52 8 The Rt. Hon. George Knox, on Bitumen in stones. 
analysis of a stone can be perfectly relied upon, unless the 
stone itself has been distilled, and the product of the distilla- 
tion examined.* 
To call the whole volatile matter which escapes when the 
stone has been ignited, water, is evidently a misnomer. How 
many stones must we not now expect to contain bitumen as 
well as water ? From how many does not carbon escape in 
the shape of carbonic acid gas or carburetted hydrogen ? 
In conclusion, I hope I may be allowed, from what is above 
stated, to recommend a previous distillation in all analyses of 
stony substances, in order to obtain the liquid bitumen, and 
also the carbon which has escaped in the shape of gas : and 
that the residuum in the retort should be afterwards exa- 
mined for the remaining carbon, either by burning it off, or 
in such other manner as may seem best to the operator. 
* In these distillations a matter often condensed in the retort, which was exceed- 
ingly volatile, and which was easily raised in vapour by the heat of the hand. 
