Page:Popular Science Monthly Volume 18.djvu/506

490 the expanding gases allowed to do the work of the remainder, the piston is subjected to a pressure entirely similar to and as readily controlled as that exerted by steam in the steam-engine. The piston is lubricated by its lower edge dipping into a shallow pan, F, at the bottom of the cylinder, containing oil, and the other parts in the ordinary manner. The motor is easily and quickly stopped and started, and when running requires but little attention. It is made in any size desired under ten horse, but those constructed for the trade are of three and five, the former being sold at four hundred and fifty dollars and the latter at six hundred. They are of about the same weight as the Otto, of corresponding power, and occupy a somewhat less space.

The engine is economical in the consumption of fuel, and with the present abundant supply of oil is the cheapest heat-engine of small power yet made. Five gallons of crude petroleum are used, it is stated, in the three, and seven and a half in the five-horse engine for ten hours' running. This is at the rate of one sixth of a gallon or one and a quarter pound an hour per horse-power in the smaller machine, and somewhat less in the larger. As the calorific effect of petroleum is almost double that of coal, the engine is nearly as efficient as a steam-engine of large size, and much more so than one of the same power, while, on account of the cheapness of petroleum, the expense for fuel is no greater. The oil used can be obtained in comparatively small quantities at from six to seven cents a gallon, and at the latter price the cost of a horse-power per hour would be a little less than one and a quarter; cent, an expense considerably below the best results obtained in any of the engines using gas. This comparison is with the present cost of operating the latter motor, which is not one by which its possible economy is to be judged. The gas now used is the ordinary illuminating kind, and is high-priced. With a cheap fuel-gas, such as will assuredly come largely into use at no distant day, the cost would probably not be more than half that at present, and possibly less. This would bring it quite near that of the Brayton—near enough, at least, to make the advantage of the greater cleanliness and convenience of gas outweigh the gain in cheapness possessed by oil. An important objection to this engine is the one arising from the danger that accompanies the use of coal-oil. The motor itself is indeed quite safe, as much so as the gas-engine, and, if no more oil were stored than that in the tank from which the supply is drawn while working, the danger would be small. But when a considerable quantity is kept on hand in places where there is much valuable property, as in city buildings, the danger is sufficient to warrant increased insurance rates, and in some cases the prohibition of the machine. In situations where gas can not be procured, and where the use of oil would not be attended with the danger incident to crowded localities, it would probably be found one of the most satisfactory motors that can be had. Made in sufficiently small sizes of compact form, and with the oil receptacle and engine on one