METHODS OF EXAMINING MILK 257 



to rinse it and this is added to the milk or cream. A few 

 drops of phenolphthalein solution are added and the 

 alkali solution in the cylinder, after thorough shaking, 

 is added to the mixture in the cup or beaker until the 

 pink color remains permanent. The number of c.c. used 

 is then read off from the measuring cylinder. Each c.c. 

 represents one-tenth per cent, of acid in the sample 

 tested. 



TESTS FOR PRESERVATIVES 



The use of antiseptics to inhibit bacterial growth and 

 thus prevent the souring or decomposition of milk is 

 much less common than formerly, but is still practised 

 to some extent. This is also true of the addition of 

 alkalies to neutralize acidity and delay curdling. Not 

 only may the antiseptics do harm themselves, but they 

 and the alkalies conceal conditions in milk which are un- 

 desirable and may prove injurious. For these reasons, 

 the addition of these substances to milk is forbidden 

 by Federal and State laws. 



A simple test for preservatives may be made by 

 setting a sample of milk aside and observing if it curdles 

 within the usual time. If it does not, the presence of 

 preservatives or alkalies may be suspected. The pre- 

 servatives most commonly used and tests for detecting 

 their presence are given below. 



Boric Acid and Borax. Until the introduction of for- 

 maldehyde, boric acid and borax were the most popular 

 preservatives; 0.1 to 0.2 per cent, of these substances will 

 delay the curdling of milk for several days. They may be 

 detected by the following tests : 



Vllllers' and Fayolle's Test. About 10 c.c. of the 

 milk is placed in a porcelain crucible, evaporated to dry- 

 ness and the residue burned to an ash. Sufficient sul- 



17 



