136 FATTY SUBSTANCES. 



ite which thickens the walls of the cells.* The capillary force 

 which retains fatty principles combined with the tissue of certain 

 seeds must be very considerable, for havings boiled some rape-seed, 

 wiiich contained 50 per cent, of oil, in water, there was not a trace 

 of oily matter perceptible upon the surface of the liquid. Butter 

 appears to be kept diffused in milk by something of a similar force, 

 for milk when boiled yields but a very small quantity of this sub- 

 stance M. Dumas and I maintain that the oil of seeds is intended 

 for the production of heat by undergoing combustion at the period 

 of germination ; a series of experiments performed in my laboratory 

 by M. Letellier supports this opinion. 



Having ascertained by a preliminary trial the quantity of oily 

 substance contained in a certain weight of seed, some of the same 

 kind was put to germinate, and the quantity of oil which it contained 

 was tested at two periods of the germination ; it was found that in 

 the course of this process a considerable proportion of the fatty sub- 

 stance had disappeared ; one gramme or 15.438 grains of rape-seed 

 before germination contained 0.50 of oil ; after the first period of 

 germination, namely, when the cotyledons had begun to turn green, 

 the quantity of oil was found reduced to 0.43, and at the end of the 

 second period, when the cotyledons had become quite green and the 

 radicles were from 3.9 to 4.6 inches long, the oil was reduced to 0.28. 



It would be extremely interesting to ascertain the extreme loss 

 which the oily principles of seeds sustained in the course of the 

 commencement of vegetation, and to follow the return of the same 

 principles in proportion as the plant advanced towards maturity. 

 M. Letellier is going on with these experiments. 



The numberless uses to which oil is put, make its manufacture an 

 object of the highest importance. Vegetable oils are generally ob- 

 tained from olives, from oleaginous seeds, and from the nut of cer- 

 tain palms. Oil is separated by pressure ; it may often be extracted 

 from the seed in the natural state, in which case the produce is of 

 fine quality, but seldom abundant. The castor-oil bean, for example, 

 yields its oil under the simple action of the press. In America, 

 however, to obtain this oil, the seeds are first roasted slightly, and 

 being bruised they are then boiled in water ; the oil readily sepa- 

 rates from the roasted seed. A similar process is sometimes follow- 

 ed in procuring cacao butter. 



In the extraction of oil from the common oleaginous seeds, they 

 are first ground or bruised in a proper apparatus ; the paste or pow- 

 der which they now form is generally heated, and being put into 

 woollen sacks, and these enclosed in hair bags, they are subjected to 

 the operation of the press ; after one pressure, the magma which 

 remains in the bags is crushed anew, heated, and pressed again. 

 The oil obtained by the second pressing is never so pure as that 

 procured by the first. 



The oil-cake is taken out of the bags, completely dry in appear- 

 BOe» but it still contains a large proportion of oil — iron 8 to 15 per 



* Domas, Chemistrj', vol. v. 



