BY COMPRESSION. 391 



On the 12th of February, 1803, I began a feries of ex- In a vertical 

 periments with gun-barrels, refuming my former method o^ j^f b^r/ch'u^- 

 working with the fufible metal, and with lead ; but ahering wards, and 

 the pofition of the barrel from horizontal to veriical j the breech j^'^PP^'^ ^''^ 

 being placed upwards during the a6tion of heat on the car- 

 bonate. This very fimple improvement has been productive 

 of advantages no lefs remarkable, than in the cafe of the 

 tubes of porcelain. In this new polition, the included air, 

 quitting ilie air-tube on the fufion of the metal, and riling to 

 the breech, is expofed to the greateft heat of the furnace, and 

 mull therefore readl with its greateft force ; whereas, in the 

 horizontal polition, that air might go as far back as the fufion 

 of the metal reached, where its elafticity would be much 

 feebler. The fame difpofition enabled me to keep the muzzle 

 of the barrel plunged, during the action of heat, in a veflel 

 filled with water; which contributed very much both to the 

 convenience and fafety of thefe experiments. 



In this view, making ufe of the brick-furnace with the Defcription and 

 vertical muffle, already defcribed in page 384, I ordered ^'^^^^"f^°^ *^® 

 a pit (a a a Jig. 20.) to be excavated under it, for the purpofe 

 of receiving a water-vetTel. This velfel (reprefenled feparate- 

 ly, ^g. 21.) was made of caft iron; it was three inches in 

 diameter, and three feet deep ; and had a pipe ((i e) ftriking 

 off from it at right angles, four or five inches below its rim, 

 communicating with a cup (e/) at the diftance of about two 

 feet. The main veflTel being placed in the pit (a a) direflly 

 below the vertical muffle, and the cup fianding clear of the 

 furnace, water poured into the cup flowed into the velTel, 

 and could thus conveniently be made to (land at any level. 

 (The whole arrangement is reprefented in fig. 20.) The 

 muzzle of the barrel (g) being plunged into the water, and 

 its breech {b) reaching up into the muffle, as far as was found 

 convenient, its pofition was fecured by an iron chain [gf). 

 The heat communicated downwards generally kept the furface 

 of the water (at c) in a Hale of ebullition ; the wafte thus 

 occafioned being fupplied by means of the cup, into which, 

 if necefiary, aconUant ftream could be made to flow. 



As formerly, I rammed the carbonate into a tube of porce- 

 lain, and placed it in a cradle of iron, along with arrair-tube 

 and a pyrometer; the cradle being fixed to a rod of iron, 

 which rod I now judged proper to make as large as the barrel 

 E e 2 would 



