490 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
plant were operated upon at the same time. Both were prepared in the shade; an 
then the vessels containing them were each entirely excluded from the light, by means 
of a thick paper covering. In this condition each was attached to a Torricellian ex- 
hauster*. The paper was then removed from one of the vessels so as to expose it, 
with its contents, to the direct rays of the sun; the other vessel, with its enclosed plant, 
remaining covered. The exhaustion of both was then commenced immediately, and the 
action continued for half an hour. 
The following Table shows the results obtained in this manner, in sunlight, and in 
the dark, respectively. 
TasLe IV.—Showing the amount and composition of the gas evolved, during half an 
hour, into a Torricellian vacuum, by duplicate quantities of plant, both kept in the 
dark for some time before commencing the exhaustion, then one exposed to sun- 
light, and the other kept in the dark, during the process. 
(1858.) 
Per cent. 
Date. |Description] Conditions during || Total Gas «, lOxvoenand 
of Plant. Exhaustion. collected. Nitrogen. | Oxygen. ia <tc aes 
‘ acid. 
cub. cents. 
— In dark......... 25°7 66-93 2°33 30°74 33-07 
In sunlight ...]) 36°4 69°78 8°24 21°98 30°22 
In dark......... 28°3 81-63 3°53 14°84 18°37 
duly 22+ |Oats....... In sunlight .../ 25-9 |) 7027 | 1913 | 16-60 || 29-73 
In dark,........ 26-4 73-11 8-33 18°56 26°89 
July 23. \Oats .... In sunlight ...| 227 || 7225 | 16-74 | 11-01 || 27-75 
In dark......... 274 68-25 5°11 26°64 31°75 
- July 28. |Oats...... In sunlight ...| 29-2 || 67-47 | 19°86 | 12-67 || 3253 
In dark......... 31:4 77°39 6-69 15-92 22°61 
July 23. |Oats...... In sunlight ...|| 21-7 || 76:50 | 1659 | 6-91 || 23:50 
The amounts of carbonic acid and oxygen recorded in the Table, indicate very clearly 
the ready transformation of the one into the other—or, rather, the transformation of 
carbonic acid into a solid carbon compound, and free oxygen. In reference to the 
question we are considering, these results have a high importance, as showing the great 
reducing-force manifested under the influence of the sun’s rays, by which the carbonic 
acid is so suddenly reduced. 
* This term, for convenience, we apply to the apparatus which has been described at p. 487, by which the 
plant in the vessel, fig. 7, Plate XII, is exhausted. 
