201 P. W. Brkhjinan — Failure of Cavities in Crystals 



Density of Compressed Sand. 



The results already described show that in all prob- 

 ability large cavities cannot exist at considerable depths 

 in the earth's crust, but the walls will disintegrate, pack- 

 ing the cavity with fine sand. The question as to the 

 existence of microscopic cavities in this sand and the 

 average density of material which has been ruptured was 

 still untouched, and I therefore made a few further sim- 

 ple experiments in an attempt to partially answer' this 

 question. 



Quartz, orthoclase feldspar, and talc were experi- 

 mented on. These were reduced to sand in a mortar, and 

 the quartz and feldspar were separated into various 

 sizes with sieves of 40, 60, 80, and 120 meshes to the inch, 

 and then cleaned by washing them with HC1 and distilled 

 water and dried by moderate heating in the air. The 

 powder was placed in thin cylindrical copper boxes with 

 copper covers, 1-5 cm. diameter and 1-5 cm. high, and sub- 

 jected to compression between pistons of hardened steel 

 in a hydraulic press. Lateral expansion was prevented 

 by a very heavy ring of chrome-vanadium steel. The 

 intensity of pressure in these experiments was 30,000 

 kg/cm 2 . The pressure was not strictly hydrostatic, but 

 this was no objection in view of the negative nature of 

 the results. Under the conditions there must have been 

 considerable grinding past each other of the grains, which 

 is more conducive to fusion than pure normal pressure. 



As far as fusion goes, the results were entirely nega- 

 tive. Talc, as well as quartz and feldspar of different 

 sizes, pure and mingled together could not be fused to a 

 homogeneous mass. All of these materials, however, 

 could be pressed together into a cake coherent enough to 

 handle; it was a surprise that the cake of talc was not 

 especially more coherent than that of quartz. The aver- 

 age density of the cake was determined in the standard 

 way by weighing under water, and is of some significance. 

 The quartz ranged in density from 2-572 to 2-584, the 

 original material being 2-65. There was a tendencv for 

 the cakes formed from originally larger grains to be of 

 higher density, probably because a larger proportion of 

 the total volume was occupied by unfractured material. 

 The smallest density of all, 2-572, was that from a mix- 

 ture of two sizes of sand, one passing through 40 but not 

 60, and the other through 120. The fragments into which 



