68 MILK PRODUCTS 
are treated with picric acid solution. A  pre- 
cipitate indicates gelatin. In this case, the re- 
mainder of the solution is evaporated to small 
bulk, and mixed with a 10% solution of tannin 
until no more precipitate is produced. The 
liquid must in this treatment not have a tem- 
perature of over 60°. To it a few c.c of white of 
egg are added and the mixture heated to boiling 
for thirty minutes, filtered hot, concentrated 
to small bulk on the water and allowed to cool 
and gelatinize. 
