June, 1052
VISCOSITY IN CELT,UL,OSE SOLUTIONS AT CONTROLLED VELOCITY GRADIENT
Results From the measured activities of the samples, the per cent. specific activities, a,, were calculated using the formula a , = lOOA,/(zA,)
where A m is the measured activity of a given sample of surface density x (expressed in mg./cm.2), and A i is the infinite thickness activity. This latter activity is that obtained from the flat portion of a curve of A , versus x, this activity being attained a t a surface density of approximately 4 mg./crna2. The data obtained for both types of sample are presented in Table I. The mass absorption coefficient was calculated from the activities over the entire range of measurements giving an average value of 1.48 crn.”mg. It can be seen from the
683
data that the individual mass absorption coefficients decrease as the surface density becomes larger, an effect that has been observed with other nuclide^.^ Figure 1 is a plot of per cent. specific activities as a function of the surface density. As is observed, the per cent. specific activity shows a maximum in the region of 0.07 mg./cm.2, this effect having been found i n other self-absorption experiment^.^ Acknowledgment.-This work was performed under the United States Atomic Energy Commission Research Contract No. AT-(40-1)-1058. The aut,hors wish to express their gratitude For this financial assistance. (3) G. K.Schweitzer and B. R. Stein, unpublished experiments. (4) 0. I
4 0
cm
30
0
eo
1 > n
I O OB 06
W 0 3
n w K
04
03
CONCENTRATION
Fig. 1.-Martin
, G./OL.
plots for 14 celluloses measured in cuprammonium hydroxide.
100 0
so 0
400 30 0
20 0 0'
100 80 60
s
40
e !
'
30
50 70 10 2 0 30 LO 70 100 200300 500 SPECIFIC VISCOSITY, qrp.
Fig. 3.-Relation between intrinsic and specific viscosities at 500 sec.-1 at two selected concentrations for cuprammonium and cupri-ethylenediamine solutions of cellulose.
= 3 . 2 7 ~0.788 ~ ~- 0.137
or in logarithmic form
30
log
20
([TI + 0.137)
IO OB
06
[q] =
0 I1
0
Fig. 2.-Martin
= 0.514
+ 0.780 log T~~
The standard error of estimate of [ q ] is 5.2% (27 observations). For the 0.50 g./dl. level, the relation is
0
&!
20
[TI
W 0
2
10
It is evident from the figure that the points representing cuprammonium (open circles) and cupriethylenediamine (dark circles) fall on the same curves. This obviously simplifies the application of the relations. For the 0.25 g./dl. concentration level, the equntion through the points for both solvents is
60 0
a'
05 07
'
04
i
1
08 12 16 20 CONCENTRATION , G /DL
24
1
plots for 13 celluloses measured in cupriethylenediamine hydroxide,
concentration points of these samples. The failure of the Martin equation at higher concentrations, particularly in the case of cellulose of high D.P., has been n ~ t e d . ~The , ~ Martin K values show a decrease at the higher intrinsic viscosities. The specific viscosity values used for the correlation are listed in Table I. Where measurements had not been made a t the 0.25 g./dl. level, the specific viscosities were obtained by reading off the reduced viscosity a t this concentration from the Martin plots and converting. I n the case of samples 1 and 2, where the observed reduced viscosity a t 0.50 g./dl. did not fall on the regression line plotted, the observed specific viscosity was never-
1.70 vsp O.6"
- 0.160
In logarithmic form log ([TI + 0.160) = 0.230 + 0.694 log qsp The standard error of estimate of [ q ] for this expression is 5.4% (27 observations).
Discussion In view of the rather large differences in intrinsic viscosity involved, it is interesting that the same equations hold for both cuprammonium and cupriethylenediamine solvents. This means that the specific viscosities in the two solvents maintain n corresponding ratio. While the equations presented herein offer a simple means of obtaining intrinsic viscosity values, either by mathematical substitution or by construction of a chart similar to Fig. 3, it must be borne in mind that their use is valid only for the two systems studied. Whether these same relations would be valid for solvents of wider differences in copper and amine content, or of different solvent nature, than the ones studied remains to be investigated.
