Cold-water Soaps.—This term, which has made its appearance within the last 5-6 years, was at first confined to soaps made from very soft materials, but containing a very small amount of water ; such, for instance, as those produced by Morfit's process. They are sold at a low rate, aod, from their great dryness, may be kept indefinitely without losing weight, a property possessed by scarcely any other household soap ; being perfectly pure soap, they 8.re truly economical, provided they are not used with hot water. Christr. Thomas & Bros,, of Bristol, and Sinclair, of London, have a great reputation for these soaps, which have been recently introduced. Latterly, however, the Ilse of the term has been appropriated by makers of heavily-watered soaps, which run away in hot water.
Disinfecting Soaps.—In few ways can disinfectants be so ag,reenbly applied to the skin as when incorpm ated with soap. One of the last introduced, though probably one of the most efficacious, is thyme] soap—made solely by Ferris & Co., Bristol. Thymol is a non-poisonous (herein differing front carbolic acid) crystal, about 8 times as powerful an antiseptic nnd disinfectant as carbolic) acid, and is probably the only substance that combines disinfecting properties with a really pleasant smell, that of thyme. The mode of incorporating thymol and phenol (i. e. carbolic aoid) with soap is a trade secret ; Morfit states that carbolic soaps are best made by his process (p. 1771), using as a basis hot-pressed fat-acid cake, on account of the tendency of carbolic acid to soften the soap-paste.
Carbolic soaps are made in great variety and in large quantities by F. C. Calvert & Co., of Manchester, whose products contain definite specified quantities of carbolic acid of various qualities. Their "medical " soap contains 20 per cent. pure crystal ; their toilet and household soaps, 10 r cunt.; their domestic soap, 8 per cent.; and their " No. 5" or " scouring" soap, 4 per cont. liquid carbolic and cresylic acids. The comparative nntiseptic power of soaps may he tested by adding equal weights, in solution, to equal weights of flour-paste, and, after exposing these to the air under ideutical conditions, noting the day on which mould first appears on each. The so-called "coal tar " soap or " sapo carbonis detergens," owes its disinfecting properties to a small quantity of carbolic acid in tho coal-tax.
Sand Soap.—Under this heading, occur a number of soaps in which it is sought to unite the chemical power of soap with the meohanical aid afforded by sand in scouring. As much as 20 per cont. of clean send or powdered quartz is sometimes mixed with soap-paste. In a similar way,
soap is made the vehicle of many substances to be applied to the skin, medicinally or otherwise, or in any cleansing process. All these should be incorporated with " neat " soaps, freshly made or remelted, at as low a temperature as possible. Some form of soap is not unfrequently the basis of polishing pastes.
Fine Toilet Soaps.—Three distinct processes are in vogue for the fabrication of these, according to the quality of the product desired. For the commoner kinds, the basis is a good grade of fitted yellow soap, taken direct front the copper, or remelted in a small steam-jacketted pan, or in a Whitaker re-paelter, provided with continuous coils of steam-pipe. To this, are added (1) suitable colouriug matter, in a soluble form if possible, such as some aniline dye, (2) some mineral salts, as carbouate of soda or potash, salts of tartar, &c., to stiffen and " close " the soap, usually about 5 per cent in strong solution, (3) at ns low a temperature as possible, the perfume. When cold, the soap is cut up into slabs, bars, o.nd cakes, dried, and stamped, as previously described. A few formulm for perfumes are here given, calculated in each case for 100 lb. soap :— In connection' with " Brown Windsor " soap, it may be mentioned that the more it is melted, cooled, manipulated, and remelted, the better it becomes, and that the scraps of vadous sorts of soap that accumulate in the factory are usually worked into this soap.
The intermediate quality of toilet soaps are made by the cold process (pp. 1771-2), from the purest materials tbat can be prepared, and when the fatty matter (tallow, lard, &c., with occasional coco nut-oil) and leys have been well stirred together, the colouring matter, perfume, Sm., are added, and the whole is left quiet to effect the saponification. As previously directed, the fat should not exceed 49° (120° F.), and / its weight of caustic soda leys at 36° B., should be stirred into it ; in about 5 hours, when saponification occurs, the temperature will rise to 82.2° (180° F.). This method enables more delicate perfumes to be used, since they are added at so low a temperature. A marbled appearance may readily be given to this soap by drawing, in wavy lines through the mixed fatty matter and leys, a steel blade dipped in colour ground up with oil ; to produce a good effect, the peculiar wrist-turn should be used with the blade, such as is required to wield a fencing foil well. It is obvious that these soaps retain their own glycerine.