Journal of the Chemical Society 1888. [antikvár]

JOURNALofTHE CHEMICAL SOCIETY.ABSTRACTS OF CHEMICAL PAPERS PUBLISHED IN BRITISH AND FOREIGN JOURNALS.General and Physical Chemistry.Absorption-spectra of the Rare Earths. By G. H. Batlet (Ber., 20, 27692770).Kriiss and Nilson have recently published (Abstr., 1887, 890) the results of experiments on the absorption-spectra of solutions of certain minerals containing the rare earths; a comparison of various intensities of the absorption-bands observed, induces them to believe in the existence of some 20 new elements. It is here pointed out, firstly, that it is exceedingly difficult to judge the relative intensities of absorption-spectra ; and, secondly, that it is impossible to compare, for example, solutions which contain little or no erbium or samarium with those which contain salts of these metals in greater quantity. Thirdly, no consideration is given to the influence of the solvent on the intensity of the absorption-band. On these grounds, the author considers that the evidence brought forward is insufficient to prove the existence of these new elements.V. H. V.Action of Light and Reducing Agents on Silver Salts : Formation of Photo-salts. By M. C. Lea (Amer, J. 8ci., 33, 349 364, 480488, 489494; and 34, 3336).It is possible to obtain compounds of silver with chlorine, bromine, and iodine which show varied and beautiful colours, are highly stable except when exposed to light, and can be formed by chemical methods in entire absence of light. These compounds are identical with the substances forming the invisible or latent photographic image, and many of them show a tendency to reproduce colours. The author proposes to call these compounds photo-salts, a name which recalls one of their modes of origin without involving any statement as to their chemical nature. They are formed from the normal salts by the action of reducing agents, and contain a lower proportion of the halogen than the normal salts, but their high stability indicates that they are not sub-salts, and do not contain any vol. Liv.hIi I2ABSTRACTS OF CHEMICAL PAPERS.free sab-salt. It is most probable that they are compounds of tlie sub-salts with large proportions of the normal salts, and are aualogong in constitution to the " lakes " formed by colouring matters. Their composition varies considerably according to the method of prepara-tion.Silver Photochloride.Compounds of silver with chlorine can be obtained with various shades of colour, ranging from white through flesh-colour, pale-pink, rose, copper-red, reddish-purple, and chocolate, to black.Finely divided metallic silver, obtained by reduction in the wet way, treated for several hours with successive portions of a strong solution of sodium hypochlorite, yields a product which is purple-black, and sometimes even black. If the action is complete, nitric acid of sp. gr. 1'36 removes no silver, the substance, therefore, contains no metallic silver and no subehloride, as the latter would be at once decomposed. Subehloride is at first formed, but is converted into the normal chloride, which at once combines with other subehloride, forming a photo-salt, and thus removing the subehloride from tlie sphere of action. This process continues until the whole of the silver is converted into a compound of silver subehloride with the normal chloride. Prolonged action of the hypochlorite beyond this point gradually reduces the amount of sub-salt present.Strong nitric acid destroys all varieties of the photochloride, hut the degree of resistance to its action varies widely, and is sometimes very considerable, a fact which is the more remarkable since freshly precipitated subehloride is at once decomposed even by dilute nitric acidWhen protected from light, the photochloride prepared by the above method remains unaltered, even after 18 months. It is far more slowly attacked by ammonia than the normal chloride, several hours being required for complete solution even with a large excess of ammonia. Eventually only metallic silver soluble in nitric acid remains. If the ammonia is poured off shortly before this point is reached, and the undissolved portion is treated with nitric acid, a black residue is left, consisting of metallic silver mixed with a very dark variety of the chloride. This dark variety is insoluble in any acid, and has been mistaken for a passive modification of metallic silver. Some preparations of this dark chloride contained 2'49 per cent, of subehloride, and 97'51 per cent, of the normal chloride.If a solution of normal silver chloride in ammonia is added to a solution of ferrous sulphate, allowed to remain for one minute, and then mixed with dilute sulphuric acid until strongly acid, the product well washed, boiled with dilute nitric acid, again washed, treated with hydrochloric acid, and finally washed, a brilliant red photochloride is obtained, its colour resembling that of electrolytic copper. The beauty of the preparation depends on the complete removal of metallic silver and of iron compounds. Any silver salt, for instance, the phosphate, will give a similar result.Silver oxide is heated for a long time at 100°, or is roasted until the colour changes from brown to black, care being taken to avoid absorption of carbonic anhydride, and it is then treated with hydrochloric