128 PUBLIC HEALTH CHEMISTRY 



also under Addenda, page 130. (Bass 7 per cent). Ash : 

 ignite extract at a low temperature. Under 0-5 per cent. 

 Sodium chloride : extract ash with water and titrate with 

 standard AgNO 3 . 



Acidity. Total. Titrate 20 c.c. of sample (well diluted) 

 with N/io NaOH and litmus, and note number of c.c. 

 required. Calculate as glacial acetic acid (i c.c. N/io 

 soda = 0-006 grm. Ac). Is commonly 0-182 per cent, or 16 

 grains per pint. 



Fixed : Dilute 20 c.c. to 100 c.c. and evaporate down to 

 50 c.c. Dilute again, and titrate with N/io soda, i c.c. = 

 0-009 g 1711 - lactic acid. Calculate to a percentage. 



Volatile : Deduct number of c.c. required for fixed acid 

 from number required for total, and calculate as acetic. 



Alcohol. Two methods : 



1. By direct distillation. 100 c.c. of sample are taken in 

 a distilling-flask, a small piece of pumice stone is added, 

 and about 90 c.c. are distilled over. The distillate is cooled 

 to 15-5 C., and made up with aq. dest. to 100 c.c. at the 

 same temperature. The specific gravity is now taken by 

 the bottle or Westphal balance. The amount of alcohol 

 is then found from tables. 



2. Indirect or Tabarie's method. Take sp. gr. of sample 

 carefully (at 15-5 C.). Take 100 c.c. and evaporate down 

 to one-third of the bulk to get rid of alcohol and other 

 volatile substances. Cool, make up to original bulk at 

 I 5'5 C., and take sp. gr. again. Then the original sp. gr. 

 -T- new sp. gr. = sp. gr. of an alcoholic water of same strength 

 as beer. Find percentage from tables. Or, deduct 

 difference between the two specific gravities from 1000, and 

 the result is sp. gr. of an alcoholic water of same alcoholic 

 strength as the sample of beer (average 5 per cent). 



Original Gravity of Beer Wort. This is sometimes 

 needed to calculate the rebate or drawback of duty allowed 

 when beer is exported. It is obtained by deducting the 

 sp. gr. of the alcoholic distillate in (i) above from 1000. 

 The number got is the " spirit indication," and from a 

 table we get with its help the number of degrees of " gravity 

 lost." This number, added to the sp. gr. obtained by 

 Tabarie's method for the de-alcoholized beer, gives the 

 original gravity of the beer wort. A further addition for 



