ACETIC FERMENTATION. 67 



In a celebrated lecture given at Orleans at the 

 request of the manufacturers of vinegar in that town, 

 Pasteur, after having stated the two foregoing scien- 

 tific questions, proceeded to examine the difference 

 between wine and vinegar. What takes place in the 

 fermentation of the juice of the grape which yields the 

 wine ? The sugar of this juice disappears, giving 

 place to carbonic acid gas, which is exhaled during 

 fermentation, and to alcohol, which remains in the 

 fermented liquid. Formerly, chemists gave the name 

 of ' spirit ' to all volatile matters which could be 

 collected from distillation. Now, when we distil wine 

 and condense the vapour in a worm surrounded by 

 cold water, we collect the spirit of wine at the ex- 

 tremity of the worm this, when the water with 

 which it is mixed during distillation is withdrawn from 

 it, we designate by the name of alcohol. Vinegar 

 contains no alcohol. When distilled it yields water 

 and a spirit. But this spirit is acid, with a very 

 pungent odour, and not inflammable like spirit of 

 wine. Separated from the water which had accom- 

 panied it during the distillation, this spirit takes the 

 name of acetic acid. This is the form in which it is 

 used in smelling bottles in those bottles of English 

 salts the vapour of which is so penetrating. 



In the formation of vinegar in contact with air 

 the alcohol disappears, and is replaced by acetic acid. 

 The air has thus given up something to the wine. 



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