T H E SOLUBILITY OF SILVER I N MERCURY. I11 ROBERT J. MAURER Department of Chemistry, The University o j Rochester, Rochester, New YorL Received January 8, 1058
Systematic investigations of the solubility of silver in mercury have been reported by Joyner (3), Sunier and Hess ( 5 ) , and DeRight (1). Since below 3OoC. the results of DeRight were not in agreement with those of Joyner, and since DeRight encountered serious experimental difficulties in this region, the present work was undertaken in an attempt to extend below room temperature] by the use of a technique different from that of DeRight, the precise knowledge of the solubility of silver in mercury. The work has been interrupted and there is little possibility that it will be continued, but the data which have been collected are considered of sufficient value to warrant publication. MATERIALS
The silver used was in the form of 1000 fine foil obtained from the U. S. Mint in Philadelphia. One portion of the mercury used was purified by dropping it five times through a five-foot Meyer tube containing 6 N nitric acid, washing three times with distilled water in the same fashion, and triple distilling under reduced pressure according to the method of Hulctt and Minchin (2). The other portion of mercury used was obtained from the Taylor Instrument Company and was stated to have been triple distilled. The conditions of distillation were not specified. When evaporated according to the method of analysis the mercury left no weighable residue. Under the same conditions there was no detectable loss in weight of the silver. In some cases a mixture of silver foil and solid phase from previous runs was used in preparing the amalgam. APPARATUS
Except in runs F and G , where a smaller thermostat was used, the thermostat was that used by DeRight (1). The temperature was automatically controlled by a mercury thermoregulator and electrical heating units. As read on a Beckmann thermometer, the thermostat temperature was constant to better than f 0.02'C. Temperatures were read from a Hiergesell Bros. thermometer of the double diamond grade 515
516
ROBERT J. MAURER
to 0.02"C. This thermometer was calibrated against a thermometer certified by the Bureau of Standards. EXPERIMENTAL
The apparatus for preparing the amalgams is shown in figure 1. The amalgams were prepared by placing an excess of silver in contact with mercury in flask A suspended in the thermostat. The mixture was agitated by a stirrer, and after a given length of time the liquid phase was drawn off by lowering the sintered glass filter C, making connection, by means of the rubber stopper D, to a flask which could be evacuated. The thermostat temperature was always below room temperature. The filter was model 154 G-1, made by Schott and Jena, with a pore size of from 100 to 120 microns, according to the makers. With such a filter, 200 cc. of
FIG.1. The apparatus for preparing the amalgams
amalgam could be drawn off in a fev,- minutes. The liquid phase was separated into samples which were analyzed according t o the method described by DeRight (1). It should be noted that the procedure hereused differed from that of DeRight ( 1 ) and Sunier and Iless ( 5 ) in that each sample which they analyzed represented a separate solubility determination. The weights used were calibrated and compared with a weight certified by the Bureau of Standards. Table 1 shows the results of a check run upon an unsaturated amalgam. Some difficulty was experienced in run A in bringing the silver residues to constant weight, using several short periods of heating ( 5 hours) at 500°C. in a stream of hydrogen. In all succeeding runs, after evaporation of the mercury the residues were heated continuously for 50 hours or more at 500°C. in a stream of hydrogen. The r e d u e s thrn showed no change in
517
SOLUBILITY OF SILVER I N MERCURY
weight on further heating. The rather large deviation (5.8 parts per thousand) between the known and measured atomic per cent of silver in run A may be due to the above-mentioned difficulty in obtaining constant TABLE 1 Results of a run upon an unsaturated amalgam R u n A (test run): temperature, 28 ~fr2°C.; length of run, 3 hours: weight of silver taken, 0.9894 g.; weight of mercury taken, 2700 g.; atomic per cent of silver taken, 6.81 X 10-2 SAMPLE N U M B E R
OF 'ILVER
1
pams
A-1 A-2 A-3 A-4 A-5 A -6 A-7
0 0 0 0 0 0 0
0838 0725 0750 0703 0611 0627 0672
I
WEIOHT OF AMALGAM
ATOMIC PER CENT OF SILVER 1M)
x
yrams
DEVIATION FROM MEAX
P P t
226 9 195 5 203 1 191 3 167 5 170 4 182 5
!
