1890'.] 



Experiments on Vapour-density. 



51 



Series VI. Temperature, 132 0> 2 (Chlorobenzene) ; Capacity of Globe, 

 509-2 c.c. ; Volume occupied by Bromine Vapour, 254'6 c.c. 





The results are negative, as before, but no doubt dissociation would 

 be produced if the temperature were carried high enough, and I hope 

 to carry on my experiments with a modified form of apparatus until 

 dissociation takes place. I must ask my fellow-workers to kindly 

 leave to me the completion of this work. 



Remarks. One of the most sticking features in the series of 

 vapour-densities is the invariable increase in density at low pressures ; 

 this may be accounted for partly by the error unavoidable in reading 

 low pressures, and partly by the irregularity in the position of the 

 liquid in the bulb-tube G ; but these errors together would never 

 amount to more than 1 mm. of mercury, seldom so much. As the 

 chief cause of the anomaly, I would suggest that a film of bromine 

 may adhere to the glass, and thus cause the residual amount of 

 bromine to be too large. 



Vapour-density of Iodine. 



Previous Work. V. Meyer obtained vapour-densities closely corre- 

 sponding to a molecule f I 2 , at a temperature which he estimated at 

 1570 (' Deutsch. Chem. Ges. Ber.,' vol. 13, 1880, p. 394). 



Crafts and Meier found a greater amount of dissociation than 

 V. Meyer at about the same temperature, which, however, they 

 estimated at 1390 instead of 1570; the lowest vapour-density they 

 obtained was 75'6 (' Comptes Bendus,' vol. 90, 1880, p. 690). 



Deville and Troost found the vapour- density normal at 860 and 

 1034 (' Annales de Chimie,' vol. 58, 1860, p. 257). Crafts and Meier, in 

 further experiments, obtained complete dissociation of iodine vapour, 

 and they give a curve showing the amount of dissociation at different 

 pressures and temperatures (' Comptes Rendus,' vol. 92, 1881, p. 39). 

 Crafts obtained partial dissociation by a modification of V. Meyer's 

 method ('Comptes Rendus,' vol. 90, 1880, p. 183). Troost obtained 

 a very considerable amount of dissociation by the Dumas method at 

 1250 ; the lowest number obtained was 81'6 ; he also found the 



E 2 



