corrected for the barometric press., p, at 0°, by adding on 0.0001235(760–p)(273+0). The crystals are flattened octahedra, and isotropic, thus belonging to the cubic system. The sp. gr. is 3·1315 at 25°/25°; the index of refraction, 1.6296 at 20-70°; 1.6283 at 22-20°; and 1.6269 at 25°. I. I. Saskowsky found the ratio of the mol. vol. to the sum of the at. vols. of the constituent elements to be 1.21. L. M. Dennis and F. E. Hance found the sp. electrical conductivity to be less than 0.000078 mho at 30°.

C. Winkler said that the tetrabromide is decomposed by water, forming germanium dioxide. L. M. Dennis and F. E. Hance also studied the hydrolysis and noted a slight crackling sound when the tetrabromide is dropped into water. No action was observed when the tetrabromide was allowed to stand in contact with sulphuric acid for several days, at room temp. With nitric acid, the tetrabromide becomes yellow and turbid, and a layer of white germanium dioxide is formed between the two liquids; in about 15 mins. the tetrabromide has changed to a black colour and there is a copious evolution of nitric oxide. Dry ammonia forms a white solid in contact with germanium tetrabromide. An aq. soln. of potassium hydroxide (14) reacts at once with the tetrabromide, and heat is evolved; germanium oxide separates out, but immediately passes into soln. Carbon dioxide precipitates the oxide from the soln. of potassium germanate. Germanium tetrabromide is soluble in absolute alcohol, carbon tetrachloride, benzene, and ether without decomposition; but the soln. in acetone slowly liberates bromine. G. T. Morgan and H. D. K. Drew found that it reacted sluggishly with acetylacetone, forming germanium bisacetylacetone dibromide.

L. M. Dennis and F. E. Hance found that in the preparation of germanium tetraiodide by the action of the vap. of iodine on germanium at 360°, yellow crystals of germanous iodide, or germanium diiodide, Gel2, collected between the red tetraiodide and the germanium. C. Winkler made some germanic iodide or germanium tetraiodide, Gel4, by heating a mixture of germanium tetrachloride and potassium iodide in a sealed tube-the reaction was incomplete, and he could not separate the germanic chloride and iodide by fractional distillation. He also prepared the iodide by heating pulverulent germanium in the vap. of iodine carried along by a slow current of carbon dioxide. It was necessary to sublime the product repeatedly in an atm. of carbon dioxide to eliminate the iodine. L. M. Dennis and F. E. Hance observed that the reaction begins at 212°, and at 360°, the combination is rapid. During the resublimation of the product, they noticed that the colour gradually changed from a bright red to a chocolate-brown, showing that the compound is partially decomposed when sublimed.

C. Winkler said that germanium tetraiodide has an orange colour; L. M. Dennis and F. E. Hance said that while the powder is orange, the fused iodide in lump form is coral-red at ordinary temp. At -185°, the colour is canary-yellow; at -50°, buff; at -10°, orange; at 35°, salmon; at 50°, brick-red; at 90°, red; and at 144°, ruby-red. The crystals are octahedra with the plane angles 60°; and being isotropic without birefringence, they must belong to the cubic system. The sp. gr. is 4.3215 at 26°/26°. C. Winkler, and L. M. Dennis and F. E. Hance found the m.p. to be 144°; and the first-named said that on cooling it forms a crystalline mass with a marked decrease in volume. It boils at 350°-400°, forming a yellow vap., and as the iodide condenses some violet iodine vap. remains, indicating that the iodide has suffered some dissociation. L. F. Nilson and O. Pettersson said that the compound is not decomposed at 440°, but dissociates at a higher temp. They measured the vap. density, and found 20-46 at 440°, when the calculated value for Gel is 20-09; at 658°, the vap. density is 17-19, indicating that dissociation has taken place. L. M. Dennis and F. E. Hance obtained an analogous result, and showed that the agreement between the observed and calculated values does not indicate that there is no dissociation. The vap. was shown to be a mixture of germanium diiodide and iodine: Gel Gel2+I12.

