352 
have offered, of substances possessing this peculiar lustre, deriving it 
from an impregnation with bitumen, and are in full accordance with 
the experiments of Mr. Pepys. Mr. Klaproth introduced 100 grains 
of this substance into a small glass retort, inserting its neck into a 
bottle containing lime-water. The retort was placed between the 
coals, or in open fire, and the heat gradually increased to the igni- 
tion of its contents. At the very beginning there passed over some 
drops of water, and soon after the lime-water in the receiver became 
turbid. In this last, when the receiver was removed, a bituminous- 
empyreumatic smell was perceived, which at first also seemed to be 
somewhat ammoniacal. The pieces of the stone, in the retort, were 
rendered black, and resplendent like jet ; but by a still longer igni- 
tion, in an open crucible, they lost that black colour, and became at 
first bluish, then grey white, losing, at the same time, three grains 
more of their weight*. 
The result of this operation, and particularly the bituminous - 
empyreumatic smell, afford pretty strong evidence in favour of the 
supposed nature and constitution of the substances of this genus. 
Yours, &c. 
* Analytical Essays, by M. H. Klaproth, p. 452. 
