Electrical Conductivity of Flames. 481 



To farther test the applicability of the formula 



V=~+ACd 



to flames, the current between two vertical parallel platinum 

 disk-electrodes placed symmetrically in an ordinary Bunsen 

 flame was measured. One of these electrodes was 3 cms. in 

 diameter, and the other consisted of a disk 1 cm. in diameter 

 surroanded by a guard-ring 3 cms. in diameter. The annular 

 space between the disk and ring was 0*5 mm. wide. The 

 current between the large disk and the small one was 

 measured, the guard-ring being kept at the same potential as 

 the small disk 



the o-uard-rino- 



The results are shown in fig. 4 for a distance 



Fie-. 4. 











^^^^-"-"^N 



'C 



|O0 







• .— ^ 

















* 





' ^^i 









ft 













lir 













lh 













-^ 



• ^j 











50 



/ 













f 











10 



BO 



30 



40 volts- 



of 1 cm. between the electrodes. The current was very 

 nearly independent of the distance between the electrodes, 



C 2 

 which means that ACcZ in the formula V= ™ + ACW was 



negligible. Consequently we should have C 2 = B 2 V. The 

 curve drawn is the parabola C = 19'25^Y, and it will be 

 seen that the points fall very near to it. The term ACd in 

 this experiment was small, partly on account of the smallness 

 of d and partly because the flame was very hot, which of 

 course diminishes A. 



In previous experiments on the variation of C with V with 

 the electrodes near together, no guard-ring was used, so that 

 the relation obtained was probably complicated by the non- 

 uniformity of the field at the edges of the electrodes. 



Phil. Mag, S. 6. Yol. 10. No. 58. Oct. 1905. 2 L 



