(Mineral Pitch, Asphaltum, Erdpech), the most perfectly inflammable mineral known. Of this there are three varieties, elastic, earthy, and compact; the first is distinguished by its softness and elasticity, which, however, it partly loses on exposure to the air; the second, by its dull earthy appearance, and softness sufficient to take an impression from the nail; and the third, from its more or less conchoidal fracture, corresponding to the degrees of lustre it possesses. The component parts of these, however, are nearly the same; and, except in appearance and consistency, they do not differ from naphtha, a fine colourless fluid, which when first inspissated, becomes brown, and is then changed into mineral pitch by exposure to the air. Bitumen is usually of a black or brownish hue, is easily inflammable, and burns with a bituminous smell, much smoke, and a clear flame; some varieties even melt at a higher temperature. In specific gravity it varies considerably, from 0·828 to 1·160 according to its density; and in composition it consists chiefly of hydrogen and carbon. The substance called petroleum is a liquid bitumen, apparently formed of asphaltum dissolved in naphtha. The elastic variety has been found principally in the Odin mine at Castleton, in Derbyshire; and from its property of taking up the traces of a pencil in the same manner as India-rubber, it has obtained the appellation of mineral caoutchouc. The semi-liquid species abounds in Trinidad, where it forms a lake said to be three miles in circumference, and where, when mixed with grease or common pitch, it is used for paying the bottoms of ships. It has also been met with in Persia, in Dalmatia, and in the Hartz. The compact variety again, occurs, forming nodules, in the lead mines of Matlock in Derbyshire, at Hurlet near Paisley, in sandstone near Bathgate in Linlithgowshire, imbedded in sandstone in Albania, Hanover, and in many parts of the Continent. The more liquid varieties of this mineral admit of considerable application for illuminating, for fuel, in the manufacture of varnish, &c., besides its common application to pavements.

The bitumen employed by the ancient Babylonians, instead of mortar, to unite the sun-dried bricks in their colossal structures, was evidently the semi-liquid bitumen which we now designate petroleum; and the state in which the mighty ruins still exist shows how imperishable a cement this material afforded. The principal source whence this bitumen was obtained was the fountains of Is, the modern Hit, on the right bank of the Euphrates. These fountains, which are considered as an inexhaustible source of bitumen, still continue to pour it out copiously, mingled with intensely saline sulphureous thermal waters. Much fine salt is now made there by a rude process of spontaneous evaporation; but the bitumen floating on the waters is now only employed to pitch the wicker boats and coracles of the Euphrates and the Tigris. The celebrity of these fountains caused them to be visited by Alexander the Great, by Trajan, and by Julian. The geology of the district presents little peculiarity; the principal rock being an argillaceous limestone, over which in many places lies a coarsely-granular gypsum; but the cause which has for several thousand years produced a perennial distillation of bitumen in this spot, lies probably at a considerable depth below the surface.