VAPOR PRESSURES OF SULFUR DIOXIDE AND NITROUS OXIDE. 2691
TABLE V. Pruaue ( m a Hg.).
Temp.
* c.
Iao-butane.
130
...
Normal bubne. 20600
120 I IO
21700 I 8600
18100 14700
I00
15400
12500
mwk.
... ... ... ...
The critical data for propylene, normal butane, and iso-butane are given. Vapor pressures of these three gases a t temperatures ranging from oo C. to 130' C. are also shown. The authors are indebted to Dr. G. A. Hulett, consulting chemist, and to I. W.Robertson, junior chemist to the Bureau of Mines, for valuable assistance in conducting this work. PXTT.lrU.OE.
Ph
[CON1.RlaU'MON FROM TFfE
LABORATORY FOR GASRESEARCH OF
TEE
MINBS.I
u. s. BURBAVOF
THE VAPOR PRESSURES OF SULFUR DIOXIDE AND NITROUS OXIDE AT TEMPERATURES BELOW THBIR NORMAL BOILIRG POINTS. BY G. A. B-RSLL m n I. W.R o ~ l m m t t . Received September 29, 1915.
In this paper, one of a series, dealing with the vapor pressures of substances a t low temperatures, are shown the vapor pressures of sulfur dioxide and nitrous oxide. The method of procedure has been described in previous communications to THISJOURNAL.'
Preparation of Gases.
Sulfur Dioxide.-This was prepared by the action of sulfuric acid on copper. It was bubbled through water to remove sulfur trioxide and finally thoroughly fractionated a t the temperature of liquid air to remove atmospheric air or other gases of high vapor pressure a t that temperature, and a t temperatures between -70' and -1o0' to remove water vapor and other gases of negligible pressures a t those temperatures. Purification was carried to the point where the entire liquid boiled within a range of 0.2 Nitrous Oxide (N2O).-Nitrous oxide was prepared by heating ammo-
'.
l
THISJOURNAL, 37, 1893, 1902,2188, 2x93, 2482, 2486 (19x5).
2692
AND I. W. ROBERTSOH.
G. A. BURRELL
nium nitrate. The evolved gases wwe passed through caustic-potash solution and sulfuric acid and finally thoroughly purified by fractionation a t low temperatures. In the vapor-pressure observations, readings were made with a rising and falling mercury column, and checked after boiling away a part of the lzquid gas in the vapor-pressure bulb. In Tables I and I1 are shown thc observed and calculated vapor pressures for the two substances, the temperatures given being the average of one reading each on thermometers Nos. 707 and 504. The equations of the curves were calculated from the Nernst formula1
L~~ p
x ----
=
+ 1.75 log T - ---c 'r + c.
4.57rT 4.571 In the case of sulfur dioxide the constants X, e, and C were found by taking the values of 9 at the temperatures 262.1"~248.3" and 208.6' Abs. In the case of nitrous oxide the values of p at 182.5"~173.6', and 152.0' Abs. were taken. Above 182.5' Abs. nitrous oxide is liquid and below this temperature it is solid. I n this case only the solid phase was considered in calculating pressures. TABLEI.
TABLE 11.
Saturated Vapor Pressures of Sulfur Dioxide a t Low Temperatures.
Saturated Vapor Pressures of Nitrous Oxide at Low Temperatures.
Temperature. Average.
-00 c.
Pressure.
w Calc. Mm. Hg. Mm. Hg.
-------
Temperature. Average.
Obs.
Abs.
O o C.
Abs.
Pressure.
Obs. Mm. Hg.
Liquid
Liquid ----I1 .o
262, I
--rx.g -13 o
261.2 260. I
760 735 697
- 88.7
- 89.3 - 90.1
Calc. Mm. Hg.
...
184.4 183.8 183.0
. . a
...
Slid
- 90.6
---r4.7 -16.4 -20.3 -24 8 -30 * 4 -37 .a -42.3 -48.3 -57.5 4 4 . 5 Solid -72.9
258.4 256.7 252.8 248.3 242.7 235.3 230.8 224.8 215.6 208.6 200.2
15
-121.
