1909] The Electrical Properties of Flame. 465 



WEEKLY EVENING MEETING, 



Friday, February 12, 1909. 



His the Duke of Northumberlaxd, K.G. P.C. D.C.L. 



Sc.D. F.R.S., President, in the Chair. 



Professor Harold Albert Wilson, M.A. D.Sc. F.R.S. M.R.I. 



The Electrical Properties of Flame. 



If a flauie is brousrht near to an insulated conductor charged with 

 electricity, the charge disappears. This is explained by supposing 

 that the gases in the flame are partially dissociated into ions. A 

 neutral molecule splits up into two ions, one having a negative charge 

 and the other a positive charge. The conductor, if positively charged, 

 attracts the negative ions out of the flame, and their charges when 

 they reach it neutralise its charge. 



If a plate of an insulator, such as ebonite, is placed between the 

 flame and the charged conductor, the ions are still attracted through 

 the plate : but when they reach it they cannot get through, and so 

 remain on its surface. The side of the plate turned towards the flame 

 thus gets a charge of opposite sign to that on the conductor. This 

 shows that the disappearance of the charge in the first case was due 

 to an opposite charge attracted out of the flame, and not to the charge 

 on the conductor escaping into the flame. 



We have a stream of gas rising from the flame, and the ions go up 

 in the stream. The ions of opposite sign attract one another, and 

 when two come together rheir charges are neutralised and the two 

 ions are said to have disappeared by recombination. Thus, as we go 

 up in the stream of gas from the flame the number of ions diminishes. 

 If the stream of gas is allowed to pass up a long tube containing 

 along its axis a series of charged electrodes, then the bottom electrode 

 will be discharged first, and then the next one, and so on. The ions 

 are used up in discharging the electrodes, so that the electrodes are 

 discharged in order, beginning with the lowest one. AVhen the lower 

 electrodes have been discharged, the upper ones begin to be discharged, 

 but more slowly, b(5cause many of the ions disappear by recombination 

 before they get far up the tube. Another effect also comes in ; as 

 the gases cool down the ions do not move so freely through them, and 

 so are not so easily attracted by the electrodes. This makes the rate 

 of discharge of the upper electrodes still slower. 



Thus, as we go down towards the flame the number of ions and 

 their mobility rapidly increases, and right inside the flame the number 

 is so large that the flame behaves like a good conductor of electricity. 



If the terminals of an induction coil are connected to two Bunsen 



