782 SOaP.— Sopt.

with the glycerin and saline impurities always con-tained in the lyes, and which, as above stated, arenot removed from the soap.

From the great analogy which exists between sodaand potash compounds, it would be expected thatpotash soap would be separated from its solutionsby chloride of potassium, as soda soap is by chlorideof sodium. This, however, is not the case, as whento a solution of potash soap, procured by treatingoils or fats with caustic potash lyes, a considerablequantity of chloride of potassium is added, no separ-ation of soap takes place; the salt dissolves in thesoapy mixture, and the solution remains clear. Potashsoap can only be separated from the lyes and elimin-ated glycerin by adding strong potash lyes after thesoap is complete, and the excess of alkali and theglycerin may then be allowed to subside, and subse-quently be more completely removed by placing thesoap to drain. On the large scale, however, as beforeobserved, soft soap is never separated as above ; thesoap solution is boiled down until homogeneous andof a proper pasty consistence.

Soft soap is therefore practically a mixture ofpotash soap with more or less caustic lye, formingat ordinary temperatures a thick transparent jelly.Addition of salt converts it into hard soda soap.

The process of manufacture of soft soap is as fol-lows : the proportions of oil and lye being regulatedaccording to the strength of the latter, and the quali-ties operated upon at once varying with the greateror less capacity of the boiling caldron. The largerthe caldron the better and more economical. To beproperly proportional, the diameter should always begreater than their depth, and the pan should be onlyhalf filled with material, as the soap when boilingswells up considerably. In some soaperies thewhole of the oil and tallow is introduced at once,together with a portion of the lye, and the remainderof the lye is added after some hours’ ebullition; inothers, both the oil and lye are introduced gradually.The lye should indeed always be gradually added,and in small quantities at a time, spreading it super-ficially over the whole mass. As soon as the twoclear liquids, separately introduced, unite together,the whole becomes much thicker, and in some casesboils quietly, but in others swells up into froth. Inthe latter case it must be thrashed with a stirringpole, and dosed with a sufficient quantity of lye tolessen the commotion and prevent loss of the ma-terial by running over. The caldron requires to beconstantly watched while over the fire. If too muchlye is added at the commencement, no union iseffected between the oil and the alkali; and if thelyes are too strong they seize on the oil too rapidly,and instead of becoming thick and viscid, the massbecomes clotted. This latter inconvenience may beremedied by adding lyes of a lower degree of strength.If the lyes are not sufficiently strong, combinationensues so tardily that part of the superabundantwater must first be expelled by evaporation beforea perfect union between the oil and alkali can beeffected. The lyes used at the commencement ofthe operation are of specific gravity T06 to T08.

When combination is perfect and the great foam-ings have subsided, the pasty mass should becomeclear and transparent, and free from clots or granules,and no acrid taste should be perceptible. To ascer-tain if this be the case, a small sample is taken outand cooled. If it should not be of proper consist-ence and free from opacity, the boiling is continued,and after some time another sample is taken, and soon until the soap is properly finished. If the testsample thickens on cooling, has a brown colour, isperfectly homogeneous, and is not ropy when workedbetween the fingers, the soap is finished, and thefire should at once be withdrawn. A fair criterionof the quality of the soap is furnished by a peculiarphenomenon observable during its cooling; a littleopaque zoue forming around the test-portion takenfrom the caldron and placed on a glass plate for anassay, indicates perfect saponification, and is calledstrength. The absence of this zone denotes a defi-ciency in strength ; and when it vanishes soon afterhaving made its appearance, the soap is said to havefalse strength. When it comes in the best form thesoap is perfect, and may be secured in that state byremoving the fire, and then proceeding as subse-quently directed.

To allay the foaming and render the finished soapfit to be transferred to the barrels or casks withoutendangering its detergent quality or diminishing itscausticity, the soap should be cooled as rapidly aspossible. For this purpose a quantity of ready-madesoap—a ton or more, according to the size of thecaldron—is added to the hot mass. This, in melting,rapidly abstracts a portion of the heat of the recentlymade soap, until the degree of that and its own isuniform. The foaming having subsided, the soap isracked off into the barrels, in which it is sent away.In the manufacture of soft soap, it is better that theboiling should be for too long a time than for tooshort. Soap which is not sufficiently cooked changesand spoils, while the only disadvantage producedby excessive boiling is a diminution in the quantityof the product. The usual time requisite for acharge is six or seven hours; but varies with thestrength of the lyes, the temperature of the atmos-phere, and other incidental circumstances.

In Great Britain a small proportion of tallow isusually introduced as one of the materials for theproduction of soft soap. This addition is for thepurpose of producing the solid white granulationsof stearate of potash, termed figging, because thesoap then resembles the granular texture of a fig.Hence British soft soap presents the appearance ofa brownish transparent body, through which whitegrains are disseminated. These figged granulationsdo not usually make their appearance until two orthree weeks after the soap has been made, and dur-ing the hot summer months they do not appear at all.They are improperly considered to be a proof of thegood quality of the soap, and hence the figgedappearance is sometimes imitated by the admixtureof starch.

The Scotch process for manufacturing soft soap isas follows :—278 gallons of whale or cod oil, and