Soap

The bulk of high-grade toilet soap is made from settled soap by the milling process, originally introduced from France.

The soap from the frames is cut into bars and reduced to fine shavings or chips, which are exposed to warm air in drying cham bers until the moisture content (originally 30%) is reduced to about 15%. The chips are mixed with perfume, colouring mat ters, glycerin, or superfatting material, such as lanolin, etc., as required, and "milled" by passing through a series of smooth granite rollers. On leaving the rolls the soap sheet is again shredded and re-milled, and the process repeated several times until the material is homogeneous. The soap ribbons are then forced through a "plodder," a machine which compresses and extrudes the soap through a heated nozzle in the form of a bar with a glossy sur face. The bar is cut into short blocks, which are finished for distribution by moulding in stamping machines to the shape required for the final tablet.

Elaborate blends of essential oils (q.v.), both natural and syn thetic, are used for the perfuming of soaps. It is necessary to select such perfumes as will not discolour or decompose in the presence of the materials of the soap. Many brands of toilet soap are associated with particular perfumes, e.g., "Brown Wind sor" is characterised by the odour of oil of cassia. Vegetable colouring matters, such as chlorophyll, are popular, but the coal tar dyes have also large application. Shaving soaps should be made from a good tallow base ; usually a mixture of potash and soda is used for the saponification in order to obtain a suitable consistency. Occasionally gum tragacanth is added to increase the stability of the lather. Floating soaps are made by stirring kapok fibre or, more generally, air into the soap, so that on cooling the tablet possesses a density less than that of water. A solid transparent soap may be prepared by the cold process by the use of a mixture of coconut and castor oils, with the addition of small amounts of rosin, glycerin, alcohol or sugar (all bodies con taining one or more hydroxyl groups in the molecule). Excess of glycerin renders the soap liable to sweating, and it is usual to add rosin and sugar syrup to obtain transparency. Better quality transparent soaps are produced by the older method of dissolv ing a settled soap, usually a "primrose" or tallow-rosin base in alcohol. The solution is concentrated until the mixture sets to a

solid cloudy mass on cooling. This is cut and moulded into tablets, and these are stored in drying chambers for 3-6 months. The bulk of the alcohol evaporates and the soap gradually becomes clear and transparent.

Household and "Washer" Soapt.

The best grade household soaps consist of tallow-rosin, curd and settled soaps (e.g., 20% rosin, 40% tallow, 40% coconut, cottonseed oils, etc.). Lower grades are made from bone-fat, kitchen grease and other low grade oils and fats. All qualities are made, from a genuine soap (63% fatty acids) through all gradations of carbonated, silicated, "filled" and "run" soaps down to "scouring" soaps, which may contain as little as o% fatty acids.

Soap powders consist of powdered dried soap admixed with sodium carbonate and silicate, and frequently oxidising agents such as persulphates or perborates.

Mottled Soaps.

If somewhat low-grade fatty material, e.g., kitchen-grease, low quality olive oils, is used in the preparation of curd soaps, it is necessary to finish on a stronger lye, produc ing a coarse-grained curd. By careful control of the clear-boiling stage, followed by slow cooling in the frames the soap crystal lises fractionally : harder soaps separate first, the more liquid portions solidifying later are segregated into translucent veins in which are trapped any impurities (usually coloured) such as iron soaps, etc. The crude barilla soda used in the earlier days of the soap industry frequently contained impurities of a blue colour, causing a blue "mottle." If excessive water were added to the soap this marbling was not produced; consequently the presence of "mottle" was regarded as a guarantee of a genuine soap. Such a soap is termed "curd mottled" or "genuine mottled." Now, however, the colour is usually supplied by the deliberate addition to a curd soap of e.g., ultramarine (blue) or manganese dioxide (black mottle). Further, it has been found possible to produce "artificial mottled" soaps from heavily liquored low grade soaps; the presence of mottle, therefore, can no longer be accepted as an indication of genuineness.