FIXED OILS. 209 



put into a large pan in a heated oven, and when 

 thoroughly hot the bruised seeds are laid between 

 coarse linens and subjected to pressure. Hemp- 

 seed by this process commonly yields one-fifth of its 

 weight in oil. 



A duty amounting to a prohibition is laid on the 

 importation of rape, hemp, and linseed oil from 

 foreign countries ; but they are allowed to be im- 

 ported from British possessions at the trifling import 

 duty of l per tun. Foreign seeds are subjected 

 to only a small impost of Is. per quarter. In 

 1828 we imported 428,905 bushels of rape and 

 ] ,996,414 bushels of linseed. The best of the latter, 

 however, classed as flax-seed, is used for propa- 

 gating the plant, and a small proportion is likewise 

 abstracted for other purposes. 



Numerous oil-mills are erected in this country for 

 the purpose of extracting the oil from these seeds ; 

 but it is generally considered that the Dutch carry 

 on the process in the greatest perfection. Their 

 mills for expressing oils from oleaginous seeds are 

 constructed on the best principles of economy in 

 time, labour, and seed ; while at the same time they 

 combine the most careful and ingenious contrivances 

 for the production of good oil. 



The great oil cistern is divided into several cham- 

 bers, by which means the different qualities obtained 

 in each stage of the process are kept separate. 



By one machine the seeds are in turn bruised, 

 pressed, pounded, and stirred. They are first crushed 

 by the mill-stones, when self-acting rakes successfully 

 perform the office of " a hand directed by a careful 

 eye and unceasing attention," constantly changing the 

 surface of the seeds and scraping off the paste 

 which adheres to the stones. When the bruising has 

 been carried to the proper point, another motion, by 

 means of an elbow joint, is given to one of the 



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