BOILER No. 47. 



175 



Boiler No. 47 em- 

 braces four sets of 

 cylinder boilers ar- 

 ranged in the manner 

 shown in the follow- 

 ing cuts. Each boiler 

 consists of three 

 shells placed over a 

 single furnace, the 

 lower portions of 

 which are exposed 

 their entire length to 

 the heat of the pro- 

 ducts of combustion. 

 The upper portions 

 are covered with brick 

 work. These boilers 

 have a ratio of only 

 7.5 square feet of 

 heating surface to one 

 of grate. In this 

 respect they possess 

 their special charac- 

 teristic. The ratio 

 in a horizontal tubu- 

 lar boiler, is seldom 

 below 25 to 1, and 

 the proportion of 

 water-heating surface 

 in the vertical bjiler 

 is seldom below 15 

 to 1. 



