THE problem of using solid and liquid fuels in intimate admixture for general industrial purposes is not new. Tentative proposals were made from time to time which did not lead to commercial or technical application.

The exigencies of the War directed attention to the possibilities of substituting indigenous coal for imported fuel oils, particularly for naval purposes. Towards the end of 1917, Capstaff and Sheppard began work on preparing colloidal mixtures of coal and oil, and this work led to intensive investigation by the American Submarine Defence Association, under the direction of Lindon W. Bates. At about the same time, and without knowledge of the work begun in America, R. Lessing studied the problem on behalf of the Fuel Oil Section of the Admiralty.(Samples of oil-coal mixtures prepared at the beginning of 1918, i.e. 151 years ago, were exhibited at the meeting.) The exploitation of the preparation of " colloidal " fuels was prosecuted by L. W. Bates after the War, but without leading to successful commercial application.

Experiments carried out in England about 1922 by the Great Central Railway, with mixtures of Yorkshire coal or coke breeze, and creosote oil or fuel oil on locomotives gave satisfactory results, but were not followed by the use of such mixtures- under regular service conditions.

The general adoption of oil fuel for naval purposes had shown the great advantages, the saving in stokehold personnel and the general convenience of liquid fuels, and rapid advances were made during the last decade in the use of oil for the propulsion of ships of the Mercantile Marine, both in the furnaces of steam-driven vessels and in Diesel engines of motor ships.

Although an immense amount of literature was published, particularly in the immediate post-War period, on the subject, much of which was based on somewhat inadequate scientific evidence or interpretation, general interest in the problem showed signs of flagging, until it was revived in the summer of 1932 by the announcement that so important an undertaking as the Cunard Steam Ship Company had fitted out one boiler of S.S. Scythia for burning a 60/40 mixture of oil and coal, and that this vessel had made a voyage from Liverpool to New York during which 150 tons of this fuel were fired. The results were stated to be satisfactory, although the burners required more frequent cleaning than when oil alone was used.

Interest was further stimulated by the news that experiments with mixtures of tar oil and coal on land boilers in Germany gave promising results.

The advantages of firing a coal in admixture with oil are obvious: (1) Coal can be stored in bunkers without interstitial air spaces. The bulk weight of an oil-coal mixture is higher than that of either coal or oil, and the calorific value per u

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