FUELS AND THEIR UTILIZATION. 35 



is less. The form of kiln varies from a rectangular construction with 

 arched roof, holding one hundred cords or over, to a conical one having a 

 capacity of but twenty-five cords. Between these two extremes the shapes 

 of kilns vary as well as their capacity; some are of the form of a truncated 

 cone, with solid cover and with a flat dome roof, while others more closely 

 approximate the bee hive form. Although some kilns are constructed of 

 stone masonry, brick masonry is preferred, and thin walls are less liable to 

 crack and cause leakage than thick walls. 



Several attempts have been made to introduce semi-portable kilns or meil- 

 ers in which the walls are made of metal, but unless these are protected by 

 an outside covering, the loss from radiation is so great as to prevent a good 

 control of the coaling operation. As a rule, kilns are fired internally in the 

 same manner as meilers; that is, a portion of the wood which is placed in 

 the kilns is consumed to furnish the necessary heat for carbonization, the 

 admission of air being controlled by suitable openings placed in the walls. In 

 some batteries of kilns which have been used in connection with the utiliza- 

 tion of the by-products of carbonization, the heat is obtained from an outside 

 fireplace, the results of combustion being carried into the kilns. In these 

 instances the batteries of kilns are connected by series of trunks or pipes 

 with an exhaust, which draws the smoke from them, passes it through con- 

 densers to obtain pyroligneous acid ; the remaining gas, which is combustible, 

 being returned to the fireplace outside of the kilns. 



As ordinarily built, kilns will produce from thirty-three to fifty bushels of 

 charcoal, the average in this country being about forty bushels of the stand- 

 ard named, so that taking the same volume of wood it is possible to obtain 

 from the ordinary form of kiln from twenty per cent to twenty-five per cent 

 more charcoal than is yielded in meilers or pits, and if the outside fireplace 

 is used a still greater saving is produced, of course at the expense of fuel 

 burned elsewhere than in the kilns. 



(C) Retort charring is the carbonization of wood in closed metallic ves- 

 sels, the heat being applied externally and the products of combustion carried 

 to condensors so as to obtain the pyroligneous acid, the uncondensed gases 

 being passed under retorts to assist the solid fuel in the combustion chamber. 



Retorts are of various forms; they are horizontal cylinders with one end 

 arranged to be opened so as to receive the wood, or they are cylindrical 

 buckets filled with wood, elevated by a crane and placed over a fire, or they 

 are cylinders placed on an incline. The form most used in the latter posi- 

 tion is a modified lune shape, in cross section, the object being to secure a 

 practically uniform thickness of the wood over the fireplace. As none of 

 the wood need be consumed, the possible output from retorts is greater than 



is obtained from kilns, the yield ranging from forty-five to sixty bushels, the 

 10— geol. 



