484 The Electrical Conductivity of Flames. 



When the distance between the electrodes is large, the 

 current with K 2 C0 3 on the cathode is about 50 times greater 

 than the current when no salt is present. The electric in- 

 tensity in the region between the electrodes, however, is only 

 three or four times greater, so that it seems as though putting 

 salt on the negative electrode increased the conductivity o£ 

 the rest of the flame. This effect is of a rather unexpected 

 character, and the writer hopes shortly to carry out further 

 experiments with the object of elucidating its real nature. 



With salt on the cathode, most of the fall of potential 

 occurs in the uniform gradient between the electrodes, so 

 that the current which is proportional to the gradient varies 

 roughly inversely as the distance between the electrodes and 

 directly as the potential-difference. 



It has been shown recently by F. L. Tufts* that coating 

 the negative electrode with calcium oxide greatly diminishes 

 the fall of potential at this electrode, and so increases the 

 current. This effect is clearly exactly of the same nature as 

 the effect of putting an alkali salt on the electrode. Tufts 

 also finds that when the negative electrode is coated with 

 CaO, then putting a bead of salt anywhere in the flame 

 between the electrodes increases the current considerably. 

 It was consequently to be expected that with salt on the 

 negative electrode a similar effect would be obtained, and 

 this was found to be the case. With the electrodes 18 cms. 

 apart and K 2 C0 3 on the cathode, putting a bead of K 2 C0 3 

 nny where in the flame increased the current about 10 per 

 cent., and the same effect was obtained with beads of other 

 alkali salts. Two beads put in at the same time in different 

 positions increased the current about 20 per cent. The 

 portion of the flame occupied by the salt becomes a much 

 better conductor than the rest of the flame, so that the electric 

 intensity in it becomes very small. The electric intensity in 

 the rest of the flame is consequently increased, and the current 

 is proportional to this intensity. The salt from one bead 

 occupied about 2 cms. of the flame, so that with the elec- 

 trodes 18 cms. apart an increase of ^ in the current ought to 

 have occurred, and with two beads f. With the electrodes 

 nearer together, the effect of putting in a bead was greater, as 

 was to be expected. With the electrodes 9 cms. apart, putting 

 in a bead increased the current about 20 per cent. It appears, 

 therefore, that the snlt vapour is ionized anywhere in the 

 flame, and not only when in contact with the electrodes. 

 In an earlier paper (Phil. Trans. A. vol. cxcii. 1899) the 



* F. L. Tufts, Phys. Zeitschr. v. p. 76 (1904). See also F. L, Tufts, 

 •& J. Stark, Phys, Zeitsc.hr. v. p. 248 (1904;. 



