18 
BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 
milk. In order to determine how much carbon dioxid was required 
to cause a positive test with 68 per cent alcohol, the gas was passed 
into a flask of fresh milk until a positive alcohol test was produced. 
The amount of C0 2 in this milk and in the original milk was then 
determined. 1 It was found that the normal milk contained 0.76 per 
cent of C0 2 by volume at 32° C, and the milk through which the gas 
had been passed contained 13.05 per cent of C0 2 by volume. In this 
experiment it was necessary to increase the C0 2 content to 13.05 per 
cent by volume in order to cause a positive alcohol reaction with 
68 per cent alcohol. According to Kastle and Roberts (14) carbon 
dioxid is present in milk to the extent of 3 to 4 per cent by volume 
and partly escapes into the air when the milk is drawn. This being the 
case, it is evident that there is not enough carbon-dioxid gas in normal 
milk to cause of its own accord a positive alcohol test with 68 per cent 
alcohol. Of course, the presence of CO, may assist other factors to 
cause a positive alcohol test and in the case of bacterial fermentation 
where the gas is produced it might play a small part, but we believe 
that when 68 per cent alcohol is used in the test the influence of C0 2 
in mixed market milk would be very small, if it has any effect. 
Table 14. — Effect of Mat on alcohol test with milk-made acid to phenolphthalein with 
carbon dioxid. 
Milk heated 
to— 
Acidity. 
Alcohol test. 
75 per cent. 
68 per cent. 
° C. 
Not heated 
40 
50 
60 
70 
80 
90 
100 
Original milk 
2.36 
2.32 
2.30 
2.19 
2.05 
2.05 
1.91 
1.92 
1.90 
+ L 
+L 
+L 
+M 
+VS 
+L 
+ L 
+M 
+vs 
See footnote under Table 1. 
THE RELATION OF THE ALCOHOL TEST TO THE BACTERIA IN MLXED MARKET MILK. 
Having discussed the effect of acidity and the effect of rennet 
action on the alcohol test, let us consider the relation of the test to the 
bacteria in market milk. Since an increased acidity and also rennet 
action may cause a positive test, it is natural to suppose that there 
may be some definite relation between the alcohol test and the number 
of bacteria in milk, as the increase in the acidity and the rennet in 
milk is the result of bacterial growth. 
It is claimed by some authorities that the alcohol test is of great 
value for determining the freshness of milk, and as this is a question 
i We are indebted to Dr. Clark, of the Dairy Division laboratory, for this analysis. 
