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 showed 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 unnaturally, affected locally the indigo and logwood with which the cloth had been dyeu.
For ordinary scouring purposes, there are few better soaps than the old-fashioned curd-mottled; many other?, however, are used, such as curd soaps boiled very dry, made from cheap and inferior greases, cotton-oil foots, etc, and fitted soaps from greases and black rosin. For scouring goods of finer quality, a white curd soap from tallow, or tallow and lard, with or without the addition of a small quantity of cocoa-nut oil, is used, or a curd soap from olive or cottonseed oils, or a mixture of both.. The soaps made on Morfit's plan 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, an absolutely neutral soap is required, as e.g. where delicate dyes are employed, either a "finely-fitted" soap should be used, or a curd soap from which the caustic lye has been pumped off and the soap finished by boiling on brine.
A very ingenious mode of making, soaps of any kind absolutely neutral was introduced in 1885 by Dr. C. R. Alder Wright. Some salt of ammonia, such as ammonium sulphate or chloride, is mixed up with the soap paste while hot. The caustic soda present turns out the ammonia (producing sodium sulphate or chloride), and much of the ammonia is volatilised at once by the heat of the mass, while the remainder escapes after the soap has been cut up and exposed to the air for some days.