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 4, .. 
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.¢., 
65.96) by the sp. gr., add roc.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 + 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. 
Fie. 2. 
