Conductivity produced by Heating Salts. 



745 



than the positive, although the difference was not so marked 

 as in the above cases. 



With zinc iodide no difference in the weight of the elec- 

 trodes was noticed. 



Hence it appears that some of the products in the first 

 three cases become positively charged, and so tend to accu- 

 mulate on the negative electrode ; and it is probable that a 

 good deal of the salts sublime without undergoing chemical 

 decomposition, the particles being positively charged. 



IX. Rate of Decay of Activity with the Time. 



In our first experiments with zinc iodide (loc. cit.) 

 Dr. Willows and I found that the activity first increases to 

 a maximum, then gradually decays with the time, following 

 an exponential law if the temperature is kept constant. I 

 have made some further experiments on the decay of zinc 

 iodide under different conditions of temperature and pressure. 



A typical decay-curve is shown in fig. 5. 



Fi°\ 5. 



280 

 260 

 ZK 



ZOO 

 -J80 



i 

 1 



>140 

 180 

























/ 







































( 



> J 



\ 





















\ 

















1 







V 











































\ ® 















v I 

















x x 





<s>c 



'/ILCULflr£ 









© 











-eo o 20 



Time in Minutes. 



J?Q 



In this the times are plotted as abscissa? and the rates of 

 leak as ordinates. 



