Leaving the question of drilling methods, I cannot fail to mention the interesting fact that in oil-field operations progress is now being recorded in another direction, and that is by the increasing utilization of electrical power in the place of steam. At the time of writing, it is safe to say that fully 60 per cent. of the power requirements on the oil-fields is provided for by steam plants, with their attendant waste. Oil and gas engines, with their greater efficiency, may claim to be operated to an extent of 35 per cent., while not more than 5 per cent. of the requirements are satisfied by the use of electric motors. There is no doubt that prejudice has had a deal to do with the very minimized use of electrical power on the oil-fields in the past, but this is being gradually swept aside, and, in the next few years, I have no doubt that both electrical manufacturers and the petroleum industry generally will materially benefit from the use of this cheap and very economical form of power. In the past, many disastrous oil-field conflagrations have been due solely to the use of open-fired engines in close proximity to the wells, but with the use of electrical energy this fire danger will be rapidly removed. Before closing this chapter, I would say a word or two with respect to the bringing into the producing stage of the oil-wells when once they have been drilled. In the early history of oil-held developments, it was not infrequent to find the crude oil ejected from the well by natural pressure, but to-day it is the exception to find those oil-fountains which have made the early history of the Russian oil-fields so famous. In many of the fields, explosives are used to promote the flow of oil, and when the well “comes in” to production, the ordinary methods of bailing or pumping are resorted to. Compressed air is also used for bringing about and sustaining production. The quantity of air and the periods of admission naturally vary with the diameters of the wells, the amount of gas present, the level of the liquid, etc., which latter also determines the pressure of air necessary. The natural exhaustion of oil-wells can obviously have no remedy, but areas conveying that impression can often be revived by methods, the study of which is being carefully continued. As I write, I find that the officials of the United States Bureau of Mines, who have been studying this question of exhaustion, have arrived at the conclusion that from 20 to as much as 90 per cent. of the crude oil remains in the strata tapped by the well, even when it is abandoned as no longer capable of profitable production. This conclusion opens up what may prove some day to be a most interesting chapter in oil-field history. CHAPTER IV THE REFINING OF PETROLEUM