ANALYSIS OF MILK-PRODUCTS 47 



separates in minute crystals, which on long standing 

 sink to the bottom. It is not generally heated to an 

 extent sufficient to affect the milk sugar, and milk and 

 cane sugar may be estimated by Harrison's method. 



Harrison s Method. Prepare the nitrate with acid 

 mercuric nitrate as usual (p. 30), taking, however, double 

 quantities ; place as much of the nitrate as possible 

 in a 100 c.c. flask and weigh this ; immerse for exactly 

 seven minutes in a briskly boiling water-bath to invert 

 the cane sugar, cool, and make up with distilled water 

 to the original weight. Fill the 200 c.c. tube with this 

 solution (cleared if necessary by nitration), polarise 

 and at once note the temperature. Multiply the dif- 

 ference between the direct and the inverted readings 



by T7 F' ai *d this will <nve the reading due to 



142.66 -.1 



cane sugar ; this divided by 1.2 will give the per- 

 centage of cane sugar in the diluted milk ; the per- 

 centage of anhydrous milk sugar in the diluted milk 

 is given by the difference between the direct reading 

 and that due to cane sugar. These percentages multi- 

 plied by 3 will give the amounts in the condensed 

 milk. 



The Werner- Schmid method for the estimation of ^ 

 fat should not be used, and the Gottlieb method is 

 recommended. 



Sour milk is difficult to analyse, and the results 

 are generally less satisfactory than those obtained with 

 fresh milk. If approximate results only are wanted, 

 such as would be furnished by a determination of 

 specific gravity and fat alone, the following modification 

 of WeibulPs method may be used ; measure the sour 

 milk, and to each 100 c.c. add 5 c.c. of a solution of 

 ammonia (i part of ammonia, sp. gr. 0.880, to 4 parts 

 water) ; shake gently, and allow to stand till the 

 precipitated casein is all dissolved ; the specific gravity 

 is estimated by a lactometer, and a correction (usually 

 about 2.7 or 2.8 degrees), found experimentally by 

 noting the decrease of specific gravity in fresh milk 



