RICHARDS. — SIGNIFICANCE OF CHANGING ATOMIC VOLUME. 591 



of the average internal pressure alone, but also of other variables, none of 

 them alone furnishes certain evidence ; but when all point in the same 

 direction the probability of their combined verdict is great. If then, zinc 

 is in a more compressed condition than cadmium, it should not contract 

 so much as cadmium upon further compression. Here the difference in 

 cohesion of the two metals affects the result in the same direction as that 

 of the salts, instead of in the opposite direction, as in the case of silver 

 and zinc. 



These two probable circumstances — namely, the greater internal 

 compression of the salts of cadmium and the less internal compression of 

 metallic cadmium — seem to me quite enough to afford an explanation 

 of the fact that greater contraction occurs during the formation of 

 cadmic salts than during the formation of zincic salts. 



On comparing the chlorides with the bromides the result is essen- 

 tially similar. The contraction on forming bromides is less in proportion 

 to the energy-change than that on forming chlorides, chiefly because 

 bromine is less compressible than chlorine, but partly also because the 

 resulting bromides are less compressed than the chlorides, judging by 

 their lower boiling points. 



* Freyer and V. Meyer, Ber. d. deutsch. ch. Ges., 25, 622 (1892). 



t Camelley and Carleton-Williams, J. ('hem. Roe., 37, 125 (1880). 



1 Baxter and Lamb, Am. Cliem. Jonrn., 31, 229 (1904). 



§ Baxter and Hines, Am. Cliem. Journ., 31, 220(1904). The previous data, 

 obtained by Knight under the direction of V. W. Clarke, were much too low. 

 Sill. J., (3) 16. 202 (1878); Am. Chem. J., 5, 240 (1883). 



|| Richards and Rogers, Z. anorg. ('hem., 10. <; (1895). 



