222 QUANTITATIVE ANALYSIS. 



paper cartridge of the Soxhlet extraction apparatus (in case a 

 closed Schleicher and Schull extraction-thimble is not availa- 

 ble, this cartridge may be placed in a cylinder made out of per- 

 forated sheet metal and closed at one end), dry by long heat- 

 ing at 105, and extract for three hours in the Soxhlet appara- 

 tus with anhydrous ether. 



The determination of the dry residue may also be com- 

 bined with the determination of the fat. For this purpose 

 dry the extraction-thimble containing the kaolin and the 

 milk to constant weight. Determine the loss of weight 

 which it undergoes when extracted with ether. This must 

 be the same as the weight of the fat. Frequently traces of 

 kaolin or gypsum are carried over mechanically into the 

 ether extract. 1 In this case the ether extract must of course 

 be filtered before it is evaporated, and then, too, the weight of 

 the fat will not coincide with the loss of weight of the extrac- 

 tion-thimble. 



(b) Warm 25 cc. of milk with the same amount of hydro- 

 chloric acid of 1.12 specific gravity for some time in a flask 

 on the water-bath, let cool, and transfer to a separating-fun- 

 nel, rinsing with warm water. Rinse the flask several times 

 with ether, which is poured into the separating-funnel until 

 the volume of the ether equals that of the aqueous fluid. 

 Then shake with the ether, separate the ether extract, and 

 shake once or twice more with ether. The ether extracts 

 are freed from hydrochloric acid by shaking with water and 

 filtered through a dry filter which is washed with ether. By 

 evaporating the ether the fat is obtained. This frequently 

 requires to be purified by dissolving once more in ether. 



4. Determination of the Total Nitrogen according to 

 Kjeldahl. Five cubic centimeters of milk are heated in a 

 Kjeldahl flask with 20 cc. of concentrated sulphuric acid, 



1 When a paper cartridge made by Schleicher and Schull is used this 

 is less liable to occur. 



