346 



NATURE 



\^Aug. 27, 1874 



and the essentinl cliarr.cter of chemical combinations. In these 

 latter we find in weight all that is ponderable in their ele- 

 ments. These, in uniting to form compound bodies, do not lose 

 any of their proper substance ; they lose only an imponderable 

 thin"-, the heat disengaged at the moment of combination. 

 Hence that conception of Lavoisier that a simple body such as 

 oxygen is constituted, properly speaking, by the intimate union 

 of the ponderable matter oxygen with the imponderable fluid 

 which constitutes the principle of heat, and which he named 

 caloric — a profound conception, which modern science has 

 adopted, giving it a different form. It is, then, unjust that, 

 in recent times, Lavoisier should be accused of having miscon- 

 ceived what is physical in the phenomenon ef combustion, and 

 that an attempt should be made to rehabiUtate the doctrine of 

 Phlogiston which he had the honour of overturning. It is true 

 that in bui-ning bodies lose something : " It is the combustible 

 principle," said the partisans of Phlogiston ; " It is caloric," said 

 Lavoisier; and he adds, an essential thing, that they gain in 

 oxygen. 



Thus Lavoisier perceived completely the phenomenon, of 

 which the great author of the phlogiston theory, G. E. Stahl, 

 liad only a glimpse of the external appearances, and of which 

 he misconceived the characteristic feature. Such is, gentlemen, 

 I maintain, the foundation and the origin of modern chemistry. 

 Is that to say that the monument raised upon these bases by 

 Lavoisier and his contemporaries subsists in all its parts, and that 

 it was accomplished at the end of last century? It would not 

 hi fronr want of materials, and even in its outlines we may notice 

 lines whicli have in time disappeared. It has then been added 

 to and in part transformed ; but it still rests upon tlie same foun- 

 dations. Such has been in all sciences and in all times the lot 

 of theoretical conceptions ; the best of tlienr contain obscurities 

 and gaps which, on disappearing, become the occasion of im- 

 portant developments or of a new generalisation. 



That of I>avoisier embraced especially the bodies best known 

 in his time, i.e., the compounds of oxygen, the true nature of 

 which was discovered by him in his researches on combustion. 

 All these bodies are formed of two elements ; their constitution 

 is binary, but it is more or less complicated. Some, oxides or 

 acids, contain a simple body united to oxygen ; others, more 

 complex, are formed by the combination of acids and oxides 

 among themselves, a combination which gives rise to salts. 

 These last then are formed of two constituent parts, each of 

 which contains oxygen united to a simple body. Such is the 

 formula of Lavoisier on the constitution of salts ; it is in harmony 

 with the fundamental idea which he enounced on chemical com- 

 bination, an idea according to which all compound bodies are 

 formed of two immediate elements, which are either simple 

 bodies or themselves compound bodies. 



This dualistic hypothesis was embodied, in his time and with 

 his consent, in P'rcnch nomenclature, the work of Guyton de 

 Morveau, the principle of which may be thus summarised : two 

 words to designate each compound, one to mark the genus, the 

 other the species. Thus, one of the fandamental conceptions of 

 the system of Lavoisier — dualism in combinations — lonnd a 

 striking expression in the binary structure of the names, and is, 

 as it were, insinuated into iha mind by the very terms of 

 chemical language ; and we know what is, in such a case, tlie 

 power of words. 



The great successor of Lavoisier, Berzelius, extended to the 

 whole of chemistry the dualistic hypothesis of Lavoisier on the 

 constitution of salts. Wishing to give it a solid support, lie 

 added to it the electro-chemical hypothesis. All bodies are 

 formed of two constituent parts, each of which possesses, and is, 

 as it were, animated by, two electric fluids. And as the electro- 

 positive fluid attracts the electro-negative, it is natural, it is 

 necessary that in every chemical compound tlie two elements 

 should reciprocally attract each other. Is not the one carried 

 towards the other by electric fluids of opposite kinds? We 

 see that the hypothesis of Berzclius gives at once a striking inter- 

 pretation of the dualism in combinations and a simple and 

 profound theory of chemical affinity. This elective attraction 

 which the final particles of matter exercise upon each other 

 was referred to electric attraction. 



