OILS 445 



To obtain the above proportions of oil, the fruits must be all of good quality, 

 deprived of their pods, coats, or invohicra, and of all the parts destitute of oil. 



Purification of Oils. As the oils are obtained from the mills they generally contain 

 some albuminous and mucilaginous matter, and some other impurities which require 

 to be removed in order to render the oil perfectly clear and fit for burning, &c. 

 Several processes have been proposed for this purpose, but the one most generally used 

 is that known as Thenard's process. 



Although concentrated sulphuric acid acts so strongly on the oils, it is found that, 

 when added only in small quantities, it attacks principally the impurities first. 

 Thenard's process consists in adding gradually 1 or 2 per cent, of sulphuric acid to 

 the oil, previously heated to 100, and well mixing them by constant agitation. To 

 effect this the process may bo carried on in a barrel fixed on an axis and kept re- 

 volving, or in a barrel which is itself immoveable, but having fixed on its axis a 

 moveable fan. After the action of the acid is complete, which is known by the oil, 

 after 24 hours' rest, appearing as a clear liquid, holding flocculent matter in sus- 

 pension, there is added to it a quantity of water, heated to 140, equal to about two- 

 thirds of the oil ; this mixture is 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 flocculent matter will have fallen to the bottom of the acid liquid. 

 The oil may then be drawn off, but requires to be filtered to make it perfectly clear. 

 The filtration is always a difficult matter, and is conducted in various ways. It is 

 sometimes placed in tubs, in the bottom of which there are conical holes filled with 

 cotton, but the holes become speedily choked with solid matters. Another and more 

 speedy process is by the means of a displacing-funnel, the apertures in the diaphragm 

 being stopped with cotton. 



Several patents have been taken out for the purification of oils ; some passing hot 

 air through the oil while at the same time exposed to the action of light ; others, 

 passing steam through the oil. 



Cogan's process is a combination of the latter with Thenard's. He operates upon 

 about 100 gallons of oil, and for this quantity he uses about 10 Ibs. of sulphuric acid, 

 which he dilutes previously with an equal bulk of water. This acid mixture is 

 added to the oil, placed in a suitable vessel, in three parts, the oil being well stirred 

 for about an hour between each addition. It is then stirred for 2 or 3 hours, in 

 order to ensure a perfect mixture, and thus let every particle of the oil be acted on 

 by the acid. It then has assumed a very dark colour. After being allowed to stand 

 for 12 hours, it is transferred to a copper boiler, in the bottom of which are holes, 

 through which steam is admitted, and, passing in a finely-divided state through the 

 oil, raises it to the temperature of 212. This steam process is carried on for 6 or 

 7 hours ; the oil is then transferred to a cooler, having the shape of an inverted cone, 

 terminating in a short pipe, provided with a stop-cock, inserted in its side a little dis- 

 tance from the bottom. After being allowed to stand till the liquids are separated, 

 which generally takes about 12 hours, the acid liquor is drawn off through the pipe 

 at the bottom, and the clear oil by the stop-cock in the side of the cooler ; all below 

 this tap is generally turbid, and is clarified by subsidence, or mixed with the next 

 portion of oil. 



Sometimes an infusion of nut-galls is used to separate the impurities, the tannic 

 acid contained in which renders the impurities less soluble ; the infusion is well mixed 

 with the oil by agitation, and, after separating the two liquids, the oil is deprived of 

 any tannic acid it may have retained, by treating it with acetate of lead, or sulphate 

 of zinc. When the oil is to be used for machinery it must be dried by treatment with 

 freshly-calcined sulphate of lime, or carbonate of soda. 



GENERAL REMARKS ON THE NON-DRYING OILS. 



Olive Oil. Few vegetables have been so repeatedly noticed and so enthusiastically 

 described by the ancient writers as the olive tree. The preserved or pickled olives 

 are the green, unripe fruit deprived of part of their bitterness by soaking them in 

 water, and then preserved in an aromatised solution of salt. There are several 

 varieties met with in commerce, but the most common are the small French or Provence 

 olive and the large Spanish olive. When ripe the fruit abounds in a bland fixed oil, 

 which is an unctuous fluid, of a pale yellow or greenish yellow colour, with scarcely 

 any smell and a bland and mild taste. In cold weather it deposits white fatty globules 

 (a combination of oleine and margarine). Pure olive oil has less tendency to become 

 rancid than most other fixed oils, but the second qualities rapidly become rancid, 

 owing probably to some foreign matters. It is not a drying oil, and is less apt to 

 thicken by exposure to the air, and for this reason is preferred for greasing delicate 

 machinery and clock-work. Brando described a process for preparing it for thesa 



