398 ACTIOV OF HEAT MODIFIED 



Remarkable The workman whom I employed to take out the remains of 



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



which appear to r ■ , • • i i 



have been form- three or lOur iiiches 111 length. As I was examining the crack 

 rd by fublima- whicii was feen in this piece, I was furprifed to fee the infide of 

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

 ftals, of final! fize, yet vifible by the naked eye. They lay (o- 

 getlier in (ome places, foas 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 fubfiance 

 was loo fmall to admit of much chemical examination ; but I 

 immediately afcertained, that it did not in the leaft efFervefce 

 m acid, nor did it feem to dilTolve in it. The cryflals 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 cryfials of the Lamellated Stylbite of 

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

 their form and tranfparency unchanged. Whatever this fub- 

 fiance may be, its appearance, in this experiment, is in the 

 higlieft degree interefling, as it feems to afford an example 

 of the mode in which Dr. Hutton fuppofes many internal ca- 

 vil ies to have been lined, by the fublimation of fubftances in 

 a flale of vapour; or, held in folution, by matters in a gafeous 

 form. For, as the cryftals adhered to'apartof the barrel, 

 which mufl: have been occupied by air during the aftion of 

 heat, it feems next to certain that they were produced by fub- 

 limation. 

 The oid Sable The very powerful effe6ls produced by this laft barrel, the 

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

 hi^h heats. ^ above an inch fquare, made me very anxious to obtain barrels 

 of the fame fubftance, which being made of greater fize, ought 

 to afford refults of extreme intereft. I found upon inquiry, 

 that this barrel was not made of Swedifla iron, as I at firft fup- 

 pofed, but of what is known by the name of Old Sable, from 

 the figure of a Sable (lamped upon the bars ; that being the 

 armorial badge of the place in Siberia where this iron is 

 made.* 

 All iron is -^ workman explained to me fome of the properties of differ- 



cniflied under ent kinds of irons, moft interefiing in my prefent purfuit; and 



the hammer at 



fome dertnite 



heat. Caft iron * I was favoured with this account by the late ProftfTor Robifon. 



at a low h^atj u^ 



