746 Electrical Conductivity produced by Heating Salts. 



If the ascending branch is produced backward and the 

 point where it cuts the axis is taken as the zero of time, it is 

 found that the curve can be represented by an equation of 

 the form 



1 = A0" A2 ' --<T M ); 



where I = leak at time t, A is constant, and X 2 and Xj are 

 constants (\ 1 = 25 x 10~ 6 , X 2 = 157 X 10" 5 ). 



The O's represent points calculated from this formula on 

 the assumption that the curve produced backward meets the 

 axis 14 minutes behind the origin. 



If we may reason from the analogy of radioactive change, 

 such a curve would mean (see Rutherford, '• Radioactivity/ 

 Ch. ix.) that two successive changes are produced. The first 

 of these produces no ions, but the second does. The presence 

 of water is necessary to start these changes. These successive 

 changes are of interest when taken in conjunction with the 

 fact observed by Allen *, that the decay of photo-electric 

 activity of zinc can be represented as the sum of two 

 exponential terms. 



Fig. 5 also shows that after the material has been heated 

 for some time the rate of decay becomes very much, slower ; 

 in fact, for the last 90 minutes the rate of leak undergoes 

 very little decrease. For the part of the curve which can 

 be represented by the formula, the activity declines to one- 

 half its value in about 46 minutes. 



Conclusions. 



(1) Many inorganic compounds when heated up to tempe- 

 ratures below 360° C. have the power to produce electrical 

 conductivity. 



(2) That in the case of some of these compounds (e. g., 

 halogen salts of zinc) chemical changes take place, and the 

 conductivity produced has its origin in these changes. The 

 ions so produced are similar to those which have been observed 

 in the cases of recently prepared gases, and the conductivity 

 produced by phosphorus. 



(3) That in all cases the ions are of a large size, as is 

 shown by their relatively small velocities. They probably 

 consist of a charged centre surrounded by particles produced 

 from the heated compound, and in some cases water- vapour. 



Their nature could be best demonstrated by determining — , 



but means for producing a strong enough magnetic field were 

 not available. 



(4) The presence of water is in some cases intimately 



* Proc. Roy. Soc, Feb. 1906. 



