128 THE ESTIMATION OF FAT. 



blown off 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 off into the tube containing the 

 water and transferred to the flask. 



To reduce the time necessary for separation, the tubes may 

 be centrifuged. 



That this method gives good results is due to a compensation 

 of errors, as the fat is in this, as also in the Gerber method, 

 attacked slightly by the sulphuric acid. 



Babcock's Asbestos Method. Babcock has used asbestos 

 as a medium for evaporation of the milk previous to extraction 

 with ether. Originally it was contained in a glass tube and 

 dried in a current of air, but he has modified it by the use of 

 a perforated metal cylinder. 



The following is the method as adopted by the Association of 

 Official Agricultural Chemists (of America) : Provide a hollow 

 cylinder of perforated sheet metal, 60 mm. long and 20 mm. in 

 diameter, closed 5 mm. from one end by a disc of the same 

 material. The perforations should be about 0-7 mm. in diameter 

 and about 0-7 mm. apart. Fill loosely with 1-5 to 2-5 grammes 

 of freshly -ignited woolly asbestos, free from fine and brittle 

 material ; cool in a desiccator and weigh. Introduce a weighed 

 quantity of milk (3 to 5 grammes) and dry at 100 C. to constant 

 weight for the determination of total solids. Extract with anhy- 

 drous ether until fat is removed, evaporate the ether, dry the 

 fat at 100 C. and weigh. The fat may also be determined by 

 difference, drying the extracted cylinders at 100 C. 



This method has been studied by the Association and has been 

 found to give the same results as the Adams method. It has 

 the advantage that fat, solids not fat, and total solids are directly 

 estimated. 



Macfarlane has described a method essentially the same, but 

 uses chrysotile or Canadian asbestos for the purpose ; this being 

 a hydrated mineral cannot be ignited. He uses a cup-shaped 

 glass tube with a hole at the bottom, and operates with 10 grammes 

 of milk. 



The author finds that this method gives results for fat prac- 

 tically identical with those obtained by the Adams method, but 

 the solids not fat and total solids are low. It is used to a con- 

 siderable extent in Canada for official work. 



The Ritthausen Method. If milk be diluted with water, 

 a solution of copper sulphate added, and the acid neutralised, 

 the proteins are precipitated as copper salts ; these carry down 

 with them the whole of the fat. After washing, to remove milk- 