C. Winkler said that the vap. of germanium tetraiodide is inflammable in air;

and that a mixture of the vap. with air explodes feebly with a reddish flame, forming germanium dioxide and iodine. He added that the tetraiodide is sehr hygroskopisch, and deliquesces in air, forming a brown liquid coloured by free iodine and which gradually forms white germanium dioxide owing to the volatilization of the iodine. He found a 50 per cent. gain in weight the first day, and a steady loss during the next 18 days, so that the residue weighed about a fourth as much as the original sample. Au contraire, L. M. Dennis and F. E. Hance observed no signs of a gain or loss of weight when exposed in air for 2 days; and only a slight decrease in weight after 5 months' exposure owing to the formation of a slight white incrustration. Presumably the hygroscopic sample was contaminated with something other than the tetraiodide. C. Winkler found that the tetraiodide is decomposed by a small proportion of water, forming germanium dioxide, which dissolves when more water is added, forming a clear, colourless soln. having an acid reaction. The soln. acquires a coloration on standing owing to the separation of iodine from the hydriodic acid. L. M. Dennis and F. E. Hance obtained analogous results, and found that the tetraiodide is not affected by conc. sulphuric acid at room temp. during 24 hrs.; but at 85°, iodine was slowly liberated. At room temp., conc. hydrochloric acid slowly dissolves the tetraiodide, dissolution being complete after some weeks. The tetraiodide is decomposed under conc. nitric acid, with the evolution of nitric oxide. The acid acquires a black coloration. When dropped into conc. aq. ammonia, the compound is at once decomposed and decolorized, forming a white solid; with dry ammonia gas, a white powder is slowly formed. which is soluble in water. When placed in a soln. of potassium hydroxide (1: 4), germanium tetraiodide is slowly dissolved. The tetraiodide dissolves in benzene, in monochlorobenzene, and in carbon disulphide, forming an orange-red soln.; in methyl alcohol, forming a deep orange soln. ; in ethylene chloride, and in carbon tetrachloride, forming light orange soln.; and in ethylene glycol, and in ethylene chlorohydrin, forming light yellow soln. These soln. underwent no visible change on standing 4 months; but there was a distinct change of colour with soln. of the tetraiodide in hexane (orange-red), chloroform (pale orange), nitrobenzene (orange-red), petroleum (pink), butanol (orange), and glacial acetic acid (pale yellow), owing to the liberation of iodine. Soln. in acetone, ether, turpentine, oil of lavender, absolute alcohol, isopropyl alcohol, pyridine, and amyl alcohol decomposed at

once.

REFERENCES.

1 C. Winkler, Journ. prakt. Chem., (2), 34. 177, 1886; (2), 36. 177, 1887; L. F. Nilson and O Pettersson, Zeit. phys. Chem., 1. 27, 1887; L. M. Dennis and F. E. Hance, Journ. Amer. Chem. Soc., 44. 299, 1922; G. T. Morgan and H. D. K. Drew, Journ. Chem. Soc., 125. 1261, 1924; I. I. Saskowsky, Zeit. anorg. Chem., 146. 315, 1925.

§ 9. The Germanium Sulphides

Germanium forms two sulphides, germanous sulphide, or germanium mono, sulphide, GeS; and germanic sulphide or germanium disulphide, GeS2. C. Winkler1 made the former by heating to redness a mixture of germanium disulphide with an excess of germanium in a current of carbon dioxide. The product appeared partly as dark grey crystals, and partly as a reddish-brown powder. He obtained a crystalline mass of the monosulphide by heating the disulphide in a stream of hydrogen-hydrogen sulphide was evolved. If argyrodite be similarly heated in a stream of hydrogen, germanium monosulphide appears as a brown dust the microscopic appearance of which has been described by K. Haushofer. C. Winkler observed that when hydrogen sulphide is passed into a soln. of germanous oxide in hydrochloric acid, reddish-brown, amorphous germanous sulphide is precipitated. The amorphous powder readily forms with water an orange-red or brown, opalescent, colloidal germanium monosulphide. It can be kept without change

VOL. VII.

T

in a closed vessel, but in air it is oxidized and loses its colour. Acids flocculate the suspended colloid.

Germanium monosulphide appears as a brown powder and in crystals of different habits; those prepared by heating the disulphide in hydrogen appear in thin plates with a lustre and colour recalling the appearance of iodine, or iron glance. According to A. Weisbach, the plates are doubly refracting and either monoclinic or rhombic. L. F. Nilson and O. Pettersson found that germanous sulphide melts to a dark liquid which, in turn, freezes to a crystalline mass. The vap. density is 3-54 at 1100°, and 3-09 at 1500°. The monosulphide dissociates at a white heat. According to C. Winkler, when germanium monosulphide is heated in air, sulphur dioxide is evolved and germanium dioxide is formed. When heated in a stream of hydrogen, most of the monosulphide is volatilized undecomposed, but in the hottest part, a part of the monosulphide is reduced forming octahedral crystals of germanium. The amorphous sulphide readily dissolves in hot conc. hydrochloric acid with the evolution of hydrogen sulphide and the formation of germanous chloride; crystalline germanous sulphide dissolves in hydrochloric acid with difficulty. Germanous sulphide dissolves vigorously in molten potassium hydroxide, and it is readily soluble in an aq. soln. of potassium hydroxide, especially when warmed, any germanium present remains undissolved. When the soln. is acidified, amorphous, reddish-brown germanous sulphide is precipitated. Amorphous germanous sulphide dissolves in a soln. of ammonium sulphide, (NH4)2S, forming a thiogermanate, and the soln. deposits white germanic sulphide when treated with an acid. Crystalline germanous sulphide is said to be insoluble in a soln. of ammonium sulphide. When the sulphide is mixed with potassium nitrate and heated, it detonates.

