NOTES
1464
THE CONCENTRATION DEPENDENCE O F THE DIFFUSION COEFFICIENT OF RAFFINOSE I N DILUTE AQUEOUS SOLUTION AT 85' BY PETER J. DUNLOP Contribution from the Department of Chemistry, University of Wisconsin. Madison, Wwconsin Received May 10, 1866
Since the introduction of certain interferometric techniques for studying the diffusion process in liquid accurate diffusion data have been reported for both two and three-component systems. This note presents data, obtained by means of the Gouy Diffusiometer, for the trisaccharide raffinose in dilute aqueous solution. The concentration dependence of the density, specific refractive increment and the relative viscosity of this system were also measured over the same concentration range a t 25" and are included. Materials, Solutions and Experimental Procedure Hydrated ralffinose' was heated in vacuo at 80" to remove the water of crystallization. This was necessary since, in agreement with the observations of previous workers,s it was found that the hydrated sample did not contain exactly five water molecules of hydration. Solutions of raffinose were prepared by weight, using as solvent doubly-distilled water which had been saturated with av. Concentrations, c, in g./100 ml. of solution were calculated from the weight percentages in uucuo and the measured density data. Pyrex pycnometers of 30-ml. capacity were used to measure the densities, d; the data are reproduced by the equation
Vol. 60
represent the experimental diffusion coefficients the method of least squares was used to obtain the expression D X lo6 = 0.43592 - 0.00677~ c G 5.0 (3) with an average deviation of =k0.05%. TABLE I DIFFUSION COEFFICIENTS OF RAFFINOSB IN WATERAT 25' 1 5, g./ 100 ml.
2 Ac," e./ 100 ml.
3
4 (Anlac) X 106
jm
5 D X lo6, cin.1 set.-'
0.3795s 0.7591s 51.16' 1466.0b 0.4329: 0.62480' 1.24960 84.27 1467.0 .43201 0.75004 1 . 5 0 0 0 ~ 101.19 1467.4 .43080 1,50028 1.99974 101.14 1466.4 .42261 3.50031 1.50086 101.18 1466.5 .4123( 5.00608 1.49867 100.87 1464.1 .40196 a Ac is the difference in concentration between the bottom solution, CZ,and the upper solution, c1. b These values may be compared with those of Longsworth who, a t this same concentration, obtained 1467.1 X for An/Ac and 0.4339 X lo-' for D. The Rayleigh Integral Fringe method was used in his experiment. c T h e author is indebted to Mr. I. J. O'Donnell of this Laboratory for the results of this experiment.
Specific refractive increments were calculated from the relationship A n / A c = (Aj,/aAc), where j , is the total number of fringes in a Gouy experiof the ment and X is the wave length, 5460.7 8., green mercury line in air. These values are listed in column 4 of Table I. It should be noted that the values of A n / A c are almost constant, thus indicat-
+
d = 0.997075 0.003927~ c < 5.75 (1) with an average deviation of &0.0006~0. Using a Ubbelohde type viscometer with a water flow time of 265.8 sec., relative viscosities were determined on portions of the solutions prepared for diffusion. The kinetic energy correction applied in each case was never greater than 0.15%. The data are best represented by the quadratic equation qrsl
=1
+ 0.02742~+ O.O007e~*
c Q 5.75 (2)
with an average deviation of &0.04%. The Gouy diffusiometer used to measure the diffusion coefficients, D, and the specific refractive increments, An/Ac, has been previously described,gJo a8 have the methods employed to obtain D, An/Ac and the graph of the relative fringe deviations, Q j , versus the reduced fringe numberf(S.j).ll An average 6 correction of +6 p was applied in all experiments and in all cases the same Tiselius cell, with a 2.5103 cm. "a" dimension, was used. All experiments were performed within 0.004' of 25' and the diffusiopcoefficients corrected to 25.000' by means of the Stokes-Einstein relation.
Raffinose b .
'O1
,.
