LXXIX.-Sorrle Double Salts with Acetone of Crystal- Lisation and the Crystallisation of Silvei- Iodide, Silver Bromide, and Cuprous Iodide
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View Article Online / Journal Homepage / Table of Contents for this issue MARSH AND RHYMES: SOME DOUBLE SALTS, ETC. 781 Published on 01 January 1913. Downloaded by University of Michigan Library 23/10/2014 01:44:16. LXXIX.-SorrLe Double Salts with Acetone of Crystal- lisation and the Crystallisation of Silvei- Iodide, Silver Bromide, and Cuprous Iodide. By JAMESERNEST MARSH and WILLIAMCLAUDE RHYMES. IN 1910 (T., 97, 2297) some liquid ether compounds of double halogen salts were described, which were chiefly mercury compounds, but silver iodide, cuprous iodide, and lead iodide were found to give liquid compounds with lithium iodide and ether. In the present paper a complete series of crystalline double salts of silver iodide with the alkali-metal iodides is described. These salts are of the type M1,ZAgI. Evidence is also given of the existence of salts of the type MI,SAgI, and of salts containing less than 2AgI. View Article Online 782 MARSH AND RHYMES: SOME DOUBLE SALTS WITH We have also made, but have not completed the examination of, a series of double cuprous iodides. It was found that when the ethereal solution of lithium silver iodide (Zoc. cit., p. 2308) was allowed to evaporate, crystals of silver iodide were deposited, and that these crystals, together with the deliquesced lithium iodide, were soluble in acetone, and crystallised out again on evaporation of the acetone. In a similar way, silver bromide and cuprous iodide have also been obtained in the crystalline state. The salts described in this paper were obtained by crystallisation from acetone, and most of them contain acetone of crystallisation. They lose this acetone with great rapidity on exposure to the air, and either effloresce and crumble to powder or deliquesce. The determination of the acetone of crystallisation thus presented considerable difficulty. The method which was in general adopted is as follows: The double salt with some excess of solvent was con- tained in a Liebig drying tube; a current of dry air was passed through the tube until the excess of solvent was removed; acetone vapour was then passed through the tube until the crystals began to liquefy; then dry air was passed until the crystals were just dry. The method, perhaps, does not lend itself. to extreme accuracy, but it gave fairly consistent results. The lithium, sodium, ammonium, and potassium double silver salts deliquesce in contact with acetone vapour under these conditions; the rubidium and czesium salts do not. Caesiuin Silver Iodide, CsI,2AgI. This is the only salt of the series which does not take up acetone of crystallisation. It is more soluble in cold than in hot solution, differing in this also from the other salts. It is also much the least soluble. It was obtained by dissolving a mixture of caesium and silver iodides in the molecular proportion of 1 to 2 in 20 to Published on 01 January 1913. Downloaded by University of Michigan Library 23/10/2014 01:44:16. 30 times its weight of acetone copled with ice and salt. The solution was filtered from a little sediment, and crystallised by evaporation of the acetone. If the solution is warmed, the salt is precipitated, but not in good crystals. On evaporation the salt separates in long, hair-like crystals, which are colourless and double refracting with straight extinction. They remain colourless up to their melting point at about 210O. The fusion is yellow, and quickly separates a yellow solid, probably silver iodide. The crystals are free from acetone, and are stable in the air. They do not absorb acetone or water vapour, but when placed in water decompose with separation of silver iodide. The crystals lost less than 0.3 per cent. of their weight on heating, and were therefore free from acetone and water. Found, AgI = 63-9. CsI,2AgI requires AgI = 64.4 per cent. View Article Online ACETONE OF CRYSTALLISATION, ETC. 783 Rubidium Silver Iodide, RbI,2AgI,2C3H,0. This salt is obtained when rubidium iodide and silver iodide are dissolved in acetone, and the solution evaporated in dry air. It is extremely soluble in the solvent, and a hot, strong, saturated solution crystallises on cooling. The crystals were obtained in transparent, colourless needles, double refracting, with straight extinction; on exposure to the air they lose their acetone and crumble to powder. The dry salt does not deliquesce, but absorbs water slightly from the air: Found, C,H60 = 14.8. RbI,2AgI,2C3H,O requires C3H60= 14.5 per cent. Found (in dried salt) AgI=68.67. RbI, 2AgI requires AgI = 68.9 per cent. Rubidium iodide does not appear to form a double salt with silver iodide in equal molecular proportions, or, at any rate, the compound RbI,AgI* is not soluble