In curd soaps, however, which form the basis of most household soap, the uncombined alkali and the glycerin are separated by " salting out, " and the soap in this condition contains about 30% of water.
Curd soap and London grey mottled are prepared from kitchen or ship fat, whilst fuller's fat is employed in the manufacture of soft soaps.
(See under Curd Soap.) Curd Soap. - This variety is manufactured by boiling the fat with alkali and removing the unused lye, which is afterwards worked up for glycerin.
But in all countries a mixture of several oils enters into the composition of curd soaps and the proportions used have no fixity.
The contents of the pan are once more allowed to cool and settle, and the soap as now formed constitutes a pure curd coap, carrying with it some proportion of uncombined alkali, but containing the minimum amount of water.
In this way curd, mottled or marbled soap is formed, and such mottled appearance was formerly highly valued as an indication of freedom from excess of water or other adulteration, because in fitted soaps the impurities are either washed out or fall to the bottom of the mass in cooling.
Being thus soluble in salt water it cannot, of course, be salted out like common soaps; but if a very concentrated salt solution is used precipitation is effected, and a curd soap is separated so hard and refractory as to be practically useless.
Coconut soap also forms a principal ingredient in compound soaps meant to imitate curd and yellow soaps.
According to the second plan, the ordinary oil is treated as for the preparation of a curd soap, and to this the coconut soap separately saponified is added in the pan and both are boiled together till they form a homogeneous soap.
This property is usually obtained by mixing soft and hard soaps, or, more rarely, by adding gum tragacanth to a hard soap. In the textile trades the wool scourer employs a neutral olive-oil soap, or, on account of its cheapness, a neutral curd or curd mottled brand; the cotton cleanser, on the other hand, uses an alkaline soap, but for cleaning printed cottons a neutral olive-oil curd soap is used, for, in this case, free alkali and resin are objectionable; olive-oil soap, free from caustic alkali, but often with sodium carbonate, is also used in cleansing silk fibres, although hard soaps free from resin are frequently employed for their cheapness.
Soft or green soap (potassium oleate), made by acting on olive oil with caustic potash, is also used; its preparation (Linamentum saponis) is known as opodeldoc. Curd soap is also used, and is chiefly a stearate of sodium.
Medicated soaps are made by adding the drug to either hard soap or curd soap in the desired proportions.
For sodii arsenas and cacodylate see Arsenic. Sapo durus (hard soap) is a compound of sodium with olive oil, and sago animalis (curd soap) is chiefly sodium stearate.
When about too lb of silk has been bagged, the whole is placed in a large wooden tub and covered with boiling water in which 12 to 20 lb of white curd soap has previously been dissolved.
A similar cement is a mixture of dried fresh curd with i nth of its weight of quicklime and a little camphor; it is made into a paste with water when employed.
Dairy produce is important in Afghan diet, especially the pressed and dried curd called knit (an article and name perhaps introduced by the Mongols).
Of Kan-suh are cloth, horse hides, a kind of curd like butter which is known by the Mongols under the name of wuta, musk, plums, onions, dates, sweet melons and medicines.