A History of the Growth of the Steam-Engine

by Robert Henry Thurston

Now, looking back over the history of the steam-engine, we may briefly note the prominent improvements and the most striking changes of form, and may thus endeavor to obtain some idea of the general direction in which we are to look for further advance.

Beginning with the machine of Porta, at which point we may first take up an unbroken thread, it will be remembered that we there found a single vessel performing the functions of all the parts of a modern pumping-engine; it was, at once, boiler, steam-cylinder, and condenser, as well as both a lifting and a forcing pump.

The Marquis of Worcester divided the engine into two parts, using a separate boiler.

Savery duplicated that part of the engine of Worcester which performed the several parts of pump, steam-cylinder, and condenser, and added the use of water to effect rapid condensation, perfecting, so far as it was ever perfected, the steam-engine as a simple machine.

Newcomen and Calley next separated the pump from the steam-engine proper, producing the modern steam-engine—the engine as a train of mechanism; and in their engine, as in Savery’s, we noticed the use of surface condensation first, and subsequently that of the jet thrown into the midst of the steam to be condensed.

Watt finally effected the crowning improvements, and completed the movement o£ “differentiation” by separating the condenser from the steam-cylinder. Here this process of change ceased, the several important operations of the steam-engine now being conducted each in a separate vessel. The boiler furnished the steam, the cylinder derived from it mechanical power, and it was finally condensed in a separate vessel, while the power which had been obtained from it in the steam-cylinder was transmitted through still other parts, to the pumps, or wherever work was to be done.

Watt, also, took the initiative in another direction. He continually increased the efficiency of the machine by improving the proportions of its parts and the character of its workmanship, thus making it possible to render available many of those improvements in detail upon which effectiveness is so greatly dependent and which are only useful when made by a skillful workman.

Watt and his contemporaries also commenced that movement toward higher pressures of steam and greater expansion which has been the most striking feature noticed in the progress of steam-engineering since his time. Newcomen used steam of barely more than atmospheric pressure and raised 105,000 pounds of water one foot high with a pound of coal consumed. Smeaton raised the pressure somewhat and increased the duty considerably. Watt started with a duty double that of Newcomen and raised it to 320,000 foot-pounds per pound of coal, with steam at 10 pounds pressure. To-day, Cornish engines of the same general plan as those of Watt, but worked with 40 to 60 pounds of steam and expanding three or four times, do a duty probably averaging, with the better class of engines, 600,000 foot-pounds per pound of coal. The compound pumping-engine runs the figure up to above 1,000,000.

The increase in steam-pressure and in expansion since Watt’s time has been accompanied by a very great improvement in workmanship—a consequence, very largely, of the rapid increase in perfection, and in the wide range of adaptation of machine-tools—by higher skill and intelligence in designing engines and boilers, by increased piston-speed, greater care in obtaining dry steam, and in keeping it dry until thrown out of the cylinder, either by steam-jacketing or by superheating, or both combined; it has further been accompanied by a greater attention to the important matter of providing carefully against losses by radiation and conduction of heat. We use, finally, the compound or double-cylinder engine for the purpose of saving some of the heat usually lost in internal condensation and reëvaporation, and precipitation of condensed vapor from great expansion.

It is evident that, although there is a limit, tolerably well defined, in the scale of temperature, below which we cannot expect to pass, a degree gained in approaching this lower limit is more remunerative than a degree gained in the range of temperature available by increasing temperatures.[116]