T H E SOLUBILITY OF GASES I N LIQUIDS1
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B. S. NEUHAUSEN
In an article by the writer2 and Prof. W. A. Patrick, i t was shown that the solubilities of NH3, HC1, COz and SO2 in water could be expressed by the equation V
=
K
(
In this formula V is the volume of liquefied gas dissolved per gram of water (i. e., the weight of gas dissolved per gram divided by the density of the liquefied gas at that temperature) ; Pa is the vapor tension and 6 the surface tension of the liquefied gas at the temperature of measurement while P is the equilibrium gas pressure. K and l / n are specific constants. The fact that this formula fitted likewise the adsorption data for various gases by solid adsorbents, was considered as a support for the theory first advanced by Graham3 that solutions of gases in liquids are cases of condensations of the gases in liquids. In that paper solubility data in water only were presented. To show the extent of the validity of this generalization in solvents other than water, the following data on the solubilities of NH3, HCI, SO2,and C 0 2in methyl and ethyl alcohols are plotted according to this formula in Fig. 1. I n curves IM and IE there have been plotted the solubility data of de Bruyn4 for SO2 in methyl and ethyl alcohol, respectively, at atmospheric pressure and at temperatures of Contribution from the Laboratory of the Department of Physiology of the Johns Hopkins University. Jour. Phys. Chem., 25, 693 (1921). 3 Annals of Philosophy, 12, 69 (1826). Rec. Trav. chim. Pays-Bas, 11, 112 (1892).
B . S . Neuhausen
554
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0" C t o 26" C. The values of the surface tension of liquid SOz were calculated from values given by Landolt-Bornstein to be
Fig. 1
Temperature OC
0
7
12.3
18.2 -26 23.52
Surface Tension 28.4 27.2 26.13 25.0
The density of liquid SOz a t the different temperatures was obtained by interpolation from the data of Cailletet and Mathias.l Regnault's values for the vapor tensions as given by Zandolt-Bornstein were used. On curves 2M and 2E have been plotted de Bruyn's4 solubility data for NH3 in methyl and ethyl alcohol a t from 0" C to 30" C. The values of the surface tension of liquid NH3 were obtained from the data of Berthoud;2 the liquid densities from Cragoe and Harper;3 the vapor tensions from Cragoe et ale4 On curves 3M and 3E are found de Bruyn's4 data on solubility of HC1 a t temperatures from -10" C to 32" C. The 1 2
Comptes rendus, 104, 1565 (1887). Hel. Chim. Acta I, 84-7 (1918) ; Jour. Chim. phys., 16,429 (1918). Bureau of Standards, Sci. Paper, 420. Ibid., 369.
Solztbility of Gases in Liquids
555
values of the surface tension were calculated from the work of McIntosh & Steelel to be
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Temperature Surface Tension
-10 9.4
0
6.5
11.5
7.6 6.48 5.64
18
4.5
20 4
23.5 3.37
32 2
The liquid densities were interpolated from values of Ansdell;2 the vapor tensions up to 0" C from Faraday3 and over 0" C from A n ~ d e l l . ~ On curve 4 8 and 4M are plotted Just'sS data on the solubility of COz the values given in terms of the Ostwald solubility coefficient being recalculated into weights per gram of water. The values of the surface tension were interpolated from data given by Landolt-Bornstein, 1.82, 1-00, and 0.50 dynes being used for 15, 20, and 25" C respectively. Liquid densities were obtained from data of Warburg and v. Babo;6 the vapor tensions from the data of Tate.' From these curves i t is evident that the formula
holds very well for each individual gas. It may be noted that, with the exception of SOz, the curves of each gas in the two solvents are parallel, but as was already found in the case of water as a solvent, these curves do not coincide. When the above formula is written in logarithmic form the following equation is obtained : log V = log K
Pu + l / n log Pa -.
Zeit. phys. Chem., 55, 141 (1906). Proc. Roy. SOC.,30, 117. * Phil. Trans., 135, I, 155 (1845). Chem. News, 41, 75 (1880). Zeit. phys. Chem., 37, 343 (1901). Ber. Berl Akad., 1882, 509. Phil. Mag., (4)26, 592. 1
B . S.Neuhausea
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556
I n this equation there are two constants K which becomes PG equal to V when - is set equal t o 1, and 1/n which obviously Po is the slope of the line. As Chwolsonl has so painstakingly pointed out, it is incorrect to attribute any physical significance t o a proportionality constant, and if its value is other t h i n 1, the law has been incompletely expresseed or a factor omitted. As may be seen from the table below of the value K of the four gases in water ethyl, and methyl alcohol as solvents, it is not a proportionality constant but is a variable depending on some physical quantity. TABLE I Value of. K of gases in different solvents
3"
HC1
so2 coz
Water
Methyl alcohol
0.49 1.05 0.012 0 . OOG
0.205 1.23 0.04 0.0126
I
Ethyl alcohol
0.108 0.979 0.04 0.0103
If solutions of gases in liquids are considered as binary liquid mixtures it is evident that the greater the degree of miscibility of the gas in the liquefied form with the liquid solvent the greater the solubility, for miscibility may well be taken as an indication of the degree that molecules of the solute fit into the interstices of the solvent and vice versa. Upon examining Table I i t is seen that HC1 which is miscible with water and methyl and ethyl alcohols in all proportions gives a high value for K in all three cases. NH3 likewise gives a high value for K in water though the values are lower for the alcohols. SO2which in the liquefied form is miscible with water only in a limited extent gives a much lower value for K ; while in the alcohols with which it is miscible to a greater extent, K has a greater value. COZlikewise gives a very small value for K in water, with which C02 in the liquefied form is only slightly miscible, while with the alcohols with which liquefied gas is 1
edition.
Section on Physikalische Gesetze. Lehrbuch, d. Physik, I, 1, 25, 2nd
557
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Solubility of Ga.ses in Liquids
much more miscible the values of K are twice as great. That the values of K for COz in the alcohols are so much lower than those for HCl is not surprising for COz and the alcohols though they possess a great range of miscibility are not miscible in all proportions as has been shown by Buchi1er.l The value of K may therefore be taken as a function of the degree of miscibility of the liquefied gas and solvent. The other constant occurring in the equation is l/n. The values of l / n for the 3 gases are given in the following table: TABLE I1 Values of l / n for the gases
1 3"
HC1
so2
c02
Water
I Methyl alcohol I
Ethyl alcohol
0.69 0.062 1.20 0.07
0.71 0.065 1.00 0.055
O.G8
0.12 0.91 0.33
is applicable to the solubility data of NH3, HC1, SOz and COZin ethyl and methyl alcohols, as was previously shown for water. The values of K and l / n are given for these gases in the three solvents. Baltimore, Md.
*
Zeit. phys. Chem., 54, 665 (1906).
