SOAP 845 



We said that by boiling fats or oils with an aqueous solution of potash or of soda 

 a solution of soap "was produced. The object of the soap-maker is to obtain the soap 

 thus produced in a solid form, which is done by boiling the soapy mass so as to 

 evaporate the excess of water to such a point that the soap may separate from the 

 concentrated liquor and float on the surface thereof in a melted state, or by an 

 admixture of common salt, soap being insoluble in lyes of a certain strength or degree 

 of concentration, and in solutions of common salt of a certain strength, the glycerine 

 remaining, of course, in solution in the liquor below the separated soap. Such is the 

 theory of soap-making ; but the modus operandi followed by practical soap-makers 

 will be described presently. 



On the Continent olive oil, mixed with about one-fifth of rape oil, is principally 

 used in making hard soap. This addition of rape oil is always resorted to, because 

 olive oil alone yields a soap so hard and so compact that it dissolves only with 

 difficulty and slowly in water, which is not the case with rape oil and other oils of a 

 similar nature, that is to say, with oils which become thick and viscid by exposure, and 

 which on that account are called drying oils, experience having taught that the oils 

 which dry the soonest by exposure, yield with soda a softer soap than that made with 

 oils which, like olive oil, remain limpid for a long period under the influence of the 

 air. The admixture of rape oil has, therefore, the effect of modifying the degree of 

 hardness of the soap, and, consequently, of promoting its solubility. In England tallow 

 is used instead of olive oil ; the soap resulting from its treatment with soda is known 

 under the name of curd soap, and is remarkable for the extreme difficulty with which 

 it dissolves in water. The small, white, cubic, waxy, stiibborn masses, which until a 

 few years ago were generally met with on the washing-stand of bedrooms in hotels, 

 and which for an indefinite period passed on from traveller to traveller, each in turn 

 unsuccessfully attempting, by various devices and cunning immersions in water, to coax 

 it into a lather, is curd soap. Rape or linseed oil, added in certain proportions to tallow, 

 would modify this extreme hardness and difficult solubility, but it is now the general 

 practice to qualify the tallow with cocoa-nut oil, an oil, which, converted into soap, has 

 the property of absorbing incredible quantities of water, so that the soap into the 

 manufacture of which it has entered lathers immediately. Cocoa-nut oil, however, 

 acquires by saponification a most disagreeable odour (due to the formation of caprylic 

 acid), which it imparts to all the soaps in the manufacture of which it enters, an odour 

 which persists in spite of any perfume which may bo added to mask it. 



The admixture of one-fourth or one-fifth of resin with tallow, in the process of 

 saponification, modifies also the hardness and considerably increases the solubility of 

 curd soap, and this, in fact, constitutes the best yellow soap. 



It has been said above that soap was more or less hard in proportion as the melting- 

 point of the fats employed in its manufacture was higher or lower. There are cer- 

 tain fatty substances, technically called ' weak goods,' such as kitchen fat, bone-fat, 

 horse oil, &c., which could hardly be used alone, still less with resin, the soap which 

 they yield being too soft, and melting or dissolving away too rapidly in the washing- 

 tub. This led the writer to think, that if a means could be devised of artificially 

 hardening soap, a larger class of oleaginous and fatty substances could be rendered 

 available, at any rate to a greater extent than they theretofore had been, and that, by 

 thus extending the resources of the soap-boiler, he should be enabled to produce a good 

 and useful soap from the cheapest materials, and thus convert soaps of little com- 

 mercial value into useful and economical products. 



In making experiments with this view, he found that the introduction of a small 

 quantity of melted crystals of sulphate of soda into the soap answered the purpose 

 admirably, and that the salt in recrystallising, imparted to the soap, which other- 

 wise would have been soft, a desirable hardness, and prevented its being wasted 

 in the tub. The iise of sulphate of soda acts, therefore, inversely, like the addition 

 of rape oil, or linseed oil, or of resin to tallow, in the manufacture of soap. This 

 process, which was patented in 1841, has been, since the removal of the duties on 

 soap, extensively employed by soap-makers, and continues to be highly approved 

 of by the public. We shall describe further on the manner of practising this process, 

 and the further improvements which were made to it in 1855. 



Of the manufacture of hard soap. The fat of this soap, in the northern countries 

 of Europe, is usually tallow, and in the southern, coarse olive oil, Different species 

 of grease are saponified by soda, with different degrees of facility ; among oils, the 

 olive, sweet almond, rapeseed, and castor oil ; and among solid fats, tallow, bone- 

 grease, and butter, are most easily saponified. According to the practice of the United 

 Kingdom, six or seven days are required to complete the formation of a pan of hard 

 soap, and a day or two more for settling the impurities, if it contains resin. From 

 12 to 13 cwts. of tallow are estimated to produce one ton of good soap. Several years 

 ago, in many manufactories the tallow used to be saponified with potash-lyes, and the 



