206 VEGETABLE SUBSTANCES. 



In the month of September the plants are trans- 

 planted at the distance of twelve or fourteen inches 

 apart from each other. The seed comes to maturity 

 from July to September of the following year. The 

 plants are then cut down with a sickle and spread 

 on the ground to dry. The more careful cultivator 

 shelters them immediately from the vicissitudes of 

 the weather, and lays them to dry in some airy, but 

 covered situation. When sufficiently dried, the seed 

 is rubbed out on a large cloth prepared for the pur- 

 pose. The straw and chaff on being burnt afford, 

 it is said, excellent potash. The seed, as soon as 

 collected, is taken to the mills, where its oil is ex- 

 tracted. If it be used in the manufacture of soap, 

 no farther process is necessary, but if intended for 

 lamps, means must be taken to discharge it of its 

 impurities. M. Thenard recommends the following 

 method of purifying the oil previously to its being 

 used for this purpose: with one hundred parts of oil 

 two parts in weight of concentrated sulphuric acid are 

 mixed, and the whole is then subjected to considerable 

 agitation. The fluid immediately becomes turbid, and 

 assumes a dark green hue; the stirring is continued 

 until the acid combines with the mucilage and co- 

 louring matter. In less than an hour these are 

 seen to collect and gradually precipitate in flakes of a 

 blackish-green colour. A quantity of water, equal to 

 double that of the oil, is now added, and agitation is 

 again applied ; this is done to deprive the oil of any 

 acid which may not have passed in combination with 

 the impurities. 



The whole is left for subsidence during several 

 days, after which the oil, floating free above the 

 water, is drawn off and put into tubs. The bottoms 

 of these tubs are perforated, and the holes are 

 filled with cotton, through which the oil filters 

 into other vessels, when it is perfectly pure and 



