482 Dr. H. A. Wilson on the 



(2) The Effects due to introducing Salt Vapours into 

 the Flame. 



The quartz-tube burner enables the effect of putting salt 

 into different parts of the flame to be easily studied. A bead 

 of an alkali salt on a platinum wire was put into different 

 parts of the flame, the electrodes being about 18 cms. apart. 

 It was found, in agreement with earlier results, that the 

 current through the flame was not affected unless the salt 

 vapour came in contact with the negative electrode, when a 

 large increase in the current occurred. This result was 

 previously explained by supposing that the salt vapour is 

 only ionized when in contact with the hot electrodes, but it 

 now appears that the true explanation is that the salt vapour 

 is ionized anywhere in the flame, and that the absence of 

 effect except close to the cathode is due to the non-uniformity 

 of the potential gradient. 



Two wires connected to a quadrant electrometer were sup- 

 ported in the flame so that the electric intensity between them 

 could be measured. In one experiment, using a P.D. of 

 700 volts between the principal electrodes, the electric in- 

 tensity was 1'6 volts per cm. at about midway between the 

 electrodes. On bringing a bead of K 2 C0 3 into the flame 

 just below the two wires, the P.D. between them fell to a 

 very small fraction of a volt, but the current through the 

 flame was not appreciably increased. The part of the flame 

 occupied by the salt vapour is thus a much better conductor 

 than the rest of the flame. In the experiment just described, 

 the potential fall at the cathode was 700 — 18 x 1*6 = 671 volts, 

 and, as we have seen, C = A^/V 2 . Now the effect of putting 

 in the salt is to diminish the electric intensity to practically 

 zero in the part of the flame occupied by the salt, which was 

 a length of about 2 cms. of the flame. Thus putting in the 

 salt must have increased the cathode fall by 3*2 volts, which 

 according to the formula (3 = A^/Y 2 , since V 2 is 671 volts, 

 should have increased the current by one part in 400. Now r 

 the deflexion due to the current in this experiment was about 

 200 rams., so that putting in the salt ought to have increased 

 the deflexion to 200*5 rams.; but since the deflexion was 

 never perfectly steady owing to small oscillations of the 

 flame, so small an increase could not have been detected. 

 It thus appears that the absence of effect on putting in salt, 

 except close to the cathode, is not inconsistent with the view 

 that the salt is ionized anyAvhere in the flame. 



Fig. 5 shows the variation of the current with the distance 

 between the electrodes for several P.D.'s when some K 2 00 3 



