LECTURE IX.] HISTORY OF CHEMISTRY. 157 



ence of Rochelle salt and of tartrate of potash and ammonia, 

 which can be obtained from the acid potassium compound by 

 neutralising with the corresponding bases, prove to Liebig 

 that tartaric acid also possesses the property of neutralising 

 two atoms of base ; and this leads him to double its atomic 

 weight, i.e. to write it C 8 H 8 O 10 . The talented author of this 

 famous paper thus understood very well that the considerations 

 here advanced furnish a new aid to the determination of the 

 atomic weight. 



Liebig justifies the separation of the acids into different 

 groups, in the following words : 13 



" The acids might be divided into monobasic, dibasic, and 

 tribasic. By a dibasic acid there would be understood one 

 whose atoms unite with two atoms of base in such a way that 

 these two atoms of base replace two atoms of water in the 

 acid. The conception of a basic salt thereby remains un- 

 changed. . . . Accordingly, when two and more than two 

 atoms of base combine with one atom of an acid, and only one 

 atom of water is separated during the operation (fewer there- 

 fore than the number of equivalents of the fixed base), then a 

 really basic salt is produced." . . , 14 



This great step was thus taken. The way had been pre- 

 pared for it by the labours of Graham ; the change was carried 

 through and established by Liebig's investigations. If we 

 desire to be strictly just (and we set some value upon this), we 

 must not suppress the fact that Liebig published the first 

 paper on this subject along with Dumas in i837. 15 This was 

 the only fruit of the proposed association of these two chemists. 



In the same paper in which Liebig develops, in detail, the 

 theory of the poly basic acids (in accordance with which the 

 acids fall into several classes), he endeavours, by means of a 



13 Annalen. 26, 169. 14 In the property of forming pyro-acids 

 Liebig also finds a ground for classing acids as polybasic (loc. cit. 169). 

 15 Comptes Rendus. 5, 863. According to a letter which Liebig addressed 

 to the French Academy in 1838 (Comptes Rendus. 6, 823 ; Annalen. 44, 

 57), it appears that the share of Dumas in this investigation was very 

 unimportant. 



