190 



Some Electrical Properties of Flames. 



an electrical machine in the further end of the room. The 

 flame to be tested is then lighted, and the change of deflexion 

 of the electrometer, if any, is noted. If the change of the 

 deflexion is towards negative, the flame is put out and the 

 room is further electrified negatively by turning the machine; 

 but if the change of the deflexion is towards positive we wait 

 for some time till the electrification of the room decreases by 

 some scale-divisions, and the flame is again tried to see the 

 effect. This process is continued till no change is observed 

 on lighting the flame. The reading at that time is taken as 

 the maximum effect of the flame. The following observation 

 on a spirit-lamp connected to a gas-pipe may be taken as a 

 specimen : — 



Deflexion before 

 lighting. 



Deflexion after 

 lighting. 



Direction and 

 amount of change. 



30 



20 



+ 10 



]5 



13 



+ 2 



13| 



12 



+ H 



12 



11 



+ i 



6 



81 



- 21 



81 



8h 







The maximum effect is therefore 8J divisions, equal to 0'6 

 volt negative, 14 divisions of the scale corresponding to one 

 volt. 



When this same lamp was put on an insulating stand and 

 connected to the negative pole of one Daniell's cell, the other 

 pole being connected to gas-pipe, the maximum deflexion was 

 40 scale-divisions ( = 3 volts), and when two Daniell's cells 

 were used in the same way the maximum deflexion was 60 

 scale- divisions ( = 4f volts). 



Experiments the arrangements for which are shown dia- 

 grammatically in fig. 4, were also tried. A, B are metal plates 

 supported about 2 millim. apart by the insulating material C, 

 and joined by wires to the terminals of the electrometer. A 

 spirit-lamp is placed about a foot below, so that the hot air 

 from the flame passes between the two metals. Differences 

 of potential produced by this arrangement are given in the 

 following table : — 



