134, 699, 1926; Bull. Soc. Chim., (4), 37. 854, 1925; (4), 39. 43, 1926; B. Köhnlein, Liebig's Ann., 225. 171, 1884; A. C. Vournasos, Zeit. anorg. Chem., 150. 147, 1926; G. T. Morgan, S. R. Carter, and W. F. Harrison, Journ. Chem. Soc., 127. 1917, 1925. § 21. The Stannic Iodides J. L. Gay Lussac 1 prepared stannic iodide, SnI4, by heating a mixture of tin and iodine; J. Personne found that in a sealed tube the reaction begins at 50°, and is attended by incandescence. The excess of tin remains unaffected without producing stannous iodide. A. E. Nordenskjöld melted a mixture of iodine and tin, and obtained stannic iodide by the sublimation of the product. J. Personne, and E. R. Schneider allowed a warm soln. of iodine in carbon disulphide to act on tin. E. R. Schneider obtained it by mixing conc. soln. of stannic chloride and potassium iodide; and by the action of iodine on stannous or stannic selenide. J. J. Berzelius prepared it from a soln. of stannic hydroxide in hydriodic acid; and W. C. Henry obtained it by sublimation from stannous iodide, heated in air-stannic oxide remains. He also found that stannic iodide is formed by mixing a conc. soln. of stannous chloride with an equal proportion of iodine. P. Groth said that crystals obtained from carbon disulphide are red and singly refracting, belonging to the cubic system; but A. E. Nordenskjöld showed that B C FIG. 75.—Arrangement of the Stannic Iodide. -340° they belong to the rhombic system. J. W. Retgers obtained octahedral crystals by evaporating a soln. of the salt in an excess of hydriodic acid, in carbon disulphide, methylene iodide, and other solvents. R. G. Dickinson found the X-radiograms corresponded with a mol. of (Sn), per unit cube with edge 12-23 A. The iodine atoms are not all in eq. positions, and are probably at points eq. to (vvv) and (xyz), while the tin atoms are at points (uuu). The arrangement is illustrated by Fig. 75, where the cube has been divided along the plane ABCD for convenience in drawing. Measurements were also made by H. Ott, and H. Mark and K. Weissenberg. E. Beckmann and P. Geib found the raising of the b.p. of stannic chloride by stannic iodide corresponded with only one-third the normal mol. wt. ; but E. Beckmann and F. Junker found the lowering of the b.p. of antimonic chloride by the dissolved stannic iodide does not agree with the normal mol. wt. C. H. D. Boedeker gave 4-696 for the sp. gr. at 11°; J. Personne said the crystals melt at 160°, and the molten liquid freezes at 142°; F. Emich gave 160°, and W. Reinders and S. de Lange, 143-5° for the m.p. W. C. Henry said the salt sublimes at 180°, forming reddish-yellow needles. J. Personne could not measure the b.p., but he found a thermometer near the surface of the boiling liquid registered 295°; F. Emich gave 341° for the b.p. W. Reinders and S. de Lange found the m.p. of mixtures of stannic iodide and iodine consists of two branches with a eutectic at 79-6°, and 12.06 at. per cent. or 60 per cent. by weight of tin, Fig. 76-vide supra, stannic chloride. The b.p. curve follows the normal course, and the curves indicated. A fused mixture of stannous and stannic iodides forms two 340° 320° 300° 280° 260° 240° 220° 200° Vapour 180° 783° 160° 140° 120113.2 100°F 80 79-6 60° 0 4 8 12 16 20 24 28 32 36 Atomic per cent. of tin FIG. 76.-Fusion and Boiling Curves of Mixtures of Tin and Stannic Iodide. liquid layers. At 350°, the one layer consists of stannic iodide with traces of stannous iodide; and the other, of stannous iodide with a maximum of 6 per cent. stannic iodide. Tin is not perceptibly soluble in molten stannous iodide, and there is a very narrow line of homogeneous mixing which, at 350°, extends from pure stannous iodide to stannous iodide with 6 per cent. by weight of stannic iodide. Similar results were obtained by H. S. van Klooster, and A. M. Vasiléeff. The latter found the eutectic at 77-8° and SnI+3-257I. A. H. Chapman measured the emission spectrum of stannic