Chemical Properties attributed to Light. 79 



The heat which existed at that distance from the 

 flame, on the side of it where this coloured stripe was 

 produced, was sufficiently intense, as I found by exper- 

 iment, to melt very fine silver wire, flatted, such as is 

 used in making silver lace. 



The objects I had in view in the following experi- 

 ments will be too evident to require any particular 

 explanation : — 



Experiment No. 5. — Two Hke pieces of ribbon were 

 wetted at the same time in the solution, and suspended 

 while wet in two thin phials, A and B, of very trans- 

 parent and colourless glass, the mouths of the phials 

 being left open. Both these phials were placed in a 

 window which fronted the south ; that distinguished 

 by the letter A being exposed naked to the direct rays 

 of a bright sun, while B was enclosed in a cylinder of 

 pasteboard, painted black within and without, and 

 closed with a fit cover, and consequently remained 

 in perfect darkness. 



In a few minutes, the ribbon in the phial A began 

 sensibly to change its colour, and to take a purple hue ; 

 and at the end of five hours it had acquired a deep 

 crimson tint throughout. 



The phial B was exposed in the window, in its dark 

 cylindrical cover, three days; but there was not the 

 smallest appearance of any change of colour in the 

 silk. 



Experiment No. 6. — Two small parcels of magnesia 

 alba, in an impalpable powder (about half as much in 

 each as could be made to lie on a shilling), were placed 

 in heaps in two china plates, A and B, and thoroughly 

 moistened with the before-mentioned aqueous solution 

 of the oxide of gold. Both plates were placed in the 



