194 BRIDGMAN. 



pressure; their mean value, corrected for the new value for iron, was 

 9.4 X 10 -7 , both results agree very closely with the value above. 



Aluminum. For these measurements I was fortunate to obtain 

 two samples of exceptionally high purity. One was in the shape of a 

 hard drawn rod and the other a casting, both 1.3 cm. in diameter. 

 The density of both specimens at atmospheric temperature was the 

 same, 2.700. The analysis of both specimens was also the same: 

 Si 0.008, Fe, 0.013, Cu 0.014, Mn Nil, Al (by diff.) 99.965. For 

 measurements these pieces were turned to a diameter of 0.6 cm., 

 and were mounted as compression specimens in the lever apparatus 

 for long specimens. The length of the casting was 7 cm. and that of 

 the drawn piece 12 cm. 



By way of curiosity I made measurements on the hard drawn piece 

 first before annealing. I expected hysteresis and other evidence of 

 internal stress, but to my surprise the results were perfectly smooth 

 and gave evidence of nothing of the sort. These measurements were 

 made only at one temperature and to a maximum pressure of 10000 

 instead of 12000, there being some temporary trouble with the pressure 

 apparatus. This hard drawn piece was then annealed at 300° for 

 several hours, and then the regular series of runs at 30° and 75° was 

 made. The average arithmetical departure from a smooth curve of 

 the 28 observed points (one discard) was 0.3% of the maximum pres- 

 sure effect, and the maximum departure from linearity was 0.75%. 

 The departure from linearity seemed to be somewhat greater at 30° 

 than at 75°, but on the other hand the accuracy of the readings at 30° 

 was materially greater than at 75°. The mean of the departures found 

 at the two temperatures was used in the final computations. 



The cast specimen was used without annealing; it showed no 

 hysteresis or other evidence of internal strain. The average arith- 

 metical departure from a smooth curve of the 28 observed points (one 

 discard) was 0.3%, and the maximum departure from linearity 1.43%. 

 The deviation from linearity was exactly the same at both tempera- 

 tures, and this quantity seemed to be given much more satisfactorily 

 bv the measurements on the castins; than by those on the drawn rod. 



Besides the runs just described, at least six other complete sets of 

 runs were made on aluminum, mostly with shorter specimens. A 

 number of the preliminary forms of apparatus were tested by measur- 

 ing with them the compressibility of aluminum. These early results 

 were of course less accurate than the final ones, but agreed with them 

 within the wider limits of error. 



