10 BULLETIN l-H, IT. S. DEPARTMENT OF AGRICULTURE. 



shell. Soleplates are placed on the brick avails to receive the brack- 

 ets, the end-wise expansion being taken care of by rollers between 

 the brackets and soleplates. It is important to have the brackets 

 completely covered by the brickwork; otherwise they will be burned 

 by the hot gases, 



The other and better method is to suspend the boiler from a 

 frame made up of channel bars or angle iron supported b} r columns, 

 the setting being built around the framework. B} T this method the 

 weight of the boiler and contained water is carried on the piers, sup- 

 porting the- columns. With this method the walls of the setting 

 have to support only their own weight; hence the expansion and con- 

 traction of the boiler are more easily provided for and the walls 

 of the setting are not so liable to crack. As before stated the back 

 end of the boiler should always be set about 1 inch lower than the 

 front in order to drain the boiler toward the blpw-off pipe, which 

 is usually at the back of the boiler. The blow-off pipe should be 

 carefully protected from direct contact with the hot gases by cov- 

 ering with a sleeve or by building a baffle of fire brick on the side 

 next the furnace. 



CLEAN-OUT DOORS. 



With large boilers two clean-out doors should be- provided for 

 the combustion chamber in order to facilitate cleaning, but with 

 small boilers one is usually sufficient. It should be placed in the cen- 

 ter of the back wall of the setting and the bottom of the door should 

 be on a level with the bottom of the combustion chamber. Great 

 care should be used in making the clean-out doors air-tight, as air 

 leaking into the combustion, chamber at this point seriously affects 

 the draft. 



CONSTRUCTION OF FURNACES. 



The functions of the boiler and of the furnace are diametrically 

 opposed to each other, that of the furnace being to develop a maxi- 

 mum of heat from the combustion of the fuel on the grates, while 

 that of the boiler is to absorb as much heat as possible of that pro- 

 duced in the furnace. In order that the furnace may develop the 

 maximum quantity of heat from the fuel complete combustion of 

 all material is necessary. The volatile gases which are driven off 

 from the coal must be allowed to ignite before their temperature is 

 lowered to a point at which they will not burn. Even a compara- 

 tively slight reduction in temperature will prevent some of the gases 

 from igniting, with the result that quantities of combustible gases are 

 driven off without being consumed and fine particles of carbon are 

 forced up the chimney without combining with the oxygen to pro- 

 duce heat in the combustion chambers. As hot gases and vapors 

 rise at a rate proportional to their temperature, there must be a 



