382 Transactions. — Chemistry and Physics. 



Art. XLVIII. — Note on the Vapour-density of Mercury. 



By Douglas Hector. 



Communicated by Professor Easterfield. 



[Read before the Wellington Philosophical Society, 12th March, 1901.] 



It is well known that the vapour-densities of many elements 

 diminish at high temperatures owing to dissociation of the 

 gaseous molecules. Thus the researches of Victor Meyer* 

 and of Crafts and Meierf have shown that the vapour-density 

 of iodine is constant between the temperatures of 250°-700°, 

 but that above the latter temperature dissociation commences, 

 and is complete at temperatures above 1,400° (at 152 mm. 

 pressure). 



Very few systematic experiments appear to have been 

 made in the opposite direction — i.e., with the object of de- 

 termining to what extent, if any, an association of the 

 gaseous molecules occurs when the temperature is reduced. 



Professor Easterfield has suggested to me that a certain 

 interest would attach to determinations of the vapour-density 

 of the elements made at the lowest possible temperature. I 

 have therefore chosen quicksilver for the first series of experi- 

 ments. 



V. Meyer]: has shown that mercury is monatomic at tem- 

 peratures between 440° and 1,565°. More recently H. Brere- 

 ton Baker has determined the vapour-density of the carefully 

 purified metal in absolutely dry nitrogen at 440°, but no 

 evidence of association could be detected. Vapour-density 

 determinations at lower temperatures than 440° do not appear 

 to have been attempted. 



By employing a slightly changed form of the beautiful 

 method described by V. Meyer, § in which the substance 

 under investigation is gasified in an atmosphere of hydrogen 

 at the ordinary pressure, we have been able to determine the 

 vapour-density of mercury at 236° — i.e., 121° below its boiling- 

 point. Even at this low temperature, however, the molecule 

 of mercury remains monatomic. The actual vapour-density 

 found was 112; calculated for monatomic mercury, 100. 

 The experiment is being extended to other elements. 



* Berichte der doutachen Chein. Gesellsch., xiii., 401, 1723; xiv , 

 I 453. 



f " Comptes Rendus," 92, 39. 

 { Berichte, xii., 1426. 

 § Berichte, xxiii., 313. 



