82 Prof. Draper's Experiments on the Light 



Bichromate of potassa. 



Chromate of potassa. 



Yellow hydrosulphuret of ammonia. 



Hydrosulphuret of lime. 



Muriate of iron. 



Chloride of gold. 



Chloride of platinum. 

 It is to be remarked, that every one of these solutions is 

 yellow^ but I also found that a great many vegetable coloured 

 infuuons would in like manner absorb the chemical rays, 

 especially those which have 2iyello*w tint, 



2. When I exposed pieces of paper covered with a layer 

 of chloride of silver, to a beam which had passed through the 

 red sulpho-cyanate of iron, the paper became of a brick-red 

 colour; if to a beam which had passed through a solution of 

 sulphate of copper and ammonia, it became of a blue brown; 

 and lastly, on exposing a piece in a box which I shall pre- 

 sently mention, for five days, to light which had been acted 

 on by bichromate of potassa, it became perceptibly of a faint 

 yellowish green. 



3. It is very probable, that there exist in the sunlight, rays 

 having particular chemical powers. 



A beam which has passed through bichromate of potassa, 

 does not appear to cause the union of a mixture of chlorine 

 and hydrogen. I kept such a mixture for several hours in it, 

 and could not perceive any change. 



But this same beam can nevertheless enable vegetable leaves 

 to effect the decomposition of carbonic acid. I took a wooden 

 box, about a cubic foot in dimensions, and having removed 

 its bottom, replaced it with a pair of parallel plates of glass, 

 so adjusted that there was an interstice between them of half 

 an inch or thereabouts. Into the trough thus formed, I poured 

 a solution of bichromate of potassa, or any other salt under 

 trial, and the box being raised on one end, served as a closet 

 in which bodies could be exposed to the action of beams that 

 had passed through any given medium. 



In this little chamber, its trough being filled with a solu- 

 tion of the bichromate, I placed a mattrass containing water 

 slightly impregnated with carbonic acid, and a few vegetable 

 leaves ; after a little while, air bubbles were copiously given 

 off; there had been placed, similarly in all respects, another 

 mattrass in the direet rays of the sun, and when a quantity 

 of gas sufficient for analysis was evolved, it was found that 

 carbonic acid had in both cases been decomposed, though, 

 as might have been expected, in the latter more energetically. 

 The result gave a mixture of carbonic acid, oxygen, and ni- 



