FERMENTATION OF SUGAR. 387 



CHAPTER V. 



Fermentation of Sugar. 



The peculiar decomposition of sugar may be viewed as a type 

 of all the transformations designated fermentation.* 



The analysis of sugar from the cane, proves that it contains 

 the elements of carbonic acid and alcohol, minus 1 atom of water. 

 The alcohol and carbonic acid produced by the fermentation of 

 a certain quantity of sugar, contain together one equivalent of 

 oxygen and one equivalent of hydrogen ; the elements, therefore, 

 of one equivalent of water more than the sugar contained. The 

 excess of weight in the products is thus explained most satisfac- 

 torily ; it is owing, namely, to the elements of water having taken 

 part in the metamorphosis of the sugar. 



It is known that 1 atom of sugar contains 12 equivalents of 

 carbon, both from the proportions in which it unites with bases, 

 and from the composition of saccharic acid, the product of its 

 oxidation. Now none of these atoms of carbon are contained in 



* When yeast is made into a thin paste with water, and 1 cubic centi- 

 metre of this mixture introduced into a graduated glass receiver filled with 

 mercury, in which are already 10 grammes of a solution of cane-sugar, 

 containing 1 gramme of pure solid sugar ; it is found, after the mixture 

 has been exposed for 24 hours to a temperature of from 20 to 25 C. (68 — 

 77 F.), that a volume of carbonic acid has been formed, which, at 0° C. 

 (32° F.), and an atmospheric pressure indicated by 0"7G metre Bar : would 

 be from 245 to 250 cubic centimetres. But to this quantity we must add 

 11 cubic centimetres of carbonic acid, with which the 11 grammes of liquid 

 would be saturated ; so that in all, 256 — 261 cubic centimetres of carbonic 

 acid are obtained. This volume of carbonic acid corresponds to from 

 0'503 to 0-5127 grammes by weight. Thenard also obtained from 1 gramme 

 of sugar 0*5262 grammes of absolute alcohol. 100 parts of cane-sugar 

 yield, therefore, of alcohol and carbonic acid together 103*89 parts. Now 

 in these two products are contained 42 parts of Carbon, or exactly the 

 quantity originally present in the sugar. 



