Vapor Pressure Nomographs for Aqueous Sodium Hydroxide Solutions D. S. DAVIS Wayne University, Detroit, Mich.
HE latest data on the vapor pressures of aqueous solutions of sodium hydroxide a p p e a r ,to b e those of Akerlof and Kegeles ( I ) , a table of logarithms of vapor pressures for molalities of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0,1.5, and 2 to 17 in steps of 1 mole for temperatures of 0" t o 7 0 " C., i n steps of 10". To devise a convenient method of interpolation for intermediate concentrations and temperat u r e s , i t was necessary t o effect a correlation suited to the requirements of a line coordinate chart. Theintegrated Clausius-Clapeyron equation, a s s u m i n g cons t a n c y of t h e l a t e n t h e a t of vaporization, v a l i d i t y of the gaslaws for water vapor, and negligibility of solution volume in comparison with vapor v o l u m e , yields :
T
logp = a b/T
+
Tempe m t u r e t, Dey. C.
Vapor P r e J s u r e ,q mm. Hq
(1)
Equation 1 suggests the use of logarithmic pressure and reciprocal absolute temperature axes, but appreciable curvature in the plots is encountered. Satisfactory straight lines result when log ( p - 6) is plotted a g a i n s t l/(t 230), acc o r d i ng t o the equation
+
log ( p
A
+
- 6) B
=
rn(2)
where p = vapor pressure, mm. mercury t = temperature, ' C. 6 = 0.10 x (10)-0.10
/
/
/
F ~ U R1E 1131
P
and A and B depend upon the concentration of sodium hydroxide as shown in Table I. Equation 2 is largely empirical, but this function of temperature has a precedent in the Cox method (3) of p l o t t i n g vapor pressure d a t a as s h o w n p r e v i o u s l y (9, 4). It has been
1132
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 9
TABLE I. VARIATION OF A AND B WITH CORCENTRATION OF SODIUM HYDROXIDE Molality
’1
Temperature t, De9 c.
t
60
my ,
/
‘j;
/
/’
of NaOH
A
0.1 0.2 0.4 0.6 0.8 1.0 1.5 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
7.98632 7.98547 7.98202 7.97927 7.97711 7.97355 7.96619 7.95769 7.94304 7.93081 7.92252 7.91801 7.92019 7,92909 7.94692 7.97600 8.01875 8.07724 8.10618 8.14039 8.18029 8.22770 8.28290
B
1685.97 1685.97 -1686.10 -1686.01 - 1686.23 -1686.10 1686.31 -- 1686.36 - 1687.70 1690.65 -1695.73 - 1703.07 - 1713.40 - 1726.77 - 1743.56 - 1764.22 - 1789.01 -1818.00 -1839.19 - 1862.58
- 1888.23 -1916.75 -1948.13
+
shown that plots of log p against l / ( t 230) result in straight convergent lines, within the family, for metal, benzene, alcohol, organic acid, and silicon hydride series. Plots of log ( p - 6) against l / ( t 230) for various concentrations of sodium hydroxide exhibit a rough convergence in the neighborhood of 610” C. and 1200 atmospheres, although this point is not definite enough to be used in a system of correlation. I n Figure 1, which covers the range of 1 to 17 molal, the index line shows that the vapor pressure of a 10-molal solution of sodium hydroxide is 6.1 mm. of mercury a t 15’ C. Figure 2, confined t o concentrations of 0.1 t o 7 molal, can be read a little closer than can Figure 1. The index line shows that the vapor pressure of a 3.6molal solution of sodium hydroxide is 48 mm. of mercury a t 40” C. The average deviation of pressures read from the chart from the original data is about 0.5 per cent.
+
5
L
-i E-
L FIGURE 2
Literature Cited (1) Akerlof, G., and Kegeles, G., J . Am. Chem. SOC., 62, 620 (1940).
(2) Calingaert, G., and Davis, D. S., IND. ENG. CHEM.,17, 1287 (1925). (3) Cox, E. R., Ibid., 15, 592 (1923). (4) Davis, D. S., Ibid., 17, 735 (1925).
Silver Plating of Optical Glassware-Correspondence SIR: In connection with this article by Robert D. Barnard [IND.ENQ.CHEM.,34 637 (1942)], I wish to call attention to the fact that reduction of inorganic and organic compounds by ethanolamines was reported in my article entitled “Reduction of Organic Compounds with Ethanolamines” [J.Am. Chem. Soc., 57, 2554 (1935)]. Further, the use of ethanolamines-. g., triethanolamine-for the production of silver reflecting surfaces is the subject of U. S. Patent 1,989,764, granted me in February, 1935. M. MEV~SNER College of the City of New York New York, N. Y.
SIR: I have gone into the literature carefully and admit the justification of Meltsner’s claim to originality in devising the method. I think he is entitled to priority rights and have so notified those who have corresponded with me about the method. However, the use of the amino alcohols was not original with either of us in this connection, since this method was in use in 1933. I believe the modifications which I introduced for the specific purpose of applying the method to optical glassware justified my report, but it was an unfortunate oversight that I did not give proper credit to Meltsner for his contributions. ROBERT D. BARNARD
4404 Drexel Boulevard
Chicago, Ill.
