102 Dr Gilby on the Respiration (^Plants. 
of a cubic inch. I then filled them with atmospheric air, 
mixed with a certain proportion of carbonic acid. Having 
stoppered them accurately, I dipped one of them in a glass jar 
filled with a transparent infusion of litmus ; a second in a simi- 
lar vessel of a clear infusion of roses ; and the third was placed 
in a jar of pure water. I then, by quickly turning them, con- 
trived that each jar should stand inverted upon a plate ; and 
thus prepared, I insulated them during four or five hours ; and 
if there was not more than 20 or 25 per cent, of carbonic acid, 
1 always found, that the same change had taken place in each 
phial, namely, that the whole of the carbonic acid, excepting 
2 or 3 parts, had been converted into oxygen. But if the pro- 
portion of carbonic acid was greater, suppose 40 or per cent. 
I invariably found, that there was more oxygen in the litmus 
and pure water phials, than in that immersed in the red tincture. 
I instance the following indifferently, out of very many expe- 
riments that 1 have performed, upon this point. 
I exposed the three jars, with their respective phials, to a full 
.sunshine on the 5th of July. At the beginning of the experi- 
ment, there were in each phial, of Carbonic Acid, 43.00 ; Oxy- 
gen 11.97 ; Nitrogen 45.03 = 100. At the expiration of four 
hours, the analysis gave me % — 
In the Phial belonging to 
the Red Infusion. 
In that in the Litmus 
Infusion. 
In that in the Clear 
Water. 
Carbonic Acid, 1 9.5 
Oxygen, - 29.5 
Nitrogen, » 51.0 
Carbonic Acid, 12.5 
Oxygen, - 36.5 
Nitrogen, 51.0 
Carbonic Acid, 12 
Oxygen, . 37 
Nitrogen, - 51 
100.0 
100.0 
100 
It thus appears, that the red rays are sufficiently powerful to 
decompose the carbonic acid, if the proportion of it be small ; 
but if a larger proportion of it be present, then it is evident that 
more oxygen is elaborated by the violet rays than by those of 
the red colour. 
• In repeating the experiment, but varied, by substituting cabbage leaves, I 
; found that very little change had taken place in the mixed air, which seems to 
prove, that their leaves, on account of the delicacy of their coats, are much more 
^permeable by air. 
