Dr. Wright on the Behaviour of Mercury as an Electrode. 131 
connecting wire in such a position that the mercury when ex- 
tending fel] against it, a series of contractions and extensions 
took place in such rapid succession that the eye had some diffi- 
eulty in following them. 
' Experiment 5.—Two portions of mercury were immersed in 
dilute sulphuric acid; A was brought into connexion with the 
anode or positive pole of a Daniel’s battery of six pairs, and B 
with the cathode or negative pole of the same. A instantly 
became covered with a silvery film of oxide, flattened itself out 
into a thin plate, and slowly crept up to and around B, which 
was contracted and covered by bubbles of hydrogen. 
Experiment 6.—Dilute hydrochloric acid was substituted for 
the sulphuric acid solution of the last experiment. A instantly 
became covered with a dark brown coating of chloride, and in 
this state could be drawn out into long threads or branches. The 
direction of the current was now suddenly reversed, when A 
drew in all its branches as by magic, and, after rotating violently, 
assumed the contracted state. 
Experiment 7.—A quantity of mercury was strained through 
muslin into a solution of common salt in water, and lay in a 
divided state at the bottom of the vessel. When gll was quiet, 
the induced and interrupted current from the primary wire of a 
powerful electro-magnetic coil machine was passed through the 
solution. The globules of mercury instantly began to unite with 
each other, and did not cease to do so until the whole formed a 
single mass. 
_ The above experiments seem to me to prove the propositions 
of Erman :—1st. “That so soon as chemical affinities are excited 
im the galvanic processes, there takes place at the same time an 
inereased intensity of the attraction of surfaces” (that is, of 
capillary attraction). 2nd. “That the connexion which has been 
supposed to exist between capillary or surface attraction and 
chemical affinity, receives from this a notable confirmation.” 
It has been already stated that in solutions of chloride of 
sodium, and other alkaline salts, contraction occurs in mercury 
when rendered the negative element or cathode of a single circle. 
When, however, in such solutions mercury is made one of the 
negative elements of a compound circle of high tension, a stronger 
chemical affinity is set up between the mercury and the liquid, 
the metal of the alkaline solution is reduced and combines with 
the mercury, and the latter yielding to an increase of capillary 
attraction, mstead of contracting, expands. 
Experiment 8.—One ounce of mercury was placed in a saucer 
containing a solution of chloride of sodium, and was connected 
with the negative wire of a Grove’s cell. The positive wire of the 
same cell, armed with a piece of zinc, was now dipped into the 
K 2 
