VAPOR PRESSURES OF CZRTAM AMALGAMS.
545
[CONTRIBUTIONFROM THE CHEMICAL LABORATORY OF THE UNIVERSITY OF CALIFORNIA.1
THE VAPOR PRESSURES OF CADMIUM, LEAD AND TIPS AMALGAMS. BY JOELH. HILDEBRAND, A. H. POSTER
AND
G . W. BEEBE.
Received Jamary 15, 1920.
The work here presented is part of a series of measurements which has been carried our during recent years upon the vapor pressures of amalgams. The previous papers give vapor-pressure measurements upon the following amalgams: zinc,’ silver,2 gold,2bismuth,2 thallium,S and supplement the important investigations of T. W. Richards* and 6.A. Hulett6 and their eo-workers upon the electromotive forces of amalgam-concentration cells and other properties of amalgams a t ordinary temperatures. The experimental procedure was essentially the same as that used in the earlier investigations and need not be again described. The accuracy is somewhat inferior to that of earlier mewu-ements, although the “probable error” of the average value a t each concentration is less than *O.OOI in all cases except with the concentrated lead amalgams, where, for some iinknown reason, it increased. The results are given in Tables I, I1 and 111, where 12 represents the number of rnols. of mercury per mol. of the other constituents, N repreI ) ; p the vapor pressure sents the mol-fraction of mercury (equal to w/(n of mercury over the amalgam of composition N , and pa that of pure merckvy a t thie same temperature. The calculated values were obtained by the aid of the equation: log PlPo = log c a/(n cnI2 (1) i ~ s i t l gthe following values of a and c:
+
+
Pb-amalgams
Sn-amalgams
a .....................
-1.40
$0.252
$0 . 2 2 0
c......
$1.90
$0.31
$0.26
Cd-amalgams.
................
This equation is to be regarded simply as an empirical expression for smoothing vapor-pressure data, as was done in the earlier papers of this series. The results are also expressed graphically by the curves in the figure. I t will be noted that the vapor pressures of cadmium amalgams are less than are demanded by Raoult’s law, p / p o = N , and that the deviation becomes much greater at high concentrations of cadmium. Tin and lead 1 J. R.Hildebrand, Orig. Comm. 8thInter. Cong. Appl. Chem., 2a, 139, 147; Trans. Am. Electrochem. soc., l a , 319,335 (1912);THISJOURNAL, 35, 501 (1913). * Ermon D. Eastman and J. H. Hildebrand, THISJOURNAL, 36, 2020 (1914). a Ibid., 37, 2452 (1915). 4 Carlzegis Inst. Pub., 56,118; Z.physik. Chem., 58,683 (1907);72, 129, 165 (1909); f i 1 S JOURNAL, 41, 1332 (1919). 8 Tars JOURNAL, 30, 1812(1908); J . Phys. Chem., 14, 158 (T~IO).
JOnL €1. HILD&BIUND, A. €I. POSTER AND C. W. BEEBE.
546
amalgams a t 324' show almost identical deviations from Raoult's law, just as they do at ordinary temperatures, as seen from the e. m. f . measurements of Richards and Garrod-Thomas. N 1.0
0.9 0.8
0.7
0.6
0.5
0.4 0.3 0.2
0.1
o I .o
0.8 0.7
0.6 0.5
-P
0.I 0.0 1.0
0.9
0.8 0.7
0.6
0.5
c.4
0.3
0.2
0.1 0.0
N
The values for lead amalgams of high lead content are very unsatisFactory, so far as consistence is concerned, and, from theoretical considerations, are doubtless too low. It is extremely improbable that thc curve contains any inflection a t the lower end, as the measurements would seem to demand. There is no other case known to us in all the literature oil vapor pressure where such behavior is indicated. More careful investigation of this region was prevented by the entrance of all of us into war service, and it has not since seemed worth while to hold up the publication of these results for the experimental work it would Iequire. TABLEL-CADMIUM AMALGAMS AT 322'. Wt. Cd.
Wt. Hg.
1.046
G. 25.23
2.050
22.61
4.752
23.90 20.67
G.
7.034 8.874 8.879 xo.08
n.
N.
Nu rnb er of obs.
---P/Bo.
Obs.
Caic.(l).
Calc.(Z).
13.51 6.19 2.815
0.931 0.861
6
0.920
0.927
5
0.845
0.738
1.650
0.623 0.488 0.418 0.331
6 6 5 6 6
0.850 0.688
0.525 0.322 0.232
0.522
0.323 0.235
0.928 0.847 0.682 0.513 0.317 0.235
0.148
0.148
0.154
15.10
0,953
11.36 8.90
0.720 0.495
0.680
TABLG II.---LEAD Wt. Pb.
c.
