SOAP: is supposed to be of Celtic origin. Its first introduction to civilization took place after the invasion of Gaul by the Romans. During the 8th century, Italy and Spain were the centers of the industry. Five hundred years later, pre-eminence had been won by the soap-makers of Marseilles, France. To-day, the honors are evenly shared by the United States and several European countries. It is interesting to note that the first patent granted by the United States was in the interest of soap manu facture, protecting a method of making potash and pearl-ash devised by a Samuel Hopkins.
Soap manufacture on an extensive scale was greatly stimulated by Le Blanc's discovery in 1791 of the method of obtaining Caustic Soda from crude common salt. and by Chevreul's enlightening exposition of the true chemistry of soapmaking, half a century later. The Le Blanc method is still employed, though it has recently been largely superseded by the Solvay ammonia and Electrolytic processes.
The soaps of ordinary domestic use consist of fats or other oily substances, saponified by mixing with water and alkalies. The finest varieties are made from vegetable oils—olive, palm, cocoanut, peanut, cottonseed, etc.; the cheapest from ani mal fats, principally tallow. Common soap generally consists of tallow, blended with a varying proportion of vegetable oil—cocoanut for quick lather, oleo or cotton seed oil for mildness, etc.—as tallow alone discolors and hardens with age. Its cleans ing properties are attributable chiefly to the fatty acids into which the bulk of the fat is converted during manufacture.
For ordinary, or "hard," soap, caustic soda or soda-ash is the alkali employed. For Soft Soap, caustic potash is the chief alkali, only enough soda being used to give the product fairly stable consistence, the result being the retention of the glycerine and a large proportion of water.
By the most widely used method for the production of common soap—which is also the basis of the finer toilet and special soaps—the melted fat or oil is first boiled in caustic soda lye. As soon as it commences to emulsify, stronger lye is added—this being repeated from time to time as long as the lye is absorbed and until the soap is smooth and dry when pressed and has a slight persistent caustic taste. Boiling, with out further additions, is then continued until the mixture is nearly neutral again, then dry salt, brine, or, in some cases, caustic soda lye, is added to the paste and boil ing continued until "separation" begins to show. It is then allowed to cool, the crude soap forming on top and the spent lye—a mixture of crude glycerine, salt, alkali, etc.,—settling at the bottom and being run off. Next comes, in many cases, a fur
ther strengthening—the soap, together with a certain quantity of water, undergoing a prolonged boiling, caustic soda lye being added from time to time in the first stages. Another settling follows and the lye is again drawn off. The soap is then boiled, water being added to produce the right consistence, and is left to settle and rest for several days. The pans will then show four layers—the top is a thin soap which is taken off and sent back for further treatment ; second, is the good "settled" soap, constitut ing about 65% of the contents of the pan ; third, is a dark weak soap which is also worked over in various ways ; and at the bottom is a weak lye solution. The good settled-soap is ladled or pumped out, melted, cleaned, "crutched" or mixed, etc.— rosin, sodium of silicate, soda-ash, etc., being added in many cases—finally going into large frames, which consist of iron plates clamped together and set on wooden bot toms, fitted with wheels so that they can be easily taken to the cooling room. In four or five days, when the soap is cool enough to strip, the sides of the frames are undamped and the soap stands on the wooden bottoms in solid masses of half a ton or more. They are later cut, first into bars and then into squares, by machines with regulated wires.
Toilet Soaps of the better grades are generally known in the trade as Milled Soaps. Common soap of the best quality is chipped, dried by hot air and passed through rollers which blend and flatten the chips into thin sheets which are automatically cut into ribbons. The desired color is added, and the milling and cut ting are repeated two or three times. The perfume is then added and a final milling takes place. The product goes next to pressing machines and is later stamped or shaped in molds. A mixing machine which blends the "ribbons" together with the color or perfume, is frequently substituted for the second and subsequent milling processes. Milled soap contains less water and therefore lasts longer than other soap.
The perfumes employed in scenting soaps vary with the market grade of the product—from expensive natural oils to the cheapest of imitation and artificial essences (see PERFUMERY). Compound odors are, in all grades, more frequently employed than single odors.
Re-melted Soap is toilet soap produced by one of the older methods. The settled soap or soap basis is remelted, agitated, treated with a pearlash solution to make the product finer and smoother, and variously colored and perfumed.