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: 
Villiers’ 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 
