Var'wus Decompofitions of Soap by Double Ajjiiniy. 1 7 1 



■make this foap ; and that, for this purpofe, I might ma1<e ufe of the aftion of double affini- 

 ties in a different manner. 



I therefore mixed a folution of common foap with a folution of fal ammoniac, and I faw 

 clots formed at the fame inflant, which confided of the ammoniacal foap, and were retained 

 ■on the filter; fo that the fixed alkali of the foap united with the marine 'aciil, while the 

 volatile alkali combined with the oil. Strongly perfuaded as I am, that new medicines 

 ought not to be propofed but with extreme circumfpeflion ; and that we fhould rather en- 

 deavour to diminifh than increafe the lift of materia medica, I am neverthelefs tempted to 

 propofe the medical ufe of this foap, which muft poiTefs more aftive virtues than the com- 

 mon foap, and which has the advantage over that of Starkey, of a very eafy and fpcedy 

 compofition, uniformity of properties, and is capable of being preferved in clofe veflels. I 

 am aware that ufe has been made in medicine of a mixture of volatile alkali and oil, of 

 which a combination is attempted to be made by agitation or triturating ; and that a mixture 

 of this kind is to be found in the London Plrarmacopeia, under the name of volatile lini- 

 ment. But the combination obtained in this way is very imperfeft, and totally different 

 from the foap here defcribed, as may be eafily feen by infpe£tion. 



When common foap is mixed with felenitic watsr, two decompofitions and two new 

 ■combinations take place, as Mr. Coftel has proved. The alkali of the foap unites with the 

 acid of the felenite, and the earth of the felenite combines with the oil of the foap, form- 

 ing an infoluble oleo-calcareous matter in flocks, which cannot anfwer the purpofes of ordi- 

 nary foap. Hence the felenitic waters have been diftinguiihed by the name of hard water. 

 Selenite, however, is not the only fubflance proper to form the oleo-calcareous combina- 

 tion ; for every folution of this earth is equally proper. The folution in the marine or ni- 

 trous acid may be ufed for this purpofe. When foap is therefore decompofed in hard wa- 

 ters, the effedt depends not only on the felenite and the calcareous earth held in folution 

 by carbonic acid, but likewife upon all the faks with bafis of lime, or even magnefia, 

 which may exift in the water, as will hereafter be (hewn. 



The mixture of a folution of foap and a folution of Epfom falts afforded a combination 

 of the utmoft whitenefs. It is unctuous, dries with difficulty, and preferves its white co- 

 lour after deficcntion. It is infoluble in boiling water, but has neverthelefs a decided taflc 

 of foap. Expreffed oil, as well as fpirit of wine, diffolves it in confiderable quantity ; when 

 water is added to the folution in the latter fluid, it becomes milky. This combinatioa 

 melts with a moderate heat, and forms a tranfparent mafs flightly yellow and very brittle. 

 The oleo-calcareous combination cannot be fufed but very imperfedly, and at a much 

 ilronger heat. 



I have combined oil with clay by mixing a folution of alum with a folution of foap. Tlic 

 refult of this mixture was a flexible combination, foft to the touch, which preferves its 

 fupplenefs and tenacity in drying. It appeared to me to be infoluble in water, fpirit of 

 wine, and oil. It very readily enters into fufion, after whicli it exhibits a mafs of a beauti- 

 ful tranfparence ratlier yellow. 



The folution of ponderous earth in marine acid, afforded with foap a combination nearly 

 thc'famc in appearance and properties as the calcareous compound. 



The very fimple method ufed in thefe experiments to form combinations of oils and 

 earths, was attended with equal fuccefs when applied to metallic fubllanccs. 



^' 2 Wlien 



