidneys Tissue metamorphosis affected by alterative 
 medicines Activity of loosely combined oxygen Nitric oxide as a carrier 
 of active oxygen Comparison of iodine with nitric peroxide Eesem- 
 blances and differences between iodine and chlorine Their actio*n as 
 oxygenants in presence of water Free chlorine more active than iodine, 
 and combined iodine more mobile than chlorine Eeducing action of iod- 
 hydric acid Alterative action of iodine dependent on its chemical mobi- 
 lity Similar characters of arsenic, mercury, &c. Effect of alkalies on 
 tissue-oxidation Gorup-Besanez's experiments with ozone Conclusion. 
 
 (134.) OF all the incompletely oxidised products of tissue- 
 metamorpliosis, uric acid is, I suppose, the most important, whe- 
 ther regarded from a physiological and pathological, or from a 
 purely chemical point of view. In combination, chiefly with 
 ammonia, it forms the principal urinary constituent voided by 
 insects, land -reptiles, and birds. Normally, it occurs but in 
 small proportion in the urine of man, while it is found in yet 
 
HISTORY OF URIC ACID. I2J 
 
 smaller proportion in that of carnivorous, and can scarcely be 
 said to exist if, indeed, it does habitually exist in that of 
 herbivorous and omnivorous quadrupeds. According to various 
 authorities, it is to be found constantly in the juices of the human 
 spleen, liver, lungs, and brain. The merest traces of it are also 
 met with normally in blood, but its proportion therein under par- 
 ticular forms of disease, such as albuminuria, and more especially 
 gout, becomes very appreciable. In certain cases of gout, indeed, 
 all the fluids of the body are found more or less saturated with 
 uric acid, and some of them even supersaturated, so as to deposit 
 those well-known concretions of urate of sodium, commonly called 
 chalkstones. I need scarcely refer also to the frequent excess of 
 uric acid discharged by the human kidneys, under greater or less 
 derangements of bodily health, and to its deposition in the forms of 
 urinary sediment, gravel, and calculus. Now this acid, as shown 
 by its formula C 5 N 4 H 4 3 , consists of only sixteen elementary 
 atoms, and is consequently, as regards its ultimate composition, a 
 far more simple body than many of those we have previously 
 considered. Nevertheless, the problem of its intimate constitu- 
 tion for a long time baffled all attempts at solution, and cannot, 
 even at the present day, be considered as quite satisfactorily un- 
 ravelled. 
 
 (135.) Uric acid was discovered in 1776 by the renowned 
 Swedish chemist, Scheele ; but it was first submitted to a minute 
 investigation by Liebig and Wohler, whose efforts resulted in the 
 production and identification, among other new bodies, of alloxan- 
 tine, alloxanic acid, dialuric acid, uramile, mesoxalic acid, allan- 
 toine, mycomelic acid, parabanic acid, &c., and whose admirable 
 work, published in 1838, forms the broad and sound basis of all 
 our subsequent knowledge. These chemists had been preceded 
 by Brugnatelli and Prout the discoverers of alloxan and murexide 
 respectively and were succeeded more particularly by Schlieper, 
 Pelouze, Fritzsche, Gregory, and Hlasiwetz. To the number of 
 bodies already described, Schlieper added the leucoturic, allituric, 
 
 dilituric, hydantoic, hydurilic, and allanturic or lantanuric acids 
 
 the last also discovered by Pelouze. In 1 8 5 3 , Gerhardt, in his cele- 
 
128 ANIMAL CHEMISTRY LECTURE YI. 
 
 
 
 brated ' Traite de Cliimie Organique,' gave a very complete account 
 of the then known uric acid products, and, by dividing them into 
 two well-defined natural groups, simplified very greatly the con- 
 ception of their origins and metamorphoses. Among subsequent 
 workers, Strecker has added considerably to our knowledge ; and 
 Baeyer has increased the list of compounds by his discovery of 
 pseudo-uric acid, hydantoine, violantine, and the violuric and 
 barbituric acids, the last-named being a body of very great inte- 
 rest; while he has also thrown considerable light upon the nature of 
 the bodies previously discovered by Schlieper. Moreover, adopt- 
 ing Gerhardt's classification as a basis, and viewing both old and 
 new products from the extreme height of modern doctrine, he has 
 published by far the most complete and connected account of the 
 uric acid group of compounds which has hitherto been given to 
 the world. The scheme which I am about to bring under your 
 notice, and which, I think I may say, is even more comprehen- 
 sive, does not differ greatly from that of Baeyer in principle, and 
 is indebted very largely to him for its elaboration. I propose, 
 however, to differ from him in disregarding altogether the mole- 
 cular arrangement of the different compounds, preferring to limit 
 myself in this, as in previous lectures, simply to questions of 
 origin and relationship. 
 
 (i 36.) I have already told you that the great majority of com- 
 plex organic bodies are built up of the residues of comparatively 
 simple molecules ; that hippuric acid, for instance, is constituted 
 of the residues of benzoic acid and glycocine, while tyrosine is 
 constituted of the residues of salicic acid and ethylamine the 
 glycocine and ethylamine themselves containing residues of am- 
 monia and of glycolic acid and alcohol respectively. Now, uric 
 acid is evidently built up in a similar manner, and contains the 
 residues of several constituent molecules. But a hitherto insupe- 
 rable difficulty in determining its exact mode of construction 
 arises from the circumstance of its never having been decomposed 
 into the actual molecules of which its constituent residues are the 
 representatives, but only into the oxidised, or rather dehydro- 
 genised, products of these molecules. Add to uric acid an atom 
 
EXISTENCE OF UREA IN URIC ACID? 1 29 
 
 of oxygen, so as to burn off two of its atoms of Irydrogen, and it 
 breaks up with the greatest ease, though without this additional 
 oxygen it has hitherto proved undecomposible. You 'will observe 
 from its formula, C 5 N 4 H 4 O 3 , that uric acid contains five atoms of 
 carbon and four atoms of nitrogen, while urea CN 2 H 4 0, contains 
 only one atom of carbon and two atoms of nitrogen. Accord- 
 ingly, we find that when dehydrogenised uric acid undergoes 
 complete decomposition by an absorption of water, it breaks up 
 into two molecules of urea (containing C 2 N 4 ) and one molecule 
 of a non-nitrogenous 3 -carbon acid. Whether, however, the re- 
 sidues of the two molecules of urea, obtainable by the oxidation 
 or dehydrogenation of uric acid, pre-exist in uric acid, the 
 3 -carbon acid alone being the dehydrogenised product, or whe- 
 ther the residue of the resulting 3~carbon acid pre-exists in uric 
 acid, the two atoms of urea being formed by dehydrogenation, 
 there is no evidence to show. The great stability of uric acid 
 under treatment with even strong acids and alkalies is certainly 
 opposed to its containing pre-formed residues of urea, since in all 
 undoubtedly so constituted bodies the residues of urea are re- 
 movable or decomposible with the greatest facility. On the 
 other hand, the assumption of pre-existent urea-residues in uric 
 acid very greatly facilitates our conception of its decompositions, 
 and, receiving the general consent of chemists, may, I think, be 
 provisionally admitted by us on the present occasion. 
 
 (137.) Be this as it may, when uric acid is subjected to an 
 oxidising agent in presence of water, it gives up two of its atoms 
 of hydrogen to the oxidising agent, while the dehydrogenised 
 product reacts with water to form mesoxalic acid and urea. 
 Employing chlorine as the oxidising agent, we have the following 
 reaction, 
 
 Chlorine Uric acid Water Mesoxalic Urea CMorhydric 
 
 Cl a + C 5 N 4 H 4 3 + 4H a O C 3 H a 5 + aCN a H 4 + aHCl; 
 
 or, supposing the reaction with water to take place after the 
 removal of the hydrogen by chlorine, 
 
130 ANIMAL CHEMISTRY LECTURE VI. 
 
 Dehyd-uric? Water Mesoxalic Urea 
 
 C 5 N 4 H 2 3 + 4 H 2 = C 3 H 2 5 + 2CN 2 H 4 0. 
 
 In the above equations I have represented both atoms of urea to 
 be simultaneously separated from the mesoxalic acid ; but in 
 reality their separation is usually effected at two successive stages, 
 the first of which results in the formation of alloxan, and the 
 second in its decomposition, thus : 
 
 Dehyd-uric? Water Alloxnn Urea 
 
 C 5 N 4 H 2 3 + 2H 2 = C 4 N 2 H 2 4 + CN 2 H 4 0. 
 
 Alloxan Water Mesoxalic Urea 
 
 C 4 N 2 H 2 4 + 2H 2 = C 3 H 2 5 + CN 2 H 4 0. 
 
 We have, you perceive, three mesoxalic compounds, first the 
 non-nitrogenous acid, then the compound of the acid with one 
 atom of urea minus 2H 2 0, and lastly, the compound of the acid 
 with two atoms of urea minus 4.H 2 0, thus : 
 
 Mesoxalic Alloxan Dehyd-uric ? 
 
 C 3 II 2 5 C 4 N a H 2 4 C 5 N 4 H 2 3 
 
 Now, by hydrogenising mesoxalic acid, we obtain tartronic 
 acid C 3 H 4 O 5 , and by hydrogenising alloxan we obtain dialuric 
 acid C 4 N 2 H 4 O 4 , which two bodies accordingly bear to uric acid 
 the same relation that mesoxalic acid and alloxan bear to dehvd- 
 uric acid, thus, 
 
 Tartronic Dialuric Uric acid 
 
 C 3 H 4 5 C 4 N a H 4 4 C 5 N 4 H 4 3 ; 
 
 and, just as our hypothetical dehyd-uric acid yields mesoxalic 
 acid and alloxan, so should actual uric acid yield us the tartronic 
 and dialuric acids. 
 
 In reality, however, these bodies have not been obtained by 
 the mere breaking up of uric acid, but only by rehydrogenising 
 the mesoxalic acid and alloxan which result from the breaking 
 up of its dehydrogenised product. Despite, however, this flaw in 
 
AN-UREIDE ACIDS. 131 
 
 the demonstration, we may provisionally, as I have said, regard 
 the dialuric and uric acids as tartron-ureide and tartron-diureide 
 respectively. 
 
 (138.) The several bodies I have just mentioned are typical of 
 three well-defined classes of compounds, to one or other of which 
 the immense number of uric acid products are, with but very few 
 exceptions, assignable. We have first the class of simple non- 
 nitrogenous acids, or an-ureides, like the tartronic and mes- 
 oxalic acids. Then we have the class of bodies containing a 
 residue of the acid plus one residue of urea, or the mon-ureides, 
 such as dialuric acid and alloxan ; and lastly, we have the class 
 of bodies containing a residue of the acid plus two residues of 
 urea, orthedi-ureides, such as uric acid itself. Confining our 
 present attention to the an-ureides, let us consider briefly their 
 derivation and mutual relationship. Mesoxalic acid, then, the 
 most complex non-nitrogenous product obtainable directly from 
 uric acid, constitutes the third term in the following series : 
 
 An-ureides 
 
 C H a 3 Carbonic. 
 C 3 H Z 4 Oxalic. 
 C 3 H 3 S Mesoxalic. 
 
 Oxalic acid, you observe, differs in composition from carbonic 
 acid by one atom of carbonic oxide CO, in excess ; while mes- 
 oxalic acid differs in composition from oxalic acid by a further 
 atom of carbonic oxide CO, in excess. Now, when mesoxalic 
 acid is acted upon by nascent oxygen O, its excess of carbonic 
 oxide CO, is removed in the form of carb-anhydride C0 2 , so as 
 to leave oxalic acid, thus; 
 
 Mesoxalio Oxygen Carb-anhyd. Oxalic 
 
 C 3 H,0 5 + = CO, + C a H 2 4 . 
 
 Hence when uric acid is subjected to a more active oxidation 
 than suffices to produce mesoxalic acid we obtain oxalic acid, 
 which may occur in its simple an-ureide state, or conjugated with 
 one atom of urea to form a mon-ureide such as parabanic acid, 
 
 K 2 
 
132 ANIMAL CHEMISTRY LECTURE VI. 
 
 or conjugated with two atoms of urea to form a diureide, such as 
 mycomelic acid, a body having exactly the same relation to 
 oxalic acid that uric has to mesoxalic acid. 
 