iodide. F. de Carli studied the reducing action of hydrogen. The salt is hydrolyzed in aq. soln., as noted by J. L. Gay Lussac, C. F. Rammelsberg, W. C. Henry, and J. Personne; but no definite stannic oxyiodide was observed. E. R. Schneider said that 100 parts of carbon disulphide at ordinary temp. dissolve 145 parts of stannic iodide; and J. Personne noted that it is soluble in chloroform, alcohol, ether, and benzene, forming compounds with all but the first of these four solvents. J. W. Retgers found that methylene iodide at 10° dissolves 22.9 per cent. of stannic iodide, and the sp. gr. of the soln. is 3-481 at 10°. W. Biltz and E. Kuenecke observed no reaction or dissolution with liquid hydrogen sulphide at -78.5°. Arsenic tribromide dissolves the salt; the sp. gr. of the sat. soln. is 3-73 at 15°, and, according to P. Walden, the soln. is a poor electrical conductor. J. H. Mathews found the salt is soluble in allylthiocarbamide, and the sp. conductivity of the soln. is 4.08 × 1044 mhos at 25°. A. Rosenheim and H. Aron prepared complexes with pyridine and quinoline. There is evidence of the formation of hydroiodostannic acid by the union of stannic iodide and hydrogen iodide. The soln. is readily hydrolyzed. V. Auger and T. Karantassis observed that stannic iodide is gradually hydrolyzed in dil. hydriodic acid soln. and more readily in aq. soln. The addition of sodium, potassium, or ammonium iodide to these soln. does not modify their properties, but the addition of rubidium or cæsium iodides or of the hydriodides of strong bases leads to the formation of stable complex salts; e.g. rubidium iodostannate, Rb2SnIe, by adding rubidium iodide to a soln. of stannic iodide in hydriodic acid; and similarly with cæsium iodostannate, Cs2SnIe; but ammonium, potassium, and sodium iodostannates could not be made. They also prepared mixed crystals of potassium bromoiodostannate, K,Sn(Br5.75Iu-25), and ammonium bromoiodostannate, (NH4)2Sn(Br5.35Io.65), as well as of tetramethylarsonium iodostannate. J. G. F. Druce made methyl stannic iodide, Sn(CH3)I3; and normal propyl stannic iodide, Sn(C3H7)I3. M. Wildermann studied the reaction with several organic bromides. V. Auger and T. Karantassis studied some complexes with organic compounds. J. Personne said that dry ammonia reacts with stannic iodide dissolved in carbon disulphide or ether, forming stannic triamminoiodide, SnL4.3NH3; stannic tetramminoiodide, SnI4.4NH,, and stannic hexamminoiodide, SnL4.6NH3. F. F. Fitzgerald showed that in liquid ammonia it reacts with potassium amide, forming potassium stannic tetramminoimide, Sn(NK)2.4NHg. F. Ephraim and T. Schmidt prepared stannic octamminoiodide, SnI4.8NH3, by passing ammonia into a soln. of stannic iodide in carbon disulphide and evaporating off the solvent on a bath of warm water; also by passing ammonia over the solid iodide, when much heat is evolved. Evidence of higher ammines was obtained, but they were not stable. Stannic iodide dissolves in stannic chloride, and antimonic chloride as indicated above. A. Ditte noted the formation of a basic nitrate, 4SnO4.N2O5.4H2O, by reaction with nitrogen peroxide. Stannic iodide was found. by H. Moissan to be reduced when heated with boron. G. Scagliarini studied complexes with organic bases. C. Lenormand heated a mixture of stannous chloride and iodine in a flask or in a sealed tube at 100°, and obtained stannic dichlorodiiodide, SnCl,I2, as a red mobile liquid of sp. gr. 3.287 at 15°. The liquid fumes in air, and it begins to distil at 190°, and the b.p. during distillation remains stationary at 297°. It is decomposed by repeated distillation. The dichlorodiiodide is soluble in water with the development of much heat; with a small proportion of water, a hydrate is formed which is soluble in an excess of water. The dil. soln. at 65° is quantitatively decomposed into stannic hydroxide, and hydrochloric and hydriodic acids. The dichlorodiiodide is soluble in benzene, chloroform, and