'•'»'> //. Z. Kip — Determination of the Hardness of Minerals. 



Akt. XI. — Determination <>f the Hardness of Minerals, II ; 

 by II. Z. Kip. 



In the issue of this Journal for July, 1907, an article by the 

 writer on the subject of mineral hardness appeared, whose 

 threefold object was outlined as follows : 1. To invite general 

 acceptance of a single definition of hardness. 2. To establish 

 theoretically in conformity with the definition the best method 

 of investigation. 3. To put this method in practice by means 

 of suitable apparatus and adequate mathematical calculation. 



Inasmuch as it is my present purpose to act as my own critic 

 as well as to publish the results obtained in carrying out the 

 investigations indicated above under 3, it will be found excuse- 

 able, perhaps, if I depart from the general practice of contribu- 

 tors to the extent of speaking in the first person instead of the 

 third.* 



In regard to the formula for determining hardness, estab- 

 lished in my previous paper, H=vV+?/ 2 , I may say that no 

 mineralogist or physicist who has favored me with his opinion 

 has taken exception to this equation. Indeed so long as the 

 generally accepted definition of hardness prevails (resistance to 

 abrasion) this is, and can be, the only adequate formula. 



If in what follows I appear to view my own results witli 

 some scepticism, I wish it to be understood that this is not the 

 result of a lack of faith in the method employed, but merely 

 an acknowledgment of the difficulty of dealing accurately 

 with molecular forces by mechanical means, such means, at 

 least, as I have had at my disposal. 



The apparatus employed was described in its general prin- 

 ciples in my previous paper. As actually constructed it dif- 

 fered from the description given in two points only. A pulley 

 and weight were substituted for the spring scale (see iig. 3, 

 loc. cit.) in determining y (lateral force), the mineral and car- 

 riage, meanwhile, remaining immovable. This made it nec- 

 essary to determine x (vertical force) and y in two separate 

 operations, which, however, proved to be rather an advantage 

 than a disadvantage. Likewise two arms were substituted for 

 four in the frame carrying the diamond point. These arms 

 were bent and continued down beneath the level of the sur- 

 face of the mineral so that the frame and point remained in 

 equilibrium even when no weight was attached. The method 



*This is rendered the more necessary by the fact that it is my duty, no 

 less than my privilege, to make due acknowledgment in this place to the 

 trustees of the Elizabeth Thompson Science Fund (Boston) for the appro- 

 priation (Grant No. 136) without which these investigations would hardly 

 have been undertaken. 



