AMERICAN INSTITUTE. 699 



cold for efficient condensation. High pressure engines demand 

 great accuracy in fitting the joints, that they may be steam tight, 

 yet they possess the advantage that leaking is sooner discovered in 

 them than in low pressure engines. The usual practice in high 

 pressure engines of blowing through at starting, by which both 

 time and steam are lost is unnecessary, and should not be resorted 

 to, as the pressure of air in the engine, is rather an advantage 

 than otherwise, as when expanded by the heat, it serves to assist 

 the motion. 



The use of high pressure steam, allows a temporary augmenta- 

 tion of the usual power of the engine by slightly increasing the 

 production of steam in the boiler. All the parts are constantly 

 in readiness to receive and apply a higher pressure of steam. It 

 is not so with the condensing engine, as the condensation is only 

 adapted for a certain quantity of steam at each stroke, and if a 

 larger amount were to be thrown in, there would be an imper- 

 fect exhaustion of the cylinder, which would neutralize any 

 attempt to increase the power of the engine, by an augmented 

 pressure of the steam. It is on this account that the high pres- 

 sure engine is invaluable for locomotive purposes. Mr. Gurney 

 proposed to use in the boilers of his locomotive carriages, steam 

 of a high pressure, which was wire drawn to two or three atmos- 

 pheres in the engine by a diminution of the opening of the throttle 

 valve. When therefore he washed to increase the power of his 

 engine, he opened this valve a little wider, by which means he 

 proposed to adapt his engine to overcome the ascent of hills. 

 This plan of wire drawing the steam is considered a favorable one 

 in regard to economy. 



The high pressure is more economical in fuel, which advantage 

 is developed partly in the generation of high pressure steam, and 

 partly in consequence of its more suitable application to its pur- 

 pose in the machine itself The Americans have positively deter- 

 mined this important but doubted fact. If we could supercharo-e 

 steam with free caloric in an engine, much economy would result. 

 It is difficult to do this without destruction to the packings and 

 other working parts of the machine. The peculiar economy of 

 the high pressure engine arises from a more suitable application 