693
T.1., WARDAND W.S. SINGLETON
A second consideration in the use of these equations is whether or not the viscosity data have been adjusted to a mean velocity gradient of 500 see.-'. As Conrad and others have S ~ O I V I I , ~the ~ J ~apparent viscosity of 0.5 g./dl. solutions of cellulose in cuprammonium can vary as much as 1 0 0 ~ o in , the case of high D.P. cellulose, depending on the rate of shear existing during the measurement. This rate of shear effect becomes less significant at lower D.P., and in the case of celluloses having an intrinsic viscosity of less than 5-6, may be neglected for many purposes. Thus, the equations presented would be approximately valid for use with unadjusted data when the intrinsic viscosity was below 5-6, but their use with higher D.P. celluloses requires adjustment of the data to the gradient specified. While the velocity gradient effect is of lesser absolute magnitude at lower concentrations, it is of equal significance when the absolute viscosity is converted to reduced viscosity, so that it cannot be obviated by going to smaller concentrations. The standard error of estimate of [ q ] by these equations is about 5%. This error would amount to about 250 glucose units in the case of a cellulose
Vol. 56
of D.P. 5,000, or about 3 glucose units in a cellulose of D.P. 50. Errors of this magnitude are usually permissible in ccllulose investigations. The ratio of the intrinsic viscositics measured in cupri-ethylenediamine to those measured in cuprammonium was shown in a previous investigation6 of a group of seven samples having intrinsic viscosities ranging from 20 or 30 to 2 to be approximately constant and equal to 1.365. For the thirteen celluloses measured in both solvents in this study, which included seven of those examined previously,Bthis ratio was found to be 1.354, in excellent agreement with the earlier value. Thus, if the factor of 260 proposed for conversion of intrinsic viscosities to D.P. for cuprammonium measurements is accepted, over the entire range of D.P. from 50 to 5,000, 190 would seem to be appropriate for use with cupri-ethylenediamine data. Acknowledgment.-Thanks are expressed to Miss Hilda M. Ziifle for the construction of the figures and the statistical calculations of the data, and to Mr. Bernard J. Barrett for some of the viscosity measurements.
PT-IYSTCAL PROPERTIES OF FATTY ACIDS. 11. SOME DILATOMETRIC ANI) THERMAL PROPERTIES OF PALMITIC ACID BY T. L. WARDAND W. S. SINGLETON Southern Regional Research Laboratory,l New Orleans, Louisiana Received JuZv 16, 1961
Pure palmitic acid has been examined by dilatometric and calorimetric methods. The properties investigated and the values found were expansion of the acid in the solid and liquid states, 0.000280 and 0.000968 ml./g./"C., respectively; melting dilation, 0.1806 ml./g.; specific volume over the range of temperature from solid to liquid; specific heat; heat of fusion, 51.2 cal./g. (13.12 kcal. per mole); and entropy. Equations were developed for expressing the specific heat (C,) of palmitic 0.0013t; (liquid state) C, = 0.4624 0.00175t. acid at any temperature ("C.): (solid state) Cp = 0.3831
+
The expansibilities and the volume changes which accompany melting of the saturated fatty acids have received scant attention. The data of Normann,2and Garner and Ryder3 on a limited number of fatty acids comprise the only sources of information on transition dilation. Garner, Madden and Rushbrooke4 have reported values for the heats of fusion and mean specific heats for some of the fatty acids. The present investigation, extends the previous work of the authors6 to cover the specific volumetemperature relationship, expansibility of the solid and liquid states, and the melting dilation of palmitic acid, and includes data for the specific heat, heat, of fusion and entropy of this acid. Purification of Palmitic Acid.-Commercial grade palmitic acid (85%) was sulfonated and thoroughly washed with water to rcmovc unsaturated impurities. The sat( I ) One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture. Article not copyrighted. (2) W. Normann, Chem. Umachau Fette, ole, Wachae Harze, 38, 17 ( 1 931 ).
(3) W. E. Garner and E. A. Ryder, J. Chem. Sac., l a T , 720 (1925). ( 4 ) W. E. Garner, F. C. Madden and J. E. Rushbrooke, ibid., 2491 (1928). (5) W. S. Singleton, T. L. Ward and F. G. Dollear, J. Am. Oil
Ckemists' SOC.,27, 143 (1050).
+
urated portion was esterified with methanol, the methyl esters fractionally distilled, and the methyl palmitate fraction reconverted to palmitic acid. The free acid was crystallized from atetone 14 times which gave a product having a constant value for its solubility. After drying over phos horus pentoxide, the palmitic acid melted (capillary tubef a t 62.8-63.0'. Its freezing point, determined by modification of the method of Glasgow, el al.,n WFS 62.75 and its absolute density was 0.8414 g./ml. a t 80.0 Palmitic acid has been shown by Francis, et al.,' to exist in two principal polymorphic modifications one of which was obtained by crystallizing the acid on a n X-ray mount from a solution of benzene; the other was obtained by a similar crystallization from a solution of glacial acetic acid. The forms were identified by X-ray diffraction patterns obtained immediately after formation of the crystals. The crystals which separated in the benzene solution were of the thermodynamically unstable B-form, those which formed in the solution of lacial acetic acid weie of.the stable C-form. Thibaud and%aTour,a however, experienced considerable difficulty in obtaining similar patterns by crystallizing thin layers of palmitic acid. These workers found it necessary to carry out the crystallization below room temperature in order to obtain the unstable B-form. At room temperature or above, they obtained the C-form of the acid and single crystals were always obtained in this form. The present authors6 have shown that the temperature
.
(6) A. R. Clasgow, Jr.. A. J. Streiff and F. D. Rossini, NalE. Bur. Sfandards, J . Research, 86, 355 (1945). (7) F. Francis, F. J. E. Collins and S. H. Piper, Proc. Rov. Soc. ( L o n d o n ) , A168, 691 (1937). (8) J. Thibaud and F. D. LmTour, J. chim. phys., 29, 153 (1933).
