Chemical Properties attributed to Light. 93 



alcohol be made to rest on the surface of the aqueous 

 solution, without mixing with it. 



I wished to have been able to collect and examine 

 the elastic fluids which probably were formed in most 

 of the preceding experiments ; but my time was so 

 much taken up with other matters that I had not leis- 

 ure to pursue these investigations farther. 



In order to see what effects would be produced by 

 the heat generated at the surface of an opaque body, 

 of a nature different from those hitherto used in the 

 reduction of the metallic oxides, and one that is little 

 disposed to form a chemical union with oxygen {mag- 

 nesia alba) when, being immersed in an aqueous solu- 

 tion 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 dis- 

 tilled 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 to- 

 gether 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. 



