COMPOSITION OF MILK 23 



2. Evaporate to dryness over a water bath or dry- 

 sand bath. 



3. When the contents are thoroughly dried, reweigh 

 and subtract the original weight of the dish. The weight 

 in grams will be the per cent of total solids in the milk. 



4. The loss in weight represents the water in the milk. 



Note: To make sure that the sample was thoroughly dried 

 it should be again placed on the bath and heated for some time. 

 If there is no further decrease in weight it may be taken for 

 granted that the sample was dry. 



The solids of skim-milk, cream, and whey can be deter- 

 mined in the same manner. 



LABORATORY PROBLEMS 



II. To Detebmine the Casein in Milk 



The casein in milk can be precipitated by very dilute 

 acid. Albumen cannot be so precipitated. 



1. To 100 grams of carefully separated skim-milk 

 add a few cubic centimeters of dilute acetic acid to cur- 

 dle it. If it does not curdle readily add a few cubic 

 centimeters more. The temperature of the skim-milk 

 should be from 80 to 100 degrees F. Care should be 

 taken not to add too much acid, as it will have a tendency 

 to dissolve the curd. If acetic acid is not available, 

 dilute sulfuric acid may be used, but it does not answer 

 the purpose so well as acetic acid. A few drops of rennet 

 may also be used. 



2. "When coagulated break up the coagulum and 

 filter. The filtration process can be hastened by allow- 

 ing the curd to settle to the bottom of the beaker after 

 heating up the curd about 10 degrees. Dry the curd on 

 a water bath after filtration. It will be nearly pure 

 casein. 



