224 Testing Milk and Its Products. 



the lower end of which is narrow and graduated to 

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

 the tubes then whirled 7y 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 

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

 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 properly conducted. 



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

 ence, the sum of fat, casein and albumen (totalNX6.25), 

 and ash, being subtracted from the total solids. It may 

 be determined directly by means of a polariscope, or 

 gravimetrically by Fehling's solution; only the former 

 method, as worked out by Wiley, 1 will be given here. 



The specific gravity of the milk is accurately deter- 

 mined, and the following quantities of milk are meas- 

 ured out -by means of a 100 cc. pipette graduated to .2 

 cc. (or a 64 cc. pipette made especially fcr this purpose, 

 with marks on the stem between 63.7 and 64.3 cc.), ac- 

 cording to the specific gravities given : 1.026, 64 3 ce. : 

 1.028, 64.15 cc. ; 1.030, 64.0 cc.; 1.032, 63.9 cc.; 1.034, 

 63.8 cc.; 1.036, 63.7 cc. These quantities refer to the 

 Schmidt-Haensch half-shadow polariscopes, standard- 

 ized for a normal weight of 26.048 grams of sugar. The 

 milk is measured into a small flask graduated at 100 cc. 



i Agricultural Analysis, ill, p. 275; Am. Ohem. Jour., 6, p. 289 et seq. 



