Soap

Soap. Soap has been known for a considerable time; it is spoken of by Pliny and certain other classical writers, while a soap manufactory was discovered within the ruins of Pompeii, containing specimens of the substance which did not differ essentially from what we at present employ.

Although known for such a lengthy period of time, the improvements in the process of its manufacture have been but slight. All soaps consist of alkalies united with the acid present in various oils or fats. These latter compounds consist of an acid combined with glycerine, and in the process of soapmaking this glycerine is replaced by soda or potash, so that the resulting soap is really merely the sodium (or potassium) salt of the organic fatty acid. The chief acids present in the fats are stearic, margaric, and, to a smaller extent, oleic acids, and it is the salts of these compounds which, in different proportions, constitute most soaps. For the manufacture the fat, such as tallow or palm oil, is placed in a large cauldron or boiler, the necessary amount of soda solution or lye is added, and the whole is kept boiling until the action is completed (from 1 to 2 hours). A quantity of salt is then added, which causes the soap to separate out and rise to the surface, as it is not soluble in salt solution. It is then ladled into wood or iron frames or moulds and allowed to set, after which it is cut into sticks by wire and placed in a drying-room to dry. Cakes, etc., and those used for toilet purposes, are made by pressure in moulds. For white soap or curd soap, tallow, palm-oil (which should be first bleached), or olive oil is usually employed, whilst the addition of lard improves the quality of the soap. In the yellow soaps resin is also added to the other ingredients, while marbled soaps or mottled soaps owe their appearance to the introduction of salts of iron. Toilet soaps do not differ essentially from the ordinary washing or curd soap, but are merely clarified and perfumed and coloured or marbled by mixing in small quantities of pigments or dyes. Soft soap contains potash in place of soda - i.e. a potassium salt of the organic acid - and is usually made from a drying oil, as hempseed oil, etc., instead of from tallow or palm oil. By lime and other salts soap is precipitated, as the lime salts of these organic acids are insoluble; owing to this hard water is not suitable for washing purposes, as the lime salts in the water combine with the soap acids, and no lather results until all have been thus got rid of. According to the great chemist Liebig, the quantity of soap used may be regarded as a measure of the civilisation of a country. Judged by this standard, England maintains its leading place, more being manufactured in this than in any other country. and the quantity used per head is equivalent to about 8.5 lbs. per annum, exclusive of that used in manufacturing operations.