DETERMINA TION OF FAT 197 



dish and its contents again weighed. The weight of 

 butter actually taken is thus determined. 



The whole is then heated in the steam oven for an 

 hour, cooled in the desiccator, weighed, then reheated 

 in the oven for another half-hour, and the process 

 repeated until no further loss in weight occurs. 



The combined duration of heating should not be 

 too long, as part of the butter may undergo oxidation, 

 resulting in an actual increase in weight. 



188. Determination of Fat. 



The material left in the basin after the estimation 

 of water according to the above method may be con- 

 veniently employed for the determination of the fat, 

 provided too great a time be not allowed to elapse. 



The pumice is transferred into a previously extracted 

 filter-paper cartridge, and the cartridge and contents 

 placed in a Soxhlet extractor in the bottom of which 

 is placed a layer of extracted cotton-wool. 



To ensure complete removal of the fat from the 

 basin, the latter should be washed out several times 

 with ether, which is then poured into the cartridge 

 while the latter is in the extractor. Another layer of 

 extracted cotton-wool is then placed on the top of 

 the cartridge, and the whole extracted with dry ether 

 on the water-bath in the usual way, a weighed flask 

 having been fitted to the extractor. After a few hours 

 the flask and its contents are removed, the ether 

 entirely evaporated off in the water-bath, the flask 

 placed for a few minutes in the steam oven, then cooled 

 in the desiccator, and weighed. The increase in weight 

 of the flask will give the amount of fat. 



The extracted residue left in the cartridge after the 

 above operation may, if necessary, be used for the 

 determination of common salt (see 190 below). 



N 2 



