SOAP. 



.\-aps are perfeftly infoluble. And fince any of the earths 

 have a ftrongcr attraiftion for oil than the alkalies, the alka- 

 line foaps are always decompofed by the earths. This occa- 

 fions the curdy appearance when foap is ufed with water 

 containing any eartliy or metallic fait. It is from this qua- 

 lity that waters are faid to be hard. 



The earthy foaps are of a greyilh-white colour, of a curdy 

 '.pcarance. The metallic foaps are of different colours, 

 •joth thefe and the earthy foaps are formed by adding a 

 folution of an alkaline foap to a folntion of an earthy or 

 metallic fait. A precipitate is formed, which is the foap to 

 be obtained. With a folution of iron containing the red 

 oxyd, the foap is of an orange-red colour. It has the con- 

 fiftency of a falve or plafter, but by expofure to the air it 

 becomes dry and friable, but may be foftened by heat. 

 When a fimilar folution of foap is added to a folution of ful- 

 phate of copper, a green foap is formed, which is a fluxible 

 mafs like wax. Corrofive fubhmate, treated in this manner, 

 gives a red foap. All the metallic oxyds mny be combined 

 with fat or oil in a fimilar way. 



Soap, in the ManufaBures and Domejlic Economy. This is 

 confined to foaps made with the fixed alkalies, combined with 

 different kinds of fat and oil. Thefe, in the manufacture 

 of foap, are divided into two principal varieties, viz. hard 

 and foft. 



I. Hard Soap. — The alkali employed for hard foap is 

 foda, generally obtained from the different fea vegetables, 

 and called by different names, according to the name of 

 the plant in different countries. Moft of the alg£, but 

 particularly the fucus and falfola, afford foda by burning. 

 The vegetables are iirit dried, and then burnt in pits formed 

 with loofe Clones. The earthy matter and the foda, with 

 fome neutral falts, fufe into a crude mafs, in which ftate it 

 is fold. This fubltance is furnifhed in great abundance from 

 the Highlands of Scotland, under the name oilelp, and from 

 Alicant in Spain, under the name of barilla. In France it is 

 known by the name of varec ; this being the name of the 

 plant from which it is generally produced there. 



It is commonly, however, in this ftate that it comes to the 

 foap-makcr, varying frequently in its value, and often occa- 

 fioning much uncertainty in its employment. It fhould be 

 the firlt bufinefs, therefore, of the manufafturer, to affay the 

 fubftance from which he gets his alkali, even before he pur- 

 chafes it. For this purpofe a given quantity fhould be 

 dried and weighed. After reducing it to powder, it mull be 

 treated with hot rain-water, till the water coming from it 

 has no tafte, referving all the portions of water added from 

 time to time. Concentrate this liquid by evaporation, till 

 the quantity of liquid is not more than three times the weight 

 of the quantity taken to be allayed. Now weigh out a 

 quantity of fulphiiric acid, fay half the weight of the affay. 

 From this quantity take fmall portions at a time, and add 

 them to the folntion above-mentioned, flirring it at the fame 

 time with a wooden rod. When the cfcape of gas begins to 

 diminifh on the addition of frefh acid, let the additional por- 

 tions be very fmall. Now take bits of paper flained blue 

 with litmus : on dipping one into the liquid, if more acid is 

 wanting, the paper will not be changed, but the moment 

 the paper is turned red by the liquid, ceafe to add ful- 

 phuric acid. Let the remaining acid be now weighed, in 

 order to know what has been ufed, and note this down. Now 

 take pure fal foda (carbonate of foda) in well-formed cryf- 

 tals, exaitly of the fame weight with the firft allay, and dif- 

 fohe it in three times its weight of pure water. Weigh out 

 the fame quantity of fulphuric acid as before, and jull fol- 

 low the fame fleps as above direfted, till the litmus paper jult 

 turni red, tkeu weigh the remaining acid, to obtain the quan- 



tity ufed, and note down as before. Then fay, as the acid 

 confumed by the fal foda is to that confumed by the affay, 

 fo is 100 to a number which will give the per centage of 

 carbonate of foda contained in the crude alkali. Thirty *<r 

 cent, of the carbonate of loda fo indicated will be real foda, 

 the only fubltance which combines with the fat to form foap. 

 When the exaft value of the alkali is known, it is then to be 

 treated as follows, to prepare it for mixing with the fat. 



The kelp or barilla is firft to be pounded, and then mixed 

 with one-fifth its weight of quickhme, in a large vat. Thefe 

 vats are generally three or four in number to each boiler. 

 They are frequently made with brick-work, from four to 

 five-feet cubes, but fometimes of caft-iron. Befides thefe vats 

 for the infufion of crude alkali, each of thefe has a fimilar 

 cavity under it. The bottom of the vat is even with the 

 ground, the under vat being funk below, and is intended to 

 receive the liquor which runs from a plug-hole in the upper 

 vat, when the infufion has gone on to a certain extent. One 

 of thefe vats, with its under refervoir, is fuflicient for one 

 boihng, but they are generally all at work, in order to give 

 time for the folution of the alkali from the crude mafs. 



In chara^ing a vat, the barilla, kelp, or potadi, and fome- 

 times mixtures of thefe, are firft coarfely powdered, and 

 mixed with quicklime alfo coarfely powdered ; fome water is 

 then thrown upon thefe to flake the lime. In the fide of the 

 vat fome ftraw is firft placed about the plug-hole, to prevent 

 bits from pafling through. The vat is now charged, and 

 water poured upon the materials till it ftands confiderably 

 above the folid mafs. After Handing feveral hours the plug 

 is withdrawn, to let out the folution into the lower refervoir. 

 The plug is now returned, and frefti water poured upon the 

 materials. Some or all the firft ley is now removed into one 

 of the other lower refervoirs before the fecond infufion is 

 drawn off. This is done, that the foap-boiler may always 

 have at command two leys of different degrees of ftrength, 

 as in the courfe of every boiling he finds it neceffary to ule 

 fometimes the weak and at other times the ftrong. 



The number of waters to be added to the materials de- 

 pends upon the judgment of the workman, who by his 

 tafte can tell when the water has diflblved the whole of the 

 alkali. The times of charging the vats are irregular with 

 rcfpedl to the times of charging the boiler. Some one of 

 the vats is conftantly employed, in order to infure a con- 

 ftant fnpply of the ley. 



The boilers are made to hold from about 20 to 25 cwt. of 

 foap ; they are made in two parts, the lower part being about 

 three feet in diameter, and the fame in length : under the 

 bottom of this the fire afts. The top part has a flange, to 

 which the upper part is fcrewed. The latter is nearly an 

 hemifphere, rifing above the floor juft fuflicient to allow the 

 workman to flir the foap when he ftands up. 



The ley being ready to lade out of tlie refervoir, which 

 is near to the boiler, the tallow or oil firft weighed is put 

 in. When it is fufficiently melted, the workman begins by 

 adding the ley, and Itirring the mixture. The alkali and 

 the oil foon begin to unite, forming a milky fluid. As more 

 ley is added, and the ftirring continued, the liquid thickens. 

 This is continued generally for 30 hours, and frequently 

 more, till fmall portions of the foap, taken out from time 

 to time, affitme a proper confiflence, which the workman 

 by conftant experience undcrltands. He now adds a quan- 

 tity of common fait, which has the effeft of feparating the 

 watery part from the foap, which contains a portion of 

 neutral falts, that exifted in the crude alkali, and fometimes 

 alfo free alkali, cfpecially when more than enough has been 

 added. The fire is now to be withdrawn, and the mafs left 

 to ceol. The watery part will be found at the bottom, and 



requires 



