292 Effects of Heat modified ly Compression. 



vertical muffle, already described in page 197, I ordered a 

 pit {aaa, fig. 20.) to be excavated under it, for the purpose 

 of receiving a water vessel. This vessel (represented sepa- 

 rately, fig. 21-.) was made of cast iron; it was three inches 

 in diameter, and three feet deep ; and had a pipe {de) striking 

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

 communicating with a cup {ef) at the distance of about two 

 feet. The main vessel being placed in the pit (a«) directly 

 below the vertical muiBc, and the cup standing clear of the 

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

 and could thus conveniently be made to stand at any level. 

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

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

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

 convenient, its position was secured by an iron chain {gf). 

 The heat conti.iiunicated downwards generally kepi the sur- 

 face of the water (at c) in a slate of ebullition; the waste 

 thus occasioned being supplied by means of the cup, into 

 which, if necessary, a constant stream 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 an air-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 bar- 

 rel would admit, in order to exclude as much of the fusible 

 metal as possible ; for the expansion of the liquid metal being 

 in proportion to the quantity heated, the more that quantity 

 could be reduced, the less risk there was of destroying the 

 barrels. 



, In the course of practice, a simple mode occurred of re- 

 moving tlic metal and. withdrawing the cradle : it consisted 

 in placing the barrel with its muzzle downwards, so as to 

 keep the breech above tlie furnace and cold, while its muzzle 

 was exposed to strong heat in the muffle. In this manncF 

 the metal was discharged from the muzzle, and the position 

 of the barrel being lowered bv degrees, the whole metal was 

 removed in succession, till at last the cradle and its contents 

 became entirely loose. As the metal was delivered it was 

 received in a ciucible filled with v> alcr, standing on a plate 



of 



