Passage of Electricity through Liquids. 277 



by the solution of sulphate of copper, was given off in conse- 

 quence of the increased temperature caused by the current. 



The following experiment confirms this explanation. A highly 

 concentrated solution of commercial sulphate of copper was 

 boiled for a long time in order to free it from the absorbed air. 

 It was poured whilst boiling into a large beaker and cooled as 

 quickly as possible in a freezing-mixture of snow and common 

 salt. When the solution was cooled to a temperature of 20° C, 

 the glass trough was filled W'ith it to a height of 42'5 millims., 

 the two electrodes were placed on each side of the mica plate at 

 a distance of 30 millims., and the current of a Grove's battery 

 of 77 cells passed through it. 



At first a few gas-bubbles w^ere generated ; but these pro- 

 ceeded from the air in the hollow spaces of the mica plate, and 

 soon completely ceased. 



The liquid near the opening became very warm. At the cop- 

 per plate which served as cathode no evolution of gas was to be 

 seen ; but it appeared abundantly when, instead of the broad 

 copper plate, a copper wire was dipped in the solution, although 

 the section of the wire was very much greater than the opening 

 in the mica plate. 



t 



If the density of the current (or the quantity — - in expres- 



qX 



sion 4, § 52) had occasioned the decomposition of the water, 

 then in two places in the liquid changes must have appeared, 

 perhaps hydrated oxide of copper and sulphuric acid— that is, iu 

 the places where the section q was so small that the force k suf- 

 ficed for the decomposition of the w^ater. But no change in the 

 interior of the liquid was perceptible. 



In order to be certain that I had not overlooked any sub- 

 stances liberated by the electrical current in the interior of the 

 liquid, I examined a concentrated solution of sulphate of copper 

 (specific gravity =1*2) in an apparatus similar to that just de- 

 scribed, but of larger dimensions, with the apparatus contrived 

 by Toepler*. 



A trough made of very perfect glass plates, 200 millims. in 

 length and 60 in breadth, was filled to the height of 45 millims. 

 with a solution of blue vitriol, and divided into two chambers by 

 a mica plate which had a hole in its centre '22 millim. in dia- 

 meter. Two large copper plates 60 millims. in breadth con- 

 ducted the current of a Grovel's battery of twenty cells into and 

 out of these compartments. The distance of the copper plates 

 from the mica plate varied from 30 to 100 millimetres. 



The light of an argand lamp, passing through an opening of 



* Beobachtungen nach einer neiien optischen Methode. Bonn, 1864. 8vo. 

 Phil. Mag. vol. xxxiii. p. 75» 



