PAPERS ON PHYSICS 289 
One of the characteristics of a free-burning coal appears to 
be the rapidity with which its volatile matter is liberated at 
moderate temperatures, In a slow burning coal the volatile 
matter appears to be liberated much less rapidly at moderate 
temperatures, rapidly only at relatively high temperatures. If a 
heavy charge of fresh free-burning coal, sufficient for a 6 
or 12-hour run, is shoveled into a furnace upon a bed of 
glowing coals, the volatile portion will be liberated rapidly 
and the distillation will soon be complete. In order to regulate 
the temperature and keep it fairly constant the draft damper 
must soon be closed and the check damper opened. With the 
oxygen supply thus shut off the volatile matter largely escapes 
up the chimney unburned, thus entailing a considerable loss of 
fuel and aggravating the smoke nuisance. A slow-burning coal, 
one in which the volatile matter is but slowly liberated at mod- 
erate heat, is therefore much to be preferred, other things be- 
ing equal, for ordinary house heating. 
The investigation here described was planned to show the 
relative rates at which some typical Illinois coals burn under 
similar conditions. The coals studied in Test I are shown in 
the chart on the page folllowing: 
EXPERIMENT I. 
A Majestic No. 1 laundry stove was used having a heating 
surface of 12x21 inches, or 251 sq. in., and a grate area of 
approximately 7x16 inches, or 114 sq. in. The fuel charge 
consisted of 2 pounds of yellow pine and % pint of kerosene 
for kindling and 25 pounds of lump coal broken into chunks of 
1 pound or less. Upon the stove was placed a large copper 
boiler containing 80 pounds of water at 57° F. The tempera- 
ture of the basement room in which the experiments were 
conducted remained at practically constant temperature, 68° F, 
In this experiment the boiler was covered with a fairly close- 
fitting cover. In every case care was taken to set the draft 
damper in exactly the same position, The graph (Fig. 1) 
shows the resulting temperatures of the last one of four de- 
terminations of each of the four samples of coal. It will be 
noted that these observations extended over a period of but 
four hours. They were taken at intervals of 15 minutes. It 
will also be noted that three of the four coals boiled the water 
