A very firm soap may be made on a small scale from the oleic acid from candle-factories, known commercially as oleine or red-oil, by heating it to about l 00° (212° F.), and adding thereto one-half its weight of caustic soda leys at 36° B. The combination takes place instantaneously, and it is only necessazy to allow the soap to get cold, when it is fit for use. For the preparation of the leys, see p. 1767. They need not be perfectly caustic, hut if any carbonate of soda be present, they must be of proportionately higher sp. gr., and the vessels employed must be capacious, in consequence of the effervescence that occurs.
Hard soaps may also be made on a amall scale without boiling, by adding to a mixture of 2 parts tallow and 1 part coco-nut-oil, or of 3 parts tallow and 2 pszts coco-nut-oil, oue-balf its weight of caustic soda leys at 36° B., the whole being at a temperature of 55°-60° (130°-140° F.); the mixing, after being well atirred, should be set aside for a day or tvio. Here also the presence of common salt is a serious obstacle to the combination.
Soaps that require boiling cannot be well prepared in small quantities. Those who wish to make them, however, would do well to study the description of the process on a large scale. In making small quantities of hard soap, it will be well to boil together the fat and the soda leys previously well causticized by lime, and to calculate from the table on p. 1768 how much leys is necessary, taking as a basis that for every 10 lb. of fat, about 1 lb., or rather less, of pure soda (100 per c,ent.) is required. Combination will not take place unless the solution is quite weak, say 12° B., and when it is effected, salt may be added to separate the excess of water. The salt should be sprinkled in gradually, Clue being allowed for each portion to dissolve, and when a small sample, taken out on a shovel and allowed to cool, separates into liquor end soap, enough salt is added ; the boiling ahould then be stopped, and the whole allowed to repose ; in an hour's time, the soap may be skimmed off. Soft soap is more easily made by boiling on a small scale, since the process is the same whatever quantities of materials are employed. The reader is, therefore, referred to p. 1776 for instructions under this head.
In considering the manufacture of soap in large qnantities, the subject may be conveniently and naturally divided under the following beads :— I. The apparatus and processes employed in effecting the chemical c,ombination between the
fatty matter and alkali, including in this a general description of the mode of boiling (or otherwise preparing) soaps of different typea.
II. The machinery and me,chanical and physical contrivances made use of in converting the chemical compound so produced into a marketable soap.
III. Ingredients and formulm for the production of special kinds of soaps for particular purposes, including toilet soaps, manufacturers' soaps, 8ce.
IV. Theory of the action of soap ; methods for its analysis and valuation.
V. General considerations of the industry—its location, prospects, legislative condition, &c.
It will be convenient to treat, in the order of their complexity, the somewhat extensive range-of subjects included under I., c,ommencing with the simplest, and accordingly we find the following natural sub-divisions : I a. Soaps produced by the direct union of fatty acids and caustic alkali, or by the decom position of carbonated alkali by fatty acids.
I b. Soaps produced by the action of the precise quantity of alkali necessary for saponification upon a neutral fat, without the separation of any waste liquor, the glyc,erine being retained in the soap. This class includes—a. Soaps made by the " cold proc,ess," O. Soaps made under pressure.
I c. Soaps produced by the ordinary methods of boiling in open vessels, working with indefinite quantities of alkaline leys, the processes being controlled by the experience of the operator. These are again subdivided into--a. Soft soaps, in which the glycerine is retained, potash being the base ; 13. The so-called "hydrated " soaps, in which the glyceriue is retained, and of which " marine " soap may be taken as the type ; Hard soaps, with soda for a base, in which the glycerine is eliminated, comprising three kinds--eurd, mottled, and yellow soaps.
It may be noted that a very large proportion of all the soape manufactured is inclnded in this last and most complex subdivision, since practical experience shows that, all things being con eidered, they are the most marketable.
Full directions for the fabrication of these several kinde will now be given, the paragraphs treat ing of each being numbered to correspond with the above classification.