144 Effects of Heat modified by Compression. 



at the muzzle with a convex surface; a cylinder of iron, of 

 about an inch in diameter and half an inch thick, was laid 

 on the muzzle (fig. 35 and 37), and to it a compressing 

 weight was instantly applied. This was first done by the 

 pressure of a bar of iron (de, fig. 35), three feet in length, 

 introduced loosely into a hole (d), made for the pur- 

 pose in the wall against which the furnace stood, the di- 

 stance between this hole and the wall being one foot. A 

 weight was then suspended at the extremity of the bar (e), 

 and thus a compressing force was applied equal to three 

 times that weight. In the course of practice, a cylinder of 

 lead was substituted for that of iron, and a piece of leather 

 was placed between it and the muzzle of the barrel, which 

 last being dressed to a pretty sharp edge, made an impres- 

 sion in the lead : to assist this effect, one smart blow of a 

 hammer was struck upon the bar, directly over the barrel, 

 as soon as the weight had been hung on. 



It was essential, in this mode of operation, that the whole 

 of the metal should continue in a liquid stale during the ac- 

 tion of heat ; but when I was satisfied as to its intensity and 

 duration, I congealed the metal, either by extinguishing the 

 furnace entirely, or by pouring water on the barrel. As 

 soon as the heat began to act, drops of metal were seen to 

 force themselves between the barrel and the leather, follow- 

 ing each other with more or less rapidity, according to cir- 

 cumstances. In some experiments there was little exuda- 

 tion; but few of them were entirely free from it. To save 

 the metal thus extruded, I placed a black lead crucible, hav- 

 ing its bottom perforated, round the barrel, and luted close 

 to it (fig. 37); some sand being laid in this crucible, the 

 metal was collected on its surface. On some occasions, a 

 sound of ebullition was heard during the action of heat; but 

 this was a certain sign of failure. 



The results of the most important of these experiments 

 have been reduced to a common standard in the second table 

 placed in the Appendix ; to which reference is made by the 

 following numbers : 



No. 1. — On the 16th of June 1803, I made an experi- 

 ment with these arrangements. I had tried to use a weight 



of 



