324 Mr. Knox’s experiments and observations 
top down on a chafing dish of charcoal, and in a few minutes 
the whole was volatilised, and the silver became bright. 
On evaporating the alcohol, in order to ascertain how much 
lime the acid had taken up, I observed a dark oily substance 
collecting as the alcohol diminished, and which, when the 
solution was nearly dry, was collected, and weighed 3,70 
grains. It had an empyreumatic smell, was insoluble in 
ether, but dissolved in spirits of turpentine, and inflamed with 
difficulty with a thick smoke and pungent odour. Naptha 
dissolved it only in part, and changed the colour to grass- 
green. It seemed to retain some muriatic acid, and gave 
indications of containing some iron ; it was therefore impure 
bitumen. 
All these circumstances combined to urge me to obtain the 
bituminous matter of the stone, if possible, in a state of pu- 
rity, and to ascertain the quantity which existed in it. 
I therefore engaged in the following experiments : 
I procured an iron retort about 6 inches long and half an 
inch in diameter, one end of which was screwed to a bent gun- 
barrel, and the other, or bottom, closed by an iron screw. 
This apparatus was perfectly well made, and air tight. 
Experiment 1 . 
Into the retort I put 480 grains, in coarse powder, of the 
dark leek-green thin slaty Newry pitch-stone, as, from its 
appearance, I judged that that variety contained the greatest 
proportion of bitumen. 
The retort was then enclosed in a long earthen crucible, 
the interstices being filled up with glass-house sand, and 
placed in a powerful side furnace. To the end of the gun- 
