STEAM BOILERS 347 



test shows all leaks around stays, tubes, joints, etc. ; 

 while in old boilers, if they are carefully watched as the 

 pressure increases, it will disclose weakness by bulging 

 in some places and distortion of joints in others. 



Hammer test. The inspector who conducts this test 

 should go over the boiler before it has been cleaned inside 

 and out and carefully note all places where there is 

 corrosion or incrustation. At the same time he should 

 carefully strike all suspicious places a sharp blow with 

 the hammer to detect weaknesses. A good plate will 

 give a clean ring at every blow of the hammer, while a 

 weak one has a duller sound. 



Although a boiler may be carefully inspected and 

 tested by both methods, it does not insure it against 

 failures. The greatest strain upon a boiler is due to un- 

 equal expansion, and neither of these methods takes this 

 into account. 



Some authorities recommend hot water to be used in 

 the test, but there seems to be no advantage in this, since 

 it is the unequal expansion of boilers and not the rise in 

 temperature which causes the failure of certain parts and 

 consequently so much destruction. 



FUELS 



475. The fuels most commonly used for making steam 

 are coal, coke, wood, peat, gas, oil, boggasse, and straw. 

 Those used for traction engines and threshing purposes 

 are coal, wood, straw, and occasionally cobs. 



Anthracite coal. Anthracite coal, commonly known as 

 hard coal, consists almost entirely of carbon. It is 

 hard, lustrous, and compact, burns with very little flame, 

 and gives an intense heat. It has the disadvantage when 

 being fired of breaking into small pieces and falling 

 through the grates. 



