Maltha (Gr. , soft wax; also denoting a mixture of wax and pitch, used for the surface of writing tablets, and for some kinds of cement). Pliny describes under this name an inflammable mud flowing from a pool at Samo-sata, on the Euphrates, which he says was similar in nature to naphtha; and this use of the word has led to its later application to viscid bitumens. It is the proper name for mineral tar, or all bitumens having the consistence of tar, and holding water and air in mechanical admixture in consequence of their viscidity. It occurs on the surface of the ground and issuing from springs, often accompanied by water, in various parts of the world, but most frequently in localities noted for the production of petroleum, for which substance maltha is frequently mistaken. It appears to be a product of the partial oxidation or decomposition of certain unstable varieties of petroleum, and doubtless in all cases has a common origin with it (see Petroleum), as it passes by insensible degrees into petroleum on the one hand and asphal-tum on the other.
It is found in this country throughout the length of California, in Texas, and at various places in the southwest, on both flanks of the Rocky mountains, and in Alaska. Among foreign localities may be mentioned Enniskillen in Canada, the islands of Barba-does and Trinidad, many localities in South America, some of the islands of the Grecian archipelago, and the Caucasus. In California, where there are immense quantities of this material, it occurs in every variety of density, from 0-94 to 1. In consistence it varies from that of a thin sirup to that of soft mortar. It issues there from a stratum of shale of considerable thickness which occurs in the miocene sandstones of the Coast range. It oozes from springs upon hillsides, over which it trickles; it accompanies water in pools, and flows upon the surface of streams. It has been obtained from artesian borings at a depth of more than 450 ft. of the consistence of tar, and at a depth of 117 ft. so tenacious as to prevent the drill from penetrating further. In a few localities in this region the maltha is mixed with sand, the mixture forming strata or beds of great | extent. At Enniskillen the maltha forms what are known as - gum beds." Barbadoes tar was long an article of commerce, used in medicine as a liniment.
The California malthas have been used to some extent as a crude material for the manufacture of kerosene; but they have not been found to possess much value for this purpose when treated in the same apparatus as is used for petroleum; when it is distilled under pressure, or "cracked," a better result is obtained both as regards yield and quality. - Little is known regarding the chemical constitution of maltha; but it is without doubt a mixture of hydrocarbons more dense than those found in petroleum. Some specimens contain nitrogen, as is proved by the fact that maggota are developed in immense numbers in pools of this substance. It is also possible that oxygen is a constituent of some varieties. While this substance is widely distributed and occurs in vast quantities in some localities, it is at present very much less valuable than petroleum. It is readily distinguished from it by its greater viscidity and its tendency to froth when heated, the froth often occupying 20 times the bulk of the maltha at the temperature of boiling water.