280 SUGARS AND [CH. XIII 



[Allowance is made for a deficit (products other than 

 COa and alcohol) of oo p.c] 



The sugars in solution may also be estimated by 

 finding the loss of specific gravity of the solution on 

 fermentation (after distilling off alcohol). 



The specific gravity of the solution is taken by an 

 accurate hydrometer or v^^ith a specific gravity bottle, 

 the volume exactly noted, and yeast added. After the 

 fermentation is complete the whole (or a definite part) is 

 filtered and the alcohol distilled off, after which the liquid 

 is made up exactly to its original volume with distilled 

 water, and the specific gravity again taken. 



The loss of specific gravity is due to the destruction of 

 the sugars, and the amount of the latter can be calculated 

 as shown below. 



The specific gravity of dilute sugar solutions in- 

 creases by about '00386 for every gram of sugars in 

 100 c.c. of solution (at 15° C), if therefore the specific 

 gravity of the solution had diminished by '008 after 

 fermentation we should conclude that the sugars in 



100 c.c. of the original solution = - grams. 



Or the percentage by weight of sugars may be obtained 

 by the use of tables^ (of which a number have been pub- 

 lished) shewing the relation between specific gravity and 

 percentage by weight of sugars. 



At a temperature of 18° — 20° C. fermentation will 

 usually be complete in thirty to forty hours, but it is safer 

 to let the action continue for three days. 



1 See Chemiker-Kalender (1893, pp. 78—80). 



