76 THE SUN'S GIFT OF HEAT 



the stove or furnace, where the supply of oxygen is even more 

 scant and the temperature is below the kindling point of the 

 gases. The result of this incomplete .combustion is that 

 part of the carbon in the gases is set free and floats away in 

 the form of smoke. 



This not only results in the formation of the smoke nuisance 

 in cities but also in a great loss of available heat. It is 

 estimated that in Pittsburgh alone the loss of heat due to 



Courtesy of Underfeed Stoker Company of America 

 BEFORE INSTALLING AN UNDERFEED FURNACE 



When a blanket of fresh fuel is thrown on the glowing coals, great quan- 

 tities of carbon and fuel gases escape as smoke. This may be likened 

 to burning a candle upside down. 



non-combustion of smoke has been fully $10,000,000 in 

 a single year. This is aside from the tremendous total 

 damage to clothing, house furnishings, and stocks of mer- 

 chandise, and from its menace to health. 



In order to burn the gases that rise to the upper part of 

 the stove or furnace, there must be a supply of fresh air 

 above the burning coal. When a furnace has too heavy a 

 draft from below, and no supply of fresh air through the 

 feed door, unburned fuel gases are driven up the chimney. 



