Sixty years have hardly passed since that ever-memorable epoch when, in the presence of this very assemblage, there began to appear the first essays of that so fecund chemical doctrine which we owe to the genius of Lavoisier. This short space of time has suffered for deep examination of the most delicate questions of mineral chemistry, and everyone may easily convince himself that this branch of our knowledge possesses nearly all that it may acquire with the means of observation at its disposal.
Not only is this an incontestable fact, but it is a fact which everyone can explain. Mineral chemistry occupies itself indeed with the history of elementary substances, of their binary and saline combinations. Now elementary substances fall very naturally into several groups in such a manner that if one studies attentively the properties of one species of a group, one can nearly always forsee and divine the properties of neighboring species. The study of oxygen teaches us the history of sulfur; that of chlorine suffices to initiate us into the slightest details of the properties of iodine, etc.
Thus this task which appeared at first beyond human ability, for it was no less a matter than that of studying and analyzing thousands of substances of very diverse aspects and properties, this task has been nonetheless accomplished in less than half a century, and there remain here and there hardly any lacunae to fill.
Chemists have recognized that in mineral substances there exist bodies which act as elements; that these bodies combine among themselves; that their combinations may unite anew; and in these three orders of substances they have found the means of forming natural groups which render the study simple, easy, and at the same time broad and philosophical.
Of course, that which they have called element, or undecomposable substance, has been considered as such only with regard to the state of acquired experience. We have not wished to prejudice the question, but we have sought to construct the edifice of science in such a fashion that, if these elements were later decomposed, nothing would be changed in the architecture of the monument, although its foundations would be more profoundly excavated.
It is easy to see that with the 54 elements known today one may, with the aid of a very small number of laws and combinations, and forming all the binary compounds and salts possible, produce not only all the compounds known in the inorganic kingdom but also a great number of analogous compounds.
But how apply with some success such ideas to organic chemistry? There, there are encountered no fewer and no less diverse species than in mineral chemistry. There, however, in place of 54 elements, we encounter scarcely more than three or four in the majority of known compounds. In a word, how can we with the aid of the laws of mineral chemistry explain and classify the so varied substances obtained from living matter and which nearly all are formed solely of carbon, hydrogen, and oxygen, elements to which nitrogen is sometimes added?
That was an important and fitting question of natural philosophy, a question well calculated to excite to the highest degree the emulation of chemists; for once it was resolved, the finest triumphs were promised to the science. The mysteries of vegetation, the mysteries of animal life were going to be unveiled to our eyes; we were going to grasp the key to all the modifications of matter which transpire in animals and in plants so promptly, so suddenly, so spectacularly; further, we were going to find the means of imitating them in our laboratories.
Well, we do not fear to say it, and this is not on our part an assertion lightly made: this important and fitting question is today resolved; it remains solely to unfold all the consequences which its solution entails. And certainly, if before experiment had opened this new route one had demanded of any chemist his opinion on the nature of organic substances, however great his genius, he would have imagined nothing, one may be sure, which could be compared with these simple, regular, and so handsome laws which experiment has revealed to us for the last few years.
Actually, to produce with three of four elements combinations as varied as and perhaps more varied than those which form the mineral kingdom, nature has taken a course as simple as it was unexpected; for with the elements she has made compounds which manifest all the properties of elementary substances themselves.
And that, we are convinced, is the whole secret of organic chemistry.
Thus organic chemistry possesses its own elements which at one time play the role belonging to chlorine or to oxygen in mineral chemistry and at another time, on the contrary, play the role of metals. Cyanogen, amide, benzoyl, the radicals of ammonia, the fatty substances, the alcohols and analogous compounds--these are the true elements on which organic chemistry is founded and not at all the final elements, carbon, hydrogen, oxygen, and nitrogen--elements which appear only when all trace of organic origin has disappeared.
For us, mineral chemistry embraces all substances which result from the direct combination of the elements as such. Organic chemistry, on the contrary, should comprise all substances formed by compound bodies functioning as elements would function.
In mineral chemistry the radicals are simple; in organic chemistry the radicals are compound; that is all the difference. The laws of combination and of reaction are otherwise the same in these two branches of chemistry.