THE SOLUBILITY O F NITROGEN AND ARGON IN SEA WATER1 NORRIS W. RAKESTRAW
AND
VICTOR M. EMMEL
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts Received April SO, 1.998 INTRODUCTION
W e recently described a method for the determination of dissolved nitrogen in sea water (4), in which the air is removed from the water sample in vacuo and the oxygen, nitrogen, and inert gas residue are measured separately. In making such determinations on actual sea water it is often necessary to compare the values obtained with the equilibrium solubility of nitrogen from the atmosphere. The only figures available for such comparison arc those obtained by Fox (2, 3), which have never been seriously questioned. Using these for comparison, however, our analyses consistently indicated an unsaturated condition of water from nearly all sources, with respect to gaseous nitrogen. Believing this to be unlikely, and convinced of the accuracy of our own method, we undertook a redetermination of the solubility of nitrogen in sea water of different teniperatures and chlorine contents, within the range ordinarily encountered. Fox’s method consisted in the measurement of the volume of “atmospheric nitrogen” absorbed by a fixed volume of water from a known total volume of the gas. This requires a correction for the argon content of the “atmospheric nitrogen,” which can probably be made with sufficient accuracy for our purpose, even though the absorption coefficient of argon in sea water is not well known. But in addition to this, considering the use to which these figures are to be put, it would seem preferable to let the water come into complete equilibrium with the actual atmosphere, rather than with nitrogen alone, and to determine the dissolved nitrogen directly, assuming a constant composition of the atmosphere. The results of such a procedure, described below, are slightly lower than those of Fox (corrected for argon), but are more consistent with the nitrogen content which we find in sea water in nature. Examining Fox’s method more closely, we suspected that his systems might have been supersaturated. He saturated the water by vigorous shaking for several minutes, followed by only a short period of standing, until the pressure became constant. We have found that on shaking sea Contribution No. 175 from the Woods Hole Oceanographic Institution. 1211
1212
NORRIS W. RAKESTRA4Ur AKD VICTOR M. EWMEL
TABLE 1 Experimental data EQUILIBRIUJI SOLURILITY AT 760 MJI, ATMOSPHERIC 'RESSURE I N MILLILITER8 PER 1000 ML. OB WATER
~
ME.ASUHED VOLUME CHLORINE CONTENT
grams p e r
kilogram
Xitrogen
'
Residue
1
ml.
"C.
mm.
ml.
' i
~-
Nitrogen
"hrgoa"
i
A
2.11
766,3
1.434
I'
A
7.08 7.08
758.7 758 7
1.262 1.262
A B
12.15 12.15
767.0 767.0
1 160 1 162
1 0 0317 1
0 0312
A B
18.03 18.03
765.5 766.5
1 038 1 041
1 1
0 0289 0 0290
10.33
0.288
25.05 25.05
764.0 764.0
925 0 920
I'
0242 0 0244
9.19
0.240
2.11
767.0
1 394
I 1
l B
16.03
-
____
i
7.08 7.08
758 I7 758.7
12.15 12.15
766 3 766 3
18.03 18.03
768.5 767,7
25 .05 25.05
1 283 1 234
1
1 134 1 134
I
0.0356 0,0346
I
I1 1
'
12 68
,
0 352
11.53
1
0.312
13.81 0 0339 0 0340
12.40
0.341
0 0301 0 0309
11.27
0.303
1.016 1.015
0 0274 0 0272
763.2 762.5
0.903 0.903
0 0237 1 0 0236
2.11
767 .0
1.363
7.08
758.7
7.08
758.7
1.203 1.201
0 0324
12.15 12,15
766.3 766.3
1.103
0 0298
18.03 18.03
764.7 764.7
0.991 0.997
25.05 25.05
762.5 762.5
0.270 ~
'3
oo
0.23G
I
1
0.880 0.886
13 50
1
0 0338
12 o8
0.332
I
10 95
0 296
9 89
0.266
i
81
~
I
0 0226
0 0230
I
0.227
___-
~~
* Sample A was saturated with air a t a temperature above the equilibrium temperature; sample B a t a temperature below.
