68 CHEMICAL EXAMINATION 



alcohol, and 10 c.cms. of sulphuric acid are mixed in the usual 

 way, rotated for three minutes, then inmiersed in a water bath 

 at 140° F. for a minute and the percentage of fat read off on the 

 graduated neck. 



Skim milk is treated exactly as ordinary milk except in the 

 Gerber process in which two to three minutes shaking are 

 required previous to whirling and a longer period is given in the 

 water bath to bring the temperature to 140° F. 



For cream, special bottles are provided in the Babcock 

 method, but the ordinary ones may be used, as in the Leffmann- 

 Beam method, with a reduced quantity of sample. An appro- 

 priate weight of the sample is washed into the bottle with suf- 

 ficient water to bring the total volume to the normal volume of 

 the bottle, and the determination carried out as in the case of 

 milk. The result is multiplied by the ratio of the normal 

 weight of the method (Leffmann-Beam 15.5 grms., Babcock 

 18.0 grms.) to the weight of the sample taken. In the Gerber 

 process (normal weight 11.35 grms) 0.5 gram of cream, 6 c.cms. 

 of hot water, 1 c.cm. of amyl alcohol, and 6.5 c.cms. of acid 

 are used with a further addition of 6 c.cms. of hot water pre- 

 vious to rotation. 



Gravimetric Methods 



Gottlieb's Method. In this method, which is probably 

 the best known one of group two, the caseinogen is dissolved in 

 ammonia and the liquid then extracted with ether and petro- 

 leum ether. The solution of fat is evaporated and the residue 

 weighed. For further details of this process Richmond's 

 Dairy Chemistry (Chas. Griffin & Co., London, 1914) should 

 be consulted. 



Adam's Method. 5 grams of milk are weighed out in a 

 porcelain or glass dish and absorbed on a coil of fat free paper 

 (special strips of fat-free paper are manufactured for this pur- 

 pose by various firms). The dish and coil are placed in the 

 water oven until thoroughly dry when the coil is placed in a 

 Sohxlet extraction cone and the residue in the dish extracted 



