324. Importance of coal, estimated in steam horse-power.—A horse-power, the technical unit adopted for measuring the working capacity of an engine, is for practical purposes equal to the force that can be got from several (perhaps three) horses, or from a number of men variously estimated at ten to twenty-four. Now in round numbers the steam horse-power of the world was a million and a half in 1840, and had increased, at the end of the century, to fifty times that amount. A simple operation in arithmetic will show the amount of work, in human equivalent, now done by steam. Taking, for example, a modern country, Germany, we find engaged in industry and transportation slightly over ten million people, while we find engaged beside them another population of mechanical iron slaves (steam-engines), variously estimated as equivalent to one hundred to two hundred and fifty million people. These slaves cost for food (coal), attendance, doctor’s bills (repairs), and burial expenses (including the cost of replacing them once in twenty-five years), only about $2.50 a year apiece. Admit some exaggeration in the figures, and still the contrast with the cost of human labor is most striking.
325. Technical history of the steam-engine.—The steam-engine has been in practical use in Europe since about 1700. The earliest engines, however, seem ludicrously crude now, and could be used only for pumping water. Progress was slow until the last part of the eighteenth century, when James Watt introduced improvements (separate condenser, double-acting piston, use of cut-off, etc.), which greatly increased the efficiency of the engine, and caused a gradual extension of its use from mining to manufactures. The introduction of the non-condensing, high-pressure engine about 1800 prepared the way for the use of steam on railroads. The compound engine, in which the steam passes through two or more cylinders before it is allowed to escape, was invented about the same time, though it was not brought into general use until about 1850. Since then improvements in details of the engine and in the form of boilers have enhanced still further the efficiency of steam power, until it now produces about two thirds of the work possible under ideal conditions. Practical engineers expect now no rapid progress or startling changes. Some measure of the progress achieved is furnished by the fact that Watt’s engines required ten pounds of coal an hour for each horse-power, the engines of the next generation required five, while the best modern engines require but one and a half, or, in rare cases, one.
The previous paragraph referred to the reciprocating engine in which the piston moves constantly forward and back. Since rotary motion is the form in which the power is commonly transmitted and applied, it would be desirable to get the motion in this form originally, and many attempts have been made to make rotary engines. Success has been attained in the case of the steam turbine, in which jets of steam strike against the blades of a turbine wheel, and cause it to revolve. Originally applied by Dr. De Laval of Sweden to operate the centrifugal cream separator which he had devised, it has come into common use for the generation of electricity and for the propulsion of ships. While the steam turbine has proved its efficiency for special purposes it is less adaptable than the old form of reciprocating engine, and still leaves to that the larger part of the field.
326. The internal combustion engine.—In the ordinary power plant there are two units, the boiler in which steam is generated, and the engine in which the steam is put to work. An internal combustion engine is designed to burn the fuel in the engine itself. This is practicable when the fuel is a gas or a liquid whose vapor will unite with the oxygen of the air to form an explosive mixture. The internal combustion engine offers several advantages over the steam power plant: it uses more effectively the heat that is generated, it is less bulky, it is more easily tended. In spite of characteristic disadvantages, particularly the need of an auxiliary starter, and restricted flexibility as regards speed and power, the internal combustion engine has proved indispensable. In large units it serves the steel mills, which put the waste gases from their blast furnaces to work, and in its application to the automobile it has effected a revolution in transportation and travel. Although in the manufactures of the United States in 1914 the internal combustion engine still accounted for less than 5% of the total horsepower, the aggregate horsepower of the gasoline engines of automobiles has since that time considerably exceeded the total horsepower from all sources employed in manufacturing industry.
QUESTIONS AND TOPICS
1. Do not attempt to remember any of the figures in sect. 316, unless possibly the first two of the last line.
Prepare a graphic chart in the following way. Lay off the time periods on the horizontal line at the bottom of your paper, and on the perpendicular, near the right-hand margin, lay off the figures of the last line of the table. This will insure space in the chart for all the lines. Divide the perpendicular into, say, forty units. Each unit may then be made to represent: 1,000 million dollars of value; $1 per capita; 40 million tons of coal; 2 million tons of iron. Indicate the figures for 1913 on the perpendicular (commerce 40, per capita commerce 24, coal 36, iron 39); and perform the same operation for the figures on perpendiculars above each of the other dates. Use for each item a characteristic mark, (cross, circle, triangle, square), which will enable you to distinguish it from the others. Then unite the marks of each kind by a curved or crooked line. Choose a characteristic form of line (dotted, wavy, or colored) for each item. If the chart be made on a large scale and with sufficient neatness, later tables of statistics (development of railroads, trade of particular countries, etc.), can be entered upon it.
With regard to each one of the items: when was the increase (measured by the slope of the line) greatest? When least? What relation is apparent in the increase of different items? Many of the questions suggested by a study of the figures will be treated in later sections.
2. Prepare a small chart of the figures, giving the estimated value of commerce 1700-1899; note the enormous gains made in the nineteenth century.
3. Development of printing, especially of periodical publications, in recent years. [Encyc., preferably the new International or Supplement to the Britannica, under Printing, Newspaper, etc. Cf. Scribner’s Magazine, 1897, vol. 22, p. 447 ff., on the modern newspaper business; Taylor in Depew, One hundred years, chap. 25, Williams in same, chap. 26.]