To ascertain the hardness of a stone, rub it over the edge of another stone of known hardness. If it neither scratches nor is scratched by it the two are identical in degree of hardness. If it scratches, say, No. 7, but is scratched by No. 8, its hardness will lie between the two numbers. Simple as the test seems to be, it requires con­siderable skill in some cases to obtain satisfactory results. To the student of Precious Stones it is only the first four degrees of hardness that are of interest. It is con­venient to have representatives of these mounted in tubes, or handles, for ready use. A small case containing these stones, conveniently mounted, may be purchased for a guinea, and will enable any ordinary judge to test a doubt­ful stone.