6/2 PHILOSOPHICAL TRANSACTIONS. [aNNO 1790. 



into a small round bead, smooth, whitish, and opaque, not in the least adhering 

 to the calcareous mass. On a bed of powdered quick -lime it formed a brownish 

 scoria, which in great part had sunk into the lime, and seemed to have united 

 with it. On Mr. Henry's magnesia, uncalcined, it melted and sunk in com- 

 pletely, leaving only a slight brownish stain on the surface where it had lain. On 

 beds of the baroselenite and barytic quick-lime, it likewise melted and sunk in, 

 leaving a discoloured spot behind ; but whether it really united with the substrata, 

 or only penetrated into their interstices, could not be determined with certainty, 

 on account of the smallness of the quantity of the mineral he had to work on. 

 On a bed of powdered charcoal, in a crucible closely luted, this substance likewise 

 melted ; and therefore it may be presumed not to have owed its fusion, in the 

 above experiments, to the same cause to which some of the common simple earths, 

 in certain circumstances, owe theirs, namely, their union with the matter of the 

 vessel or support, that is, with an earth or earths of a different kind from them- 

 selves ; but to possess a fusibility strictly its own, which takes place in a fire of 

 150°, or perhaps less. 



As charcoal in fine powder assumes a kind of fluidity in the fire, similar to 

 that which powdered gypsum exhibits in a small heat, its surface had changed from 

 concave to horizontal, and the bead had sunk to the bottom ; it was rough and 

 black on the outside, and whitish within. On repeating the experiment in a 

 cavity scooped in a piece of charcoal, the result was a blackish bead like the for- 

 mer, only smooth on the outside, with something of metallic brightness, not 

 unlike that of black-lead. Both beads were very light, and had a considerable 

 cavity within. All the internal part was whitish, without the least metallic 

 aspect ; and the external glossy blackness appeared to be only the stain which 

 charcoal powder communicates, in strong fire, to some earthy bodies that have a 

 tendency to vitrify. By boiling in concentrated marine acid a part of the beads 

 was dissolved, precipitable as at first by water ; but an accident prevented the 

 process from being continued sufficiently to determine whether the whole could 

 be dissolved or not. 



By this fusibility in the fire ; solubility in one only of the common mineral 

 acids, and parting with the acid in a heat below ignition ; precipitability by water, 

 and non-precipitability by Prussian lixivium ; this substance is strongly discrimi- 

 nated from the known earths and metallic calces. And as it suffers no decom- 

 position from any of the alkalis, in any of the usual modes of application, it can- 

 not be considered as a combination of any of those earths or calces with any of the 

 known acids ; for all the combinations of this kind would, in one or other of the 

 above methods of trial, have had the earth or metal disengaged from the acid. 

 Whether this substance belongs to the earthy or metallic class, he cannot abso- 

 lutely determine ; but is inclined to refer it to the earthy ; because, though 



