SOAP.— Materials Used.

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Historical Notice. —Although the word soap, orrather sope, is occasionally met with in the transla-tion of the sacred records, it must not be supposedthat the substance now known by that name wasused by the Israelites . The word so rendereddoubtless refers to the juice of some plant, or moreprobably to the ashes of a plant; as the substancein question appears to have detersive properties.The earliest mention of the term soap, as applied tothe substance now under discussion, occurs in thewritings of Pliny , who also describes a process forits preparation differing but little from that pursuedat the present day. This writer ascribes its inven-tion to the Greeks, from whom the Romans, andsubsequently other nations, derived a knowledge ofits manufacture. Homer makes no mention of soap,and it was doubtless unknown to him. In the exca-vations at Pompeii a complete soap-boiling estab-lishment was discovered, containing soap still perfect,though it must have been prepared upwards of seven-teen hundred years.

The Germans were at a very early period distin-guished for their production of superior soap, andhence probably the Latin term sapo, from the originalGerman seipe, now written seife, and from this by atransposition of letters the English soap is derived.Owing in a great measure to natural advantages ofthe country, France is now a great mart for soap,and especially for toilet soaps.

Materials. —The materials used in the manufac-ture of soap are various kinds of oil or fat, resin,and the alkalies, potash and soda. All oils and fatsof whatever kind, vegetable or animal, yield soapswhen treated with alkali. Only a very limitednumber, however, is used in this manufacture. InGreat Britain palm oil is consumed in greaterquantity than any other, and principally in theproduction of hard soap ; for soft Soaps , the variouskinds of fish oils, the drying oils from seeds, andtallow are mostly employed.

In France , and on the Continent, olive oil isextensively used in soap-making; for soft soapshemp-seed oil.

Tallow, saponified with soda, yields white curdsoap ; this is superseded in great part by the softerand otherwise superior palm-oil soap. Cocoa-nutoil soap, on account of its property of dissolvingpretty readily in salt water, is useful for washingduring long sea voyages. Of all soaps the mostemollient are those of palm oil, castor oil, and ofspermaceti.

Most of the oils and fats are met with in com-merce in a sufficient state of purity for their con-version into soaps without previous preparation.

Palm oil, however, and occasionally tallow, areexceptions to this rule, and therefore the methodsmost effectual for their purification before beingused in the manufacture will be afterwards stated.

The mixture of oleic acid with small quantities ofstearic and margaric acids, which is obtained in theseparation of stearic acid by pressure, affords anexcellent soap.

Experiments were made by Darcet, Lelievre,

and Pelletier, on the relative value of differentkinds of oil and fat in the manufacture of soap.The oils or fats were saponified by means of causticsoda lyes, and the products were, therefore, sodasoaps. The results of these experiments were asfollows:—■

Olive-oil soap. —3 lbs. of olive oil gave a block ofsoap weighing 6 lbs. 10 ozs., which on exposure tothe air for two months became 4 lbs. 15 ozs. It wasthen dry and perfectly solid, of excellent colour,resembling that of Marseilles soap. By furtherexposure in a dry place it became still lighter, owingto loss of water.

Sweet almond-oil soap was found to be next to theolive-oil soap in consistency. This was very white,uniform, and of an agreeable odour. Its weightfrom 3 lbs. of oil was 5j lbs.; and after two month’sexposure it lost 1 lb. of water.

Rape-seed oil soap is of a greyish-yellow hue, ismore consistent than that of colza oil, and pos-sesses the peculiar odour of the oil from which it isproduced.

Oil of beech-nut soap is of a dirty-grey colour,softer than the preceding, and has the smell of theoil. This soap is greasy, pasty, and clammy, andwhen exposed to the air becomes yellow.

By associating these oils with proportionate quan-tities of suet or tallow, mixtures will be formed, ofwhich soaps of proper quality and consistence canbe made.

Poppy oil. —The soaps made from this oil are of adirty grey, without any disagreeable smell; areclammy, and of medium consistence. They becomeyellow in the air, and when exposed to cold be-come soft at the surface. This oil, when mixedwith the greases, yields a soap much resembling inappearance that of olive oil.

Hemp-seed oil soap is of a green colour, very pasty,and so soft that the least addition of water rendersit liquid. Exposed to the air, it loses its green tintexteriorly, bleaches, and afterwards becomes brown.Nut-oil soap is of a yellowish-white colour, with butlittle consistence, is greasy and clammy, and assumesa brown appearance on exposure. Linseed oil yieldsa whitish soap, which, however, becomes yellow bycontact with the air. This soap is greasy, pasty,and viscous, of a slight consistence and powerfulodour, and is reduced to a thin paste by a slightaddition of water. Sperm-oil soap is of a dirty-greycolour. It retains the peculiar smell of the oil,becomes reddish-brown and of some firmness, butmuch less than olive-oil soap.

Fish oil is very similar to the last named.

Cod - liver oil soap differs only in having a moreunpleasant smell and less consistency.

Suet or tallow soap is white and solid, and has a slightodour of the fat. Exposed to the air, it loses waterand becomes brittle. Soap prepared from lard isvery white, solid, inodorous, and especially valuablefor the production of toilet soaps.

Rancid butter yields a soap which is white, and inproperties similar to tallow soap, but retains a rancidsmell.