The Art of Soap-Making. Soap is a chemical combination of a fatty substance with caustic lye, the base of which is either potash or soda; the former producing soft, and the latter, hard soaps.

519. To Make Soap-makers' Lye

519.     To Make Soap-makers' Lye. To 1 part of quicklime, slacked by sprinkling on it sufficient water to crumble it, add a solution of 3 parts soda in 5 parts water. For soft-soap lye, an equal quantity of potash is substituted for the soda. Stir the mixture and allow it to settle; the clear liquid is then poured off, and constitutes the first lye, and is of a strength of 25° to 30° Baum'e; the second, third and fourth lye is each obtained by adding successively 5 parts water, stirring thoroughly, allowing it to settle, and pouring off the clear liquid; producing respectively a lye of from 12° to 18°, 8° to 10°, and 2° to 5° Baum'e.

520. To Make Soap

520.     To Make Soap. Having thus prepared the lye, the first, second and third yes being sufficient for general purposes, take 20 pounds of pure grease, and melt it slowly in an iron vessel; keep it at a moderate heat, and stir in, a little at a time, 10 pounds third lye ; after stirring for about an hour, let the mixture get up to a boiling heat, and then stir in, by degrees, 10 pounds second lye ; this will complete the first stage of the process, which is termed saponification. The next step, called cutting up the pan, is to add, by degrees, a mixture of soda and lye with from 2 to 3 pounds common salt; this separates the excess of water from the curd, leaving a soapy paste; boil and stir for some time, then let it settle, and draw off the water. The third operation, clear boiling, has now to be performed; stir into the paste, by degrees, 5 pounds first lye ; and, when perfectly mixed and smooth, boil the whole for two hours; should the soap, during the intervals, become too liquid, which may happen when too weak a lye has been used, some salt, or a weak lye containing salt, must be added. The boiling is terminated when large, regular, dry scales appear on the surface; when this is the case let it settle, and draw off the fluid which remains. Put the soap into frames lined with cotton cloth which has been well powdered with a mixture of lime and starch, and as soon as the soap has become firm, lay it out to dry.

521. Hard and Soft Soap

521.    Hard and Soft Soap. Soaps are thus of two kinds, hard and soft, this condition being influenced both by the fat and alkali employed. The firmer and harder the fat, the solider will be the resulting soap. "With the same alkali, therefore, tallow will make a harder soap than palm or olive oil, and stearic acid than oleic acid. But the consistence of soaps depends far more upon the alkali employed. Potash is very deliquescent, that is, has a strong attraction for water, so that when exposed it will absorb it from the air and run down into a fluid or semi-fluid state. The potash retains this water in the condition of soap, so that potash soaps are always liquid and soft. The hard soaps, therefore, all contain soda, those with tallow or stearic acid being the hardest. Potash soaps will not dry, but retain their soft, jellylike condition, while some kinds of soda soap become so hard by drying that at last they can be pulverized. The admixture of a very small quantity of sulphate of soda hardens soap and also checks waste from too rapid solubility in hot water. "When soda and potash alkalies are used in combination, a proportion of from 10 to 20 per cent, of the latter is employed, according to the degree of hardness the soap is desired to possess.