32 Kij) — Determination of the Hardness of Minerals. 



the level of the diamond point runs in the direction ha and joins 

 a spring balance s, which is suspended between two uprights. 

 As the mineral is drawn in the direction ah the diamond point 

 rides with it until the tension in s is so great as to cause the 

 point to become stationary. A scratch will now be produced 

 on m provided the weight w (including the weight of the 



diamond point and arms) be not less than the critical pressure 

 for the mineral. The critical pull will be shown at once by 

 the spring balance s. 



It will be observed that the two forces producing abrasion 

 are used for that purpose alone, with the exception of what 

 force is absorbed by friction at the point n. The friction at 

 this point can be calculated in advance for all weights or ten- 

 sions likely to occur by the method suggested in fig. 4. Two 

 A weights of x mg. each are attached to the 



ends of a thread running over two pulleys, 

 one of which is the same as used at the 

 point n in fig. 3 and the other identical in 

 construction. The weight which it is nec- 

 a-tl [b-P essar J t0 a dd to either a or h in order to 



destroy their balance is evidently the meas- 

 ure of friction in the two pulleys, and one half of this will be 

 the amount of friction at the point n for a tension of x mg. 



All minor details of the apparatus are omitted in order that 

 its main princrples may come the more clearly into view. The 

 carnage upon which the mineral rests, the graduated disc by 

 means of which it can be turned at any angle, the tracks upon 

 which the carriage runs, screws for levelling the surface of 

 the mineral, a device for regulating rate and other details can 

 be easily supplied by the imagination. 



Results obtained experimentally by means of this apparatus 

 will be published later. Meanwhile the writer would be glad 

 to have anyone interested in the problem of mineral hardness 

 avail himself of the contents of the present paper. 

 Vanderbilt University, Nashville, Term. 



