Open AccessA phenomenon connected with the discharge of electricity from pointed conductors
Author(s) -
H. T. Barnes,
A. Norman Shaw,
John Zeleny
Publication year - 1909
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1909.0038
Subject(s) - moisture , electricity , cathode , point (geometry) , anode , electrical conductor , materials science , mechanics , geology , chemistry , mathematics , physics , composite material , electrode , electrical engineering , geometry , engineering
The discharge of electricity from pointed conductors has been the subject of many important investigations, notably by J. J. Thomson, Chattock,Warburg, Zeleny, and others. The effect of moisture on the discharge has recently been studied in detail by Zeleny, who was the first to observe the formation of a coloured deposit on steel needle points when observed under a microscope. He describes this deposit as having a reddish-brown colour, resembling ordinary rust, which is attached to the point in irregular pieces which extend outward some little distance, and finds it produced even in fairly dry air. A marked difference in the volume of the deposit was observed, depending on the direction of the discharge to the point. As anode the amount was much in excess of that produced when the point was made the cathode. As Prof. Zeleny passes over this phenomenon with but a brief mention for the steel' points he used, we considered it of interest to study this deposit more in detail, using pointed conductors of various metals, and to observe what effect the presence of the deposit had on the discharge. It appeared to us probable that the deposit was connected with the presence of moisture in the air surrounding the point, and that it could be eliminated altogether by having absolutely dry air. We have found this to be the case, and in consequence one of the disturbing factors connected with point discharge may be eliminated only by working with air from which every trace of moisture has been removed. Most metals react easily with oxygen in the presence of moisture, but especially when made the anode in an electric circuit. It has been shown by one of us, working with Mr. G. W. Shearer, that the metals aluminium, magnesium, and zinc, form, as the first stage of their oxidation, hydrogen peroxide, when immersed in water containing dissolved air or oxygen. The amount of peroxide formed was observed to be considerably increased when the metal was made an anode. Other metals, such as iron, appear at once to decompose any peroxide produced as fast as it is formed. It seems highly probable that the first three metals form over their surface a protective' film which, in the case of aluminium, is exceedingly resistant. The non-formation of this surface film allows free action between the nydrogen peroxide produced and the metal, resulting in the decomposition of the former and further oxidation of the latter. The formation of the surface film on aluminium has been frequently studied, especially in connection with the asymmetric conductivity of that metal. The readiness with which the surface film may be broken down by the current, when travelling from the metal as cathode, indicates, we think, the incompleteness of the oxidation producing the film.