THERMAL TRANSPIRATION OF GASESAT Low PRESSURES
April, 1958
$0.’ 10
20
m BeF,.
4
0
5
a
Ea
457
m
mole per csnl.
Fig. 4.-Partial pressures a t 890’ on the basis that NaF, BeFz and NaBeFa exist in the vapor phase.
in establishing definitely the existence of such a vapor phase complex. I n the absence of firm evidence of the existence of gaseous NasBeFa, the vapor phase of the NaFBeFz system was treated as consisting only of the NaF, BeFzand NaBeF3molecular species. A tabulation of all the derived constants of the partial pressure equations for NaF, BeF2, and NaBeF3 is given in Table 111. Total Vapor Pressures of the NaF-BeF2 System.-Figure 5 shows how the total pressure of the NaF-BeF2 system changes with composition for various temperatures. Previously obtained vapor
Fig. 5.-Total vapor pressures of the NaF-BeF2 system on the basis that NaF, BeF2 and NaBeFa exist in the vapor phase.
pressure data for pure NaF” were used in the construction of this plot. The phase diagram by Thilo and Schroders was used to determine the compositions which melt at the various temperatures. Acknowledgments.-The authors express their sincere thanks to Dr. J. W. Droege for many helpful discussions. They also thank the analytical department a t Battelle Memorial Institute, as well as Tom Culbertson for his assistance in carrying out the experimental work. (11) K. A. Sense, C. A . Alexander, R. E. Bowman, R. W. Stone and R. B. Filbert, Jr., T H I SJOURNAL, 62,384 (1957).
THERMAL TRANSPIRATION OF GASES AT LOW PRESSURES BY A. J. ROSENBERG AND C. S. MARTEL,JR. Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts Received December 6. 1967
Measurements of the thermal transpiration of krypton have been extended to low pressures. The functional dependence of p l / p 2 on p 2 D has been verified, but Liang’s equation does not represent the data when p z D < 75 p mm. A general empirical correction t o Liang’s equation, applicable to gases which obey the equation at higher pressures, is proposed for the region dgpzD 3 300 p mm.
In recent years the thermal transpiration2 of I n the conventional apparatus for adsorption gases has received considerable attention by work- measurements10the sample chamber is separated by ers in the field of low pressure gas a d s o r p t i ~ n . ~ - ~ (1) The research reported in this document was supported jointly by the Army, Navy and Air Force under contract with the Massa-
chusetts Institute of Technology. ( 2 ) M. H. C. Knudsen. “Kinetic Theory of Gases,’’ Methuen and Co., Ltd., London, 1934; Ann. P h y s i k , 81,205,633 (1910). (3) S. C. Liang, J . A p p l . Phys., 22, 148 (1951). (4) S. C. Liang, THISJ O U R N A 66, L , 6GO (1952).
(5) 9. C. Liang, ibid., 67, 910 (1953). (6) 9. C. Liang, Can. J . Chem., 33, 279 (1955). (7) J. M. LOBand R. R. Ferguson, Trans. Faraday Soc., 48, 730 (1952). (8) G. L. Kington and J. M. Holmes, ibid., 49, 417,425 (1953). (9) A. J. Rosenberg, J . Am. Chem. Soc., ‘78,2929 (1956). . (10) 8. Brunauer, “Adsorption of Gases and Vapors on Solids,” Princeton University Press, Princeton, N. J., 1943.
4 58
A. J. ROSENBERG AND C. S MARTEL, JR.
Vol. 62
R p l / p z = f (pzD, Ro) (2) He has also proposed a general empirical formula for R, viz.
where cwe
=
2.52 X 10-6
,u-2
mm.-2
P H ~= 7.68 X 10-3(1 - Ro)p-' mm.-' and +g is a constant characteristic of the gas in question (e.g., + H ~= :, $ K ~= 3.84). Equation 3 accurately describes existing data on thermal transpiration. Suitable test data have been lacking, however, in the region 0 < p2D Ts, AFIo+ = 27.5, AHlo+ = 5.9, ASTo* = -63. In 2.0 M KCNS AFso* = 25.9, AHw* = 13.3 AS 60 = -38.9 while AFl0* = 27.0, AHlo* = 6 . 7 , ASlo* = -59.2. Since A&o* .= +361 e.u. and AHso+ 141 for shrinkage, it is evident that imbibition of solvent rather than thermal shrinkage is essential for extraction. The discontinuity in AS* occurred when the molecular species being extracted was changed rather than a t Ts as would have been expected if H-bonds were the primary cause of the insolubility of collagen. The origin and distribution of the cross-linkages is discussed. j
a
*
Introduction peptide linkages. The interchain stabilizing forces The native fibrous proteins are particularly inter- have been ascribed t,o salt links,2interchain hydroesting polymeric systems since, in contrast to the gen bonds,2 covalent cross-linkages3 and small synthetic cross-linked random-chain high polymers, amounts of cementing mucopolysaccharides.6 I n any int’erchain cross-linkages which are present are view of the fact that acid-swelling and high salt “superimposed on, or in, a previously ordered sys- concentrations do not necessarily disrupt the collatem.”l By studying the disaggregstion process, gen structure, and since thermal shrinkage does not and characterizing the molecular species involved, involve salt-links,6J we prefer to disregard these one may approach the question of the nature and links in our subsequent considerations. We shall distribution of the cross-linkages and the influence also assume, with perhaps less justification, that of these linkages on solubility, thermal stability and collagen-mucopolysaccharide interact,ions are unbiological properties. Collagen fibers are especially likely to be of importance in the systems we have suited to such an investigation since it is well recog- s t ~ d i e d . ~ , ~ It remains, then, to differentiate between the efnized that their stability is a function of the fiber sourc,e? Consequently, n number of different ini- fects of hydrogen-bond and interchain-covalent tial cross-linkage distributions or structures must be bond rupture on the solubility of collagerl and on the available for study. Further, it is our belief that a resulting molecular species distributions. We have, knowledge of these distributions lies at the very therefore, examined the solubilization of native heart of the understanding of the collagen-gelatin steer hide collagen in water, H-bond competing transition as well as of a variety of problems con- solvents, and in 1-1 salt of equivalent ionic strength. cerned with the aging of connective tissue. Procedure On the basis of our recent investigation^^^^ of the A . Experimental.-Sma11 cubes of native steer hide collagen-gelatin transition, we may tentatively collagen ( N = 18.4%, ash
