142 
mens * from the oxygenated marine acid, or from the kindling influence of 
any required proportion, the piston must be pushed towards the conical part of the pistol, then unscrew¬ 
ing the barrel, the aperture of the pistol is applied to the neck of the bladder containing the mixture 
of inflammable and common or oxygen air, and drawing back the piston, that mixture of elastic 
fluid is introduced into the chamber or box of the pistol. This done, the bladder is detached from 
the extremity of the pistol, and at the same time a small leaden bullet, wrapped up in soft leather, 
is applied to the said aperture, and the barrel is screwed over it; thus the pistol is charged, and is now 
ready to be fired. Vide Cavallo on the different factitious airs. 
* The bitumens generally taken notice of by writers on Natural History are, with respect to their 
consistence, either as fluid as oil, or as thick and tenacious as tar, or quite solid. The fluid bitumens 
are two, naptha, and petroleum, or rock-oil. These are oils which differ from each other in colour 
and consistence, and some other properties; the naptha is pale, light, and very inflammable; the petro¬ 
leum is yellow, brown, or blackish, heavier and less inflammable than naptha: its difference from the 
naptha is attributed to its containing a greater quantity of acid in its composition. Both these oils are 
found in many parts of the globe, either floating on spring water, or dripping from the crevices of 
rocks. Mineral pitch is a bitumen which differs from petroleum in being thicker, heavier, and more 
glutinous; it was formerly found in the environs of Babylon, and constituted, according to Vitruvius, 
when mixed with lime, the cement which was used in building the walls of that city. At present it 
is met with in several parts of Europe, and in America,, where it drips from rocks, and is called bv us 
Barbadoes tar: it has a very offensive smell, and great tenacity, and is called by the inhabitants of 
Auvergne, in France, where it exudes from the earth, and sticks to the feet, devils dung. The asphal- 
tum, or Jews pitch, is a bitumen much resembling mineral pitch; it is thrown up in a liquid form from 
the bottom of the lake where Sodom and Gomorrah stood, otherwise called the Dead Sea, or the lake 
Asphaltes, from a Greek word denoting a bitumen. This lake in the time of Esdras yielded bitumen— 
“ remember what I did to Sodom and Gomorrah, whose land lieth in clods of pitch:’ The bitumen 
floating upon the suiiace of the salt water, is condensed by the heat of the sun into a solid form, and 
is gathered by the Arabs on the shore where it is thrown. It is said to be the same substance which 
the Egyptians used in embalming their mummies, and it was called by them mummia mineralis. This 
bitumen has been found in many places of Asia and Europe, as well as on the shores of the Dead Sea; 
all that we meet with in the shops, is either an artificial composition, or an European asphaltum, the 
eastern ones being seldom brought into Europe, but used by the natives either as pitch for their ships, 
or as an ingredient in varnishing, or dying wool. 
There is a very curious experiment which illustrates the relation which these four bitumens bear to 
each other. The most transparent oil of turpentine, resembling naptha, may be changed into an oil 
resembling petroleum, by mixing it with a small portion of the acid of vitriol; with a larger proportion 
of the acid, the mixture becomes black and tenacious, like Barbadoes tar; and the proportions of the 
ingredients may be so adjusted, that the mixture will acquire a solid consistence, like asphaltum. This 
experiment teaches us to conclude that naptha, petroleum, Barbadoes tar, and asphaltum, differ chiefly 
fiom each other, with respect to the quantity of acid which enters into their composition; and the 
substances procured by distilling pitcoal, or resinous vegetables, may furnish no improbable conjecture 
concerning the origin of these bitumens. 
Let us suppose then a subterraneous fire to be situated in or near a stratum of pitcoal, of turf, of 
fossil wood, or of any other such bituminous matter; it is manifest that the inflammable air, and the 
different kinds of oils, which were collected by distilling small portions of these substances, would be 
elevated by the heat into the crevices of the superincumbent strata; the light and pale oil would be a 
sort of naptha, or petroleum, the black and tenacious oil would be a Barbadoes tar, and this might be 
so dried by the heat as to become an asphaltum. The oils not being miscible with water, would be 
found floating upon its surface, as it issued out of the bowels of the earth, and being very inflammable, 
might constitute burning wells, such as have been met with near Wigan, at Brosely, and in many 
other places: or where the oil did not meet with water, or was too heavy to float on it, we may con¬ 
ceive that it would impregnate the porous strata of several kinds of stones and earth. It has been 
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