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 C0 2 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 heat 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 



i+L 

 +L 

 +L 

 +L 

 +M 

 +VS 



+L 

 +L 

 +M 

 +VS 



1 See footnote under Table 1. 



THE RELATION OF THE ALCOHOL TEST TO THE BACTERIA IN MEXED 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. 



