Profi Draper on the Chemical Action of Light. 375 



bulb being again exposed to the focus, and kept there for three 

 hours. Howevei', the sun had become less powerful, and clouds 

 were from time to time crossing. A mere trace of gas was col- 

 lected, a little bubble, perhaps not more than j^th of an inch in 

 diameter. 



Considering the intensity of the light in this case, it would 

 seem that bromine cannot effect the decomposition of water. 



Some chloride of silver, recently prepared, and washed from 

 all adhering traces of nitrate, was exposed (June 24, 1848) to 

 the focus of the lens, in a little crucible of platinum foil so in- 

 chned that the rays could come in at its mouth. In this experi- 

 ment the absorbing trough was not used. Although the srm- 

 rays were not brilliant, the chloride at once entered into fusion, 

 forming a reddish-looking liquid : it was kept in that condition 

 all day. When cooled, it proved to be in the state of hornsilver, 

 easily cut by a knife, and having a gray appearance. It should 

 be remarked, that when the rays first fell on it, a fume was dis- 

 engaged, due probably to the escape of the vapour of water, but 

 presently all became quiet. From this we should gather, that 

 chloxide of silver, when perfectly dry, is not decomposable by 

 the rays of the sun, though it is so sensitive at common tempe- 

 ratures when moist. 



Under similar circumstances, protoxide of copper undei*went 

 immediate fusion ; but no further change was effected, though 

 the exposure continued three hoiu's. 



Bichromate of potash, exposed in like manner for two hours 

 and a half, underwent no further change after the first fusion. 

 Tliis substance is, however, kno\Mi to be readily changeable, when 

 a piece of paper which has been soaked in its solution is exposed 

 to the sun. 



Cyanide of mercmy, exposed on a platinum spoon in the inte- 

 rior of a glass globe one inch in diametci", volatilizes and con- 

 denses on the cooler parts of the glass. 



A solution of peroxalate of iron was placed in a matrass about 

 one inch in diameter, and exposed to the focus. The moment 

 the rays fell on it, a violent ebullition occurred from the escape 

 of carbonic acid, and a yellow incrustation was formed on the 

 glass, — a disc of about a quarter of an inch in diameter, corre- 

 sponding to the size of tlie section of the cone. This, by the 

 partial opacity it occasioned, reduced the intense action of the 

 light. By turning the matrass a Httle round, a second spot was 

 formed, and in like manner a third. The liquid was, however, 

 kej»t in constant agitation by the escaping bubbles of gas. After 

 four hours and a half the ex])eriment was closed, but in the result 

 it seemed to differ in no respect from an t;xj)osure to the ordinaiy 

 uncon verged rays. After the liquid had become perfectly colour- 



