198 PHENOMENA, ATOMS, AND MOLECULES 



of molecular hydrogen in cubic mm. per sq. cm. per minute. We then have 



R = 7.2X10^ CO {77) 



whence from (76), by placing Ta = 300 



R = 9.6Xio« VKPT-^'". (78) 



Substituting in this the values of K from Table XV and taking the 

 values of P and T given above, we obtain the values given below as "R cal." 

 For comparison these are placed side by side with those found by ex- 

 periment. 



T. R calc. R obs. 



Expt. 160 :... 1200 9.8 1.4 



Expt. 173 1270 27.4 3.7 



These results indicate that under the most favorable conditions realized 

 in the experiment, only about one-seventh of the hydrogen dissociated 

 was deposited as "active hydrogen" on the bulb. In the great majority of 

 cases the fatigue effect made the observed rate of clean-up much slower. 



The fact that the observed rates are less than the calculated, yet of the 

 same order of magnitude, is a satisfactory confirmation of the theory that 

 the disappearance and activation of hydrogen are caused by its dissociation 

 into atoms. 



There is thus quantitative evidence of the dissociation of hydrogen over 

 the whole range of temperature from 1200° to 3500°. The substantial 

 agreement of the calculated and observed results over such a wide range 

 proves that the value we have found for the heat of dissociation, namely, 

 84000 calories, cannot be far from correct.^*'^ 



EXPERIMENTS WITH MIXTURES OF HYDROGEN AND NITROGEN 



Some experiments have been made to determine the heat losses from 

 tungsten wires in mixtures of nitrogen and hydrogen. The wire was the 

 same as that previously used in the experiments with hydrogen. The bulbs, 

 after being exhausted in the usual way, were filled with the mixture of 

 gases, the total pressure in each case being 600 mm. Mixtures containing 

 1.25, 3.0, lo.o and 30% of hydrogen were used. The results given in 

 Table XX were obtained by subtracting from the observed watts per 

 centimeter, the energy radiated (W^). These figures are directly compar- 

 able with those given in Table I of Part I. 



To obtain the heat carried from the wire by the dissociation, it is 



^^ For example, it now becomes impossible to reconcile our experiments with tbe 

 value q2 = 63000 calculated according to the method of Bohr, Phil. Mag., 26, 863 

 (1913) ; 27, 188 (1914)- 



