CHAPTER XVI 



ATOMIC WEIGHTS OF THE METALS 



A. VAPOUR DENSITIES 



The vapour-density of metallic compounds. Avogadro's 

 hypothesis, which enabled Cannizzaro to establish on a 

 firm basis the atomic weights of the non-metals, failed him 

 in the case of the metals, because of the lack of volatile 

 compounds. Very few of the metals can be vaporised, 

 either as elements or compounds, even under the wide range 

 of conditions now available for vapour-density determina- 

 tions. The most favourable cases-*re those of mercury and 

 arsenic, two elements which in some ways serve to bridge the 

 gap between metals and non-metals. The data already given 

 for these two elements, with others derived from their 

 volatile organic compounds, are sufficient to establish the 

 atomic weights, Hg = 2oo, As = 75. 



The following table contains almost all the data that are 

 available for other metals l : 



1 The references are : Dumas, Ann. Chim. Phys., 1826, 88,385; 

 Dumas quoted by Bineau, Ann. Chim. Phys., 1838, 68, 427-428 ; 

 Frankland, Phil. Trans., 1855, 145, 266; Deville and Troost, Ann. 

 Chim. Phys., 1860, 58, 257-299; Wanklyn, Jour. Chcm. Soc., 1861, 

 13, 128; Frankland and Duppa, Jour. Chem. Soc., 1864, 17, 33; 

 Buckton and Odling, Proc. Roy. Soc., 1865, 14, 19-21 ; Ladenburg, 

 Liebig's Annalen, 1872, 8, Suppl. 55-80; V. and C. Meyer, Ber., 

 1879, 12, 1195-1200 ; Menschingand Meyer, Ber., 1886, 19, 3295-3298, 

 and Ber., 18,87, 20, 582-583; Scott, Proc. Roy. Soc. Ed., 1887, 14. 

 410 ; Friedel and Crafts, Comptes rendus, 1888, 107, 306 ; Nilson and 

 Pettersson, Trans. Chem. Soc., 1888, 53, 814-831 andZizV. Phys. Chem., 

 1889, 4, 206-225 5 Biltz and Meyer, Ber., 1889, 22, 725 or Zeit. Phys. 

 Chem., 1889, 4, 249-269 ; Mond, Langer and Quincke, Trans. Chem. 

 Soc., 1890, 57, 752 ; Dewar and Jones, Proc, Roy, Soc,, 1905, 76, 567, 



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