SOL'C'BILITY OF GASES I N SEA WATER
1213
water with air and allowing to stand until the air bubbles are no longer visible, the nitrogen content is regularly about 2 per cent higher than the equilibrium value at that temperature. It has long been known that the surface water of the sea may be supersaturated with air, from the abnormal solubility of fine bubbles of foam. We are of course in no position to urge that the difference b e h e e n our solubility values and those of Fox is entirely due to this. METHOD
Samples of natural sea water coiltailling approximately 16, 18, and 20 g. of chlorine per kilogram were prepared by dilution from the highest concentration. Duplicate portions, of about 250 ml., were placed in 36
FIG.1 FIG.2 FIG.1. Solubility of nitrogen in sea water of different chlorine contents and temperatures. Solubility is expressed in milliliters of gas (at standard temperature and pressure) per liter of water, in equilibrium with air a t 760 mm. FIG.2. Solubility of "argon" (total inert gas in atmosphere) in sea water of different chlorine contents and temperatures. Solubility is expressed in milliliters of gas (at standard temperature and pressure) per liter of water, in equilibrium with air a t 760 mm. The curve for the solubility in pure water is taken from results of Estreicher (1).
citrate bottles, one of these warmed to about 30°C. and the other cooled to about 8"C., and both shaken for 30 min. to saturate them with air. They were then placed in a thermostat a t 25°C. for 18 hr. to come to equilibrium, open to the air, with occasional but not too vigorous agitation. Both samples were then analyzed for nitrogen. The same was done a t temperatures of 18", 12", 7", and 2"C., the duplicate portions being always saturated a t temperatures above and below the final equilibrium temperature, except in the case of the lowest one, in which this was not possible. It may safely be assumed that complete equilibrium was reached in this latter instance also, in view of the satisfactory agreement of the two samples a t all other temperatures. The data are given in table 1. The barometric pressure is included,
1214
NORRIS W. RAKESTRAW AND VICTOR M. EMIMEl,
from which, in the last column, is calculated the equilibrium solubility in contact with a normal atmosphere of 760 mm. It was thought worth while to measure the residual gab, after removal of carbon dioxide, oxygen, and nitrogen, and to include this as “argon,” TABLE 2 Solubilzty of nitrogen in sea w a t w Expressed in milliliters (at standard temperature and pressure) per liter of water, from a normal atmosphere of 760 mm. CHLORINE CONTENT.. ,.
... . . . .
15
!
16
~
17
TEPPERATURE
8 9 10
11 12 13 14 15 16 17 18 I9 20 21 22 23
24 26
26 27 28
18
-
,
‘9
‘
I
_ _ . _ . _ . . I _ . .
20
-
~
-.
21
____
SOLUBILITY
‘C.
0 1 2 3 4 5 6 7
i
I ml.
15.22 14.81 14.43 14.07 13.73 13.43 13.14 12.88 12.62 12.38 12.15 11.92 11.69 11.47 11.25 11 04 10 83 10 63 10 44 10.26 10.08 9.91 9.75 9.60 9.45 9.30 9.1C 9.02 8.89
_ _ _ _ ~
1
15.02 14.61 14.24 13.89 13.56 13.26 12.98 12.72 12.47 12.23 12.00 11.78 11.56 11.34 11.13 10 92 10 72 10 52 10 33 10.15 9.98 9.82 9.66 9.51 9.36 9.21
-
14.82 14.42 14.06 1 13.72 13.40 1 13.10 12.82 12.56 ’ 12.32 12.08 1 11.86 11.63 11.42 1 11.21 10.99 10 79 10 59 10 40 1 to 21 10.03 9.87 ’ 9.71 9.56 9.41 9.26 9.11 ’
I 1
I
i
I ~
~
1
I 1
, I I
1
14.61 14.23 13.88 13.54 13.24 12.94 12.67 12.41 12.17 11.94 11.71 11.49 11.28 li .07 10.86 10.66 10.47 10.28 10.10 9.92 9.76 9.61 9.46 8.31
9.16 9.02 8.88 8.75 8.62
ml.
