chemical Properties attributed to Light. 
and one that is little disposed to form a chemical union with 
oxygen, ( magnesia alba,) when, being immersed in an aqueous 
solution of the oxide of gold, the rays of the sun were made 
to impinge on it, I contrived the following experiment. 
Experiment No. 16. I took four small thin phials, A, B, C, 
and D, of very fine glass, and, putting into each of them about 
five grains of dry magnesia alba, I filled the phial A, nearly full, 
with a saturated aqueous solution of the oxide of gold. 
I filled the phial B, in like manner, with some of the same 
solution, diluted with an equal quantity of distilled water ; and 
the phials C and D were filled with the solution still farther 
diluted. 
These phials, open or without stoppers, were exposed one 
whole day to the action of the direct rays of a bright sun, their 
contents being often well mixed together, during that time, by 
shaking. 
The contents of all these phials changed colour, more or less, 
but they acquired very different hues. The contents of the 
phial A became of a very deep rich gold colour, approaching to 
orange, the earthy sediment being throughout of the same tint. 
The contents of the phial B, which were at first of a light 
straw colour, first changed to a light green, and then to a 
greenish blue. The phial having been suffered to stand quiet 
several days, in an uninhabited room, in a retired part of the 
house, the solution became nearly colourless, and the sediment 
was found to be of a dirty olive colour. 
The colour of the contents of the phials C and D was changed 
nearly in the same manner; and, having been suffered to stand 
quiet two or three days, to settle, the solution was found to be 
quite colourless, and the sediment to be deeply coloured. There 
3 O 2 
* 
