212 BRIDGMAN. 



annealed at a temperature of 150° for several hours after casting, of 

 density 7.296 at 20°, or in the form of an extruded easting, the extru- 

 sion reducing the diameter from 1.2 cm. to 0.0 cm. The extrusion 

 was performed at a temperature of about 125°, and after extrusion 

 the piece was seasoned at 150° for several hours. The density of this 

 piece at 20° was 7.302. 



Two runs were made on the extruded pieces; one was with a pre- 

 liminary form of apparatus and the results were not as accurate as 

 those finally obtained. The preliminary run gave for the average 

 compressibility to 12000 kg. at 30° 16.2 X 10~ 7 . The other run on the 

 extruded piece was on a sample about 16 cm. long, mounted as a com- 

 pression piece in the apparatus for direct measurement without mag- 

 nification. The average arithmetical deviation from a smooth curve 

 of the 40 readings (three discards) was 0.23°^ and the maximum devia- 

 tion from linearity was 2.0°^ of the maximum pressure effect. The 

 runs on the simple casting were also made in the final apparatus for 

 direct measurement, and the specimen was also 16 cm. long. The 

 mean arithmetical deviation from a smooth curve of the 28 readings 

 (no discards) was 0.25 r o and the maximum deviation from linearity 

 was L.09* , of the maximum pressure effect. The values of cubic 

 compressibility given by these two samples, assuming in the computa- 

 tion equal compressibility in all directions, was: 



AT' 

 Extruded rod, At 30° — = - 1(H (19.53 - 9.6 X 10-* p) p 



' o 



AT 

 At 75° — = - 10- 7 (20.11 - 9.9 X 10-*p) p 

 ' 



Cast rod, At 30° A I* 



To 



10- 7 (17.01 - 5.17 X lO-^p) P 



AT" 

 At 75° — = - 10- 7 (17.37 - 5.75 X 10^) p. 



I 







The difference between extreme values is not as large as in the case 

 of bismuth. Again the direction in which the linear compressibility 

 is the greatest is the direction in which the pressure and the tempera- 

 ture coefficients of compressibility are the greatest. The crystal 

 structure of ordinary tin determined by X-ray methods is side-face- 

 centered tetragonal. 



The initial compressibility at 20° of tin of density 7.29 is given by 

 Richards as 19 X 1Q- 7 . A. W. J. give 1S.5 for the initial and 17.0 X 



