402 



THE KEEPING OF MILK. 



most common additions for this purpose are boric acid and its 

 sodium salt, borax ; salicylic acid, either alone or mixed with 

 borax and boric acid, and sometimes in alcohol or glycerol 

 solution ; fluorides, such as sodium fluoride or potassium acid 

 fluoride ; fluosilicates and fluoborates ; /?-naphthol and salts 

 of the /9-naphthol-sulphonic acids (abrastol), formaldehyde, and 

 benzoic acid. Potassium nitrate has also been recommended, 

 but it is a comparatively weak antiseptic, and is little, if at all, 

 used. Hydrogen peroxide is also used. 



Effect of Preservatives. The effect of boric acid preser- 

 vative and formaldehyde has been studied by the author and 

 Harrison ; taking milk which just curdles on boiling as the 

 limit of fresh milk, the following are the extra times that the 

 preservatives will keep milk fresh : 



TABLE CXXXIX. 



Table CXXXIX. shows how useless these preservatives in small 

 amounts are, and an equal effect is produced by a few degrees 

 lowering of temperature. 



TABLE CXL. COMMERCIAL PRESERVATIVES. 



Monier- Williams. 



Salicylic acid. 



f Sodium benzoate. 



