32 ILLINOIS ACADEMY OF SCIENCE 
in fines in the coal means a distinct loss in value. The prob- 
lem, therefore, was to test Illinois coals from the different dis- 
tricts, under varying conditions, to discover any laws govern- 
ing this breakage, and to establish some standard of relative 
friability by which the reduction in market value due to degra- 
dation might be impartially estimated. 
PROCEDURE 
The procedure involved a search of literature on the sub- 
ject and a study of any methods and apparatus which had 
been used previously. After testing some of these methods 
they were rejected as unsuited to the problem, and new appa- 
ratus devised. 
A drop test machine was constructed, in which a box filled 
with 50-100 pounds of the coal to be tested and provided with 
a gate on the bottom is elevated to any height up to ten feet 
above the floor. 
The gate is opened suddenly and the coal falls to the floor, 
which may be wooden, steel or concrete. By screening this 
coal through a standard set of screens the breakage of the 
larger sizes into the smaller is determined quantitatively. A 
great deal of care is necessary in manipulation to secure results 
which are in agreement. 
RESULTS 
The results have shown a surprising individuality among 
different coals in regard to their comparative friability. It 
seems possible to give definite coal of definite size a fixed com- 
parative friability factor. The difference among Illinois bitu- 
minous coals in themselves is about as great as between anthra- 
cite and the least friable of the Illinois coals. A great differ- 
ence was noted as to the material of the floor on which the 
falling coal struck. Steel and concrete causing much more 
breakage than wooden floors or bins. The size of the coal 
and the amount of moisture present in the coal are other 
important factors. For example, it was found possible to 
place coal in water for a minute or two and greatly reduce the 
amount of breakage. 
