22 BULLETIN 753, U. S. DEPARTMENT OF AGRICULTURE. 
10 per cent. These briquets are hard and firm and resemble coal 
briquets in general appearance. 
Although the various presses differ greatly in the details of their 
‘construction, most of them work on the cylinder-and-plunger prin- 
ciple, the plunger being driven by means of crank and connecting 
rod or by some toggle-joint system of levers so designed that it is 
capable of exerting a very great pressure at the end of the stroke. | 
Practically all of them also are automatically fed. In systems in 
which binders such as pitch are used and in those in which the resins 
of the wood serve as binders, it is necessary to provide a long cooling 
trough, sometimes as much as 150 feet in length for the finished 
briquets. In systems using mechanical binders these cooling troughs 
are unnecessary. | 
The cost of manufacturing briquets is not inconsiderable, conserva- 
tive estimates placing the figures at not less than $3 a ton. The bulk 
of the fuel prevents its economical shipment over long hauls. This 
applies both to the finished briquet and to the raw sawdust. It is 
believed that the ultimate consumer will have to pay at least $6 a 
ton for the briquets to make the success of their manufacture assured. 
MANUFACTURE OF CHARCOAL. 
There are two chief methods of producing charcoal, the old kiln 
method and the modern method of destructive distillation in a closed 
retort. Most of the commercial charcoal is still made in the kiln, the 
erection and operation of which costs, for the labor, about 60 cents © 
per ton of charcoal. 
Wood loses 75 per cent in weight and 50 per cent in volume in char- 
ring. Two cords of hardwood will yield 1 ton of charcoal; 1 bushel 
of charcoal, the selling unit, weighs about 25 pounds. 
For miaking charcoal the wood should be thoroughly seasoned, 
free from knots, and of but one species for each kiln charge. 
The ground is prepared near water by leveling and hoeing the 
soil, removing roots and stones, and raising the center of the circle 
to be occupied by the kiln about 10 inches above its circumference. 
The usual diameter of the circle is from 15 to 30 feet. The best soil 
is loamy sand, which secures proper regulation of the drait. The 
site should be protected from wind. 
A “chimney” is erected by placing three or four poles of even 
height at 1 foot distance from a central pole, and fastening them 
around the central pole by withes. It is cylindrical if the kiln is 
lighted from above, and pyramidal if the kiln is lighted from below; 
and is filled with inflammable substances, such as dried twigs, char- 
coal, ete. 
1 Logging and Lumbering or Forest Utilization, pp. 167-168, a textbook for forest 
schools, by C. A. Schenck, director Biltmore Forest School. a 
