ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 395' 



I by no means press this probably accidental agreement ; and the true 

 meaning of any results obtained by such methods as I have described I 

 leave for the present open. 



On my cursorily mentioning these very preliminary results in a 

 circular to the committee on Electrolysis, Professor S. P, Thompson 

 suggested using a jelly, and we at once tried it. One cannot use any 

 strong acid with gelatine, for it seems to spoil it, but acetic acid serves ; 

 and the siphon tube was accordingly filled with an acetic acid gelatine 

 jelly, which went stiff when cold. Agar-Agar jelly, suggested, I think, 

 by Prof. Clowes, can be used with stronger acids. 



The use of jelly makes the experiment much less troublesome, be- 

 cause there is now no difficulty in the manipulation, no special need for 

 adjustment of the solution densities, nor danger from changes of level. 



One objection to it is, that, supposing the ionic velocities were deter- 

 mined in jelly, they could not easily be compared with Kohlrausch's 

 numbers, which apply to weak aqueous solutions. There is of course no 

 difficulty in determining the conductivity of the jelly and the slope of 

 potential, as required in formula (1) ; but it is difficult to assign a value 

 to N. The hypothesis that the solvent does none of the conduction, even 

 though it be true for water, can hardly be pressed to include the case of a 

 jelly of unknown and complicated constitution; especially as we found 

 that the conductivity of plain jelly was actually considerably greater than 

 that of dilute acetic acid ^ (see p. 406). 



The endosmose difficulty is not got over by the use of jelly — in fact, it 

 may perhaps be accentuated; and another and unexpected difficulty pre- 

 sents itself. Gelatine swells under the action of the current and exudes 

 from the tube ; but always in one direction only, viz., against tbe current. 

 A cylinder of jelly an inch or two in length was ultimately protruded 

 from the anode end of the tube ; and cracks appeared in the substance 

 of the jelly, of curious serpentine form, which underwent noteworthy 

 metamorphoses. 



The position of the precipitate in these jelly tubes was not far from 

 the middle of the tube, indicating that Ba and SO4 travelled at nearly 

 equal rates (see pp. 401 and 411). 



Second Series of Experiments. 



1 next proceeded to another form of the experiment, where a detecting 

 substance was placed in the tube so as to be able to follow the motion of 

 the ions along their journey, instead of only noting their time and place 

 of meeting. 



Various detectors were tried, but a simple and obvious one, able to 

 show both anion and cation, is sulphate of silver. 



A jelly tube containing, besides acetic acid, a solution of sulphate of 

 silver, was arranged to join two vessels, each full of baric chloride solution. 

 When the current passes, the barium travels with it and causes a preci- 

 pitate of BaS04, which may be watched creeping on from point to point ; 

 the CI at the same time travels against the current and causes a precipi- 

 tate of AgCl, which may be likewise watched. The poor solubility of 

 Ag2S04 is of no consequence, because it is only wanted to detect the ions, 

 not to absorb them and stop their motion ; hence, however soluble a 



' In this Connection see Dr. Arrhenius' previous experiments on conductivity of 

 jelly as detailed above, p. 344. 



