154 HartrLtey—An Investigation of the Connexion between 
distinct and fine, but there appears a sharply defined dark space between 
them. 
A survey of the facts shows that we have bands of different characters, which 
are to be assigned to the mass, the atom, and the molecule, respectively, of the 
different elements. The question as to the complexity of the molecules of many 
of the metallic elements has been studied by Tammann,* who concluded, from 
observations on the freezing points of metals dissolved in mercury, that even at 
low temperatures nearly all metals have monatomic molecules. Heycock and 
Nevillet concluded that at high temperatures also copper, silver, gold, and lead have 
molecules which are monatomic. In a series of elaborate experiments H. von 
Wartenberg} has determined the vapour densities at very high temperatures, and 
calculated therefrom the average molecular weights of a number of metals and non- 
metallic elements. For instance, silver at 2000°C. has a vapour density which 
proves the molecule to be monatomic.§ 
The temperatures measured do not exceed that which is obtained in the 
oxyhydrogen blow-pipe flame. 
The following table gives some of von Wartenberg’s determinations :— 
Average Molecular 
Element. Atomic Weight. Weight. Temperature. 
Antimony, 6 0 6 120:2 128 2070° C. 
Bismuth, : ‘ : 208 224 2070° 
Zine, b ; ; ; 65°4 72 1200° to 2070° 
Lead, . : : 6 206°9 225 1600° to 1870° 
Thallium, : : ; 204:1 220 13820° to 1690° 
The boiling points of the following metals are given :—Thallium, 1280°C. ; 
Lead, 1580° ; Silver, 2050° to 2100°. 
Copper, gold, magnesium, aluminium, and tin all boil at temperatures above 
2200°. 
The temperature of the oxyhydrogen blow-pipe is such that considerable 
quantities of silver can be placed in rapid ebullition and distilled, this being the 
method by which Stas obtained pure silver, and by which the banded flame 
spectrum of the metal was first photographed. Gold, copper, and tin, though 
very freely vapourized by the same means from considerable quantities of the 
metal, cannot with certainty be made to boil, though tobacco-pipes may be gilded 
in a few minutes by the condensation upon them of the gold vapour. Lead is so 
* Zeit. f. physik. Chemie, 1882, 3, p. 441. + Zeits. Anorgan. Chemie, 1907, 56, pp. 320-336. 
oil eenrans sl SO Aran o mel Oe § Metallurgie, 1906, 39, p. 381. 
|| Hartley: ‘‘ Flame-Spectra at High Temperatures.’’—Scient. Trans. Roy. Dublin Soe. 
