SOAP. 



requires to be pumped out by a pump, which is a fixture 

 on the fide of the boiler. When this has been removed 

 the fire is rekindled, and if the mafs does not melt freely, 

 a little water is added. As foon as the whole becomes 

 liquid, and is made uniform by agitation with wooden poles, 

 the fire is again withdrawn, and the mafs allowed to affume 

 a proper confiftence for lading. It is laded into fquare 

 moulds : thefe are compofed of a number of ftrata lying 

 one upon another, fo that when the foap has become folid, 

 each layer of frame-work can be removed, beginning at 

 the top, and the foap is cut into cakes - with a piece of 

 fmall brafs wire at every interval : thefe cakes are after- 

 wards cut into fquare prifmatic pieces, in which ftate they 

 are fold. 



Some manufafturers proceed in a different manner in boil- 

 ing the foap. In tlie method above defcribed, and which is 

 praftifed by a judicious foap-boiler in Derby, the watery 

 part, or what is called the fpent ley, is not feparated till 

 all the ley is added. This method is called clofe working, 

 becaufe the liquid is of an uniform thicknefs all the time, till 

 the fait is added : it then affumes what is called the granular 

 form, in which the watery part is feparated from the foap, 

 like the whey and the curd in making cheefe. This arifes 

 from the foap being infoluble in falt-water. In this ftate 

 the foap is faid to be open, to diftinguilh it from the 

 ftate in which it exifts before the fait is added, and in 

 which the foap is faid to be clofed. In the open working 

 the common fait is added at feveral intervals, in order to 

 keep the foap feparated from the water. The fire is alfo 

 withdrawn feveral times, and as many times the fpent leys 

 are pumped off. After each time, except the laft, frefti 

 ley is added and the ftirring repeated. The proper ftate 

 for the foap is known by the appearance of the bubbles. 

 The very hard foap, or that which is made with all foda, is 

 not the moft convenient for praftice ; it is neither fo fit for 

 waffling the hands, nor fo eafily reducible to a pulpy ftate 

 for the different manufaftures in which it is employed. 

 The hard white foap, produced in the maiiufaftory above 

 alluded to, is in great repute from its whitenefs and its proper 

 confiftency. This foap is formed with tallow and a mix- 

 ture of foda and potafti. The boiler holds from about 25 to 

 27 cwt. of foap. The following are the average proportions 

 of the materials employed ; 13 cwt. 2 qr. 16 lbs. of tallow, 

 5 cwt. 3 qr. 12 lbs. barilla, 3 cwt. 2 qr. 6 lbs. American 

 potafti, 4 cwt. 2 qr. 7 lbs. quicklime, and 3 qr. 16 lbs. 

 common fait (muriate of foda.) Thefe materials produce 

 1 ton 4cwt. o qr. i lb. of white foap. The hme, the 

 barilla, and the potafti, are mixed together, and placed in 

 the vat already defcribed. In order to furnifti the ley 

 which is added to the melted tallow, the lime is em- 

 ployed merely to rob the potafti and foda of their carbonic 

 acid, and of courfe does not enter into the compofition of 

 the foap. The neutral falts, which both the barilla and 

 potafti contain, are pumped out with the fpent leys with a 

 portion of uncombined alkali : of this we fliall fay fome- 

 thing hereafter. 



Hence it will appear, that the foap is a compound of 

 pure alkali, with the fat, and a portion of water. 



In the making of foap, as in all other chemical combina- 

 tions, the proportions appear to be definite. Every foap- 

 boiler knows, that where too much ley is added to the fat, 

 the excefs will be found in the watery part under the foap ; 

 and that if the fat were in excefs, the foap would be greafy 

 to the feel, and would otherwife ftiew the prefence of un- 

 combined fat. Hence it will be found on analyfis, that the 

 proportions will be uniform, becaufe they are definite. The 

 quantity of foda which combines with olive-oil and tallow. 



is about 30 of the former to 212 of the latter; and fmce 

 an atom of potafti is to that of foda as 29.25 to 44.5, 

 45 of potafti will combine with 212 of oil or tallow. 



The following is an analyfis of foap by Darcet, Lelievre, 

 and Pelletier : 



Oil 



Soda 

 Water 



60.94 

 8.56 

 30-5 



100 



If the alkali were potafti inftead of foda, then the pro- 

 portions would be. 



Oil - - - 



Potalh - 



Water ... 



100 



In the firft of thefe analyfes, the foda is to the oil ai 

 85 to 609, or as 1 to 7.28 nearly. In the fecond, the potafti 

 is to tlie oil as 12.3 to 58.4, or as i to 4.6 nearly. The 

 fpecimen of foap before alluded to contains a mixture of 

 potafti and foda. The 3 cwt. 2qr. 6 lbs. of American 

 potafti, according to the average value of that article, ought 

 to give 2 cwt. 2 qr. of pure potafti. By the above ana- 

 lyfis, the I ton 4 cwt. oqr. lib. of foap ought to contain 

 7 cwt. I qr. 7 lbs. of water. There ought to be therefore 

 only 1 6 cwt. 3qr. 2 1 lbs. of the alkah and tallow. It 

 appears, that in forming this fpecimen of foap, loolbs. of 

 common fait were added, which gives to the foap 55.5 lbs. of 

 foda, and takes away from it 83.25 lbs. of potafti. Hence, 

 the alkali refulting from the potafti in this foap will be 

 I cwt. 3 qr., and 55.5 lbs. of foda derived from the common 

 fait, or 2qr. 4 lbs. nearly. In order to know what foda 

 is derived from the barilla, we muft fubtraft the tallow and 

 the alkali from the whole ; that is (i6cwt. aqr. 27lbs.) 

 I cwt. 3qr. of potafti, 2qr. of foda, and 13 cwt. 2 qr. 

 1 6 lbs. of tallow, will leave 3qr. 6 lbs. of foda derived 

 from the barilla. 



The proportions of the foap in queftion will, therefore, 

 be, in 2689 lbs. of foap. 



Tallow 

 Soda 

 Potafti 

 Water 



1528 

 146 

 196 

 819 



2689 



100 



This refult, although it contains a little too much of the 

 mixed alkali to correfpond with theory, is ftrikingly near 

 the truth. We may therefore conclude, that foap, in 

 general, contains from 8 to 1 2 per cent, of alkali, as more 

 or lefs of each prevails, and about 30 per cent, of water. 

 The hardeft white foap made with foda would contain 

 8 per cent. ; and the foft foap, in which potafti alone is ufed> 

 would be a little more than 1 2 per cent. 



In the above fpecimen of hard foap, it will be feen that 

 39S lbs. of crude potafti furnifti 280 lbs. of real alkali, 

 which is feveu-tenths of the whole. With this were em- 

 ployed 656 lbs. of barilla, which furnifti 90 lbs. of real 

 alkali. Now 192 lbs. of American potafti will produce 

 135 lbs. of pure potafti, and this will difengage from 

 126 lbs. of muriate of foda, or common fait, 90 lbs. of 

 pure foda. Hence 192 lbs. of American potafti and 126 lbs. 

 of fait will produce as much foda as 656 lbs. of barilla. 



This 



