Page:The New International Encyclopædia 1st ed. v. 18.djvu/337

SOAP. 'rosin change' operation is left out. Many soapmakers, however, use very small quantities of rosin in making toilet soaps, believing that this tends to 'pitch the nigre,' i.e. clarify the product.

Rosin soap is allowed to cool in the kettle to about 140° C. (about 280° F.) and then run into the 'crutcher'—a horizontal iron cylinder provided with a shaft bearing paddle blades. These revolve and thoroughly mix the soap, yielding a product uniform in texture and color. In this operation it is also customary to make various additions, such as carbonate of soda to soften hard water, silicate of soda to harden the soap and prevent too rapid wasting, and many other substances, some of doubtful utility. After crutching, the warm mixture is run into large iron frames or molds and allowed to cool. When the soap is hard, the sides of the frame are removed and the soap is cut into slabs and bars with a steel wire. After a short drying operation, the soap is pressed and ready for use. An ordinary rosin soap freshly made has the following composition:

Fatty and rosin acids 66.21 per sent. ' /-.tti i h i. i n n Free alkali 0.36pereent. the free alkali (^aOH) shall not exceed 0.5 per Combined alkali 6.83 per cent, cent.; carbonated alkali (NaXJOj) mav be ptes- Water 28.00 per cent.

Settled toilet soap is not crutched, but run at once into frames. When hard the soap is cut by wires into thin bars which are dried on racks in a warm, well ventilated room, and when the moisture is reduced to about 10 per cent., the slabs are cut into fine thin chips or shavings and dried once more. The required perfume and coloring matter having been added, the chips are fed into a roller mill, coming out in thin crêpe-like sheets. These are passed through again and again until the mass is homogeneous. The thin sheets then pass into the 'plotter,' a revolving screw press which is gently heated and delivers the soap in long slender bars. The bars are cut into short lengths and pressed into cakes by suitable dies. Often settled and half boiled soaps are mixed in the mills, but as a rule the finest grades of toilet soaps are made exclusively from settled soap which is entirely free from glycerin.

'Half boiled soap' is an evident misnomer, no higher temperature than that necessary to melt the fatty materials (50° to 65° C. = 120° to 150° F.) being used in the process. The operation is usually carried out in small cast iron jacketed kettles, in which the fat, which must be of good quality, and usually consists of tallow or tallow and cocoanut oil, is liquefied by heat. An exactly calculated quantity of strong lye (36° to 40° Baumé), consisting of soda alone or mixed with a small amount of potash, is now gradually added, and the mass vigorously stirred with a wooden paddle. When emulsification is complete and saponification is well under way, the mass is ladled into an iron frame and allowed to stand for several days, during which time the fatty matter is completely saponified, cools down to the normal temperature, and hardens. The frame may now be stripped and the soap cut and pressed in the usual manner.

Transparent soaps are made by remelting half boiled soaps with the addition of a small quantity of alcohol, some additional glycerin and cane sugar or glucose. This operation leaves the soap as a transparent jelly-like mass, which is cut up and allowed to stand until the alcohol has evaporated. The bars are then planed down, again cut, and pressed into any desired shape. Of late years it has been the custom of various manufacturers to introduce some form of saponified rosin into this class of soaps to increase the lathering quality.

Floating soaps were originally made exclusively from cocoanut oil. At the present time such soaps are extensively made by incorporating with the soft warm mass of any soap whatever enough air to reduce the specific gravity below that of water, the operation being usually conducted in a jacketed kettle provided with a screw stirrer. As a rule floating soap is now made from a mixture of tallow and cocoanut oil, 'half boiled,' with mixed potash and soda.

Marine or salt water soap is a 'half boiled' mixture made from pure cocoanut oil with potash and soda lye and a further addition of salt and carbonate of soda. The United States Navy specifications call for a soap of the following composition: the fatty matter shall consist of pure cocoanut oil only; water should not be present to an extent of more than 55 per cent.; the free alkali (NaOH) shall not exceed 0.5 per cent.; carbonated alkali (Na2CO2) may be present in quantities varying between 2 and 3 per cent.; foreign mineral matter should not exceed 0.5 per cent. Such a soap will wash freely in salt as well as in fresh water, a peculiarity due to the solubility of the alkali salts of lauric acid (a fatty acid present in cocoanut oil) in solution of salt. The soap, however, does not keep well, decomposition of the salts taking place during drying, which causes a liberation of free fatty acid and hence rancidity of the soap.

Soaps made from olive oil with soda or mixed soda and potash by the 'half boiled' process are known as Castile soap, a recognized standard. Such soaps, however, are now largely adulterated with cottonseed oil soap.

Marseilles soap is a settled olive oil soap made with rather more soda than necessary for saponification and then boiled down until the excess lye is strong enough to cause a precipitation of the soap. The mottled varieties receive an addition of copperas solution before boiling down. During the long continued boiling operation, the iron partially oxidizes and remains suspended in the hot mass, producing the characteristic blue, green, or red mottling.

Soft potash soaps are now rarely made, the soft soaps found in the market being soda soaps that contain an excess of water.

Medicated soaps are merely mixtures of pure neutral soaps with various remedial agents. The term 'antiseptic soap' is misleading, a pure settled soap being aseptic by itself and hardly anything being capable of improving this quality. Pure olive oil soap is used in medicine both internally and externally. It may be used as a laxative in the form of pills, or as an enema in children for the same purpose; or a plug of soap may be inserted into the rectum. Soap is also valuable as an emergency remedy in poisoning by the mineral acids. Externally soap is valuable as a stimulating liniment in psoriasis, lichen, eczema, and other chronic affections of the skin.

Manufacturing soaps, such as the wool and silk scouring soap, consist of neutral compounds of olive oil with potash. It is very essential that these soaps should be neutral and freely soluble. A strongly alkaline soap would injure the deli