50-4 M. Dumas on the Law of Substitutions, 



formed into another which presents the same chemical ac- 

 tions, these two products belong to the sa7ne gejius. 



Alcohol, hydrated acetic acid, chloracetic acid, belong to 

 the same natural family. Acetic acid and chloracetic acid 

 belong to the same genus. 



Such are the bases of the natural classification of organic 

 substances, which I shall have soon an opportunity of deve- 

 Ipping before the Academy. 



Before going further, it is just to notice here the labours of 

 the chemists who have directed the science towards the point 

 of view which now occupies us. 



M. Regnault not only takes the first place in this respect, 

 by the date of his observations, but by the importance of his 

 researches and with respect to the ideas he has deduced from 

 them, we must consider this young chemist as having ad- 

 vanced more than any one the state of the science on this 

 point. 



In my own name I can speak more freely than when I was 

 commissioned to express the opinion of the Academy, and I 

 think it my duty to declare here that the views of M. Reg- 

 nault are connected with physical studies of the highest or- 

 der, and that they give to the theory of substitutions a de- 

 velopment as fortunate as it was unlocked for, in its applica- 

 tion to the study of the most intimate physical properties of 

 bodies. 



At the same time with M. Regnault, two other chemists 

 well known to the Academy, MM. Persoz and Laurent, were 

 also occupied in researches concerning the theory of substitu- 

 tions. 



One of them indeed, M. Persoz, did not appear to occupy 

 himself with the application of this theory; but the formula 

 b}' the help of which he endeavoured to express the composi- 

 tion of a great number of mineral bodies, agreed perfectly 

 with the developments which the theory of substitutions re- 

 ceived by degrees from experience. The system of foi'mulee 

 adopted by M. Persoz, and the views which they express in 

 mineral chemistry, have then found a fortunate application 

 in a great number of facts which the theory of substitutions 

 has led to the discovery of in organic chemistry. 



M. Laurent on his side has made a multitude of researches, 

 and has published a great number of memoirs in support of the 

 laws by which he sought to foresee and to explain all the 

 phcenomena of substitutions. As we saw above that the prin- 

 cipal difficulty which is opposed to the approximation of 

 acetic acid and of chloracetic acid consists in the similar func- 

 tion which we are compelled to attribute to chlorine and to 



