I9o MODERN METHODS OF TESTING MILK 



incorporated in the body of the milk. The desired 

 amount of mercuric chloride may be approximately 

 measured by taking the quantity that will easily lie on 

 the surface of a silver dime for one quart of milk or, 

 more conveniently, the amount held by a o.22-inch, pis- 

 tol cartridge-shell ^ inch long, when loosely filled. 

 A stiff wire soldered to such a shell makes it conven- 

 ient to handle. Commercial mercuric chloride tablets 

 containing color-matter can not be used. 



Summary of Precautions. Below we give in out- 

 line the special points to be observed with care in per- 

 forming the operations of the test, assuming that the 

 graduated glassware is accurate and the solutions of 

 correct strength. 



(1) Preliminary neutralization. In the neutraliza- 

 tion of the sample of milk, excess of alkali must be 

 avoided ; this can be controlled by the use of a properly 

 prepared color-standard. 



(2) Conditions of precipitation. Before precipitat- 

 ing with acid, have the dilute, neutralized milk at a 

 temperature between 60 and 80 F. Add enough acid 

 to cause the casein to separate promptly in large flakes,, 

 leaving the supernatant liquid clear. Shake the mixture 

 vigorously at intervals during the addition of acid; 

 also after complete precipitation and again after dilu- 

 tion to the 200 cc. mark. 



(3) Filtration. Allow most of the liquid to run 

 through the filter before making the final titration with 

 alkali. 



(4) Titration with alkali. In titrating the filtrate 

 with alkali, avoid an excess of alkali. Add the alkali 

 solution cautiously until, after thorough agitation, a 



