THE BOTLKR. 93 



Danger of Using an Old Boiler. There is danger of a 

 boiler exploding with plenty of water in it, if any part 

 has corroded or been weakened so that a considerable 

 portion of it is liable to give way at any time. The 

 water in a steam boiler under pressure, is explosive, and 

 anything that reduces the pressure suddenly, will- precipi- 

 tate an explosion. Return flue boilers are especially dan- 

 perous when old, on account of the large flue. 



Testing a Boiler. To test an old boiler is not an easy 

 matter. We advise making the "cold water test" as follows : 

 Fill the boiler nearly full of water and build a fire to heat 

 the water luke warm. When this is done, withdraw the fire, 

 fill the boiler to the top of the dome and attach a small hand 

 pump. The steam gage will register the 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 boiler may be tested with a hammer, 

 but when coated with scale, this is not easy, even for an 

 expert. 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 par- 

 ticularly, 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 



