TESTS FOR PRESERVATIVES ovl 
contents are yellow or white. After the flask has cooled add about 200 
c.c. of ammonia-free water, 20 c.c. of a potassium sulphide solution (40 
gms. potassium sulphide per liter of water) and a small piece of zine. 
Connect the flask to a condenser and, after adding carefully 50 ¢.c. of a 
60 per cent of sodium hydroxide solution, distill, receiving the distillate 
in standard acid solution. Titrate the excess of acid with standard 
alkali, using methyl orange and compute the amount of nitrogen in the 
milk, This percentage of nitrogen multiplied by 6.25 will roughly give 
the percentage of protein. 
Test for Coloring Matter in Milk. Shake about 10 c.c. of the milk 
with 5 or 10 ¢.c. of ether. Fresh milk will give a colorless supernatant 
ether layer, while, if coloring matter has been added to the milk, this 
ether layer will be colored. 
Detection of Preservatives. The refusal of milk to sour when 
placed in a warm place is evidence that a preservative has been added. 
The following preservatives are often found in milk and their detection 
may be carried out as follows: 
Benzoic Acid. Adda few drops of lime water to 300 c.c. of the sam- 
ple and reduce the volume to about 75 c.c. Mix powdered calcium 
sulphate with this to a paste and evaporate to dryness. When dry, 
grind and moisten with dilute sulphuric acid; shake out in 50 per cent 
alcohol. Repeat this three times and reduce the acid alcohol solution 
to small volume on the water bath after adding barium hydroxide to 
neutrality. Acidulate with sulphuric acid and extract with ether. 
When the ether is evaporated, the benzoic acid is left behind. This 
precipitate may be subjected to further study. 
Boric Acid. Add sodium hydroxide to 75 or 100 c.c. of the milk and 
evaporate to dryness. Fuse and dissolve the ash in water. Add a 
little hydrochloric acid and filter. Moisten a strip of turmeric paper 
with the filtrate and dry on a watch glass. <A red color indicates boric 
acid or its salts. 
Salicylic Acid. Add a little sulphuric acid to 15 or 20 c.c. of the milk 
and shake out with ether. Evaporate to dryness and treat the residue 
with alcohol and ferric chloride. The presence of salicylic acid is indi- 
cated by a violet color. 
Formaldehyde. To 5 c.c. of the milk add 5 c.c. of distilled water 
and 10 c.c. of hydrochloric acid, containing a little ferric chloride. 
The presence of formaldehyde is indicated by a violet color. 
Detection of Heated Milk. Storch’s Method. Five c.c. of milk 
are poured into a test tube; a drop of weak solution of hydrogen dioxide 
(about 0.2 per cent) which contains about 0.1 per cent of sulphuric acid 
