﻿'652 Mr. St. Landau-Ziemecki on the Emission 



spectrum of the molecule. To verify it experimentally the 

 writer chose iodine, the dissociation o£ which has been well 

 studied and which dissociates at a relatively low temperature. 



II. The Experiments. 



Bodenstein and Starck * have shown that the dissociation 

 equilibrium can be expressed by the formulae : 



P±=K; log K= - 1 A^+ T75 log T-O000416T + 0*422, 



where p 1 is the pressure of the monatomic iodine vapour, 

 p 2 the pressure of the diatomic vapour, K the equilibrium 

 constant, T the absolute temperature. This expression agrees 

 well with the experiments. Applying that formula, we obtain 

 the following table for the degree of dissociation — that is, the 

 ratio of dissociated molecules to the total number of the 

 molecules which would be present were there not any dis- 

 sociation. 



Degree of dissociation as a function of pressure and temperature. 



t=500°C. 600°. 700°. 800°. 900°. 960°. 

 mm. 



P = l » 

 jp=10„ 



Taking these data as the starting point for my experiments, 

 I prepared a Greissler tube from quartz of the form shown 

 in fig. 1 t- B 



The iodine crystals were at C, and that part of the tube 

 was immersed in a water-bath, the temperature of which 

 varied in the different experiments from 15 c -20° C. • thus the 

 corresponding vapour-pressure was always less than 0*25 mm. 

 of mercury (for 20° C). The central part of the Greissler 

 tube was placed in an electric oven, and the temperature 

 raised from 960°-1000° C. It is seen from the above table 

 that in these conditions the dissociation was fairly complete. 



* Zeitschrift fur Elektrochemie, vol. xvi. p. 961 (1910). 



t Some months after this work was published in the Bulletin of the 

 Pol. Acad., W. Steubing described in the Physikalische Zeitschr. (1921, 

 p. 507) his experiments touching the influence of the temperature on the 

 band spectrum of iodine. The experimental arrangement of this author 

 was similar to mine. Glass tubes were used b}' him, and thus he was 

 unable to go further than 450° C, when practically there is no possibility 

 of observing any trace of the line spectrum of monatomic iodine, the 

 percentage of dissociated molecules being quite insignificant. The ex- 

 periments of W. Steubing gave interesting results touching the weakening 

 of the band spectrum with the rise of the temperature. His observations 

 are limited to the visible part of the spectrum. This part of the 

 spectrum was inaccessible to me in the experiments touching the 

 spectrum of monatomic iodine on account of the radiation of the electric 

 oven. 



0-05 



0-19 



0-52 



0-83 



094 



1 



0-02 



0-06 



0-19 



0-42 



0-68 



0-81 



