FERMENTATION 



583 



Alcoholometry . — Unfortunately in Great Britain and her colonies alcohol 

 is measured in " proof " ; a more annoN^ng system could barely have been 

 devised. By proof is meant one which at 62° F. weighs ^f of an equal bulk 

 of water ; 40 over proof (O.P.) means that 100 volvunes of the spirit contain 

 as much alcohol as 140 volumes of proof ; 40 under (U.P.) means that 140 

 volumes of the spirit contain as much alcohol as 100 volumes of proof. 

 Absolute alcohol is 75-25 O.P., so that to convert volmnes of proof spirit to 

 alcohol it is necessar}^ to divide by 1-7525 and vice versa. Proof spirit 

 contains 49-3 per cent, by weight or 57-06 per cent, by volume of alcohol. 

 In France, and also in Germany, the Gay-Lussac scale is used ; this is the 

 most rational one and gives directly the percentage of alcohol by volume. 

 The Cartier scale is an empirical one, 43 beiijg absolute alcohol and 22 being 

 proof spirit. The Beck scale is also an empirical one, 43-9 being absolute 

 alcohol and 14-8 being proof spirit. In the U.S.A. the Gendar scale is used ; 

 200 is absolute alcohol, 100 is U.S. proof [i.e., 50 per cent, by volume) and 

 o is water. 



The bubbles used in distilleries as a guide in the test case are based on 

 the Cartier scale ; they are numbered from 16 to 30 ; bubble 25 corresponds 

 to 25 Cartier, but bubble 26 corresponds to 24 Cartier, (Sec. 



Comparison of the Different Alcohol Scales. 



Bubble 



17 

 19 

 21 



23 

 25 

 27 

 29 



30 



Obscuration. — The obscuration of a spirit is the difference between 

 the actual proof strength and the apparent proof strength as determined by 

 an immersion alcoholometer. Thus spirit sho\Ning 40-0 over proof by the 

 alcoholometer, and of actual strength 43 • i over proof is said to have an 

 obscuration of 3-1. In some cases, however, the obscuration is expressed 

 on the proof spirit, so that for the example quoted the obscuration is 



3*1 r • . 



= 2 • 17 per cent, on proof spint. 



