OIL. 



to the analysis of olive oil by Lavoisier, it 

 is composed of hydrogen and carbon, viz. 



Carbon 78.92 



Hydrogen 21.08 



100.00 



The fixed oils are insoluble in water. 

 "When it is necessary to combine them 

 with this liquid, it is by means of mucila- 

 ginous substances, in which case the mix- 

 ture is known under the name of emul- 

 sion; or with alkaline substances, when it 

 is distinguished by the name of soap. 

 Some of these oils become thick, opaque, 

 white, granulated, and are analogous in 

 appearance to tallow. Oils subject to this 

 change are called fat oils ; such, for in- 

 stance, is olive oil, almond oil, and rape- 

 seed oil. This change is more or less 

 rapid in different circumstances. If a 

 thin layer of oil be spread on the surface 

 of the water, and exposed to the air, it 

 takes place in a few days, and this effect 

 is owing to the absorption of oxygen, 

 which combines with the oils. But other 

 oils, when they are exposed to the air, 

 dry altogether, yet have the property of 

 retaining their transparency. Oils which 

 have this peculiar property are called dry- 

 ing oils. The oil of poppies, hemp-seed 

 oil, and particularly linseed oil, are pos- 

 sessed of this property. The nature of 

 the change which takes place in these 

 drying oils is supposed to depend on the 

 absorption of oxygen ; and this oxygen 

 combining with the hydrogen of the oil 

 forms water. This opinion is supported 

 by the practice which is fol'owed to in- 

 crease the drying property of linseed oil. 

 It is usually boiled with litharge, before 

 it is employed by painters. The litharge 

 In this case is partly reduced to the me- 

 tallic state, by being deprived of its oxy- 

 gen, which is supposed to combine with 

 the oil. Phosphorus combines with oils, 

 with the assistance of heat. A small por- 

 tion of the phosphorus is dissolved, which 

 communicates a luminous property to the 

 oils, so that when they are spread upon 

 any surface they shine in the dark. Hence 

 some twenty years ago a person exhibit- 

 ed in London, as the everlasting lamp of 

 the ancients, a vessel containing phos- 

 phorus immersed in oil. 



The various purposes to which fixed 

 oils are applied, are too well known to 

 require particular enumeration. They 

 are employed in domestic economy, either 

 as articles of food, and for this purpose 

 are used alone, or in combination with 

 other substances ; pr they we employed 



for giving light, by being burnt in lamp?. 

 They are used in medicine, either on ac- 

 count of the properties which peculiar 

 oils possess, or on account of the proper- 

 ties they communicate toother substances 

 with which they are combined. In this 

 state the use of oils is well known in the 

 form of unguents, plasters, and liniments. 

 In the arts, fixed oils are of the most ex- 

 tensive utility. They are employed in 

 the fabrication of soaps, for mixing colours 

 in painting, for some kinds of varnish, 

 and for defending substances from the ac- 

 tion of air and moisture. 



Volatile oils are distinguished from th,e 

 fixed oils by their volatility, fragrance, 

 and acrid taste. They are also known 

 under the name of aromatic oils, from 

 their odour ; or essential oils, or simply 

 essences, from being supposed to consti- 

 tute the essence or the existence of the 

 vegetable matters which furnish them. 

 Volatile oils are not limited to particular 

 parts of plants, but are found to exist in 

 every part of the plant, excepting in the 

 seed, which furnishes the fixed oils. A 

 great number of roots, which are general- 

 ly distinguished by an aromatic odour, 

 and have more or less of an acrid taste, af- 

 ford volatile oils. They are furnished 

 also by many woods, such as those of the 

 pine and fir tribe, and by many of those 

 which are natives of warm climates. The 

 leaves of a great number of plants be- 

 longing to the Didynamia class also afford 

 volatile oil, as well as many of the umbel- 

 liferous plants. It is obtained also from 

 many flowers of vegetables, and also from 

 the covering of many fruits, as the skin 

 of oranges and lemons. It is likewise ob- 

 tained from a great number of seeds ; but 

 it is never found in the cotyledons or 

 lobes themselves, but only in the external 

 covering. The quantity of volatile oil 

 which is obtained from vegetables, varies 

 according to the age, the soil in which 

 they grow, and the state of the plant. 

 Some plants while green furnish it in 

 greatest abundance, while others yield 

 most when they are dry. There are two 

 processes by which volatile oil may be 

 obtained. When it exists in plants in 

 great abundance, and in vesicles in a fluid 

 state, it may be separated by mechanical 

 means. Thus, by simple expression, the 

 volatile oils are extracted from many 

 plants, as, for instance, from the fruit of 

 the orange and the lemon. From the 

 outer rind of these fruits, when they are 

 fresh, the volatile oil is obtained in the 

 liquid form ; but in general the volatile 

 oils of plants are neither so abundant, nor 

 do they exist in that state of fluidity, b.y 



