30 MANUAL OF MILK PRODUCTS 



That portion of the milk consisting of water and the com- 

 pounds in solution is known as the milk-serum. In studying 

 the individual constituents of milk, it is necessary to separate 

 the serum. Various methods have been used to separate milk- 

 serum from the other constituents of milk, but the one best 

 adapted for investigational purposes depends upon the fact 

 that when milk is brought into contact with a porous earthen- 

 ware filter, the water passes through, carrying with it the com- 

 pounds in true solution, while the compounds insoluble in 

 water or in suspension remain on the surface of the filter. 

 We have made use of the special form of apparatus designed 

 by Briggs 1 for the purpose of obtaining water-extracts from 

 soils. Briefly stated, the process consists in putting the milk 

 to be examined into a tubular chamber surrounding a Pasteur- 

 Chamberland filtering tube ; pressure, amounting to 40 to 

 45 pounds a square inch, is applied by means of a pump which 

 forces air into the chamber containing the milk and causes the 

 soluble portion of the milk to pass through the walls of the 

 filter from ;the outside to the inside of the filtering tube, from 

 which it runs out and is caught in a flask standing underneath. 

 The insoluble residue accumulates on the outside surface of 

 the filter tube from which it can easily be removed by light 

 scraping. 



Before being placed in the apparatus for filtration, the milk 

 is treated with some antiseptic to prevent souring during the 

 process of filtration. 



The composition of the solid portion of milk removed by the 

 filtering tube is ascertained by difference; from the figures 

 obtained by an analysis of the original milk we subtract the 

 results of analysis given by the serum. 



1 U. S. Dept. Agr. Soils. Bui. 19, p. 31, and Bui. 31, pp. 12-16. 



