34 Mr. Hunt on Actino-Chemistry. 



iodide of silver formed in the other, which blackens as quickly 

 as it is formed. 



" Place a similar arrangement to the above (31.) in the 

 dark, iodine is slowly liberated. No iodide of silver formed^ 

 but around the 'wire a beautiful crystallization of' metallic silver. 



** A piece of plalina wire was sealed into two glass tubes ; 

 these when filled, the one with hydriodate of potash in solu- 

 tion, and the other with a solution of the nitrate of silver, were 

 reversed into two watch-glasses containing the same solutions, 

 the glasses being connected by a piece of cotton. A few hours 

 of daylight occasioned the hydriodic solution in the tube to 

 become quite brown with liberated iodine; a small portion of 

 iodide of silver was formed along the cotton, and at the end 

 dipping in the salt of silver. During the night the hydriodic 

 liquid became again colourless and transparent, and the dark 

 salt along the cotton became yellov) as at firsts 



I have resumed this inquiry under modified conditions, 

 but the results have been invariably of a similar character to 

 the above. I shall for the present merely describe two sets 

 of experiments, from which 1 draw these conclusions: — 



1st. That electro-metallic precipitation is prevented by the 

 influence of the sun's rays. 



2nd. That light is not the retarding agent, but that the 

 exercise of electrical force is negatived by the direct influence 

 of actinism. 



I placed in a test-tube a strong solution of nitrate of silver; 

 in another tube, being closed at one end with a thin piece of 

 bladder, I placed a solution of iodide of potassium ; this was 

 supported in the solution of nitrate of silver by being fixed in 

 a cork, and a piece of platina wire was carried from one solu- 

 tion into the other. An arrangement of this kind was kept in 

 the dark; iodine was liberated in the inner tube, and a cry- 

 stalline arrangement of metallic silver was formed around the 

 platina wire in the outer one. Another was placed in the 

 sunshine; iodine was liberated in the dark, but no silver was 

 deposited. 



Having exposed the above solution to the sunshine of July 

 during a long day, the tube was placed in a dark cupboard, 

 but the actinic influence which had been exerted on the solu^ 

 tion of silver had produced a permanent change in its condi- 

 tion ; after several days no trace of any metallic deposit could 

 be detected, but the whole of the iodine again entered into 

 combination, whereas this was not the case in the unexposed 

 glasses. 



In the inner tube I placed the solution of silver, and in the 

 outer one the hydriodate of potash. One arrangement was 



