296 Introduction to the Study of Science 



condensing the steam. Locomotives must also have some 

 means of forcing draft, which is readily secured by the exhaust 

 through the smokestack. 



The fundamental fact in the operation of the condenser is 

 illustrated simply in the steam-heating system. In this the 

 steam is cooled in the pipes and radiators and the water or the 

 condensed steam is returned to the boiler by gravity, or by a 

 pump where the return is from pipes lower than the boiler. 

 In condensers on engines the steam is cooled and condensed 

 more quickly by being conducted through pipes that are im- 

 mersed in cold water. 



SUMMARY 



The modern steam locomotive represents the work of many inven- 

 tors. Locomotives of to-day are powerful and heavy and may be made 

 up of two or more engines. 



The essential parts of a steam engine are the steam chest, slide 

 valve, cylinder, and piston with connecting rod to crank or driving 

 wheel. 



By the connecting rod, the to-and-fro motion of the piston is trans- 

 formed into the rotary motion of the wheel. 



The condenser saves heat energy by exhausting the steam at less 

 than atmospheric pressure, and returning to the boiler the hot water 

 condensed from the steam. 



REVIEW QUESTIONS 



1. During what period was the steam engine developed? 2. What 

 men in England and America are associated with its development? 

 3. What distinctive advance was made by the Stephensons? 4. De- 

 scribe the big locomotives of the Erie Railroad. 5. Describe any big 

 locomotive you have seen. 6. Compare the hauling power of early 

 and recent locomotives. 7. What other motive power is a competitor 

 with steam in transportation? 8. What are the working parts of a 

 steam engine? 9. How does the steam perform work in the cylinder? 

 10. How is the slide valve moved and controlled? 11. What use is 

 ordinarily made of exhaust steam in a locomotive? 12. What two 

 economies are effected by a condenser? 13. In the condenser how is 

 the steam condensed ? 



