Dissociation of Water Vapour. 



Ill 



pressure o£ the vapour diminishes, and as one of the experi- 

 mental difficulties is the estimation of the electrolytic gas 

 produced, it follows that the larger the amount the smaller 

 the error in its estimation. The percentage decomposition 

 was calculated for atmospheric pressure by the following 

 formula : — 



D^Dx^/ 



P 



760 



where D is the percentage decomposition at a water-vapour 

 pressure P, and D x the decomposition at atmospheric pressure 

 (760 mm.). 



The results obtained between 1220° and 1640° are in good 

 agreement with those of other experimenters, and, ODce the 

 apparatus is set up and calibrated, the experiments can be 

 performed easily and with expedition. 



The apparatus is shown in fig, 1. It is essentially the 



Fig. 1. 



same as that previously described, but has various minor 

 improvements in order to minimise possible errors. 



