Mr Rudge, On the Electrification given to the Air, etc. 127 
On the Electrification given to the Air by a Steam Jet. By 
W. A. Douctas RupcE, M.A., St John’s College. 
[Received 30 March 1915] 
Many investigators from the days of Faraday and Armstrong 
have made observations on the electrification manifested during 
the escape of steam under high pressure and it is well known 
that an insulated body suitably placed in a current of steam does 
acquire a charge. Armstrong showed that the magnitude of the 
charge increased enormously with increase of pressure, and devised 
his Hydro-electric machine by which large quantities of electricity 
were produced. The sign of the charge given to conductors placed 
in the current of steam was usually positive but occasionally 
negative, and the magnitude of the charge seemed to be associated 
with the amount of disturbance present in the jet, for a quiet 
flow of steam was accompanied by a small charge and a noisy flow 
by a large one. 
The writer has shown* that when steam under pressure 
escapes, it gives to the air a strong charge which persists for 
some time after the condensation of the steam. ‘he experiments 
now to be described were made with the object of ascertaining 
the conditions under which a positive or a negative charge was 
given to the air, and also to find out whether the jet was uniformly 
charged. 
The apparatus employed consisted of a small spherical copper 
boiler 20 cm. diameter furnished with a pressure gauge to indicate 
pressures up to about one and a half atmospheres. A set of taps with 
nozzles of different sizes and materials allowed of the flow of steara 
being controlled. The jet could be projected in any direction, 
but the actual direction did not make an appreciable difference 
in the sign or magnitude of the charge when the observation was 
made in a room, but out of doors a vertical jet seemed to give the 
greatest charge. The boiler was heated by a gas burner or by an 
electrical arrangement, the latter being particularly useful when 
inflammable liquids were mixed with the water. The charge 
carried by the steam could be easily detected by arranging an 
insulated conductor in the path of the steam, whilst that given up 
to the air was indicated by a small radium coated collecting plate 
attached to an electroscope. 
The electroscope used was of the usual type with single gold 
leaf but was made double, and the images of the gold leaves were 
projected upon scales fixed to the wall a metre or twoaway. The 
movements of the leaves could thus readily be followed even when 
* Proc. Roy. Soc. A. Vol. 90, 1914. 
