356 
PETROLEtJM. 
the distillation of bituminous coal ; by the ignition 
of wood, as happens in preparing charcoal in iron 
cylinders for the manufacture of gunpowder ; and 
also in the making of pyroligneous acid. Petro- 
leum, then, and carburetted hydrogen gas, may be 
considered as the products of the beds of bitumi- 
nous coal which lie deep in the earth, and are gen- 
erally found to accompany the salt water in greater 
or less quantities. Where gas is discharged freely, 
it greatly assists the ascent of the water in the 
wells, and saves the expense of forcing it up by the 
aid of a pump worked either by horse or steam 
power. If constant and abundant. Dr. Hildreth 
states that it might be conducted by pipes under 
the kettles, and used as a fuel in boiling away the 
brine, thus relieving one of the heaviest items of 
expenditure in working a furnace. In some wells 
in Ohio the discharge of gas is periodical, and at in* 
tervals of eight or ten days, bringing up with it 
large quantities of petroleum, to the amount of sev- 
eral barrels. In some the discharges of gas are 
tremendous, throwing the water all out of the wells 
to a height of thirty or forty feet. The eruptions 
are attended by a flow of petroleum, which in some 
instances has amounted to from thirty to sixty gal- 
lons at each flow, and returning at intervals of two 
to four days. The salt wells now average only 
about a barrel a week. At a locality near the 
gravel coal-beds on the Hockhocking, the earth and 
rocks have been blown out to a considerable dis- 
tance, leaving a cavity of several feet in diameter 
^nd depth. Probably the true reason why saline 
fountains are commonly attended by inflammable 
ga3 is, that the coal formation and salt deposites are, 
geologically, close neighbours, the salt being usual- 
ly above in Europe and other countries, but below 
in the Valley of the Ohio and its confluent springs. 
This fact also lends great force to the opinion that 
ito qpal formation doeg not exist in this state. 
