ESTIMATION 



17 



solution ; once in the flask the ether is again vaporized 

 and goes through the same process as before, the oil, how- 

 ever, remains behind. The ether is allowed to siphon over 

 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 . 



,, flask, chips and oil 



,, ,, and chips 



oil . 



Per cent fat = 



100 (y — z) 



X 



y 



z 

 y-z 



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 

 determined, from which the amount of fat originally present 

 can be estimated. 



Appended are a few figures giving approximately the fat 

 content of some of the commercially exploited seeds : — 



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. 



The following method, which is due to Liebermann and 



* 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 continue the extraction for some time 

 longer and again weigh. 



