610 REGNAULT’S HYGROMETRICAL RESEARCHES, 
TaBLeE III.—Tensions of Aqueous Vapour in Nitrogen Gas. 
e ! 5 ! a K | 
enous of/Tensions of, Tensions of|Tensions o 
Tempera- | the vapour the vapour) pjiffer_ _ | the vapour | the vapour + for. 
caren! observed in} calculated eee, Tempers observed in} calculated ee 
Centig. | Ditrogen by the Centig nitrogen by the 
gas. formula. gas. formula. 
° mm mm mm ° mm mm mm 
18°91 15:97 16:26 | —0-29 29°56 30°15 30°77 | —0°62 
18-95 16:03 16:30 | —0:27 29°58 30°16 30°81 | —0-65 
15-90 12:69 13°45 | —0-76 31°88 34:51 35°16 | —0-65 
15°92 12°75 13°47 | —0-72 31:90 34:53 35:21 | —0-68 
20:00 16:78 17:39 | —061 34:30 39°58 40:24 | —0-66 
19-98 16°72 17:37 | —0°65 34:32 39°54 40:28 | —0-74 
21:80 18:71 19-43 | —0°72 37°75 47°67 48°65 | —0-98 
21°79 18°72 19:42 | —0-70 37-77 47-73 48:70 | —0:97 
23°88 21°34 22-03 | —0°69 37-74 47°80 48°63 | —0-83 
23:90 21:33 22:06 | —0°73 39°81 53°63 54:36 | —0°73 
25°44 23°41 24:18 | —0°77 39°81 53°70 54:36 | —0-66 
25:44 23°47 24:18 | —0-71 39°81 53°72 54:36 | —0-64 
26-96 25°63 26:44 | —0°81 31:00 32°68 33°41 | —0°73 
26:97 25°76 26-44 | —0°68 30°99 32°66 33°39 | —0°73 
The first series of experiments was made in air; it is seen by 
Table I. that the tensions of the aqueous vapour in air are con- 
stantly weaker than those which are obtained in vacuo. 
I feared that this circumstance was produced by the absorp- 
tion of a small portion of the oxygen of the air by the mercury, 
experience having shown that, in moist and rather warm air, 
mercury is rapidly oxidized on its surface. To obviate this pre- 
sumed cause of error, I made two other series of experiments, 
filling the balloon with nitrogen, but the results were stil! the 
same, as may be seen in Tables II. and III. 
It would appear to result from this that the tension of the 
aqueous vapour in the air is rather weaker than that which 
exists for the same temperature in vacuo; but the difference is 
very small, and it may perhaps be attributed to a constant error 
in the process. My efforts to determine the cause of such an 
error have led to no result. 
I propose to determine with the greatest care the elastic forces 
of the vapour of «ther im vacuo and in air. As these elastic 
forces are much more considerable at the temperatures of the 
atmosphere than those of aqueous vapour, we may hope to ascer- 
tain more easily whether the tensions are identical or different 
in the two cases. 
Meanwhile we admit, in the calculations which we shall have 
to make of the fractions of saturation of the air, the elastic forces 
inserted’in the table which I have cited, and which gives the 
tensions in vacuo. It will be easy to make subsequently the re- 
