FERMENTATIONS BEFORE LAVOISIER 55 



violent movement, which communicates to the liquid 

 the gas, or spirit, which is set free. Adjust these two 

 phenomena, end to end, generalize them, and you have 

 the definition, cited above, of Stahl and his predecessors. 

 If with Stahl it ended in assuming a more definite form, 

 it was because the atomic theories of Descartes had 

 penetrated into chemistry. Save for this addition from 

 without, which appeared rather in the way of stating 

 it than in the idea itself, the theory of Stahl says nothing 

 more than that of Lefdvre and Le'mery, and other 

 chemists of the time. It has been said of this theory 

 that it was philosophical and seducing. A theory does 

 not need to be philosophical and seducing; it does not 

 even need to be true in the absolute sense of the word, 

 as we have shown; it suffices that it be fertile. But 

 the theory of Stahl was not fertile. 



Progress in the field of fermentation came from without 

 and had for its origin new facts observed in the study of 

 gas by scientific men who were contemporaries of Stahl. 

 Moitrel d'Ele*ment (1719) learned to make gases visible 

 by passing them through water; Hales (1677-1761) 

 snowed how to manipulate them; Black (1728-1799), 

 how to distinguish them one from another. He isolated 

 especially carbonic acid, learned to know its properties, 

 and discovered, something which Van Helmont had not 

 been able to do, that, aside from alcohol, it is the sole 

 product of the transformation of sugar in the alcoholic 

 fermentation. He placed thus in the hands of the 

 chemists all the principal elements for the solution of 

 the problem; it remained only to coordinate these ele- 

 ments and to establish their mutual relations: this was 

 the work of Lavoisier. 



