KOTEB
May, 1962 ing the orifice plate, either by making a per‘foration at a suitable height or by using a short tube with its upper end below the upper meniscus, attached to a rod for support. The iaterface energy is then (PZ
-
P1)
(2)
where X is r multiplied by the value of X / r , obtained by successive approximations from the table of Sugderi,5 given also by Adam,6 and Harkins.7 D is the inside diameter of the crucible containing the liquids and d is the outside diameter of the orifice tube. It also is satisfactory to allow a layer of the upper liquid to be entrapped in the tube, for its volume remains unchanged from the moment that the bottom of the orifice plate touches the interface and cuts off connection with the upper layer. In this case, the density function in equation 1 becomes p2 alone, and a correction is applied to the pressure term to allow for the displacement of the liquid within the thickness of the plate, ie.
A s in the capillary-height and maximum-bubblepressure methods, it is necessary to use a sufficiently large vessel to ensure that the change in pressure due to the curvature of the nieniscus between the container wall and the tube will be insignificant: a clearance of 1 cm. or more usually is adequate. The densities of the liquids may be determined by measuring as a function of depth the change of pressure of a neutral gas bubbling through the orifice, using, of course, an external manometer. For visual observation the upper liquid must be reasonably transparent. The method could, however, be adapted to opaque liquids by the use of electrical probes, force-displacement measurements, 01’ X-ray fluoroscopy to observe the critical heights. I n high temperature studies it is often difficult to find a material for making the orifice and crucible that will be inert. In some cases a solid soluble in the liquid under study but in equilibrium with it may be used. For example, sintered sodium fluoride has been used in studies of the interface between fused alkali halides and tellurium. The method was proven by measuring the well known water-air and water-carbon tetrachloride interfaces at room temperature, and then employed for the metal-salt systems recently reported.* As an example we report here measurements of the surface tension of tellurium. Tellurium of moderately high purity was used (less than 0.001% each of Si, Mg, Cu, Al. Cr, and Ni; 0.002% Ag and Fe; and 0.005% Pb) in an atmosphere of purified ( 5 ) S.Sugden, J . Chem. Soc., 121, 858 (1922). (6) N. K. Adam, “The Physics and Chemistry of Surfaces,” London, 1941, p. 372. (7) yi’. D. Harkins, “Determination of Surface and Interfacial Tensions.” in “Physical Methods of Organic Chemistry,” edlted by A. Weissberger, 3rd Ed., Interscience Publishers, New York, N. Y., 1959, Vol I part 1,pp. 757-814. ( 8 ) D. P. Spitzer, J Fhus. Chem., 66, 31 (1962).
947
nitrogen. The orifice plate, tube, and crucible were made of Pyrex glass. The density at 460” was found to be 5.58 g./cc, Six different experimeiits a t 460° gave the results shown in Table I, the average being 178.4 f 1.5ergs/cm2. Measurements on fresh interfaces only are reported: the surface tension decreased with time, eventually by as much as lo%, probably as a result of the pick-up of impurities. TABLEI THESURFACE TENSION OF TELLURIUM AT 460’ r,
--(N-Ho),
cm.cor.a
0 0853 .0853 .0853 .0853 ,0855 ,0855
0 860 ,870 877 872 ,846 ,848
0 812 ,824 ,832 ,826 ,822 ,824
cm.
obsd.
a2
0 06426 ,06528 06597 06525 ,06528 06545
Surface tension, ergs./cm.’
175.7 178.5 180 3 178 4 178 5 178 9 ~
a
178 4 f 1 5 Corrected for liquid displacement as in eq. 2.
The interface energy of the Te-CsC1 interface, measured in a Pyrex apparatus a t 640” was found to be 133.5 f 1.2. The interface energy between these same liquids saturated with KaF, (measured using an orifice and crucible made of sintered NaF powder) was 97.1 f 0.5 ergs/cm.2 a t 600”.
A TECHNIQUE FOR THE RAPID DETERMINATION OF IOYIZATION AND APPEARANCE POTENTIALS1 B Y ROBERT MT. K I S ~ AND R ~ EMILIO J. GhLLEGOS Department of Chemzstry, Kansas State Unzverszty, Manhattan, Kansas Recezved November SO, 1961
A number of methods have been reported3 and used for obtaining ionization and appearance potentials from ionization efficiency curves. The ionization efficiency curves (a plot of ion intensity us. electron energy) are obtained from electron impact investigations using a mass spectrometer. A method of obtaining approximate ionization and appearance potentials has been developed and employed in our Laboratory, using a Bendix timeof-flight mass spectrometer. The general features of our mass spectrometric system have been described.* Using this new method, which we term the “energy compensation technique,” ionization and appearance potentials may be obtained usually in less than one minute. The energy compensation (e.c.) technique follows the concept of the method introduced by Lossing, et aL6 The e.c. method, (1) This work was supported in part by the U. S. Atomic Energy Conimission under contract No. -4T(11-1)-751 with Kansas State University. (2) Address reprint requests to this author. (33 See, for example, F. H. Field and J. L. Franklin, ”Electron Impact Phenomenon and the Properties of Gaseous Ions,” Academic Press, New York, N. Y., 1957, pp. 24-37. (4) E. J. Gallegos and R. W. Kiser, J . Am. Chem. SOC.,83, 773 (1961). (5) F. P. Lossing. A. W. Tiokner, and W. A. Bryce, J . Chern. Phys., 19, 1254 (1951).
