39Q ACTION OF HEAT MODIFIED 



The gun-bar- The foregoing experiiMents proved the fu per ior efficacy of 

 fuperior^to'' ^^^" ^'^^^'^ ^""^^ ^"°^"^ "^ pc^rcelain, even where the Ihicknefs 

 porcelain were was not great ; and I perfevered in making a great many ex- 

 ftill too weak, periments with gun-barrels, hy which I occafionally obtained 

 very fine refults : but I was at la(i convinced, that their 

 thickaefs was not fufficient to enfure regular and fteady fuccefs. 

 For this purpofe, it appeared proper to employ velTels of fuch 

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

 celTary; fince, occafionally, (owing to our ignorance of the 

 relation between the various forces of expanfion, affinity, tena- 

 city, &c.) much more ftrain has been given to the veffels than 

 was requifite. In fuch cafes, barrels have been deftroyed, 

 which, astherelults have proved, had aded with fufficient 

 /Irenglh during the firfi ftages of the experiments, though they 

 had been unable to refifl the fubfequent overftrain. Thus, my 

 fuccefs with gun-barrels, depended on the good fortune of 

 having ufed a force no more than fufficient, to con ftrain the 

 carbonic acid, and enable it to a61 as a flux on the lime. 

 I therefore determineil to have recourfe to iron barrels 

 of much greater firength, and tried various modes of con- 

 flrudion. 

 Sarrdsformed i had lOme barrels executed by wrapping a thick plate of 



byboringinfolidiron round a mandrel, as is nraaifed in the formation of gun- 

 bars or iron u r j i i / 



which proved barrels ; .and likewile by bringing the two flat fides together, 

 excellent. fo as to unite them by welding. Thefe attempts, however, 



failed. I next thought of procuring bars of iron, and of 

 having a cavity bored out of the folid, fo as to form a barrel. 

 In this manner I iucceeded well. The firft barrel 1 tried in 

 this way was of (mall feore, only half an inch : Its perform- 

 ance was highly fatisladory, and fuch as to convince me, that 

 the mode now adopted was (he beft of any that I had tried. 

 Owing fo the fmallnefs of the bore, a pyrometer could not be 

 ufed internally, but was placed upon the breech of the barrel, 

 as it flood in the vertical muffle. In this pofition, it was 

 evidently expofed to a much lefs heat than the fiducial part 

 of the apparatus, which was always placed, as nearly as 

 could be guefied, at the point ot greateft heat. 

 Finely levigated Gn the 4th of April, an experiment was made in this way 

 IS-'JinatTdby )^.'^^ ^""^^ ^\'''' ' ^'^^ P>'ometer on the breech giving 33«. 

 heat; femi- ^ 1 he fpar came out clean, and /ree from any contamination, 

 SeourS a" ^^'^^'■'"g to the infide of the porcelain tube : it was very much 

 few facettes. , (lirunk 



