278 M^^-mii^M'MirmmMsi-f^ 



became of a pale brown colour, and was found to hold silver 

 in solution. The dilute nitric acid also dissolved off some 

 oxide from the plate, as was shown by its becoming milky on 

 the addition of muriatic acid. On adding some potash to the 

 ammonia, and dissipating the ammonia by heat, a black pre- 

 cipitate was formed. The precipitate from nitric acid by 

 potash was dark brown. The general characters of this oxide 

 were the same as those of the suboxide of silver examined 

 by M. Wohler. '-? "* ?-y;>yiq odi btin jirij^iy abysa 



8. After havin^'remBVfeJd'asf'mtiich'a'^'ji'bssible from the gla^^ 

 plate by solution in ammonia, there was still a film upon the 

 surface of the glass, which upon drying became nearly black, 

 appearing of a fine olive-green colour when looked through. 

 It was now ascertained that this film conducted an electric 

 current, and on pouring over the plates nitric acid diluted 

 with an equal quantity of water, the films were dissolved off 

 with the formation of nitrous acid fumes. V^'"\ 



9. These results prove to us that the influence of thfef'filleJ* 

 raical rays (actinism) on the protoxide of silver, converts it 

 into a suboxide and into metal. I have not been able by 

 the longest exposure to sunshine to reduce all the suboxide 

 to the state of metal, unless organic matter was present. 



10. Pure protoxide of silver being spread whilst moist upon 

 paper, by means of a camel-hair pencil, and carefully dried, 

 passes in the course of a few hours, if the sun shines strongly, 

 into a perfect black, the whole of which dissolves off' in am- 

 monia. This salt precipitated by potash, the ammonia being 

 dissipated by heat, gave upon reduction the exact formula of 

 Wbhler's oxide (Ag20). 



11. By continuing the exposure of these papers for a few 

 days, their colours were changed from black to an olive. Am- 

 monia dissolved nothing, and diluted nitric acid was equally 

 inactive. In moderately strong nitric acid, however, the 

 paper was almost immediately rendered white with the forma- 

 tion of nitrous acid fumes. Any analytical results from pre- 

 parations on paper are so liable to error, from the inconstant 

 character of the composition of the paper itself, that they are 

 scarcely to be depended upon. But by very carefully drying 

 two weighed pieces of paper until they lost no further weight, 

 and even heating them up to a point but a little below that at 

 which the paper would scorch, placing them both in warm 

 tubes and hermetically sealing them, exposing one to the ac- 

 tinic influence whilst the other was preserved in the dark, 

 opening the tubes under the same circumstances, burning the 

 papers at the same temperature, and weighing the ashes 

 against each other, I succeeded in reducing the sources of 