in acetone at the ordinary temperature. Some of the rubidium iodide is left undissolved. More of it, how- ever, is dissolved than corresponds with the formula RbI,2AgI. Since rubidium iodide and silver iodide separately are scarcely at all soluble in acetone, another double salt, containing a larger amount of rubidium iodide, is perhaps indicated possibly 2RbI,3AgI. A salt with excess of silver iodide, of the formula RbI,3AgI, is also indicated, but has not been analysed. It was noticed, when dissolving the salts in the proportion 1: 2, that the silver iodide dissolved before the rubidium iodide, and on addition of another molecular proportion of silver iodide it dissolved when the liquid was cooled. A little below Oo, the whole solution froze to a hard, solid mass. Published on 01 January 1913. Downloaded by University of Michigan Library 23/10/2014 01:44:16. Potassium Silver Iodide, KI,2AgI,2C3H60. The potassium salt was obtained in the same way as the rubidium salt, and gave crystals closely resembling the latter in appearance : Found, C3H60= 16-36. KI,2AgI,2C3H60 requires c3H,o= 15.4 per cent. The result is perhaps as accurate as one could expect from the slight hold the salt has on its acetone of crystallisation: Found (in dried salt), KI = 25.5. KI,2AgI requires KI= 26.1 per cent. The salt on exposure to the air loses its transparency with loss of acetone. The acetone-free salt takes up water from the air * The salt RbIAgI,&H,O has since bcen obtained by crystallisation from a mixture of acetone and water, View Article Online 784 MARSH AND RHYMES: SOME DOUBLE SALTS WITH without deliquescing. Like the rubidium salt, a solution can be obtained in acetone of potassium and silver iodides in the proportion of KI to 3AgI. In a freezing mixture of ice and salt, the solution, if not too diluted, freezes to a solid mass. When warmed, the solution deposits some of the silver iodide in the amorphous form. Potassium and silver iodides dissolve in acetone also in the proportion of KI to AgI. On evaporation of the acetone, crystals are left which deliquesce in moist air, forming a solution from which crystals of silver iodide eventually separate. Potassium silver iodide, KI,2AgI, is soluble in other ketones, such as methyl ethyl ketone, which gives a solution of a deep orange colour. Diethyl ketone also dissolves it, but not quite completely, and possibly some decomposition occurs. The solution in diethyl ketone, like that in acetone, is nearly colourless. Sodium Silver Iodide, NaI,2AgI,3C3H,0. This salt f orms colourless, transparent, needle-shaped crystals, double refracting, with straight extinction. It is extremely soluble in acetone, and on evaporation of the acetone a jelly-like mass is left, in which the crystals gradually form : Found, C,H60 = 21.59. NaI,2AgI,3C3H,0 requires C,H,O = 21.91 per cent. Found (in dried salt), AgI=76.1. NaI,2AgI requires AgI = 75.8 per cent. Sodium and silver iodides dissolve in acetone in equal molecular proportions, but the crystals on evaporation do not appear to be homogeneous. Nor has the phenomenon of solution in these pro- portions the same significance as the solution of the salt KI,AgI, Published on 01 January 1913. Downloaded by University of Michigan Library 23/10/2014 01:44:16. since sodium iodide by itself is readily soluble in acetone. Lithium Silver Iodide. This salt crystallised well from dry acatone in colourless needles, with strong double refraction and straight extinction. The determination of the acetone of crystallisation did not give very concordant results, the amount varying between three and four molecules. The salt does not crystallise out at all when the solution is allowed to evaporate exposed to the air. The crystals are obtained by evaporating the acetone in a current of dry ah. When the acetone solution is exposed to the atmosphere crystals of silver iodide are gradually formed. This phenomenon is referred to again later. View Article Online ACETONE OF CRYSTALLISATION, ETC. 785 A mmonium Sil u er Iodide; NH41,2AgI,3 C3H,0. This salt crystallises well from acetone in colourless needles, double refracting, with straight extinction. We have not at present sufficient crystallographic evidence to determine whether the crystal- line form of this salt is different from that of the potassium salt. Found, C,H,O = 21.8. NH41,2AgI,3C,H,0 requires C,H,O = 22.0 per cent. Found (in dried salt), Ag1~77-0. NH,I,ZAgI requires AgI = 76.4 per cent. An ethylamine hydriodide-silver iodide was also crystallised from acetone, and resembled the ammonium salt in general appearance. There seems to be no doubt that a whole series of organic compounds of this type are capable of existing. Crystallised Silver Iodide. When a solution of silver iodide in lithium iodide and acetone is exposed to the air, after some days crystals of silver iodide begin to form and grow in the solution.