BY COMPRESSION. IP7 



difficulties that have been suggested. — The Fibres of Wood in 

 some cases ohliferatedy and in some preserved under compres- 

 sion. — Uescniblance which these Results hear to a series of 

 Natural Siibstances described by Mr. Hatchett. — These re- 

 sults seem to throw light on the history of Surturbrand. 



.OlS I intend, on some future occasion, to resume my ex- Inflammable 

 periments with inflammable substances, which I look upon 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 detern;ined fii-st to 

 (Satisfy myself with regard to the carbonate of lime, 



y( ■ Observing, in many of the last-mentioned class of expcri- Incidental oc- 

 jnents, that the elastic matters made their escape between the ^jjevein leather 

 inuzzle of the barrel and the cylinder of lead, I was in the ha- was exposed to 

 bit, as mentioned above, of placing a piece of leather between compression, 

 the lead and ihe 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 28th of November 1803, in 

 order to ascertain the power of the machinery, and the quantity 

 of metal driven out by the expansion of the liquid, there being 

 nothing in the barrel but metal, I observed, as soon as the com- 

 pressing 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 

 beat to which it had been exposed. What leather lay withiu 

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

 pietal, 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 — and converti 

 black substance, with a shining fracture, exactly hke pitch or ^^J."*° '"'^^^^ 

 pure coal. It burned, though not with flame. "While hot, it 

 smelt decidedly of volatile alkali. The important circumstance, 

 liere, is the different manner in which the heat had acted on the 

 leathei", without and within the rim of the barrel. The only 

 difference consisted in compression, to which, therefore, the dif- 

 ference of etlect must be ascribed : by its force, the volatile 



matter 



