PHYSICAL AND CHEMICAL EXAMINATION OF MILK 209 



presence of acid, rennet, or both. Ayers and Johnson could find 

 no relation between a positive alcohol test and any of the follow- 

 ing conditions: 



1. Large numbers of bacteria. 



2. Large numbers of streptococci. 



3. Large numbers of cellular elements. 



4. Large numbers of cellular elements and streptococci com- 

 bined. 



They suggest that the alizarin test may give more valuable 

 information. This test is made as follows : L2 grams of fresh ali- 

 zarin, or 0.4 gram dry ahzarin, are dissolved in 1000 c.c. of 68 

 per cent, alcohol. Two c.c. of this solution are mixed with 2 c.c. 

 of the milk to be tested. The condition of the milk is judged by 

 the color developed, as alizarin is very sensitive to" acids. Ayers 

 and Johnson give the following table as a result of their tests 

 with aUzarin-alcohol solutions: 



REACTION OF MILK WITH ALCOHOLIC SOLUTION OF ALIZARIN 



Color with alizarin 



solution. 



Lilac red 



Pale red 



Brownish red 



Van Slyke states that when equal parts of fresh normal milk 

 and alcohol (spec. grav. 0.89) are mixed, there is no change, but 

 that when old milk or milk from diseased udders is used, there is 

 more or less coagulation of casein. The author states further that 

 there is no close relation between the alcohol test and real acidity 

 of milk, though milk containing more than 0.21 per cent, of acid 

 commonly gives a marked precipitation. 



In regard to the alizarol test, Van Slyke adds that when 2 c.c. 

 of the alizarol solution are mixed with an equal volume of milk, an 

 intense reddish color develops similar to that of lilac or red clover 

 blossoms. Morres gives the following color reactions accord- 

 ing to the amount of acid in milk: 



COLOR REACTIONS IN MILK WITH ALIZAROL SOLUTION 

 Acidity of milk. Color reaction. 



0.16 (fresh, normal) Lilac red 



0.18 Pale red 



0.20 Brownish red 



0.22 Reddish brown 



0.25 Brown 



0.27 Yellowish brown 



0.31 Brownish yellow 



0^36 and over .■ Yellow 



On the whole,- it would seem that neither the alcohol test nor 

 the alizarin modification are of much practical value. 



14 