carbon disulphide. It yields complexes with ether, and with ethyl, propyl, butyl, and amyl alcohols. If this liquid be fractionally distilled, substances corresponding with stannic trichloro 360° 340° 320° 300° 280° 260° 240° 220° 200° 180° 160° 140° 120° 100° 80° Liquidus curve iodide, SnCl,I, and stannic chlorotriiodide, SnI,Cl, as well as stannic chloride, and stannic dichlorodiiodide are formed. C. Lenormand also found that iodine is without action on stannous bromide in the cold, but when the mixture is heated in a sealed tube at 100° an orange-red, crystalline mass of hexagonal plates is produced, consisting of stannic dibromodiiodide, SnBr2I2. The compound begins to melt at 50°, and forms a ruby-red liquid which does not fume in the cold. The sp. gr. is 3 631 at 15°; it boils at 225°, or at 130° in vacuo. It is soluble in cold water, and the soln. decomposes at 80° into stannic oxide, and hydrogen iodide and bromide. When this compound is fractionally distilled, stannic tribromoiodide, Sn Brgl, passes over at 230°-250° and condenses as a mass of yellowish-red crystals and of undecomposed stannic dibromodiiodide; and stannic bromotriiodide, SnBrIg, remains as a residue. If the dibromodiiodide be distilled in vacuo, the undecomposed salt passes over at 130°; the tribromoiodide, at 180°, and the bromotriiodide remains as a residue. M. G. Räder said the method of preparation of the dibromodiiodide really gives a mixture of the two salts; and there is no evidence on the f.p. or b.p. curves, Fig. 77, to show the existence of salts of the mixed acids; with stannous bromide and iodine, the reaction is symbolized: 2SnBr2+212 SnBr4+SnI4. 60° 40° 20° 19-35 Solidus Ο 20 40 60 80 100 Molar per cent. of Sn 14 FIG. 77.-Freezing- and Boiling point Curves of Mixtures of Stannic Iodide and Bromide. REFERENCES. 1 J. L. Gay Lussac, Ann. Chim. Phys., (2), 1. 40, 1816; J. J. Berzelius, ab., (1), 87. 50, 1873; (2), 5. 149, 1817; J. Personne, Compt. Rend., 54. 216, 1862; H. Moissan, ib., 114. 617, 1891; E. R. Schneider, Pogg. Ann., 127. 624, 1866; C. F. Rammelsberg, ib., 48. 169, 1839; F. de Carli, Atti Accad. Lincei, (5), 33. ii, 94, 1924; H. Mark and K. Weissenberg, Zeit. Physik, 16. 1, 1923; A. M. Vasiléeff, Journ. Russ. Phys. Chem. Soc., 49. 88, 1917; W. C. Henry, Phil. Mag., (3), 5. 354, 1845; Phil. Trans., 135. 363, 1845; A. H. Chapman, Phys. Rev., (2), 4. 28, 1914; J. W. Retgers, Zeit. Kryst., 22. 270, 1894; Zeit. anorg. Chem., 3. 343, 1843; E. Beckmann and P. Geib, ib., 51. 96, 1906; E. Beckmann and F. Junker, ib., 55. 175, 1907; A. Rosenheim and H. Aron, ib., 39. 170, 1904; H. S. van Klooster, ib., 79. 223, 1913; P. Walden, ib., 29. 377, 1902; W. Biltz and W. Fischer, ib., 129. 1, 1923; M. G. Räder, ib., 130. 325, 1923; W. Reinders and S. de Lange, Proc. Acad. Amsterdam, 21. 474, 1912; Zeit. anorg. Chem., 79. 230, 1913; S. W. Young and G. L. Thomas, Journ. Amer. Chem. Soc., 19. 515, 1897; F. F. Fitzgerald, ib., 29. 1693, 1907; R. G. Dickinson, ib., 45. 958, 1923; Phys. Rev., (2), 22. 199, 1923; C. Lenormand, Journ. Pharm. Chim., (6), 8. 249, 1898; (6), 10. 114, 1899; V. Auger and T. Karantassis, Compt. Rend., 180. 1845, 1925; A. E. Nordenskjöld, Bihang. Svenska Akad. Handl., 2. 2, 1874; J. H. Mathews, Journ. Phys. Chem., 9. 647, 1905; M. Wildermann, Zeit. phys. Chem., 9. 12, 1892; F. Ephraim and T. Schmidt, Ber., 42. 3856, 1909; E. and P. Fireman, Amer. Chem. Journ., 30. 127, 1903; F. Emich, Monatsh., 25. 907, 1904; C. H. D. Boedeker, Die Beziehung zwischen Dichte und Zusammensetzung, Leipzig, 1860; P. Groth, Chemische Krystallographie, Leipzig, i, 231, 1906; A. Ditte, Ann. Chim. Phys., (5), 27. 159, 1882; J. G. F. Druce, Chem. News, 120. 229, 1920; 127. 306, 1923; V. Auger and T. Karantassis, Compt. Rend., 180. 1845, 1925; G. Scagliarini, Atti Accad. Lincei, (6), 1. 582, 1925; W. Biltz and E. Kuenecke, Zeit. anorg. Chem., 147. 171, 1925; H. Ott, Zeit. Kryst., 63. 