220 
nally necessary to the forming of the bitumen in conjunction with 
the carbon*,” 
The origin of amber, the next bituminous substance which de- 
mands our attention, is an enigma, the solution of which appears 
to be fraught with considerable ditHculties. The analysis of this 
substance, as has been already seen, manifests plainly that it pos- 
sesses, in every respect, the chemical properties of bitumen. Amber, 
exposed to the fire, liquefies if the heat be strong, softening and 
bubbling, without running into drops ; which circumstance distin- 
guishes it from the resins. When inflamed, it diffuses a thick smoke, 
with a pungent odour. Its flame is yellow, but variegated with blue 
and green. It leaves, after combustion, a black shining coal, which 
yields by incineration a very small quantity of earth, mixed with a 
very slight proportion of iron. From these properties we should 
therefore be led, without the least hesitation, to seek for its formation 
in the subterranean laboratory of nature ; were it not for its bearing 
accidental, but unequivocal marks, of having existed, during some of 
the stages of the process, by which it has been formed, either actually 
on, or very near to, the surface of the earth. 
Naturalists have by no means agreed in their opinions respecting 
the origin of this substance. Theophrastus speaks of amber as a 
stone, dug out of the earth in Liguria, and which possesses a power 
of attraction. Sir John Hill, in his notes on this passage, gives it as 
his opinion that it is, as he says, the best of the modern writers seem 
certain of its being, a mere native fossilf. Dioscorides thought it 
to be an exudation from the black poplar. Pliny, who particularly 
noticed this substance, supposed it to have run from the trunks of 
trees, resembling pines, in the same manner as rosin is known to flow 
from the pines, and gum from the cherry-trees ; and hence he ima- 
* Philosophical Journal, vol. ii. p. 203. 
f Theophrastus on Stones, translated by John Hill, M. D. p. 133. 
