Measuring Hardness

For determiningthe hardneesor friability of certain substances M. Roeiwal haa described to the Vienna academy a new metbod devised by him which is characterized by entire simpliciiy. The measurements consiat in comparing the losses of weightsustained by the bodies under investigation by scratching them with a given weight of polishing material tuouuted on a metallic or glass base until tbe substance loses its I ciency, the poliehing ajipliances comprising dolomitio saud, einery and puro corundum. Tüe diamond is assigned its place in the ecale of haidness by comparing its effectiveness as a polishing agent with that of corundum, proving 140 times a hard as the latter, and to these Eucceed topaz, 194; quartz, 175; adularia, 59.2; apatite, 8.0; flourspar, 6.4; calcite, 5.6; rock galt, 2.0, and tale,