10 BULLETIN 141, IT. S. DEPARTMENT OE AGEICE-LTTJBE. 
shell. Soleplates are placed on the brick walls to receive the brack- 
ets, the endwise 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 ga-es. 
The other and better method is to suspend the boiler from a 
frame made up of channel bars or angle iron supported by columns, 
the setting being built around the framework. By this method the 
weight of the boiler and contained water is carried on the piers, sup- 
porting the columns. TTith 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 blow-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. 
CLE AX-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 jurevent 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 umgt be a 
