8 
BULLETIN 747, U. S. DEPAETMENT OF AGEICULTUEE. 
If a stone foundation is used it should consist of hard, durable 
stone solidly imbedded in cement mortar. If practicable, the stones 
should be of a length equal to the width of the foundation trenches, 
but if stones of that size can not be» obtained, two stones may be used, 
with the joints under the walls". 
ERECTION. 
After the foundation has been laid and allowed to set thoroughly 
the boiler should be placed in position and raised to the proper 
height by means of jackscrews and held by cribbing built up of short 
pieces of timber. The cribbing* should be placed in the spaces that 
are afterwards to be the furnace and combustion chamber, care being 
used to clear the location of the bridge wall and blow-off pipe. If 
the boiler is to be supported by columns and overhead' beams, they 
should be put into place and the slings adjusted". The rear of the 
boiler should be 1 inch 
lower than the front 
so as to- drain prop- 
erly to the blow-off 
•pipe. The boiler front 
should be- placed in 
position and propped 
up until the walls 
have been carried to 
a height sufficient to 
enable bolts or anchor 
rods to be inserted to 
hold the front in posi- 
tion. The walls should then be built up to their proper' height, 
allowing pockets for the supporting brackets. 
The side stays should then be put into place and drawn tight. The 
boiler and setting should rest on the cribbing (see figure 4) until 
the brickwork has thoroughly dried out, when the' cribbing may be 
removed and the weight of the boiler allowed to rest on the walls. 
Care should be taken to see that the brackets rest squarely on the 
soleplates in the walls ; otherwise there will be a racking strain on 
the boiler during expansion and contraction. Then the setting 
should be closed and finished. 
There is a general belief that because air is a poor conductor of 
heat, an air space built in the walls of a furnace will prevent or 
reduce the dissipation of heat through the walls. Experiments by 
the United States Bureau of Mines, 1 however, have shown that, so 
far as loss of heat is concerned, a solid wall of brick or any other 
Fig. 4. — Boiler blocked up ready for setting. 
1 Bulletin of the Bureau of Mines No. 8, " The Flow of Heat Through Furnace Walls." 
