348 CAPILLARY ATTRACTION, ETC. [MEMOIR XXVI. 



quicksilver. A drop of water remains on the surface of 

 quicksilver in the same manner that a drop of oil re- 

 mains on water. As soon, hoWever, as their electro- 

 chemical relations are disturbed by the aid of a voltaic 

 battery, the phenomenon of wetting at once occurs. 



2. Take a tube, Fig. 71, in the form of an inverted 

 siphon, one branch of which, , is about half an inch 

 wide, and the other, Z>, not more than 

 the tenth of an inch. Fill the siphon to 

 a given height, a b, with mercury ; the 

 metal, of course, does not rise in the nar- 

 row branch, Z>, to its hydrostatic level, 

 for mercury is depressed in a capillary 

 Fiir 71 tube, inasmuch as it cannot wet glass. 



Introduce a small column of water, b c. 

 The mercury may now be regarded as being in contact 

 with a tube of water, because that liquid wets the sides 

 of the glass intervening between it and the mercury. 



Pass a slender platinum wire, a?, down the tube, so as 

 to touch the water ; let it be in communication with the 

 positive electrode of the voltaic battery ; with the nega- 

 tive electrode, y, touch the mercury in the wide branch 

 of the siphon, a, and in an instant the metal will rise in 

 the narrow tube, and fall again to its former position as 

 soon as the current is stopped. 



If into a watch-glass fifty or sixty grains of mercury 

 be poured, and over that as much water acidulated with 

 sulphuric acid as is sufficient to cover the surface of the 

 mercury, on the mercury being placed in contact with 

 the negative pole of a battery, and the water with the 

 positive, currents are produced both in the water and 

 the mercury, as was first observed by Erman and Ser- 

 rulas. 



If the wires be on opposite sides of the mercury, as 

 shown in Fig. 72, the metal instantaneously elongates, as 



