due to Heating Aluminium Phosphate. 577 



and the equation of the curve is of the form A(e~^ li — e~ x<it ). 

 The curve of decay of aluminium phosphate can be represented 

 by an equation of the same form up to the point (J, beyond 

 this the exponential curve lies below the experimental. 

 Neglecting this latter point for the moment, if the physical 

 analogy as well as the algebraical one holds, we can suppose 

 the first effect of the high temperature is to produce from the 

 phosphate and the surrounding gas a substance A which does 

 not emit ions, that this next produces a substance B which is 

 the agent producing the conductivity. As in Rutherford's 

 case the curve alone does not allow one to say to which sub- 

 stance the different X's refer. 



If the analogy holds further and the salt also independently 

 produces C, the latter supplying ions but decaying so slowly 

 that its decay can be neglected, the activity due to C is 

 represented by a curve having an equation of the form 

 B(l — <?~ A3 0> and the whole curve EDCAB should be capable 

 of being fitted by an equation 



A(e-^-e-^) + B(l ~e~™). 



This is actually found to be the case. The values of the X's 

 depend of course upon the temperature of the salt. 



In PL XI. fig. 3 the dots represent experimental points, the 

 O's points calculated from the above formula. 



It can be seen from the curve that immediately after the 

 very rapid decay there is a somewhat steady state which is in 

 turn succeeded by a gradual rise in the current to a final 

 steady state. Owing to the small scale used, this is not well 

 shown in the curve at AB, although in the experiment there 

 illustrated the actual rise amounted to about 20 per cent, of 

 the previous steady values. The upper curve AB represents 

 this section on a larger scale and makes this point more 

 distinct. 



The relatively large current at the beginning of the heating 

 appears to depend very largely upon the nature of the gas in 

 the tube, while the final steady current is due entirely to the 

 heated salt. 



The results obtained with hydrogen were always of a most 

 irregular nature. The rate of decay was also much slower 

 in that gas than in air or 00 2 . It was quicker in C0 2 than 

 in air. 



No alteration of the gas contained makes any difference to 

 the current when in the steady condition if the pressure and 

 temperature are kept constant. Further, although an in- 

 creased current is obtained with higher temperatures, and an 



Phil. Mag. S. 6. Vol. 20. No. 118. Oct. 1910. 2 Q 



