498 FRANK D. ADAMS 



was poured around the selenite crystals until the tube was filled, the 

 usual precautions already referred to being observed, and a brass 

 plate was placed on either end, when it was inserted in the press and 

 served as a top and bottom to the tube. The pressure being gradually 

 raised, a large ring-shaped bulge gradually developed near one end 

 of the copper tube, and eventually the metal began to tear open at 

 one point on this bulge. The pressure was then taken off, the tube 

 removed from the press, the paraffine melted away, and the selenite 

 crystal obtained. The crystal was found to have undergone a very 

 marked deformation. 



In order to obtain further deformation, the crystal was then 

 placed in the same position in another tube, having the same diameter 

 as that formerly employed but only i . 5 inches (38. i mm.) high, and 

 this, after the residual space had been filled with parafiine, was 

 compressed in the same manner as before. In this shorter tube a 

 further deformation of the selenite was secured. The maximum 

 load employed was 24,000 pounds (10,872 kilos), and the total time 

 during which deformation was actually going forward was 70 minutes. 

 The selenite crystal, after removal from the tube, is shown in Fig. a, 

 Plate I, there being placed beside it another crystal of the size and 

 shape which it originally possessed. It will be seen that the acute solid 

 angles of the monoclinic pTism have been turned back by movement 

 along a plane coinciding approximately in direction with an ortho- 

 dome, while both ends have also been bulged out laterally and the 

 whole crystal has also been slightly curved. There are no traces of 

 fracture, tearing, or cleavage, but the surface of the crystal — ^more 

 especially in those parts which are most deformed — is minutely 

 wrinkled. The extremities of the crystal, where the deformation is 

 most intense, have for the most part lost their transparency and are 

 now translucent. 



In the case of selenite, therefore, deformation under differential 

 pressure can be produced readily and at comparatively low pressures. 

 It is certain that in tfie case of the selenite crystal in question, a much 

 greater deformation might have been secured by placing the crystal 

 in successively shorter and wider copper tubes as each showed signs 

 of rupture, and thus flattening it out by stages. 



Rock salt. — A large cleavage cube of clear transparent rock salt 



