MILK AND ITS PRODUCTS 203 



to retard the separation of the cream. Sodium benzoate 

 (CeHsCOONa), salicylic acid (CeH^OHCOOH), potassium 

 nitrate (KNOs), calcium peroxide (Ca02) and hydrogen 

 peroxide (H2O2) in milk are all harmful. The fluorides, 

 fluosilicates and fluoborates are dangerous poisons. Milk 

 that is properly produced will keep as long as is necessary 

 without preservatives, and the use of preservatives but 

 serves to hide filthy handling and bad management. 



The pasteurization of milk consists in keeping it at a 

 temperature between 63 C. and 75 for at least twenty min- 

 utes, then rapidly chilling the milk. The necessity for 

 pasteurizing milk should be avoided, because lecithin, which 

 is beneficial to growing children, is destroyed, and also 

 because enzymes which are helpful to digestion are killed. 

 Pasteurization serves to kill disease-producing bacteria 

 when present. Imperfect pasteurization of milk is, how- 

 ever, a source of danger, because incomplete heating kills 

 the harmless lactic acid bacteria, while the dangerous putre- 

 factive bacteria may not be affected. Such milk will keep 

 from souring for a long time, and so the buyer, deceived by 

 the absence of souring, may use milk impregnated with dis- 

 ease-producing germs. 



150. The Detection of Formaldehyde in Milk. The pres- 

 ence of formaldehyde in milk may be detected as follows: 



Method 1: Sulphuric Acid Test: Place 5 to 10 cubic 

 centimeters of the milk in a large test-tube, or clean bottle, 

 and add one-half the amount of commercial sulphuric acid, 

 carefully pouring the acid down the side of the tube or bottle 

 so that the milk and acid are not mixed. As the acid is 

 heavier than the milk, it will sink to the bottom of the vessel. 

 If a violet zone is formed at the junction of the two liquids, 

 formaldehyde is present. The sulphuric acid should 

 contain some iron; if chemically pure acid is used, a little 

 ferric chloride must be added. 



Method 2: Hydrochloric Acid Test. First prepare the 

 acid for the test by adding two drops of ferric chloride 



