'2Q3 Effects of Heat modified hy Compression. 



adhering to the inside of the porcelain tube : it was verv. 

 nuicli shrunk, stili retaining a cyUndrical form, though 

 bent by partial adhesions. Jts surface bore scarcelv any re- 

 mains of the impression taken by the pov^ der on ramming 

 it into the tube : it had, to the naked eye, the roughness and 

 semi-transparency of the pith of a rush stripped of its outer 

 skin. By the lens this same surface was seen to be glazed 

 all over, though irregularly, showing here and there some 

 air-holes. In fracture it was semi-transparent, more vi- 

 treous than crystalline, though having a few facettes : the 

 mass was seemingly formed of a congeries of parts, in them- 

 selves quite transparent ; and, at the thin edges, small pieces 

 were visible of perfect transparency. These. must have been 

 produced in the fire; for the spar had been ground with 

 Avatcr, and passed through sieves, the same with the finest 

 of those used at Etruria, as described by Mr. Wedgewood. 

 in his paper on the construction of his pyrometer. 



With the same barrel I obtained many interesting results, 

 giviiig as strong proofs of fusion as in any former experi- 

 ments ; with this remarkable difference, that, in these last, 

 the substance was compact, with little or no trace of froth- 

 ing. In the gun-barrels where fusion had taken place, 

 there had always been a loss of 4 or 5 per cent., con- 

 uected, probablv, with the frothing. In these experinjents, 

 for a reason soon to be stated, the circumstance of weight 

 could not be observed; but appearances led me to suppose, 

 that here the loss had been small, if any, 



On the 6th of April I made another experiment with the 

 square barrel, whose thickness v^as now much reduced by 

 successive scales, produced by oxidation, and in which a 

 small rent begaji to appear externally, which did not, how- 

 ever, penetrate to the bore. The heat rose high, a pyro- 

 meter on the breech of the barrel giving 37°. On removing 

 the metals, the cradle was (ound to be fixed, and was broken 

 in the attempts made to withdraw it. The rent was much 

 widened externally : but it was evident that the barrel had 

 not been laid open, for part of the carbonate was in a state 

 of saline marble; anollier was hard and white, ^vithout any 



saline 



