AND OF PLANTS UPON THE ATMOSPHERE. 
173 
In the following experiments a succession of different plants were introduced at 
intervals of from four to twelve hours, into ajar containing about 240 cubic inches of 
common air, together with generally about ten cubic inches of carbonic acid. The 
following Table will show the increase of oxygen caused. 
Experiment 16 . 
Oxygen. 
Date. 
Circumstances of the experiment. 
Proportion 
Calculated 
per cent. 
cubic inches. 
May 23. 
Before any plant was introduced 
21 
50 
After a pot of Sinapis alba had continued in contact with the air during 
six hours of bright sunshine 
25 
60 
After a pot containing Hydrangea hortensis, only in leaf, had continued 
in contact with the air during twelve hours of bright sunshine .... 
26-5 
63-5 
May 24. 
After a pot, containing a Crassula lactea, had continued in contact with 
the air during four hours of bright sunshine 
32-75 
77 
After a pot of Lepidium sativum had continued in contact with the air 
during four hours of bright sunshine 
33-5 
80-5 
May 25. 
After a pot containing a Geranium (Pelargonium) had continued in con- 
tact with the air during four hours’ bright sunshine 
36-5 
87-0 
After the same Hydrangea as before had continued in contact with the 
air during five hours’ bright sunshine 
33-25 
80-0 
May 27. 
After a Geranium had continued in contact with the air during five 
hours’ bright sunshine 
37-0 
88-0 
After a healthy Myrtle had continued in contact with the air during 
four hours’ bright sun 
39-0 
93 
May 28. 
After a young but apparently healthy plant of the Sweet Pea ( Lathyrus 
odoratus ) had continued in contact with the air for four hours .... 
33 
78-5 
May 30. 
After a Geranium had continued in contact with the air for five hours 
36-5 
87-0 
Observations. — Here, owing to an accident, the experiment was suspended ; but it was carried far enough 
to show how much oxygen may be added to the air during the day by plants in a healthy condition. The 
increase was progressive until I employed the same plant a second time : it probably had suffered from its 
previous confinement, or from being passed backwards and forwards through the water of the pneumatic 
trough on which the jar rested. The only other plant which diminished the amount of oxygen was the 
Sweet Pea ; all the others added somewhat to its quantity. 
Experiment 17- 
Capacity of jar 620 cubic inches (600 atmospheric air, 20 carbonic acid). 
August 7 . 
Before any plant was introduced 
21 
126 
6 p. m. After a Geranium had continued in contact with the air during 
five hours’ strong sun - 
23 
138 
August 8. 
10 a.m. After a second Geranium had remained in contact with the 
air during the previous night and morning 
22 
132 
5 p. m. After a Myrtle had been in contact with the air during the pe- 
riod since the previous experiment made 
24-5 
147 
August 9. 
11 a. m. After a second Myrtle had continued in contact with the air 
ever since the last experiment 
26 
156 
5 p. m. A common garden Lettuce growing in a pot, having continued 
in contact with the air since the last experiment : day fine 
29 
174 
August 10. 
11 a.m. A second Lettuce, having continued in contact with the air 
since the preceding experiment : day wet 
30 
180 
5 p.m. After a Geranium had been introduced since the preceding ex- 
periment : day wet 
35 
210 
August 1 1 . 
11a. m. After a second Geranium had continued in contact with the 
air during the interval since the last experiment 
28 
168 
Finding a temporary difficulty in procuring healthy plants, I here 
suspended the experiments. 
Observations. — This latter series of experiments was undertaken in order to show, that even when the 
plants were confined in the air of the jar, by night, as well as by day, the balance was still greatly in favour 
of their purifying influence. 
