Chris,
Those remnants from burnt coal are called "Clinkers".
I remember the alley at my Grandmothers in Chicago, Which everyone
dumped their clinkers in and falling off my bicycle, a few times on that
stuff, and it was as sharp as razors!
Many a cut palm of hand or legs.
Too bad no one burns coal around here any more.
This stuff would be great for roads in the winter, instead of the
calcium chloride.

Terry

85 GL