This is made of tallow only, in the propor tion of 16 cwt. of tallow to 200 gallons of ley, which is boiled with a moderate fire for about two hours, and the fire being withdrawn, is left to settle for another two hours, and then the ley pumped off. As the ley separates quickly from curd soap, two or three boils a day may be given with care, until the soap appears something like a curdy mass, and when pressed between the finger and thumb forms a thin, hard, clear scale, not sticking to the finger. Then, withdraw the fire, add a few pails of cold ley, and when settled pump the ley clean off. The soap is purified by melting it over again with a fresh supply of water repeating the process until it has not the slightest blue cast. The moulds for white curd soap should be lined with coarse cloth, and covered with matting, after the soap has been put into the moulds, and well stirred, in order that it may cool slowly and uniformly. A cwt. of tallow is computed to make 3 cwt. of white curd soap, but it is seldom that so much can be obtained. The ley is usually made of 3 cwt. of potash with 3 cwt. of so da, but kelp is sometimes used, and as it contains much sulphuretted hydrogen and oth er impurities, the water pumped off will be of a dark bottle-green color. White curd soap, scented by adding some oil of caraway seeds, just before it is poured into the moulds, makes Windsor soap.
This article was originally published with the title "White Curd Soap" in Scientific American 8, 28, 218 (March 1853)