226 Testing MUk and Its Products. 



Olson^: P=T— _T_ The results obtained by this 



1.34 



formula are quite satisfactory. If we assume that .8 

 of the milk protein is casein, this component can also be 

 obtained from the solids of the milk by a simple calcula- 

 tion by the use of the preceding formula. 



258. Hart's test for casein in milk. The following 

 test for casein in milk has been published by the Wis- 

 consin experiment station.^ 



Two cc. of chloroform, 20 cc. of a .25 per cent, solu- 

 tion of acetic acid, and 5 cc. of milk (both these latter 

 of a temperature of about 70° F.) are measured into 

 small tubes of special construction holding about 35 cc., 

 the lower ends of which are narrow and graduated to 

 .1 cc. The mixture is shaken for 10 to 20 seconds and 

 the tubes then whirled 7I/2 or 8 minutes in a centri- 

 fuge of 15 inches diameter, making 2000 revolutions per 

 minute. (The use of a metronome is recommended to 

 facilitate the control of the speed.) After whirling, 

 the tubes are taken out of the centrifuge and allowed 

 to stand for 10 minutes, and the percentage of casein 

 read off directly from the scale on the lower end of the 

 tubes, each division of which represents .2 per cent, of 

 casein when 5 cc. of milk are measured out. The test 

 calls for considerable nicety of manipulation, but ap- 

 pears to give reliable results when the directions given 

 are strictly followed.* 



259. e. Milk sugar is generally determined by differ- 

 ence, the sum of fat, casein and albumen (total NX6.25) . 



iJourn. Ina. and Eng. Chemistry, I, 1909, p. 253. 



' Report 24, p. 117 : "A simple method for the estimation of casein 

 In cow's milk." 



' See also Clrc. 10. Wis. expt. sta., Operating the casein test at cheese 

 factories. 



