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BENEDIKT (R.) and M. CANTOR. Estimation of Glycerol
PLANCHON (V.). Estimation of Glycerol by Oxidation
LEGAL. Acetone in Urine
NEUMANN (G.). Valuation of Crude Sodium Acetate
DENIGÈS (G.). Test for Uric Acid
SCHMID (C.). Determination of Fat in Milk, Cream, &c.
MORSE (H. N.) and W. M. BURTON. Analysis of Butter, Oleomargarine, &c.
MILLAU (E.). Detection of Cotton-seed Oil in Olive Oil
LINDO (D.). Tests for Antifebrin, Antipyrine, and Fahlberg's "Saccharin
OSBORNE (T. B.). Filtering Crude Fibre and Silver Chloride
THE CHEMICAL SOCIETY,
ABSTRACTS OF CHEMICAL PAPERS PUBLISHED IN
General and Physical Chemistry.
Absorption-spectra of the Rare Earths. By G. H. BAILEY (Ber., 20, 2769-2770).-Krüss and Nilson have recently published (Abstr., 1887, 890) the results of experiments on the absorptionspectra 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. Sci., 33, 349 -364, 480-488, 489-494; and 34, 33-36).-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 photosalts, 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
free sub-salt. It is most probable that they are compounds of the sub-salts with large proportions of the normal salts, and are analogous in constitution to the "lakes" formed by colouring matters. Their composition varies considerably according to the method of preparation.
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 purpleblack, 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 subchloride, as the latter would be at once decomposed. Subchloride is at first formed, but is converted into the normal chloride, which at once combines with other subchloride, forming a photo-salt, and thus removing the subchloride from the sphere of action. This process continues until the whole of the silver is converted into a compound of silver subchloride 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, but the degree of resistance to its action varies widely, and is sometimes very considerable, a fact which is the more remarkable since freshly precipitated subchloride is at once decomposed even by dilute nitric acid.
When 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 subchloride, 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
acid; or silver carbonate is roasted until black, and then treated with hydrochloric acid. The product has a pale-pink, copper-red, deep red, or burnt carmine colour, according to circumstances.
Ferrous sulphate mixed with excess of potassium hydroxide, then with a solution of a silver salt, and finally with hydrochloric acid, yields a photochloride, the colour of which depends mainly on the amount of reduction. Manganous oxide behaves similarly, but the reducing action is weaker, and must be assisted by heat. Chromous oxide has still less effect, and with cobaltous oxide, reduction is scarcely perceptible without long-continued heating.
Ferric chloride behaves with metallic silver in much the same way as an alkaline hypochlorite, but is less energetic, one or two days being required for a complete reaction. If the action has taken place in the cold, the product is dark purple-black, and contains from 1.52 to 75 per cent. of silver subchloride. Prolonged contact with ferric chloride eventually converts the photo-salt into the normal chloride, especially on heating.
When freshly precipitated and moist silver subchloride is treated with nitric acid, there is a brisk effervescence with evolution of nitrogen oxides, but when the substance has been converted into a photochloride by the combination of the normal chloride with the unaltered subchloride, the action ceases. The proportion of subchloride varies from 1.96 to 8.62 per cent., and depends mainly on the strength of the acid and the duration of its action. The colour varies from rose to purple, and is always rendered paler by the removal of silver subchloride by prolonged action of nitric acid, although it by no means follows that the darkest varieties contain the highest proportion of subchloride. With sodium hypochlorite, silver subchloride yields a purple photochloride.
Cupric chloride attacks silver in the same way as ferric chloride, and the action is more energetic, but the removal of copper from the product is difficult. In one case the proportion of subchloride in the photo-salts was 6:28 per cent. If a very dilute solution of silver nitrate is added to cuprous chloride, and the bulky, black powder which is formed is boiled with nitric acid, a red photochloride is obtained.
When a solution of silver chloride in ammonia is added to ferrous chloride, and the greyish or olive-black precipitate is washed with dilute sulphuric acid, it becomes brownish-purple, and the colour is still brighter after treatment with nitric acid. One specimen contained 4 26 per cent. of subchloride.
If hydrogen is passed over silver citrate at 100°, and the product is treated with hydrochloric acid and then with nitric acid, it yields a fine purple photochloride, which in one case contained 3·11 per cent. of subchloride.
A very good method is to act on a silver salt with potassium hydroxide and an organic substance such as lactose, dextrose, gum, tannin, alcohol, &c. The time required varies widely, a few minutes being sufficient with lactose, whilst dextrin requires half an hour. The product is mixed with hydrochloric acid, and after washing is boiled with nitric acid. The best result is obtained if the product is