310 Report of the Department of Chemistry of the 



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 PORTION OF MILK 

 IN SUSPENSION OR COLLOIDAL SOLUTION. 



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 can 

 not 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 suspension 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. 



(1) Appearance. — When prepared by the method of filtration 

 previously described, 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, etc., 

 it resembles in appearance dried white of egg. 



(2) Behavior with water. — The deposit of insoluble milk-constituents 

 on the outside of the filtering tube, when removed and shaken vigor- 

 ously 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 con- 

 stituents but can be readily purified by shaking with distilled water 

 and filtering several times. The purified material goes readily into 

 suspension on shaking with water and, if treated with a preservative, 

 will remain indefinitely without change other than the separation 

 of fat-globules. It has been held by some that the citrates of milk 

 perform the function of holding the insoluble phosphates in suspen- 

 sion, but this is not supported by the behavior of the insoluble portion 

 shown in our experiments. 



(3) Reaction. — A suspension of the insoluble constituents of milk, 

 prepared in the manner described above, is neutral to phenol- 

 phthalein. We purified the deposit made from 1000 c.c. of milk, made 

 a suspension of it in water, and, after the addition of 10 c.c. of neutral 

 solution of potassium oxalate, it was found to require only 0.5 c.c. 

 of T ^ solution of sodium hydroxide to make it neutral to phenol- 

 phthalein. We interpret this to mean that there are no tri-basic 

 (alkaline) phosphates in milk or in the serum, because the serum, 



