20 PROXIMATE CONSTITUENTS OF PLANTS 



in plant products is of the greatest importance (see Ether Extract, 

 142, p. 149). 



The proportions of fats and oils in different plants vary 

 considerably, being in the case of ordinary crops generally less 

 than 5 per cent., and often less than i per cent. Some plants, 

 however, such as flax and cotton, contain in their seeds such 

 a high percentage that they are cultivated very largely for the 

 sake of the oil. 



Percentages of Fats in different Plant Products. 



Potatoes . . . . o-i 



Lucerne hay . . .2*2 



Wheat straw . . .1*3 



Timothy grass . . . 1*2 



In agricultural analysis the fats are generally given under the 

 head of "Ether Extract," or "Crude Fat," together with other 

 substances soluble in ether (see 142, p. 149). 



For the determination of the oil in cotton seed or 

 other oil seed, the sample should be in the dry state, 

 having been previously heated to 100° C. for twelve 

 hours in the steam oven. In the case of linseed and 

 other substances containing unsaturated compounds, 

 this hfeating must be carried out in an atmosphere of 

 hydrogen or coal-gas. About 3 or 4 grams of the dry 

 sample are accurately weighed out and placed in a filter- 

 paper cartridge which has previously been extracted 

 with ether for some time in a Soxhlet extractor. The 

 cartridge is then placed in a Soxhlet extractor fitted 

 with a condenser and a weighed flask (see Figs. 4, 5 and 

 6). Anhydrous alcohol-free ether is then poured 

 through the condenser on to the cartridge in sufficient 

 amount to start the syphon, and then another 20 c.c. 

 or so are added. The flask is then heated on the 

 water-bath for from two to six hours, depending upon 

 the nature of the sample. The lower the percentage 

 of fat in the latter the longer should be the time of 

 extraction, as in this case any small quantity of un- 



