ESTIMATIOX OF FAT— GOTTLIEB METHOD. 119 



Place 5 CO., or about 5 grammes, of milk in a tall narrow stop- 

 pered 50 c.c. cylinder, add 0'5 c.c. of ammonia (sp. gr. 0'96), 

 and shake ; add 5 c.c. of alcohol and shake, and if the solution 

 contains lumps (as may happen with sour milk) warm in 

 hot water till they all dissolve ; add 12-5 c.c. of ether and 

 shake well ; finally add 12"5 c.c. of petroleum ether and again 

 shake well ; allow the tube to stand a few minutes and again 

 shake. In about five minutes the ethereal layer is removed as 

 completely as possible to an unweighed flask, and the residue 

 shaken with three successive quantities of a mixture of equal 

 parts of ether and petroleum ether (the recovered solvent serves 

 very well for this purpose), which are transferred to the flask. 

 The solvent is evaporated and recovered, and when only 2 or 

 3 c.c. are left in the flask (this is chiefly alcohol) it is placed in 

 the water oven and dried to constant weight. After weighing, 

 the fat is melted, and extracted from the flask by treatment 

 with four successive quantities of about 5 c.c. each of petroleum 

 ether, and the flask placed in the water oven for half-an-hour, 

 and again weighed. 



There is always a minute residue left after the petroleum ether 

 treatment, which may be, however, neglected without great error. 



Though the description is somewhat long, the method gives 

 little trouble, and is expeditious. It is not wasteful, as the 

 reeovi^red mixed solvents can be used for many purposes. 



Sie^rfeld has found from 0-()(V29 to 0-00.36 per cent, of 

 cholesterol, and from 0'0079 lo 0"01<i(J per cent, of lecithin 

 in milk: tliese are soluble in the solvents usetl in (Jottlicb's 

 method, and may form an appreciable portion of the fat in 

 machine-skimmed milk. 



Richmond and Rosier's Method. — Rosier and the author 

 estimate fat in milk as follows : — 9 c.c. of sulphuric aeid (9C) to 

 91 per cent. H.^S04) are measured into a tube holding about 

 50 C.C., and constricted just above the point where 20 c.c. reach ; 

 10 grammes of milk are weighed into this tube, care being taken 

 to prevent the milk and aeid mixing ; 0'9 c.c. of amyl alcohol 

 is added, the tube corked, and well shaken ; after cooling to 

 about 25° C, 20 c.c. of petroleum ether are added, and the tube 

 well shaken. When separation is complete, the contents of the 

 tube are again well mixed, and allowed to separate : a second 

 re-mixture and separation is given, and the petroleum ether 

 blown o£E into a tube containing 20 c.c. of water, with which 

 it is shaken and allowed to separate. After separation from 

 the water, the petroleum ether is blown off into a tared flask. 

 Further portions of petroleum ether are added to the tube con- 

 taining the acid liquid, blown ofE into the tube containing the 

 water, and transferred to the flask. 



