Influence of Voltaic Currents on the Diffusion of Liquids. 69 



downwards through the meniscus, may be explained as follows : — In 

 the former case the layer of liquid accumulated above the meniscus 

 by the united action of electrolysis, ordinary and electric diffusion, is 

 of less specific gravity than the layer produced below it, and con- 

 sequently the two layers do not as readily mix with each other ; but 

 in the latter case the layer produced above the meniscus is usually of 

 greater specific gravity than that immediately below the meniscus, 

 and the liquids more readily mix. These circumstances probably also 

 partly explain the greater frequency of the lines at the positive 

 meniscus than at the negative one. 



Numerous observations have shown as very probable that the upper 

 line nearly always originates at some distance from the meniscus, and 

 in some cases subsequently moves down to it, whilst in others it 

 separates from it (see Experiment No. 40) ; and in cases where the 

 two liquids have somewhat mixed, and there is no definite meniscus, 

 the line commences in an extremely dilute and nearly colourless 

 stratum of the lower liquid. The line sometimes commences nearly 

 •5 millims. above the visibly coloured layer. 



The apparent thickness of the lines is probably due to convexity. 

 The lines produced are usually straight with a moderate current, and 

 curved with convexity downwards with a strong one. The commonest 

 case is, that the line at first is curved and barely visible, but gradually 

 becomes definite and flat, and remains so. The form of the meniscus 

 is sometimes changed by the passage of the current ; this would be a 

 necessary consequence of the alterations produced in the composition 

 and adhesive properties of the layers of liquid on each side of the 

 meniscus. Each newly formed line also possibly acts as a meniscus, a 

 liquid electrode, and a diffusion diaphragm. A series of lines could 

 probably only occur where each successive layer of liquid in ascending 

 order was lighter than the one next below it, and heavier than the 

 one next above it. Such a series occurs more frequently at the 

 meniscus beneath the cathode than in the one beneath the anode. 



Whether the meniscus is rendered more permanent or not by tem- 

 porary passage of an upward current through it, and the accumulation 

 of ions against each of its surfaces, I have not definitely ascertained ; 

 the free acid of the upper layer, and the free base of the lower one 

 must, however, subsequently unite and form a third separating stratum 

 close to it. 



Time is an important element in the formation of the lines ; long 

 continued action is, within certain limits, more favourable than a 

 strong current to their production. The first line usually appears in 

 about one to five minutes, the second takes more time, especially if 

 the current has been passing a long time in an opposite direction ; the 

 length of time required for the line to appear in the opposite tube on 

 reversal of current, depends upon the period during which the current 



