220 GREENHOUSES 



It is easier and cleaner to handle, and re- 

 quires less attention in firing, but in most 

 sections is more expensive. 



Soft coals are of two general types; The 

 free burning and the coking. The latter 

 fuses together in burning and is somewhat 

 more difficult to handle in the furnace than 

 the free burning, though it is preferred by 

 some firemen. 



The heating value of a coal depends upon 

 the percentage of total combustible matter 

 contained, and upon the heating value per 

 pound of the combustible portion. In some 

 semi-bituminous coals the heating value runs 

 as high as 15,750 B. T. U. per pound. The 

 heating value of a few common types of 

 coals as given by Kent are shown in the fol- 

 lowing table. 



Kind of coal B.T.U. Kind of coal B.T.U. 



Anthracite Cambria Co., Pa. ...14450 



Northern Coal field ..13160 Somerset Co., Pa. ...14200 



East Middle field ...13420 Cumberland, Md 14400 



West Middle field ...12840 Pocahontas, Va 15070 



Southern field 13220 Bri er Hill, 13010 



Scott Co., Tenn 13700 



Semi-'bituminous gj g Muddy, 111 12420 



Clearfield Co., Pa. ...14950 Missouri 12230 



Soft coal is more commonly used in green- 

 houses than is hard coal. Thisjs especially 



