Experiments on IVhiTi/lone and Lava. 1 1 



formation of both to tlie fame caufe, and to believe that whinftone, as well as lava, has 

 been expofed to the action of heat. In the courfe of the paper, 1 fliall mention fcveral ac- 

 cidental rcfults, which, if confidered feparately, might feem unworthy of notice, but 

 which, by affording the means of comparifon between the two clafTes, are of great fervLcc 

 in the general inveftigation. 



The whin (tone firft employed was taken from a quarry * near the Dean, on the water of 

 Lelth, in the neighbourhood of Edinburgh. This (tone is an aggregate of black and 

 green ifli-black hornblend, intimately mixed with a pale reddifh-brown matter, which has 

 fome refemblance to felfpar, but is far more fufible. Both fubftances are imperfectly and 

 confufedly cryftallized in minute grains. The hornblend is in the greateft proportion ; 

 and its fra£ture appears to be ftriated, though in fome parts foliated ; that of the reddifh- 

 brown matter is foliated. The fra£lure of the (tone en majfe is uneven, and it abounds in 

 fmall facettes, which have fome degree of luftre. It may be fcratched, though with diffi- 

 culty, by a knife, and gives an earthy fmell when- breathed on. It frequently contains 

 fmall fpecks of pyrites. 



On the 17th of January 1798, I Introduced a black lead crucible, filled with fragments 

 of this ftone, into the great reverberating furnace at Mr. Barker's iron foundery. In about 

 a quarter of an hour, I found that the fubftance had entered into fufion, and was agitated 

 by a Itrong ebullition. I removed the crucible, and allowed it to cool rapidly. The refult 

 was a black glafs, with a tolerably clean fracture, interrupted however by fome fpecks. 



In fubfequent experiments, I endeavoured, by flow cooling after fufion, to prevent the 

 whinllone from becoming vitreous, and to compel it to refume its original character by 

 cryftallization. In this I fo far fuccceded as to obtain a fubftance, which was not glafs, 

 though it did not pofTefs the properties of whinftone. The production of this interme- 

 diate fubftance, which much refembled the liver of an animal, is accompanied with fome 

 curious particulars, which I fhall enumerate and explain in another part of this paper. On 

 fome occafions, too, I obtained a vitreous mafs in which were a multitude of little fpheres, 

 having a dull or earthy fra£lure. 



At laft, on the 27th of January, I fucceeded completely In the ohje£t I had in view. A 

 crucible, containing a quantity of whinftone, melted in the manner above defcribed, being 

 removed from the reverberatory, and conveyed rapidly to a large open fire, was imme- 

 diately furrounded with burning coals, and the fire, after being maintained feveral hours, 

 was allowed to go out. The crucible, when cold, was broken, and was found to contain 

 a fubftance, differing in all refpe£ls from glafs, and in texture completely refembling whin- 

 ftone. Its fracture was rough, ftony and cryftalline ; and a number of fhining facettes 

 were interfperfed through the whole mafsf. The cryftallization was ftill more apparent in 



cavities 



• Called Bell's Mills Quarry. 



t It contained a number of fmall globules like lead /hot, which were found to confift of regulus of 

 iron, reduced from the oxide in the whinftone, by means «f the carbonic matter of the black lead crucible. 



C» By 



