Another mode of producing these soaps is to make a portion of the fat employed (usually all the coco-nut-oil, with or without some portion of the other oils) into hydrated soap (p. 1777); the remainder of the fatty matter is made either into a " fitted soap " or a " flat curd " soap, and then transferred to the hydrate previously prepared in another copper ; after both are incorporated by thorough boiling, the soap is finished as before directed. This method, for which Blake & 'Max well and C. N. Kottula had various patents, was introduced into England from Germany by the last named. about 25 years ago ; it is said to produce a more solid and close soap from the same materials than any other method, but when a blue-mottled has to be made, the greatest care must be used to allow no impurities in the materials used for the hydrated soap, or the brilliancy of the blue mottling will be interfered with.
Manufacturers' Soaps.—The various kinds of household soaps having now been described, a few remarks will be made upon the soda-soaps suitable for various manufacturing purposes. Most of these are dissolved in water for use, and hence it is immaterial into what sized bar they are cut. Care, however, should be taken that they are dissolved ; a case occurred in the writer's knowledge when the quality of a soap was much complained of, as producing greenish stains upon black cloth. The soap-maker asserted his ignorance of anything deleterious in the soap, and subsequent investigations showsd that the cloth-manufacturer's workman, instead of completely dissolving the soap, had impregnated the cloth with a solution containing undissolved pieces, and the soda in these, not unnatmally, affected locally the indigo and logwood with which the cloth had been dyed.
For ordinary scouring purposes, there are few better soaps than the old-fashioned curd-mottled : many others, however, are used, such as curd soaps made from cheap and inferior greases, and boiled very dry ; and fitted soaps from greases and black rosin. For scouring goods of finer quality, a white curd soap from tallow, or tallow and lard, is used, or a curd soap from olive- or cotton-seed-oils, or a mixture of both. The soaps made on Morfit's plan (p. 1771) are also good scouring soaps. As a rule, traces of unsaponified fat (or indeed any extraneous material) are very deleterious in manufacturers' soaps, which, under ordinary circumstances, should contain a, very slight excess (as curd and mottled soaps always do) of caustic soda. When for any purpose, as
e. g. where delicate dyes are employed, an absolutely neutral soap is required, either a " finely fitted " soap should he used, or a curd soap from which the caustic leys have been pumped off, and the soap finished by boiling on brine.
Ac,cording to Crace-Calvert, soaps for dyers' use are not indiscriminately applicable to all colours. To produce the maximum effect in brightening the shade, the soap should be :— For some purposes, a soap that will remain liquid in solution at a low temperature is required ; such soaps aro well made by Morfit's process, and should contsin large quantities of oleic acid. For " fulling," this soap is often employed, mixed with curd soap made from unbleached palm-oil only.
Much has been written about the frauds practised by unprincipled soap-makers upon manufac turers using soap, and the latter have been advised, in self-defence, to make their own soaps. Reasons have been given (p. 1777) against this course ; it is much to be desired, however, that soap-users would take soap-makers personally more into their confidence in explaining their requirements, and would themselves superintend (and not leave to their foremen) any experiments made on the working of different kinds of soap. A system, too, on which manufacturers' soaps should be sold, guaranteed to contain a given percentage of fatty matter of a definite quality, with its full equivalent of soda, is greatly needed. Such arrangements, if carried ont, would very pro bably put this trade upon a far better footing than it h3 at present.
Special Musehold and Laundry Soaps.—A few of these, including the cotnmoner kind of scented soaps, will now be considc rt d. Cheap toilet soaps are thus made on a large scale. For " honey " soap, a good "neat " yellow soap is taken, and a solution of some yellow dye is mixed with it ; 5 per cent. carb. soda crystals, or 5 per cent. sil. soda at 1.700 sp. gr., is then added to stiffen it ; the whole is crutched, and scented by the addition at as low a temperature as possible of as much eitronella-oil as is deemed necessary. For " brown almond soap," an inferior grade of yellow soap is similarly treated, and scented with about 10 lb. to the ton of mirbane (i. e. nitro-benzol) or arti ficial almond-oil. When cold, these soaps are cut into bars or cakes, superficially dried, and stamped with one of the foot-power or steam stamping-machines (p. 1784).