MODIFIED by COMPRESSION. 107 
wood ; fo that this colour, which has occurred in almoft every 
fimilar cafe, remains to be accounted for. The carbonate ef- 
fervefced violently with acid ; the fubftance in contact with the 
tube, doing fo, however, more feebly than in the heart, lea- 
ving a copious depofite of white fandy matter, which is doubt- 
lefs a part of the tube, taken up by the carbonate in fufion. 
~ On the 24th of March, I made a fimilar experiment, m-a 
ftout gun-barrel, and took fome care, after the application of 
heat, to cool the barrel flowly, with a view to cryftallization. 
The whole mafs was found in a fine ftate, and untouched by 
the lead; having a femitranfparent and {aline ftructure, with 
various facettes. In one part, I found the moft decided cry- 
ftallization I had obtained, though of a fmall fize: owing to 
its tranfparency it was not eafily vifible, till the light was made 
to reflect from the cryftalline furface, which then produced 
a dazzle, very obfervable by the naked eye : when examined by 
means of a lens, it was feen to be compofed of feveral plates, bro- 
ken irregularly in the fra@ture of the fpecimen, all of which are 
parallel to each other, and reflect under the fame angle, fo as to 
unite in producing the dazzle. This ftruéture was obfervable 
equally well in both parts of the broken fpecimen. In a for- 
mer experiment, as large a facette was obtained in a piece of 
folid chalk; but this refult was of more confequence, as having 
been produced from chalk previoufly pounded. 
Tue foregoing experiments proved the fuperior efficacy of 
iron veflels over thofe of porcelain, even where the thicknefs 
was not great; and I perfevered in making a great many experi- 
ments with gun-barrels, by which I occafionally obtained very 
fine refults: but I was at laft convinced, that their thicknefs 
was not fuffiicient to enfure regular and fteady fuccefs: For 
this purpofe, it appeared ‘proper to employ veffels of fuch 
ftrength, as to bear a greater expanfive force than was juft ne- 
repay 3 fince, occafionally, (owing to our ignorance of the re- 
O2 lation 