According to C. Winkler, when acid soln. of germanium dioxide are treated with hydrogen sulphide, a white precipitate of germanic sulphide or germanium disulphide, GeS2, is formed. An aq. soln. of germanium dioxide gives no precipitate with hydrogen sulphide, but when the soln. is acidified with sulphuric or hydrochloric acid, a white turbidity appears which settles to a voluminous white precipitate. With a feebly acidified soln., the germanium is only partially precipitated as sulphide; for complete precipitation a strongly acidified soln. is necessary. Acetic acid and other organic acids will not do. Germanium disulphide is precipitated when an alkali sulphogermanate is treated with an acid, and for complete precipitation a large excess of sulphuric or hydrochloric acid is necessary, and the soln. should be sat. with hydrogen sulphide. The sulphide precipitated from acid soln. is peptized when washed, forming colloidal germanium disulphide, which is opalescent after long standing and repeated filtration-one such soln. had one part of germanium sulphide in 221.9 parts of water. The sol is flocculated by acids, and with metal salt soln. it gives colorations characteristic of the metal sulphides. It also decomposes, giving off hydrogen sulphide.

Germanium disulphide shows but little tendency to crystallize or volatilize. When the white amorphous disulphide is heated in a stream of carbon dioxide, it shrinks very much and acquires a yellow or yellowish-grey colour; if the temp. is raised to bright redness, a part is volatilized, forming a white coating which is partly crystalline. When germanium disulphide is heated in air, it forms sulphur and germanium dioxides, and possibly also an oxysulphide since the complete elimination of sulphur is not possible by mere roasting. When heated with hydrogen, the monosulphide is formed (q.v.). The dried and calcined sulphide decomposes in moist air; and when the moist disulphide is dried on a water-bath some hydrogen sulphide is given off. Acids favour the reaction. When the disulphide is evaporated with hydrochloric acid, the germanium is volatilized as tetrachloride; when evaporated with sulphuric acid, until a large proportion has been driven off, germanium dioxide is formed and it retains some adsorbed acid very tenaciously; and when treated with nitric acid, there is a vigorous reaction and the resulting germanium dioxide retains some sulphuric acid. Aqua regia dissolves germanium disulphide with the separa

tion of sulphur. The disulphide dissolves readily in aq. ammonia, and in soln. of the alkali hydroxides, or alkali sulphides. Presumably sulphogermanates are formed, but none has been isolated. The soln. of germanium disulphide in potassium sulphide gives precipitates-possibly sulphogermanates when treated with salts of the heavy metals. If the soln. of germanium disulphide in potassium hydroxide be treated with chlorine or bromine, sulphur is separated. The soln. of germanium disulphide in aq. ammonia is oxidized by hydrogen dioxide without the separation of sulphur. Argyrodite and canfieldite can be regarded as a basic silver sulphogermanate, a derivative of the acid Ge(SH) 4.2H2S. S. L. Penfield 2 represented its composition by AggGeSe, and that of canfieldite, by Agg (Sn, Ge)Se-vide supra. A. Weisbach described a steel-grey mineral as monoclinic, but S. L. Penfield showed that the crystals belong to the cubic system. The sp. gr. is 6-0856-111; and the hardness 2.5. E. T. Wherry found argyrodite to have poor qualities as a radio-detector. O. Pufahl's mineral germanite previously indicated has a composition Cus(Cu, Fe),AsGeS12, and sp. gr. 4.46.

C. Winkler 3 reported the formation of a white germanous phosphate when a soluble phosphate is added to a germanous salt soln.; but otherwise germanium phosphates, nitrates, carbonates, and sulphates have not been described.

REFERENCES.

1 C. Winkler, Journ. prakt. Chem., (2), 34. 177, 1886; (2), 36. 177, 1887; K. Haushofer, Sitzber. München. Akad., 133, 1887; L. F. Nilson and O. Pettersson, Zeit. phys. Chem., 1. 27, 1887; A. Weisbach, Jahrb. Berg. Hütt. Sachsen, 89, 1886; Neues Jahrb. Min., ii, 67, 1886.

2 S. L. Penfield, Amer. Journ. