MILK 229 



crucible over a low flame. Treat the ash with a drop of dilute HC1. An 

 effervescence indicates bicarbonate of soda. 



Detection of Hydrogen Peroxide in Milk. Add 2 or 3 drops of a 2 per 

 cent aqueous solution of paraphenylenediamine hydrochloride to a small amount 

 of milk. A blue color indicates the presence of hydrogen peroxide which was 

 added to keep the milk from souring. 



Detection of Coal Tar Dyes in Milk. Coloring matter is sometimes added 

 to milk to give it a rich, creamy appearance. To 2 teaspoonfuls of milk add an 

 equal volume of hydrochloric acid and mix thoroughly. A pink coloration 

 indicates the presence of Azo Orange, a coal tar dye. Annatto is also used to 

 color milk. 



Test for Foreign Matter in Milk. Sometimes milk is contam- 

 inated by dirt, hair and other matter which is dangerous to the 



FIG. 146. Two cotton discs, one of which shows large quantities of dirt, 

 manure, and other foreign matter. The other shows that the milk Is 

 fairly free from foreign material. The milk was strained through the discs 

 as explained. Test your milk at home. 



purchaser. A simple test may be made by pouring a bottle of milk 

 through absorbent 'cotton placed in a glass funnel. All foreign 

 matter such as dirt, manure, hair, etc., will be left on the absorbent 

 cotton. 



Disease-producing germs or bacteria are often introduced through 

 foreign matter which gets into the milk. Typhoid fever, sore throat, 

 scarlet fever and tuberculosis may be traced to unclean milk. 



Pasteurization. Milk is often heated for twenty minutes at a 

 temperature between 140 and 180 to kill most of the active bac- 

 teria. Heating at this temperature does not destroy the taste of 

 the milk. This process was originated by the famous French 

 chemist Pasteur. 



Number of Bacteria Allowed in Milk. Some parts of the country 

 allow 50,000 bacteria per cubic centimeter of milk. Milk which has 



