26 Waterhouse — Electrical action of Light upon Silver. [No. 1, 



became less sensitive. They were covered with a strong loose deposit 

 of iodide, under which the silver surface was darkened. A faint 

 image of the exposed part was visible. 



Dilute Glacial Acetic Acid. 



With plates freshly immersed in dilute glacial acetic acid of 1 per 

 cent., the plate exposed to sunshine was positive, the deflection being 

 about + 65 divisions, without the magnet ; a second exposure gave a 

 deflection of + 8"3 divisions. By keeping for 24 hours the plates were 

 less sensitive, but remained positive. 



Plates immersed in dilute acid of 5 per cent, and kept 24 hours 

 before exposure were less sensitive than the above, the deflection with 

 sunshine being only + 3 divisions without the magnet, and they became 

 less sensitive by further exposure, but were always positive. 



Dilute Formic Acid. 

 The only other organic acid I have yet tried is formic acid, one per 

 cent, in distilled watei\ After the cell had been standing 24 hours, ex- 

 posure to sunshine gave a deflection amounting to about 8 divisions, the 

 exposed plate being positive. The same plates after another 24 hours 

 standing were found to have become very insensitive, the deflection 

 being only one or two divisions of the scale, the exposed plate still being 

 positive. 



lir. Silver plates in Alkaline Solutions. 

 Becquerel found that when platinum or gold plates were immersed 

 in alkaline solutions, the plate exposed to light was negative. So far 

 as my experience goes, this rale does not hold good with silver, the 

 sign of the exposed plate being almost always positive. I have not 

 tried these solutions very thoroughly, but the results obtained with 

 potash and other salts used seem conclusive. 



Solution of Potassium Hydroxide. 



With a solution of one per cent, of caustic potash in distilled water, 

 the cell having been standing 22 hours, the cell current was nil. 



Exposure to bright sunshine gave a deflection of about 9 - 5 divisions 

 without the magnet, the exposed plate being positive. With the 

 magnet the deflection was about -f 45 divisions in sunshine, and + 9 

 divisions in daylight. With sunshine under blue glass the deflection, 

 with the magnet, was + 31; under green + 9; yellow + 8; red + 

 4-5. There was no deposit on the plates and no image of the exposed 

 parts. 



