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 provid ed 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 erutehing, 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 re moved and the soap is cut into slabs and bars with a steel wire. After a short drying opera tion, the soap is pressed and ready for use. An ordinary rosin soap freshly made has the follow ing composition: Fatty and rosin acids 66.24 per cent.
Free alkali 0.36 per cent.
Combined alkali 6.82 per cent.
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, coining out in thin crepe-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.) beimg used in the process. The opera tion is usually carried out in small east 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 (3(3° to 40° Baum6), consisting of soda alone or mixed with a small amount of potash. is DOW 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 al lowed to stand for several days, during which time the fatty matter is completely saponified, cools down to the normal temperature, and hard ens. 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 quan tity 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 saponi fied rosin into this class of soaps to increase the lathering quality.
Floating soaps were originally made exclusive ly 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 con ducted 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.
Marin(' 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 follow ing composition: the fatty matter shall consist of pure eoeoannt oil only; water should not he present to an extent of more than 55 per cent.; the free alkali (Na011 ) shall not exceed 0.5 per cent.; carbonated alkali (Na,C00 may be pres ent 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 laurie 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 sapon ification and then boiled down until the excess lye is strong enough to cause a precipitation of the soap. The mottled varieties receive an ad dition 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 misleadimr, a pine set tled soap being aseptic by itself hardly any thing being capable of improving this quality. Pure olive oil soap is used in medicine both in ternally 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 he inserted into the rectum. Soap is also valuable as an emergency remedy in poisoning by the mineral acids. Externally soap is valu able as a stimulating liniment in psoriasis, lichen, eczema, and other chronic affections of the skin.
Maim faetwing 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 he neutral and freely soluble. A strongly alkaline soap would injure the deli cote fibre and at the same time not prove so all' Merit a detergent.