THE BOILER 117 



when there is water in the boiler, as the jar of the hammer- 

 blows will be transmitted to the other tubes and loosen 

 them. Use plenty of oil on either style of expander, and 

 carefully clean the end of the tube of soot and scale before 

 inserting the tool. Care must be taken, in expanding 

 the tubes, not to expand them so hard as to stretch or en- 

 large the hole in the tube sheet, and thereby loosen the 

 adjoining tubes. When all of the leaky tubes ha've been 

 expanded, they must be beaded down against the sheet 

 with the beading tool. 



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 por- 

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

 in a steam boiler under pressure, is explosive, and any- 

 thing that reduces the pressure suddenly, will precipitate 

 an explosion. Return flue boilers are especially dangerous 

 when old, on account of the weakness of the large flue. 



How to Test a Boiler. To test an old boiler, so that 

 one is sure of its exact condition, is not an easy matter. 

 One method is by tapping with a small hammer, but when 

 coated with scale, this is not easy, even for an expert. 

 We advise making the "cold water test" as follows : Fill 

 the boiler nearly full of water and build a little 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 



