In making potash soaps it is practically impossible to obtain any glycerine directly because of the pasty consistency of the soap, and no graining is possible because the addition of salt to a soft soap, as already explained, would form a soda soap. Large quantities of soft soaps are required for the textile industries who desire mostly a strong potash soap, and the large number of automobiles in use at the present time has opened a field for the use of a soft soap for washing these. A soap for this purpose must be neutral so as not to affect the varnish or paint of automobiles.
A suitable soap for textile purposes may be made as follows:
Red oil 80 parts House grease 20 parts Caustic soda lye, 36 degs. B. 3 parts Carbonate of potash 5-1/2 parts Caustic potash 23-1/4 parts
Olive oil, corn oil, soya bean oil, olive oil foots or cottonseed oil may replace any of the above oils. A large quantity of cottonseed oil will cause the soap to fig.
To carry out the process, the caustic potash and carbonate of potash are dissolved and placed in the kettle together with the soda lye, and the oils added. This is most satisfactorily accomplished by being finished the day before the boiling is begun. The next day the boiling is begun and water added to bring the soap up to the desired percentage of fatty acid, due allowance being made for the water formed by the condensation of the open steam in boiling. Care must be taken that the soap in the kettle does not swell and run over during the saponification. A good procedure is to use open steam for a period of about two hours, then close the valve and allow the saponification to continue without boiling, and repeat this until it is entirely saponified. After the saponification has been completed the soap is briskly boiled all day and the proper corrections made; that is, if too alkaline, more oil is added, and if free fat is present, more potash. About 2 per cent. carbonate of potash is the proper amount for a soap containing 50 per cent. fatty acid. The soap is sampled by allowing it to drop on a clean, cold glass surface. In so doing, the soap should not slide or slip over the glass surface when pressed thereon, but should adhere to the glass, or it is too alkaline. A sample worked between the fingers showing too much stringiness should have more strong potash and oil added. A sample taken out in a pail and allowed to cool over night will serve as a guide as to the body of the soap in the kettle. When the soap has thus been properly finished it is run into barrels.