8 



BULLETIN 747, U. S. DEPARTMENT OF AGRICULTURE. 



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." 



