156 FOSSIL HYDRO-CARBONS, 



from tliein by the agency of volcanic heat. The precise conditions tinder 

 which nature effects the distillation of these fossil hydro-carbons cannot be 

 accurately explained, but that they vary considerably, the results afford 

 striking evidence. Sometimes a gas is evolved from the springs or wells, 

 which burns with great brilliancy if ignited, and if there be any analogy 

 between the operations of nature and art, the presence of this gas indicates 

 considerable heat below. Accompanying the gas, there is usually an oily 

 ejection, of dark-coloured, bituminous matter, and of varying consistency, 

 partly dependent on the time of its exposure to the atmosphere. The oils 

 of America (United States), and Canada, just now exciting so much 

 attention, are of this class ; also the petroleum of Rangoon, and of the 

 Caspian Sea ; ■ the tar of Barbados, &c. In Asia Minor, this substance 

 exists to a considerable extent, in what are termed slime-pits ; indeed, an 

 abundant supply seems forthcoming from most parts of the world. Another 

 variety of bitumen is of the consistency of pitch — solid, but slightly 

 unctuous, as the Trinidad pitch ; and, lastly, there is the solid and brittle 

 form of bitumenfm the shape of asphaltum. Thus we have the different 

 gradations distinctly marked in the natural as well as in the artificial 

 products — gas, light naphtha, petroleum, pitch, and asphaltum. 



Coal-tar, and peat-tar, which may be not inappropriately called artificial 

 petroleums, are strikingly analogous to the liquid bitumens, both in external 

 characteristics, and chemical composition ; and the various products which 

 each contain, are, I believe, only combined mechanically, and can be easily 

 separated. The original difference existing in the vegetation, from which 

 all the fossil hydro-carbons have sprung, is equally illustrated by the 

 bitumens, as by the coals. Some are of great value, whilst others are 

 comparatively worthless, yet all possess certain properties in common, 

 which proves further their intimate relationship. 



Rangoon Tar, of which there is almost an unlimited supply to be had, 

 is of the consistency of treacle, of a dark, green colour, and powerful tarry 

 odour. 



Barbados Tar, and Baku Petroleum are of a similar consistency to the 

 Rangoon product, their colour, however, being of a dark brown, and odour 

 tarry. 



The American Rock Oils are much more liquid, of a green colour, and 

 not very powerful odour ; fabulous quantities of these hydro-carbons can 

 be supplied from Canada and the United States. 



Trinidad Pitch, although at first in a fluid state, quickly hardens by 

 exposure, and is generally received here in a solid form ; there is a great 

 abundance of it in the Island. 



Asphaltum Proper, so called after the mysterious lake (Asphaltites), upon 

 whose leaden waters it is found floating, is imported into this country in 

 moderate quantities. 



Besides these few enumerated Bitumens, there is an immense variety of 

 kindred products, too numerous to mention within present limits, but many 

 of which will doubtless be in industrial requisition before long. 



