MILK AND MILK PRODUCTS II 



used. Satisfactory results may be secured by the following 

 simple method: A flat platinum dish, 3.5 cm. in diameter, 

 with sides 0.5 cm. high, is provided with a thin flat watch-glass 

 cover that fits rather closely. The total weight of the cover 

 and dish is noted. 2 or 3 c.c. of the sample are run into the 

 dish from the pipet, the watch-glass placed on, and the weight 

 taken as rapidly as possible. The glass prevents appreciable 

 loss from evaporation during an ordinary weighing. The cover 

 is removed, the dish heated on the water-bath or in the water- 

 oven, and weighed from time to time (with cover on it) until the 

 weight is sensibly constant. The percentage of residue can be 

 easily calculated. About three hours may be required to secure 

 constant weight. 



The A. O. A. C. method is: Heat at 100° to constant weight, 

 about 3 grams in a tared platinum, aluminum or tin dish of 

 5 cm. diameter, with or without the addition of 15 to 30 grams 

 of sand. Cool and weigh. 



The use of aluminum or tin as substitutes for platinum is 

 inadvisable; much better results will be obtained with nickel, 

 porcelain or glass. 



Ash. — The residue from the determination of total solids is 

 heated cautiously over the Bunsen burner, until a white ash 

 is left. The result obtained in this manner is apt to be slightly 

 low from loss of sodium chlorid. This may be avoided by 

 heating the residue sufficiently to char it, extracting the sol- 

 uble matter with a few cubic centimeters of water, and filtering 

 (using paper extracted with hydrofluoric acid). The filter is 

 added to the residue, the whole ashed, the filtrate then added, 

 and the liquid evaporated carefully to dryness. The ash of 

 normal milk is about 0.7 per cent, and faintly alkaline. A 

 marked degree of alkalinity and effervescence with hydro- 

 chloric acid will suggest the addition of a carbonate. 



The method of the A. O. A. C. is as follows: In a weighed 

 dish put 20 c.c. of milk from a weighing bottle; add 6 c.c. of 



