Use melted alum mixed with burr-stone pulverized to the size of grains of sand.

Burrs, To prevent heating, -Dress from centre to circumference, leaving no bosom. Draw a line across the centre, each way, dividing a four-foot burr into 16 squares or divisions, and other sizes, more or less, in the same proportion, with all straight furrows. Let the draft be -1/2 the diameter of the rock. Lay off the lands and furrows 1/4 inch each, observing to dress smooth. Sink the furrow at the eye 1/4; inch deep for corn, and run out to 3/10 at the periphery; for wheat, 3/16 at the eye, and 1/8 at the periphery. When thus finished, crack the lands in straight lines, square with the draft of cross-lines, so as to make the lands face in the runner and bed direct. This will never heat.