c I" 0
I
8
0.5
I I
f (5) Fig. 1.-Relative fringe deviation graph for the experiment in which c = 5.00008. At a given value of f ( f ) crosses indicate the average of the experimental points obtained from ten different Gouy photographs of the same boundary. Individual points are represented with dots. a
ing that the refractive index of raffinose solutions is nearly a linear function of solute concentration when the latter is expressed as weight per unit volume of solution. A similar dependence of n on c Results has been found for sucrose.12 The density measurements provide a value of - Values of D obtained at the mean concentrations c = (cl c2)/2 and concentration increments Ac = 0.60g1ml./g. for the partial specific volume of raf(c2 - C I ) are tabulated in column 5 of Table I. To finose in the concentration range studied; this may be compared with the value of 0.6078 ml./g. previ(1) L. 0. Longsworth. J . A m . Chsm. SOC.,69,2510 (1947). ously determined by Longsworth.18 A fringe devi(2) G. Kegeles and L. J. Gosting, ibid., 69, 2516 (1947). ation graph for raffinose is shown in Fig. l. That (3) C. A. Coulson, J. T. Cox, A. G. Ogston and J. St. L. Philpot, Proc. Roy. SOC.(London), A192, 382 (1948). the values of Qj are virtually zero at all values of (4) J. St. L. Philpot and G. H. Cook, Research, 1, 234 (1948). f ( l j ) indicates that the boundary was of Gaussian Svensson, I. Acta Chem. Scand., 3, 1170 (1949). (51 € form within the error of measurement. (6) L. G. Longsworth, J . A m . Chem. floc., 7 4 , 4155 (l952). It is hoped that some of the data presented above (7) Obtained from Pfanstiehl Chemical Co., Waukegan, Illinois. (8) E. J. MaDonald and B. G. Goss, Report E, 11th Session, Int. will be of use in testing the experimental accuracy of Comm. Uniform Method Sugar Analysis, Paris, 1954. a new Beams type equilibrium ultracentrifuge (9) L. J. Gosting. E. M. Ranson, G. Kepeles and M. S. Morris. which is being installed in this Laboratory. From Rev. Sci. Instruments, 20, 209 (1949).
+
(10) P. J. Dunlop and L. J. Gosting, J . A m . Chem. SOC.,7 5 , 6073 (1953). (11) D.F. Akeley and L. J. Gosting, ibid.. 75, 5685 (1953).
(12) L. J. Gosting and M. 1. Morris, J . A m . Chem. SOC.,71, 1998 (1949). (13) L. G. Longsworth, ibid., 76, 5705 (1953).
Oct., 1956
1465
NOTES
experiments with such a centrifuge it should be possible to measure molecular weights14if the necessary activity data are available, or, for substances of known molecular weight, one may obtain ratios of activity coefficients16 at two different concentrations. Acknowledgments.-It is a pleasure to thank Professors J. W. Williams and L. J. Gosting for their criticism of this manuscript. Financial support to make this investigation possible was supplied by the U. s. Public Health Service (G4196-C). Grateful acknowledgment is hereby recorded. (14) J. W. Beams. H. M. Dixon, 111, A. Robeson and N. Snidow, THIEJOURNAL, 69, 915 (1955). (15) J. S. Johnson, K. T. Kraus and T. F. Young, J . Am. Chsm. Soc., 1 6 , 0 (1954).
THE PHOTOSENSITIZED OXIDATION OF CARBON MONOXIDE ON CUPROUS OXIDE’ BY WILLIAMM. RITCHEY AND JACIC G. CALVERT~ The Mcpherson Chemical Laboratory, The Ohio State Ulziuersity. Columbus, Ohio Received M a y 17, 1066
Photosensitization of the oxidation of CO on Cu20 has been observed in this work. Significant evidence has been obtained for the importance of electron-reactant interaction at the Cu20surface in a rate-determining step of the reaction. The composition, surface area and electrical properties of the catalyst samples used in the study are summarized in Table I. The photochemical rate data for varied reactant pressures and the different catalyst samples are shown in Table 11. Comparison of reaction rates in consecutive runs at a given light intensity (within a pair of horizontal lines in Table 11)is necessary to avoid the complications of arc aging and possible catalyst structural changes which may result from prolonged reactions.
TABLE I1 PHOTOCHEMICAL RATESOF CO OXIDATIONAT 25’ WITH VARIOUS REACTANT PRESSURES AND s- AND Sb-DOPED CuzO SAMPLES Run
1 2 3 4 5
Rcon, mm./ 6 hr.
sample
Cur0
Irrad. time, hr.
Por, mm.
Pco, mm.
d d d d d
6.00 6.00 0.00” 6.00 6.07
162.5 200.3 164.1 160.2 319.3
80.8 42.2 39.5 40.8 83.5
0.504 .546
d e e b c
6.00 6.00 6.00 6.00 6.00
80.6 79.9 80.7 79.7 80.1
20.1 19.4 19.7 21.0 20.2
.542 .400 .424 .432 .332
a
6.00 6 00 5.00 6.07 2.00 6.05 6.00 6.00 6.00 6.00
80.2 80.3 79.9 80.5 78.7 80.2
19 7 19.8 21.0 19.2 20.3 20.0 20.4 20.7 19.0 81.1
.365 ,313 ,339 ,321 ,267 .252 ,294 ,260 ,336 .264
.001 .504
.589 ------------------------
8 9 10 11 12
------------------------16 17 18 19 20 21 22 23 24 25
d d d d e b c d d
80.0 79.6 80.1 80.0
----------------L-------
d 4.00 81.1 20.8 0 .186 3Ib d 4.00 79.8 21.7 .025 10 Dark run; time that the reactants were in contact with the CuzO was the same as in the 6 hr. photochemical runs. b A glass filter was added in this run. It removed 89% of the ultraviolet light X
