CHEMISTRY AND CHIEF PRODUCTS. 485 



of alcohol, figures corresponding to 46.9 per cent, and 47.6 per 

 cent, respectively. In a second experiment, however, these 

 workers (2) obtained 50.4 per cent, of alcohol ; but these figures 

 should not be compared with those given above, the latter having 

 been obtained with grape sugar (glucose, see p. 513), which 

 furnished, theoretically, 48.89 per cent, of carbon dioxide and 

 51.11 per cent, of alcohol, whereas not more than 51.45 per cent, 

 and 53.62 per cent, respectively can be formed from saccharose. 



In order to obtain the above-mentioned yields highly favourable 

 working conditions are essential ; but it is immaterial whether the 

 whole of the sugar is fermented or a portion remains behind, 

 provided the weight of sugar actually fermented be ascertained and 

 referred to the alcohol and carbon dioxide recovered. JODLBAUER(!). 

 points out that, with increasing age, yeast undergoes some modifi- 

 cation, inasmuch as the quantity of carbon dioxide produced from 

 the fully fermented sugar diminishes progressively. This is true 

 of pure yeast as well as of ordinary yeast. Jodlbauer obtained 

 49.02, 48.97, and 49.17 per cent, of carbon dioxide from saccharose, 

 when using fresh yeast, but only 47.67, 47.44, and 46.98 per cent, 

 with the same yeast grown old. If, on the other hand, instead 

 of interrupting the fermentation directly after the sugar has 

 completely disappeared, the carbon dioxide determination be 

 carried further, a surplus of carbon dioxide, formed by the auto- 

 fermentation (see 334) of the yeast, is often obtained. 



The ratio of alcohol to carbon dioxide produced is therefore 

 approximately i : i ; and in zymase fermentation according to 

 BUCHNER and HAHN (I.) it varies between i : 0.90 and i : i.oi. 

 However, if the ratio be examined during the various stages of 

 fermentation, ifc appears according to LINDET and MARSAIS (I.) 

 that the proportion of carbon dioxide to alcohol is lower at the 

 beginning of the process than it is toward the end. These 

 workers obtained the following relative values of alcohol : carbon 

 dioxide at the start : 



i :o.93, i :o.79, i 10.89, i 10.91, and i =0.79, 

 and 



i : i.oi, i : i. oo, i : 1.09, T : 1.03, and i : 1.02 



at the end. The results were unaffected by the fermentation 

 temperature or by the presence or absence of acid in the wort. 

 The amount of yeast produced per i grm. of alcohol was found 

 by Lindet and Marsais to range from 0.048 grm. in the initial stage 

 of fermentation to 0.0002 grm. at the end. 



The simplest way of expressing the chemical reaction of 

 fermentation is by the equation already given, viz.: 



C 6 H 12 O 6 = 2C0 2 + 2C 2 H 6 0. 



Of course the decomposition of the sugar is not effected in this 

 elementary manner. As far back as 1858, TRAUBE (I.) expressed 