 (139.) Now, just as we can convert mesoxalic into oxalic acid 
 by burning off its excess of carbonic oxide, so may we convert 
 oxalic acid itself into carbonic acid by a precisely similar 
 oxidation, thus : 
 
 Oxalic Oxygen Carb-anhyd. Carbonic 
 
 C 2 H 2 4 + = C0 3 + CH 3 3 . 
 
 The rapidity with which the oxidation of oxalic acid can be 
 effected is easily capable of experimental illustration. In this tall 
 beaker, for instance, I place some ordinary black oxide or per- 
 oxide of manganese Mn0 2 , a compound which readily parts with 
 one of its two atoms of oxygen to become converted into prot- 
 oxide of manganese MnO ; while I introduce into the flask an ounce 
 or so of commercial oxalic acid. Now, upon drenching the acid 
 with hot water and pouring the resulting mixture of solution and 
 crystals upon the oxide of manganese, we get, you perceive, a 
 most rapid oxidation of the oxalic acid, accompanied by a violent 
 effervescence of carb-anhydride gas which we shall be able to re- 
 cognise in a minute or two by its high specific gravity and by its 
 power of extinguishing flame and rendering lime-water turbid. 
 The effervescence is at first so great as to be almost unmanage- 
 able, and a very slight agitation would cause the liquid contents 
 to froth over the beaker; but now that the action is a little mode- 
 rated I may prove to you the nature of the gas evolved by pour- 
 ing some of it on to a lighted taper, which you see is immediately 
 extinguished; and by pouring some more of it upon this clear 
 solution of lime, which by agitation therewith is immediately 
 converted into an opaque mixture of chalk and water. Hence, 
 when uric acid is subjected to a more powerful oxidation than 
 suffices to produce oxalic acid, we obtain carbonic acid, which, 
 like the oxalic and mesoxalic acids, is also capable of colligation 
 with urea. No ureide of carbonic acid, indeed, has yet been 
 formed directly from uric acid the active treatment required to 
 
MON-UKEIDE COMPOUNDS. 133 
 
 effect the complete oxidation of the uric acid effecting also a 
 separation from one another of the resulting carbonic acid and 
 urea, which, however, may be obtained in combination by other 
 means. Allophanic acid, for instance, is a well known artifi- 
 cial mon-ureide of carbonic acid, but so far as I am aware no di- 
 ureide of the acid has hitherto been produced by any process 
 whatsoever. 
 
 (140.) The mon-ureide of mesoxalic acid, of which I have 
 already spoken namely, alloxan, is formed from mesoxalate of 
 urea by an elimination of two atoms of water ; but there is another 
 ureide namely, alloxanic acid, which differs from the original 
 salt by the loss of only one atom of water. Similarly oxalic acid 
 forms two mon-ureides namely, parabanic acid or paraban ana- 
 logous to alloxan, and oxaluric analogous to alloxanic acid. 
 Carbonic acid, however, forms but a single ureide, which is pro- 
 duced by the elimination of only one atom of water, and accord- 
 ingly belongs to the same series as the oxaluric and alloxanic acids, 
 thus : 
 
 Acids Ureides 
 
 CH 2 3 Carbonic ^W> 3 Allophanic. 
 
 n TT ~ n T (CJSTjHX), Oxaluric. 
 
 C 2 H 4 4 Oxalic \ 3 3 4 4 
 
 ( C 3 N a H 4 3 Paraban. 
 
 (C A N,ILOe Alloxanic. 
 C 3 HA Mesosahc ' 
 
 Similarly among the di-ureides, some are formed from their 
 corresponding mon-ureides by an elimination of one atom, and 
 others by an elimination of two atoms of water. 
 
 (141.) Now, mesoxalic acid is convertible by deoxidation or 
 hydrogenation into tartronic acid, as I have already observed ; 
 and by pushing the deoxidation a stage further we obtain 
 inalonic acid, both of them capable of forming mon-ureides 
 and di-ureides ; and, in a similar manner, the oxalic and carbonic 
 acids furnish a variety of similarly behaving deoxidation -products. 
 When we consider, then, the total number of carbonic or I -carbon, 
 
ANIMAL CHEMISTRY LECTURE VI. 
 
 of oxalic or 2 -carbon, and of mesoxalic or 3 -carbon, hydrogenised 
 products; and that the majority of these products, like their ori- 
 ginal acids, are capable of forming mon-ureides by an elimination 
 of one atom, and other mon-ureides by an elimination of two 
 atoms of water ; and, further, that many of these mon-ureides 
 are capable of forming di-ureides by a further elimination of one 
 atom, and other di-ureides by a further elimination of two atoms 
 of water, we are no longer surprised at the great number and 
 variety of known compounds belonging to the uric acid group, 
 and shall not be surprised at the discovery of very many more. 
 The most important of those already known are included in the 
 following table. It is divided perpendicularly into three columns 
 of an-ureides, mon-ureides, and di-ureides ; and horizontally into 
 three layers of carbonic, oxalic, and mesoxalic products. The 
 compounds connected by means of dotted lines differ in composi- 
 tion from one another by an excess or deficit of one atom of urea 
 minus one atom of water ; while those standing on the same level 
 in the adjoining columns and unconnected by dotted lines, differ 
 from one another by an excess or deficit of one atom of urea 
 minus two atoms of water. 
 
 An-ureides Mon-ureidea 
 
 CH 4 Methylic C 2 N 2 H 6 Methyl-urea 
 
 CH 3 3 Carbonic C 2 N 2 H 4 3 Allophanic 
 
 Di-ureides 
 
 C 3 N 2 H 6 Z Acet-urea 
 ''C 3 N 2 H 6 3 Hydautoic 
 
 C 4 N 4 H 6 2 Glycoluril 
 ./' C 4 N 4 H 6 3 Allantoine 
 
 C 2 H 4 2 Acetic -''..-' 
 C 2 H 4 3 GlycohV' / 
 C 2 H 4 4 G-lyoxylic'"' 
 
 C,H 4 3 Glyoxalic ''.', 
 C 3 H 2 4 Oxalic 
 
 '' C 3 N 2 H 4 0,, Hydantoine '' , 
 C 3 N 2 H 4 3 Lantanuric 
 ,--''"C 3 N 2 H 4 4 Oxaluric 
 
 C 3 N 2 H 2 3 Parabanic 
 
 C 4 N 4 H 4 2 Mycomelic 
 
 C 3 H 4 4 Malonic 
 C 3 H 4 5 Tartronic 
 
 C 3 H 2 5 Mesoxalic 
 
 C 4 N 2 H 4 3 Barbituric 
 C 4 N 2 H 4 4 Dialuric .. 
 C 4 N 2 H 4 5 Alloxanic 
 
 C 4 N,H,0 4 Alloxan 
 
 C S N 4 H 4 Hypoxanth. 
 C 5 N 4 H 4 2 Xanthine 
 C 5 N 4 H 4 3 Uric acid 
 -.C 5 N 4 H 6 4 Pseudo-uric 
 
 ti 
 
DIAMERONE MON-UREIDES. 
 
 135 
 
 (142.) Even this table, however, is far from -being complete. 
 Thus I have introduced only one alcoholic urea as a type 
 namely, the methylic, excluding its homologues. I have also 
 omitted uroxanic acid and several amidated and nitro-compounds, 
 to which I shall presently refer. Moreover, between some of 
 the consecutive mon-ureides shown in the table, there exist 
 diameric bodies formed by the union of the two consecutive mon- 
 ureides with elimination of water. Allituric acid, for instance, is a 
 diamerone of hydantoine and lantanuric acid ; while leucoturic 
 acid is a diamerone of lantanuric acid and oxaluric or parabanic 
 acid, thus : 
 
 Allituric Water Hydantoine Lantanuric 
 
 C 6 N 4 H 6 4 + H a O = C 3 N a H 4 O a + C 3 N a H 4 3 . 
 
 Leucoturic Water Lantanuric Parabanic 
 
 C 6 N 4 H 4 5 + H a O = C 3 N a H 4 3 + C 3 N a H a 3 . 
 
 In a precisely similar manner, among mesoxalic compounds we 
 have hydurilic acid, a diamerone of barbituric acid and dialuric 
 acid ; while alloxantine is a diamerone of dialuric acid and 
 alloxanic acid or alloxan, thus : 
 
 Hydurilic Water 
 
 C 8 N 4 H 6 6 + H a O 
 
 Alloxantine Water 
 
 C 8 N 4 H 4 7 
 
 H a O 
 
 Barbituric 
 C 4 N a H 4 3 
 
 Dialuric 
 C 4 N a H 4 4 
 
 Dialuric 
 C 4 N a H 4 4 . 
 
 Alloxan 
 C 4 N a H a 4 , 
 
 (143.) Of the many bodies above formulated, only a few call 
 for any special remark. Hydantoic acid is also known as gly- 
 coluric acid, which is, perhaps, a better name for it. Again, the 
 body here called lantanuric acid is probably identical with the 
 allanturic acid of Pelouze, and also with difluan. Oxaluric 
 acid is interesting from the alleged occurrence of its calcium-salt 
 in human urine, in the form of the dumb-bell crystals so often 
 associated with octahedral crystals of the oxalate. That these dumb- 
 bells may consist of oxalurate of calcium, as suggested by their 
 discoverer, Golding Bird, is not indeed improbable ; but the evi- 
 
136 ANIMAL CHEHISTKY LECTURE VI. 
 
 deuce that they really are so constituted is anything but satis- 
 factory. The relations of lantanuric and oxaluric acids to another 
 uric acid product known as oxaluramide are obviously those of 
 hydrogen and water to ammonia, as illustrated in the case of so 
 many previously considered compounds, thus : 
 
 H.H Hydrogen C 3 N a H 3 (H)0 3 Lantanuric. 
 
 H.HO Water C 3 N a H 3 (HO)0 3 Oxaluric. 
 
 H.H a N Ammonia C 3 N a H 3 (H a N)0 3 Oxaluramide. 
 
 Allantoine, as shown by the fine specimen lent me by Messrs. 
 Hopkins and Williams, is a beautiful crystalline body existing in 
 the allantoic fluid of the fetal, and in the urine of the sucking 
 calf. It has also been noticed by Frerichs and Stadeler in the 
 urine of two dogs, upon whose lungs they had been experiment- 
 ing, and is easily procurable from uric acid by oxidation with 
 peroxide of lead. By deoxidation, it yields glycoluril (Rheineck). 
 Mycomelic acid may be obtained, among other processes, by 
 heating uric acid with water under pressure,* thus : 
 
 Uric acid Mycomelic acid Carbonic oxide 
 
 C 5 N 4 H 4 3 = C 4 N 4 H 4 0, + CO. 
 
 As I have before observed, it stands to paraban in exactly the 
 same relation that uric acid stands to alloxan. From the obser- 
 vations of Hlasiwetz it seems probable that some supposed urate 
 of ammonia deposits, occurring in urine, really consist of myco- 
 melic acid, which similarly evolves ammonia when treated with 
 alkalies, and yields murexide when evaporated with nitric acid. 
 
 (144.) Ofmesoxalic mon-ureides, alloxan and barbituric acid 
 appear to be the most important. Alloxan, the first discovered 
 product cf the artificial oxidation of uric acid, has recently been 
 recognised by Liebig as a pre-formed constituent of urine. By 
 treatment with bromine, it yields dibromobarbituric acid, 
 
 * Possibly, thus : 
 
 Uric acid Water Mycomelic Formic 
 
 C 5 N 4 H 4 3 + H a O = C 4 N 4 H 4 O a + CH a O a . 
 
MESOXALJC MON-UREIDES. 137 
 
 convertible by successive hydrogenation into bromobarbituric, 
 and barbituric acid, which last serves as a sort of nucleus in 
 the following series of compounds : 
 
 Mesoxalic Mon-ureides 
 
 C 4 N 2 H a (HO) a 3 Alloxanic. 
 
 C 4 N a H a (Br a )0 3 Dibromobarbituric, 
 
 C 4 N a H 4 3 Barbituric. 
 
 C 4 N a H 3 (Br)0 3 Bromobarbituric. 
 
 C 4 N 2 H 3 (HO)0 3 Dialuric. 
 
 C 4 N 2 H 3 (H a N)0 3 Uramile. 
 
 Qtiyi^H^SOjJOj Thionuric. 
 