14.40 14.04 13.69 13.36 13.06 12.78 12.51 12.26 12.02 11.79 11.56 11.34 11.13 10.93 10 73 10 53 10 34 10 15 1 9 98 9 81 9 65 9 50 9 35 9 20 D 06 8 92 8 79 1 8 66 8 53 __
I
ml.
ml.
14.21 13.85 13.51 13.19 12.89 12.62 12.35 12.10 11.87 11.64 11.42 11.20 10.99 10.79 10 59 10 39 10 21 10 03 9 86 9 69 9 54 9 39 9 24 9 10 8 96 8 82 8 60 8 56 8 44
14.01 13.66 13.33 13.01 12.72 12.42 12.19 11.95 11.71 11.19 11.27 11.06 10.85 10,66 10.45 10.26 10.08 9.91 9.74 9.58 9.43 9.28 9.14 9.00 8.86 8.73 8.60 8.47 8.35
although these figures are of a distinctly lower order of accuracy. This crude fraction of inert gas will therefore be designated as argon, although obviously impure. These figures were obtained by measuring the pressure of the residual gas, when contained in the capillaries between the stopcocks
1215
SOLUBILITY O F GASES IN SEA WATER
1, 2, and 3 in the apparatus, shutting off the reservoir C, ordinarily used during the measurement of the oxygen and nitrogen. Plotting the nitrogen and argon content against chlorine content, at different temperatures, gave a series of straight lines, from which points were taken for the construction of the curves in figures 1 and 2. From these curves tables 2 and 3 have been constructed. TABLE 3
Solubility of “argon” in sea water Expressed in milliliters (at standard temperature and pressure) per liter of water, from a normal atmosphere of 760 mm. CHLORINE CONTENT.. , ,
. . .. . . .
15
’
16
~
17
,
ml.
j
BOLUBILITY
TEXPERATURE
‘C.
ml.
ml.
2 4 6 8 10 12 14 16 18 20 22 24 26 28
0.405 0.384 0.365 0.347 0.331 0.317 0.304 0.292 0.282 0.272 0.262 0.253 0.244 0.235
0.400 0.379 0.360 0.343 0.327 0.313 0.300 0.288 0.278 0.268 0.258 0.249 0.240 0.231
ml.
0.395 0 389 0 374 1 0 369 0 355 0 350 0.338 0.333 0.323 0.318 0.309 0.304 0.296 0.292 0,284 0.280 0.274 0.270 0.264 0.260 0,255 0.251 0,246 0.242 0.237 0.233 0.228 0.224 ____ ~
1
ml.
ml.
ml.
0,384 0.363 0.345 0,329 0.314 0.300 0.28’8 0.277 0,267 0.256 0.247 0.238 0.229 0.220
0.379 0.358 0.340 0.324 0.310 0.296 0.284 0.273 0.263 0.253 0.244 0.235 0.226 0.217
0.373 0.352 0.335 0.319 0.305 0.292 0.280 0.269 0.259 0,249 0.240 0.231 0,222 0.213
ItEFERESCES (1) (2) (3) (4)
ESTREICHER, T.: 2. physik. Chem. 31, 176 (1899) Fox, C. J. J . : Publ. de circonstance. Cons. perm. internat. #41 (1907). Fox, C. J. J.: Trans. Faraday Soc. 6, 68 (1909). RAKESTRAW, N. W., AND EMMEL, V. 31.: Ind. Eng. Chem., Anal. Ed. 9, 344 (1937).
