ESTIMATION OF FATS 25 



The thimble is suspended in a steam oven for half an hour, 

 and is then placed inside the extractor ; a few small chips of 

 porcelain are placed in the flask F, and the whole carefully 

 weighed and then half-filled with freshly distilled ether. The 

 apparatus is then connected up. The ether in the flask F 

 volatilizes and passes up the tube T into the extractor and 

 condenser, and gradually fills the Soxhlet ; on reaching a 

 certain level it siphons over into the flask, carrying with it 

 the fat in solution ; once in the flask the ether is again 

 vaporized and goes through the same process as before, the 

 oil, however, remains behind. The ether is allowed to siphon 

 off at least a dozen times,* and then, when most of the ether 

 is in the extractor, the flask is disconnected. The ether in 

 the flask is evaporated off and the flask is placed in a steam 

 oven for half an hour, it is then allowed to cool in a desiccator 

 and finally weighed. 



Weight of seeds x 



Weight of flask, chips and oil y 



Weight of flask and chips z 



Weight of oil . . . . . . . . . y-z 



Per cent fat = I^Mj^ 



X 



If the ether has extracted substances other than fats, the 

 result obtained will, of course, be too high. In such cases the 

 ether extract may be saponified and the amount of fatty acid 

 may be determined, from which the amount of fat originally 

 present may be estimated. 



2. By Saponification. — Apart from the fact that in some 

 cases it is not possible to extract the fat quantitatively by 

 Soxhlet' s method with less than forty-eight hours' continuous 

 extraction, the method is open to the objection that the sub- 

 stance must be dried previous to extraction, and this may 

 involve loss or alteration of the fat ; furthermore, the residue 

 which is weighed as fat may not consist entirely of fat but 

 may contain other substances which are extracted by the 

 same solvents as the fats ; this consequently necessitates a 

 further examination of the residue for its saponification value, 

 etc. 



*The number of times the liquid should be allowed to siphon off varies in 

 every case. In order to ensure complete extraction the only safe method to 

 adopt is to weigh the fat extracted after a certain time, then to attach the flask 

 again and contmue the extraction for some time longer and again weigh. 



