150 EFFECTS of HEAT 
lead. In an experiment, made on the 28th November 1803, in 
order to afcertain the power of the machinery, and the quantity 
of metal driven out by the expanfion of the liquid, there being 
nothing in the barrel but metal, I obferved, as foon as the com- 
prefling apparatus was removed, (which on this occafion was 
done while the lower part of the barrel was at its full heat, and 
the barrel ftanding brim full of liquid metal,) that all the leather 
which lay on the outfide of the circular muzzle of the barrel, 
remained, being only a little browned and crumpled by the 
heat to which it had been expofed. What leather lay within 
the circle, had difappeared; and, on the furface of the liquid 
metal, which ftood up to the lip of the barrel, I faw large drops, 
of a fhining black liquid, which, on cooling, fixed into a crifp 
black fubftance, with a fhining fracture, exactly like pitch or 
pure coal. It burned, though not with flame. While hot, it 
finelt decidedly of volatile alkali. The important circumftance 
here, is the different manner in which the heat has aed on the 
leather, without and within the rim of the barrel. The only 
difference confifted in compreffion, to which, therefore, the dif- 
ference of effeét muft be afcribed: by its force, the volatile 
matter of the leather which efcaped from the outward parts, 
had within the rim, been conftrained to remain united to 
the reft of the compofition, upon which it had aéted as a 
flux, and the whole together had entered into a liquid ftate, 
in a very low heat. -Had the preflure been continued till 
all was cool, thefe fubftances muft have been retained, pro- 
ducing a real coal. 
On the 24th April 1803, a piece of leather ufed in a fimilar 
manner, (the comprefling force being continued, however, till 
all was cold,) was changed to a fubftance like glue, owing 
doubtlefs to compreflion, in a heat under that of melting lead. 
Turse obfervations led me to make a feries of experi- 
ments with animal and vegetable fubftances, and with coal; 
the 
