RELATIONS TO OTHER SCIENCES 255 



Biology therefore unites again inorganic and organic chemistry. 

 The truth is, there is but one chemical science; every separation is 

 artificial. Just as energy is one, chemistry is one. The splendid 

 researches of Curtius on nitrohydric acid, and our own investiga- 

 tions of the metallic carbides and of the hydrides, of the alkalies 

 and alkaline earths, show how the two chemistries constantly inter- 

 penetrate, and demonstrate the unity of the science. 



It is true, however, that inorganic chemistry has a technique of 

 its own. To make discoveries there, the precision of physics must 

 be applied. A few examples will make my thought clearer. 



Lavoisier only overthrew the theory of Stahl as the result of rigor- 

 ous experiments prepared with the greatest care and exactitude. 

 We may refer in this connection to his experiments on combustion, 

 on respiration, and on fermentation. 



Cavendish, when studying the action of the electric spark on a 

 mixture of oxygen and nitrogen, pushed the experiment till there 

 remained but a very small quantity of gas incapable of uniting with 

 oxygen. He mentions its existence. Since his time, over a century 

 ago, in how many universities, lycea, and gymnasia has this experi- 

 ment of Cavendish been repeated? And yet no one, during the cen- 

 tury, completed the experiment. It was always begun, but never 

 finished. Any one who had carried it on patiently till the nitrogen 

 was entirely absorbed would have discovered argon. It was needful 

 that Lord Rayleigh should determine the densities of the gas, vouch- 

 ing for the third decimal place, in order that the discovery should 

 be realized. The method is elegant, but the path of discovery is 

 rather circuitous. 



Shall I cite you another example? When Gay Lussac, in 1815, 

 discovered cyanogen, that first example of a compound playing the 

 part of an element, that first radical formed of nitrogen and carbon, 

 he prepared it by moderately heating pure, dry cyanide of mercury. 

 The cyanide in these conditions split into cyanogen gas and mercury. 

 The experiment is of the simplest. Only a few years before, Proust 

 also had heated cyanide of mercury in a retort. He. had obtained 

 ammonia, an apparently oily compound, nitrogen, carbon dioxide and 

 monoxide. The reason was that Proust used damp cyanide. This 

 difference in manner of conducting the same experiment between 

 two men of the ability of Gay Lussac and Proust seemed to me very 

 interesting. 



To return to Gay Lussac's preparation of cyanogen. He had left 

 in the bottom of his retort a small quantity of a black powder. After 

 establishing the formula of cyanogen, the existence of hydrocyanic 

 acid and of the cyanides and cyanates, he made an analysis of this 

 powder. It had exactly the same composition as cyanogen. Gay 

 Lussac notes this fact, but he takes care not to go farther, and 



