‘The structure consists of slightly distorted octahedrally coordinated complexes of two glycine residues and two water molecules about the nickel atoms. These complexes are held to each other by strong oxygen-to-oxygen hydrogen bonds and by both strong and weak nitrogen-tooxygen hydrogen bonds. Because of the unfortunate orientation of the
[CONTRIBUTION FROM THE
molecule with respect t o the axes of the crystal, some of the parameters were not evaluated from projections but were in part calculated from assumed interatomic distances. The structure of the glycine residues is substantially the same as t h a t found by Corey and Albrecht’ for glycine. I’ASADESA,
CALIFORNIAK I K E I V E ~SEPTEMBER 15, 1944
DEPARTMENT OF CHEMISTRY OF LAPAYETTE COLLEGE]
The Diffusivities of Concentrated Sucrose Solutions’ BY ANDREWVAN HOOKAND HARRYD. RUSSELL~
I. Introduction Although dilute sucrose solutions are frequently employed as primary standards in diffusion studies, relatively little attention has been paid to the evaluation of this property a t higher temperatures and a t concentrations of the order of saturation. It is exactly these conditions a t which the diffusivity is of much interest and value for the kinetic interpretation of the crystallization of sucrose.’ This paper reports the results of an endeavor to supply this desirable information.
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11. Experimental and Results The Northrup4-McBain6porous disk technique was employed. Five different cells were employed, and each value presented in Fig. 1 is the p r a g e of a t least two determinations in different cells. Solutions were analyzed refractometrically with a Bausch and Lomb dipping instrument, previously calibrated in almost perfect agreement with the values of the “International Sugar Tables.”6 Weight percentages were computed to molarities, etc., by means of Plato’s tables.* Sucrose,’ potassium chloride7 and hydrochloric acida were used to calibrate the cells9 a t tempera-, tures below 35’ while mannitol’0 was used a t higher temperatures. Excellent agreement was realized with these different standards. The calibrated cell constant is essentially the ratio of the effective area of all pores to the thickness of the disk; and since the former will vary quadratically with the temperature and the latter changes only linearly, the net change of the cell constant will be a fractional increase of a A t , where CY is the linear expansion coefficient of the glass of which the disk is constructed. a of Pyrex glass is of the order of lo+, which with the maximum temperature spread encountered in this work (SO’) indicates an insignificant correction to the cell constant. Actually some slight increase in the cell constant is observed a t increasing temperatures. Some values determined for some of the cells used in this work are presented in Table I. The values in parentheses were obtained when the cells were not previously well aged a t the temperatures designated. I t was- intended initially to investigate the diffusivities of supersaturated solutions in par-
3 I 3 (4) J. H. Northrup and M. L. J. Anson, Gcn. Physiol., 14, 543 (1929). Molarity. ( 5 ) J. W. McBain and T. H. Liu, Tars JOUPNAL, I S , 59 (1931). Fig. 1.-Integral diffusivities of sucrose solution: 0, (6) International Scale (1936) of Refractive Indices of Sucrose this work; 0, Oholm, at 12, 20 and 29”, respectively, Solutions, C. A. Browne and F. W. Zerhan, “Sugar Analysis,” 3rd edition, New Y o r k , N . Y., 1941. “I.C.T.”; A , McBain,‘ 2.5’.
0
I
(7) Landolt-Bdrnstein, “Tabellen,” 1936
(1) Investigation supported hy a grant from t h e Sugar Research Foundation, Inc. (2) Present address: University of Wyoming, Laramie, Wyoming; and Tannusville, New York,rcspectivcly. (3) A. Van Hook, Ind. En#.Chcm., 86, 1042 (1944).
(see Fig. 3). (8) W. A. James and Gordon, J . Chcm. Phys., 7 , 963 (1939). (9) E. J. Cohen and J. T. Edsall, “Proteins,” Reinhold, Publ. Corp., New Y o r k , N. Y . , 1943. (10) J. D R. Scheffer and F. E. C. Scheffer, Vow Kon. A k . Wet. Amsl., 19, 148 (1916).
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Ifarch, 194.5
371
~ I I ~ P U S I V I T I I SOF S CONCENTRATED SUCROSE SOLUTIONS
least squares method and the computed values TABLEI are computed as the full lines in Fig. 2, and where WITH TEMPERATURE VARIATION OF CELL CONSTANT slle-Temp., "C.
1
2
3
8.3 30.2 40.0
270 (301) 274 272 278 ...
241 (266) 235 343 (272) 238 245 245
268
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69.2 73.0 88.0 87.2
...
... ...
... ...
... ...
