124 



BOILER TESTS. 



boiler is the same as that shown in the cuts of Boiler No. 6. 

 The two boilers are identical, both as to size and general man- 

 ner of setting, with the exception that No. 20 is provided with 

 perforated plates at the sides of the furnace and top of the 

 bridge wall, for admitting air above the fuel, the air first pass- 

 ing back and forth through ducts in the side walls. Boiler 

 No. 21 is provided with the ducts in the same manner as No. 

 20, but the entrance to these is closed, and no outlets are pro- 

 vided opening into the furnace. 



BOILERS No. 20 AND No. 21, FRONT ELEVATION. 



Dimensions of Boilers No. 20 and No. 21. 



Diameter, of each shell, . 60 in. 



Length between heads and length of tubes, . . . 15 ft. 



Number of tubes 3i inches outside diameter, .... 64 



Area of heating surface, ........ 959 sq. ft. 



Area of grate surface, 25 8 sq. ft. 



Area through tubes, , . . 3.7 sq. ft. 



