Influence of Voltaic Currents on the Diffusion of Liquids. 59 



contact surfaces of the two liquids (and especially upon the portions 

 of liquid immediately above them) continually observed and noted. 



To those of the lower liquids which were colourless, strong colour 

 was imparted by addition beforehand of solution of litmus. Although 

 purity of the liquids does not appear to materially affect the pheno- 

 mena under examination, distilled water, pure acids, and usually salts 

 of a high degree of purity were employed in all cases. In all the first 

 six experiments of the following series a current from a single row of 

 five Grove's elements, each of one pint capacity, was used: and the 

 apparatus already described was employed in all those to No. 36. 



Experiment 1.— Meniscus tubes 12 milhms. high and 3*5 millims. 

 bore. Lower liquid, a saturated solution of cupric chloride of a green 

 colour ; upper one, dilute sulphuric acid, 1 in 10. After passing the 

 current during five minutes, the cupric solution in the tube under 

 anode was deep green, and its meniscus indefinite ; and under cathode 

 blue, with meniscus definite. Reversed current repeatedly and obtained 

 similar effects each time after about ten or fifteen minutes. Remarks. — 

 The blue colour at the positive end of the cupric solution was probably 

 due to the accumulation of basic chloride by the influence of the 

 current. 



Exp. 2. — Same tubes. Lower liquid, a saturated aqueous solution 

 of cupric sulphate ; upper one, same as in last experiment. Free con- 

 duction. Positive meniscus definite and negative one indefinite.* By 

 reversing the current the previously definite one thickened out and 

 rapidly became lower in position, whilst the other one gradually be- 

 came definite and rose in position, as if the mass of the liquid moved 

 in the same direction as the current. 



Exp. 3. — Same tubes. Lower liquid same as last; upper one, 1 

 volume of hydrochloric acid and 6 of water. Conduction free. No 

 green colour at negative meniscus below anode. (Found by a separate 

 experiment that the addition of hydrochloric acid to a solution of 

 cupric sulphate did not make the latter green.) Positive meniscus 

 was definite, negative one indefinite and diffused. The anode became 

 coated with solid hydrate of chlorine, which fell off and decomposed 

 with evolution of gas on stopping the current. 



Exp. 4. — Meniscus tubes 15 millims. long and 4 millims. bore, were 

 now used in all experiments to No. 12. Lower liquid a saturated 

 solution of cupric chloride ; upper one a saturated solution of potassic 

 sulphate. Conduction moderate. Positive meniscus definite, and soon 

 a second and parallel line appeared beneath it, the intervening stratum 

 being weak in colour; negative meniscus diffuse. Reversed the 

 current, first an upper, and then a second and lower line appeared 

 under the cathode ; the other meniscus became diffuse and indetinite. 



* By positive meniscus I mean the one under the cathode, and by negative that 

 under the anode. 



