GOTTLIEB METHOD. 127 



further quantities of ether and petroleum ether to extract the 

 whole of the fat. By mixing and allowing to separate several 

 times a homogeneous layer is obtained, but this procedure renders 

 the method a slow one. 



Popp has shown that the strength of the ammonia used is 

 immaterial, and that no saponification of the fat occurs. 



The author finds the following modification to work well : 

 Place 5 c.c., 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 shake again. 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 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 

 recovered mixed solvents can be used for many purposes. 



Siegfeld has found from 0-0029 to 0-0036 per cent, of 

 cholesterol, and from 0-0079 to 0-0166 per cent, of lecithin 

 in milk ; these are soluble in the solvents used in Gottlieb's 

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

 machine-skimmed milk. 



Richmond and Hosier's Method. Hosier and the author 

 estimate fat in milk as follows : 9 c.c. of sulphuric acid (90 to 

 91 per cent. H 2 S0 4 ) 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 acid mixing ; 0-9 c.c. of amyl alcohol 

 is added, the tube corked, and shaken well ; 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 mixed well, and allowed to separate ; a second 

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



