ACTION OF HEAT MDDIII£» 



to the employment of various devices, which I fliall now fijort» 

 ly enumerate, as they occurred in the courfe of pra^ice. The 

 iimple application of the principle was found infufficicnt, froqi 

 twocaufes: Firft, The carbonic acid being driven from the 

 breech of the Tube, towards the muzzle, among the' pores of 

 the ])ounded filex, efcaped from the comprelling force, by 

 lodging itfelf in cavities which were comparatively cold: 

 Secondly, The glafs of borax, on cooling, was always found to 

 crack very much, fo that its tightnefs could not be de- 

 pended on. 

 And the method To obviate both thefe inconveniences ^t once, it occurred to 

 of part% nbvi- -ine, in addition to the firft arrangeriienl', to place fome borax 

 {Fig. 10. C) fo near the breech of the tube, as to undergo heat 

 along with the carbonate (A); but interpoling between this 

 borax and the carbonate, a ftralum of filex (B), in ofder to 

 prevent contamination. I trufted that the borax in a liquid 

 or vifcid ftate, being thruft outwards by t'ne expanfion of tlie 

 carbonic acid, would prefs againft the iilex beyond it (D), 

 and totally prevent the elallic fabftances from efcaping out of 

 ' the tube, or even from wandering into its cold parts. 



In fome refpedls, this plan anfwered to expectation. Tiie 

 glafs of borax, which can never be obtained when cold, with- 

 out innumerable cracks, unites into one continued vifcid mafs 

 in the loweft red-heat; and as the ftrefs in thefe experiments 

 begins only with rednefs, the borax being heated at the fame 

 time with the carbonate, becomes united and impervious, as 

 foon as its afliqn is neceffary. Many good refults were accord- 

 ingly obtained in this way. But I found, in pra6lice, that as 

 the heat rofe, the borax began to enter into too thin fufion, and 

 was often loft among the pores qf thefilex, the fpace in which 

 it had lain being found empty on breaking the tube. It was 

 therefore found necelTary to oppofe fomething more fubftan- 

 tial and compadi, to the thin and penetrating quality of pure 

 borax.. 

 Bottle glafs was In fearching for fome fuch fubftance, a curious property of 

 found much pre- {jQ,(|g|gCj. occurred accidentally. Some of this glafs, it> 

 terablc to pure ^ , , • m , 



borax for the povvder, havmg been nilroduced ?nto a mu^ie ai the tempe-. 

 purpofeofre- rature of about 20"^ of Wedgwood ; the powder, in the fpace 

 carbonic acid, of about a minute, entered into a ftale of vifcid agglutination^ 

 like that of lipncy, and in about a minute more, (the heat al- 

 ways continuing unchanged), .con.fplidat,Qd into a (i/maod comr 



