66 



PKESJDliNTIAL ADDRESS SE< TIOX A. 



has been one of the most satisfactory features of the present 

 war, has, in the main, been due to the petrol engine. 



The world's supply of crude oil, which, as already stated, 

 was 57,000,000 tons in 1914, has only increased at the rate of 

 6 ])er cent, for the three previous years. The amount of petrol 

 obtainable from crude petroleum does not exceed 10 per cent., 

 so that in 1914 the total yield was not much over 1.700 million 

 gallons. America al)sorbed 1,200 million gallons of this, and 

 Great Britain, which in 1910 imjiorted 55 million gallons, took 

 120 million (rallons. 



1906 1907 1908 



1909 1910 

 YE/\R. 



1911 191? 1913 1914 



Fig. 41. — Diagram slinwing production of crude oi! and ini])i)i-t of petrol 

 into the United Kingdom. 



\ motor sjjirit is one sufficiently volatile to furiii an explo- 

 sive mixture at ordinary atmospheric temperature. T'etrol, 

 which is distilled from petroleum at a temi)('rature below 25o°F., 

 and has a specific gravity below .75. has admirabh met this con- 

 dition, but as the su])])ly decreases, there is a gradual tendency 

 to carr\- the distillation fin-ther and increase the sjiecific gravilv 

 so as to increase the yield, producing a less volatile sj)irit, and 

 decreasing the facilit}- of starting of tiie motor, b^fforts are 

 further l)eing made to increase the yield of motor spirit by 

 cracking heavier distillates of ]>etroleuin into more volatile 

 fluids, and by the destructive distillation of coal and shale. 



Benzol, the most generally used petrol substitute, is obtained 

 from tlie light oils obtained by coal tar distillation, and extracted 

 from the gases and vapours given oft from recovery coke ovens. 

 Tt has a lower calorific value than ])ctrol. but, since its specific 

 gravity is greater ( .SS^^)), its caloritic \-alue ;)er gallon is greater, 

 and greater power is obtained for e([tial consumption. In 1914. 

 nine million gallons of benzol were used in spirit motors — a verv 



