496 FRANK D. ADAMS 



embedding material may be employed, flows around the specimen 

 without producing any effect upon it. If an embedding material 

 could be secured which under compression developed additional 

 "stiffness," the required deformation of the substance might be 

 secured, as when steel is used to inclose the specimen. 



When, however, the length of the tube is so arranged that, after 

 bulging has gone forward to a certain extent and the specimen inclosed 

 in it has been submitted to the conditions above described, a point is 

 reached when the top and bottom of the tube, backed by the press 

 plates of the machine, come in contact with the specimen and com- 

 mence to squeeze it between them, and a much more powerful 

 vertical pressure is brought to bear upon the specimen. Under this, 

 deformation is often produced in a specimen which cannot be obtained 

 by the movements of the embedding material. It may happen, of 

 course, that the vertical pressure thus exerted is relatively too great 

 and the specimen breaks. This pressure, however, may be adjusted 

 so as to yield excellent results. 



It seems clear that, under the • experimental conditions which 

 obtain in Kick's method, it is impossible to arrive at more than a 

 general approximation in endeavoring to estimate the pressure to 

 which the specimen is submitted. The pressure exerted by the 

 machine is divided between the copper tube, the embedding material, 

 and the specimen itself, and the resistance offered by each of these 

 changes continually as the deformation proceeds. It is thus impos- 

 sible properly to apportion the vertical pressure borne by each of the 

 three elements, and when an attempt is made to go one step farther 

 and estimate the lateral pressure exerted on the specimen by the 

 material which incloses it, many additional and at present insuperable 

 difi&culties are encountered. 



DEFORMATION OF CERTAIN MINERALS 



As preliminary to the study of the deformation of rocks, a series of 

 experiments was made on the deformation of rock-making minerals 

 under differential pressure. A number of minerals possessing a 

 progressively greater hardness were selected, with the view to obtain- 

 ing a series of results, beginning with minerals which are known to 

 be readily susceptible of plastic deformation and passing to others 



