REPORT OF CHEMICAL DEPARTMENT. 
A VOLUMETRIC METHOD FOR THE DETER- 
MINATION OF CASEIN IN MILK.*7 
L. L. VAN SLYKE anp ALFRED W. BOSWORTH 
SUMMARY. 
A given amount of milk, diluted with water, is made neutral 
to phenolphthalein solution by addition of a solution of sodium 
hydroxid. The casein is then completely precipitated by ad- 
dition of standardized acetic acid; the volume of the mixture 
is made up to 200 cc. by addition of water, thoroughly shaken 
and then filtered. Into 100 cc. of the filtrate a standardized 
solution of sodium hydroxid is run until neutral to phenol- 
phthalein. The solutions are so standardized that 1 cc. is 
equivalent to 1 per ct. of casein when a definite amount of 
milk is used. The number of cubic centimeters of standard 
acid used, divided by 2, less the amount of standard alkali 
used in the last titration gives the percentage of casein in the 
milk examined. When one uses 17.5 cc. (18 grams) of milk, 
the amount used in the Babcock milk-fat test, the standard 
acid and alkali solutions are made by diluting 795 cc. of tenth- 
normal solutions to 1 liter. By using 22 cc. of milk, tenth 
normal solutions can be used directly; or by using 20 cc. of 
milk and tenth-normal solutions, adjustment is made by multi- 
plying the final result by 1.0964. 
The method usually gives results within 0.2 per ct. of those 
obtained by the “ official’ method. 


* Presented in abstract before the meeting of the American Chemical 
Society, Detroit, Mich., June 29-July 2, 1909. 
7 A reprint of Technical Bulletin No. 10. 
[333] 
