Petroleum : Us Sources and Uses. 
379 
from 1 to 15. The Caucasian oil has the general formula C„H 2 „ ; 
and olefiant gas or ethylene, CjH^, appears to be the lowest of the 
series, n rising in value to 15. When exposed to heat — either in 
the ordinary process of distillation, or when, by working under 
pressure, the temperature is raised above that due to the atmospheric 
boiling point — the crude oil “ cracks,” as it is termed, and the 
vapours of different boiling points, but still of a homologous chemical 
composition, are given off in succession, and in varying proportions ; 
indeed, in some districts rock oil issues from the ground in the form 
of gas, even at ordinary temperatures and pressures. 
Petroleum, in a form not to be distinguished from the natural 
product, has been produced artificially by the action of steam at 
high temperature and pressure upon the carbides of metals, more 
especially on those of iron : the water is decomposed, the oxygen 
combining with the metal, and the hydrogen, in part at least, with 
the carbon. This cii’cumstance, among others, led Dr. Mendeleeff 
in 1877 to propound a theory which I will sketch very briefly, be- 
cause, if correct — and I believe it to be gaining in general accept- 
ance, — it gives an assurance of inexhaustible supplies of oil, and 
also indicates the probability of the occurrence of this product in 
every part of the world, quite irrespective of the age of geological 
formations ; and so holds out motives to engineers to perfect the 
means of penetrating much deeper into the heart of the earth. 
Laplace’s theory of the origin of the planetary system is generally 
accepted as correct ; and according to it the earth must be composed 
of the same materials as the sun. This view has in latter days 
received striking confirmation from the spectroscope, by means of 
which it has been demonstrated that there exist in the sun many 
of our metals, and especially iron, in the state of vapour : while 
meteoric stones, which belong to the same order of substances as the 
planets, have been found by actual analysis to be largely composed 
of iron and its carbides. The law of the diffusion of gases would lead 
us to expect that on the condensation of the metallic vapours the 
substances of higher specific gravity or greater atomic weight would 
collect chiefly nearer the centre of the future globe, while the 
lighter matters would tend to aggregate on the surface. The mean 
specific gravity of the earth is about 5, while that of its superficial 
deposits ranges from only 2^ to 4 : so that it is evident that the 
interior of the globe must be composed of substances having high 
specific weights — such as iron, for example, which ranges between 
7 and 8. Moreover, it is certain that the rocks at a comparatively 
short distance down from the surface exist in a highly heated if not 
in a molten condition ; and that the solid crust covering them is 
relatively thin and easily fissured, as is abundantly proved by the 
upheaval of the land in geological and even in modern times, and 
by the earthquake disturbances which prevail more or less over the 
whole world even now. 
Dr. Mendeleeff points out that the oil-bearing regions generally 
lie parallel to mountain ranges, such as the Caucasus in Russia, the 
Alleghanies in America, and the Andes in Peru ; and that petroleum 
