A. L. Parsons — New Sclerometer. 



163 



column (S) and witli this can be raised or lowered in the socket 

 (B). The rod (St) behind the column prevents lateral move- 

 ment of the spring in raising or lowering the same. On the 

 free end of the spring is screwed the test point holder (H ]5 H 2 



or 



H 3 ) which carries the crystal point or metal point with 

 which the test object is to be scratched. 



The following three point-holders seem desirable and are 

 provided with the instrument : H 1 with diamond point. This 

 is preferably a tetrahedral cleavage fragment, as this form gives 



Fig. 1. 



the sharpest cutting edge and is least liable to variations in 

 hardness. H 2 , a holder in which a needle of steel or other 

 metal can be fastened. Generally a sewing needle is used, as 

 there is little variation in hardness in needles from the same 

 packet. For very soft substances a brass pin or a copper point 

 may be employed. H 3 , a holder with a cup-like depression in 

 which a crystal or other substance may be fastened by means 

 of wax "kit."* This may be either a substance of known 

 hardness with which another is to be compared or one of 

 unknown hardness which is to be tested by scratching the sur- 

 face of a substance whose hardness is known. 



* A piece of " kit " is provided with each instrument. . 



