j 88 CLEAN MILK 



Milk Preservatives 



The most commonly used preservatives are formaldehyde, 

 "borax and boric acid. Occasionally salicylic acid and sodium car- 

 bonate are employed. Formaldehyde may be detected, during the 

 process of determining fat by the Babcock test, by observing the 

 color of the line of contact of the acid with the milk. When pure 

 milk is used for the Babcock test, the color of this line is dirty 

 brown, but, when formaldehyde is present in the milk, a distinct 

 purple hue will appear at the junction of the acid and milk. 



This test may be applied in other ways by using a separate 

 sample of milk. Place about 20 cubic centimeters * of milk in 

 a small glass vessel, dilute with an equal volume of water, and 

 add commercial sulphuric acid, allowing it to flow slowly down 

 the inside of the vessel. If formaldehyde is present the purple 

 color will appear at the junction of the acid and milk. 



Boric acid or borax are detected by adding to a few drops of 

 milk, contained in a white dish, a drop or two of hydrochloric acid, 

 and then several drops of a saturated alcoholic solution of turmeric. 

 Heat the dish gently for a few minutes and, if boric acid or borax 

 are present, a pink or dark red color will appear. Cool, and add 

 a drop of ammonia, when a dark blue-green should be seen. 



Sodium carbonate is detected by adding to the suspected 

 sample of milk an equal volume of alcohol and then two drops 

 of a one % solution of rosolic acid. If sodium carbonate is 

 present a red-rose color will appear. The test may be performed 

 with more certainty if a comparison test is made with a sample 

 of milk known to be pure. 



Salicylic acid is rarely used, but may be detected by adding a 

 few drops of sulphuric acid to a small quantity of milk and then 



*A cubic centimeter (metric system) is a volume of fluid equal to 16 

 drops of water. Any apothecary can prepare the substance required to make 

 the above tests and at the same time could perform the tests with the assist- 

 ance of the description given above and show the farmer or dairyman how 

 to perform them himself. 



