68 LOUIS PASTEUE. 



Atmospheric air every one knows to be a mixture 

 of nitrogen and oxygen, the nitrogen in the proportion 

 of four-fifths of the total volume, and the oxygen of 

 one-fifth. Well, in the transformation of wine into 

 vinegar the nitrogen remains inactive. It is the 

 oxygen alone which enters into combination with the 

 alcohol. You ask for the proof of this? Take a 

 bottle of wine turned sour, a bottle which at the same 

 time is stopped hermetically ; if the oxygen of the air 

 contained in the bottle has combined with the alcohol, 

 then, instead of air, there will be nothing in the bottle 

 but nitrogen gas. Turn the bottle upside down and 

 open it in a basin of water. The water of the basin 

 will rush into the bottle to fill the partial vacuum 

 created by the disappearance of the oxygen. The 

 volume of water which enters the bottle is precisely 

 equal to a fifth part of the total original volume of 

 the air which the bottle contained at the time when 

 it was closed. Moreover, it is easy to show that the 

 gas which remains in the bottle has the properties of 

 nitrogen gas. A lighted match is extinguished in it 

 as if plunged into water, and a bird dies immediately 

 in it of asphyxia. 



If we confine our knowledge to what has gone 

 before, it would seem that alcohol diluted with water 

 and exposed to the air ought to furnish acetic acid. 

 It is not so, however. Pure water alcoholised to the 

 degree of ordinary wines may remain for whole years 



