504 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 /OQ. 



form upon charcoal by drawing thence this oily substance. That, in short, 

 this oily part, contained in the coal, is little different from the sulphur of iron. 

 Yet it must differ in some particulars, as melted iron, that has been saturated 

 with it, crackles and sparkles very much, when melted again on the stone or 

 cupel. Iron being the only metal in which I have observed this sparkling, I 

 take it to be a property peculiar only to iron, and not to any other metal. Per- 

 haps we may attribute it to the vitriolic salt with which this metal so plentifully 

 abounds, which greedily absorbs sulphur. And to this quality in the vitriolic 

 salt of iron we may also attribute the facility with which iron consumes the 

 coals ; for there is no other metal that so soon wastes the coal in the focus of 

 the glass as iron does. It is also observable that iron is the only one of the 

 four imperfect metals on which vitrified drops arise, while in fusion on the coal; 

 the reason of which I have not yet been able to discover. 



Copper, exposed to the focus of the burning-glass, at first turns white on its 

 surface, but afterwards black, and is covered with a kind of skin, or with black, 

 furrowed, and uneven scales, till at last it quite melts. On withdrawing this 

 metal out of the focus, as soon as this white colour appears, and after it has 

 been cold, I found nothing extraordinary on its surface; but by degrees it recovers 

 again very nearly its former colour. I have not been able to discover from 

 whence this white colour proceeds, unless we may attribute it to some volatile 

 arsenical salt contained in the copper, which is driven by extremity of heat to 

 the surface of the metal ; or purely to the alteration made in the grosser parts 

 of the surface of the metal when it begins to melt. The black colour which it 

 afterwards assumes, seems to arise from the sulphureous matter, which melts 

 first in this metal as well as in iron, and is raised to its surface by the extreme 

 heat. 



Placing a piece of copper in the focus upon charcoal, it melted, and emitted a 

 very thin fume, which gradually diminished, till it was all evaporated. I put a 

 piece of red copper on a cupel into the focus of the glass; it melted, and 

 emitted some thin fumes; and after being some time in fusion, it became liquid 

 like an oil. I withdrew this melted matter, and as it cooled, it fixed into a 

 regulus of a reddish brown colour, which was hard and brittle. When broken, 

 it becomes a red powder, like cinnabar of antimony ; and when viewed with a 

 microscope, there appear many small, red, transparent grains, like small rubies, 

 insomuch that one would readily take this regulus to be a deep-coloured red 

 glass. 



I endeavoured to make this vitrified copper spread abroad in melting, by 

 mixing it with common white glass ; for which end I powdered some of this 

 vitrified copper and common glass, and mixing them, I melted them together ; 



