and Mocks under Pressure. 247 



irregular. The average diameter of the hole was meas- 

 ured by weighing the mercury which exactly filled it. By 

 using the optically plane surface of the other piece of the 

 crystal to rub off any mercury which might rise in the 

 meniscus above the surface, it was particularly easy to 

 get the hole always exactly full. All of these measure- 

 ments were made at atmospheric pressure, after each 

 exposure to pressure. The procedure was to expose the 

 cylinder to a known pressure for a known time, take the 

 apparatus apart, make all the measurements above, and 

 set the apparatus up again and expose to a higher pres- 

 sure. These measurements simply show, therefore, 

 whether there has been any permanent deformation pro- 

 duced by the pressure. It would have been most desirable 

 also to have made all these measurements while pressure 

 was applied, and so obtain the strain for a given stress. 

 But to do this would have been of excessive difficulty. By 

 the use of a simple device it was possible, however, to 

 obtain rough measurements of the diameter of the hole 

 while under pressure. A little disc of solder mounted 

 on a brass rod to facilitate handling and to keep it in posi- 

 tion was turned in the lathe so as to be initially a push 

 fit for the hole. This was placed in the hole during the 

 application of pressure. The effect of pressure is of 

 course to diminish the size of the hole. The solder disc 

 offers inappreciable resistance, and because of its low 

 elastic limit is permanently deformed to very nearly the 

 minimum diameter reached by the hole. After applica- 

 tion of pressure the disc may be removed and the mini- 

 mum diameter obtained by direct measurements. 



Collapsing tests of this kind were made on two speci- 

 mens of quartz, two of tourmaline, and one each of calcite, 

 barite, feldspar, andesite, porphyry and glass. Negative 

 crystals of quartz were also tried. These experiments 

 will now be described in detail. 



Quartz.— The first specimen was in the shape of fig. 1, 

 a long hollow cylinder with a shorter solid cap. The 

 dimensions were: Outside length of hollow part 4-5 cm., 

 external diameter 2-0 cm., inside diameter 0-36 cm. This 

 cylinder was subjected to ten applications of pressure, 

 beginning at 2000 kg/cm 2 ., and continuing at approxi- 

 mately equal intervals to 11,500 kg. Each application was 

 for ten minutes. The first noticeable effect of pressure 

 was at 3000 kg. and was a chipping off of slivers from the 



