In England, mottled soaps are usually made from kitchen-grease and from bleached palm-oil. In Marseilles, from mixtures of various seed-oils, of which olive-oil is the principal, and cotton seel-, poppy-, hempseed-, gingelly-, and ground-nut-oils are frequent components. In these mottled soaps, little or no e,oco-nut- or palm-kernel-oil should be used, although such oils form an ahnost essential constituent of the new mottled soaps referred to above.
Yellow Soaps. —The finishing operation for these is termed " fitting " in England, and liquidation in France, and requires considerable judgment on the part of the operator. After being thoroughly well " made," the copper stands at rest for at least 12 hours ; the half-spent leys are then pumped off, and the open steam is turned on. When the copper is again boiling, it should be e,ontinued so until its content,s are perfe,ctly homogeneous (the time depending much on the size of the copper), and the soap should then be examined with a clean trowel. When in proper condition, a thin layer should drop off a hot trowel held edgeways, in two or three flakes, leaving the metallie surface quite clean ; but if, as is more probable, the layer breaks up into several small flakes, and the soap is stiff, water should be cautiously added, to reduce the sp. gr. of the still-entangled leys. If, on the other hand, the film will not leave the trowel at all, a small qua,ntity of strong leys (say 15°-20° B.), or of brine, may be cautiously added, to cause it to do so. In the first case, the " fit " is said to be " open " or " coarse " ; and in the second, to be " close " or " fine." Here, again, practice and observation alone enable the operator to obtain " a good fit," and when it is obtained, the steam is turned off, and the whole is allowea to stand. The copper is then covered up with planks, or an iron cover, and kept as warm as possible ; small coppers may stand a day or two, large oncs as loug as a week. During this period, the contents arrange themselves in three layers, (1) a light crust full of air bubbles, technically called " fob," (2) the finished or " neat" soap, forming about I of the whole, (3) the " nigre," which is an impure solution of soap in leys, and contains all the impurities present in the copper. The size of this last depends entirely upon the character of the " fit." A
fine fit gives a very large nigrc, containing much soap ; while a coarse fit gives a small nigre, composed chiefly of impure leys. The Eoglish practice is to fit rather "fine,'' competition among the various makers for purity and colour being excessive; while the Americans are usually content with a coarse fit.
The finest yellow soaps s,re made from the best tallow and rosin, which last is a,n essential constituent of them ; in some cases, lard, or lard-stearine, is used. Inferior qualities may be made from the nigres of better sorts, from bleached palm-oil, greases of all kinds, and in fact any sapeni fiable solid fat ; fluid oils must be used, if at all, in small quantities and vvith caution. The proportion of rosin may vary from t--+ of the total fat, to an equal weight, or even more, according tho quality of soap required. In England, the very best quality is knovrn in the trade as " primrose," and is mad° from tho finest (unbleached) tallow and " window-glass" rosin; tho lowest grade of brown from the nigres of the gradee above, mixed with eurriere' grease, leather tallow (" sod-oils"), and other dark and foul but hard fats, with black rosin.
The soap having been finished in the copper, the next etage is to transfer it to the cooling boxes, or " frames," as they are usually called. Curd soaps should always bo carefully skimmed ,11 the leys by ladles, einee they are too stiff to pump, and most mottled boaps are in this condition also; if, however, much leys be entangled in them, and the curd be flat, they may be pumped out. In large factories, fitted soaps are invariably transferred to the frames by suitable pumping machinery. A peculiar method of emptying coppere that contain perfectly homogeneous ..,naps. without any nigre or leys beneath them, was invented by Gossage, and is represented in Figs. 1255-6.
An air-tight cover is mewed on to the copper, and a blast of air is turned in through A ; the pressure thue exerted forces the soap out throngh the delivery-pipe B in a continuous stream, until the lower end of that pipe becornes uncovored, when air rushee through it. Thie chiefly used for the " blue-mottled " amps, deecribed on pp. 1787-8.