Chemical Analysis of Milk and Its Products. 225 



and 102.6 cc. ; 30 cc. of mercuric-icdid solution (pre- 

 pared from 33.2 grams potassium iodid, 13.5 grams mer- 

 curic 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. 



260. 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 first dried on water bath and then ignited in a 

 muffle oven at a low red heat. Direct heat should not 

 be applied in determining the ash in milk, since alkali 

 chlorids are likely to be lost at the temperature to which 

 milk sclids have to be heated to ignite all organic carbon. 



Example: Weight of porcelain dish -f milk 49.0907 grams. 



Weight of porcelain dish 28.3538 grams. 



Weight of milk 20.7369 grams. 



Weight of dish + milk, after ignition 28.5037 grams 

 Weight of dish 28.3538 grams. 



Weight of milk ash 1499 gram. 



Per cent, of ash^r^^^ 72 per cent. 

 The residue from the determination of solids (252) 

 may also be used for the ash determination. 



261. Acidity of milk. The acidity of milk is conven- 

 iently determined by means of Farrington's alkaline 

 tablets (see p. 122), or by a tenth-normal soda solu- 

 tion. In the latter case 20 cc. of milk are measured into 



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