ENGINES. STEAM, STATIONARY RECIPROCATING. Great progress has been made in stationary steam-engine practice during the last ten years along the lines indicated in the article on steam-engines in Appletons' Cyclopedia of Mechanics. No revolutionary invention has been made during this time, but there has been a steady and rapid development in the direction of stronger and more rigid engines, higher steam-pressures, higher speeds, the substitution of automatic ent-off for throttling-engines, the more general employment of condensers, and the quite general use of compounding. The ('orliss engine still holds the first rank as the most economical and generally satisfactory type. and the number of makers of this engine has greatly increased. The changes consist chiefly in higher rotative speeds, 100 revolutions per min. being, now not uncommon. A speed of 100 revolutions per mi.. or 1,120 ft. piston-speed, has been recorded in the Corliss engine (20 in. X 42 in.) in the Trenton (Trans. A. S. p. 72.) With the increase of speed there has sarily come greater constructive stiffness and larger hearing surfaces. The Corliss engine is now usually compounded for large powers. with considerable increase of economy. The two cylinder cross-eomponnd engine at the Pawtucket (l(. 1.) Water-Works has shown a water consumption of less than 14 lbs. per hour per horse-power. and the triple-expansion engine at the Narragansett Electric Light Station, Providence, R. I., a water consumption of less than 13 lbs. (Sec Trans. A. S. it. E., vol. xii.) The automatic cut-off engines, with shaft or fly-wheel governors, of which the Buckeye and the St Line engines. shown at the Centennial Exhibition in 157G, were the first. prominent examples. have come very largely
into use, especially for small and moderate powers, supplanting the n111 forms of slow-speed throttling-engines. There has been a eontinnal increase in the speed of these engines, 300 revolutions being quite common for engines of 12-in, stroke, and for longer stroke engines a piston-speed of from 600 to SOO ft. per min. is frequently used. The especial advantages of this form of engine are great compactness, moderate first outlay, low cost of foun dations and erection, and great regnlarity of speed. due to the sensitiveness :aid efficient netion of the governor, which makes them especially well fitted for eleetrie-light purposes. They generally show eonsiderable gain in economy of steam over the Itrottling-engine, but have not yet sqmde11 the Collis,: engine in thig rospoct. Their greater percentages of (dear:ince, and apparently greater tendency to valve leakage, are probably the chief canses of their defects in this particular. Condensation and compounding are now frequently used with these engines, and for elvetrie-lighting purposes n vertical three-cylinder compound, with eranks 120°, is becoming a favorite form of constrnetiou. More eetntnon, ever, is the two-cylinder tandem compound horizontal engine. either with or without con denser.
The enormous increase in the demand for steam-engines during the past ten years. chiefly due to the introduction of electricity for lighting and for transmission of power, has led to a great increase in the number of engine-building firms, and to great diversity in the mechanical details of the engines.