222, 1926. § 22. Stannous Sulphides Estimates of the affinity of sulphur for tin were made by K. Jellinek and J. Zakowsky. Tin forms two well-established sulphides, stannous sulphide, SnS, and stannic sulphide, SnS2; and a less well established tin sesquisulphide, Sn2S3. There are also hydrated forms of these sulphides, and a series of sulpho-derivatives. J. Kunckel, in his Völlstandiges Laboratorium chymicum (Berlin, 1767), described the product obtained by fusing tin with sulphur. J. L. Proust 1 supposed that when molten stannous chloride is treated with sulphur, stannic chloride and sulphide are formed, but E. R. Schneider showed that stannic chloride and stannous sulphide are formed, and that the latter dissolves in the excess of molten stannous chloride from which it crystallizes on cooling. According to G. C. Winkelblech, narrow strips of tin-foil catch fire in sulphur vapour. Stannous sulphide is formed when a mixture of sulphur and tin is heated above the m.p. of the metal; and since the product still contains uncombined tin, it is pulverized, mixed with fresh sulphur, and again heated in a closed vessel. This method of preparation was used by P. Berthier, and E. R. Schneider. W. Biltz and W. Mecklenburg said that the yield of stannous sulphide obtained by fusing tin and sulphur is poor because of the volatilization of most of the latter; they made it by heating to 900° a mixture of tin with twice the calculated quantity of sulphur in a tube; and repeating the operation with the resulting product. A. Ditte sublimed the stannous sulphide from the product obtained by the repeated fusion of a mixture of sulphur and tin. 400° 4,000° 800° 600° Boiling curve +881° SAS J. L. Gay Lussac found that at a red-heat stannic sulphide decomposes into stannous sulphide and sulphur; and F. Damm and F. Kraft, that when heated in vacuo in the cathode rays, stannic sulphide, even at 250°, gives off half its sulphur and passes into the more stable stannous sulphide. According to H. Pélabon, the f.p. curve for mixtures of tin and sulphur rises rapidly from 232°, the f.p. of tin, to 840°, the f.p. of the mixture containing 5 per cent. of sulphur, and then rises more gradually to the maximum point 880°, the f.p. of stannous sulphide; beyond this point the mixtures lose sulphur on being heated, but 1,200° their m.p. are lower than 880°. W. Biltz and W. Mecklenburg found that with mixtures containing over 23.4 per cent. of sulphur, the sulphur is lost by volatilization. The compound melts at 881°, and the eutectic at 232° is almost pure tin. The sulphide passes into a viscous liquid at 950° and becomes limpid again at near 1100°, Fig. 78. W. Spring obtained stannous sulphide by compressing a mixture of powdered sulphur and tin. O. B. Kühn obtained stannous sulphide by melting a mixture of tin and sodium pentasulphide; J. Milbauer, by melting stannic oxide mixed with potassium thiocyanate; and G. Tocco and N. Jacob, by the alternating current electrolysis of soln. of sodium thiosulphate using tin electrodes. 400° 232 5 10 15 20 25 Per cent. sulphur FIG. 78. The Fusion Curve of According to A. Ditte, when tin is heated to 100° in a stream of hydrogen sulphide, it acquires a coating of stannous sulphide; and when the tin melts, the formation of the sulphide proceeds more quickly. Above the decomposition temp. of hydrogen sulphide, the production of stannous sulphide is due to the direct union of sulphur and tin. K. Jellinek and J. Zakowsky studied the reaction between 500° and 1100°. When hydrogen sulphide is passed into a neutral or feebly acid soln. of stannous chloride, dark brown or black stannous sulphide is precipitated; and A. Ditte added that it is necessary to exclude air because, otherwise, the stannous 2 H VOL. VII. chloride would be partially oxidized, and therefore some stannic chloride formed. H. Reinsch found that if a soln. of one part of stannous chloride in 100 parts of water and 15 parts of hydrochloric acid, of sp. gr. 1.168, be treated with hydrogen sulphide, all the tin is precipitated at once, but if 25 parts of acid be used, a precipitate appears SnS in solution SnS precipitated SAS dissolved Per cent. HCL FIG. 79.