CONDENSED MILK 77 
marked at 55 c.c., a piece of litmus paper dropped 
in, and the excess of nitric acid cautiously neu- 
tralized by sodium hydroxid solution. The 
liquid is then faintly acidified by a single drop of 
acetic acid (it must not be alkaline), a few drops 
of an alcoholic solution of thymol are added, 
and then 2 c.c. of a solution of invertase, prepared 
by grinding half a cake of ordinary compressed 
yeast with 10 c.c. of water and filtering. The 
flask is corked and allowed to remain at a tem- 
perature of 35° to 40° for twenty-four hours. The 
cane-sugar will be inverted, while the milk-sugar 
will be unaffected. The flask is filled to the mark 
(55 c.c.) with washed aluminum hydroxid and 
water, mixed, filtered, and the polarimetric 
reading taken. The amount of cane-sugar can 
be determined from the difference in the two 
readings by the formula 
Se tooa + ° 
142.68 — . 
in which S is the percentage of sucrose; a, the 
reading before, 0b, after inversion; 1t, the 
temperature. 
LACTOSE, SUCROSE AND INVERT-SUGAR.—Bige- 
low and McElroy propose the following routine 
method to include invert-sugar. The reagents 
are: 
