no EFFECTS of UEAt 



marble ; another was hard and white, without any faline grains, 

 and fcarcely effervefced in acid. It was probably quicklim e, 

 formed by internal calcination, but in a ftate that has not oc- 

 curred in any other experiment. 



The workman whom I employed to takeout the remains of 

 the cradle, had cut off a piece from the breech of the barrel, 

 three or four inches in length. As I was examining the crack 

 which was feen in this piece, I was furprifed to fee the iniide of 

 the barrel lined with a fet of tranfparent and well-defined cry- 

 ftals, of fmall flze, yet vifible by the naked eye. They lay to- 

 gether in fome places, fo as to cover the furface of the iron with 

 a tranfparent coat \ in others they were detached, and fcattered 

 over the furface. Unfortunately, the quantity of this fubftance 

 was too fmall to admit of much chemical examination \ but I 

 immediately afcertained, that it did not in the leaft effervefce 

 in acid, nor did it feem to diffolve in it. The cryftals were 

 in general tranfparent and colourlefs, though a few of them 

 were tinged feemingly with iron. Their form was very well 

 defined, being flat, with oblique angles, and bearing a ftrong 

 refemblance to the cryftals of the Lamellated Stylbite of 

 Hauy. Though made above two years ago, they ftill retain 

 their form and tranfparency unchanged. Whatever this 

 fubftance may be, its appearance, in this experiment, is in 

 the higheft degree interesting, as it feems to afford an ex- 

 ample of the mode in which Dr Hutton fuppofes many in- 

 ternal cavities to have been lined, by the fublimation of fub- 

 ftances in a ftate of vapour 5 or, held in folution, by matters in 

 a gafeous form. For, as the cryftals adhered to a part of the 

 barrel, which muft have been occupied by air during the ac- 

 tion of heat, it feems next to certain that they were produced 

 by fublimation. 



The very powerful effeds produced by this laft barrel, the 

 fize of which (reduced, indeed, by repeated oxidation) was not 



above 