948
Vol. 66
NOTES
being iiistrumental in character, eliminates the necessity of obtaining the usual ionization efficiency curve in the determination of ionization and appearance potentials. A similar method, termed “simplified procedure,” has been employed5 to determine ionization potentials. Using the e.c. method, the ion currents of the calibrating gas and the gas under investigation are measured a t 50 e.v. and recorded on separate channels of a dual channel recorder. The sensitivity of the tmo amplifiers (one for each ion out-put) is increased 100-fold (or, if desired, 1000-fold) and the electron energy decreased until the ion current intensity reads the same for each ion as previously a t 50 e.v. The difference in the voltages is taken as the difference in the appearance potentials of the calibrating gas and the gas under study. Although this method has been used only with a time-of-flight instrument for appearance potential determinations, it also should prove suitable for use with other types of mass spectrometers. The nearly identical “simplified procedure” of Lossing, et CJZ.,~ has been used previously for ionization potential determinations. Table I summarizes some results of ionization potentials determined for various compounds using the linear extrapolation method, the logarithmic
the calibrating gas for the determinations shown in Table I. An ionization potential of 12.13 e.v. was taken for xenon.’ Most of the values shown as having been determined by extrapolated voltage differences already have been reported.8-11 From this table it is seen that the e.c. method gives results for ionization potentials which may be taken as acceptable to within about 4 0 . 2 e.v. A similar study was made of the determination of appearance potentials of fragment ions. Our studies have shown that appearance potentials of fragment ions determined by the linear extrapolation method and the logarithmic plot method for interpretation of the ionization efficiency curves are not always reliable. The method due to Warred has given results which we generally find satisfactory for the determination of appearance potentials. The results we have obtained using the e.c. method indicate that appearance potentials so obtained are generally low by about 0.1-0.2 e.v. (even though the determinations were reproducible) for fragment ions whose appearance potentials are less than the ionization potential of the xenon calibrating gas. Using the e.c. method, values of appearance potentials greater than the ionization potential of the xenon calibrating gas were observed to be high by 0.2 e.v. or more, and the results became considerably less reliable with an TABLE I IONIZATION POTENTIALS OBTAINED USINGVARIOUSMETH- increase of the appearance potential. KevertheODS OF INTERPRETING IONIZATION EFFICIENCY CURVES less, fairly accurate (*0.2 e.v.) appearance potenCOMPARED TO THOSEOBTAINEDUSING THE ENERGY tials may be obtained rapidly with the e.c. method if their values lie near to or lower than the ionizaCOMPENSATION TECHNIQUE tion potential of the calibrating gas. -Ionization potential (e.v.)a-Molecule
Nitrogen dioxide Ethylenimine Ethylene sulfide Azetidine Trimethylene oxide Trimethylene sulfide Pyrrolidine Tetrahydrofuran Tetrahydrothiophene Piperidine Tetrahydropyran Tetrahydro thiapyran Thiadioxane Dioxane (1,4-) Hexamethylenimine Tetramethylsilicon Tetramethyltin Krypton(11) Benzene Nitrogen Oxygen Ammonia
L.E.
L.P.
E.D.
E.C.
Lit.b
11.1 11.3 11.39 11.3 10.2 9 . 8 9.94 9 . 8 9 . 1 8 . 7 8.87 8 . 9 8.9 9.1 9.2 9 . 1 9.9 9.9 9.85 9 . 7 8.9 9.2 9.1 8 . 9 8.9 9 . 2 9 . 1 9.0 9.5 9 . 2 9.45 9.3 8 . 7 8 . 5 8.57 8 . 4 8.7 8.8 9.0 8.9 9.6 9.6 9.53 9.7 8.5 9 . 0 8.6 8 . 5 8 . 6 8 . 3 8.50 8 . 5 9.7 9.2 9.56 9 . 8 8 . 9 8 . 6 8.76 8 . 5 10.0 10.1 9.80 9.8 8.9 8 . 0 8.25 8 . 4 24.2 9.7 15.7 12.5 10.3
24.56 9.25 15.6 12.2 10.1510.50 Phosphine 10.3 10.1 a L.E. = linear extrapolation; L.P. = logarithmic plot; E.D. = extrapolated voltage difference; E.C. = energy compensation. b A comparison to literature values is made only for those molecules where comparisons to L.E., L.P., and E.D. were not made. For a summary of literature values, see R. W . Kiser, “Table of Ionization potentials,” TID-6142, U.S. Atomic Energy Commission, June 20,1960.
plot r n e t h ~ d the , ~ extrapolated voltages difference methodlaand the e x , method. Xenon was used as
(6) J. W. Warren, Nature, 166, 811 (1950). (7) C. E. Moore, Natl. Bur. Standards Ciro. 467, Vol. 3, 1958. (8) E. J. Gallegos and R. 17. Kiser, J . Phys. Chem., 65, 1177 (1961). (9) E. J . Gallegos and R. W. Kiser, zbzd., 66, 136 (1962). (10) R. W. Kiser and I. C. Hisatsune, ibid.. 66, 1444 (1961). (11) B. G. Hobrook and R. W. Kiser, ibzd., 66, 2186 (1961).
THE THERMAL EXPANSION OF POTASSIUM CHLORIDE1 BY THOR RUB[N,H. L. JOHNSTON, AND HOWARD w.ALTMAN Cryogenic Laboratory of the Department of Chemistry, The Ohio State University, Columbus 10, Ohio Received OCtObET 31, 1061
The apparatus and the experimental techniques used for the determination of the thermal expansion of potassium chloride were the same as those described for the determination of the expansion coefficient of copper.2 Large pieces of potassium chloride were obtained from the Harshaw Chemical Company. They were cut into three pillars, then filed to approximately the same length, These pillars separated the plates of the interferometer. By carefully filing one pillar or another, circular fringes finally were obtained with the interferometer which did not expand or contract to the eye moving transversely (1) This work was supported in part by the Air Material Command, Wright Field. (2) T. Rubin, H. W. hltman, and Ii. L. Johnston, J . Am,Chsna. Soe., 76, 52 (1956).
