Mr. Hunt on Actino-Chemistry. 279 



error considerably ; and the result was, in several experiments, 

 that the actinized oxide lost in weight exactly (or very nearly) 

 the weight of the oxygen of the oxide employed. 



12. Several trials were made to ascertain if the films of 

 oxide of silver on the glass plates lost weight upon darken- 

 ing; but, although some evidence was obtained that they did 

 so, it must be admitted that it was not at all satisfactorily 

 proved to be the case by this means. The films seldom ex- 

 ceeded a grain in weight, and the pieces of glass upon which 

 they were spread generally weighed 200 grains; it will 

 therefore be easily conceived how difficult a thing it was after 

 an exposure of some hours to sunshine, and under all the va- 

 rying conditions of temperature and atmospheric moisture, 

 to decide with anything like accuracy the loss by weight of 

 oxygen of the oxide employed ; the more so as evidence was 

 obtained to show that the finely divided metal had the pro- 

 perty of condensing water within its pores with some rapidity. 

 I cannot refrain from venturing to express my opinion, that 

 the silver reduced by actinic power is different in many re- 

 spects from silver brought to an equally fine state of division 

 by mechanical means. 



13. The oxide of silver, as is well known, is soluble in am- 

 monia ; by exposing such a solution to the action of the at- 

 mosphere, a pellicle forms upon its surface, which Faraday 

 considers a peculiar oxide. If this solution is spread over 

 paper and dried, I believe a similar oxide of silver is formed. 

 This paper darkens by exposure to light with some rapidity, 

 as does also the film formed on the surface of the ammonia. 

 After darkening, it will be found that the darkened parts are 

 no longer soluble in ammonia, or in diluted nitric acid, but 

 that moderately strong nitric acid dissolves it with the forma- 

 tion of nitrous acid vapours. In this case, consequently, we 

 may conclude that the oxide is reduced t^^lJiCj metallic state 

 at once by the action of the sun's rays. = 



14. Perfectly pure silver, as is well known, does not com- 

 bine with oxygen by exposure to the air ; but silver reduced 

 as above by solar action, becomes oxidized by exposure, and 

 after a short, Mwe ammonia will disspjLv^.o^^a.cppsiderable 



portion. rri'! off .("♦a <;';r>':*if! 1>'«('_' 



ji, ,;,i, Nitrate of Silver, 



f^ lis. Nitrate of silver does not change by the action of light, 

 unless organic matter is present, for which it is so delicate a 

 test, that Dr. John Davy recommended it as the most useful 

 for ascertaining the presence of minute quantities in a solu- 

 tion. It has been stated that the " nitric acid appears to be the 

 agent which destroys the animal texture, and the black stain 



