Separation (French, relargage).—To effect this, a quantity of common salt is sprinkled into the copper while still boiling, or the strongest brine (24° B.) is run in. Since the quantity necessary depends entirely on (1) the sp. gr. of leys used in the last operation, (2) the amount of condensed water where free steam ia used for boiling, and (3) whether there is much eaco-nut- or palm-kertiel oil in the fat employed (p. 1769), no directions c,an be given as to how much salt should be added ; the addition should be made cautiously and gradually (taking care to allow time far the solution of the salt), and continued until a small sample removed upon a spatula or trowel allows clear liquor to run frorn it. During this operation of "graining," the contents of the copper are very apt to boil unsteadily, and occasionally to boil over with great viulence. When this point is reached, the whole process should be stopped, aod, the ateam being tamed off, the copper should staud at least 2-3 hours. Its contents then divide thernselvea into two portions, the upper consisting of soap paste holding about 40 per cent. water, and the lower of a solution known as " apent leys," con taining common salt, any carbonate and other soda salts present in the origioal leys as impurities, and nearly all the glycerine of the fat employed (see p. 1800). It ahould contain no caustic soda, and no soap or aaponifiable material ; if it contains the latter, enough salt has uot been used. For the presence of caustic soda, a sensitive tongue will be found a sufficiently delioate test, while the addition of a mineral acid will throw up a scum of fatty matter, if any be present ; it will also be found useful to observe the sp. gr. of the spent leys, as a means of controlling the amouot of salt used. After the capper has stood for some hours, the spent leys should be pumped off, and, if there is then sufficient room, more fat may be run in, and the whole operation repeated ; at this stage, the rosin is usually added fur a yellow-soap, being broken into lumps, and shovelled in, unless it is combined with soda in a aeparate copper, nod mixed with the fat-soap an the next operation.
Clear-boiling (French, coction).—All the geode ha\ log been " killed," and the spent leys removed, a small charge of lays at about 12°-14° B. is run in, and the copper boiled for 2-3 hours ; at the end of this operation, the soap ehould have a faint but decided caustic taste, and a small sample on a spatula should allow clear leya to run off it ; if this be not the case, more, and in same cases stronger leys, must be added. This operation communic,ates additional soda to the soap, nod washes out, as it were, some of the salt eotangled in it. After some hours' subsidence, the " half-spent " leys that sink to the bottom are puroped off, aud may be used in another copper for " killing" mare fresh geode ; the soap from such leys, however, will be of an inferior colour.
The next stage of thia operation is to boil the copper with open steam ; if the contents are not perfectly homogeneous, and in a etate resembling a stiff paste, i.e. if the copper be oat " cloae," but have a tendency to aeparate into leya and soap, when examined on a spatula, the ap. gr. of the entangled leys is reduced by the addition of water, until the desired condition is reached. A small atream of leys at about 12° B. is then allowed to trickle in, uotil the homogeneous paste again eeparates into flakes of eoap and dear leys, boiling being continued all the time ; the soap should now taste atrongly of caustic soda, and feel hard when cold ; this operation is technically called "making" the soap, and when enough leys have been run io, boiling ahould be continued for same hours, to enaure complete saponificatien, since it is difficult to make neutral fats take up the last portions of eoda. The large coppers previously alluded to require a whole day (12 hours) for this operation.
The operations above described, may in experienced hands be somewhat reduced in number and time, but much greater care is then required. By the proper use of leys of various strengths, and of salt, it is possible to " kill " 40-50 tons of mixed tallow and rosin in one copper in a day—to diapense with the next operation—and to " make " the copper on the day following, finishing it on the third day. The mode of finishiog depends entirely on the kind of soap required.
d SfnirS.—The raw materials for curd soaps should contain no rosin, and but little, if any, coco-nut- or palm-kernel-oil, but any other oils or fats may be used. White curd IS usually made from tallow or lard, or a mixture thereof ; brown eurd, from bleached palm-oil, or kitchen-grease, or bone-tallow ; and manufacturera' curd-soaps, from various fats. When the soap is "made," the open steam is shut off, and the bailing is continued either with fire or with close-steam; this concentrates the lays, and the flakes of aoap gradually approach the apheiical form. From time to time, the boiling ia stopped, the sp. gr. of the leys is observed, and a sample of the soap, from which the leya have been allowed to separate, ia put out to cool. When it is sufficiently hard, the boiling ia finally stopped, and after a few hours' subsidence, the soap is ready to be removed ; the amount of water left in it axle@ inveraely as the ap. gr. of tho leys in which it is boiled.
Mottled Soaps.—The term is here used to denote the old-fashioned curd-mottled soaps, not those marbled with blue, grey, or red, which have appeared in the English and foreign markets within the last 20 years, and which are described on p. 1787. In the fabrication of soap, it is impossible to avoid entirely the presende of earths and metallic oxides. These consequently decompose a small portion of the soap, combining with its fatty acids, and forming soaps of lime, magnesia, and iron (from the " coppers ''), which are insoluble, but softened by heat, and disseminated in a state of minute division through -the soap-paste ; any slight impuritiesl in the fat employed, when not dissolved in the caustic soda solution, are similarly diffused. If, after a soap is " made," the leys in which it is suspended are concentrated to a point short of that necessary to produce bard curd-soap, and it is then transferred to the cooling-frames, with a certain quantity of leys entangled in it, these insoluble particles will, during the solidification of the soap, collect together, and produce the appearance known as "mottling." No rule can be given for the point of concentration; it va,ries with the fat used, with the amount of leya in the copper, with the quantity of salts other than caustic soda in them ; and in short, the proper " mottling condition " is a physical one, chemical tests being of no use in deciding it. Nothing but practice and careful observation can make a successful mottled-soap boiler. The principle of the process has been clearly laid down, and the various formulas given in books, involving in many instances several changes of leys, are but different modes of arriving at the same result, viz. the suspension of pure soap, and of soaps of the metallic oxides, in soda leys of a given sp. gr. If the soap be boiled too long, it " sets " in cooling before the mottling has had time to a,ggregate; if it is not boiled enough, an undue quantity of leys remain in the soap ; hut, from their mode of manufacture, mottled-soaps always must contain some leys in the cavities between the curds ; hence they are the most suitable and really economical soaps for hard waters. It not unfrequently happens that the copper does not contain enough metallic soaps, &c., to produce a definite mottle. In this case, some "mottling " iH added ; for a grey, Frankfort-black, or very finely levigated black oxide of manganese, may be used ; the peculiar greenish mottle which becomes red on exposure, characteristic of Marseilles and Castille soaps, is produccd by adding some solution of protosulphate of iron to the copper when it is nearly finished (about 4 oz. of the salt to 100 lb. fat); the precipitated protoxide of iron suspended in the soap is greenish, but becomes peroxide in contact with air, to which the change to a red colour on exposure is due.