ECONOMICAL USE OF FUEL IN CREAMERIES. 9 
ordinary material is preferable to a hollow wall of the same total 
thickness, especially if the air space in the hollow wall is near the 
furnace side. 
While the solid-wall construction for boiler settings may be better 
from an insulating standpoint than a wall of the same total thickness 
containing an air space, in practice it is advisable to build the walls 
in two parts in order to assist in preventing the formation of cracks 
by the expansion and contraction of the brickwork on the furnace 
side of the wall. The space between the walls, however, should be 
filled with some solid insulating material, such as mineral wool, 
crushed brick, ash, or sand, as that kind o refilling offers a higher 
resistance to the flow of heat through the walls than an air space and, 
furthermore, reduces air leakage into the furnace, which is a very 
important feature affecting its operation. The air space, however, 
should be kept so far as practicable from the furnace side. 
The construction of boiler settings differs widely in details, de- 
pending on the type of boiler used and the local conditions, but the 
principles governing it remain the same. The brickwork should be 
substantial, so that it will not crack and crumble, conditions which 
always produce air leaks and cause extensive repairs. The exterior 
walls of the setting should be built of hard-burned brick, laid in 
cement mortar, while the inside lining of the furnace and combustion 
chamber should be of fire brick laid with fire-clay mortar, care be- 
ing taken in both cases to use no more mortar than is absolutely 
necessary. The fire brick should be thoroughly bonded into the 
outer walls, but in such way as to allow replacing' if occasion de- 
mands. The side walls of the furnace and combustion chamber may 
be either vertical or tapered. In either case from 2 to- 4 inches 
should be allowed on the sides of the boiler just below the water 
line, so that the hot gases can circulate up to the point where the 
setting meets the boiler, which is usually just below the water line. 
The upper half of the boiler may be covered with a brick arch or 
some nonconducting insulating material. When a brick arch is used 
it is advisable to lay it over strips of wood about three-quarters of 
an inch thick. When the boiler is fired these wooden strips are 
burned out, leaving an open space between the boiler shell and the 
arch through which the hot gases may- circulate. Sand should be 
spread over the arch to close any small crack that may occur and 
also to act as an insulator. 
METHODS OF SUPPORT. 
Two principal methods of supporting horizontal return-tubular 
boilers are employed. The one more commonly used, especially with 
comparatively small return-tubular boilers, is to support the weight 
on the walls of the setting by means of brackets bolted to the boiler 
82693°— 19 2 
