some Electrical Properties of Flames. 189 



vol. xxvi. No. 666.) In fig. 3 is shown the curve of potential 

 obtained after several observations. It will be observed that 

 the potential at the middle line of the flame is nearly zero, 

 and the surface of maximum negative potential lies just inside 

 of the flame, while the surface of maximum positive potential 

 lies at a distance of 2 millim. from the boundary of the flame. 

 The maximum difference of potential between these two sur- 

 faces was found to be between 2 J- and 3 volts. 



Similar results were obtained with other flames ; but in 

 the case of glowing charcoal the point of the platinum wire 

 had to be brought very close to it in order to obtain the indica- 

 tion of positive potential of the film of air surrounding it. 



Having thus made quantitative measurements of the 

 potentials of different parts of a flame, it was expected that 

 the magnitude of the electrification of the air would depend 

 on the part of the flame that was earthed ; that is, that maxi- 

 mum positive electrification would be obtained when the most 

 negative part of the flame was earthed and vice versa. This 

 expectation was verified by placing the Bunsen burner 3 feet 

 below the nozzle of a water-dropper connected in the usual 

 manner to a quadrant-electrometer. 



The flame of the Bunsen burner was next surrounded by a 

 wire-gauze cage, which was made to lie on the surface of the 

 flame. The burner and wire gauze were connected to a gas- 

 pipe for earth. Under this arrangement the effect of the 

 flame was just like that of glowing charcoal, the electro- 

 meter connected to the water-dropper showing 6 volts positive. 



Another cage open at the top, and connected to earth, was 

 made to lie on the surface of maximum positive potential 

 surrounding the flame. This was difficult to do, and only a 

 part of the cage fulfilled the condition. In this case the air 

 was electrified to 2| volts negative, while the burner without 

 the cage electrified the air to less than one volt. 



These experiments help to explain why glowing charcoal 

 electrifies air positively, for it acts like a solidified flame 

 connected to earth. For a similar reason spongy platinum, 

 when it glows in hydrogen or coal-gas, is negatively electrified 

 like glowing charcoal. 



In these experiments it was desirable to know the maxi- 

 mum electrifying effect of the flame, and this was done by 

 the following method : — The flame to be tested is placed 

 on a stand insulated or uninsulated about 3 feet below the 

 nozzle of the water-dropper, which is connected to the electro- 

 meter. The room is electrified, say negatively, to a certain 

 potential which is indicated by the electrometer, by turning 



