THE ALCOHOL TEST IN RELATION TO MILK. 



11 



the acidity to 2.55 and yet the alcohol test was negative. When 7 

 c. c. of N/10 lactic acid was added to the normal milk, the acidity was 

 increased to 3.00 and the milk coagulated with large flakes with all 

 the different percentages of alcohol. When 7 c. c. of N/10 lactic 

 acid was added to milk with dibasic phosphate the acidity was 

 increased to 3.05 and only the 75 per cent alcohol test was positive, 

 and the coagulation was in the form of small flakes. When 8 c. c. 

 of acid was added to the milk with dibasic phosphate the acidity 

 was 3.19 and the alcohol test with both 75 per cent and 68 per cent 

 alcohol was positive. It was found by titration that 10 c. c. of a 

 0.5 solution of dibasic phosphate required 1.56 c. c. of N/10 lactic 

 acid to convert the dibasic into the monobasic phosphate; therefore 

 50 c. c. of milk containing 0.5 per cent of dibasic sodium phosphate 

 would require 7.8 c. c. of N/10 lactic acid to convert the dibasic 

 into the monobasic phosphate. It will be seen from Table 6 that 

 when from 7 to 8 c. c. of N/10 lactic acid was added to the milk 

 with dibasic phosphate, the alcohol test became positive; that is, when 

 the dibasic phosphate had been converted into monobasic phosphate 

 then further increase in acidity caused a positive alcohol test. 



As a very general explanation of this result it may be said that when 

 acid is added to milk it converts the dibasic phosphate into the 

 monobasic phosphate. It follows that the acid and also the monobasic 

 phosphate probably affect the casein and thereby change it into a 

 condition in which it is possible to precipitate the casein by alcohol 

 and cause a positive test. This action on the dibasic phosphate prob- 

 ably explains in part the positive alcohol tests with different low 

 acidities. 



Table 6. — Influence on the alcohol test of the addition of dibasic phosphate to milk. 



N/10 





Normal milk. 





Normal milk + 0.5 per cent 

 dibasic sodium phosphate. 



lactic 

 acid 





















added 





Alcohol test. 





Alcohol test. 



to 



50 c. c. 



of 



Acidity. 







Acidity. 





75 



68 



44 



75 



68 



44 



milk. 





per 



per 



per 





per 



per 



per 







cent. 



cent. 



cent. 





cent. 



cent. 



cent. 



c. c. 

 



1.85 









2.03 









1 



2.01 



!+S 



— 



— 



2.13 



— 



— 



_ 



3 



2.37 



+ L 



+M 



— 



2.55 



— 



— 



— 







2.63 



+ L 



+ L 



+ S 



2.81 



— 



— 



— 



6 



2.80 



+ L 



+ L 



+ M 



2.92 



_ 



— 



_ 



7 



3.00 



+L 



+ L 



+ L 



3.05 



+s 



— 



— 



8 











3.19 



+ L 



+M 





9 











3.43 



+ L 



+ L 



_ 



11 











3.97 



+ L 



+ L 



+L 











1 See footnote under Table 1. 





