22 BULLETIN 747, U. S. DEPABTMEXT OF AGRICULTURE. 



shoveled directly from the car into the furnace. By using a car the 

 dust and dirt from the coal are kept down to a minimum and the 

 inconvenience and unsightly appearance of coal scattered over the 

 floor is prevented to a great extent. 



Ample room for working should be allowed the fireman. In many 

 small plants the space for firing is often so limited that it is difficult 

 to fire effectively. The fireman is forced to stand so close to the 

 firing door and the heat from the furnace is so great that to avoid 

 the heat as much as possible he stands to one side so far that he can 

 not see where coal is needed, thus making it necessary to level the 

 fuel bed frequently by the use of the rake. 



In firing bituminous coal the large lumps should be broken up into 

 pieces about the size of a man's fist or smaller. Adding large lumps 

 of coal makes it impracticable to regulate the draft so as to get an 

 even flow of air through the fuel bed ; especially is this true in small 

 boiler plants which are fired at a slow rate and in which a compara- 

 tively thin fuel bed is maintained. 



METHODS OF FIRING. 



There are three methods of hand-firing boiler furnaces, known as 

 the spreading, alternate, and coking methods. 



The. spreading system, which is the simplest and perhaps the one 

 most commonly used, consists in spreading the coal in a thin and 

 even layer over the entire fuel bed. With this system it is harder 

 to prevent smoking than with the other systems, especially if too 

 much coal is added at a time. Consequently, the firing should be 

 done often and only a small quantity of coal fired at a time, thus 

 providing for better combustion. "When the coal is spread in a thin 

 layer over the entire fuel bed the volatile gases are quickly driven off 

 and burned. This system of firing is particularly applicable to small 

 boilers that have only one firing door, since the entire surface of the 

 fuel bed can be easily seen. A difficulty experienced with the spread- 

 ing system is that, unless specially guarded against,, holes are liable 

 to be formed in the fuel bed near the bridge wall. A modification 

 of the spreading system is sometimes used which consists in keeping 

 the fuel bed much thicker at the bridge wall than at the front, thus 

 preventing it from burning out so quickly. Except for the fact that 

 the fuel bed is kept wedge-shaped, the firing is the same as previously 

 described. In firing hard coal the spreading system is used almost 

 entirely, as coal of that kind contains very little volatile matter. 



In order to prevent smoke a system of firing has been devised 

 known as the alternating method. It consists in alternately adding 

 coal to the front and back of the furnace or to the right and left 

 sides. The object is to burn the volatile gases which are driven off 

 in large volumes when soft coal is heated. By placing fresh coal on 



