1 Per square inch above atmosphere.

2 Based on the i.h.p. and the lower heating value of the fuel.

It must be borne in mind that by far the larger proportion of the work that has been done on internal combustion engines has been carried out with the object of perfecting them for use with petrol. It may well be that when a similar amount of research has been directed to the use of alcohol, this liquid will be found even more suitable than petrol as a motor fuel.

Possibly the question already is less one of suitability than of price. To be the more economical fuel, alcohol must be at a lower price per unit of volume than petrol. Benzol, also, which at the time of writing is being produced in large quantity for war requirements, may prove to be a serious competitor when no longer needed for munitions of war.

Whilst it is true that most of the work on internal combustion engines has been done with reference to petrol, yet, as already stated, a good deal of experimentation with alcohol-motors for agricultural work, and also for locomotive purposes, has been carried out on the Continent. This has been the case more especially in Germany, where the industry has been carefully fostered. The practicability of alcohol motors has been proved, and a good number of such engines of French and German make are in use for driving light machinery, pumping, threshing, and similar work. Alcohol-driven engines made in England have been employed for several years in Egypt and parts of South America. How far the use of such engines will be extended depends upon the relative working costs, upon questions of supply and distribution, and on the facilities obtainable in particular circumstances. For example, in a country which must import its petrol, but can produce its own alcohol, considerations of expediency might lead to preferential fiscal treatment of alcohol used for motors, in order to diminish the country's dependence upon foreign supplies of motor fuel, and also incidentally to foster its agricultural industry through the increased demand for grain, potatoes, or beet required to produce the alcohol.

In fact, though the day is not yet at hand, through the dim but perhaps not very distant future there looms the probability that when the stores of coal and petroleum at present "in sight " begin to get depleted - as some are even now - the world's industrial needs will have more and more to be met by utilising the sun's present energy through the instrumentality of alcohol employed as a source of heat and motive power, as well as his past energy stored in the form of coal and petroleum.

In this connection it may be noted that some years ago a United States official estimate indicated that the older oil-fields would probably become exhausted in about thirty-five years if the rate of increased production observed at that time were maintained. Of course any estimate of future supplies may be affected by the discovery of new oil-fields, or of new methods for utilising shale oils such as those of the Kimmeridge deposits in this country, which are at present unmarketable on account of their sulphur content; but the eventual exhaustion is only a matter of time. Meanwhile, industrial demands for liquid fuel become greater and greater. About 120 million gallons of petrol were imported into the United Kingdom in the year 1914-15, the quantity having more than doubled in four years.