 C 4 N 2 H 3 (NO)0 3 Violuric. 
 
 C 4 N 2 H 3 (NO a )0 3 Dilituric. 
 
 C 8 N 4 H 6 (N a 3 )0 6 Violantine. 
 
 The last body on the list namely, violantine seems to be not 
 a diamerone or residuary, but a completed compound of the vic- 
 luric and dilituric acids. It is observable that the mutual rela- 
 tionship of barbituric acid, dialuric acid, and uramile in this 
 subs-group is strictly parallel to that of lantanuric acid, oxaluric 
 acid, and oxaluramide in the preceding one. Moreover, the 
 malonic and barbituric acids are homologous with the oxalic and 
 parabanic acids respectively ; or, in other words, the most oxidised 
 of known 2-carbon uric acid products are homologically the re- 
 presentatives of the least oxidised 3 -carbon products thus, 
 
 C a H 2 4 Oxalic C 3 N 2 H 2 3 Parabanic 
 
 C 3 H 4 4 Malonic C 4 N,H 4 3 Barbituric; 
 
 although from another point of view they correspond more nearly 
 with mesoxalic acid and alloxan, as I have already remarked. 
 
 (145.) The relationship subsisting between the three mesoxal- 
 di-ureides, though long suspected from the similarity of their 
 formulae hypoxanthine C 5 N 4 H 4 O, xanthine C 5 N 4 H 4 2 , and uric 
 acid C 5 N 4 H 4 O 3 has but very recently received an experimental 
 demonstration at the hands of Strecker and Kheineck. With the 
 first of these bodies, or hypoxanthine, originally found by 
 Scheerer inhuman and bovine splenic juices, the so-called sarcine, 
 
138 ANIMAL CHEMISTRY-f-LECTURE VI. ' 
 
 subsequently discovered by Strecker in juice of flesh, and thought 
 to be a distinct base, has since proved to be identical. From the 
 results of Scheerer, Strecker, Gorup-Besanez, and others, it ap- 
 pears that hypoxanthine exists to a very appreciable extent in 
 most glandular juices and in muscular tissue, particularly of the 
 heart, while it has also been recognised in brain-substance and in 
 the blood and urine. It occurs as a white crystalline powder, 
 insoluble in cold and sparingly soluble in hot water. Strecker 
 has shown that by oxidation with nitric acid, it yields xanthine, 
 and gives accordingly with nitric acid, the characteristic reac- 
 tion of xanthine a compound which has also been detected in 
 blood and in most animal juices. Under the name of xanthic 
 oxide, it was discovered in 1819 by the elder Marcet, in a variety 
 of urinary calculus which subsequent experience has proved to 
 be very rare. It has been met with, more frequently indeed, 
 though still very seldom, as an amorphous urinary deposit, and 
 in one case recorded by Bence Jones it occurred in lozenge- 
 shaped crystals. Its habitual presence, however, in small quan- 
 tity, as a dissolved constituent of urine, seems now to be very well 
 established. Xanthine, moreover, is not only known as a urinary, 
 but also as an intestinal concretion, for Gobel has met with it as 
 the chief constituent of certain oriental bezoar stones obtained 
 from ruminating animals. I have already mentioned Strecker's 
 artificial production of xanthine by the oxidation of hypoxanthine 
 or sarcine with nitric acid. Conversely, Strecker and Rheineck 
 have very recently shown that uric acid, by deoxidation with 
 sodium-amalgam, yields a mixture of xanthine and hypoxanthine, 
 the latter in greatest proportion, so that the actual relationship of 
 the three bodies is now placed beyond all question. Hitherto 
 hypoxanthine and xanthine, having been obtained in small quan- 
 tities only, have not been subjected to any detailed examination. 
 It can scarcely be doubted, however, that xanthine is a mon- 
 ureide of barbituric and a di-ureide of malonic acid, in the same 
 sense that uric acid is a mon-ureide of dialuric and a di-ureide of 
 tartronic acid. We may hope, indeed, to have these relations 
 very soon established by experiment ; for, even if it should not 
 
MESOXALIC DI-UEEIDES. 139 
 
 prove possible to prepare xanthine advantageously from uric acid, 
 still the fact of its close relationship thereAvith would lead us to 
 expect its more abundant existence than has hitherto been ima- 
 gined particularly, for instance, in the excreta of those animals 
 whose normal mode of tissue-waste results in the production of 
 uric acid rather than of urea. 
 
 (146.) This expectation is strengthened by the extraction from 
 guano, the well-known dried excrement of sea-fowl, of a feeble 
 base called guanine, which bears to xanthine the same often- 
 referred-to relation that ammonia bears to water, as shown in the 
 following series of formulae : 
 
 C 5 N 4 H 3 (H)0 Hypoxanthine. 
 
 C S N 4 H 3 (HO)0 Xanthine. 
 
 C 5 N 4 H 3 (H 2 N)0 Guanine. 
 
 C 5 N 4 H 3 (HO) 3 Uric acid. 
 
 Just, in fact, as uric acid, and doubtless xanthine, yield by oxi- 
 dation parabanic acid and urea, so does guanine yield by oxidation 
 parabanic acid and amido-urea or guanidine,* thus : 
 
 Xanthine Parabanic Urea 
 
 C 5 N 4 H 3 (HO)0 + H a O + 3 = C 3 N 2 H 2 3 + CN a H 3 (HO) + C0 2 ? 
 
 G-uanine Parabanic Guanidine 
 
 C 3 N 4 H 3 (H 3 N)0 + H 2 + 3 = C 3 N 4 H 2 3 + CN a H 3 (H 2 N) + C0 a . 
 
 Moreover, xanthine itself occurs in small quantity as a secondary 
 product of the above oxidation of guanine, and may be obtained 
 
 * By the oxidation of kreatine, which has been already described as a 
 polymerone of glycolic acid, methylamine, and urea, its glycolic residue is 
 converted into oxalic acid, while its methylamine and urea residues are left 
 in combination to form methylainido-urea or methyluramine, a compound 
 homologous with amido-urea or guanidine, thus : 
 
 CN 3 H 3 (HO) Urea. 
 
 CN 2 H 3 (H 3 N) Guanidine. 
 
 CN 2 H 3 (CH 3 HN) Methyluramine. 
 
 Again, biuret C 2 N 3 H 5 O a , or C 2 N.5H 3 (H s lS[)O a , may be regarded as carbo- 
 guanidinic acid, just as allophan C 2 N 3 H 4 3 or CaN a H 3 (HO)0 2 is regarded as 
 carb-ureic acid. 
 
140 ANIMAL CHEMISTRY LECTURE VI. 
 
 in larger quantity by treating guanine with nitrous acid, accord- 
 ing to the general method adopted for converting amidated into 
 hydrated bodies, thus : 
 
 Guanine Nitrous Xanthine 
 
 C 5 N 4 H 3 (H a N)O + (HO)NO = C 5 N 4 H 3 (HO)0 + N, + H 4 0. 
 
 That the guanine extracted from guano is a constituent of the 
 birds' excrement as voided, and not a product of decomposition, 
 is rendered probable by its occurrence under other circumstances. 
 Thus it forms the chief portion of the excrement of the garden 
 spider, has been recognised by Scheerer in the pancreas of the 
 horse, and is occasionally met with in human urine. 
 
 (147.) We have now only left for consideration the pseudo- 
 uric and uroxanic acids, which we may regard as terms in the 
 following series : 
 
 C 5 N 4 H 4 3 Uric. 
 
 C 5 N 4 H 4 3 + H,0 = C 5 N 4 H 6 4 Pseudo-uric. 
 C 5 N 4 H 4 3 + 2 H 2 = C 5 N 4 H 8 5 
 C 5 N 4 H 4 3 + 3 H 3 = C 5 N 4 H 10 6 Uroxanic. 
 C 5 N 4 H 4 3 + 4H<0 = C 3 H 4 5 Tartronic * 2CN a H 4 Urea ? 
 
 Pseudo-uric acid is a recent discovery of Baeyer's. It has 
 not actually been produced by the direct or indirect hydration of 
 uric acid, but only by the combination of cyanic acid vapour 
 with uramile or amido-barbituric acid. Just, in fact, as cyanic 
 acid converts ammonia into anomalous cyanate of ammonia or 
 urea, so does it convert the residue of ammonia contained in ura- 
 mile into a residue of urea, thereby changing the amido-monureide 
 into a simple diureide, thus : 
 
 Uramile Cyanic acid Pseudo-uric 
 
 C 4 N a H 3 (NH a )0 3 + CNHO = C 4 N,H 3 (CN a H 3 0)0 3 or C 5 N 4 H 6 4 . 
 
 Pseudo-uric acid occurs as a white crystalline almost insoluble 
 powder. Hitherto it has not proved dehydrateable into uric acid ; 
 but by dehydrogenation, in presence of water, it behaves like 
 uric acid, breaking up into alloxan and urea. The compound 
 C 5 N 4 Hs0 5 is unknown, while uroxanic acid C 5 N 4 H 10 06, is 
 
ULTIMATE CONSTITUTION OF URIC ACID. 14! 
 
 known but very imperfectly. Unlike pseudo-uric acid, it really 
 results from the absorption of water by uric acid, and is produced 
 in the form of its potassium-salt by boiling uric acid for a long 
 time in solution of caustic potash. In the free state it occurs as 
 a white, glistening, sparingly soluble powder. The absorption of 
 a fourth atom of water by uric acid would doubtless lead, not to 
 the formation of a new hydrate, but to the breaking up of the 
 acid itself, most likely into tartronic acid and urea. 
 
 (148.) I have already referred to upwards of forty uric acid 
 products, by no means all that are known, and I have indicated 
 the existence of many more, as yet unknown, to fill up gaps in 
 the different series. Now, when we reflect that in all probability 
 most of these compounds, actual and problematical, do not stand 
 alone, but are associated each with a more or less numerous set 
 of isomers, that is to say, of bodies having the same ultimate 
 composition, but a different molecular arrangement we scarcely 
 venture to contemplate the almost overwhelming intricacy with 
 which we are threatened. To us, as physicians, however, the 
 subject is capable of assuming a simpler aspect. On any view of 
 its constitution, hydrated uric acid differs in composition from 
 two atoms of urea by the addition of three atoms of carbonic 
 oxide CO, capable of oxidation into carb-anhydride C0 2 , and by 
 that oxidation of generating a certain amount of heat, or its equi- 
 valent of motion : 
 
 Water "Uric acid Oxygen Carb-anhyd. Urea 
 
 *H a O -f C 5 N 4 H 4 3 + C 
 
 or C 3 3 (CN a H 4 0) 3 
 
 CM 
 3 [ 
 
 Hence, uric acid must be considered to result from an incomplete 
 oxidation of nitrogenous tissue, whereby, in addition to urea, 
 carbonic oxide is produced instead of carbonic anhydride. In 
 accordance with this deduction, then, we are not surprised to 
 find that the tissue-metamorphosis of reptiles, whose motions are 
 so sluggish and temperature is so low, should yield imperfectly 
 burned and used carbonic oxide in the form of uric acid, or 
 rather ui#te of ammonia, instead of the perfectly burnt and used 
 carb-anhydride excreted by mammals. On the other hand, this 
 
142 ANIMAL CHEMISTRY LECTURE VI. 
 
 view seems at first sight altogether discordant with the similar 
 excretion of urate of ammonia by birds and insects, whose motions 
 are so active and temperatures so high. But by having regard 
 to the following considerations, it will, I think, appear that the 
 loss, or rather non-liberation, of force resulting from the merely 
 half-burning, so to speak, of the excess of carbon excreted as uric 
 acid, is less than at first sight appears, and is, moreover, largely 
 compensated for by certain consequent advantages. 
 
