MODIFIED by COMPRESSION, 107 



wood \ To 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. 



Om the 24th of March, I made a fimilar experiment, in a 

 flout 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 j having a femitranfparent and faline ftructure, with 

 various facettes. In one part, I found the moft decided cry- 

 flallization 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 fiirface, 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 fracture 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 ftructure 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. 



The 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 lafl convinced, that their thicknefs 

 was not fufficient to eniure regular and fleady fuccefs : For 

 this purpofe, it appeared proper to employ veflels of fuch 

 ftrength, as to bear a greater expanfive force than was juft ne- 

 ceflary 3 fince, occafionally, (owing to our ignorance of the re- 



O 2 lation 



