209 



The addition of water to milk lowers the specific gravity, 

 while the skimming of cream from the milk raises the specific 

 gravity. It is therefore possible, by skillful manipulation, 

 for dishonest handlers both to water and to skim the milk 

 so as to leave it with a specific gravity corresponding to 

 normal milk. Such tampering, however, will give the milk 

 a suspicious appearance, and if the percentage of solids, 

 not fat, falls below 7.7, such milk may be considered adulter- 

 ated. 



154. Determination of Water and Total Solids. To de- 

 termine the water and total solids in milk the procedure is 

 as follows: Clean and weigh crystallizing dishes with a 

 capacity of about 100 cubic centimeters or, if available, a 

 platinum dish 3 inches in diameter. Weigh these with small 

 glass rods in each for use in breaking the surface film so 

 as to increase the rate of drying. With the pipette run 5 

 cubic centimeters of the well-mixed milk sample into the 

 dish and obtain the exact weight of the milk. Dry it in an 

 oven at 100 C. or on the surface of a steam bath to constant 

 weight. Two or three hours ought to be sufficient for com- 

 plete drying. Weigh and compute the dried residue as 

 total solid and the loss by evaporation as water. If the 

 ash is not to be determined, an excellent dish for the deter- 

 mination of water and total solids is the shallow cover of 

 a tin baking-powder box. 



155. Determination of Ash. If a platinum or a porcelain 

 dish was used for the determination of water and total solids, 

 the dried residue from that process may be ashed by heating 

 cautiously to a temperature just below red heat till the ash 

 is white or of uniform light gray color. When the weight 

 is constant, compute the residue as ash. 



156. Butter. Butter, in addition to butter fat, con- 

 tains water, curd and salt. In making butter, where the 

 work is carefully conducted, the butter procured is 

 usually one-sixth more than the butter fat contained in the 

 cream. 



