the Electricity of Flame. 171 



electrodes appears also from the kind of metal which conducts 

 from the flame to the earth having an essential influence upon 

 the result. When the base-electrode -was formed by water, 

 and the electricity conducted from the apex of the flame by 

 different metal plates of equal thickness, determination of the 

 electromotive force E, when the conductor was 



A platinum plate, gave E= 73"6, 

 An aluminium plate, gave E = 176*8. 

 The electromotive force of the combination aluminium, flame, 

 hot air, water, platinum is therefore as much again as that 

 between platinum, flame, hot air, water, platinum, completely 

 in accordance with the previous experiments with two metal 

 electrodes. 



§ 8. Dependence of the Electromotive Force on the Nature of the 

 Flame. 



Since the electromotive force of flame depends on the nature 

 of the metal introduced into it, it is to be expected that, when 

 the constituents of the flame-gases are changed, an alteration 

 of the electromotive force must also occur. Such an altera- 

 tion can be readily brought about by introducing, for example, 

 a bead of soda into the flame, on a well insulated wire. Indeed 

 a deflection of the electrometer-needle then takes place imme- 

 diately; only with sodium there is the great inconvenience 

 that within a short time the entire atmosphere of the room is 

 so impregnated with sodium vapour that the flame burns with 

 a strong resemblance to a sodium-flame, which affects the trust- 

 worthiness of the results. On this account a salt to which 

 flame is less sensitive was chosen, namely potassium chloride. 



It was first ascertained, by a series of careful experiments, 

 that the introduction of a well-cleaned and insulated platinum 

 wire into the flame did not alter the electromotive force. It 

 may be sufficient to allude to this point here, as we shall sub- 

 sequently return to it. 



When the electrodes are in the position shown in fig. 2 a, 

 and a bead of potassium chloride is introduced on an insulated 

 platinum wire, the needle receives an impulse which indicates 

 an increase of the electromotive force ; but it quickly goes 

 back again, and, indeed, far below the value of the deflection 

 which had been given with a pure flame. According to this, 

 there was a diminution of the electromotive force ; but it was 

 only an apparent diminution ; for if the bead of potassium 

 chloride be now taken out of the flame, the needle approaches 

 still nearer to its resting-place. This indicates that with the 

 electrode which was in air an alteration must have taken 

 place. Upon it a thin dash of potassium chloride has formed, 



