152 Effects of Heat modified ly Compression. 



as far from complete, I shall add but a few observations to 

 what I have already laid before this society, in the sketch I 

 had the honour to read in this place on the 30th of August 

 last. 



The following incidental occurrence led me to enter upon 

 this subject rather prematurely, since I had determined first 

 to satisfy myself with regard to the carbonate of lime. 



Observing, in many of the last-mentioned class of experi- 

 ments, that the elastic matters made their escape between 

 the muzzle of the barrel and the cylinder of lead, I was in 

 the habit, as mentioned above, of placing a piece of leather 

 between the lead and the barrel ; in which position, the heat 

 to which the leather was exposed was necessarily below that 

 of melting lead. In an experiment, made on the ^8th No- 

 vember 1803, in order to ascertain the power of the ma- 

 chinery, and the quantity of metal driven out by the expan- 

 sion of the liquid, there being nothing in the barrel but 

 metal, I observd, as soon as the compressing apparatus was 

 removed, (which on this occasion was done while the lower 

 part of the barrel was at its full heat, and the barrel standing 

 brim full of liquid metal,) that all the leather which lay on 

 the outside of the circular muzzle of the barrel remained, 

 being only a little browned and crumpled by the heat to 

 which it had been exposed. What leather lay within the 

 circle, had disappeared ; and, on the surface of the liquid 

 metal, which stood up to the lip of the barrel, I saw large 

 drops of a shining black liquid, which, on cooling, fixed 

 into a crisp black substance, with a shining fracture, ex- 

 actly like pitch or pure coal. It burned, though not with 

 flame. While hot, it smelt decidedly of volatile alkali. 

 The important circumstance here, is the different manner in 

 which the heat has acted on the leather, without and within 

 the rim of the barrel. The only difference consisted in com- 

 pression, to whu.h, therefore, the difference of effect must 

 be ascribed : by its force, the volatile matter of the leather 

 which escaped from the outward parts, had within the rim 

 been constrained to remain united to the rest of the compo- 

 sition, upon which it had acted as a flux, and the whole 

 together had entered into a liquid state, in a very low heat. 



Had 



