Oils. A large number of bodies, varying greatly in their nature, mode of occurrence, and chemical characters, is included under the term oils. They are more commonly understood to be more or less viscous, liquid substances, flammable, and insoluble in water. They arc composed chiefly of carbon and hydrogen, with oxygen frequently and sometimes sulphur, etc. Formerly, however, many other liquids of an oily consistency were known as oils which are not now so regarded, e.g. oil of vitriol. The name is usually restricted to substances which are liquid at ordinary temperatures, and so distinguished from the fats, which are, however, not chemically distinct. Oils maybe divided broadly into three classes: the mineral oils, the fixed oils, and the essential or volatile oils. The first of these form a class of very flammable liquids, which are chiefly obtained from borings or wells in the earth, largely at Pennsylvania and Canada. They consist almost entirely of hydrocarbons, and are very largely employed as illuminants, for fuel, and in a number of industrial purposes, e.g. naphtha, petroleum-fuel. The fixed oils are all more or less closely chemically related to one another, being compounds of different organic acids with glycerine. They exist largely in animal and vegetable organisms, and are obtained from the natural sources. From vegetation the oils are usually extracted by incisions, by pressure of the. containing organs with, if necessary, the aid of heat, or by dissolving out the oil by means of a suitable solvent. The chief acids present in these compounds and the fats are palmitic, stearic, and oleic, the two former being in greater quantities in the solid fats than in the liquid oils. Some oils dry and harden if exposed to the air. Such drying oils are largely used as media for paints, etc. Other oils do not dry, but remain greasy under the same conditions, and are hence useless for mixing with pigments. Linseed oil, hemp oil, nut oil, poppy oil, are examples of drying oils; while olive oil, almond oil, colza oil, rape oil, castor oil. etc., are non-drying. A number are used medicinally, as croton, castor, cod-liver, almond oils, etc. Very many are used as articles of diet, while others find employment as illuminants and fuels. They are also extensively used for the manufacture of soaps (q.v.) and candles (q.v.), as lubricants, varnishes, in painting and perfumery, and for many other purposes. The essential oils do not exhibit the thick oily feel of the previous class. They are usually colourless or slightly yellow liquids, insoluble in water, and very flammable. They are obtained chiefly from plants by pressure, maceration, extraction, or by distillation. They are usually of the nature of ethereal salts of organic acid, and find application in perfumery, many of them possessing most agreeable odours. Almost all arc used in medicine, and many are employed as flavouring materials, as, e.g. oils of cloves, nutmeg, carraway, etc.