256 P. II'. Bridgman — Failure of Cavities in Crystals 



1-5894 to 1-6032 inches. The effect of slip on length was 

 irregular, however, at 1000, there being a slight decrease 

 instead of an increase. At 1000 the diameter was little 

 changed, nearly all the effect coming betwen 1000 and 

 1500. 



It was not possible to make measurements of the inter- 

 nal diameter under pressure with the solder plugs, the 

 effect being too small. In spite of its easy cleavage and 



i 



Fig. 6. 



Fig. 6. Slip figure on plane face of ealcite cylinder after exposure to 

 1500 kg. 



mechanical softness, the elastic constants of ealcite are 

 high, its cubic compressibility, for example, being the 

 same as that of quartz. 



Apart from cleavage effects, these results show that 

 in ealcite there is present the same mechanism of rupture 

 by flaking-off as was shown by quartz and by tourmaline. 



Feldspar. — This was a white microcline feldspar, pre- 

 pared in the same form and dimensions as the second 

 specimen of quartz. Feldspar crystallizes in the triclinic 

 system; quartz, tourmaline, and ealcite are all trigonal. 

 This material is of course opaque, but there were no evi- 

 dent flaws in it. 



It was exposed to 3000 kg. for 40y 2 hours, to 5000 for 4 

 hours, and to 3000 again for 15y 2 hours. There was no 

 noticeable change of appearance after the first applica- 

 tion of 3000; no fissures appeared, and there was no 

 change of dimensions, but a very minute quantity of fine 

 dust had flaked off from the inner surface. After expo- 

 sure to 5000 the disintegration of the interior was com- 

 plete, the hole being packed with fine sand, as we have 

 come to expect. The average density of this sand was 

 1-77 against 2-57 of the original crystal. The shape of 

 the eroded region was more symmetrical than usual, 



