231 



become too weak. Never pour water into strong sulphuric 

 acid. 



8. The graduated test bottle, the pipettes, the acid measure, 

 should be thoroughly cleansed immediately after finishing the 

 test. The waste from the bottles contains a large per cent, of 

 sulphuric acid and this is very corrosive; it should be emptied 

 only into glass or glazed earthen vessels. 



9. The temperature of the milk should be between 60 and 

 70 degrees F. 



For the analysis of cream special cream testing bottles 

 are made; the best one is Winton's. Cream may be diluted 

 with a definite quantity of Avater and the milk test bottles can 

 then be used, but the cream test bottles give more accurate 

 results. Market or dairy cream may contain as low as 9.5 per 

 cent, of fat or as high as 40 per cent. However the per cent, 

 of fat in cream will usually range from 15 to 30. Cream con- 

 taining 25 per cent, of fat is rated as a rich cream. 



There are also special bottles for testing skim or separated 

 milk, buttermilk and whey, in order to find their fat con- 

 tent. The double-necked test bottle is the one that should be 

 used. With it the fat may be estimated to single hundredths 

 of one per cent. 



The Gravimetric Method of determining the fat content 

 of milk is the most accurate. There are several modifications 

 of this method, but the process given here is known as 

 Adams' method.* 



"About 5 grams of milk are rapidly and accurately weighed 

 in a tared platinum dish. A paper coil, made by loosely 

 rolling up a strip of fat-free paper, about 20 inches long and. 

 2^ wide, held in position by a wire clamp, is held, one end 

 up, in the dish, allowing a portion of the milk to be absoibed. 

 The coil is reversed and the remainder of the milk to the last 

 trace is absorbed by the other end of the coil, care being taken 

 to handle it by the clamp only. The coil is placed in the air 

 bath, being held in vertical position by introducing the loop 

 of the clamp into a clasp attached to the sides of the bath. 

 As in the case of the determination of the solids, the temper- 



* New York City Board of Health report 1896, p. 168. 



