3904
YOTES
h
= ho -
SC'/'
+ ECIn c + J C
have been calculated based on the expression given for the tetra-n-butylanimonium ion6
has been used to establish A, values by extrapolating plots of A' (A Sc"' - Ec In e) us. c to c = 0. The viscosity of hydrogen cyanide at 18" is 1.955 X and at 25" it is 1.834 X 10-3.4 The dielectric constants at 18 and 25" were taken as 118.3 and 106.8, respecti~ely.~ The slopes of the A'-c plots vary between 150 and 600 but because of the low precision and since both slight association and as yet uninvestigated viscosity corrections are undoubtedly included in the J value (A' = A. J c ) it seemed pointless to calculate "a" values. It can however be stated that the slopes do correspond to center-to-center distances that are not totally unreasonable. The values of A, are given in Table VI and are esti-
+
+
R+D
=
21.484
+ 4.4610
and the Stokes relation Xo+ = 0 . 8 2 / R + ~giving , for the Bu4N+ ion at 18 and 25' values of 90 and 96, respect ively. ~
~~
(5) G. E. Coates and J. E. Coates, J . Chem. SOC.,77 (1944). (6) R. M.Fuoss, Proc. .Vatl. Acad. Sci. U . S., 45, 807 (1959).
Mutual Solubility of Perfluoroheptane with Carbon Tetrachloride and with Carbon Disulfide a t 25" by Kozo Shinoda and Joel H. Hildebrand Department of Chemistry, Cnirersity of California, Berkeley. California (Receiued J u l y 13, lQ6.4)
Table VI : Limiting Equivalent Conductances of Salts in HCN a t 18 and 25" 9alt
ho
EtdNI
358 282 290 291 293 281 283 206 197
Et4NPi OTMCl OTMBr OTMI DDMCl DDMI DDMPi ODDPi
8(382) 9(301 1) 6 (309 4) 4(310) O(311 6) O(299) O(302) 7 (222) O(210 5 )
Salt
An
Bu4NI Bu,NPi Bu4NXOa OTECl OTEBr OTEI OTENOa OTEPi
307.5 (325) 231.6 (246) 297,9 (317) 285.2 (302) 286.5 (303) 287.1(303) 276.8 (295) 210.9
mated to be good to within h0.3. The values a t 23" are given in parentheses and where only three figure numbers appear, these are to be regarded as good to about =tl.5 since they have been obtained by crude free-hand extrapolation from as few as two points on a *l-c'/z plot. Limiting equivalent ion conductances (Table VII)
Table VII: Limiting Equivalent Ion Conductances in Hydrogen Cyanide a t 18 and 25" /Values at, 25" in Parentheses) Ion
Et4N Bu~K O~tdMe~N OctdEtaN DodzMezN (Octd)(Dod)MezN+ +
+
+
+
+
hn
+
141 (151) 90 (96) 75 (81) 69 (73) 65 (72) 55 (61)
The Journal of Phyeical Chemistry
Ion
C1Br-
INO$Pi-
ho -
216(229) 216 (229) 218 (231) 208 (221) 142 (150)
Fujishiro and Hildebrand,l in 1962, reported on the liquid-liquid solubility of cyclohexane and perfluorotributylamine at 25'. They pointed out the advantage of such measurements for systematic studies of solubility over the usual method of observing the temperature at which separation into two liquid phases occurs, saying : "This can be done accurately only in the region around the critical point, and most composition-temperature curves have not been carried very far down the descending branches. The reliable portions of available curves fo'r different liquid pairs extend over different rangcs of hmperature, and it is difficult to make a systematic comparison of such systems at a conunon temperature. Parameters calculated from critical temperatures are unsatisfactory also because the structure of mixtures near the critical point is extremely complex, and not amenable to model treatments that are reasonably applicable outside this region. It is very desirable to have figures for liquid-liquid solubilities a t a standard temperature, preferably at 2 5 O , by determining the composition of both phases by analysis." Such data offer the further advantages for systematic tests of theory that they are free, on the one hand, from the uncertainties of gas law deviations that are involved in studies by measurement of vapor pressures, and free, on the other hand, from the uncertainties involved in extrapolating liquid properties far below melting points when dealing with the solubility of solids. (1) R. Fujishiro and J. H. Hildebrand, J . Phys. Chem.. 6 6 , 573 (1962).
