24 
BULLETIN 747, IT. S. DEPARTMENT OF AGRICULTURE. 
on account of lack of air to burn them will cause smoke. The smoke 
thus formed will issue from all cracks and openings in the setting 
and boiler doors, which should be marked for repairs. 
Another method is to go over with a lighted candle the outside 
surface of the setting around the boiler front, flue doors, clean-out 
doors, and other points where air leaks are liable to occur. Where 
leaks occur the flame of the candle will be drawn in, due to the 
inrush of air. In order to make the flame more sensitive, the candle 
may be placed in a box having both ends open, one end of the box 
being moved over the surface of the setting. 
After finding the leaks the openings should be packed wj-th 
asbestos rope saturated with fire-clay mortar. The rope should be 
forced well into the crack and the latter pointed up with the mortar. 
After all the leaks have been stopped several coats of a good quality 
of heat-proof paint should be applied to the entire setting. The paint 
effectually seals all small cracks that may have escaped detection 
and also prevents 
the absorption of air 
through the walls, 
due to the porosity 
of the bricks. 
A large part of the 
excess air which en- 
ters through cracks 
in the walls of the set- 
ting does little or no 
good in completing 
the combustion of 
the fuel. Air enter- 
ing at the rear of 
the setting or into 
the uptake, breeching, or chimney not onty has no effect on the 
combustion of the fuel but cuts down the draft at those points and 
makes it difficult to get the necessary volume of air through and 
over the fuel bed. It is very important, therefore, that all parts of 
the setting, uptakes, breeching, and chimne} 7 be made tight. 
Figure 6 shows the points where air leaks are most commonly 
found in a horizontal return-tubular boiler and its setting. 
The cast-iron boiler front is a frequent source of air leaks, as it 
is frequently warped or broken, due to the heat from the furnace, 
and often it is not placed in position properly, cracks through which 
the air passes being left between the front and the brickwork. 
When installed the space between the front and the brickwork 
should be carefully filled with cement mortar. Should a crack 
Fig. 6. — Common sources of air leaks in horizontal 
return-tubular boiler settings. 
