Soap
3 of the 7 encyclopedias on this shelf carry an entry for Soap. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
strictly speaking, a salt consisting of a fatty acid in combination with a metallic base. In common parlance, however, the term is applied to the soluble salts formed by the union of the fatty acids with the alkalies. If oil and water be shaken together mechanical union will take place; but on allowing the mixture to rest, the oil will gradually separate and float on the surface of the water. If a small quantity of caustic soda or potash be added to the mixture, and it be then agitated, union will take ies, a milky place between the three bodies Auid being formed. If a sufficient quantity of alkali has been added, and the solution be boiled, it gradually becomes clear, giving rise to a soapy fluid, which froths strongly on agitation, presenting all the properties of a solution of soap. If to a portion of this clear liquid a strong solution of common salt is added, a peculiar curdling is produced. The liquid separates into a clear fluid, containing glycerin, while the curdy portion rises to the surface. This substance is the fatty acid of the oil, in combination with the alkali used and a certain proportion of water, and if pressed and dried, exhibits the properties of ordinary soap. Ordinary soaps are of two kinds, soft and hard. Soft soap is a combination of some fatty or oily substance with potash, and contains an excess of alkali; hence it is used for cleansing purposes where very highly detergent powers are required. The hard soaps are combinations of the fatty acids with soda; the principal varieties being yellow soap, made from tallow and palm oil, and containing a certain proportion of resin to give it lathering properties; curd soap, which is made from tallow, only a small portion of olive oil or lard being added, to give it softness; mottled soap, which is prepared from tallow, palm oil, and kitchen stuff, and contains a portion po of insoluble iron soap giving it a marbled appearance. Marseilles and Castile soaps are made of olive oil and soda, a small quantity of sulphate of iron and sulphuretted lye being added to them while in a pasty condition. The object of marbling soap with an insoluble matter is to show that they contain but little moisture, since, if too large a proportion of water were present, the coloring matter would sink to the bottom and remain there, instead of being diffused through the mass. The United States stands at the head of all other countries in the use if not in the manufacture of soap. New York, Illinois, New Jersey, Ohio and Pennsylvania lead, in the order named, all other states. Over 2 billion pounds of hard soap (including about 170,000,000 pounds of toilet-soap) are annually produced and 57,000,000 pounds of soft soap.
Aiton's Encyclopedia (1910)
a well known household article used for cleansing and washing. Soaps differ greatly in appearance and quality, but all alike are made of some fatty substance compounded with potash or soda. Old-fashioned soft soap may be made of wood lye, leached from the ashes preferably of some hard wood, as maple, hickory, oak, or beech, and scraps of fatty matter from the kitchen. There are almost as many soaps as oils. Laundry soaps are made usually from tallow or cotton-seed oil. Yellow soaps owe their color to a certain addition of rosin, which is not only cheaper, but rather improves the quality of the soap. White soaps are made usually from tallow, palm oil, or cocoanut oil. Castile soap is made from olive oil, with the addition usually of oil of cocoanut. A mottled appearance is produced by the addition of some coloring material. Palm oil makes an excellent toilet soap. Soap is made usually in a large mass in vats or kettles, and is cut into cakes of the required size by wires. These cakes are then pressed in a mold, provided usually with lettering by way of a stamp. The finger soaps are made with especial care. Their delicate odor is imparted by the admixture of some volatile oil by way of a perfume. Transparent soaps are made by dissolving a toilet soap in alcohol. The solution is then poured off, leaving the dregs behind. When the alcohol is distilled, the residue, consisting of the soap, is beautifully transparent. Many soaps are made transparent also by the addition of glycerine well stirred in. Scouring soaps are common strong laundry soaps with a grit secured by an intermixture of finely powdered sand, glass, or pumice stone. The making of soap and the making of candles have long been linked. Fat the chandler could not use for candles he turned into soap. The common grades of American soap are now turned out as a by-product of the great packinghouses. Someone has said that the general use of soap is an index of advanced civilization. In 1900 the United States soap and candle manufacturers turned out $53,231,017 worth of products. There were 558 establishments. Small manufacturers are being forced out of the business by the larger concerns. An attempt to form a British soap trust was foiled in 1906 by the refusal of the British public to buy soap not bearing the stamp of an independent maker. See Potash ; Oil
The Encyclopedia of Founding (1892)
The alkalies used for soap-making are potash and soda. They must be in a caustic state, and this is produced by dissolving them and passing the solution through newly slacked lime, which takes away the carbonic acid. In this caustic lye the fats are boiled, their glycerine set free, and the soap formed in a state of solution in the water. The soap is obtained in the solid form by boiling this solution until the soap ceases to be soluble and rises to the surface, when it is drawn off into moulds. Castile-soap is composed of olive-oil and soda; oxide of iron is the cause of its mottled appearance. See OILS; PANS; SOAP-KETTLE.