. ECONOMICAL USE OF FUED IN" CREAMERIES. 45 
ashes or sand or some similar material, thus reducing heat losses, and 
should cracks form in the walls, this fine material will run into and 
fill them and prevent the air from leaking into the furnace or com- 
bustion chamber. The exposed top of the boiler should also be cov- 
ered with a layer of sand or ashes, or a layer of asbestos blocks or 
insulating brick may be substituted. By properly insulating the 
boiler setting, uptakes, and breeching the heat loss can be easily 
reduced one-half or more. 
The heat los$ through incomplete combustion is an extremely 
variable quantity in creameries where the firing of the boiler is done 
at irregular intervals. In most of the smaller plants no regular fire- 
man is employed, hut some one engaged in other work around the 
plant is depended upon to fire the boiler; consequently the firing 
is not given the proper attention. In the larger and better-managed 
plants, however, this loss is not more than about 2 per cent, which 
can be practically eliminated .through careful firing. 
There is a certain amount of heat loss in the stack that is neces- 
sary to maintain the dr*aft for burning the fuel, and hence can not be 
eliminated. In practice it is found that twice the theoretical amount 
of air is necessary for complete combustion of the fuel. Assuming 
that twice the theoretical amount of air. is supplied and that the coal 
used has a heat value of 13,500 B. t. u. per pound, then the neces- 
sary heat lost in the stack, as given in the table, is 19.15 per cent. It 
is impracticable to reduce this loss to any appreciable extent. 
The greatest operating loss is that due to excess air which is allowed 
to leak into the furnace and combustion chamber through cracks in 
the walls of the setting, firing doors, doorframes, and other points. 
This is a loss that can be entirely eliminated if all cracks are care- 
fully stopped and the air supply through the openings in the ash pit 
and firing doors is properly controlled. 
The loss due to. heating the moisture in the coal is one that is im- 
practicable to eliminate or- reduce. The loss depends, of course, upon 
the amount of moisture contained in the coal, but seldom exceeds 2 
or* 3 per cent. 
Soot is one of the best-known insulators. Consequently if allowed 
to collect on the heating surfaces of the boiler it will reduce mate- 
rially the amount of heat passing through the heating surfaces to the 
water inside the boiler. The loss from this source may be entirely 
prevented. The remedy lies in keeping all heating surfaces clean. 
Nearly all boilei'-feed water contains scale -forming impurities. 
Rain water, while not containing scale- forming material, always 
contains carbonic and often sulphuric acid, and hence should never 
be used as boiler-feed water on account of pitting and corroding the 
boiler plates. The heat loss front scale deposit depends, of course, oil 
the thickness and nature of the scale formed. While in the foregoing 
