Influence of Voltaic Currents on the Diffusion of Liquids. 57 



heavier into the lighter solution, but also (in certain cases) at the sur- 

 face where it passed from the lighter to the heavier one ; 2nd. The 

 production in some cases of two or three separate lines at the former 

 situation, and less frequently also at the latter one ; and, 3rd. An 

 apparent movement of the mass of the heavier solution, usually in the 

 direction of the electric current, but in certain exceptional cases in a 

 reverse direction. In all cases there occurred in addition the more or 

 less influencing circumstance, rise of temperature (by conduction, 

 resistance, &c), with its usual effects. 



The earliest allied experiment known to me is one by Faraday 

 (Exp. Hes. 494), who passed an electric current from forty cells, four 

 inches square, by means of platinum plate electrodes, through a strong 

 solution of magnesic sulphate into a layer of distilled water, half an 

 inch deep and about seven square inches in area, lying upon it. In 

 less than one minute magnesia appeared at the boundary surface of the 

 two liquids, forming a layer one-eighth of an inch deep in the water 

 immediately upon the magnesic solution. The water above was quite 

 clear. There was no alkali at the negative platinum plate, but plenty 

 of acid at the positive one. This experiment was repeatedly verified. 

 Daniell subsequently in a research on the " Electrolysis of Secondary 

 Compounds " (" Phil. Trans.," 1840, pp. 209-224), passed an upward 

 current through solutions of the nitrates of silver, mercury, and lead, 

 and the sulphates of palladium, copper, iron, and magnesium into 

 a dilute one of caustic potash, separated from them by a thin hori- 

 zontal diaphragm of bladder. Oxygen was determined to the upper, 

 and the respective metals to the lower, surface of the diaphragm, and 

 deposits of metal, more or less oxidised, were formed upon the latter 

 surface, the oxidation being more complete the more oxidisable the- 

 metal ; with the magnesium salt oxide alone was obtained. 



2. The Influence of Kind and Strength of the Liquids. 



In order to obtain a general basis of facts, I made a number of 

 experiments with the following apparatus : — 



A is a glass cylinder, 20 centims. high and 6 or 7 centims. diameter, 

 open at both ends ; B is a vulcanised india-rubber bung, tightly fitting 

 the cylinder ; C is a glass cup (of nearly equal diameter to that of the- 

 inside of the cylinder), with a perfectly flat and watertight lid of gutta- 

 percha, secured by means of varnish ; D and E are open tubes of glass, 

 about 15 or 18 millims. high and 8 or 10 millims. internal diameter,, 

 flat at their ends, and fitting tightly in the lid of the cup ; F is an 

 open glass tube, about 17 centims. high and 26 millims. diameter, per- 

 fectly flat at its lower end ; Gr and H are large electrodes of sheet 

 platinum. 



The apparatus whilst being used should be situated in a strong 

 light. The cup is first filled with a heavy and strongly coloured elec- 



