316 



pipe, thus preventing the free egress of the escape steam, 

 and diminishing the effective pressure upon the piston. 



That the boiler being much exposed, and passing through 

 the air with great velocity, is subjected to considerable loss 

 of heat. 



That the engine, boiler, tender, stock of fuel and water, 

 have to be transported at a high velocity, in addition to the 

 useful weight of the train. 



It is perhaps impossible accurately to calculate numerically 

 the separate amount of each of the foregoing deductions from 

 the power of the engine, but it has been practically ascer- 

 tained, that in the aggregate they amount, in the case of 

 average trains, to more than the amount of useful effect or 

 duty obtained from the engine. 



But when the trains are small in proportion to the engine, 

 the loss becomes much more than 50 per cent. 



The cost of the coke consumed by the locomotive is, on 

 the average, at least twice that of the coal required for pro- 

 ducing an equal amount of power with a stationary engine ; 

 so that the loss of power of the locomotive, as regards the 

 cost of fuel, must be multiplied by two ; so that out of an 

 amount of power estimated in money, only 25 per cent, is 

 usefully applied in working locomotive engines. 



But the loss of power is by no means the greatest disad- 

 vantage attendant on the use of the locomotive engine. 



The great weight of the engine, and the avoiding much 

 play of the crank axle, by which it might in some measure 

 escape from the impulse of the piston rods, renders it ne- 

 cessary that the bearing springs be very rigid ; so that the 

 machinery is liable to constant derangement from concus- 

 sion.. 



Many parts of the engine are subject to much friction, 

 under heavy weights and at high velocities ; so that the wear 

 and tear by friction is very considerable. 



