100 „ „ palmitate „ 35 „ SI 100 „ sodium stearate „ 7i In the manufacture of soft soap, oils that are fluid or semifluid at the ordinary air-temperature are usually employed, and especially linseed- and other seed-oils, and the cheaper varieties of fish oils. Certain oils make a bard or a soft soap, according at:3 the alkali employed is soda or potash, or, in some cases, a mixture of both. Aa a general rule, not more than of the potash in a soft soap can be replaced by soda (for cheapness sake) without impairing the quality of the soap.
Hard soaps invariably contain aoda as their base, and, cetera paribus, tbe hardness varies inversely as the quantity of water in the soap. An oil as fluid as commercial oleic acid will pro duce a hard soap with soda, if the process be so conducted that but little water is present during the operation. Tallow, mixed with varying proportions of rosin, ia employed for household " yellow " soap ; kitchen-grease, bone-fat, disc,oloured lard, and other greases, with rosin, for inferior grades of the same ; while the same greases, and palm-, cotton-seed-, olive-, coco-nut-, and palm kernel-oils, are used either alone, or in various combinations, for the different kinds of mottled soap. The raw materials for soaps for special manufacturing, toilet, and other purposes, will be mentioned when treating of those soaps.
It has been already noticed that coco-nut- and palm-kernel-oils combine with a larger quantity of soda than any other known fat, and hence that the yield of soap from these oils is greater than from other fats. Further, the soap so produced has the power of combining (and making a hard soap) with more water than can ever be communicated to tallow soap, a property which has frequently given rise to dishonest traffic. This soap is more soluble in water than any other, and requires a much larger quantity of common salt to separate the exceas of water from it. In technical lan guage, it is said to " work close." Reference to the table on p. 1765 will show the reason for this. Coco-nnt-oil contains a number of low terms of the fatty-acid series, whose salts are so very soluble, that even the lime and baryta salts of the lower among them are quite soluble in water, just as are the lime and baryta salts of formic and acetic acids, the lowest terms of all.
Among the raw materials used by the soap-boiler, not enumerated under Oils, are various bye products of other manufactures, among which may be meutioned—the oleine or oleic-acid from eandle-worka (see Candles, pp. 580, 584, &c.); the grease recovered from washwaters of woollen factories, pp. 1155-6, which is vcry apt to contain unsaponifiable oils, and should be employed with caution ; the " foots" from various oil-refineriee, which either contain strong mineral acids (p. 1460) or are partly-formed soap when an alkaline refining process has been need (p. 1460); waste fats recovered by carbon bisulphide or petroleum-epirit (pp. 1454-5), aleo liable to contain unaaponi flable oils ; " euint," or the greaae derived from natural woel, accompanied by potiush salts ; and, especially in France, the yolks of eggs, see pp. 1365-6 (of which the whites hnve been used in the preparation of albumen), which contain a considerable percentage of fatty matter. This might be largely increased.
The value of soap-making material is beat ascertained by eaponifying a weighed quantity (say 5-10 grm.) with aoda, diseolving the soap in water, decomposing it with a mineral acid, and then washiug, drying, weighing, and examining the resultant fatty acid°, as is described on pp. 1462-3 of Oila, and, in a modified form, on p. 1794 of this article.
Rosin (see Resinous and Gummy Substance°, p.1680).—The kind used in soap-making is known as eolophony. The lighter shades only can be used for better-class soaps. Such are liable to contain a little turpentine, which, to some alight extent, injutioualy affects the hardness of the map ; and they are apt to become unpleaeantly soft in very hot weather. Opaque rosin° contain turpentine, and, iu rare cases, water. Dark rosins may be improved in colour, and deprived of euspended impurity, by being melted, allowed to nettle, and then boiled on a weak solution of common salt. Dark roein may be distilled with eteam under a pressure of 10 atruoa. to make it nearly white for aoap-making. Like many other distilled products, however, it hae a tendency, both alone and in combination, te oxidize rapidly, and deteriorate in colour. When fine rosin is unusually dear, however, this process may be employed with advantage.