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 3 s° 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 

 (SS 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 



„ _ 100 a -f- fe 



t 



142.68 



2 



in which 5 is the percentage of sucrose; a, the 

 reading before, h, after inversion; t, the 

 temperature. 



Lactose, Sucrose and Invert-sugar. — Bige- 

 low and McElroy propose the following routine 

 method to include invert-sugar. The reagents 

 are: 



