76 MILK PRODUCTS 



and made up to 200 c.c. plus the volume of the 

 precipitated fat and proteins (see page 38). The 

 liquid portion, which now measures 200 c.c, is 

 passed through a dry filter. The reducing power 

 with alkaline copper solutions is determined at 

 once upon 50 c.c. of this filtrate. To another 

 50 c.c, 1% of citric acid is added, the solution 

 boiled at least thirty minutes, and the reducing 

 power also determined. The increase over that 

 of the first solution is due to the invert-sugar 

 formed by the action of the citric acid on the 

 sucrose. It is necessary to bear in mind that the 

 reducing equivalents of lactose and invert-sugar 

 are not the same. Volumetric methods may be 

 employed. 



The following method is based on the difference 

 in polarimetric reading before and after action of 

 invertase. 75 c.c. of the diluted milk are placed 

 in a loo-c.c flask, diluted to about 80 c.c, 

 heated to boiling, to correct birotation, cooled, 

 and 10 c.c. of acid mercuric nitrate solution 

 (page 37) added. The mixture is made up to 100 

 c.c, well shaken, filtered through a dry filter, and 

 the polarimetric reading taken at once. It will 

 be the sum of the effect of the two sugars. The 

 volume of the sugar-containing liquid is calcu- 

 lated by allowing for the precipitated proteins 

 and fat, as described on page 38. 



50 c.c. of the filtrate are placed in a flask 



