The chemical composition of petroleum consists essentially of carbon and hydrogen, together with oxygen and varying amounts of nitrogen and sulphur. The crude from Pennsylvania--and this is the finest crude in the United States--consists chiefly of a large number of hydrocarbons of the paraffin series, whilst in the Russian petroleums, the predominant constituents are naphthenes or polymethylenes. Then the crude petroleum of the Dutch Indies and Burmah is of a different character from that found elsewhere, for in it aromatic hydrocarbons are largely present. The various series of hydrocarbons found in crude oils--the paraffins and naphthenes--readily lend themselves to conversion into other compounds of carbon and hydrogen by dissociation, and this conversion produces compounds of higher volatility, such as motor spirits, etc. When the compounds of hydrogen and carbon are submitted to distillation, certain chemical changes occur, as the result of which other series of hydrocarbons are formed, and, though it is not my intention here to dive into this comparatively new realm of chemical investigation, it is interesting to mention that, by carrying the treatment of the compounds still further, it is possible to obtain aromatic hydrocarbons, including trinitrotoluene (generally known as the explosive T.N.T.), in addition to various dye products. In the earlier methods of refining, the stills usually consisted of a vertical cylinder in which the charge of crude oil was distilled almost to dryness, but this method was completely revolutionized many years ago, especially in the United States, by the introduction and immediate success of a principle known as the “cracking” process, and by the separation of the distillation into two portions, one for the removal of the more volatile constituents in the crude oil (such as motor spirit) and the other for the treatment of the heavier products. CRUDE OIL