Page:Popular Science Monthly Volume 13.djvu/79

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THE GROWTH OF THE STEAM-ENGINE.

improvement we may feel assured will rapidly take place, as it is now becoming well understood that care, skill, and intelligence, are absolutely essential to economical management, as well as to safety, and that they repay liberally all the expenditure of time and money that is requisite to secure them. It is truer of labor than of anything else in the market that "the best is the cheapest."

In attempting improvement in the directions that I have indicated, it would be the height of folly to assume that we have reached a limit in any one of them, or that we have even approached an impassable limit. If further progress seems checked by inadequate returns, when efforts are made to advance, in any promising direction, beyond present practice, it becomes the duty of the engineer to detect the cause of such hinderance, and, having found it, to find a way to remove it, if such removal is not physically impossible.

A few years since the movement toward the expansive working of high steam was checked by experiments seeming to prove positive disadvantage to follow advance beyond a certain point. A careful revision of results, however, showed that this was true only with engines built, as was then common, in utter disregard of all the principles which should have been observed in such use of steam, and of the precautions necessary to be taken to insure the gain which science has taught us should follow the intelligent use of higher pressures of steam. The obstructions are purely physical and mechanical, and it is for the engineer to remove them.

An analysis of the methods of waste of heat, in the operation of the modern steam-engine, would show that a very large proportion—nearly all, in fact—is due to the rejection of unutilized heat with the exhaust steam. In the best engines in general use this loss amounts to from eight-tenths to nine-tenths of the total amount of heat derived from the fuel. Modern steam-engines lose nearly all wasted heat in this way; the losses by conduction and radiation are comparatively small. It is at once evident that the only way in which any very great additional economy can be secured is to reduce to a minimum the quantity of heat remaining at the opening of the exhaust-valve, and then to retain this rejected heat within the system, so far as is possible, and to thus prevent its waste by escape from the system. The reduction of the great quantity of heat left for rejection at the end of the stroke of the piston can only be effected, to any important degree, by expedients which check that internal condensation and reëvaporation which, with great expansion, transfer to the condenser, unutilized, an immense amount, often, of the heat supplied. As already stated, these expedients are the use of dry steam, the adoption of the steam-jacket and of high engine-speed, and the use of a material for the interior lining of the cylinder which has the least possible conductivity.

The retention of the heat actually rejected from the cylinder, and its complete utilization by reworking, is practically a matter of diffi-