Pure silver 

 Silver coin 

 Pure silver 

 Silver coin 

 Pure silver 

 Silver coin 

 Pure silver 

 Silver coin 

 Pure silver 

 Silver coin 

 Pure silver 



436 Dr. Waller's Experiments on Coloured Films. 



was exposed to iodine with a piece of pure silver; as the 

 former was so much the harder of the two, it was naturally 

 supposed that the chemical action would be slower in exerting 

 itself on it than on the latter. This, however, was not the 

 case, as may be seen by the following statement of the result 

 of the experiment : — 



Silver coin . . . pale gold colour, 

 pale gold, 

 deep gold, 

 deep gold, 

 light blue, 

 light blue, 

 yellow. 



blue, white, yellow not visible, 

 yellow, red at edges, 

 yellow, no red edges, 

 red, blue at edges, 

 yellow, no red apparent. 

 The intensity of the resistance offered by the different films 

 of iodide of silver to a continuation of the chemical combina- 

 tion, may be determined by noting the moment at which the 

 various spectral tints make their appearance. 



Colour of the film of iodide of silver. 

 . . beginning to darken. 

 . . pale gold. 

 . . deep gold. 

 . . orange blue. 

 . . blue. 

 . . light blue. 



. . commencement of yellow. 

 . . orange red. 

 . . blue. 

 . . deep blue. 

 . . green. 

 . . yellowish green. 

 . . ruddy brown. 

 . . green. 

 . . green. 

 . . red. 

 . . green. 



By comparing the thickness of the colours with the space 

 of time required for their production, it will be found, how- 

 ever imperfect the table given by Newton may be when ap- 

 plied to this subject, that towards the end of the experiment 

 above given, the chemical combination is retarded by the pre- 

 sence of the inert film, and that to obtain the same thickness 



