﻿Intelligence and Miscellaneous Articles. 335 



This he found to be 128,300 gramme-calories per gramme of 

 hydrogen. This number must be regarded as an upper limiting 

 value for the heat of dissociation of H 2 , for in it that quantity of 

 heat is contained which must be used to bring the hydrogen to the 

 boundary of dissociation. Yet this value is in any case very near 

 the true heat of dissociation. 



Hence direct calorimetrical measurements give for hydrogen 

 AV H < 1283 X 10 5 cal., or for a molecular weight of hydrogen 

 W H < 2566 x 10 5 cal. 



In the case of iodine vapour Boltzmann*, from the course of the 

 dissociation with the temperature according to the observations of 

 Meir and J. M. Crafts, has calculated the heat of dissociation at 

 y — 1125 calories per gramme. Hence, in order to dissociate a 

 weight equal to the molecular weight 253*6 of I 2 , there are required 

 2853 xlO 4 calories. 



This number, as will be seen, is of the order of that obtained for 

 hydrogen by M. E. Wiedemann by a totally different method. 

 That it is smaller agrees with the fact that iodine vapour is dis- 

 sociated at temperatures at which this is not the case with hy- 

 drogen, that the band-spectrum of iodine vapour is very difficult 

 to obtain, and so forth. 



In ergs, Wiedemann's measurements give for hydrogen _the 

 work of dissociation 



A h <1-1x10 13 ergs. 



The theoretical reasonings of Boltzmann give tor the work of 

 dissociation of iodine, 



A^l^xlO^ergs. 



All other data required for making the calculation are furnished 

 by electrolysis and the kinetic theory of gases. 



From the most recent determinations of E. and W. Kohlrausch 

 on the volume of detonating gas liberated by 1 ampere in a second, 

 Richarz {vide antea) calculated the magnitude of the elementary 

 quantum of electricity 6=1-29 X 10- 10 O.G.S. I myself f found by 

 a totally different way the assumption that the energy of radia- 

 tion of a luminous vapour depends on electrical vibrations of 

 these valency-charges 0=0-14 x 10 ~ 10 C.Gr.S. ; a number, therefore, 

 which in the order of magnitude is quite comparable with the first, 

 and therefore conversely justifies the assumption in question. 



The kinetic theory of gases gives for the molecular diameter 

 cZ=10 -8 cm., and for the number of hydrogen molecules in the 

 unit of weight 6*7 xlO 23 ; in the molecular weight of any gas or 

 vapour there are thus 2=1*3 x 10 29 molecules. 



If these values, taking Eicharz's for <?, be placed in the above 

 formula, we get 



A=4-3xl0 12 ergs. 



* Wiener Berichte, 1883, p. 861. 



t 11. Ebert, Wied. Ann. xlix. p. 651 (1893). 



