90 



Prof. J. J. Thomson. 



[Mar. 9 r 



II. « The Electrolysis of Steam," By J. J. Thomson, M.A., 

 F.R.S., Cavendish Professor of Experimental Physics in 

 the University of Cambridge. Received February 18, 1893. 



It is well known that steam is split up into hydrogen and oxygen 

 when an electric discharge passes through it. A very careful ex- 

 amination of the laws of this phenomenon was made more than thirty 

 years ago by Perrot ;* as his results are very remarkable, and seem 

 to be not at all well known, I will describe, as briefly as possible, his 

 apparatus, and the results he obtained with it. The apparatus used 

 by Perrot in his experiments is represented in fig. ] , taken from his 

 paper. The spark passed between two platinum wires sealed into 



Fig, l.f 



r 



glass tubes, cfg, dfg, which they did not touch, except at the places 

 where they were sealed ; the open ends, c, d, of these tubes were about 

 2 mm. apart, and the wires terminated inside the tubes at a distance 

 of about 2 mm. from the ends. The other ends of these tubes were 

 inserted under test-tubes e, e, in which the gases, which passed up the 

 tubes, were collected. The air was exhausted from the vessel A, and 

 the water vapour through which the discharge passed was obtained 

 by heating the water in the vessel ; special precautions were taken 

 to free this water from any dissolved gas. The stream of vapour 

 arising from this water drove up the tubes the gases produced by the 

 passage of the spark; part of these gases was produced along the 

 length of the spark. Part of the gases so collected has been 

 decomposed by causes which would not be affected by reversing the 

 electrical conditions of the electrodes, e.g., by such causes as the heat 



* 4 Annales de Chimie et de Physique ' [3], vol. 61, 1861, p. 161. 



f From 'Notes on Electricity and Magnetism' (Clarendon Press, Oxford). 



