494 



Mr. R. Sabine on the Motions produced 



pahding surface where the 

 suboxide was formed, and a the 

 contracting- surface where it 

 was reduced. The motions ofits 

 surface were observed by slightly inclining the trough, w r hich 

 prevented the mercury travelling. When the negative wire was 

 plunged into the mercury globule instead of into the water, so 

 as to leave the process of oxidation to the simple contact be- 

 tween the mercury and the acid water, similar motions w r ere 

 observed, but not so energetic. With the oxidation of the 

 surface b in acidulated water, a quantity of insoluble sulphate 

 was formed and carried mechanically over to a, where, after a 

 time, it accumulated sufficiently to form a shell which remained 

 perfectly still, covering the end «, whilst the end b was in active 

 circulation. This shell increasing gradually, at last covered 

 the whole globule, which nevertheless was found to be circu- 

 lating actively beneath it. The appearance of this sulphate 

 shell is very deceptive, as one is inclined sometimes to conclude 

 that because it is at rest, the mercury underneath must be at 

 rest also, which is not the case. 



The mechanical effect produced by the rapid circulation of 

 mercury found in the last experiment was also observed as 

 follows : — The globule of mercury, instead of being placed in 

 a horizontal trough, was deposited at the bottom (M) of the 

 bend of a U-tube (fig. 7) and acid w r ater poured into each 

 limb above. The quantity of mercury Fig* 7. 



was just sufficient to form a valve, 

 that is, to prevent communication 

 between the acid water in the two 

 limbs, but not much more. Tw r o 

 platinum wires, connected with a 

 reversing-key and five Smee cells, 

 dipped into the acid water in the 

 limbs. When the circuit was closed, 

 the current, going from] A to B, began 

 to oxidize the mercury face in B, and 

 to deoxidize that in A. The mercury 

 was at once set in rapid circulation and mechanically car- 

 ried the water from limb B into limb A until the different 

 heights of the columns of liquid balanced the pressure of the 

 circulating mercury. The battery-circuit was then broken ; 

 and the acid water remained at its unequal level, the mercury 

 acting as a valve. Then the direction of the current was re- 

 versed and circulation of the mercury commenced in the op- 

 posite direction, carrying the acid water back with it from A 

 and heaping it up in B as in the figure. 



J^ 



AG 



