If the available power cannot be utilized near at hand by centralizing the industries near the source, there is no reasonable limit to the dis tance to which it can be transmitted if occa sion should require. The problem resolves itself largely into a question of voltage, which has steadily increased from the 4,000 to 6,000 volts in use not so many years ago to 40,000 and 60,000 volts which are now quite commonly employed ; but it appears that even 60,000 volts which was regarded as a high value a few years since has been far exceeded in the most recent developments. The Los Angeles transmission line for instance uses 150,000 volts, and the hydro-electric development at Victoria Falls, in South Africa, contemplates a line pressure of 200,000 volts through a distance of 700 miles. The possibility of electrical transmission thus permits the utilization of available sources of power at great distances from the centre of distribution; but while it is interesting to know that a certain amount of power may be trans mitted a given distance with a high degree of efficiency, it is more important to know whether the same amount of power could be obtained at the objective point more economically by other means.
Petroleum Fuel.— It has been suggested that the future of long-distance transmission depends largely upon the development of oil as a fuel; but at the present time the outlook for oil fuel in general competition with coal or long-distance transmission is not encouraging. While the development of the Texas and South ern California of fields has increased the visible supply and brought about increased activity in the use of liquid fuel, yet it is doubtful whether the advantages would be sufficient to cause it to come into general use as a fuel, since with a limited production and an increased demand for this and other purposes the cost would be cor respondingly increased.
A number of railroads contiguous to the oil-producing centres have equipped their loco motives to burn this fuel, and it is used to an increasing extent for marine and naval boilers, with great satisfaction,— since its displacement for a given heating value is only about one-half that of coal and the labor cost is materially re duced. It is also used quite extensively in certain sections of the country as a steam pro ducer in power plants, but it is hardly possible that liquid fuel will be a serious competitor of coal for steam generation. At present, as far as power for manufacturing plants is concerned, it is largely a question of transportation, whether oil can be laid down and handled at a given point more cheaply than coal. It is prob however, that oil fuel will supply a local demand in certain sections where transporta tion charges, and possibly insurance, will permit its use at a low cost, and it is in this connection that it may become a competitor of electrical transmission.
Internal Combustion Engines.— One inter esting phase of the power problem which forcibly presents itself at the present time is the vast possibilities possessed by the modern com bustion engine, which includes the various types of gas and oil engines. While its use as a motor in industrial establishments has been somewhat limited, yet there is a marked tend ency to employ the gas engine in manufactur ing works, and consideration of its advantages and cost of operation, together with its high thermal efficiency and possibility of still further improvement, indicates that, for a great many purposes, both steam engines and electric mo tors may be ultimately replaced by some form of internal combustion engine. That the gas engine in both large and small sizes has reached a point in its development where it can fairly rival the steam-engine in reliability and satis factory running qualities there can be no ques tion. In point of fuel economy, a gas engine of moderate size is on a parity with the largest triple-expansion steam engines, and will give a horse power on less than one pound of fuel. The high price of gas in this country has con tributed largely to those causes which have prevented a more common use of the gas engine as a motor. For this reason the gas engine has generally been used, not so much because of its high efficiency as a thermo-dynamic machine, but rather on account of its convenience and saving in labor. It is true that natural gas is cheap, but it is equally true that natural gas is not generally available. Fortunately the manu
facture of producer gas has reached a high state of development, and there are now in suc cessful use several processes by which power gas can be made from cheap bituminous coals as well as anthracite and coke. The leanness of such gases renders them less effective per cubic foot of gas, as compared with the richer coal gas or even water gas; but this difference is more than compensated for by the low cost of production.
A prominent factor in gas engine practice which has attained a high degree of develop ment in European practice is the small gas pro ducer. These generators are very simple in operation, and furnish a convenient and eco -nomical means of obtaining power at a much lower rate than with the ordinary city lighting gas. The economy of these small producers is shown by tests which give one horse power on a 16 horse-power engine with a consumption of only 1.1 pounds of fuel. For engines above 40 horse power one horse power can be obtained on seven-eighths pound of fuel. The success ful employment of large combustion engines with blast furnace gases as the explosive me dium utilizes vast sources of power which a few years ago were allowed to go to waste or, at most, were used very inefficiently. The high thermal efficiency of the gas engine has long been recognized and the possibility of further development is a promising factor in this field. The accomplished efficiency of 38 per cent re ported by Professor Meyer, of Gottingen, greatly exceeds the maximum theoretical effi ciency of the steam engine. With higher com pression even greater efficiencies may be ex pected. But with high compression there is danger of premature explosion, due to the gen eration of heat in compressing the gas in the presence of oxygen; for this reason Herr Diesel compresses the air separately. Under a pres sure of 500 pounds or more, which is used in the Diesel motors, the air becomes very hot and readily ignites a charge of liquid fuel which is injected into the compression chamber. There is no explosion; combustion occurs while ex pansion goes on, and the heat generated dis appears in the form of work. The United States census report for 1900 shows that about 135,000 horse power derived from gas or in ternal combustion engines were used in the industries, whereas, according to the latest (1910) report 750,000 horse power from gas and internal combustion engines were so used. That is, an increase of more than 500 per cent had taken place during the decade. The present development is toward the improvement of the internal combustion engine similar to the Diesel type, and this is accompanied by a marked tendency to use this type in marine engines ; especially is this noticeable in European practice where it is employed in sizes up to 2,500 horse power per cylinder. In the larger sizes these engines are of vertical construction double act ing two-cycle, and usually with six cylinders; but the fuel consumption is slightly greater in this type than in the four-cycle. The experi ence already obtained with Diesel engines in scores of vessels indicates that they may be made as reliable and that they are as suitable for ship propulsion as steam engines, which in a number of cases they have displaced. In many locations the crude oil used as fuel is available and cheap, and since its value in heat units per pound is from one-third to one-half greater than that of steam coal, the space occu pied by the fuel in the vessel is greatly reduced; moreover remarkably high thermal efficiencies are obtained in this type of engine and even greater may be expected in the future since tests with various oil fuels have shown that thermal efficiencies of 45 to 48 per cent are pos sible. At the present time one ton of oil will accomplish approximately as much work in a Diesel engine as four tons of coal converted into steam power. In addition to the greater economies due to the fuel there is a marked saving in space and weight in the power plant, since the internal combustion engines weigh only about half as much and occupy only two thirds of the space of the steam engines and boilers, which saving may be profitably used for cargo. These advantages and others indicate that internal combustion engines using crude oil, especially those of the Diesel or semi-Diesel type, must inevitably be used to an increasing extent both for land and marine engines.