52 MILK ANALYSIS 



with 10 c.c. of water and filtering. The flask is corked and 

 allowed to remain at a temperature of 35° to 40° for 24 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 polari- 

 metric reading taken. The amount of cane-sugar can be de- 

 termined from the difference in the two readings by the formula 



143- 



b_ 



t 



in which S is the percentage of cane sugar; a, the reading 

 before, h, the reading after inversion; t, the temperature. 



Bigelow and McElroy propose the following routine method 

 for the determination of the sugars, including invert- sugars, in 

 condensed milk. The solutions used are : 



Acid Mercuric lodid. — Mercuric chlorid, 1.35 grams; potas- 

 sium iodid, 3.32 grams; glacial acetic acid, 2. c.c. ; water, 64 c.c. 



Alumina- cream. — A cold saturated solution of alum is divided 

 into two unequal portions, a slight excess of ammonium hydroxid 

 is added to the larger portion and the remainder added until a 

 faintly acid reaction to litmus is obtained. 



The entire contents of the can are transferred to a porcelain 

 dish and thoroughly mixed. A number of portions of about 25 

 grams are weighed carefully in 100 c.c. flasks. Water is added 

 to two of the portions, and the solutions boiled. The flasks are 

 then cooled, clarified by means of a small amount of the acid 

 mercuric iodid and alumina-cream, made up to mark, filtered, 

 and the polarimetric reading noted. Other portions of the milk 

 are heated in the water-bath to 55°; one-half of a: cake of com- 

 pressed yeast is added to each flask and the temperature main- 

 tained at 55° for five hours. Acid mercuric iodid and alumina- 

 cream are then added, the solution cooled to room temperature, 

 made up to mark, mixed, filtered, and polarized. The amount 

 of cane-sugar is determined by formula given above. Correction 