 (149.) For reasons which I cannot now discuss, the experi- 
 mental results actually obtained on the quantities of heat evolved 
 by the combustion of carbon into carbonic oxide and anhydride 
 respectively, are not applicable to the point we have under our 
 consideration, which at present therefore can only be decided 
 from analogy and general principles. Let us then imagine the 
 production of carbonic oxide and anhydride under conditions as 
 nearly as possible analogous. Let us conceive, for instance, that 
 an atom of carbon first unites with an atom of oxygen gas to form 
 solid carbonic oxide CO, which then unites with a second atom 
 of oxygen gas to form solid carb-anhydride CO 2 . Remembering, 
 as explained in my fourth lecture, that the heat produced by any 
 combination is the exact measure of the force required to sepa- 
 rate the constituents of the compound from one another, and is, 
 indeed, only a setting free of the heat which at some time or 
 other was absorbed in the act of their separation, it will fol- 
 low, provided the two atoms of oxygen in carb-anhydride are 
 retained by the carbon with an equally strong affinity, that the 
 amount of heat evolved by the combustion of carbon into solid 
 carbonic oxide will be just one half of that evolved by its com- 
 bustion into solid carb-anhydride. But we have good reason for 
 believing that the first atom of oxygen in carb-anhydride is more 
 firmly retained than the second atom, and consequently that the 
 amount of heat liberated by the combination of the first atom is 
 greater than that liberated by the combination of the second atom 
 of oxygen; or, in other words, that the heat evolved in the pro- 
 duction of solid carbonic oxide CO, is more than half of that 
 evolved in the production of solid carb-anhydride C0 2 . 
 
OXIDATIONS INTO UEIC ACID AND UREA. 143 
 
 (i 50.) But we are actually concerned with a comparison of the 
 amounts of heat evolved in the oxidation of tissue-carbon into 
 the solid carbonic oxide constituent of uric acid on the one hand, 
 . and into the gaseous carb-anhydride discharged from the lungs 
 on the other. Now it would appear that the latent heat of gaseous 
 carbon, or the quantity of heat absorbed in its vaporisation, 
 amounts to fully - of that evolved by its mere combustion into 
 carb-anhydride ; * so that the ratio of the heat evolved by the 
 combustion of carbon into gaseous carb-anhydride CO 2 , to the 
 heat evolved by its combustion into solid carbonic oxide CO, would 
 be as | to l - (more exactly as -^ to j^), or of course as i to ^ 
 even leaving out of consideration the probable excess of heat 
 developed in the production of solid carbonic oxide over that 
 developed in its conversion into solid carb-anhydride. By the dis- 
 charge, then, of uric acid, instead of carb-anhydride and urea, 
 there is a loss of 50 per cent, of heat by imperfect oxidation, 
 minus a gain of 25 per cent, of heat by the discharge from the 
 body of solid carbon and oxygen in the form of uric acid, instead 
 of gaseous carbon and oxygen in the form of carb-anhydride. 
 
 I am aware that in arriving at this conclusion, which is avowedly 
 based on assumption, several modifying actions of more or less 
 importance have been disregarded ; still I think it cannot be 
 doubted that the amount of heat produced by the conversion of 
 tissue-carbon into the carbonic oxide constituent of uric acid is 
 more nearly | than J of that produced by its conversion into 
 gaseous carb-anhydride. Moreover, the amount of oxygen con- 
 sumed in the production of carbonic oxide being only one-half of 
 that consumed in the production of carb-anhydride, the amount 
 
 * While 12+16 grammes of carbonic oxide CO, in uniting with 16 
 grammes of oxygen 0, evolve 68 units of heat, 12 grammes of carbon C, 
 in uniting with twice 16 grammes of oxygen O a , evolve not 136, but only 
 96 units of heat; the difference between 136 and 96, or 40 units of heat, 
 being absorbed in changing the 1 6 grammes of carbon from the solid to the 
 gaseous state. This calculation leaves out of consideration the heat absorbed 
 and evolved respectively, in the conversion of one volume of oxygen into 
 two volumes of carbonic oxide, and of two volumes of carbonic oxide plus 
 one volume of oxygen into two volumes of carb-anhydride. 
 
144 ANIMAL CHEMISTRY LECTURE VI. 
 
 of cold air necessary to be inspired and heated up to the tempe- 
 rature of the animal will be only half as much in the one case 
 as in the other, whereby a further economy of heat will be 
 effected. 
 
 (151.) But in the liberation of pent-up force within the body, 
 we have to consider not only the tissue burnt, but also the oxygen 
 required to burn it. Now it is quite conceivable that in the 
 organism of birds, for instance, an economy of oxygen or breath 
 may be of more importance than an economy of tissue or food.* 
 Indeed, the marvellous adoption in predatory birds of every sup- 
 plemental contrivance for increasing ever so slightly their respi- 
 ratory surface, without, however, departing from its almost rep- 
 tilian type of structure, is strongly suggestive of these animals 
 being, so to speak, under-lunged, and of the necessity for econo- 
 mising their lung-action in every possible way. Now admitting 
 the correctness of our former conclusion, that by the transforma- 
 tion of a given amount of tissue-carbon into the carbonic oxide 
 constituent of uric acid, there is liberated say - of the actual 
 energy produceable by its oxidation into gaseous carb-anhydride, 
 it follows conversely that the transformation of two atoms of oxygen 
 into the carbonic oxide constituent of uric acid C 2 O 2 , will liberate 
 l^ times the actual energy producible by its transformation into 
 carb-anhydride CO 2 . So that while for a given amount of tissue- 
 carbon we obtain 25 per cent, less, for a given amount of oxygen 
 we obtain 50 per cent, more heat by the production of the car- 
 bonic oxide constituent of uric acid, than by the production of 
 gaseous carb-anhydride ; or an atom of oxygen is employed with 
 50 per cent, more economy in the one case than in the other. 
 
 (152.) Moreover, the lungs, it must be remembered, act not 
 only as receivers of oxygen but also as dischargers of carbon from 
 
 * ' Of all animals birds are most dependent upon a constant renewal of 
 the air in their lungs, and upon the purity of that with which they are sup- 
 plied. Most birds will die in air which has been but slightly charged with 
 carbonic acid, and which can be respired by mammals without immediate 
 injury.' Carpenter's 'Principles of Physiology, General and Comparative,' 
 3rd ed. p. 758. 
 
RATIO OF CARBON TO NITROGEN IN UREA. 145 
 
 the body, and, in this particular, we find the lungs of birds mate- 
 rially aided by the ejection from their kidneys of urate of am- 
 monia instead of urea. In urea CN 2 H 4 0, the ratio of nitrogen 
 to carbon is as 2 to i ; whereas in urate of ammonia C 5 N 5 H 7 3 , 
 it is as i to i , so that for an equal elimination of nitrogen, the 
 quantity of carbon discharged from the kidneys of birds in the 
 form of nrate of ammonia, is twice as great as that discharged 
 from the kidneys of mammals in the form of urea. Now, we have 
 seen that the proportion of the carbon of nitrogenised tissue 
 CsNjjH^O^, excreted by the kidneys of carnivorous mammals is -| 
 of the whole, and accordingly that excreted by the kidneys of car- 
 nivorous birds in the form of urate of ammonia will be - of the 
 whole. In other words, by the production of urate of ammonia 
 instead of urea, the lungs of birds are required to discharge only 
 - instead of | of the waste carbon resulting from the metamor- 
 phosis of nitrogenous tissue, although, as I have already observed, 
 a larger amount of nitrogenous tissue has to be transformed in 
 order to liberate the same amount of energy. On this view the 
 comparatively large kidneys of birds and insects will have refe- 
 rence not only to the absolute amount of tissue metamorphosed, 
 but also to the relative increase in the proportion of carbon ex- 
 creted by their kidneys to that excreted by their lungs. 
 
 (153.) To sum up the foregoing considerations, we perceive 
 that the amount of force lost by the metamorphosis of a given 
 quantity of tissue, or indirectly of food, into the carbonic oxide 
 constituent of uric acid, instead of into carb-anhydride, is less 
 than might at first be supposed that the amount of force gained 
 by the conversion of a given quantity of oxygen into the carbonic 
 oxide constituent of uric acid, instead of into carb-anhydride, is 
 very large and lastly, that by the production of the carbonic 
 oxide constituent of uric acid, instead of carb-anhydride, the kid- 
 neys of birds are enabled to act vicariously for the lungs as ex- 
 cernents of a portion of that carbon which in mammals is habit- 
 ually discharged by the lungs, 
 
 How far this production and excretion of urate of ammonia, 
 instead of urea and carb-anhydride, may depend upon an inade- 
 
 L 
 
146 ANIMAL CHEMISTRY LECTURE YI. 
 
 quate pulmonic oxidation of the blood of birds, not entirely com- 
 pensated for by its considerable systemic oxidation ; and how far 
 upon the connection with the portal circulation and inferior type 
 of structure of their kidneys, as well as upon the small amount of 
 water they drink and discharge, whereby their blood is less con- 
 stantly and thoroughly washed than is the blood of mammals, 
 are questions which it is for the physiologist rather than the 
 chemist to determine. 
 
 (154). I can scarcely venture to conclude this course of lec- 
 tures on ' Animal Chemistry ' without saying a few words upon 
 the influence exerted on tissue-metamorphosis by those chemical 
 agents which are usually included in the class of alterative 
 medicines. Although our acknowledged ignorance of the mode 
 in which medicines produce their effects is made a standing 
 reproach to medical art, only by those who, ignorant of their 
 ignorance, wrongly conceive that in other scientific arts that of 
 the chemist, for example the use of the different agents em- 
 ployed has really ceased to be empiric, and become dependent 
 upon abstract principle, still it will not do for us to regard the 
 therapeutic actions of different medicines as ultimate facts with 
 which we must ever rest contented, but rather as difficult pro- 
 blems inviting a more competent investigation, and destined 
 some day or other to yield to our inquiries. The subject, how- 
 ever, is too remote from even the present widely-extended boun- 
 dary of scientific knowledge the path from the known to the 
 unknown is yet too lengthy and intricate to warrant us in ex- 
 pecting any immediate, or, indeed, proximate resolution of the 
 darkness by which it is surrounded. In the belief, however, 
 that even a little gleam of light, insignificant in relation to more 
 advanced researches, may not prove altogether worthless here, I 
 beg respectfully to suggest the following points for your con- 
 sideration. It will be found, I think, that those mineral sub- 
 stances which act more especially as alteratives, actually are, and 
 necessarily ought to be, characterised, not by their chemical 
 energy, but by their chemical mobility ; and I do not know that 
 I can make my meaning better evident than by directing your 
 
OXIDATION BY PEROXIDES. 147 
 
 attention to the chemical properties of iodine in comparison 
 with those of its intimate congener, chlorine. As I shall pre- 
 sently show you, both elements possess in a striking degree the 
 property of oxidising various substances which resist the action 
 of ordinary oxygen ; and this observation leads me to make a 
 few preliminary remarks upon the process of oxidation in 
 general. 
 
 (155.) It is well known that many oxidisable bodies which 
 are unable or scarcely able to combine directly with free oxygen, 
 can nevertheless combine on the instant with oxygen that is 
 already in a state of combination. It seems, indeed, as if the 
 fact of previous combination conferred upon the transferable 
 oxygen a greater activity or tendency to unite with other bodies. 
 Of this peculiarity of behaviour, the non-oxidation or slow oxi- 
 dation of sulphurous acid H 2 S0 3 , into sulphuric acid H 2 S0 4 , by 
 mere exposure to oxygen or air, and its rapid oxidation by means 
 of certain hyper-oxygenised compounds, such as the peroxides 
 of hydrogen and nitrogen, affords us an excellent illustration. I 
 have here a freshly made solution of sulphurous acid, and to it I 
 add a little chloride of barium, which, you observe, does not in 
 the least disturb its transparency, thereby showing its freedom 
 from any trace of sulphuric acid. I now draw a rapid current of 
 air through the mixed liquid, but with no obvious effect. The 
 sulphurous acid and oxygen, despite their agitation together, 
 remain sulphurous acid and oxygen, instead of combining with 
 one another to form sulphuric acid. Accordingly, we have not 
 enough sulphuric acid produced to afford even a turbidity 
 with the previously added barium-salt, although, by a pro- 
 longed agitation with one another, some sulphuric acid would 
 be slowly formed. I now divide the mixed solution of sul- 
 phurous acid and chloride of barium, and to one portion add a 
 little peroxide of hydrogen, when immediately we get a copious 
 white precipitate of sulphate of barium, showing that the sul- 
 phurous acid, which would not unite with the free oxygen of the 
 air, has united at once with the combined oxygen of the peroxide, 
 thus : 
 
 L2 
 
148 AXIMAL CHEMISTRY LECTURE VI. 
 
 Sulphurous Hydric perox. Sulphuric "Water 
 
 H a S0 3 H 2 0.0 = H 2 S0 4 + H a O, 
 
 The second half of the liquid I now pour into this bottle, 
 charged, as you see, with brown fumes of peroxide of nitrogen, 
 and agitate the whole for an instant or so ; when the rapid oxida- 
 tion of the sulphurous acid is rendered evident, in this as in the 
 former experiment, by an abundant precipitation of sulphate of 
 barium, while the brown peroxide is simultaneously reduced to 
 the state of colourless oxide of nitrogen, thus : 
 
 Sulphurous Nitric perox. Sulphuric Nitric oxide 
 
 H a S0 3 + NO.O = H 2 S0 4 + NO. 
 