NOTES
3!305
Table I : Liqutd-Liquid Solubilities,
2, and
Mole Fractions in Phases A and B a t 25’
7
1.
cc14
2.
GFie
1. csz 2. GFie
~
F _ -
ZA
QA
ZA
0 ,3026’0 0.698
0.157 0.843
0.140 Q ,860
0.042 0.958
-
0.970 0,0299 -1 .ID0 5 . 4 x 10-4
-
Experimental n-Perfluoroheptane was purified by the method described by (>lewand Reeves. Carbon tetrachloride and carbon disulfide were Spectro-quality reagents. They were distilled shortly before the experiments. The solubility of CiF16 in CS2 and in CCl, is very small, so we applied the method devised by Reeves and Hildebrand3 that measures the diminution in volume of the fluorocarbon after equilibrating with the other liquid, taking advantage of the fact that the latter wets glass preferentially. Calibrated tubes were sealed to bulbs of about 130cc. capacity. The volumes of these tubes, chosen after preliminary experiments, were 0.45 cc. for the CElz system and 2 cc. for the CC1, system. Measured volumes of the components were introduced into their respective vest,els, which were then sealed and rocked in a thermostat. After saturation was reached, thle remaining ciF16 was collected in the calibrated side tube and its volume read. Corrections were made for the CC14and CS2dissolved in the C7Fl6. Concordant figures for the solubility of CC14 in CiF16 were obtained by Hildebrand, Fisher, and Benesi4 and by Kyle and Reed.5
Results and Discussion Our results, together with those on CCl, in CiFltr from ref. 5 arid 6, are given in Table I, together with values of the difference between the solubility parameters that are calculated from the measurements by the equation used by Fujirihiro and Hildebrand
RT(LlnZ’Ii”++In2
v1
x1A
VZ
=
62)’
(1)
The molal volumes of the components a t 25’ are: 225.6 cc. Equation CC14,97.1 CC.;(282,60.7 cc.; C~FIB, 1 is obtained by combining the standard equation
RT In (azlxz)
=
v2(p12(61 - 6z)2
(PA
0,067 O.
0’gg8] 0.002
61
-
8a
61
6n
3.08
8.6
5.5
4.48
10.0
5.5
-
The concordant values for 62 = 5.5 for CiF16 agree well within the usual limit of accuracy with the value 5.6 obtained for the system Brz CiF16 by Reeves and Hildebrand,3 calculated from the solubility of 13r2 in C7F16. These values of the solubility parameter of C7F16 are distinctly less than the value, 5.85, derivled from its energy of vaporization, a difference not unusual among systems departing appreciably from the simple model used in deriving eq. 2. However, the value here calculated agrees well with that found from the solubility of iodine, where & - 61 = 8.6, which with the standard value for I,, 14.1, gives 61 = 5.5. In this case, as in many others, a solubility parameter determined directly from solubility data is to be preferred, for practical purposes, over one based upon the heat of vaporization.6
+
Acknowledgment. This work has been supported by the Atomic Energy Commission. ~
~~
-
(2) D. N. Glew and L. W . Reeves, J . P h y s . Chem., 6 0 , 615 (1956). (3) L. W. Reeves and J. H. Hildebrand, ibid., 60, 949 (1956). (4) J. H. Hildebrand, B. B. Fisher, and H. A. Benesi, J . Am. Chem: Soc., 72, 4348 (1950). (5) B. B. Kyle and T. M. Reed, 111, ibid., 80, 6170 (1958). (6) For other examples, see R. L. Scott and J. H. Hildebrand, “Regular Solutions,” Prentice-Hall, Englewood Cliffs, N. J., 1962, pp. 145-147.
The Production of Molecular Beams in the Mass Spectrometer1
by Benjamin P. Burtt and Jay n!L Henis
xx2A) 2B ((OlB - (plA)(81-
B-
(2) with the corresponding equation for the other component.
Department of Chemistry, Syracuse University, Syracuse, >Vew York 18310 (Received J u l y 17, 1964)
In the course of studies of negative ion-molecule reactions in N20 and CClBF a t relatively high pressure in the mass spectrometer, evidence has been obtained to indicate that many of the accelerated negative ions lose their charge by collision in the analyzer tube. Volume 68, Number 19 December, 1964