-Effect of the only after some time, and if 40 parts of acid be used, no tin sulphide is precipitated, although it is if some water be added. The meaning of H. Reinsch's crude data is represented diagrammatically, Fig. 79. Fig. 79 means that there is a state of equilibrium in the system: H2S+SnCl2 2HCl+SnS. A. Ditte found that 8.3 per cent. hydrochloric acid at ordinary temp. begins to act on stannous sulphide, forming a soln. of stannous chloride, and giving off hydrogen sulphide. The formation of stannous chloride is faster the greater the conc. of the acid, and the higher the temp. According to A. Ditte, the precipitate dried in vacuo at 20° has the composition tritahydrated stannous sulphide, 3SnS.H2O, with a sat. soln. of stannous chloride; the first product of the action of hydrogen sulphide appears as an orange-red crystalline separation, the colour then changes to brown and finally to black; the brownish-red crystals are formed if an acid soln. of stannous chloride be treated with a small proportion of hydrogen sulphide, or if water be added to an acid soln. of stannous chloride sat. with hydrogen sulphide. These coloured crystals are considered to be stannous hydrosulphochloride, Sn(HS)Cl, which is transformed by hydrogen sulphide into stannous sulphide; the intermediate hydrosulphochloride was not isolated because it is decomposed when washed with water. When the hydrated stannous sulphide is thoroughly dried, it passes into the anhydrous sulphide. Stannous sulphide appears as a dark brown crystalline powder when the tritahydrate is dissolved to saturation in molten stannous chloride, and the cold product washed with dil. hydrochloric acid. The physical properties of stannous sulphide. The product obtained by the direct union of molten sulphur and tin is a dark lead-grey mass of lamellar, micaceous crystals; the sublimed product appears in long, needle-like crystals. The native sulphide appears in thin scales, plates, or blades, which are pliable but not elastic, and resemble flaky graphite. A. C. Becquerel claimed to have obtained cubic crystals by the method indicated above; but W. P. Headden found iron-black or graphite-black crystals of stannous sulphide as a deposit on some slags from an old Cornish tin furnace, and he considered the crystals to be monoclinic; but S. Stevanovic showed that the crystals are rhombic bipyramids with axial ratios abc=0·3883:1:0-3566; or, according to C. O. Trechmann, 0-3874:1:0-3558. L. J. Spencer showed that the crystals of rhombic tin reported by C. O. Trechmann, and H. von Foullon, were really crystals of stannous sulphide. Owing to the thinness of the plates-mm.-it was not possible to determine if there is any cleavage parallel to the surface. There is often a repetition of parallel growths giving rise to comb-like and feathery forms and also to plates with serrated edges. L. J. Spencer gave illustrations of the twinning of these crystals. W. P. Davey discussed the sizes of the tin atoms in stannous sulphide. C. J. B. Karsten gave 4.852 for the sp. gr. of stannous sulphide; P. A. Boullay, 5-267; E. R. Schneider, 4·973; and A. Ditte, 5.0802 at 0°. The hardness is 2. When molten stannous sulphide freezes, A. Ditte said that there is a considerable dilation; and that it melts at a red heat. J. Guinchant gave 950°-1000° for the m.p.; H. Pélabon, 880°; and W. Biltz and co-workers, 882°-Fig. 78. As indicated above, W. Biltz and coworkers found that stannous sulphide has two m.p. The lower m.p. is at 882°, and as the temp. is raised quickly from 1000° to 1100°, the viscosity increases very quickly, so that at the latter temp. the sulphide has the properties of a solid. At about 1200°, liquefaction again occurs. A. Ditte said that stannous sulphide begins to give off greenish vap., and to sublime close to its m.p.; and |