34 MANUAL OF MILK PRODUCTS 



sorbing action of the casein is practically prevented and little 

 or no albumin is carried down with it. In the case of the 

 addition of formaldehyde to milk, the adsorbing power of 

 casein is greatly diminished, probably due to the chemical 

 reaction between casein and formaldehyde. 



Properties and composition of that part of milk in suspension 

 or colloidal solution (Van Slyke and Bosworth) 



Some of the constituents of milk are suspended in the form of 

 solid particles in such an extremely fine state of division that 

 they pass through the pores of filter paper and they do not 

 settle as a sediment on standing, but remain permanently 

 afloat. They cannot be seen except by ultra-microscopic 

 methods. When substances are in such a condition, they are 

 said to form a colloidal solution. In passing milk through the 

 Pasteur-Chamberland filtering tube, the constituents in sus- 

 pension as solid particles, and in colloidal solution, are retained 

 in a solid mass on the outside of the tube and can therefore be 

 readily obtained for study. 

 Appearance. 



When prepared by the method of filtration previously de- 

 scribed, the insoluble portion of milk collecting on the outside 

 of the filtering tube is grayish to greenish white in color, of a 

 glistening, slime-like appearance and gelatinous consistency. 

 When dried without purification by treatment with alcohol, 

 and the like, it resembles in appearance dried white of egg. 

 Behavior with water. 



The deposit of insoluble milk-constituents on the outside 

 of the filtering tube, when removed and shaken vigorously 

 in a flask with distilled water, goes into suspension and the 

 mixture has the opaque, white appearance of the original milk. 

 The deposit is, of course, more or less mixed with adhering 

 soluble constituents but can be readily purified by shaking 



