SOAP is supposed to be of Celtic origin, and became known to the Romans when they invaded Gaul. A complete soap factory has been unearthed at Pompeii. Soap consists of fats or other oily substances, mixed with water and alkaline ashes, so that saponification results. Its manufacture is more a matter of skill than of exact science, as the chemical composition of the articles which enter into it vary very widely, and much depends on the close attention and care of the workmen. Water being added to the alkali, a solution is formed, which is known as soap-lye. In making this lye, quick lime is added to the soda-ash to deprive it of its carbonic acid and render it caustic. Weak lye is poured into a large copper pan and mixed with oil or fat, which are then boiled together and portions of stronger lye are added gradually until the saponification sets in and the soap begins to separate from the water. Salt is added at this stage, to hasten the sepa ration, and the fire being extinguished, the soap collects above and the glycerine, the impurities, and the uncombined chemicals settle to the bottom. This salt water or spent lye is drawn off by cocks in the bottom of the pan. The soap is boiled somewhat longer to drive off the surplus water, and is then run into frames to cool. These frames are made of iron plates clamped together and set on wooden bottoms. The bottoms are mounted on wheels, so that they can be easily taken to the cooling-rooms. In four or five days the soap is cool enough to strip, when the sides of the frames are unclamped and the soap stands in a solid mass on the wooden bottoms. A machine with regulated wires cuts this mass into bars Borax Soap (which see) is made of tallow and borax, and is a bard, white soap, possessing remarkable detergent qualities.
Castile Soap is made of olive and rape-seed oils. The imported article is a very superior soap, but plenty of American and Eng lish Castile are now sold which are very inferior. In making Castile soap, great care is taken to avoid an excess of alkali (the soda), only just enough being used to neutralize the oil. On this
account the soap is much milder, and may be used on wounds and other surfaces where a common soap would irritate and give pain. The mottled appearance of Castile soap is due to a small solution of copperas (sulphate of iron) which is stirred into it before it hardens ; this leaves a bluish oxide of iron in the soap, which, when exposed to the air, becomes changed to the red oxide. White Castile soap is sold, which is the same as the other, without the coloring. Though called Castile, it is by no means exclusively made in Spain, the largest share coming from the south of France, and, indeed, it is generally known in Europe as Marseilles soap.
Cocoanut Oil Soap is known as Marine Soap. It is very hard, and not being as much affected by salt water as other soaps, is much used at sea.
Cold Water Soaps are so prepared as to be serviceable in cold water, and find ready sale in families where it is inconvenient to have fires in summer.
Sand Soap is made by adding silver sand, or some of the sili cates, to ordinary soap.
Sapolio is an article of silica soap, manufactured by Enoch .Morgan's Sons & Co., and is the best of its class.
Soft Soap is a fluid compound made by boiling potash or alka line wood ashes with fats or oils, and making a soap containing the glycerine and a large proportion of water.
Transparent Soap is made by dissolving the soap in alcohol and solidifying it again ; shaving soaps are generally of this class.
The Frank Siddalls Soap is a pure and reliable soap, which, when used according to the Frank Siddalls way of washing clothes, gives great satisfaction and meets with unbounded praise.
Oleine Soap is made from rid vegetable oil, which may be considered one of the best materials for the manufacture of soap, and consequently the pure Oleine Soap is more expensive than many other kinds, and is one of the best soaps in the market for general use.