Oil - animal, vegetable, essential, and mineral - PDF book by C. Ainsworth Mitchell

Oil - animal, vegetable, essential, and mineral

In the following pages, I have endeavoured to tell in language free from technicalities the story of the origin, methods of preparation, and uses of that immense class of commercial products to which the name of " oil " may be applied. It will readily be understood that the ground to be covered was so extensive, that it was necessary to dwell chiefly upon the most typical products in each class and to make little or no mention of some of the less common substances, such as the little known vegetable fats from Central Africa, which have as yet chiefly a scientific interest.

Nature of Fixed Oils. The term "fixed oil" is employed as a convenient description for distinguishing between ordinary vegetable and animal oils and fats, and volatile minerals and essential oils. Strictly speaking, there is no sharp distinction between fats and oils, the former being reduced to an oily condition by heating and the latter converted into solid fats when sufficiently chilled.

Apart from this, they are for the most part of similar chemical composition, consisting in the main of compounds of glycerin with various acids known as "fatty acids" from the fact that they were first isolated from fats. Thus, for example, lard consists of compounds of glycerin (known as glycerides) with solid fatty acids (stearic acid, palmitic acid), and with a smaller proportion of liquid fatty acids (oleic and linoleic acids). In tallow, there is a larger proportion of the hard stearic acid, less palmitic acid, and still less liquid fatty acids.

Again, in the case of olive oil, the chief constituent is the liquid fatty acid, oleic acid, whilst the solid fatty acids are only present to a relatively small extent. In other oils, other liquid fatty acids such as linoleic and linolenic acids are present, while in other solid fats, especially those of the vegetable kingdom, glycerides of 1 i (1464) 2 OIL other, solid fatty acids are important constituents.

The waxes, of which beeswax may be regarded as typical, differ from the ordinary oils and fats, in consisting of compounds of various fatty acids, with alcohols other than glycerin. It is chiefly by means of the separation and properties of these various fatty acids and their compounds that it is possible to distinguish between different oils and fats.

Fixed oils and fats have many properties in common. Thus, they cannot be evaporated (like essential oils) at the ordinary atmospheric pressure without decomposition, and when heated they do not give off inflammable vapours until a temperature sufficient to decompose them is reached. Saponification. When boiled with a solution of potash or soda, oils and fats are slowly decomposed or saponified, and form soaps, the nature of which will depend upon the alkali used and the kind of oil or fat. For instance, a very hard soap is obtained from tallow and from earthnut oil, whereas cocoanut fat yields a soft soap, which is readily soluble even in hard waters and is therefore used as the basis of the so-called " marine soaps," which will give a lather with seawater.

Oil - animal, vegetable, essential, and mineral - PDF book by C. Ainsworth Mitchell