To Pulverize Saltpetre
Take a copper kettle, the bottom being spherical, and put into it
fourteen pounds of refined saltpetre, with two quarts or five pints of
clean water; then put the kettle on a slow fire, and when the
saltpetre is dissolved, if any impurities arise, skim them off, and
keep constantly stirring it with two large spatulas, till all the
water exhales; and when done enough, it will appear like white sand,
and as fine as flour; but if it should boil too fast, take the kettle
off the fire, and set it on some wet sand, which will prevent the
nitre from sticking to the kettle. When you have pulverized a quantity
of saltpetre, be careful to keep it in a dry place.