 (156.) The peroxides of hydrogen and nitrogen, therefore, are 
 deoxidised by sulphurous acid in a precisely similar manner ; but 
 we shall find a great diiference of behaviour in the protoxides re- 
 sulting from their respective deoxidations. Thus the protoxide of 
 hydrogen, or water, is a far more difficult substance to peroxidisethan 
 sulphurous acid itself. It is only, indeed, by a series of indirect 
 processes that we are able to fasten on to its molecule an additional 
 atom of oxygen, so as to convert it into the peroxide; and this 
 added atom of oxygen is retained with such a feeble force, that it 
 is frequently thrown off in the gaseous state, and constantly 
 given up with the greatest readiness to any oxidisable substance, 
 such as sulphurous acid. Although, therefore, it seems strange 
 that sulphurous acid should not readily absorb oxygen from the 
 air, there is nothing strange in its taking away the additional 
 loosely combined oxygen existing in peroxide of hydrogen. But 
 the oxide of nitrogen resulting from the deoxidation of its per- 
 oxide is a very different kind of body. Of all compounds known 
 to chemists it is the one which absorbs free oxygen with the 
 greatest avidity. No sooner, for instance, do I open the stopper 
 of this bottle than the contained nitric oxide which we reduced 
 from the peroxide a few minutes ago, combines at once with fresh 
 oxygen from the air to become reconverted into the brown per- 
 oxide ; and, on now closing the bottle and agitating its contents, 
 
ALTERATIVE ACTION OF IODINE. 149 
 
 the sulphurous acid, which is of itself unable to combine directly 
 with atmospheric oxygen, instantly robs the peroxide of nitrogen 
 of the oxygen which it had absorbed directly from the atmosphere, 
 as in the ordinary manufacture of sulphuric acid, thus : 
 
 Sulphurous 
 H a S0 3 
 
 Oxygen 
 + 
 
 Sulphurous 
 H,S0 3 
 
 Oxygen 
 f 0. 
 
 Nitric oxide 
 NO 
 
 Oxygen 
 + 
 
 Nitric peroxide 
 N0 2 . 
 
 ...-;. 
 
 Sulphurous Nitric perox. Sulphuric Nitric oxide 
 
 H a S0 3 + N0 a = H a S0 4 + NO. 
 
 (157.) Nitric oxide and peroxide, then, are the types of chemi- 
 cally mobile compounds. Eegarded as a reducing agent, there 
 are many more powerful de-oxygenants than the oxide ; regarded 
 as an oxidising agent, there are many more energetic oxyge- 
 nants than the peroxide ; but there are no two associated bodies 
 known to chemists which respectively absorb and evolve oxygen 
 with so much facility. As remarked by Laurent, ' There is no 
 substance which presents such singular properties as nitric oxide. 
 i . - . It is, perhaps, the only body which, in the dry state and 
 at the ordinary temperature, can combine suddenly with oxygen. 
 The combination, moreover, takes place without the evolution of 
 heat, and the body which results, far from retaining the oxygen 
 that it has so readily absorbed, is perhaps of all bodies the one 
 which is deoxidised most easily.' Now, while chlorine may be 
 compared to peroxide of hydrogen, it is the sort of chemical 
 mobility manifested by the oxides of nitrogen, which is charac- 
 teristic of iodine, and, I believe, of most mineral alteratives. 
 Iodide of hydrogen or potassium is, like nitric oxide, a facile 
 reducing agent, and free iodine or hypiodite of potassium, like 
 peroxide of nitrogen, a facile oxygenant so that wherever the 
 iodine travels it is capable of influencing the processes of oxida- 
 tion there going on absorbing oxygen where there is excess, 
 delivering active oxygen where there is deficiency just as our 
 nitric compound absorbs oxygen from the air and delivers it up 
 
15 ANIMAL CHEMISTRY LECTURE VI. 
 
 to the sulphurous acid. It is this chemical mobility of iodine, 
 then, which chiefly distinguishes it from its more active con- 
 geners, chlorine and bromine. The general chemical relationship 
 of these three elements to one another is most striking. With 
 the probable exception of fluorine, they possess the exclusive 
 property of uniting with hydrogen in the proportion of volume 
 to volume, the combinations, moreover, being unattended by 
 any condensation. Again, the resulting compounds namely, 
 the hydrochloric, hydrobromic, and hydriodic acids are all 
 gaseous, all fuming, all soluble in water, and all producible by 
 similar reactions. 
 
 (158.) Another common property by which chlorine, bromine, 
 and iodine are characterised, is their marked activity when in 
 the free state, which very greatly exceeds that of oxygen under 
 similar conditions. In my last lecture I showed you the violent 
 action of chlorine on metallic copper, upon which ordinary 
 oxygen is, as you know, almost without action ; and I have only 
 a few minutes back referred to the little effect exerted by free 
 oxygen upon various oxidisable bodies. But chlorine, bromine, 
 and iodine act upon different metals, pseudo-metals, and com- 
 pounds, with the greatest readiness ; and, indeed, several of the 
 iodides contained in the London and British Pharmacopoeias are 
 directed to be made by treating the respective metals at once 
 with iodine. Lastly, all three elements are capable of acting as 
 oxidising agents in cases where free oxygen is altogether, or 
 almost, impotent. They contain no oxygen, it is true, and are, 
 on the contrary, so far as our present knowledge goes, simple or 
 elementary bodies. Nevertheless, in the presence of water, they 
 act as very powerful oxygenants by uniting with the hydrogen of 
 the water, and so liberating its pre-combined, and consequently 
 active oxygen. Thus, on adding chlorine, bromine, and iodine 
 respectively to the clear mixture of sulphurous acid and chloride 
 of barium contained in these three glasses, we have in each in- 
 stance an immediate precipitate of sulphate of barium from the 
 oxidation of the sulphurous acid just as in our former experi- 
 ments with the peroxides of hydrogen and nitrogen the reaction 
 being as follows : 
 
INDIRECT OXIDATION BY HALOGENS. 151 
 
 Sulphurous Water Chlorine Sulphuric Chlorhydric 
 
 H a S0 3 + H a O + Cl a = H a S0 4 + aHCL 
 
 Here, again, I have three white magmas of protoxide of lead, 
 with an excess of dilute alkali, exposed freely to the air ; and 
 this protoxide, although it does not absorb oxygen from the air, 
 yet when treated with chlorine, bromine, and iodine, is at once 
 oxidised more or less completely into the brown peroxide, as you 
 perceive, thus : 
 
 Lead-oxide Water Bromine Lead-perox. Bromhydric 
 
 PbO + H a O + Br a = PbO a + 
 
 Lastly, I have in these three glasses some solution of blue 
 indigo exposed to the air, but unoxidised by the air. On adding 
 chlorine, bromine, and iodine, however, it is at once bleached or 
 oxidised into isatin, thus : 
 
 Indigo Water Iodine Isatin lodhydric 
 
 C 8 H 5 NO + H a O + I, = C 8 H 5 NO a + aHL 
 
 ( 1 59.) In all these particulars, then, chlorine, bromine, and iodine, 
 though so different in their medicinal action, resemble one ano- 
 ther to the greatest extent chemically. Now let us see what are 
 their chemical, and, I may add, physical differences. I will first 
 advert to their combining proportions, or the relative weights of 
 each of them, which unite with I part by weight of hydrogen. 
 These are indicated by the numbers 35*5, 80, and 127, which 
 also represent their respective specific gravities-, when in the 
 gaseous state. You will observe that the proportional number 
 of bromine is intermediate between that of chlorine and iodine, 
 and indeed approximates very closely to the true arithmetic 
 mean, ^ = 8o'8, thus : - 
 
 Cl 35*5 Chlorine. 
 
 Br 80 Bromine. 
 
 I 127 Iodine. 
 
152 ANIMAL CHEMISTRY LECTUKE VI. 
 
 The circumstance of these numbers also expressing the chemical 
 equivalents of the several elements leads to some curious medico- 
 chemical considerations. Thus, bearing in mind that sodium and 
 potassium are related to one another in much the same way as 
 are chlorine and iodine, though not perhaps quite so intimately, 
 it will follow that 58*5 parts of common salt or chloride of sodium 
 and 74-5 parts of chloride of potassium are the chemical equiva- 
 lents of 1 66 parts of iodide of potassium, thus : 
 
 NaCl 23 + 35-5 = 58-5 
 
 KC1 39 + 35-5 = 74-5 
 
 KI = 39 + 127 = 166-0 
 
 Chemically, then, 58*5 parts of chloride of sodium are just as 
 efficient as 1 66 parts of iodide of potassium ; but while most of 
 us, I suppose, are in the habit of taking fifty or sixty grains of 
 common salt twice or three times a day, none of us, I conceive, 
 would like to take 166 grains of iodide of potassium even once 
 in the same period. 
 
 (160.) The gradational difference subsisting between the 
 atomic weights or volume-weights of chlorine, bromine, and 
 iodine is typical of all their chemical and physical differences. 
 Thus their usual states of aggregation, gaseous, liquid, and solid, 
 and the colours of their respective gases or vapours, green, 
 orange, and violet, are sequential to one another ; while, in a 
 chemical point of view, we notice a successive decrease of the 
 force with which they respectively enter into and remain in com- 
 bination with most other bodies. Thus chlorine combines 
 directly with hydrogen upon simple exposure of the mixed 
 gases to ordinary daylight, and the resulting chlorhydric acid is 
 an extremely stable body. But the direct combination of bro- 
 mine with hydrogen takes place very imperfectly, and then only 
 at a red heat, while the bromine of the resulting compound is 
 liberated with comparative ease. Further, the direct combina- 
 tion of iodine with hydrogen is almost impracticable, while the 
 iodhydric acid resulting from the indirect combination of the two 
 elements is readily decomposed even by the action of atmospheric 
 
COMPARISON OF IODINE WITH CHLORINE. 153 
 
 oxygen, thus : 2HI + O=H 2 O + 1 2 . Now, it is this feebleness of 
 the force with which iodine enters into certain combinations, and 
 consequent facility with which it is separated from such combi- 
 nations, that give it that peculiar mobility to which I have 
 already adverted. The chief chemical difference, indeed, be- 
 tween chlorine and iodine seems to be that chlorine in the free 
 state is far more active than iodine, and iodine in the combined 
 state far more mobile than chlorine, while in both respects bro- 
 mine occupies an intermediate position. Hence, on adding a 
 little bromine-water to this solution of iodide of potassium, the 
 bromine expels the iodine, KI + Br = KBr + I, which, dissol- 
 ving in the chloroform I had previously introduced, manifests 
 itself to you by the production of a beautiful violet-coloured 
 stratum at the bottom of the tube. Similarly, when I add a 
 little chlorine water to this solution of bromide of potassium, the 
 chlorine expels the bromine, KBr + Cl KCl + Br, which dissolv- 
 ing in the previously introduced ether, floats on the surface as an 
 orange-brown layer ; so that while bromine expels iodine, chlorine 
 expels bromine, and a fortiori iodine, from their respective com- 
 binations. Accordingly, we may regard 35*5 parts of chlorine 
 as an energetic representative of 127 parts of iodine ; but it is 
 this very energy of chlorine, I conceive, which disqualifies it for 
 acting medicinally as an alterative. On account of its intense 
 chemical affinity, it unites more rapidly and forcibly than iodine 
 with the different basyloids it may chance to encounter, but di- 
 rectly it has entered into combination with them, its work is done, 
 its action ceases. The resulting chloride of sodium, or other 
 chloride, is of so stable a nature as to be impressionable only to 
 violent chemical agencies ; whereas, iodine, on the other hand, 
 forming very unstable compounds, is constantly, with every 
 change of circumstance, entering into a fresh state of liberation 
 or combination constantly effecting fresh oxidising or deoxidis- 
 ing actions. 
 
