22 



Reaction of Milk. 



"While former investigators assign to milk always either an acid,- 

 alkaline or neutral reaction, later investigations have proved its re- 

 action to be amphotere. Soxhlet states that a milk of only acid or 

 alkaline reaction is an impossibility, since basic, neutral or acid 

 phosphates never show a neutral reaction. To add to milk alkali 

 until no acid reaction can be observed, would produce a milk of 

 strongly alkaline reaction. The opposite takes place when, with 

 the aid of acids, we desii'e to extinguish the alkaline reaction. 



This amphotere reaction can, however, only be proved by the 

 use of specially prepared litmus paper (see Fresenius, Qual. Analy- 

 sis), or better yet, with Liebreich's litmus plaster plates {Berl. Ber., 

 1,48). _ _ . 



To test for the reaction, one drop of milk is brought by means 

 of a glass rod upon the test paper (blue or red). If the red is 

 turned blue, we have an alkaline reaction, or if the blue be turned 

 red, an acid reaction. No change on either would prove a neutral 

 reaction. 



The reaction most generally observed and reported is the neutral 

 reaction. 



Determination of Water and Solids, 



The solids are determined as follows : 



10 c.c. milk are carefully weighed in a dry, counterpoised 

 and covered platinum dish. To this absolute alcohol sufficient for 

 coagulation is added. The coagulated mass is then dried on a 

 , water bath ; and, before it has lost all its moisture, it is, by means 

 of a spatule, carefully spread over the sides of the dish to increase 

 its surface, whereby drying is greatly facilitated. It is then 

 brought into an air bath, and dried to constant weight at from 100 

 to 110° C. To this end the weighings are repeated every hourj 

 the dish, with cover, being allowed to cool in a desiccator before 

 each weighing. We thus have : 



Platinum dish + cover + dry solids, 

 Minus platinum dish ' cover. 



Leaves dry solids. 



