ANALYSIS OF SOUR MILK. Ml 



developed in the milk are filtered off, and either weighed, or 

 the nitrogen is determined in them ; in the filtrate albumin 

 is estimated as on p. 130 ; in the filtrate from this, 

 albumoses are estimated by precipitation with tannin or 

 phospho-tungstic acid, and determining the nitrogen in the 

 precipitate. 



The total nitrogen is estimated by Kjeldahl's method on a 

 weighed portion. 



Certain changes take place in the proteins in sour milk, and 

 at the Government Laboratory to estimate ammonia 2 grammes 

 of the milk are made up to 100 c.o. with distilled water, and 

 filtered to a clear solution. Ten c.c. of the filtrate, increased 

 to 50 c.c. by the addition of distilled water, are nesslerised against 

 NH4CI solution, equivalent to 0"01 milligramme of NH.. in each c.c. 

 As the Nessler colour produced in the presence of milk differs 

 somewhat from that of pure saline ammonia, the blank experi- 

 ment is carried out with the addition of 10 c.c. of the filtrate 

 from 2 grammes of new milk slightly acidified, and diluted to 

 the same extent as the sour milk. The quantity of test ammonia 

 solution required varies from 0'5 to 4'0 c.c. In the case of a 

 milk containing ammonia equal to 2'6 c.c. of the test solution, 

 the ammonia is calculated as follows : — • 



O'Ol X 2-6 X 500 = 0-013 per cent, ammonm. 



It is evident that any other degree of dilution may be con- 

 veniently adopted according to circumstances, or the proportion 

 of ammonia which may be indicated in the milk. 



The Estijiiation of Alcohol. — About 75 granmies are weighed 

 into a 300-c.c. flask for the estimation of alcohol, and half neut- 

 ralised with - soda solution ; about half the volume is distilled 

 and collected in a small flask, and neutralised with -^ soda — using 



litmus paper as indicator. From this 2-5 c.c. is distilled, and 

 the density taken at 60° F. by a Sprengel tube. From the 

 density the percentage of alcohol is calculated by Table XIV. 



At the Government Laboratory the percentage of alcohol is 

 deduced by multiplying the difference between 1 and the specific 

 gravity of the distillate by 1,000 X 1'16, and this gives it as 

 percentages of proof spirit : as proof spirit contains 49 '5 per 

 cent, alcohol by weight, it is e\'ident that the factor 1,000 X 0'572 

 will give the percentage of alcohol by weight. 



The total acidity to litmus paper may be calculated as lactic 

 acid ; from this an amount equivalent to the volatile acids is 

 subtracted. 



