The frame-moulds for hard soap are composed of strong wooden bars, made into the form of a parallelogram, which are piled over each other, and bo'tnd to gether by screwed iron rods, that pass down through them. A square well is thus formed, which in large soap facto ries is sometimes 10 feet deep, and ble of containing a couple of tons of soap.
Mr. Sheridan some time since obtained a patent for combining silicate of soda with hard soap, by triturating them to gether in the hot and pasty state with a crutch in an iron pan. In this way from 10 to 30 per cent. of the silicate may be introduced. Such soap possesses very powerful detergent qualities, but it is apt to feel hard and be somewhat gritty in use. The silicated soda is prepared by boiling ground flints in a strong caustic ley, till the specific gravity of the com pound rises to nearly double the density of water. It then contains about 35 grains of silica, and 46 of soda-hydrate, in 100 grains.
Hard soap, after remaining two days in the frames, is at first divided horizontally into parallel tablets, 3 or 4 inches thick, by a brass wire ; and these tablets are again cut vertically into oblong nearly square bars, called wedges in Scotland.
Dr. Ure examined several soaps, and found their composition somewhat differ ent. For instance : The foreign Castile soap of the apothe cary has a specific gravity of and consists of— Soda' 9 Oily fat 76'5 Water and coloring-matter 14'5 1001 A perfumer's white soap was found to consist Of— Soda 9 Fatty matter 75 Water 16 100 A London cocoa-nut oil soap was found to consist of— Soda 4'5 Cocoa-nnt lard 2210 Water 73•5 100• This remarkable soap was sufficiently solid ; but it dissolved in hot water with extreme facility. It is called marine soap, because it washes linen with sea water.
A poppy-nut oil hard soap consisted of— Soda Oil 76 Water 17 100 Soft soap.—The principal difference between soaps with base of soda, and soaps with base of potash, depends upon their mode of combination with water.
The former absorb a large quantity of it, and become solid ; they are chemical hydrates. The others experience a much feebler cohesive attraction ; but they re tain much more water in a state of mere mixture. From its solubility, more alka line reaction, and lower price, potash soap is preferred for many purposes, and espe cially for scouring woollen yarns and stuffs.
Soft soaps are usually made in this country and in England with whale, seal, olive, and linseed oils, and a certain quantity of tallow ; on the continent of Europe, with the oils of hempseed, se same, rapeseed, linseed, poppy-seed, and calza ; or with mixtures of several of these oils. The potash leys should be made perfectly caustic, and of at least two different strengths ; the weakest be ing of specific gravity 1.05; and the strongest, P20, or even 1-25. A portion of the oil being poured into the pan, and heated to nearly the boiling point of wa ter, a certain quantity of the weaker ley is introduced; the fire being kept up so as to bring the mixture to a boiling state. Then some more oil and ley are added alternately, till the whole quantity of oil destined for the pan is introduced. The ebulition is kept up in the gentlest man ner possible, and some stronger ley is occa sionally added, till the workmen judge the saponification to be perfect. The boiling becomes progressively less tumultuous, the frothy mass subsides, the paste grows transparent, and gradually thick ens. The operation is considered to be finished when the paste ceases to affect the tongue with an acrid pungency, when all milkiness and opacity disappear, and when a little of the soap placed to cool upon a glass-plate assumes the proper consistency.
The exports of American soap and tal low candles were for 1847 and 1848 re spectively, of the value, in 1847 $606,798 1849 $670,223