I
-76.0
197. I
I1
--127
.o
647 599 499 400 292 196 I49 IO1
52 30
-81.3 191.8 6 5 3.4 185.7 --87 4 0.2 178.7 -94.4 Equation of curve = Log P = -- 195~.46/T 1.75 log T - 0.01277T 9.4408 "Theoretical Chemistry," 1911,p. 719.
+ +-
- 91.0
- 91 9 - 93 9 - 96.4 - 99.5 -103.7 -106.7 -110.8 -117 2
666
182.5 182. I 181.2 179.2 176.7 173.6 169.4 166.4 162.3 155.9
646 600
500 399 300 200
I49 97 48
152.0
30 146. I 14.3 8 .O 141.8 -131 3 -138.9 134.2 4.2 I .2 -14.4 I 129.0 Equation of clime = Log P = 1.75 log T -- 1096.72/T o,ooogT 4.8665
+
+
+
VAPOR PRESSURES OF SULFUR DIOXIDE AND NITROUS OXIDE.
2693
In Figs. I and 2 are shown the plot of the temperature, oo C. and O Abs. against the pressure, mm. of Hg, and the logarithm of the pressure against
2-
P
CENT. -120
- 100
- 40
-80 -60 TEMPERATUREDEGREFS
-20
-0
Fig. I.-Plot of temperature against pressure.
the reciprocal of the absolute temperature. The straight lines shown were drawn by obtaining an equation from the average of all the results
.om 006
,004
.008 0.8
1.3
1.8 LOG. OF PRE?SURE
2.3
2.8
Fig. 2.-Plot of reciprocal of absolute temperature against log. of pressure.
computed by the method of least squares and drawing the lines according to these equations. For liquid sulfur dioxide the equation is Log P = -1448.01/T 8.425. For solid nitrous oxide LogP = -1232.2/T 9.579.
+
+
G. A. BURREL&
2 694
AND I. W. ROBBRTSON.
The average heats of evaporation over the temperature range studied (calories per gram-molecules) were calculated from the Clausius-Clapeyron cquation 9 = (d In pjRl?/d'l'.
By integrating this equation, one obtains In P = - Q/RT const. The values 1448.01and 1232.2 represent the average of all the determined points on the curve. Using these values in the Clausius-Clapeyron equation and changing from common to natural logarithms, one finds in the case of liquid sulfur dioxide: Q = 1448.01X 4.571 = 6619 calories; for solid nitrous oxide: Q = 1232.2 X 4.571 = 5632 calories. Saturated vapor pressures of nitrous oxide below the normal boiliig point have not been determined by other investigators. For the normal boiling
+
point, Faraday1 found -87.2 ', Cailletet2found - 9 2 ', and Ramsay and The agreement is not good. Our value is Shields3 found -89.8'. -88.7 '. Saturated vapor pressures for sulfur dioxide have been determined by RegnauW from -30' to 65O, and by Pictet6 from -30' to 50'. A comparison of their work with that of the authors of this paper follows : Temperature.
oc.
-10 -1
Pressures (mm.Hg.). Regnault.
Pictet.
740
760
...
I
-15 --2o
608 479
5
372
-2
-30
2 96
578 464 418 2 74
Burrell and Robertson. .
I
.
760 640 508
398 304
Neither Regnault's nor Pictet's work, when plotted, makes a smooth curve. Some of the points are from I ' to 3 ' off the curve. summary. Saturated vapor pressures of sulfur dioxide and nitrous oxide are shown. For sulfur dioxide the vapor pressures range from 760 mm. a t -11.0' to 0.5 mm. at -94.4'. For nitrous oxide the vapor pressures range from 760 mm. a t -88.7 O to I mm. at -144. I '. PITTSBURGH. PA.
2
Phil. T r a m , 135, I, 155 (1845). Arch. de Gcn., 66, 16 (1878). J . Cheni. SCG.,63, 833 (1893). Mem. de I'Acad., 26, 535 (1862). Arch. de Genbe, 13, 2 1 2 (1885).
