INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1949
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I
1
I
n
0.06
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LITERATURE CITED
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’ 0.080-VISCOSITY
AT FREEZING POINT
OF Cg AND C , A T “NORMAL“ F R E E Z I N G P O I N T
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X-VISCOSITY
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W
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1I
t-
1
2 0.04 -U < I v)
2069
I
(1) Am. Petroleum Inst., Research Project 44 on Collec%ion,Analysis and Calculation of Data on Properties of Hydrocarbons,
Washington, D.C., Natl. Bur. Standards, 1945.
(2) Am. Soc. Testing Materials, “Standards on Petroleum Products
and Lubricants,” 1936. (3) Ibid., 1944.
(4) Bingham, E., and Jackson, R., Bull. Bur. Standards, 14, 75 (1918). ( 5 ) Cannon, M., and Fenske, M., IND. ENG.CHEM.,ANAL.ED., 10, 297 (1938). (6) Egerton, A,, and Ubbelohde, A,, Trans. Faradall SOC.,26, 236 (1930). (7) Egloff, G., “Physical Constants of Hydrocarbons,” A.C.S. Monograph 78, New York, Reinhold Publishing Corp., 1940. (8) Geist, J., and Cannon, M., IND. ENG.CHEM.,ANAL.ED.,18, 16 (1946). (9) Glasstone, L., Laidler, K., and Eyring, H., “Theory of Rate Processes,” New York, McGraw-Hill Book Co., 1941. (10) Kauzmann, W., and Eyring, H., J. Am. Chem. Soc., 62, 3113 (1940). RECEIVED September 15, 1948.
Figure 2.
Effect of Molecular Weight on Freezing Point Viscosity
crystallization occurred, it was almost instantaneous in time and in temperature. Furthermore, for tetradecane the liquid was frozen and then reheated to 0.1’ C. above the freezing point, where viscosity measurements were made which were repeated at higher temperatures. The viscosities obtained in the heating cycle exactly reproduce those obtained in the cooling cycle. This shows that viscositymeasurements do not indicate any greater orientation in the remelted liqujd than in the liquid before freezing. Figure 2 shows freezing point viscosities plotted against molecular weight. The viscosities of the compounds with even numbers of carbon atoms give a smooth curve; the viscosities of the odd numbered compounds are displaced from this curve. Kauzmann and Eyring (IO)suggested that the freezing point viscosity for normal paraffins is relatively constant for compounds 8crith five t o fourteen carbon atoms. The difference in viscosity between odd and even numbered carbon compounds seems to depend on the well known anomaly between freezing points of odd and even numbered chains of normal paraffins; odd numbered compounds have relatively lower freezing points than the corresponding even numbered compounds. This anomaly has been explained by statistical considerations, as there are fewer ways of fitting the odd numbered chains together in a crystal lattice than the even numbered chains. If the freezing points of the paraffins with even numbers of carbon atoms are plotted against molecular weight, it is possible to establish a “normal” freezing point for the odd numbered compounds. The viscosities corresponding to this normal freezing point for pentane and heptane were plotted as shown in Figure 2. The points fall essentially on the freezing point viscosity curve established for the chains with an even number of carbon atoms, an indication that, as far as resistance to flow is concerned, the compound is, in a sense, supercooled below its normal freezing point. NOMENCLATURE
F* = free energy of activation, calories per mole h k
N
= Planck constant
= Boltzmann constant
V
= Avogadro number = N k , calories/” K. = absolute temperature, = molar volume, cc.
q
= absolute viscosity, poises
R T
O
K.
CORRESPONDENCE Critical Constants, Density, a n d Viscosi ty-Correspondence SIR: Attention is called to an error in the paper by Arnold Boas [IND. ENG.CHEM.,40, 2202 (1948)l. Equation 4 is taken correctly from Souders. However, as the logarithms are to the base 10, the reduced form should appear in Equation 5 a5 log ‘tr = ( 1 0 ” ~ ~ ~ ) ( 1 0 - 2 . @ - )log ‘to Further, some confusion may result from the author’s statement that, “log qo is substantially constant for the nonpolar liquids studied.” It is constant only within about 10% as shown by a tabulation of qc in the paper of Uyehara and Watson [Natl. Petroleum News (Oct. 4, 194411.
E. Harvey Barnett 5873 Julian St. Louis 12, Mo.
,.....
SIR: The comment of Mr. Barnett is quite correct. Equation 5, page 2203, should have read as he has indicated. However, this equation is not used in any further calculation but is merely used to illustrate a method of reducing a n equation and to establish the universal constant, md,. The error was noted upon publication and was corrected in every reprint that has been sent out. rlC
Benzene Ethyl ether Ethyl propionate Toluene
312 268 284 a06
log
9c
2.49 2.43 2.45 2.49
Due to the units of q in Souders’ equation-that is, millipoisesthe constancy of log q c varies much greater than if we had used a relation with the viscosity in micropoises. Using a few values of qc as noted in Table I1 of Uyehara and Watson with ?a in micropoises it is seen that log qo is practically constant. However, it should be noted that, even with the constancy of log qc within 10% as pointed out by Mr. Barnett, we are still able t o establish the universal constant md, and predict critical density values from this constant. Hydrocarbon Research, Inc. 115 Broadway New York 6, N. Y.
Arnold Boas
