H. Z. Kip — Determination of the Hardness of Minerals. 97 



of applying the vertical force by means of a weight suspended 

 beneath" the diamond point, with the necessary consequence 

 that this force, at least, is expended solely in the abrasion of 

 the mineral, proved itself to be even more efficacious than was 

 anticipated, and while experimenters are notoriously devoted 

 to their own mechanical devices, I cannot but believe that this 

 feature will be adopted in the sclerometer of the future, pro- 

 vided this instrument is ever standardized. 



The values obtained for x, y, and H for Nos. 3 to 9, inclu- 

 sive, in Mohs's scale are given in the subjoined table. Values 

 for talc and selenite could not be obtained for the reason that 

 these two minerals yielded to the diamond point even when 

 the latter was balanced merely by the weight of the frame in 

 which it was mounted. 



x y H 



Calcite 



1870 



mg. 



250 mg. 



1887 mg. 



Fluorite 



3300 





1180 



3505 



Apatite 



5010 





500 



5035 



Orthoclase 



13566 





1292 



13627 



Quartz 



22135 





2128 



22237 



Topaz 



20197 





1539 



20255 



Corundum 



24130 





2774 



24289 



Two diamond points were used in these tests, the first weigh- 

 ing in its frame 784 mg., and the second 2723 mg. The 

 former was used on calcite, fluorite and apatite ; the second, 

 and sharper, point on apatite and the remaining members of the 

 scale up to and including corundum. It was found that the 

 force required to produce abrasion on apatite with point No. 1 

 was 3 - 8 times that required with point No. 2. The values 

 obtained, therefore, with point No. 2 for orthoclase, quartz, 

 topaz and corundum were raised in this proportion and so 

 appear in the table. 



It would, of course, give more reliable results if one and the 

 same abrading instrument were used throughout. But neither 

 of the diamond points prepared at my request by Messrs. 

 Richard Muller-Uri & Cie. (Braunschweig) seemed suited for 

 all of the minerals tested, and with the time and funds at my 

 disposal it was not possible to reconstruct the apparatus and 

 repeat the tests. Future experimenters, it is hoped, will avoid 

 this error from the start. The relatively high value for y on 

 fluorite is doubtless due to the fact that a polished specimen of 

 this mineral was used, no cleavage surface being found among 

 the specimens at hand sufficiently smooth to be available. 

 For the other minerals only natural cleavage or crystalline 

 faces were tested. A polished surface is an artificial product 

 and has, in my opinion, no place in investigations which deal 

 solely with surface phenomena. 



