584 



CHAPTER XXVIII 



The easiest method of determining the obscuration is as under : — 



1. Take the apparent strength by the hydrometer. 



2. Evaporate about 200 c.c. of the spirit on a water-bath till all the 

 alcohol is removed ; take up the residue with water, and make up to the 

 volume of the spirit taken. 



3. Take the density of the solution of the residue either by the pycno- 

 meter or by a hydrometer graduated to read o-oooi. It is absolutely essen- 

 tial that all measurements be made at the temperature at which the instru- 

 ments are graduated. 



Calculation : Let x = specific gravity of the obscured spirit, and d = 



X 



specific gravity of the residue dissolved in water ; then -3-= original gravity 



of the spirit. 



Example: Coloured rum stands 21-0 Sikes at 84" F., indicating an 

 apparent strength of 40-6 O.P. ; the specific gravity corresponding to 21 

 Sikes is 0'85i2. The density of the residue dissolved in water is 1-0040. 



Then original gravity of spirit = ^ = 0-8478. 



The Sikes indication 



I • 0040 



corresponding to a specific gravity of 0-8478 is 19-0, indicating a spirit 

 42-8 O.P. ; hence the obscuration is 42-8 — 40-6 = 2-2. 



An older formula for use with this method gives x ^ d = the original 

 gravity of the spirit. 



A second method, and one generally used for beers and wines, consists of 

 distilling over the material until aU the alcohol has passed over, making the 

 distillate up to the original volume and finding the strength of the distillate 

 by an immersion alcoholometer, which in the absence of solids in solution 

 gives exact results. With strong spirit, such as rum, it is extremely difficult, 

 if not impossible, to prevent loss by evaporation and the first-mentioned 

 method is preferable. 



In the following table are calculated obscurations from the observed 

 density of the residue dissolved in water, the standards adopted for the cal- 

 culation being a spirit of strength 40-6 O.P. (= 21-0° Sikes) at a temperature 

 of 84° F. ; the table is applicable to spirits varying considerably from these 

 adopted standards. 



Obscuration Table. 



