THE STEAM LOCOMOTIVE 



The increased demand for greater speed has also 

 caused a marked increase in the amount of steam pres- 

 sure per square inch in the boilers. In 1870 the aver- 

 age was about 130 pounds; by 1890 this had been in- 

 creased to about 160 pounds; while at the present 

 time steam is used frequently at a pressure of 225 

 pounds. Naturally this increase in pressure compels 

 the use of heavier steel boiler plates. In 1890 the usual 

 thickness of the steel sheets was one-half inch; but at 

 the present time it is no unusual thing to use plates 

 seven-eighths of an inch in thickness. 



But probably the most important improvement in 

 locomotive construction in recent years is the intro- 

 duction of the compounding principle in the use of 

 steam — a system whereby practically the entire energy 

 of the steam is utilized, instead of a considerable por- 

 tion of it being a dead loss, as in the older type of 

 engine. As every one knows, the passage of the steam 

 through a single cylinder of an engine does not ex- 

 haust its entire energy. In the compounding system 

 this exhausted steam is made to pass through one or 

 more cyKnders after coming from the first, the energy 

 of all these cylinders being utilized for the production 

 of power. 



The application of this principle of compounding is 

 not new even in the field of locomotive construction. 

 As early as 1846 patents for a compound locomotive 

 were taken out in the United States, and such an en- 

 gine built in 1867; but it is only since 1890 that com- 

 pound locomotives have become popular in this coun- 

 try. In these compound locomotives the two cylinders 



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