CHAPTER XXVI. 



THE KEEPING OP MILK. 



The Action of Heat on Milk. When milk is heated the following 

 changes occur : At about 70 C. a change takes place in the 

 albumin ; it is not precipitated, but is converted into a form 

 which is precipitated by acids, magnesium sulphate, and other 

 precipitants of casein. 



The following figures (Table CXXXII.) by C. H. Stewart show 

 the percentage of albumin found in milk raised to various tem- 

 peratures : 



TABLE CXXXII. PERCENTAGE OF ALBUMIN IN MILK AT 

 VARIOUS TEMPERATURES. 



At about 80 C. certain organised principles, the nature of 

 which is not fully known, undergo a change. The presence of 

 these principles in an unchanged form is shown by the following 

 reactions : They cause an evolution of gas from hydrogen per- 

 oxide in the cold and give a blue colour with para-phenylene- 

 diamine (para-di-amino-benzene), and hydrogen peroxide. Other 

 substances may be substituted for the para-phenylene-diamine, 

 but, according to Leflmann, this substance is the most charac- 

 teristic. Rosier, working in the author's laboratory, has found 



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