TESTS USED IN CHEESE-MAKING 447 



of alkali used (B) in neutralizing 100 cc. of filtrate 

 is very simple. Divide A by 2 and from the result sub- 

 tract B; or, expressed as a formula, 



^ 



B=per cent of casein in milk. 



Example: One used 30 cc. (A) of acid in precip- 

 itating casein and 11.95 cc - (B) of alkali in neutraliz- 

 ing 100 cc. of filtrate (one-half of filtrate from the 

 casein precipitate corresponding to 9 grams of milk). 

 Substituting 30 for A and 11.95 f r B in the formula, 

 we have 



^11.95 ( = 15 ii.95)=3-<>5 ( the percentage of 



casein in milk). 



(7) Use of preservatives. In making a casein de- 

 termination by this method, it is desirable, when possi- 

 ble, to use milk not more than 24 hours old, which has 

 been kept in a cool place. Milk which is sour or which 

 coagulates on heating cannot be used with satisfac- 

 tory results. However, by adding to fresh milk pure, 

 powdered mercuric chlorid (corrosive sublimate) in 

 the approximate proportion of I part to 1,000 or 1,500 

 parts of milk, and then keeping mixture at a tempera- 

 ture of 50 or lower, one can obtain satisfactory re- 

 sults with milk that has been kept two or three weeks. 

 Milk thus treated should be shaken often enough to 

 keep the fat well incorporated in the body of the milk. 

 The desired amount of mercuric chlorid may be ap- 

 proximately measured by taking for one quart of milk 

 the amount of mercuric chlorid that will lie easily on 

 the surface of a silver dime, or, more conveniently, 

 the amount held by a o.22-inch pistol cartridge-shell, 

 one-half inch long, when loosely filled. Commercial 



