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In another experiment, made to determine how far the total amount of chlorine evolved from silver chloride during exposure was influenced by the presence of hydrochloric acid, the following results were obtained. A comparative experiment was made with silver chloride in pure water:— solution, yet the total chlorine set free—and, therefore, the amountof decomposition of the silver salt—is decreased. In order, then, to obtain the maximum amount of surface decomposition of silver chloride, it is necessary that the volume of water present should be relatively large, and that the solution of acid formed should be often replaced by pure water during the exposure. The explanation of the retarding influence of haloid salts and of oxidising agents on the darkening of silver chloride appears to be found in a study of the action of these substances on solutions of chlorine-water under the influence of light. The condition of the free chlorine in the solution is one of some interest, and was next studied. The examination of the liquid for oxy-acids of chlorine was, however, hampered by the fact that a part of the oxygen liberated was present as ozone, the smell of this substance being distinctly recognised, especially during the first periods of exposure of silver chloride, when large quantities of water were present. To further prove the presence of this substance, air was drawn through water containing silver chloride in suspension during exposure to sunlight, and was then passed through two bulbs containing solutions of silver nitrate, and finally into a solution of potassium iodide which was protected from the light; the liquid in the first bulb became milky, that in the second remained perfectly clear, whilst iodine was set free in the solution of potassium iodide. No hydrogen peroxide was detected verted into hydrochloric acid, but as the strength of acid increases its rate of formation diminishes. Free chlorine, therefore, accumulates in the solution until (the intensity of light remaining constant) a maximum is reached, at which stage further decomposition of silver chloride is balanced by recombination of chlorine with the darkened product. The formation of free chlorine is still more marked where silver chloride is exposed under a solution of hydrochloric acid in the first instance, as is shown by the following experiment, in which equal quantities of silver chloride were exposed to light in solutions of hydro chloric acid of varying strengths. After an exposure of seven days (April 20 —27) the free chlorine and oxygen liberated were determined. During exposure it was observed that the liquid in the tubes containing acid was of a distinctly green tint (especially when seen through in the liquid containing silver chloride during any period of exposure. The observations of Popper (Annalen, 227, 161) and of Pedler (Trans., 1890, 57, 613) show that hypochlorous and other oxy-acids of chlorine are formed during the decomposition of solutions of chlorine-water by light, and it seemed probable that a part of the chlorine evolved by the decomposition of silver chloride by light should, in presence of water, form similar products, and statements to this effect have repeatedly been made (B. A. lieport, 1859,107). An experiment was, therefore, made in which silver chloride, in contact with a small quantity of water (20 c.c.), was exposed to bright sunlight for six hours. The liquid was then tested for hypochlorous acid by agitation with mercury, and subsequent treatment with hydrochloric acid, as suggested by Wolters (J. pr. Chern., 74, 68). The formation of hypochlorous acid was noted the entire length of the tube), the chlorine liberated from the silver salt remaining in solution in the water. In the night, however, rechlorination of the darkened silver com pound had occurred to such an extent .that the colour had almost entirely disappeared from the solution. The estimation of the free chlorine was therefore made imme diately after exposure to bright sunshine, and again after the liquid had been left in contact with the darkened pro duct for fourteen hours in the dark. The results obtained are given in the following table :— Table III. by the fact that mercury was present in the solution. Although this test could not be applied quantitatively in the presence of ozone, yet the comparatively large quan tity of mercury in the solution could only be ascribed to the presence of hypochlorous or similar acids in the liquid, together with free chlorine. It was noticed, however, that a strong solution of hypochlorous acid was decom posed by contact with normal silver chloride, even in the dark, a green gas containing free oxygen and chlorine being evolved; the silver chloride appeared to be unaltered. How far dilute solutions of the acid are decomposed is yet to be determined. {To be continued). 1. HC1 added per 100 c.c. solution. 2. c.c. O set free. 3. Free Cl found. 4. Free Cl found after 14 hours in the dark. 4-0 minute bubble 0-042 0-014 1-97 0-5 0-035 0-019 0-38 1-9 0-024 0-003 0-19 1'7 0-007 0-0008 0-00 4-2 0 0017 0-0003 Table IV. SCI per 100 pts.! H,0 taken. Total Cl found (— HC1 added). C.mbined Cl found. Free Cl found. Fer cent, free Cl. 0-909 gram 0-201 gram 0-173 0-027 13-7 0-0 0-276 ,, 0-273 0-002 0-94 Here it is seen that, although the presence of hydro chloric acid increases the amount of free chlorine in the We clip the following note regarding Mr Robinson’s pictures at the recent Buffalo Convention from The Express (New York):—“ Strolling about the gallery, one is attracted by many handsome pictures. Mr. H. P. Robinson, considered the peer of landscape artists with the camera, makes a splendid exhibit, which never tires the eye. Sunlight and shadow are blended so perfectly that it is not difficult for the spectator to imagine himself surrounded by the charms of a summer idyl.”