328 Mr. Chenevix's Analysis 0} Corundum, and of 
extreme hardness ; and thence, the difficulty of reducing that 
substance into fine powder will be easily conceived. We are told 
by docimastic chemists, that the most advantageous method of 
pulverizing hard stones, is to make them red hot ; and, in that 
state, to plunge them into cold water. But I found that this 
operation, when performed but once, was by no means sufficient 
for corundum. I therefore repeated it, till the stone appeared to 
be fissured in every direction. After this, the specimen to be 
pulverized was put into a steel mortar, about three-fourths of 
an inch in diameter, and three inches in depth, into which a 
steel pestle was very closely adjusted. A few blows upon the 
pestle caused the stone to crumble; and the fragments were 
then easily reduced into an impalpable powder, in an agate 
mortar, with a pestle of the same material. The abrasion from 
the mortar, usual in the pulverization of hard stones, was much 
diminished by the above precaution ; rubies and sapphires being, 
in a short time, ground to a powder nearly as minute as the finest 
precipitate. * 
Mr. Klaproth, in his analysis before mentioned, had ob- 
served with how much difficulty the stones were acted upon by 
potash or soda. I found that the greatest heat a silver crucible 
could support, without melting, was not sufficient to produce 
a satisfactory fusion of one part of corundum, with six parts of 
either of those alkalis ; nor did an exposure to that tempera- 
ture during several hours, seem to render the treatment more 
effectual. >Jot more than half the quantity of the corundum 
was ever rendered soluble in any acid ; and what remained was 
the powder of the stone, wholly unchanged. The repeated 
filtrations and evaporations with which this treatment must 
be attended, not only render it tedious, but also produce 
