AND OF PLANTS UPON THE ATMOSPHERE. 
157 
Sixth series, with sprigs of Mentha viridis immersed in water of the temperature 
of 74° Fahr. 
Media through which the light 
was transmitted. 
State of 
the 
weather. 
Proportion between 
the whole quantity 
of gas obtained in 
the two jars. 
Proportion per sent, 
between the oxygen 
and nitrogen in the 
two jars. 
Proportion be- 
tween the oxy- 
gen in the two 
jars. 
Proportion be- 
tween the nitro- 
gen in the two 
jars. 
Jar 1. 
Transparent glass .... 
Cloudless 
100 
O. 59 
N. 41 
100 
100 
Jar 2. 
No. 5. (Orange) 
sky. 
70 
O. 37 
N. 63 
44 
108 
Jar 3. 
No. 2. (Blue) 
Thermo- 
22-5 
O. 8 
N. 92 
30 
50-5 
Jar 4. 
No. 6. (Bottle with cop- 1 
per solution) . ... j 
meter 
80°. 
20-0 
0. 4 
N. 96 
13-5 
47-0 
Jar 1. 
Transparent glass .... 
100 
0. 47 
N. 53 
100 
100 
Jar 2. 
No. 1. (Green) 
Ditto. 
20 
0. 7 
N. 93 
3 
34 
Jar 3. 
No. 3. (Purple) 
20 
0. 0 
N. 100 
0 
40 
Jar 4. 
No. 4. (Red) 
30 
0. 12 
N. 88 
7-7 
49 
Similar experiments made upon leaves of Rheum Rhaponticum, of Allium ursinum, 
and of various species of Meadow-grass, corroborated the same conclusions ; as like- 
wise did some on plants confined in atmospheric air, containing about six per cent, of 
carbonic acid, and exposed to these several media. 
In the above experiments the proportion of oxygen was ascertained, by heating the air 
in a bent graduated tube with phosphorus, and observing the diminution of capacity 
thereby occasioned ; two per cent, being allowed for the expansion caused in nitro- 
gen by phosphorous vapour. This method, which I have always found to give very 
uniform results, I adopted in preference to that of exploding the gas with hydrogen, 
as being less troublesome and more expeditious, in a climate so damp as ours, than a 
process requiring the aid of electricity. 
The constant presence of more or less nitrogen in the air emitted by the plant, is a 
circumstance which, although often before observed, deserves, nevertheless, here to 
be briefly adverted to. 
Its quantity appeared to be relatively smaller in proportion to the intensity of the 
solar influence, being always least under transparent glass ; and where the light trans- 
mitted was not energetic enough to cause any emission of oxygen at all, still some 
portion of nitrogen would frequently be given out. Perhaps this circumstance may 
admit of explanation, by considering the emission of gas from leaves, when exposed to 
light under water, as derived from two sources ; the first, the disengagement of a 
portion of atmospheric air which it had previously absorbed, and whose place within 
the tissue of the plant is probably supplied, either by the water with which it is sur- 
rounded, or by the carbonic acid with which this water is impregnated ; the latter, 
the emission of pure oxygen, derived from a decomposition of the carbonic acid in 
contact with it. 
Hence in Experiment 1. with cabbage-leaves, where we obtained 100 parts of a gas 
consisting of oxygen 44, and nitrogen 56 parts, we may suppose that the leaves had 
emitted, 
