due to Heating Aluminium Phosphate, 



581 



very small current due to negative ions, as compared with 

 that carried by positive ions, which can be obtained under 

 these conditions. 



VI. Effect of Temperature at Constant Pressure. — 

 Phosphate in Steady State. 



Richardson * has proved that the formula I = a6*e~ Qr2e , 

 where I = saturation current, and # = the temperature in 

 degrees absolute, while Q = a measure of the energy associated 

 w r ith the liberation of an ion, represents the connexion between 

 the saturation current and the temperature, for positive as 

 well as for negative ions given off by heated platinum 

 wires. 



The same law T holds for various chemical compounds which 

 have been tested up to a temperature of 360° C. about f. 



The following results have been obtained by heating 

 aluminium phosphate in C0 2 at 0*05 mm. pressure. 

 Different quantities of the salt having been used in these 

 experiments the absolute values of the currents are not 

 comparable. 



I. II. 



Temperature, 

 °C. 



Current, 2x10-9 

 amp. as Unit. 



880 



1 



950 



4 



970 



7 



995 



15 



1030 



35 



1055 



49 



1095 



103- 



1110 



126 



Temperature, 



°C. 



Current, 2x10-9 

 amp. as Unit. 



1036 



1 



1088 



3 



1135 



5 



1160 



8 



1195 



15 



1230 



34 



1245 



35 



1295 



74 



1330 



168 



The diagram (PL XI. fig. 5) shows the results obtained when 

 1/6 is plotted against -^log e #— log e I. The points are fairly 

 evenly distributed about straight lines, and these lines are 



* Roy. Soc. Phil. Trans. A. 207, pp. 22 et seq. 

 t Garrett, Phil. Mag. June 1907, pp. 732 et seq. 