Another theoretic conception gave a body to the electro- 

 chemical hypothesis, and has given since a solid basis to chemistry 

 as a whole. We speak of the atomic theory, revived from the 

 Greeks, but which took, at the commencement of this century, 

 a new form and a precise expression. It is due to the penetra- 

 tion of an Knglisk thinker, Daltoii, a teaclier of chemistry in 



Manchester in the beginning of the century. It was les5 a pure 

 speculation of the mind, as were the ideas of the ancient atomists 

 and of the philosophers of the Castesian school, than a theoretical 

 representation of well-established facts, viz., the parity of the pro- 

 portions according to which bodies combine, and the simplicity 

 of the relations which express the multiple combinations between 

 two bodies. 



Dalton found, in fact, that, in cases where two substances 

 combine in several proportions, if the quantity of one of them 

 remains constant, the quantities of the other vary according to 

 very simple relations. The discovery of this fact was the 

 starting-point of the atomic theory. Here is the subst.ance of 

 this theory : — That which fills space, viz. matter, is not infinitely 

 divisible, but is composed of a universe of invisible, impercep- 

 tible particles, which, nevertheless, possess a real extension and 

 a definite weight. These are atoms. In their infinitely attenu- 

 ated dimensions, they offer points of application to the physical 

 and chemical forces. They are not all like each other, and the 

 diversity of matter is owing to inherent differences in their nature. 

 Perfectly identical for the same simple body, they differ from 

 one element to another in their relative weights, and perhaps by 

 their form. Affinity sets them in motion, and when two bodies 

 combine with each other, the atoms of the one are drawn 

 towards the atoms of the other. As this approach always takes 

 place in the same manner between a determinate number of 

 atoms, which are in juxtaposition one to one, or one to two, or 

 one to three, or two to three — in other words, according to very 

 simple proportions, but invariable for a given combination — it 

 results therefrom that the smallest particles of this combination 

 present a fixed composition rigorously similar to that of the 

 entire mass. 



Thus the most important fact of chemistry, the immutability 

 of the proportions according to which bodies combine, appears 

 as a consequence of the fundamental hypothesis that chemical 

 combinations result from the coming together of atoms possessing 

 invariable weights. Berzelius compared these atoms to minute 

 magnets. He imagined theni to have two poles where the two 

 electric fluids are separated but unequally distributed, so that one 

 of them is in excess at one of the poles. " There exists," he said, 

 " atoms with excess of positive fluid and others with excess of 

 neg.ative fluid ; the first attract the second, .and this attraction, 

 the source of chemical affinity, preserve the atoms under all 

 combinations. At the moment that these last are formed they 

 are set in motion ; in the completely formed compound they are 

 at rest, and are divided as if into two camps, at once kept to_ 

 gether and maintained in opposition by the two electric fluids o 

 opposite kinds. 



Thus the electro-chemical theory, ingeniously adapted to the 

 hypothesis of atoms, raised the dualism of Lavoisier to the dig- 

 nity of a system, which appeared solidly established during the 

 first half of this century. The facts then known were included 

 in it without difliculty, and the rich materials which the patience 

 or the genius of experimenters amassed without ceasing were very 

 soon co-ordinated. 



Without attempting to enumerate the older works relating to 

 the decomposition of alkalis, to the nature of chlorine recognised 

 as a simple body, to various newly-discovered elements, such as 

 selenium, tellurium, iodine, we shall mention in a special manner 

 among so many discoveries, that of cyanogen, which we owe to 

 our own Gay-Lussac. The demonstration of the chemical functions 

 of this compound gas, which behaves like a simple body, which 

 is capable of forming the most varied combinations with true ele- 

 ments, which finally, when it is engaged in such combinations lends 

 itself to double decompositions, as.does chlorine in the chlorides, 

 was a great step in the progressive march of science. 

 Hence the definition : cyanogen is a compound radical, and the 

 triumjihant appearance of the doctrine of radicals. It had been 

 vaguely intimrvted by Lavoisier ; it really dates from the dis- 

 covery of cyanogen, and will make a rapid advance. Up to that 

 time great efforts had been directed to the side of inorganic 

 chemistry, and great ideas had arisen in this domain. Theappli- 

 cation ol these ideas to organic chemistry, upon which attention 

 then began to be directed, presented some difficulties. 



We know that the innumerable bodies which nature has dis- 

 tributed in the organs of plants and animals contain a small 

 number of elements — carbcn, hydrogen, oxygen, and often 

 nitrogen. It is then not in their general composition that 

 they differ, but by the number and arrangement of the atoms 

 which enter into their composition. By increasing more or 

 less and grouping themselves in various manners, these atoms 



