BRIDCMAN. — A DETERMINATION OF COMPRESSIBILITIES. 



263 



the zero position, the necessity of a large number of determinations of 

 which are therefore avoided. It was found that 



A/ 

 L 



= -0.0000056 + 0.0000003910 p. 



The cubic compressibility is, therefore, 0.000001173 kgm. per sq. cm. 

 In Table I are shown the observed and calculated results. The prob- 

 able error of a single observa- 

 tion is less than one per cent 

 at the higher pressures. The 

 probable error of b, the 

 compressibility, is about J 

 per cent. The value found 

 by Richards 1 for the com- 

 pressibility of aluminum is 

 1.28 X 10~ 6 . He does not 

 state the chemical purity of 

 the aluminum. The speci- 

 men used above was com- 

 mercial aluminum rod, which 

 is usually very pure. No 

 chemical analysis was made, 

 however, and the discrepancy 

 may be due to impurities. 



In an exactly similar man- 

 ner the compressibilities of 

 several samples of iron or 

 steel were determined. The 

 first piece was from a piece 

 of § in. (1.27 cm.) Bessemer 

 rod annealed by heating to 

 redness and cooling slowly, 

 and then turned down to f 

 in. (0.95 cm.). It was frtfm 

 the same piece of rod as a 

 piezometer for determining the compressibility of mercury, as will be 

 described later. The results obtained for this steel corrected for 

 the extension of the cylinder are plotted in Figure 5, the zero being 

 arbitrary as formerly. The results are better proportionately than for 



.0001 



1000 SOOO 3000 4000 5000 C000 7000 



Figure 5. The observed proportional 

 change of length of a rod of Bessemer steel 

 plotted against pressure. The zero is here 

 arbitrary. 



1 Compressibilities of the Elements and their Periodic Relations. Richards, 

 Carnegie Inst., Washington, p. 61 (1907). 



