[ 238 ] 

 XXXI. Intelligence and Miscellaneous Articles. 



ON THE ELECTRICAL AND CAPILLARY PROPERTIES OF MERCURY 

 IN CONTACT WITH DIFFERENT AQUEOUS SOLUTIONS. BY M. 

 LIPPMANN. 



"VITHEX mercur\'-is in contact with pure or acidulated water, one 

 ' * has only to add to the water a small quantity of certain sub- 

 stances in order to notably change two of the physical properties of 

 the contact surface — the capillary constant or superficial tension, on 

 the one hand, and, on the other, the electromotive force (that is to 

 say, the difference of the electrical potentials) of the water and the 

 mercury. The experiments which I have made on this question, 

 in the laboratory of M. Jamin, and which I have the honour of 

 submitting to the Academy, have conducted me to this very simple 

 relation : — For each value of the electromotive force the capillary 

 constant has a determinate value, and one only, independent of the 

 chemical composition of the liquid. In other terms, if for tivo dif- 

 ferent comhinations the electromotive force is the same, the capillary 

 constant is likewise the same. 



To verify this law, I at first employed the following very simple 

 apparatus : — Two equal capillary tubes, T, T', are placed vertically 

 side by side, and communicate by their lower part with one and 

 the same reservoir of mercury ; their upper extremities are fur- 

 nished with two funnels, E, E', to receive the liquids for experiment. 

 If the same liquid has been put into both E and E' (e. g. water to 

 which has been added one sixth of its volume of sulphuric acid*), 

 the capillary depression of the mercury is the same in both tubes, 

 since all is symmetrical on both sides. In one of the tubes a little 

 chlorhydric acid or a trace of bichromate of potash is added (the 

 former of these substances augments, the latter diminishes the de- 

 pression of the mercury) ; the meniscuses cease to be of the same 

 height in both tubes. The reservoirs E and E' are then put into 

 electric communication with one another by means of a fine tube 

 filled with acidulated water. The mercury meniscuses are imme- 

 diately seen to begin to move towards the same horizontal plane, 

 where they come to rest. The tube of communication has been 

 traversed by an electric current of short duration, the effect of 

 which has been to equalize the electromotive forces of the two 

 meniscuses ; the equality of these forces has brought with it that 

 of the capillary constants, which demonstrates the law enunciated. 

 When the electric communication is suppressed the inequality of 

 the electrical differences is reproduced, and at the same time the 

 difference of level. 



Another verification, of great nicety, has been obtained by means 

 of a more perfect apparatus. A vertical tube, open at both ends, 

 is tapered to a fine point at its lower extremity. It contains a 

 column of mercury of about 40 centims. height, which is supported 

 by the capillary pressure of the minute meniscus which is formed 

 in the slender point. This point dips into a glass vessel V con- 

 * This acidulated has over pui-e water the advantage of well wetting 

 the glass, which eliminates the variations of the angle of junction between 

 the two. 



