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the steam from the generator to the rotating arms.The lower end of the shaft is also hollow in thecentre to a height of several inches above the bottomof the pan, for the purpose of communicating
between the exit ends of the branches and thewaste pipe, l.
The gearing by which the twirl is made to revolveis shown at iij. The superheated steam passes
Fig. 3.
Fig. 2.
r^-n—■
e e
from the feed-pipe, K, down into the tubular armsof the twirl, which twirl being made to revolvesimultaneously by power applied to the gearing, ii j,the stirring and heating of the contents of the pango on uninterruptedly together.
W. Gossage of Widnes thus describes the methodof making English hard soaps:—The manufacturerprovides himself with solutions of caustic soda ofvarious strengths, called lyes, these being obtainedby boiling together a solution of carbonate of sodaand slaked lime, running off the first solutions andwashing the residual carbonate of lime with severalaffusions of water; the last liquors thus obtainedbeing used for dissolving a fresh batch of carbonateof soda.
It is a well known fact that lime, in whateverproportion it may be used, does not effect the per-fect decomposition of carbonate of soda, unless thelatter is present as a weak solution. And as anyalkali in the state of carbonate which may be intro-duced into the soap-copper is incapable of decom-posing the neutral oils or fats, it becomes wasted;therefore the manufacturer uses solutions of car-bonate of soda of such strength as will yield lyes(solutions of caustic soda) having a specific gravitynot exceeding 1-090.
The manufacturer charges his soap-pan at thecommencement with a quantity of neutral fat or oil,and adds to this weak lyes having a specific gravityof about 1-050. He causes steam to be injected toproduce ebullition and mixing. If the process goeson properly the oil or fat which was previouslyfloating on the surface of the lye becomes speedilycombined with it, producing a uniform milky emul-sion, from which no watery particles separate oncooling. If this combination does not take place,the operator adds either water or weaker lye, and
continues the boiling until a perfect emulsion isproduced. At this period all taste of alkali in thiscompound has passed away—the tongue being usedby the operator in place of turmeric paper to ascer-tain the presence of free alkali. The combinationof the oil or fat with the mineral alkali, or the dis-placement of the glycerin, having been thus fairlyput in progress, the operator makes repeated addi-tions of stronger lyes, continuing the boiling untilhe finds the presence of free alkali in the compound;he then adds more oil or fat, or some rosin (if he ismaking soap containing rosin); he also continues tomake repeated additions of stronger lyes. In thispart of the operation he takes care there shall beno excess of alkali present in the compound at theperiod when the soap-pan has become nearly filledby the repeated addition of oils and fats and lyes,lie then adds common salt to the mixture, which byits superior affinity for water, as compared with thatof the saponaceous compound, effects the decompo-sition of the emulsion, and causes this to be sepa-rated into soap combined with a definite quantity ofwater, but not having its full proportion of alkali,and a solution of common salt—which latter con-tains the glycerin of the fats or oils employed. Thesoap floats in a granulated state on the surface ofthe solution, which is then called “ spent lyes,” andshould contain no free alkali.
After a few hours for subsidence the exhaustedsolution or spent lye is withdrawn from the soap-pan, from under the imperfectly-made soap, and isrejected as worthless.
The workman commences his second operation bythe addition of some weak lye to the imperfect soap,and by boiling he brings the contents of his pan