59 



" Thenard's process consists in adding gradually 

 " one or two per cent, of sulphuric acid to the oil, pre- 

 44 viously heated to 100°, and well mixing them by 

 44 constant agitation. To effect this, the process may be 

 " carried on in a barrel fixed on an axis and kept 

 4 4 revolving, or in a barrel which is itself immovable, 

 44 but having fixed in its axis a movable fan. After the 

 44 action of the acicl is complete, which is known by the 

 " oil, after twenty -four hours' rest, appearing as a clear 

 44 liquid, holding flocculent matter in suspension, there 

 " is added to it a quantity of water, heated to 140°, 

 44 equal to about two-thirds of the oil ; this mixture is 

 66 well agitated, until it acquires a milky appearance. 

 " It is then allowed to settle, when, after a few days, 

 " the clarified oil will rise to the surface, while the 

 " floccuient matter will have fallen to the bottom of the 

 44 acid liquid. The oil may then be drawn off, but 

 44 requires to be filtered to make it perfectly clear. The 

 " filtration is always a difficult matter, and is conducted 

 44 in various ways. It is sometimes placed in tubs, in 

 44 the bottom of which are conical holes filled with 

 44 cotton, but the holes become speedily choked with 

 44 solid matters ; another and more speedy process is by 

 44 the means of a displacing funnel, the apertures in the 

 44 diaphragm being stopped with cotton. 



44 Several patents have been taken out for the 

 44 purification of oils. Some passing hot air through 

 44 the oil, while at the same time exposed to the action 

 44 of light ; others passing steam through the oil. 



44 Cogan's process is a combination of the latter 

 44 with Thenard's. He operates upon about 100 gallons 

 44 of oil, and for this quantity he uses about ten pounds 

 44 of sulphuric acicl, which he dilutes previously with an 

 44 equal bulk of water. This acid mixture is added to 

 44 the oil, placed in a suitable vessel, in three parts, the 

 44 oil being well stirred for about an hour between each 

 44 addition. It is then stirred for two or three hours, in 

 44 order to insure a perfect mixture, and thus let every 

 44 particle of the oil be acted on by the acicl. It then 



