Influence of Voltaic Currents on the Diffusion of Liquids. 71 



the lighter one, the latter being artificially coloured when necessary 

 by means of litmus. The inner vessel was supported, and capable 

 of being steadily raised by means of a vertical rack and pinion (not 

 shown in the sketch). 



In using this apparatus (after placing the electrodes in position), 

 the small cylinder was first raised, and then the exact bulk (viz., 

 ozs.) of solution was poured into the outer vessel. The inner 

 cylinder being next depressed until its lower end was level with the 

 liquid, the lighter solution was allowed to flow very slowly down the 

 inner surface of that vessel, and the cylinder simultaneously depressed 

 with great regularity (by means of the rack and pinion), so as to 

 keep the meniscus within the small tube, until the vessel was suffi- 

 ciently immersed. In cases where it was desirable to colour the 

 heavier liquid instead of the lighter one. the meniscus tube projected 

 into the lighter liquid instead of into the heavier one. 



This apparatus is more easily managed than the one described on 

 p. 58 ; the arrangement also offers less conduction resistance, and a less 

 powerful battery suffices ; the phenomena obtained with it and re- 

 quiring to be observed are less numerous, but at the same time less 

 complete ; reversal of the current, however, usually enables the 

 remainder of the changes to be perceived. In this apparatus also the 

 phenomena at one meniscus are not liable to be neutralised, or in any 

 other way interfered with by those at the other, this is particularly 

 :advantageous with regard to the visible movements. By raising the 

 inner cylinder slightly and then depressing it, a definite meniscus can 

 also be obtained at any time. The following experiments were made 

 with it by the aid of a current from twelve Grove's cells in single 

 series. 



Exp. 40. — Meniscus tube 17 millims. long, 7 millims. bore. Outer 

 liquid a saturated solution of sodic sulphate. Inner and coloured one 

 a one-fourth saturated solution of potassic chloride. Current sent up 

 the meniscus tube. Conduction moderate. A line produced at once. 

 The meniscus moved in the direction of the current. Acid accu- 

 mulated at the upper surface of the meniscus and produced a red layer 

 of liquid about 1*75 millim. thick. By reversing the direction of the 

 current the meniscus descended at once about 2'5 millims. A line 

 with its convexity upwards soon formed in the colourless portion 

 about 4*0 millims. below the border of colour ; and another in the 

 coloured portion. There was thusthree lines, the middle one being the 

 original meniscus, now somewhat indefinite and dividing the coloured 

 and colourless liquids. By raising the cylinder until a little of the 

 coloured liquid escaped, and then depressing it, a clear definite 

 meniscus was obtained, which soon became indefinite by the influence 

 of the downward current in the tube, and two other lines, one above 

 .and one below it, soon began to develop and separate further asunder, 