.I55 x .240 f .734 3.005 3.026 2.590 4.449 5.603 6.880 8 a059 8.037
W t . Eg. G.
.67 .74 9.358
II
I1 . I I
9.990 6.440 6.432 5.350 4 .558 3.426
19,
10.43 g .80 5.56 3.4.8 3.41 2.57 1.492 0.987 0 .830 0.440 0.412 0.251
AMALGAMS A T
N. 0.912 0.907 0.848 0.777 0.774
324'.
Nnmber of oba.
#/PO.
Obs.
CdC.
0.943
5
0.944 0.944 0.915
5
0.897
4 5
8
7 6 0 .599 0.497 9 0 .4.0: 4 6 0 "30.5 o $292 3.2IO 4 0.2OI 9 9.652 2.342 T .087 0.1513 0.125 9 7.846 ro.518 1 .I45 0.1122 0.101 4 a The values in parentheses are regarded as inaccurate. 0.720
0.938
0.918 0.887 0.886 0.861 0.784
0.887 0.855 0.782 o .7oa 0.597 (0.448jQ (0.452) (0.302)
o 698 0.590
0.478 0.461 0.331
(0.14.9)
0.212
(0.1371
0.174
TAELEIII.--TIN AMALGAMS, AT 324' wt. Sn. G,
Wt. Hg. G.
0.6166
15.33
s "224
18.59 18.46 19.T2 19.25 13 .oo
IL
"224
2.510 2 .jCI
3.322 4.739 5.234 5.235 5.742 6 .go4 8.851
12.03
8.930 5 4.138 2.915
.w
1.651
n.
w.
14.68 g .oo 8.93 4.51
0.936
Number of obs.
#/Po. c
'
-
Obs.
Calc.
0.958 0.944 0,943
0.959
900 0.899
5 7 5
0.818
6
0 .go8
0.912
4.300
0.81~
0.911
2.281
0.695
0.908 0.849
I .500
o .600
X .007
0.502
o .660
0.398
,428
0.299
0.250
0.200
5 5 5 6 6 8 7
0.1103
o ,099
4
0.159
Q
0
I
0.850 0.777 0.690 0.574 0 ,450 0~3?3
0.944 0~942
0.780 0.690
0.575 0.457. 0 ,312 0,160
The values for cadmium amalgams can be reproduced very closely by assuming partial solvation, according t o the equation : Cd 4-Hg = CdHg, 8s was done in a previous papcr,I for the sake of calcdsting the e, m. f, of cadmium amalgam concentration cells. The formula there given was
where B is a constant which is a function o€ the equilibrium constant for the above reaction. The values in the last cuBurnn of Table I, designated "talc (2):'' have been calculated using this formula, assigning to 23 the I
J. B. Nildebrand, "The Constitutiaa af Certain Liquid Amalgams," THISJOUR-
NAb, 353 501 (r913)-
548
NOTE.
valtie 0.75, which does not differ greatly from the value 0 . 6 6 7 , used to calculate the e. m. f. values of Richards and Forbes and of H d e t t and DeLuryl at 2.5’. The behavior of cadmium amalgams may, therefore, be explained on the basis of the formation of a new molecular species without assuming the failure of Raoult’s law. This cannot so easily be done, however, in the cases of lead and tin amalgams, for the deviations from Raoult’s law are here so great that they could be accounted for oaily by the assumption of niolecules of lead and tin more complex than Pbz and Sne, and even curves so calculated would not correspond a t all well to the actual curves.2 A theoretical discussion of all the data on amalgams obtained in this series of investigations will be the subject of a future communication.
summary. Vapor pressures of mercury over amalgams of cadmium, lead and tin at 324’ have been measured at intervals covering the entire range of concentrations. 2. The values of the constants in an empirical equation relating vapor pressure to composition are given for each amalagam. 3. cadmium amalgams gave vapor pressures less than Raoiilt’s law demands, and the deviations can be calculated on the assumption of partial solvation, varying with the concentration according to the mass law, to form moIecules of CdHg. 4. Lead and tin amalgams give vapor pressures which are nearly equal, and are niuch greater than Raoult’s law demands. The deviations cannot be accounted for by assumption of any simple molecular change. I.
BERKELBY, CAL.
NOTE. Correction.-In
the paper on “The Genesis of Petroleum as Revealed by its Nitrogen Constituents,” in the October, 1919,number of TIXIS JOURNAL, p. 1692, on line 32, the words “methyl chinolines” should read alkyl chinolines, and on p. 1694, on line 35, the words “12 kg.” should C. F. MABERY. read 3 kg. 1 2
LOG. G i t . See discussion of bismuth amalgams, JOG. cit.
