148 Effects of Heat modified I II Compression. 



depends upon the following general view : If we take a hul-» 

 low tube or barrel (AD, fig. 1, Plate IV.) closed at one end 

 and open at the other, of one foot or more in length, it is 

 evident, that by introducing one end into a furnace, we can 

 apply to it as great heat as art can produce, while the other 

 end is kept cool, or, if necessary, exposed to extreme cold. 

 If then the substance which we mean to subject to the com- 

 bined action of heat and pressure be introduced into the 

 breech or closed end of the barrel (CD), and if the middle 

 part be filled with some refractory substance, leaving a small 

 «mpty space at the muzzle (AB), we can apply heat to the 

 muzzle, while the breech containing the subject of experi- 

 ment is kept cool, and thus close the barrel by any of the 

 numerous modes which heat aflbrds, from the welding of 

 iron to the melting of sealing-wax. Things being then re- 

 versed, and the breech put into the furnace, a heat of any 

 required intensity may be applied to the subject of experi- 

 ment, now in a state of constraint. 



My first application of this scheme was carried on with a 

 common gun-barrel, cut off at the touch-hole, and welded 

 very strongly at the breech by means of a plug of iron. Into 

 it I introduced the carbonate, previously rammed into a 

 cartridge of paper or pasteboard, in order to protect it from 

 the iron, by which, in some former trials, the subject of 

 experiment had been contaminated throughout during the 

 action of heat. I then rammed the rest of the barrel full of 

 pounded clay, previously baked in a strong heat, and I had 

 the muzzle closed, like the breech, by a plug of iron welded 

 upon it in a common forge ; the rest of the barrel being 

 kept cold during this operation by means of wet cloths. 

 The breech of the barrel was then introduced horizontally 

 into a common muffle, heated to about 25° of Wedgwood. 

 To the muzzle a rope was fixed in such a manner that the 

 barrel could be withdrawn without danger from an explo- 

 sion*. I likewise, about this time, closed the muzzle of 



the 



* On one occasion the importance of this precaution was strongly feit. 

 Having inadvertently introduced a considerable quantity of moisture into a 

 welded barrel, an explosion took pl.^ce, before the heat had risen to redness, 



by 



