110 EFFECTS of HEAT 
marble ; another was hard and white, without any faline grains, 
and fearcely effervefced in acid. It was probably quicklime, 
formed by internal calcination, but in a ftate that has not oc- 
curred in any other experiment. 
Tue workman whom I employed to take out i 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 infide of 
the barrel lined with a fet of tranfparent and well-defined cry- 
ftals, of fmall fize, yet vifible by the naked eye. They lay to- 
gether in fome places, fo as to cover the furface of the iron with 
a tran{parent 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 
Haiiyv. Though made above two years ago, they ftill retam 
their form and tranfparency unchanged. Whatever this 
fubftance may be, its appearance, in this experiment, is in 
the higheft degree interefting, as it feems to afford an ex- 
ample of the mode in which Dr Hurron fuppofes many in- 
ternal cavities to have been lined, by the fublimation of fub- 
ftances in a ftate of vapour; 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 spaishein 
by fublimation. 
Tue very powerful effeéts produced by this laft barrel, the — 
fize of which (reduced, indeed, by repeated oxidation) was not 
above 
