506 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 /O^. 



posed it on a cupel to the focus, where it fumed again very much, and was re- 

 duced into sharp crystalline particles consisting of other small points. On re- 

 exposjng these crystalline particles to the focus upon charcoal, they melted 

 very easily, and took again the form of tin ; the coal having furnished them 

 with the sulphureous part which the fire had before taken away : for it is well 

 known, that by adding any fat, or the like inflammable matter, to the calx of 

 tin when red hot in the crucible, it reassumes immediately the form of tin. 



These experiments show, that tin contains a sulphur which is very easily 

 separated, since common fire can do it so readily; and that this metal calcined, 

 or deprived of its sulphur, is easily saturated again with it, from the oily part of 

 any inflammable matter. It also appears that the metallic earth, which is the 

 basis of tin, is a crystalline earth, very difficult to be melted; since common 

 fire cannot vitrify this metal by itself, and that the heat of the sun, in the focus 

 of this large burning glass, cannot perfectly melt the calx, into which this 

 metal is reduced. We may presume that the crystallization, or reducing of this 

 metal into sharp-pointed particles, proceeds from the force of the sun, break- 

 ing and melting together into a solder, as it were, some of these small crystals, 

 as the sulphureous parts evaporate; it not being strong enough to melt them all 

 •down together in one entire mass. 



Lead being held in fusion on the charcoal in the focus of the glass, it wasted 

 all away in fumes. I exposed the like quantity of lead on a stone, to the focus, 

 where it emitted great quantities of fumes, and gradually changed into a fluid 

 liquor, like oil or melted rosin. This liquor, as it grew cold, fixed into glass ; 

 which has this peculiarity, that it is disposed into plates, like Venetian talc, and 

 that it is flabby, soft to the touch, transparent, and in some parts of greenish 

 or reddish yellow. 



^" In continuing this matter in the focus, it spread upon the stone like varnish ; 

 and at last, penetrating it, helped to melt it. I placed this talcky earth in the 

 focus upon charcoal ; when it melted, and in a little time after reassumed the 

 form of melted lead. I withdrew it from the focus, and having let it cool, 

 found it nothing different from lead. 



These experiments show, that there is in lead, as well as in the other imper- 

 fect metals, a sulphureous part, that is easily separated by common fire, or the 

 heat of the sun ; and that this metal has for its basis a foliated or talcky earth. 



Quicksilver placed in the focus of the burning glass upon charcoal, or on 

 ilie cupel, or on the stone, is immediately all dispersed, and exhaled in a very 

 thick fume. I exposed on the stone, to the focus, some mercury precipitate 

 per se, in a degree of heat equal to that of digestion: it seemed to melt, but 

 presently dispersed in vapours: only there remained a small quantity of a very 



