56 MILK AND DAIRY PRODUCTS PART 



25 cm. high and 4*5 cm. wide along with 5 c.c. of caustic 

 potash (sp. gr. 1'27), and the cylinder corked and well shaken. 

 Afterwards 50 c.c. of pure, light petroleum (b. p. about 60) 

 are added, and the cylinder again thoroughly shaken. An 

 emulsion forms and to it is added 50 c.c. of alcohol (95*8-96 per 

 cent.) and the shaking repeated. 



At the end of about five minutes the petroleum ether 

 has completely separated out. A final shaking three or four 

 times for periods of four minutes, the ether being allowed 

 to separate after each time is given, and 20 c.c. of the 

 petroleum ether solution drawn off with a pipette into a 

 tared flask. After the petroleum ether has evaporated, the 

 fat is dried at 105 C. and weighed. The relation which 

 the whole of the petroleum ether bears to the 20 c.c. which 

 were drawn off is then determined, and as the specific gravity 

 of the milk is known, it is easy to calculate the percentage of 

 fat which it contains. 



This method also gives good and reliable results, and has the 

 same advantages over the extraction methods as has that 

 of Rose-Gottlieb. It is cheaper, though, than the latter, as 

 petroleum ether alone is used, and not a mixture of this 

 and ether; but, on the other hand, the evaporation of the 

 petroleum ether takes longer than does the mixed solvent. 



6. WeibuWs Desiccation Method for the Estimation of Fat 

 in Cream. 



The method proposed by M. Weibull l in 1896 for estimating 

 the percentage of fat in cream is very easy to carry out, 

 and yields results sufficiently accurate for most purposes. 

 The difference between Weibull's method and the ordinary 

 extraction method with ether (which gives very good results 

 with cream) is seldom more than 0'5 per cent., and never more 

 than 1 per cent., which for cream is accurate enough. 



Weibull's method is based upon the principle that as cream 

 consists of fat and milk serum, and the latter has a very 

 constant composition, the composition of cream serum must 

 also be fairly constant. As the total solids not fat of milk are 



1 Landtbruksakad, Handl o. Tidslcrift, 1896, p. 370. Chem. Zeitung, 1907, 

 I, p. 333, 



