Gas carbon

Gas carbon, or retort carbon, is a form of carbon that is obtained when the destructive distillation of coal is done or when coal gas or petroleum products are heated at high temperatures in a closed container. It appears as a compact, amorphous, gray, crystalline solid left by chemical vapour deposition on the walls of a container or retort. It is a good conductor of heat and electricity, similar to graphite. Unlike graphite, it does not leave marks on paper.
Applications have included battery plates, and in arc lamps. It was also used in early microphones.
Houston in 1883 described its use in arc lighting:
while Atkinson noted in 1898:
It has a specific gravity of around 2.35 to 2.4.