Ill 
to compel the disuse of the retort. In many instances the 
iron of the retort is destroyed for a considerable space, 
and its place supplied by the carbon long before it is 
necessary to destroy the retort. From the continuous 
thickening of the deposit, it is evident that the process 
of deposition once commenced by the iron is continued by 
the red hot carbon. 
The property of red hot carbon to decompose hydro- 
carbons, was proved from the fact of a common broom 
having been accidentally thrown into one of the retorts, 
which, when charred by the heat, rapidly decomposed the 
gas, the carbon of which formed a singularly beautiful 
deposit on the slender stems of the broom, being deposited 
like branches of coral, hard, elastic, of considerable length, 
and very pure. The substance assumes a variety of forms 
and appearances, some of them very beautiful. The density 
and hardness varies also as considerably. 
The form of the deposit appears to be either minute 
scales, like a section of a hollow sphere, or thin layers. 
The scales are deposited on each other till the whole takes 
the form of mammillar protuberances, sometimes of great 
metallic brilliancy, as specimen No. 1, having but little 
aggregation, and easily crumbled betwixt the fingers. This 
I believe to be pure carbon, though when heated sulphur 
is driven off, which appears to be mechanically mixed, and 
not chemically combined, for heat drives it off, and leaves 
the scales brilliant and unaltered in appearance. 
Specimen No. 2 has the same form as No. 1, but more 
aggregated. 
Specimen No. 3 has the same form, with considerable 
hardness. 
Specimen No. 4 has the same type, but the mammillar 
protuberances are large, and apparently solid, but when 
exposed to a red heat for an hour, exhibits the same 
H 2 
VOL. III. 
