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be applied, it is effected by the addition to thesolution of the silicate of sulphuric or hydrochloricacid, previously to its reduction to the viscous con-dition. The mixed silicated soaps may be obtainedof any requisite degree of hardness by the greateror less concentration of the solution of soluble glass.The compound soaps produced by the above pro-cess are possessed of valuable detergent properties,independently of the real soap contained in them.
Sheridan's Process .—Calcined flint, quartz, or sandis used for the production of soluble glass. Ifsand is the silicious ingredient, it is mixed withcarbonate of soda in the proportion of 1 part ofsand to 3 of soda, and the mixture is then fused ina reverberatory furnace. The product of calcinationis drawn out into water and dissolved by the aid ofheat. Thus far the process resembles that of W.Gossage. Sheridan, however, now passes a currentof carbonic acid through the solution of silicate ofsoda, whereby the silica is displaced from com-bination and precipitated in a gelatinous form.From this the liquid containing the soda, recon-verted to the state of carbonate, is withdrawn,and evaporated to dryness for use again; theprecipitated silica is mixed with caustic soda orpotash lye of specific gravity 1T515 = 30° Twaddell,and boiled for eight hours, with constant stirring,until it becomes a homogeneous mass.
Pami's Process .—The apparatus employed is re-presented in section, Fig. C. The boiler, b, shouldbe furnished with a man-hole, safety valve, a ther-
Fig. 6.
mam
JlliUfcL;
Jllilll. _I
mometer plunged into a mercury chamber, and allthe ordinary appendages of such an apparatus. Ais the feed-pipe, and c the pipe through which todischarge the finished product. The crushed flintor quartz to be combined with the soap is mixedwith caustic soda or potash lye, in the proportionof 1 cwt. of silica to 100 gallons of lye of specificgravity 1T6 = 32° Tw., and introduced into thesteam-tight boiler. The fire is then kindled, thevalve being so regulated as to allow the tempera-ture of the materials to rise gradually to about 310°Fahr.. or at a pressure of 50 to 70 lbs. to the square
inch. When it has remained at this temperaturefor about three or four hours, the contents are dis-charged and cooled down. The solution of silicateof potassium or sodium thus obtained is added inthe proper proportion to the soap paste, either inthe caldron or frame after the saponification is com-plete, and before the soap becomes too cold.
J. P. Wat’s silicated soap is prepared from asilicious earth found in Surrey, which containsmuch soluble silica. A steam pan is used. Intothis a soda lye is run of about 18° Tw. Thesilicious earth, ground to powder or broken intosmall pieces, is then added by slow degrees untilthe alkali has taken up as much as it will dissolve.The heat is now withdrawn, and the undissolvedearthy matter allowed to settle. The clear liquor isrun off, and the sediment washed.
In making soap the proportions used are 11-5 percent, of palm oil, 1T5 per cent, of cocoa-nut oil,30'6 per cent, of soda lye of 36° Tw. The whole isboiled until the soap becomes stiff, upon which44 per cent, of silicate of soda (prepared as justdescribed) of 36° Tw. is added, and the boilingcontinued till the soap becomes thin and limpid, atwhich stage 2‘4 per cent, of common salt is added,and the soap boiled for three or four hours longer.It is then ready to cleanse. This may be done atonce, or after it has been allowed to stand for a fewhours. If open steam is used—that is, steam blow-ing into the pan—the silicate solution and lye requireto be somewhat stronger.
Marseilles Soap. —This variety of soap is pro-duced by the saponification of olive oil alone. Theprocess does not materially differ from that describedfor white soap. The duration of the operation islonger or shorter according to the quality of the oil.Some manufacturers use, in the fabrication of thissoap, a certain proportion of poppy, or other seedoil, with the olive oil; and the addition is ratherbeneficial than otherwise, as the soap produced isless hard, and consequently more easily applicableto detergent purposes. It is at present manufacturedon a considerable scale in this country.
The value of this oil for soap-making increases asit is less coloured, and is in proportion to the amountof stearin it contains. The oils of Provence aremost highly esteemed.
The lyes used are of three strengths, the weakestis 4° to 5° B., the next strong 10° to 15° B., and thestrongest 20° to 25° B. These lyes are kept inbrickwork cisterns until required for use. Puresoda is used for the first lye boiling, in order thatno common salt may be introduced at this stage.
The saponification is begun in two boilers at thesame time, and the contents of both are joined forthe finishing operation.
The arrangement of one form of the apparatus isshown in the annexed section, though steam pansare now sometimes employed if superheated steamis accessible.
The bottom of the boiling pan, a (Fig. 7), is ofcast iron or copper; the sides are composed of brick-work, lined with cement, to resist the action of