STEAM HEATING AND ENGINEERING 153 



out every day. Close both the upper and the lower valve in 

 turn, and blow the water or steam out through the cock at the 

 bottom of the glass; also blow out the three try cocks in the 

 water column. If a water glass breaks, close the valve at the 

 bottom of the glass first and then close the upper one ; there is 

 not so much danger of getting burned in this way. 



BOILER TROUBLES 



Foaming in a boiler is shown by the jumping up and down 

 of the water in the glass and is caused by dirty water and by- 

 forcing a boiler beyond its capacity. It can be remedied by 

 cleaning out the boiler as soon as possible. Care should be taken 

 that water does not leak down on to the outside of a boiler; if 

 this happens corrosion will take place in a short time. 



Boiler tubes should be scraped out occasionally as a thin 

 carbonaceous scale is liable to form which results in a great 

 waste of fuel. This scraping is in addition to the brush or to 

 the blowing out with a jet of steam. It is estimated that 15 

 per cent, more fuel is used in a dirty boiler than in a clean 

 one to obtain the same amount of heat. 



THE CHIMNEY 



To get the best results from a chimney every bit of air that 

 enters it should pass through the grates. Round chimneys are 

 better than square ones for the gases ascend in a spiral motion. 

 In their construction brick is better than iron, for the current 

 does not get cooled off so much in its ascent. 



FEEDING THE BOILER 



Be careful w r hen feeding cold water into a boiler to do so 

 very slowly as the cold water is heavier than hot and settles to 

 the bottom of the boiler. In theory this is bad for the plates, 

 but in practice it is perhaps impossible to cool off a boiler with 

 a fire underneath it. The water should always be carried at a 

 uniform height in a boiler and there should never be less than 



