116.    --------------. [AYRES, E] The Fuel Problem.  Sci. American, vol. 181, No. 6, 1949, pp. 32-39.

                 As our petroleum resources decline (the peak of production is expected to be reached between 1955 and 1960) the 2 most abundant solid fuels, oil shale and coal, must be utilized.  The major problem in their utilization is their conversion into the liquid state.  Technological research has already developed methods to accomplish this, and it is quite possible that in a reasonably short period further development of these methods will bring these fuels into a favorable competitive position with petroleum fuels.  General discussion is given of the methods for converting the solid fuels into liquid fuels: Oil-shale retorting, direct coal hydrogenation by the Bergius process, and indirect coal hydrogenation by the Fischer-Tropsch method.  The cost problem is surveyed, and the economic evaluation of each method is discussed.  The Fischer-Tropsch method of conversion appears to have the best possibilities as an economic producer of liquid fuel.