292 Capt. Abney on the Acceleration of Oxidation, Sfc. [Apr. 11, 



and exposed to diffused light. It was then submitted to the action of 

 the solar spectrum, while immersed in a solution of potassium perman- 

 ganate, or hydroxyl. When the strength of the permanganate, or 

 hydroxyl, was correct a reversed image of the least refrangible end of 

 the spectrum was obtained, an increase in oxidation taking place when 

 the red rays acted, the reversal taking place somewhere near D, extend- 

 ing into the ultra-red. 



The accelerating effect of the red rays is most marked when the 

 solution of permanganate or hydroxyl is weak ; but there is a limit to 

 the dilution, caused by the fact that silver bromide is sensitive as far 

 as the line a, and there must be sufficient strength to oxidise the 

 invisible image as it is formed, besides gradually destroying the effect 

 of the preliminary exposure. With silver iodide this is not the case, 

 the reversed action is much more readily obtained. The strength of 

 hydroxyl solution I employed I cannot state. That of permanganate 

 was as follows : — 



1 grain of potassium permanganate was dissolved in 200 oz. of 

 water. 



When the dilution was doubled the reducing action of the red rays on 

 the bromide film was greater than its power of oxidation. A collimator 

 18 inches long, a prism of 2-inch side, a slit inch wide, and a camera 

 with lens of 2-feet focus, were employed for throwing the spectrum on 

 the plate. The exposure was five minutes, sunlight feeble ; preliminary 

 exposure four seconds in the diffused light of my laboratory. A speci- 

 men accompanies this paper. Some interesting experiments in an 

 atmosphere free from oxygen are being undertaken. 



(Addendum.) Received April 5, 1878. 



Since making my communication, which was received by the Royal 

 Society on the 16th March last, I have employed films which were sen- 

 sitive to the reducing action of the red rays to a wave-length of about 

 10,000 tenth-metres, and by modifying the strength of the oxidizing 

 solution, the acceleration of oxidation by the red rays and ultra-red 

 rays has been more strongly confirmed. The oxidation on all the films 

 is effected by potassium bichromate, nitric acid, and ozone, in addition 

 to the agents I have already given. 



Had not the sensitive film employed been capable of being reduced 

 by the action of the red rays and ultra-red rays, the proof of the 

 acceleration of oxidation by the same rays might perhaps have been 

 open to dispute. 



