New York Agricultural Experiment Station. 307 



stituents of milk, but the one best adapted for investigational 

 purposes depends upon the fact that when milk is brought into con- 

 tact with a porous earthenware filter, the water passes through, 

 carrying with it the compounds in true solution, while the compounds 

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

 In one form or another, this fact has been utilized in studying milk 

 by Lehman, Duclaux, Eugling, Soldner and others. The form of 

 earthenware filter used by us is much superior to any employed by 

 these investigators. 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 per 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. 



It has been found by Rupp 2 that the filter appears to have the power 

 of absorbing some of the soluble constituents of the serum until a 

 volume of 50 to 75 c.c. has passed through, after which the filtered 

 serum is constant in composition. In our work, therefore, the first 

 portion of serum filtered is not used. 



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 filter- 

 ing 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. 



PROPERTIES AND COMPOSITION OF MILK-SERUM. 



Serum prepared from fresh milk by the method described above 

 has a characteristic appearance, being of a yellow color with a faint 

 greenish tinge and slight opalescence. 



The serum from fresh milk gives a slight acid reaction to phenol- 

 phthalein and a strongly alkaline reaction to methyl orange. We 

 will later give the results of a special study made of the cause of 

 acidity in milk-serum. 



In the table below we give the results of the examination of two 

 samples of fresh milk, the serum of which was prepared in the manner 

 already described. These samples of milk were treated with chloro- 



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

 *U. S. Dept. Agr. An. Ind. Bui. 166, p. 9. 



