Boil this mass from 10 to 12 hours, adding every hour 5 galls, of ley of 25°. 4 or 5 hours' boiling will often be sufficient to saturate the soap; this being accomplished, extinguish the fire, leave it quiet for an hour, and then draw off the under-ley. It will measure from 25° to 30° B. To complete the process, add about 50 galls. of ley of 4° B. Let this boil gently for 1 1/2 to 2 hours, stirring from time to time with the crutch, and finally extinguish the fire and cover the pan. The soap will separate from the ley, and rise to the top. After 5 to 6 hours, while yet in a liquid state, pour it in the frames, taking due care that no lev is mixed with it. In the frames it should be well stirred for some time. For neutralizing the disagreeable tallow odour, 1 to 2 oz. of a well-scented essential oil should be added to 100 lbs. of the soap, and after 7 to 8 days it may be cut. 100 lbs. of tallow will yield about 170 lbs. of soap.
Rosin, incorporated with a soap, to a certain amount, will make it more soluble and detersive. The lighter the rosin the more it is valued; 15 per cent. of rosin with 85 per cent of tallow is allowable, but beyond that limit the soap loses in colour, in firmness, and quality. Even for the cheapest article the quantity of rosin should not exceed 33 per cent., otherwise the soap will be soft, and unprofitable to the consumer. The rosin can be saponified with alkali; 12 galls, of ley of 30° B. are needed for every 100 lbs. of rosin. Some soapmakers melt it with the fat at the commencement of the boiling for soap, but a much better product is obtaiued by first producing a tallow soap, and afterwards mixing the rosin soap with it, made in the meantime in a special kettle. Both mixtures have to be stirred and beaten thoroughly for half an hour, and the whole passed through a sieve before they are filled into the frames', and therein well stirred and crutched. Some palm oil, when saponified with the tallow, very much improves the appearance of the soap.
Place 80 galls, of ley into a kettle of sufficient capacity, first boil the contents, and then throw rosin in at intervals of 5 or 6 minutes, and in portions of 15 to 20 lbs., until 1320 lbs. have been added. The rosin must be previously well pulverised, and while one workman is occupied with throwing it in, another should be constantly-engaged in stirring it, as the mixture easily ascends. The heat must not be too rapidly increased, nor is it necessary that it should boil all the time, but keep the temperature near the boiling point. It is absolutely requisite to keep stirring the paste all the time. Saponification will be finished in 2 hours, and then the mixture, with the fat, is converted into soap as above described.
Cocoanut oil acts differently from any other fats, in combination with which weak leys produce a milky mixture. Such leys have no effect upon cocoanut oil, for it can be seen floating on the top, while strong leys of 25° to 30° very soon produce saponification throughout the whole mass. This soap is sometimes called marine soap, as it will lather well with sea water. A ley of 27°, cold weighed, will saponify an equal weight of cocoa-nut oil - 100 lbs., for instance, making nearly 200 lbs. of soap. The oil is put in the pan together with the ley, and then heat is applied. After continually stirring it for 1 or 2 hours, the paste will gradually thicken, when the temperature of the heat applied should be moderated, but the stirring continued. After a time the paste turns into a white semi-sol id mass, which forms the soap, and this has to be filled immediately into the frames, because solidification takes place very quickly. A mixture is often used of equal parts of tallow and cocoanut oil, or of bleached palm oil and cocoanut oil. which yields a very fine soap. 90 to 95 per cent, of cocoanut oil, with 5 to 10 per cent. of natural palm oil, yields also a nice soap; and all these fats, when mixed with cocoanut oil in not too large proportions, will be as easily saponified as if the latter alone were used.
Palm oil is rarely used alone as a soap stock, but generally employed with an admixture of rosin, and it then yields yellow soap; for white soap, however, these are employed in the bleached state. For some kinds of soap, palm oil is saponified with 5 to 10 per cent. of cocoanut oil; more is often used of the latter, and then filled soaps are obtained. Demi-palm is a soap consisting of equal parts of tallow and palm butter, to which is added a very small quantity of rosin and cocoanut butter. 1. Palm oil, 300 lbs.; tallow, 200 lbs.; rosin, 200 lbs. 2. Tallow, 500 lbs.; palm oil, 300 lbs.; rosin 200 lbs. 3. Palm oil, 450 lbs.; cocoanut oil, 50 lbs. 4. Hog fat, 550 lbs.; palm oil, 150 lbs.; cocoanut oil, 50 lbs.; clarified rosin, 50 lbs. Palm oil may be made into soap exactly in the same way as tallow. If rosin is incorporated, it is better to produce first the combination of the rosin with the ley, and mix the same with the finished palm-oil soap. Soap made of bleached palm oil is perfectly white, and can scarcely be distinguished from tallow.
For the manufacture of soft soaps, hempseed oil, linseed oil, poppy oil, rapeseed, colzn, whale, and seal oils are used. Saponification is commenced with a ley of 9° to 11° B., and the contents of the kettle kept boiling, until the paste becomes of sufficient consistency to draw threads out of the substance. It then undergoes the process of clear-boiling, for which purpose a ley of 25° B. should be used, stirring all the time. When the paste docs not sink any more - first it ascends - boils quietly, and shows the formation of scales, it may be considered finished. The barrels in which it is to be offered to the trade should be immediately filled. The quality of soft soaps is estimated according to their consistency. Green soap was formerly made of linseed oil. It is now, however, made principally of whale oils, but as they have a yellow colour, manufacturers mix the soaps made of the whale oils with finely-powdered indigo, or the indigo-sulphate of lime, which is prepared by dissolving indigo in sulphuric acid, diluting it with water, and saturating the whole with lime-milk. Black soft soap is made by adding to the soap a mixture of a solution of copperas and logwood or gall-nuts.