129 
stance ; showing, when broken, a conchoidal fracture, with a glassy 
lustre. It manifests a bituminous odour, when rubbed or heated. 
It melts easily, and is very inflammable ; burning away, when pure, 
without leaving any ashes. Its specific gravity, according to Kirwan, 
is from 1.0/ to 1.65. 
Asphaltum has been spoken of by Dioscorides, and other writers 
before him, by the name of pissasphaltum ; this name, according to 
Pliny*, being applied to it, on account of its being mixed with 
common pitch. Agricolaf, however, denies this, and contends, 
that it derives this name from the circumstance of its odour so much 
resembling pitch. 
Mineral Caoutchouc, or Elastic Bitumen, appears to differ 
from mineral pitch, merely in the degree of elasticity which it pos- 
sesses ; which seems to be the consequence of the confinement of air, 
or of some other elastic fluid, in its interstitial cavities. 
Having thus furnished you with the most obvious characters of 
bitumen in its simpler states, I shall proceed to show you, that at 
very remote periods, and in various parts of the world, the peculiar 
appearance and properties of bitumen procured it a considerable 
degree of attention. 
You will not only find that it furnished the early writers in na- 
tural history with an interesting subject of inquiry, but that it was 
known to mankind, as a substance capable of being applied to va- 
rious economical uses, in the earliest ages of which we possess any 
authentic record. 
Noah, we are told, coated over the ark, within and without, 
with pitchj. The builders of the tower of Babel employed some 
bituminous matter as a cement ; “ they had hrick for stone, and slime 
had they for mortar^.” Of the vessel of bull-rushes, in which Moses 
* Lib. xxiv. cap. 7. De Natura Fossil, lib. iv. p. 595. 
J Genesis, chap. vi. ver. 14. § Genesis, chap. xi. ver. 3. 
VOL. I. ® 
