10 



BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 



per cent alcohol was positive. At an acidity of 4.27 the milk coagu- 

 lated with 68 per cent alcohol but the flakes were very small. In 

 order to cause a coagulation with 68 per cent alcohol with medium- 

 sized flakes it was necessary to increase the acidity to 6.16. When 

 potassium acid phosphate was used the results were about the same. 

 These results show that it is possible by increasing the acidity of 

 milk with acid phosphates to cause a coagulation with the alcohol 

 test, but the acidity has to be increased to a high degree and there 

 would never be enough acid phosphate in a mixed market milk for 

 it to be entirely responsible for a positive alcohol test. 



Table 5.— Influence on the alcohol test of the addition of acid 'phosphates to milk. 



Sodium-acid phosphate. 



Potassium-acid phosphate. 



Amount 



of 5 



per cent 



solution 



of acid 



phos- " 



phate 



added to 



50 c. c. of 



milk. 



Acid- 

 ity. 



Alcohol test. 



Amount 



of 5 

 per cent 

 solution 

 of acid 

 phos- 

 phate 

 added to 

 50 c. c. of 

 milk. 



Acid- 

 ity. 



Alcohol test. 



75 per 

 cent. 



68 per 

 cent. 



44 per 

 cent. 



75 per 

 cent. 



68 per 

 cent. 



44 per 

 cent. 



C.c. 

 

 1 

 2 

 3 

 5 

 6 



2.15 



2.75 

 3.33 

 4.27 

 5.50 

 6.16 



i +M 

 +M 

 + M 

 +M 



+VS 

 + VS 

 +M 



+ VS 



C.c. 

 

 1 

 2 

 3 

 5 

 6 



2.52 

 3.13 

 4.00 

 5.20 

 5.62 



i+M 



+ M 

 + M 

 +M 



+VS 

 + VS 

 + M 



+ VS 



1 See footnote under Table 1. 



In some cases where we increased the acidity of milk by adding 

 lactic acid it was noticed that a very slight increase in acidity caused 

 a positive alcohol test. At other times the acidity had to be in- 

 creased to a considerable extent before the milk coagulated with 

 alcohol. It occurred to us that the explanation for these differences 

 might be that there were different amounts of dibasic phosphates 

 present in milk and that the acid converted the dibasic phosphate into 

 acid phosphate, which increased the acidity but did not cause a posi- 

 tive alcohol test. In order to test this theory one experiment was 

 performed, the results of which are shown in Table 6. Two flasks of 

 milk were used, each containing 50 c. c. of milk. One flask was left 

 normal and 0.5 per cent dibasic sodium phosphate was added to the 

 other. Various amounts of N/10 lactic acid were then added to each 

 flask. As may be seen from the table, when 3 c. c. of N/10 lactic 

 acid was added to the normal milk, the acidity was 2.37 and the 

 alcohol test was positive with both 75 per cent and 68 per cent alco- 

 hol. The flakes were large and medium, respectively. The same 

 amount of acid added to the milk with dibasic phosphate increased 