 (161.) I have already given you several illustrations of the 
 oxidising action of free iodine, and ought, perhaps, to mention 
 one or two instances of the correlative deoxidising action of com- 
 
154 ANIMAL CHEMISTRY LECTtRE VI. 
 
 bined iodine. You will remember that succinic acid, which is so 
 to speak, the oxalic acid of the butyric group, is intimately asso- 
 ciated with certain other members of the same group, thus : 
 
 Succinic Sub-group 
 C 4 H 4 4 Fumaric. 
 
 C 4 H 6 4 Succinic. 
 
 C 4 H 6 S Malic. 
 
 C 4 H 6 6 Tartaric. 
 
 Now tartaric acid, when heated with aqueous iodide of hydro- 
 gen or iodhydric acid, is converted into malic acid with liberation 
 of iodine, thus : 
 
 Tartaric Iodhydric Malic Iodine Water 
 
 C 4 H 6 6 + zHI = C 4 H 6 5 + I, + H 3 0. 
 
 Similarly the malic and fumaric acids are reducible into suc- 
 cinic acid by means of iodhydric acid, thus : 
 
 Malic Iodhydric Succinic Iodine Water 
 
 C 4 H 6 5 + aHI = C 4 H 6 4 + I, + H a O. 
 
 Fumaric Iodhydric Succinic Iodine 
 
 C 4 H 4 O 4 + aHI = C 4 H 6 4 + I,. 
 
 Accordingly, we find that while free iodine, acting as an oxi- 
 dising agent, produces iodhydric acid, this same acid, acting as a 
 deoxidising agent, reproduces free iodine. Here, for instance, 
 I have some iodhydric acid, mixed with a little starch to show 
 the results of the experiment. I now add to the iodhydric acid 
 some peroxidised substance, which it immediately reduces, with 
 liberation of iodine, as shown by the blue colour of the liquid. 
 I now add to the free iodine some suboxidised substance, which 
 it immediately oxidises, with reconversion into iodhydric acid, as 
 shown by the disappearance of the blue colour. On now adding 
 some more of the peroxidised substance, I re-liberate the iodine, 
 and, on afterwards adding some more of the suboxidised substance, 
 I reproduce the iodhydric acid, and so on ad infinitum. The 
 characteristic chemical property of iodine consists, therefore, in 
 
METALLIC ALTERATIVES. 155 
 
 the comparative feebleness of its affinities, or in the loose state of 
 combination with which it is capable of being retained by other 
 bodies ; so that, while the more energetic chlorine acts once for 
 all, the less energetic iodine .is acting and reacting upon every 
 occasion. Accordingly, while it makes all the difference whether 
 we employ free chlorine or chloride of sodium to produce the 
 therapeutic effects of chlorine, it makes very little difference 
 whether we employ free iodine or iodide of potassium to produce 
 the therapeutic effects of iodine. Wherever the element travels, 
 it either oxidises or deoxidises, accordingly as it comes into contact 
 with bodies more or less oxidisable than itself, at that particular 
 moment. It acts, in fact, not only as a converter of inactive or 
 free, into active or combined oxygen, but also as a conveyer of 
 oxygen from wherever it is in excess to wherever it is in defi- 
 ciency. 
 
 (162.) Now, what is true of iodine and its compounds is also 
 true of the compounds of mercury, of arsenic, and of another 
 metal whose alterative action is manifested in almost an opposite 
 fashion, namely, iron. Considered chemically, the compounds 
 of these three metals are, perhaps, the most constantly impression- 
 able of any with which we are acquainted. In the laboratory, 
 and even in the factory, we habitually avail ourselves of mercuric, 
 arsenic, and ferric compounds as oxygenants, and of mercurous, 
 arsenious, and ferrous compounds as deoxygenants or reducants. 
 The relationship between chlorine and iodine is parallel to that 
 between phosphorus and arsenic, the phosphoric and arsenic 
 acids, for instance, though so different in their therapeutic effects, 
 being the strict chemical analogues of one another. Phosphorus is 
 a far more active element than arsenic, and its combinations are 
 far more stable. Phosphate of sodium, once formed, is like common 
 salt; a stable innocuous body; while arseniate of sodium, like iodide 
 of potassium, is an active body, because of its instability because 
 of the liability of its arsenical constituent to affect and be affected 
 by the chemical actions taking place everywhere throughout the 
 body. I am far, of course, from thinking that this susceptibility 
 to oxidation and deoxidation furnishes a complete solution of the 
 
156 ANIMAL CHEMISTRY LECTURE VI. 
 
 medicinal efficacy of alterative salts. But when we remember 
 that every change produced in the composition of any part of the 
 animal body is a chemical change, necessitating a correlative 
 change in the composition of the reacting substance, it is obvious 
 that we must look for alterative agents among that class of sub- 
 stances which are most susceptible of chemical change ; and I 
 would add further, that an explanation of the different kinds of 
 alterative effect producible by different classes of compounds, as 
 of mercury and iron, for instance, is, doubtless, to be sought for 
 in the different chemical habitudes of the respective elements. 
 
 (163.) A few words upon the effect of alkalies in promoting 
 oxidation. I mentioned in my last lecture the peculiar decom- 
 position of animal substances resulting from their treatment with 
 caustic alkali, and consisting in an oxidation of their carbonous 
 at the expense of their hydrogenous constituents. Now, this 
 action is apparently determined by the tendency which exists 
 among differently characterised elements to arrange themselves in 
 stable groupings, and more particularly to form stable oxi-salts. 
 The presence of alkali rendering the formation of such salts pos- 
 sible, by furnishing the necessary base, we find that under treat- 
 ment with caustic potash KHO, for instance, the carbon of organic 
 matter is oxidised into various acids, which appear in the form of 
 their respective potassium-salts ; while the excessive hydrogen of 
 the organic matter, together with that of the potash employed, is 
 liberated in the gaseous state, as already exemplified by the re- 
 action of caustic potash with oil of bitter almonds. As a 
 result of this tendency, then, we obtain, as I have previously 
 remarked, very similar products by fusing animal substances with 
 caustic alkalies, and by submitting them to the action of powerful 
 oxygenants. It is observable, however, as well in artificial as in 
 natural processes, that the ultimate effects of a gentle chemical 
 action are often more complete than the immediate results of a 
 comparatively violent one ; and it is to this more gentle action 
 of alkalies that I would now direct your attention. We find that 
 many organic substances, which of themselves are scarcely affected 
 by exposure to oxygen or air, undergo a complete and even some- 
 
ALKALINE ALTERATIVES. 157 
 
 what rapid oxidation under the influence of alkalies, the tendency 
 of their constituent carbon to become oxidised, otherwise inferior 
 to that of their constituent hydrogen, becoming intensified, appa- 
 rently because of the opportunity afforded by the presence of the 
 alkali for the formation of salts instead of acids. 
 
 (164.) Be the explanation, however, what it may, the fact is 
 unquestionable, and readily admits of experimental illustration. 
 For instance, I have in this porcelain dish the watery solution of 
 a substance well known to photographers as pyrogallic acid, 
 though its acidity is of such a feeble character that it is nowadays 
 more frequently spoken of by chemists under the neutral appella- 
 tion of pyrogallin. At present, the solution in the dish, though 
 exposed freely to the air for upwards of an hour, has not under- 
 gone any appreciable oxidation. I now moisten the interior of 
 this long tube with a little aqueous potash, and invert it in the 
 solution, when the commencing oxidation of the dissolved pyro- 
 gallin is manifested to you by its almost immediate assumption 
 of a brown-black colour, followed by the gradual rising up of the 
 black liquid in the tube, through an absorption of the oxygen of 
 the contained air. The pyrogallin, which did not become oxi- 
 dised in any appreciable degree so long as there was no alkali 
 present, now becomes oxidised with considerable rapidity, as you 
 observe, yielding among other products acetate, oxalate and car- 
 bonate of potassium. Other familiar illustrations of this action 
 of alkalies are afforded us in the employment of lime to promote 
 the destructive oxidation of dead bodies, and as a manure to de- 
 stroy the organic matter of peaty soils. Some very interesting 
 results have also been obtained by Gorup-Besanez, who found 
 that glycerin, sugar, leucine, hippuric acid, oxalic acid, and the 
 fatty and aromatic acids, which of themselves were unacted upon 
 by ozonised air, underwent a very complete oxidation when sub- 
 mitted to the same reagent in the presence of caustic or even 
 carbonated alkali. Benzoic acid, for instance, which results from 
 the violent oxidation of animal matter, and consistently resists the 
 action of very powerful oxygenants, undergoes a complete and 
 somewhat speedy oxidation when submitted in alkaline solution 
 
158 ANIMAL CHEMISTRY LECTURE VI. 
 
 to the action of ozone. And in some of these oxidations the 
 curious circumstance was noted, that between the original sub- 
 stance stearic acid C^gH^C^, or benzoic acid C 7 H6O 2 , for in- 
 stance and the final carbonic acid, no intermediate products 
 could be detected. It seemed, indeed, as if portion after portion 
 of the original substance was completely oxidised and broken 
 up into separate molecules of carbonic acid, instead of the entire 
 substance undergoing a gradual oxidation and simplification, by 
 the successive burning off of its constituent carbon-atoms, one 
 after another, into carbonic acid. With such facts as these before 
 us, I would submit that the so-called resolvent action of alkalies 
 upon the animal economy, like that of iodine, is a direct conse- 
 quence of the peculiar chemical characterisation by which they 
 are enabled to act as oxidising agents. 
 
 (165.) Despite, however, the interest of these questions, upon 
 which I have been able to bestow but a very hasty notice, I must 
 now break off their discussion altogether, and regretfully take my 
 leave of you. In bringing this course of lectures to a conclusion, 
 I have to thank you, my indulgent auditors, and more particu- 
 larly the President and Fellows of the College, for the kind 
 encouragement which your continued presence has afforded me. 
 I am aware how far short my lectures have fallen of that de- 
 gree of excellence which I had hoped to attain, and you had a 
 right to expect ; and how much the measure of success which has 
 attended them must be attributed to the intrinsic merit of the 
 subject, and your good-natured willingness to be pleased with its 
 expounder. I have endeavoured throughout to bring prominently 
 before you the dynamical idea of organic chemistry, as connected 
 with changes of composition. I have shown you that, in the 
 organism of the plant, carbonic acid and water are submitted to 
 a constant deoxidising change, whereby they become successively 
 converted into more and more complex bodies, many of which 
 we are now able to produce, all of which we hope some day to 
 produce, by similar processes in the laboratory ; that the change 
 in composition undergone by carbonic acid and water is attended 
 by a storing-up of solar force in the resulting products, and that 
 
DYNAMICAL VIEW OF ORGANIC CHEMISTRY. 159 
 
 the correlative change in composition undergone by these pro- 
 ducts into water and carbonic acid is attended by a liberation of 
 the force stored up in them ; that in every organ of the animal 
 body oxidation is continually taking place to furnish that organ 
 with the force necessary for the performance both of its nutritive 
 acts and external manifestations ; that the juice of every gland 
 and muscle is crowded with oxidised products of its own meta- 
 morphosis, similar to, or even identical with, those procurable 
 by an artificial oxidation of the selfsame tissue out of the body ; 
 that inasmuch as the exercise of every function of the living body 
 is attended by, and consequent upon, a change of chemical com- 
 position, the investigation of every action of the body, even of 
 those which are the most mechanical, becomes to a large extent a 
 chemical question ; and lastly, that while perversions of nutrition, 
 perversions of metamorphosis, and the modifying influence of re- 
 medies, are many-sided subjects which may be viewed from many 
 different aspects, he must have but a very imperfect and one-sided 
 view of these subjects, who leaves the chemical aspect altogether 
 out of his consideration. 
 
INDEX. 
 
