290 Connexion between Capillary and Electrical Phenomena. 



put in communication with the earth, the wire a becomes charged 

 with free negative electricity, as was established by means of 

 Thomson's electrometer ; the deflection of the electrometer may 

 become as great as if its poles had been connected with a Da- 

 nielPs element. It is at the same time observed that the depres- 

 sion of the mercury in the glass tube is greater than when the 

 circuit is closed ; in other words, the constant of capillarity is 

 greater than before. Now the increase of the electromotive force 

 between mercury and dilute acid, with a simultaneous increase of 

 the constant of capillarity at the common surface, is just what is 

 called polarization by hydrogen : the phenomena can then be 

 thus represented : — 



If by mechanical means the surface of contact between mercury 

 and acid water be increased } the mercury thereby becomes polarized 

 with hydrogen. 



On this may be based a very striking experiment which may 

 be made with the capillary electrometer. If by blowing or by 

 suction with the mouth the atmospheric pressure over the mer- 

 curial column be varied, the column of mercury in the fine point 

 can be moved without exertion — this, however, only so long as 

 there is metallic contact between « and ft. If this contact be 

 suddenly broken, the column of mercury at once becomes im- 

 movable, as if it were frozen. This may be thus explained. 

 On blowing, for instance, the surface of mercury begins to in- 

 crease; it thereby becomes polarized, and the increase of the 

 capillary constant produces an increase of the capillary pressure 

 which cannot be overcome by the lungs. The exact opposite is 

 the case with suction. 



On the same phenomena is based an apparent disturbance 

 observed in capillary experiments, namely a slow decrease of the 

 constant of capillarity, as has been shown by Quincke for mer- 

 cury in water. If, for instance, mercury be allowed to ascend 

 in a moistened capillary tube, the surface of the mercury in the 

 tube is increased and is thereby polarized. Now polarization, 

 as is well known, diminishes with time, first rapidly, afterwards 

 continually more slowly. In accordance with this a decrease of 

 the constant of capillarity is observed. A similar thing happens 

 when a drop of mercury is brought into water : in flattening on 

 the bottom it increases its surface and assumes a slowly decreas- 

 ing polarization. 



With the electrometer or galvanometer it can be directly 

 shown that when mercury is contained in a glass vessel 

 under dilute sulphuric acid, dipping a glass rod into it or 

 merely inclining the vessel is sufficient to produce a change of 

 the capillary and electrical conditions. Similarly any agitation 

 produces an alteration of the capillary constant. But when a 



