ECONOMICAL. USE OF FUEL IK CREAMERIES. 25 
develop after the setting has been in operation it can be stopped 
easily with asbestos rope and fire-clay mortar, as previously described. 
When the front is broken it is difficult to repair and when badly 
broken should be replaced with a new one. Care should be taken to 
construct the masonry so as not to allow the intense heat of the 
furnace to be conducted to the cast-iron front. 
Fire and ash-pit doors are often badly fitted, warped, or broken, 
allowing too much cold air to enter the furnace. While it is neces- 
sary for air to be admitted at those points, the doors should fit 
tightly, and the volume of air admitted should be under the control 
of the fireman. 
Flue doors seldom close tight, or if they are capable of being 
closed tight the fireman often neglects to do so. As the hot gases 
leaving the tubes impinge directly upon these doors, they are often 
warped and broken from excessive heat, thus allowing the entrance 
of air at that point. 
With the horizontal return-tubular boiler it is very common to 
find that the weight of the boiler has caused the settling of the brick 
arch, thus leaving an opening between the end of the boiler and the 
top of the brickwork, through which the hot gases from the furnace 
pass directly to the stack instead of taking the path from the fur- 
nace through the combustion chamber and the boiler tubes, resulting 
in a high stack temperature. This short circuiting of the flue gases 
causes a large loss of heat in the stack with a corresponding decrease 
in furnace efficiency. 
Almost invariably the opening through the wall of the setting 
through which the blow-off pipe passes is made larger than necessary, 
thus allowing cold air to enter the combustion chamber and lower the 
temperature of the gases and consequently reducing the effective 
draft. The door and frame of the clean-out door are more often 
than not found to be cracked or badly fitted. The back arch is forced 
back, due to the expansion of the boiler, until there is a permanent 
opening between the end of the boiler and the arch, through which 
large quantities of air pass directly to the boiler tubes. The back 
wall of the setting is very often cracked from the expansion of the 
boiler at the points indicated in figure 5. 
While the foregoing are the places in the setting of a horizontal 
return-tubular boiler where air leaks occur most frequently, there 
are other points through which outside air finds its way into the 
furnace and combustion chamber. The side walls of the setting 
frequently develop cracks, and the entire brickwork is more or less 
porous and allows air to " soak " through even though there are no 
visible openings. It is obvious that in order to obtain reasonable 
economy in a boiler plant the air leaks must be stopped. 
