T H E ADSORPTION O F IONS ON A MERCURY SURFACE*
-___
BY TV. A. PATRICK A N D P. V. B A C H M A N
It is the purpose of this paper to present a brief preliminary statement concerning the unequal adsorption of ions by mercury from dilute aqueous solution of mercury salts. The work has been done in this laboratory during the last year, and although not completed in all its details, it was thought best to give a brief description at this time, inasmuch as the essential points have been satisfactorily verified experimentally. Later on, a more comprehensive report, together with complete description of apparatus, etc., willa4besubmitted. I
f
I
'
0.5
/N/T/AL CONC€NTRaTlON-
I
I
I
115
210
-1
MIL L/MOLS /TI? LIT57
FIG.I Adsorption in HgHS04 solution
The experiments consisted in forcing pure mercury, by slight pressure, through chamois skin directly into a column of dilute aqueous mercurous sulghate or mercurous acetate. The glass tube which contained the solution was about four feet long and one inch in diameter. The mercury, issuing through the chamois in small drops, fell through the solution by gravity and was collected at the bottom of the tube which was so arranged as to allov the mercury to drain off automatically. In passing through the column o mercury solution, the mercury drops adsorbed certain amounts of cations an( anions. The amounts adsorbed were determined by analyzing the solution both before and after a run. The analyses were made by electrolyzing t h solutions with platinum electrodes under the proper conditions of current den sity, etc. The mercury depositing on the cathode was weighed direct11 while the concentration of the sulfate ion or acetate ion was determined b titrating the remaining solution with standard sodium hydroxide. In thi manner the amount of each ion removed by adsorption could be accurately dc *Contribut.ion from the Chemical Laboratory of Johns Hqpkins University.
ADSORPTION O F IONS ON 9 MXRCURY SURFACE
I35
termined. By varying the initial concentration of the electrolyte, and keeping the time, during which the mercury was allowed to fall through, constant,the amounts of ions adsorbed at different concentrations could be compared. In regard to this, it must be remembered that although the actual mercury surface exposed during a run could not be determined with great accuracy, the working conditions were such as to make all experimental results strictly comparable. (See later paper.) It is also necessary to mention that in the case of mercurous sulfate, it was shown by electrolytic analytical methods that the ratio of mercury to sulphate corresponds to the formula HgHSOd.
FIG.2 .Adsorption in HgCH3CO0 polution.
The results of the above experiments are best illustrated by the accompanying curves (Figs. I and 2 ) which show that, contrary to previous ideas concerning these systems, the mercurous ion is adsorbed to a much greater extent than either the sulfate or acetate ion. Of course, if the length of time of run is changed, different amounts of ions are adsorbed,-but the mercury ion always to the greater extent. The curves of Fig. I and 2 are obtained from runs all extending over the same period of time-approximately eight minutes. In a later paper more complete results will be given, including the effect of acids and other electrolytes on the adsorption, the approximate thickness of the adsorbed layer of ions, and the corresponding effects attending the use of an adsorbent other t>hanmercury. Furthermore an attempt is being made to correlate the experiments with absolute electrode potentials and the modern ideas concerning solutions of strone; electro1,ytes.
Summary It has been shown that when mercury droplets are allowed t o pass through dilute aqueous solutions of mercurous sulfate or mercurous acetate, the mercurous ions are adsorbed to a definitely greater extent than the sulfate or acetate ions.
