192 ANNUAL OF SCIENTIFIC DISCOVERY. 



what was the effect of free contact with the atmosphere upon actinic 

 decompositions, two tubes containing solution of permanganate, the 

 one sealed, the other open, were fixed in phials of the ammonio-sul- 

 phate of copper, and cemented to the necks so as to prevent the 

 escape of ammoniacal fumes. In about eight hours the solution in the 

 sealed tube had become colorless, whilst the other retained a deep red 

 tinge. Peroxide of mercury exposed to blue light in a sealed tube 

 was much blackened in four days, whilst a similar portion in an open 

 tube was not affected. Periodide of mercury (prepared by tritura- 

 tion) in sealed tubes and dry, gave the following order of action 

 blue, red, white, green, yellow, the action of the two latter rays being 

 hardly perceptible, and possibly due to small portions of blue and red 

 light which had not been absorbed by the solutions. In unsealed ves- 

 sels the action was rather less rapid. Covered with water, the iodide 

 was not affected by any of the rays. This salt is far more stable than 

 is generally asserted. The sample used in these experiments had been 

 kept for ten years in diffused light without any alteration, and even in 

 the blue ray an exposure of several weeks was required to produce 

 any great effect. Periodide obtained by precipitation seemed rather 

 less stable. 



Iodide of starch, perfectly dry, gave the following order : Blue, red, 

 white, yellow, green. The decomposition under the two latter rays 

 was very slow and imperfect. When moist, the iodide was bleached 

 far more rapidly than when dry ; more rapidly also in open than in 

 closed tubes. Perchloride of mercury was acted on as follows : Blue, 

 red, white, green. The yellow ray caused no perceptible formation 

 of protochloride. This substance, under the blue ray, gives false 

 results if not perfectly screened from ammoniacal vapors. Peroxide 

 of mercury gave blue, red, (considerable,) white, green, yellow, (very 

 slight.) Alcoholic tincture of the green coloring matter of leaves 

 was decomposed very rapidly, and almost simultaneously^ in ah 1 the 

 rays ; apparent order, white, red, yellow, green, blue. Alcoholic sul- 

 phocyanide of iron gave white, blue, yellow, green, red. To deter- 

 mine whether the actinic decomposition of solutions was in any way 

 influenced by their degree of concentration, seven sealed phials were 

 placed in white light, each containing 40 parts by measure of concen- 

 trated aqueous solution of perchloride of mercury. To No. 2 had 

 been previously added 20 volumes of distilled water ; No. 3, 40 pts.; 

 No. 4. 80 pts.; No. 5, 120 pts.; No. 6, 160 pts.; No. 7, 330 pts. The 

 decomposition was most rapid in No. 6, then Nos. 5 and 4. The 

 statement that the blue ray deprives salts of their water of crystal- 

 lization, could not be verified with oxalate of ammonia and ferrocyanide 

 of potassium. Weighed portions of these salts, placed respectively 

 under blue, white and gfeen glasses, were found at the end of a month 

 to have suffered no change in weight. It has been observed by Hunt, 

 that a solution of bichromate of potash gives a greenish yellow precip- 

 itate with sulphate of copper in the sunshine. This was found to take 

 place almost equally in all the rays, whether in sealed or open vessels, 



