846 SOAP 



resulting soft soap was converted, in the course of the process, into hard soap, by the 

 introduction of muriate of soda, or weak kelp-lyes, in sufficient quantity to furnish 

 the proper quantity of soda by the reaction of the potash upon the neutral salts. J3ut 

 the high price of potash, and the diminished price, as well as improved quality of the 

 crude sodas, have led to their general adoption in soap-works. 



The first step in the production of soap consists in obtaining a solution of soda, or 

 what is termed caustic lye. For this purpose a given quantity of the soda-ash above 

 alluded to, is stratified with a quantity of recently-burnt quick-lime, in tanks of 

 wrought-iron, or cylindrical cast-iron vats, from 6 to 7 feet wide and from 4 to 5 feet 

 deep, the lowest layer being, of course, quick-lime. These vats have frequently a 

 false bottom, perforated with holes, or else a coarse piece of matting is placed over 

 the plug-hole, placed at the bottom of the said vats or tanks, which plug-hole is, of 

 course, closed generally by a wooden plug. Water is then poured upon the whole mass 

 until the tanks are full, and the whole is allowed to stand for twelve or eighteen hours. 

 The plug being then withdrawn, the saturated solution of caustic soda flows down 

 into a reservoir placed beneath, after which the plug is replaced, more water applied, 

 and this operation is repeated five or six times, until, in fact, the soda is almost 

 entirely extracted ; the various liquors thus obtained, in a clear and caustic state, 

 after infiltration through the beds of lime, being conveyed to separate and distinct 

 reservoirs, distinguished from each other by the names of first running, second running, 

 and so on ; the last, being, of course, the weakest. 



Having in this way produced a series of caustic lyes of different degrees of strength, 

 about 200 gallons of the weakest, which has a specific gravity of about 1'040, is 

 pumped into the soap-pan or boiler, or copper, as it is called, though generally made 

 of cast iron, and about 1 ton of tallow is added ; heat is applied, and after a gentle 

 ebullition of about four hours, it will be found that the lye will have lost its causticity, 

 or, in technical language, that it is killed, and that the fat is saponified, which is known 

 by taking a portion of the mass on a trowel, when it will be observed that the liquid 

 separates at once from the soapy mass, which it leaves in streaks on the towel. The 

 lyes thus used at first, if composed of pure soda, would contain about 4 per cent, of 

 alkali, but from the presence of neutro-saline matter they seldom contain as much as 

 2 per cent. ; in fact, a gallon may be estimated to contain not more than 2 ounces, so 

 that 200 gallons contain 25 Ibs. of real soda. The fire being withdrawn, the whole is 

 now allowed to cool and remain at rest for about one hour, until the lye, now deprived 

 of ibs alkali, and therefore, called spent lye, settles to the bottom of the copper. This 

 spent lye contains a portion of glycerine derived from the fat or tallow, together with 

 the sulphate of soda and common salt of the soda-ash, and is pumped off by means 

 of an iron pump, which is lowered down into the lower pan of the soap-copper, 

 a practice which might be advantageously replaced by opening a cock which might 

 be placed at the bottom of the copper, but which is retained as a remnant of that 

 abominable system of excise, which did not permit the spent lyes to be otherwise 

 withdrawn, as the excise laws forbade any cock or aperture being placed or made at the 

 bottom of soap-coppers. This constitutes what is called an operation. A second 

 similar charge of lye is now introduced into the pan along with a fresh quantity of 

 tallow or of grease, and a similar boiling process is again repeated. Three or four 

 such boilings may be practised in the course of a day by an active soap-boiler, with 

 lyes of gradually-increasing strength. Next day the same routine is renewed with 

 stronger lyes, and so progressively until towards the sixth day the lye may have the 

 density of 1-160, when a period arrives at which it will be found that the whole of the 

 tallow or fat is completely saponified, that is to say, has combined with its full equi- 

 valent of soda. This point is well known to the workmen by the consistency of the 

 compound ; in effect it is sufficient to take a portion of the mass on a trowel, and 

 to squeeze a little of the mass between the forefinger and thumb ; if not quite and 

 thoroughly finished it will still have a greasy feel, but if done it will on cooling 

 readily separate from the skin in hard scales ; neither has it the taste peculiar to 

 grease. A more certain mode, however, especially for those who have not acquired 

 sufficient practice, is to decompose a portion of the saponified or partly-saponified 

 mass with an acid, and to ascertain whether the grease is wholly soluble in boiling 

 spirits of wine, for if it is not thus wholly soluble, the saponification is imperfect. 

 The addition of common salt for the separation of the spent lyes is essential to the 

 proper granulation and separation of the soap, for otherwise the tallow and the lye 

 would unite into a uniform emulsion, from which it would be very difficult after- 

 wards to separate the spent lye ; but as soap is quite insoluble in a solution of common 

 salt, the partly-saponified mass is thus brought to float on the surface, so that the 

 spent lye precipitates to the botttom, whence as we said, it is pumped off. 



Assuming, however, that a perfect result has been secured, the soap has now to be 

 brought to a marketable condition, and for this purpose it is boiled with a quantity of 



