PETROL.
How common yet important petrol has come to be, few of us realise, though most of us are daily dependent in a measure on its usage. Its production and distribution give employment to considerable numbers of men in different parts of the world, oil wells, from which petrol is obtained being found as far apart as Mexico and Burma. The same process, however, has to be employed to render the output of these underground lakes, tapped by human ingenuity, beneficial to mankind.
The crude petroleum which sometimes gushes up, is run into large storage tanks and thence conveyed to the refineries often miles away.
The cost of its transportation has been greatly reduced by the method employed to convey it, namely: the pipe-line system which has entirely superceded other means and involves the maintenance of miles of great steel tubes.
At the refineries the crude petroleum which goes in as a thick brown sludgy substance is distilled and the products condensed separately. This process is known as the " cracking process " and is carried out as follows : The " crude " is brought to a temperature which is the vapourising point of the component desired.
Light naphthas or petrol constituents vapourise at a temperature which scarcely scalds the skin. The oil is kept at the same temperature until all the naphthas are given off and the petrol can be condensed separately.
Then the temperature can be raised to the kerosene " boiling point " and held there until the kerosene constituents have been driven off, and so on until all that can be utilised is extracted. The residue, even, is not wasted, our great liners and warships using it for fuel. The light naphthas yield aviation petrol, and intermediate naphtha the ordinary petrol used in motor cars. The heavy naphtha, commonly known as benzine, is used in cleaning and in making paints and^, varnishes.
The next fractions give respectively, illuminating oil and gas oil. The last and heaviest, yields paraffin wax and various lubricants.
The greater use of petrol has been rendered necessary and has grown to its present dimensions by the constantly increasing utilisation of the internal combustion engine, whose range varies from great dynamos and submarine engines, to aeroplanes and the tiny outboard motor-boats. The rapidity with which modern transport has progressed is mainly due to this using of nature's stored up energies.
D. POTTS.