Exatiilnation of the fufihle Earth. 4O9 



afterwards. To obviate as much as poflible the equivocal refults that might arife from water 

 contained in the precipitants, the different alkalis were applied in the drieft ftate I could 

 reduce them to ; viz. pure fait of tartar, kept for fome time in a heat juft below rednefs ; 

 cryftals of marine alkali melted and dried in the fame manner ; volatile alkali in cryftals, a 

 little furplus acid being in this inllance previoufly added to the folution to countera£t the 

 water of cryftallization in the alkali ; fait of tartar cauficated by quicklime, and hallily eva- 

 porated to drynefs ; the marine alkali catiflicated in like manner ; and the vapour of cauftic 

 volatile alkali, arifing with a very gentle heat from a retort into a phial containing the fo- 

 lution. All thefe alkalis occafioned copious precipitations. Ail the precipitates, after 

 wafhing and drying, were found to rediflblve in marine acid ; and from all thcfe folutions 

 the original fubftance was precipitated unaltered on diluting them with water. 



In ftrong fire, from 142 to 156 degrees, this fubftance difcovers a much greater fufibility 

 than any of the known fimple earths. In a fmall veflel made of tobacco-pipe clay, it melted, 

 and glazed the bottom ; and on a bed of powdered flint, prelTed fmooth in the manner of a 

 cupel, it did the fame. Magnefia or chalk would indeed vitrify in the clay veflel ; but on 

 flint no one of the known earths fliews any tendency to vitrification in that heat *. In a 

 cavity fcooped in a lump of chalk, this fubftance, in the heat above mentioned, ran into a 

 £mall round bead, fmooth, whitifli, and opake, not in the leaft adhering to the calcareous 

 mafs. On a bed of powdered quick-lime, it formed a brownifh fcoria, which in great part 

 had funk into the lime, and feemed to have united with it, On Mr. Henry's magnefia, 

 uncalcined, it melted and funk in completely, leaving only a (light brownifh ftain on the 

 furface where it had lain. On beds of the baro-felenite, and barytic quick-lime, it likewife 

 melted and funk in, leaving a difcoloured fpot behind ; but whether it really united with 

 the fubftrata, or only penetrated into their interftices, could not be determined with certainty, 

 on account of the fmallnefs of the quantity of the mineral I had to work upon. 



On a bed of powdered charcoal, in a crucible clofely luted, this fubflance likewife melted : 

 and therefore it may be prefumed not to have owed its fufion in the above experiments to 

 the fame caufe to which fome of the common fimple earths, in certain circumftances, owe 

 theirs, namely their union with the matter of the vefTel or fupport ; that is, with an earth 

 or earths of a different kind from themfelves; but to poffefs a fufibility ftridlly its own, which 

 takes place in a fire of 150 degrees, or perhaps lefs. 



As charcoal in fine powder afTumes a kind of fluidity in the fire, fimilar to that which 

 powdered gypfum exhibits in a fmall heat, its furface had changed from concave to hori- 

 zontal, and the bead had funk to the bottom ; it was rough and black on the outfide, and 

 whitifli within. On repeating the experiments in a cavity fcooped in a piece of charcoal, 



* It may be proper juft to mention that I find this to be a very commodious and fyre method of trying, in 

 fmall, whether any given earthy body be fufible with other earths. If the body is difpofcd to vitrify with any 

 proportion of clay or Aint, for inllance, it will equally vitrify when a little of it is applied, or even dufled only, 

 on the bottom of a fmall cup made of clay, or on a fmooth clofc bed of finely powdered flint. The body, in 

 this mode of application, fecmi to unite with only juft fo much of the m.ittcr of the fubllratum as is rcquilile 

 for their moft pcrfefl fufion together, and has nothing cll'c in contafl with it, (o that no dcccptiim can arifc ; 

 whereat, if mixed with the fame matter, there miijht be no .nppearance of fufion, unkfs certain favourable pro- 

 portions of the two Oiould chance to be bit upon , and even ihcn, if the quantity be fmall, it would not be cer- 

 tain but that the fufion might have originated from the matter of the crucible. W. 



Vol I.— December 1797. 3 G the 



