and Hocks under Pressure. 261 



those just described. Both of these specimens were 

 obtained for me by Professor R. A. Daly, who first 

 aroused my interest in this subject. 



The granite was gray granite, cylindrical in form, 2 

 inches long, 1 inch outside diameter, pierced for its 

 entire length with a 14-inch hole. The ends were closed 

 with flat caps of hardened steel, a rubber tube was slipped 

 over the whole, and it was completely immersed in a 

 liquid and exposed to a pressure of 5000 kg. for 1 hour. 

 The cavity was completely disintegrated into a closely 

 packed sand, just as the other specimens already de- 

 scribed. The outline of the eroded region was that of a 

 pointed ellipse. The outside had also become slightly 

 elliptical, thus showing some slight flow. There were 

 no cracks in the non-eroded region. 



The cylinder of limestone was of the same dimensions 

 as the granite, and the manner of treatment and the 

 results were the same. These two experiments, of course, 

 gave no idea of the minimum pressure at which the cav- 

 ity would close, but did show conclusively that Adam's 

 value of 11,000 kg. for the pressure of collapse of granite 

 is too high. 



Negative Quartz Crystals. — One of the questions raised 

 by these experiments is as to the effect of the plane of 

 separation of the two parts of the specimen. It is not 

 possible by any perfection of workmanship to secure such 

 precise register of the cavities in the two parts of the 

 specimen that one is exactly a continuation of the other, 

 and disturbing effects at the surface are therefore to be 

 expected. The mathematical solution would indicate infi- 

 nite stresses and strains, that is rupture, in the neighbor- 

 hood of any abrupt discontinuity, no matter how minute, 

 and as a matter of experiment, the mouths of the cavities 

 did always splinter somewhat. If experiments could be 

 made with the natural cavities which occur in some min- 

 erals this objection would not be present. 



Dr. Becker placed at' my disposal a number of singu- 

 larly perfect negative crystals of quartz, which he had 

 selected with considerable labor from the resources of the 

 National Museum. Some of these contained bubbles of 

 gas, and were therefore adapted to this purpose. Two of 

 these were exposed to 18,000 kg. under kerosene for 4V> 

 hours. No effect whatever was observable in the neigh- 

 borhood of the negative crystals, and there was no dimi- 