!
I
6 6 6 6 6 6 6
87 90 87 83 82 81 85
2 7 2 2 4 1 0
9 3 9 9 4 5 0
Average atomic per cent of silver. . , . . . . . 6.85 X 10-2 Average deviation from mean , . . . . , . . . . . 3 . 1 p a r t s per thousand Deviation from atomic per cent t a k e n . . . . . . . . . . , . . . . . 5 . 8 parts per thousand ,
o
F
~
~
SAMPLE N U X B E R
WEIQHT O F SILVER
grams
grams
G-1 G-2 G-3 G-4 G-5 G-6 G-7
0,0620 0.0611 0.0613 0,0652 0,0652 0.0658 0,0644
274.4 270.6 271.2 289.0 288.2 290.1 285.8
~~
~
______
~
PER CENT & ATOMIC y OF SILVER
x
100
DEVIATION FROM MElN
p.p.t.
4.03 4.03 4.03 4.03 4.04 4.21 4.01
0.0 0.0 0.0 0.0 2.5 45.0 Exclude 5 .O
weights of the residues. I t is not believed that a constant error of this magnitude was present in the other runs. Table 2 gives the results of a typical experiment. Table 3 summarizes the data. In it are presented the temperatures at which the solubility
518
ROBERT J. YAURER
determinations were made, the solubility in atomic per cent as measured and as calculated from DeRight's equation, the number of samples taken for analysis, the average deviation from the mean of the samples, and the TABLE 3 Summary of the data 4UN
TEMPERATURE
ATOMIC PER CENT
Measured
x 1w
From
equation
_ I _ -
"C.
B
c
D E 1." G
19.24 16.12 18.98 12.39 9.71 5.72
-_ P.P.l.
6.52 5.86 6.25 5.19 4.74 4.03
65.85 .42 6.37 5.21 4.79 4.21
74 . 17 1.4
1.5 1.3 1.3
-__
" :
9 8 8 7 6
houre
8 11 20 30
FIG.2. Plot,of the data obtained and also of the data of DeRight and Joyner
time allowed for equilibrium to be reached. I n runs D and E equilibrium was approached from the unsaturated side; in all other runs equilibrium was approached from the supersaturated side. One sample in run D and
SOLUBILITY O F SILVER I N MERCURY
519
one sample in run G were excluded because they deviated from the mean by more than four times the average deviation. DISCUSSION
The results of the present investigation are shown in figure 2 for comparison with the data of DeRight and of Joyner below 30°C. The straight line given by the equation log N = - ''05'*
T
+ 0.5894
is that proposed by 1IeRight as the best fit for his data from 80" to 10°C. If a large-scale plot of the data of Sunier and Hess, DeRight, and the present data, covering the range 5" to 20boC., is made, a slight deviation from a straight line, as suggested by the present data, is definitely noticeable. I t is felt that the use of a sintered glass filter is an improvement over the use of glass wool and a capillary for filtration as used by DeRight and by Parks and Campanella (working with lanthanum amalgams) (4),in that the conditions of filtration are more reproducible. The use of sintered filters of various pore sizes might shed light upon the question of the influence of the conditions of filtration upon apparent solubility. No support can be found in the present work for the hypothesis of DeRight that below 40°C. silver aggregates of various sizes are present. A t least the use of a sintered filter gives sufficiently reproducible conditions to eliminate erratic results. SVMMArlY
1. The solubility of silver in mercury has been determined at six temperatures between 5" and 20"C., confirming the extension of DeRight's equation into this region. 2. A sintered glass filter proved highly satisfactory as a means of separating solid and liquid phases.
The writer wishes to thank Doctor Arthur A. Sunier, who suggested this work and maintained a constant interest in it. REFERENCES (1) DERIGHT: J. Phys. Chem. 37, 405 (1933). (2) HULETTAND MINCHIN:Phys. Rev. 21, 388 (1905). (3) JOYNER:J. Chem. SOC.99,195 (1911). (4) P A R K SA N D CAYPANELLA: J. Phys. Chem. 40, 333 (1936). (5) SUNIERAND HESS: J. Am. Chem. Soe. 60, 662 (1928)
TEE JOCRNAL OF PHYSICAL CBEMISTRY, VOL, 42, NO. 4