 ACE 
 
 A CETAMIDE, residues of, 27 
 J\. Acetic acid, congeners of, 47 
 
 inflammability of, 34 
 
 synthesis of, 59-91 
 
 Acetonitrile, residues of, 27 
 Acetylene, characters of, 90 
 
 hydrogenation of, 88 
 
 synthesis of, 88 
 
 Acids and amides, mutual metamor- 
 phoses of, 1 1 8 
 Acids, oxidation by, 117 
 Alcohol, synthesis of, 89 
 Alcohols, synthetic plasticity of, 82 
 Aldehydes, acidifiability of, 1 1 1 
 
 examples of, 1 1 1 
 
 properties of, no 
 Alkalies, oxidation by, 157 
 Allantoine, a diureide, 136 
 Allophan, a polymerone, 43 
 Allophanic acid, a mon-ureide, 133 
 Alloxan, a mon-ureide, 136 
 Alterative action of iodine, 155 
 Alteratives, action of alkaline, 156 
 
 action of metallic, 155 
 Amides, cyanuric, 19 
 
 mineral, 16 
 
 organic, 17 
 
 Amid-hypoxanthine, orguanine, 139 
 Ammonia, a pabulum for plants, 52 
 
 acetate, dehydration of, 27 
 
 nitrogen a proxy for, 55 
 
 oxalate, dehydration of, 29 
 
 type, 10 
 
 Aniline, synthesis of, 94 
 Animal products, list of, 5 
 Animality, characteristics of, 77 
 An-ureide acids, 131 
 Aplones, combination of, 55 
 
 CHE 
 
 Aplone molecules, 30 
 Aromatic acids of flesh, 115 
 
 series of, 34 
 
 Asparagine, decomposition of, 92 
 
 Atomic heats, 14 
 
 Atomic weights, table of, 1 5 
 
 "DARBITURIC ACID, a mon-ure- 
 _D ide, 144 
 Benzamide, origin of, 37 
 Benzoglycolic acid, origin of, 38 
 Benzoic acid, synthesis of, 94 
 group, 35 
 
 Bile-acids, polymerones, 44 
 Birds, tissue-oxidation in, 144 
 Butyric acid group, 32 
 synthesis of, 92 
 
 nAEB-ANHYDEIDE, carbon 
 \J from, 63 
 
 reduction of, 62 
 
 Carbon -atoms, conjunction of, 51 
 
 separation of, 49 
 
 Carbon, combination-heat of, 100 
 
 combustion of, 6r 
 Carbon-compounds, complexity of, 2 3 
 number of, 23 
 
 Carbonic acid, metamorphoses of, 84 
 
 series, 36 
 
 Carbonic oxide, combination-heat of, 
 142 
 
 synthesis by, 83 
 
 Chemical action, nature of, 4 
 
 of medicines. 146 
 
 Chemical actions of plant-life, 63 
 
 elements, 7 
 
1 62 
 
 INDEX. 
 
 CHE 
 
 Chemical powers, limit to ? 58 
 
 types, 7 
 Chemistry, dynamical, 4 
 
 first principles of, 2 
 
 organic, Analytic, 49 
 synthetic, 60 
 
 statical, 3 
 
 synthetic, economy of, 96 
 
 results of, 95 
 
 Chlorides, metallic, 14 
 
 typical, 13 
 Chlorine, activity of, 152 
 Classification of uric acid products, 
 
 I 3 I 
 
 Coal-tar colours, syn thesis of, 95 
 Combination of hydrogen and car- 
 bon, direct, 89 
 Combination-heat of carbon, 100 
 
 carbonic oxide, 142 
 
 hydrogen, zoo 
 
 zinc, 72 
 
 Combustion, solar heat restored by, 75 
 Corrosive sublimate, formula of, 14 
 Cross-bow, force of, 70 
 Cyanogen, production of, 28 
 residues of, 29 
 Cyanuric amides, 1 9 
 
 TkEHYDROGENATION of uric 
 JL/ acid, 129 
 Diamerone, myricin, a, 42 
 
 spermaceti, a, 41 
 urea, a, 41 
 
 Diamerones, examples of, 40 
 
 the fats, 42 
 
 monureide, 135 
 Diamide, urea, a, 18 
 Diureide, allantoine, a, 136 
 
 mycomelic acid, a, 136 
 Dynamical chemistry, 4 
 Dynamics of uric acid, 142 
 
 E DUCTS and products, 22 
 Electrolysis, heat absorbed in, 74 
 
 nature of, 71 
 of water, 73 
 
 Elements, chemical, 7 
 
 Empiric formula of tyrosine, 1 20 
 
 Energy, actual, 7 
 
 potential, 71 
 
 HEA 
 
 Ethylene, synthesis of, 88 
 Excretion of urates by birds, 141 
 by reptiles, 141 
 
 FATS, the, diamerones, 42 
 oxidation-products of, 48 
 Fatty acid series, 3 1 
 
 acids of flesh, 114 
 
 properties of, 33 
 
 series of diatomic, 36 
 
 alcohol series, 35 
 
 aldehyde series, 35 
 Flesh, aromatic acids of, 115 
 Flesh-oxidation, acids of, 113 
 Foot-pound, meaning of, 104 
 Force absorbed in nutrition, 76 
 
 indestructibility of, 76 
 
 solar origin of muscular, 107 
 Formation of peroxides, 148 
 Formic acid, history of, 85 
 
 compounds, 85 
 
 pALLIC ACID, synthesis of, 94 
 \J Gelatin, sugar of, 119 
 Glycerin, synthesis of, 9?- 
 Glycocine, occurrence of, 119 
 
 of hippuric acid, 38 
 
 synthesis of, 91 
 Grape-sugar, synthesis of? 93 
 Group benzoic, 35 
 
 butyric, 32 
 
 propionic, 31 
 Group-terms, principal, 32 
 Guanidine, an amide, 19 
 
 production of, 139 
 
 Guanine, or amid-hypoxan thine, 139 
 
 HALOGENS, differences between, 
 151 
 
 mutual resemblances of, 150 
 oxidation by, 1 5 1 
 
 Heat absorbed in electrolysis, 74 
 in vegetation, 75 
 
 and motion, correlation of, 68 
 
 intensity of, 101 
 
 of friction, 69 
 
 quantity of, lor 
 
 solar, restored by combustion, 75 
 
 transformations of, 68 
 
INDEX. 
 
 i6 3 
 
 HEA 
 
 ORG 
 
 Heat, unit of, 100 
 Heats, atomic, 14 
 Hippuric acid, constitution of, 36 
 
 decompositions of, 37 
 
 glycocine of, 38 
 
 residues of, 39 
 
 Homologous series, 33 
 Hydrates, mineral, 16 
 
 organic, 17 
 Hydrides, typical, 13 
 Hydrocarbons, series of aromatic, 35 
 Hydrochloric acid type, 7 
 Hydrogen and carbon, direct com- 
 bination of, 89 
 
 Hydrogen, combination -heat of, 100 
 
 combustion of, 61 
 Hydrogenation of acetylene, 88 
 Hypoxanthine, occurrence of, 137 
 
 IGNITION of platinum wire, 73 
 Indestructibility of force, 76 
 Indigo, in urine, 122 
 
 nature of, 121 
 Intensity of heat, 101 
 lodhydric acid, reductions by, 153 
 Iodine, alterative action of, 1 54 
 
 mobility of, 149 
 
 KILOGEAM-METEE, meaning 
 of, 104 
 Kreatine, a polymerone, 44 
 
 LACTIC ACID, synthesis of, 92 
 Leucine, association of, with 
 tyrosine, 116 
 
 distribution of, 116 
 
 formation of, 5, 117 
 List of animal products, 5 
 
 MALIC ACID, synthesis of, 93 
 Mannite, production of, 51 
 Manures, nitrites as, 54 
 Marsh-gas, derivatives of, 88 
 
 production of, 87 
 
 Matter, kinds of, 3 
 Medicines, chemical action of, 146 
 Mesoxalic acid, deoxidation of, 133 
 oxidation of, 131 
 
 Metallic alteratives, action of* 155 
 
 chlorides, 14 
 
 Metamorphoses of carbonic acid, 84 
 Methylamine, 40 
 Methyl-compounds, 86 
 Methyluramine, a polymerone, 45 
 Mineral amides, 1 6 
 
 hydrates, 16 
 Mobility of iodine, 149 
 
 of nitric oxides, 149 
 Molecular volumes, 1 1 
 Molecules, aplone, 30 
 
 nitrogen, 52 
 
 polymerone, 30 
 Mon-ureide, allophanic acid, a, 1 3 3 
 alloxan, a, 136 
 
 barbituric acid, a, 136 
 
 Monureides, dehydration of, 133 
 Motion, arrest of, 68 
 
 and heat, correlation of, 68 
 
 transmission of, 69 
 
 unit of, 103 
 
 Muscle-heat and motion, correlation 
 of, 1 06 
 
 oxidation, economy of, 105 
 
 results of, 98 
 
 Muscular activity, conditions of, 97 
 
 force, solar origin of, 107 
 Mutual metamorphoses of acids and 
 
 amides, 118 
 
 Mycomelic acid, a diureide, 136 
 Myricin, a diamerone, 42 
 
 NITEIC OXIDES, mobility of, 
 149 
 Nitriles, acidifiability of, 113 
 
 nature of, 112 
 Nitrites as manures, 54 
 Nitrogen a proxy for ammonia, 55 
 
 molecules, 52 
 
 production of, 54 
 Nitrous acid, formation of, 53 
 
 reduction of, 53 
 
 Nutrition, force absorbed in, 76 
 
 OEGANIC AMIDES, 17 
 chemistry, analytic, 49 
 synthetic, 60 
 
 groups and series, 30 
 
 hydrates, 17 
 
164 
 
 INDEX. 
 
 ORG 
 
 SYN 
 
 Organic proximate principles, 22 
 Oxalate of ammonia, dehydration of, 
 
 29 
 Oxalic acid, oxidation of, 132 
 
 series, 36 
 
 synthesis of, 92 
 
 Oxalurate of calcium, in urine, 135 
 Oxidation by acids, 1 1 7 
 
 by alkalies, 157 
 
 by fused potash, 117 
 
 by peroxides, 147 
 
 slow or rapid, 102 
 
 Oxygen, evolution of, by plants, 50 
 
 "PEROXIDES, formation of, 148 
 JL oxidation by, 147 
 
 reduction of, 147 
 Phenol in urine, 123 
 
 Plant life, chemical actions of, 63 
 Plants, ammonia, a pabulum for, 52 
 
 evolution of oxygen by, 50 
 Platinum wire, ignition of, 73 
 Polymerone molecules, 30 
 
 allophan, a, 43 
 
 kreatine, a, 44 
 
 methylamine, a, 45 
 
 taurine, a, 43 
 
 uric acid, a, 128 
 Polymerones, the bile acids, 44 
 
 examples of, 43 
 Populin, composition of, 25 
 
 residues of, 27 
 
 Potash, oxidation by fused, 117 
 Processes, animal and vegetable, 64 
 Products and educts, 22 
 
 formation of vegetable, 79 
 Propionic group, 3 1 
 Proximate principles, organic, 22 
 Prussic acid, production of, 86 
 
 vital origin of? 58 
 
 Pseudo-uric acid, production of, 140 
 
 Q 
 
 UANTITY of heat, 101 
 
 RATIO of urea to carbonic acid, 
 99 
 
 Reduction of peroxides, 147 
 Residues, doctrine of, 26 
 
 SALICIC ACID, synthesis of, 
 94 
 
 compounds, 121 
 Salicin, composition of, 25 
 
 hydration of, 26 
 
 residues of, 26 
 Saligenin, reaction of, 25 
 Salisuric acid in urine, 123 
 Sarcosine, synthesis of, 91 
 Series of aromatic acids, 34 
 hydrocarbons, 35 
 
 carbonic acid, 36 
 
 of fatty acids, 3 1 
 
 diatomic, 36 
 
 alcohols, 35 
 
 aldehydes, 35 
 
 oxalic acid, 36 
 Spermaceti, a diamerone, 41 
 Statical chemistry, 3 
 Steam-engine, principle of, 68 
 Sub-oxidised tissue-products, 108 
 Succinic acid, synthesis of, 92 
 Sugar of gelatin, 21 
 
 Sugar, vital origin of? 57 
 Syntheses, continuous, 81 
 Synthesis by carbonic oxide, 83 
 
 of acetic acid, 59, 91 
 
 acetylene, 88 
 
 alcohol, 89 
 
 aniline, 94 
 
 benzoic acid, 94 
 
 butyric acid, 92 
 
 coal-tar colours, 95 
 
 ethyl ene, 88 
 
 gallic acid, 94 
 
 glycerin, 92 
 
 glycocine, 91 
 
 grape sugar? 93 
 
 lactic acid, 92 
 
 malic acid, 92 
 
 oxalic acid, 92 
 
 salicic acid, 94 
 
 sarcosine, 91 
 
 succinic acid, 92 
 
 tartaric acid, 92 
 
 taurine, 90 
 
 valeric acid, 93 
 
 Synthetic chemistry, economics of, 
 96 
 
 results of, 95 
 
 Synthetic methods, general, 81 
 
 plasticity of alcohols, 82 
 
INDEX. 
 
