326 APPLIED SCIENCE 



a force only. Therefore the term horse-power is merely rela- 

 tive, and when applied to a boiler conveys to the mind the 

 horse-power of an engine which a boiler of a given size is 

 capable of supplying with steam. 



Priming is that process by which the water is carried up 

 into the steam pipes in considerable quantities and frequently 

 over into the engine. The most common cause is a high 

 water line, which may be the effect of a faulty boiler design. 

 Too many tubes, the forcing of a boiler, irregular firing, or 

 sudden opening of the stop valve may also cause it. 



Questions 



1. Trace the energy used in a steam boiler from its original 

 source. 



2. Why is steam considered an aqueous vapor and not a gas? 



3. Describe the properties of steam. 



4. What properties of steam are common to gases? 

 6. What is a boiler? 



6. Describe the two classes of boilers. 



7. Explain the manufacture of boilers. 



8. Why is a boiler cylindrical and not square? 



9. State the advantages of water-tube boilers. 



10. State the advantages of return tubular boilers. 



11. How are boilers tested? Explain the principle underlying 

 each method. 



12. What objection is there to adding cold water to boilers? 



13. How are boilers repaired? What is the difference between 

 a hard and a soft patch? 



14. What are the principal parts of a boiler? 

 16. What is a fusible plug? Why is it used? 



16. Why is a manhole elliptical and not circular? 



17. What are the devices used on a boiler to tell when the maxi- 

 mum pressure is exceeded? 



18. Describe a safety valve; pressure gauge; water gauge. 



19. How is water fed into a boiler? 



