196 BRIDGMAN. 



cm. long and of square section, 0.5 cm. on the diagonal. Its density 

 at 20° was 5.302. It was mounted as a compression specimen in the 

 lever apparatus for short specimens. The compressibility measure- 

 ments, as well as those on electrical resistance, showed that their 

 is something abnormal about this substance. At 30° the points with 

 increasing pressure lay regularly on a smooth curve, but at the maxi- 

 mum pressure there was an abrupt displacement corresponding to a 

 shortening by an amount 7% of the maximum pressure shortening, and 

 the subsequent points lay on another smooth curve displaced by this 

 amount. The points at 75° showed no irregularity. On taking the 

 apparatus apart, I found that one of the corners of the specimen was 

 broken off. The abrupt displacement was ascribed to the breaking 

 off of this chip, and no more was thought of it. The fractured material 

 is more like a glass in appearance than a metal. Several days later, 

 the specimen meanwhile having rested quietly wrapped in tissue paper, 

 I found that one end of the specimen had spontaneously fractured 

 into a great many small pieces, as badly annealed glass does some- 

 times under internal strain. It suggests itself that there may be 

 another polymorphic modification at high pressures, the transition 

 not being sharp, but viscous, and that it may have been the internal 

 strains produced by the gradual transformation of this new modifica- 

 tion that caused the fracture. 



Making correction for the displacement from one smooth curve to 

 another, the average arithmetical departure from a smooth curve of 

 the 28 readings at both temperatures (no discards) was 0.33%, and 

 the maximum deviation from linearity was 2.1% of the maximum 

 pressure effect. There was no difference detectible between the 

 deviations from linearity at the two temperatures. 



The final results are given by the formulas : 



AT 

 At 30° — = - 10- 7 (13.78 - 6.8 X 10- 5 ;;) p 



I 



o 



AV 

 At 75° — = - 10- 7 (13.64 - 6.8 X 10~*p) p. 



I 



o 



Again we find a compressibility less at the higher temperature. 

 The variation with temperature seems to be well beyond the experi- 

 mental error, and perhaps is not surprising in view of the abnormal 

 behavior of the electrical resistance of this substance at higher tem- 

 peratures. 



There seem to be no previous measurements of compressibility. 



