Il8 SCIENCE OF SUCCESSFUL THRESHING 



pressure, which may be anything desired. The chill is 

 taken off the water as the boiler is less liable to be strained 

 when the iron is a little warm. The best way to test it 

 is to go over the boiler with a straight-edge, carefully 

 noting how much the sheets are out of shape. This should 

 be done first with no pressure, then repeating, increasing 

 the pressure with the pump about twenty-five pounds at 

 a time. ' On a locomotive boiler, the straight-edge should 

 be placed between the stay bolts. The parts exposed to 

 the greatest heat should be examined particularly, as 

 should also the bottom of the shell and along the riveted 

 seams, where it is liable to be corroded. If there be 

 any doubt about any part, or if the straight-edge shows 

 that the sheets spring or bulge with the pressure, the 

 only way to be sure is to drill a small hole and determine 

 the thickness. If found to be safe, the hole may be made 

 tight by tapping and screwing in a copper plug. 



Another Method of Testing Boiler. A boiler may 

 be tested without using a pump. In this case the boiler is 

 filled with water to the very top of the dome before the 

 fire is built, and the expansion of the water, as it increases 

 in temperature, gives the desired pressure for testing. 

 The boiler may be filled by removing the whistle or the 

 pop-valve and pouring the water through its pipe. The 

 throttle and all of the openings from the boiler must be 

 closed before the fire is built. Straw should be used as 

 fuel, as a fire of it may be quickly checked. When other 



