^78 M. G. Quincke on Electrolysis ^ and the 



t25 of a millim. diameter in a horizontal direction^ fell on a 

 plane-convex crown-glass lens, of whicli the focal distance was 

 1 metre and the diameter 100 millims. The rays traversed the 

 solution of sulphate of copper in the glass trough almost at right 

 angles to the direction of the electrical current. The glass 

 trough was placed close to the crown-glass lens, and projected, 

 ^t a distance of about 3 metres behind the lens, a real image of 

 the small illuminated aperture. This image, which was from 1 

 'to 2 millims. in diameter, was so screened by a diaphragm with 

 a straight vertical edge standing in front of the ocular of an 

 astronomical telescope placed at the opening of the mica plate in 

 the solution of sulphate of copper, that only a small portion of 

 light could reach the telescope. On closing the battery, cloud- 

 like veils were seen from the opening of the mica plate in the 

 solution of sulphate of copper passing out on both sides of the 

 mica plate, similar to those observed by Toepler to be produced 

 by induction-sparks in air. The phenomenon was exactly the 

 same with a different direction of the electrical current in the 

 -solution, and was manifestly due to the heating of the hquid in 

 the narrow opening by the electrical current. Although the 

 telescope commanded the vrhole space between the copper elec- 

 trodes, apart from the phenomenon described nothing unusual 

 eould be perceived within the liquid. 



When the aperture in the mica plate was enlarged, then the 

 quantity of gas liberated here, if it had arisen from the decom- 

 position of water, must have increased with the size of the aper- 

 ture, since the intensity of the current increased in the whole 

 circuit so long as the density of the current sufficed for the de- 

 composition of water in the solution of sulphate of copper. This 

 latter condition was fulfilled, as the experiment with the copper 

 wire as cathode showed; and yet the evolution of gas diminished 

 ■with the enlarging of the aperture, just because the heating was 

 smaller. 



According to this the whole phenomenon does not depend on 

 a selective property of the electrical current, but on a purely 

 secondary chemical action. 



Whether the separated hydrogen results from decomposition 

 of the water, or from a trace of sulphuric acid which is still 

 present in the solution, might be very difficult to decide. On 

 account of the exceedingly small specific conductivity of the water, 

 we should incline to the latter view; it will, hovrever, be diffi- 

 cult to give a stricter proof. 



When in the same glass trough with the mica plate and a 

 small aperture in the latter the current of the same Grove's bat- 

 tery of 77 cells was passed through a solution of pure common 

 ' salt or sulphate of potash in water mixed with some tincture of 