 ,6 S 
 
 TAB 
 
 rpABLE of atomic weights, 15 
 JL of uric acid products, 1 34 
 Tartaric acid, synthesis of, 92 
 Taurine, a polymerone, 43 
 
 occurrence of, 6 
 
 synthesis of, 90 
 Tissue-oxidation, in birds, 142 
 
 order of, 109 
 
 Tissue-products, sub-oxidised, 108 
 Trimethylamine, occurrence of, 87 
 Types, ammonia, 10 
 
 chemical, 7 
 
 hydrochloric acid, 7 
 
 water, 9 
 Typical chlorides, 1 3 
 
 hydrides, 12 
 
 Tyrosine, constitution of, 124 
 
 distribution of, 116 
 
 empiric formula of, 1 20 
 
 formation of, 117 
 
 TTNIT of heat, 100 
 U of motion, 103 
 Urea, a diamerone, 41 
 
 a diamide, 1 8 
 
 artificial production of, 86 
 
 existence of, in uric acid? 129 
 Uric acid, a polymerone, 128 
 
 decomposition of, 129 
 
 dehydrogenation of, 129 
 
 dynamics of, 142 
 
 excretion, by birds, 141 
 
 by reptiles, 141 
 
 existence of urea in ? 129 
 
 ZIN 
 
 Uric acid, history of, 127 
 
 products, classification of, 131 
 
 table of, 1 34 
 
 ultimate constitution of, 141 
 
 Urine, indigo in, 1 22 
 
 oxalurate of calcium in, 135 
 
 phenol in, 123 
 
 salisuric acid in, 123 
 Uroxanic acid, production of, 140 
 
 TTALEKIC ACID, synthesis of, 93 
 V Vegetation, experiments on, 50 
 heat absorbed in, 75 
 Vital force, actions of? 56 
 
 hypothesis of, 77 
 
 sugar formed by ? 57 
 
 views concerning, 57 
 
 Volumes, molecular, u 
 
 WATER, electrolysis of, 73 
 reduction of, 62 
 type, 9 
 Wood-spirit, production of, 87 
 
 "VANTHINE, history of, 138 
 -A. relations of, 138 
 
 ZINC, combination -heat of, 72 
 combustion of, 71 
 solution of, 72 
 
 ZONDON 
 
 PRINTED BY SPOTTJ 8WOODE AND CO. 
 NEW-STBEET SQTJAEE 
 
By the same Author. 
 
 Just published, the Second Edition, thoroughly revised, and illustrated with 
 
 70 new "Woodcuts of Microscopical Preparations and Chemical 
 
 Apparatus, in 1 vol. crown 8vo. price Is. 6d. 
 
 A COURSE OF 
 
 PRACTICAL CHEMISTRY 
 
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 THE USE OF MEDICAL STUDENTS. 
 
 THIS work is well known by name to students of the medical profession. 
 It has long been out of print; and second-hand copies, which are constantly 
 in demand, are rarely to be met with. The Author has therefore thoroughly 
 revised his work, and brought the practical information which forms its 
 basis up to the existing state of chemical science. 
 
 The arrangement of this Course is based upon an experience of fourteen 
 years' laboratory teaching. The subjects treated of in the four chapters 
 into which the work is divided are Chemical Manipulation, General Qualita- 
 tive Analysis, Toxicological Chemistry, and Animal Chemistry respectively. 
 Full instructions are given in the last chapter for the examination of 
 Healthy and Morbid Urine, Urinary Deposits, Calculi, &c. 
 
 Select Opinions 
 
 'Tins is the second edition of a 
 good book now greatly enlarged and im- 
 proved. It is said to be specially arranged 
 for the use of medical students, but, we need 
 hardly say, it is equally well adapted for 
 pharmaceutical chemists, and is indeed an 
 excellent introduction to analysis for any 
 students. It is worth mentioning that the 
 old scale of atomic weights has been exclu- 
 sively employed throughout the body of the 
 work ; and that a very useful chapter on 
 Chemical Manipulations, which greatly in- 
 creases the value of the book, now precedes 
 the analytical part.' CHEMICAL NEWS. 
 
 'DR. ODLING'S Practical Course is 
 admirably adapted for the guidance of 
 students of PHARMACY, it is also by far the 
 best laboratory guide for the student of 
 MEDICINE that has come under our notice. 
 Those who have read anything from the 
 pen of Dr. ODLING need not be informed 
 that it is extremely well written. The book 
 is furnished with an excellent index, and is 
 illustrated with seventy woodcuts of micro- 
 scopic preparations and chemical apparatus, 
 all of them engraved expressly for the work 
 from drawings of the actual objects.' 
 
 CHEMIST and DRUGGIST. 
 
 ' DR. ODLING has greatly enlarged 
 and improved the new edition of his work, 
 and arranged it specially for the use of 
 medical students. The introductory section 
 on chemical reactions calls for high praise 
 as a clear and simple account of them ac- 
 cording to the improved philosophy of 
 modern chemistry, in developing and enun- 
 
 of this Edition. 
 
 ciating which Dr. ODLING has stood promi- 
 nently f urward. A section on manipulation 
 has also been introduced in this edition, 
 fully illustrated with excellent woodcuts, 
 and one of the best short articles we have 
 read on this subject. The chapters on an- 
 alytical , tpxicological , and animal chemistry 
 have received many additions and improve- 
 ments. Besides the illustrations of chemical 
 apparatus, several others of microscopical 
 preparations are also inserted. The old 
 atomic weights are still used in the work ; 
 but with this exception modern formulae 
 are employed (with the old f ormulas added 
 when necessary), and many of the recent 
 improvements in nomenclature. As a work 
 on practical chemistry, Dr. ODLING'S book 
 in its present form supplies every want of the 
 junior medical student in an admirable 
 manner.' MEDICAL TIMES. 
 
 ' As a teacher of chemistry of many 
 years' standing, there are few professors 
 better qualified for the task of writing such 
 a work than Dr. ODLING, intimately and 
 practically acquainted as he is with all the 
 requirements of the student. It must be a 
 very difficult thing for a practical chemist 
 to write a small book ; for out of the abun- 
 dant stores of his own knowledge and ex- 
 perience he must feel constantly tempted to 
 dilate upon many parts of his subject; 
 and it is not one of the least merits of 
 Dr. ODLING, that he should have resisted 
 this temptation and have produced a work 
 remarkable for conciseness, clearness, exac- 
 titude, and thorough adaptation to the end 
 in view namely, the special use of the 
 medical and chemical student.' LANCET. 
 
 London: LONGMANS, GKEEN, and CO. Paternoster Row. 
 
By the same Author. 
 Lately published, PART I. in 8vo. price 
 
 A MANUAL OF CHEMISTRY, 
 
 DESCRIPTIVE AND THEORETICAL 
 
 ' OP DR. ODLING'S Manual of Chemistry ' 
 we are glad to speak with the greatest) 
 praise.' MEDICAL TIMES and GAZETTE. 
 
 ' THIS is an elaborate introduction to pure 
 chemistry, and may be regarded as an ex- 
 ponent of the views of the subject now taken 
 by the most eminent men of science. The Author 
 states that it was undertaken more especially at 
 the request of Prof. Brodie, who wished to have 
 for the use of his class at Oxford a chemical text- 
 book arranged in accordance with his own 
 
 method of teaching Two or at most three 
 
 sections of the extent of the present PART will 
 complete the work, which will doubtless be found 
 a very important and valuable addition to the 
 elementary works used by advanced students.' 
 GARDENERS' CHRONICLE. 
 
 'WE may congratulate the chemists of 
 this country that there is amongst them a 
 class of philosophical enquirers who will not 
 confine their teachings to the limited demands 
 of the medical student, but are determined to 
 vindicate for themselves a name amongtt the 
 philosophers of Europe. In such a class we have 
 no hesitation in placing the Author of the present 
 manual; and whether he succeeds or not in 
 obtaining for his work the position of a text-book 
 in our medical and technological schools, there 
 can be no question with regard to the scientific 
 ability and philosophical insight which he has 
 brought to bear on this first attempt to introduce 
 the new system of chemistry to the scientific 
 schools and class-rooms of this country.' 
 
 ATHENAOM. 
 
 ' THE appearance of this, the first part of 
 Dr. Odling's work, marks an epoch in the 
 history of chemistry in this country. No 
 one can fail to observe, even on merely glancing 
 at the book, the great difference between che- 
 mistry as it was a few years ago, and chemistry 
 as it is now unfolded. We can hardly say that 
 there is here expressed the science as it is, so 
 large a section of chemists having as yet with- 
 held their subscription to the new laws, but we 
 unhesitatingly assert that it is the exponent of 
 
 chemistry as it will be It requires only a 
 
 study of Dr. Odling's work to be convinced of 
 the infinite superiority of this system over the 
 old, in the expression of series, of correlations, 
 and of reactions . . . Dr. Odling scarcely touches' 
 [in PART!.] 'upon chemical physics, and very 
 briefly adverts to the technological applications 
 of chemistry. His work is most valuable, when 
 considered as affording to a generation of che- 
 mists yet to come an insight into that system 
 which will best express the marvellous relations 
 subsisting between chemical compounds.' 
 
 LONDON MEDICAL REVIEW. 
 
 ' It is with considerable pleasure that we 
 draw attention to this work. During the 
 last ten years scientific chemistry has been 
 undergoing a great and radical change. 
 The illustrious Gerhardt may be considered 
 the founder of what is now known as the 
 unitary system of notation, but for a long 
 time his system was looked upon with 
 distrust by all but a few continental che- 
 mists. Gradually, however, it was seen in 
 England that this system much facilitated 
 the generalisation of chemical truths, and 
 its views are now adopted by most of the 
 leading English chemists. But whilst the 
 opinions and teachings of the professors of 
 this science have been slowly changing, the 
 literature of chemistry has, with but few 
 exceptions, remained stationary. It will, 
 therefore, be an inestimable boon to all 
 students or teachers of chemistry to know 
 that the first part of this long-expected 
 and important manual is at last published, 
 and leaves nothing to be desired in those 
 branches of chemical science upon which it 
 treats. It only extends as far as the non- 
 metallic elements, hydrogen, fluorine, 
 chlorine, bromine, iodine, oxygen, sulphur, 
 selenium, tellurium, nitrogen, phosphorus, 
 arsenic, antimony, and bismuth, and of their 
 combinations with one another : but the proper- 
 ties of the different bodies, and their theoretical 
 and practical relations one to another, are 
 described with greater fulness than is customary 
 in text-books. The arrangement is more than 
 ordinarily systematic, and the mutual relations 
 of the elements and of their analogous com- 
 pounds are largely dwelt upon, as are also the 
 mutual relations of the various heterologous 
 compounds of the same element. The compounds 
 of mineral and organic chemistry are not con- 
 sidered apart in separate sections ; moreover, 
 the doctrines of series, types, and substitutions, 
 are applied indiscriminately to both branches 
 of chemical science. This is an entirely novel 
 feature, and one which cannot fail to consider- 
 ably simplify the science to a young student. 
 An attentive perusal of this volume has con- 
 vinced us that it in every respect deserves the 
 high expectations which were formed of it. It 
 is one of the few standard works on the science 
 in the English language, and can deservedly 
 take its place in the library by the side of 
 Gmelin's Handbook.' LONDON REVIEW. 
 
 In the press, PABT II. of 
 
 DR. ODLING'S MANUAL OF CHEMISTRY. 
 
 DESCRIPTIVE AND THEORETICAL 
 
 This Part will include an account of Carbon, with its Methylic, Formic, and Cyanic 
 compounds ; also of Silicon, Boron, and the Monad, Dyad and Triad Metals, with their 
 principal Salts. 
 
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