212 Testing Milk and Its Products. 



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

 ence, the sum of fat, casein and albumen, (total N X 6.25), 

 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, l will be given here. 



The specific gravity of the milk is accurately deter- 

 mined, and the following quantities of milk are measured 

 out by means of a 100 cc. pipette graduated to .2 cc. (or 

 a 64 cc. pipette made especially for this purpose, with 

 marks on the stem between 63.7 and 64.3cc.), according 

 to the specific gravities given: 1.026, 64.3 cc. ; 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, standardized for a 

 normal weight of 26.048 grams of sugar. The milk is 

 measured into a small flask graduated at 100 cc. and 

 102.6 cc. ; 30 cc. of mercuric- iodid solution (prepared 

 from 33.2 grams potassium iodid, 13.5 grams mercuric 

 chlorid, 20 cc. glacial acetic acid and 640 cc. water) are 

 added; the flask is filled to 102.6 cc. mark with distilled 

 water, the contents mixed, filtered through a dry filter, 

 and when the filtrate is perfectly clear, the solution is 

 polarized in a 200 millimeter tube. The reading of the 

 scale divided by 2, shows the per cent, of lactose (milk 

 sugar) in the milk. Take five readings of two different 

 portions of the filtrate, and average the results. 



257. f. Ash. About 20 cc. of milk are measured into 

 a flat-bottom porcelain dish and weighed; about one- half 

 of a cc. of 30 per cent. -acetic acid is added, and the milk 



1 Agricultural Analysis, iii, p. 275; Am. Chem. Jour., 6, p. 289 et. seq. 



