202 EXPERIMENTS MADE IN VIRGINIA. [MEMOIR XIII. 



Bichromate of potassa, 



Chromate of potassa, 



Yellow hydrosulphide of ammonia, 



Hydrosulphide of lime, 



Chloride of iron, 



Chloride of gold, 



Chloride of platinum. 



It is to be remarked that all these solutions are yel- 

 low. I also found that a great many vegetable colored 

 infusions, especially those which had a yellow tint, would 

 in like manner absorb the chemical -rays. 



When pieces of paper covered with chloride or bro- 

 mide of silver were exposed to a beam which had passed 

 through a solution of red sulpho- cyanide of iron, the 

 paper became of a brick-red color ; if to a beam which 

 had passed through a solution of ammonia- sulphate of 

 copper, it became of a blue-brown ; and on exposing a 

 piece for five days to light acted on by bichromate of 

 potassa, it became perceptibly of a faint yellowish green. 



A -beam which has passed through bichromate of po- 

 tassa does not 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. 



Hitter asserted that the opposite extremities of the 

 spectrum possess opposite powers of chemical action : he 

 states that phosphorus will emit fumes in the red ray, 

 but if the violet be thrown on it, it ceases to smoke. 

 This experiment I repeated often, and under favorable 

 circumstances, but could not make it succeed. 



I could succeed, however, in showing very beautifully 

 the interference of that class of chemical rays which 

 'blacken chloride and bromide of silver, but failed for 

 want of proper apparatus in trying to produce their 

 polarization. An electric current circulating in a wire 

 does not seem to have any influence on these chemical 

 rays. I found that the same neat magnified image of 

 the wire was obtained on chloride paper when it was 



