CHAPTER-XXYV. 
DETECTION OF PRESERVATIVES AND DIRT. 
PRESERVATIVES IN MILK. 
Milk dealers sometimes add small quantities of pre- 
servatives or antiseptics to milk to prolong its keeping 
quality. These substances check bacterial development, 
and whatever stops the growth of bacteria also acts in- 
juriously upon the human system. For this reason the 
use of preservatives in milk is strictly prohibited by law. 
Among the preservatives most commonly found in 
milk are boric acid and its compounds, formaldehyde 
and salicylic acid and some of its compounds. Methods 
for detecting these substances are given in the following 
paragraphs: 
Boric Acid. This acid, or its compounds, is often 
used as a preservative. While far less harmful than 
many other preservatives, it has been known to cause 
stomach and bowel disturbances, and its use in milk is 
universally condemned. There are a number of methods 
for detecting boric acid, two of which are here described: 
1. Treat a small quantity of milk with a few drops 
of phenolphthalein; then add, by drops, sodium hydrox- 
ide till a faint pink color is noticeable. Now divide 
the milk between two test tubes, diluting one with an 
equal volume of water and the other with a neutral 
50 per cent solution of glycerin. When no boric acid 
is present, the color of the two tubes will be practically 
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