ANALYTIC PROCESSES 



37 



a gas evolution cell and incandescent lamp, but 

 an ammeter and adjustable rheostat are better. 



Lactose may be determined by the polarim- 

 eter after removal of the fat and proteins, 

 which is best effected, as recommended by 

 Wiley, by acid mercuric nitrate 

 solution. Wiley prepared this by 

 dissolving mercury in twice its 

 weight of nitric acid of 1.42 sp. gr. 

 and adding to the solution five vol- 

 umes of water, but Revis and Bol- 

 ton advise that mercuric oxid 

 should be used. The A. O. A. C. 

 optical method is as follows: 



For polarimeters reading to 100 

 for 26.048 grams sucrose (corre- 

 sponding to 32.98 grams lactose), 

 measure, in c.c, the amount ob- 

 tained by dividing double this {i.e., 

 65.96) by the sp. gr., add 10 c.c. mercuric nitrate 

 solution, make up to 102.6 c.c, shake, filter 

 through a dry filter and examine in a 200 mm. 

 tube. Half the observed reading will be the per- 

 centage of lactose. For example, if the sp. gr. 

 of the milk is 1.030, the amount taken will be 

 65.90 -T- 1.030 = 64 c.c. 



The allowance for volume of precipitate by 

 making up to 102.6 c.c. is not accurate, except 

 with closely skimmed milks. 



Fig. 2. 