279 2%
...
the points represent some results of other workeis. The curves form a family of straight lines with a common origin a t a concentration of approximately 3.26 M . At 90' this is just about a saturated solution, thus coinciding with the questionable suggestion of Mertens,13 that the diffusivity of saturated solutions is zero; but a t the lower temperatures, where the computations are much more significant, the limiting concentration is much higher than saturation (e. g., a t IO', D = 0 at S = 1.27, where S = yo sucrose in sirup& sucrose in saturated sirup).
ticular, but after overcoming the many difliculties of filling the cells with such viscous solutions, only irregular and unreliable results were realized. After such a trial the cell employed would evaluate to its original constant only after being soaked in water. This behavior suggests a crystallization within the pores of the disk, even though this is not observed in the bulk solution. Alternatively, the sintered glass membranes may be able to swell and shrink in accordance with changes in liquids t o , which they are exposed (J. W. McBain. Communication). At the higher temperatures investigated in this work a small amount of solvent water condensed on the upper parts of the completely enclosed cell, necessitating a small correction in the volunie of the diffusate solution. In a few experiments a regular loss of water was permitted by evaporation and the computations made accordingly were in excellent agreement with the general results. All solutions were initially adjusted to a pH of 8 by the addition of a minute amount of sodium hydroxide solution. It was computed from the velocity constant of inversion, and independently confirmed (polarimetrically and refractometrically) a t the highest temperature and concentration employed, that inversion was not significant 0 I -7 3 during the period of an experiment. Molarity. The results obtained are presented in Fig. 1, Fig. 2.-Differential diffusivities of sucrose solutioiib. together with some values from the literature for interpolated from results of Fig. 1 : 0, Thovert at 18.5", comparison. Additional values a t concentrations Landolt-Borns tein' "Tabellen. " below 0.5 M were obtained, and in agreement with A series of determinations of the diffusivities of reported values they indicate a rather sharp upturning at low concentrations of these seem- 0.1 &I potassium chloride were performed at the ingly linear curves. They are not discussed in higher temperatures utilized. The computed rethis report since the primary interest was in the sults are presented in Fig. 3. values a t higher concentrations3 and also since & 5.0 they are not sufficiently comprehensive to con.fi " 4.0 tribute, other than in a confirmatory way, to 2 3.0 the need for extensive diffusion data in the dilute : 2.0 range. $ The diffusivities represented in Fig. 1, D',are Q- 1.0 integral or mean values over a range of concen275 BOO 32.5 3 50 trations and are to be related to the true dif1 / T X lo6. ferential coefficient, D,by the relation12
I
I
D
dD' dC
= D ' + C--
This has been done with the values of Fig. 1 via a (11) M.A. Lauffer, T w r s JOUXNAL. 66, 1200 (1944). (12) H.Neurath. Chcnr. Reo., SO, 359 (1842).
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I
Fig. 3.-Temperature dependence of diffusion of 0.1 N potassium chloride solution: 0, this work; 0, LandoltBornstein' "Tabellen." (13) A. Mertens. IV Cong. Ins:. Tech. Chim. I n d . AET., Brurelleo 1. 65-69 (1935).
l h e parameters usually irivoked to explain the teiiiperature am1 concentration variation of riiffusioii are the viscosity arid the activity. I'licw f ,Ic*tors are coupled in the cxliression16
With tlie viscosity data o f Binghani arid Whitelx cJthers19~20 the first factor givrs computed ralues of the diffusivity (1)) iiiuch lower than those observed, and the second activity factor" ylevates these values only slightly, t ( J within only a third to ;I fifth of the :~ctuallyobserved values. This saiiie situation obtains in dilute sucrose solutions but to a lcss magnified exteiit." Apparently soiiic. factor is oper;Ltiiig which has a inore proriouncetf effect upon viscosity than upon diffusion.& A (hydrogen bonded) 1i cluster of sucrose molecules miglit offer tremendous fluid resistance to rnoveiiient through a medium, and yet lose or exchange its in~livid~ial niembers quite freely in diffusion. aiitl
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IV.
Summary
'l'hc. diffusioti covtricieiits oi aqueous sucrose SOI u t i i I I I S tiiniiiiish litiearly frc'miconcentrations above I J I I V niolar to a t least the saturation concentration. 'l'lit~Stctkes--Bilist.eiri inzplicatioii of ari inverse
clit~usivjty-visct,si ty relation is elltirely iiiackqu;r te to cxplain the results obtained. IMTusioii cocflicierits of U. 1 .M potassiurn chloride exhibit a slight coiivexity on the usual semilogarithinic-reciprocal temperature plot,
I
A. I< I'I l1!1:1111
That salt effects also may be rather large i1i acetic acid seems probable because of the relntively iow dielectric constant of this solvent. Evidence favoring this conclusion has been rcported by several i~ivestigators.~Since none of tlicse studies of salt effect involved the use ( l i zinc acetatt., however, i t seemed of interest to investigate the effect of soine neutral salt upori the solubility of this con~j~ourid in acetic acid, i r i order that a comparison might be made between the solvent action of thr. neutral salt and that of the strong bases in this soliwit. Lithiurn nitrate w:ts chosen as a suitablc salt for the purpose, aiid this paper presents the rcsiilts of if study in which its sol\-ent effect upon zinc acetate was observed. t,'V
Sewad
and Narnblet, : b i d , 64, 5\54 (1932); Schrrll. Hiitchisou 65, 3081. (1033)
and Chuo4lee. i h i d
.
