2l8 ORGANIC AGRICULTURAL CHEMISTRY 



constituents. It has food value for domestic animals, being 

 used especially for swine. Commercially the whey is used as a 

 source of milk sugar and, after fermentation, of lactic acid. 



Food Value 



The definite consideration of food values will be given in 

 another chapter. As stated at the beginning of our study of 

 milk it is a normal balanced food in itself, containing all of the 

 essential food constituents. While primarily a normal food for 

 young animals, including babies, it is also used to a very large 

 extent as a food for adult human beings. The food value of 

 butter is largely in its fat content and of cheese in both fat and 

 protein. 



EXPERIMENT STUDY XXIX 



Separation of Milk Constituents 



(i) Casein. Dilute a pint of whole milk with an equal volume of 

 water. Add slowly with slight stirring a dilute (lo per cent) solution 

 of acetic acid. When flocculation begins, proceed very slowly and 

 stop the addition of acid as soon as the coagulum becomes nearly 

 solid. Allow to stand a few minutes until the coagulated protein 

 separates slightly, leaving a whey that is only slightly opaque. Filter 

 through a double cheesecloth and press the curd as dry as possible. 

 This curd is casein with included fat. After extracting the fat as in 

 (2) the casein should be white and quite easily pulverized. Test the 

 dry casein by the tests for protein (Experiment XVIII, 4). 



(2) Fat. Place the pressed casein in a flask or bottle and cover 

 with 95 per cent alcohol. Shake a little to aid the extraction of the 

 water. Pour off the alcohol extract. Repeat the extraction with 

 ether instead of alcohol and collect the ether extract by itself. Extract 

 again and a third time if necessary with ether, combining the ether 

 extracts. Distill off the ether from the extracts and a residue of milk 

 fat will be obtained. 



(3) Lactalbumin. If the whey from the separated casein in (i) re- 

 quires it, filter through a filter paper. Place the clear whey in an 

 evaporating dish or beaker and heat to boiling for a few minutes. 

 Notice the coagulation of the milk albumin. Filter off the albumin 

 through filter paper and repeat the heating. If more albumin sepa- 



