Testing Milk and Its Products. 27 



bonates in the alkali) that the mixture will be thrown 

 out of the neck of the test bottle when this is shaken in 

 mixing the milk and the acid (37). When powdered 

 alkali is added to the milk, it should be allowed to 

 stand for a while, with frequent shaking, until the curd 

 is all dissolved and an even translucent liquid is ob- 

 tained. Such milk may become dark-colored by the ac- 

 tion of the alkali, but this color does not interfere with 

 the accuracy of the test. 



Instead of powdered soda or potash, these substances 

 dissolved in water (soda or potash lye), or strong am- 

 monia, may be used for the purpose of dissolving the 

 coagulated casein in sour milk. In this case, a definite 

 proportion of alkali solution must be taken, however, 5 

 per cent, of the volume of milk being usually sufficient, 

 and the results obtained are increased accordingly. 



33. Sampling frozen milk. When milk freezes, it 

 separates into two distinct portions : Milk crystals, 

 largely made up of water, with a small admixture of fat 

 and other solids, and a liquid portion, containing nearly 

 all the solids of the milk. In sampling frozen milk it 

 is therefore essential that the liquid and the frozen part 

 be warmed and thoroughly mixed by pouring gently 

 back and forth from one vessel into another; the sam- 

 ple is then taken and the test proceeded with in the 

 ordinary manner (36). 



Questions. 



1. What precautions must be taken in sampling milk? Give 

 reasons. 



2. How can a fair sample be taken of (a) partially churned 

 milk, (b) sour milk, (c) frozen milkt 



3. If 15 cc. of ammonia are added to 500 ce. of sour milk, 

 and a test of 3.45 obtained, what is the correct test of the milkf 



