CASTILE SOAP.
A pure castile soap should be made from olive oil. This, however, is not always the case, as a number of oils as well as tallow are used to adulterate this oil to cheapen it, and there are even some soaps called castile which contain no olive oil at all. Most of the pure castile soap used in this country is imported, as it is a difficult matter for the American manufacturer to compete with the pure imported castile soap, since both labor and oil itself are so much cheaper in the vicinities of Europe where this oil is produced, that this advantage is more than compensated by the carrying and custom charges by importing the castile soap.
Castile soap may be made either by the full boiled or cold process. There are numerous grades of olive oil, and those used for soap making are denatured to lower the duty charges. Olive oil makes a hard white soap, usually sold in bars, and olive oil foots a green soap, due to the coloring matter contained in this oil.
To make a boiled castile soap, a composition of 10 per cent. Cochin cocoanut oil and 90 per cent. olive oil may be used. To cheapen this, peanut oil (Arachis oil) may entirely replace the olive oil, or about 20 per cent. of corn or soya bean oil may be added. The oils are saponified as usual in making a settled soap and to prevent rancidity the soap is boiled near the finish for some time in the closed state with sufficient excess of alkali to give it a sharp taste, then grained with lye, the lye drawn off, closed with water and then grained with salt. This process is repeated until the desired strength is reached. The last graining should not be too great, and on the last change the soap should not be thinned out, as it will contain too great a quantity of water when slabbed.
In making a cold castile soap the usual method is pursued as already directed under cold made soap. When the soap is taken from the crutcher it is advisable, however, to keep the soap in the frame well covered to assure complete saponification. Some manufacturers use very small frames which are placed into compartments, well insulated to retain heat. Several formulae for cold made castile soaps, follow. It may be noted that some of these contain practically no olive oil.
If any of the soaps containing a high proportion of cocoanut oil are boiled the soap will float. It is therefore necessary to keep the temperature as low as possible.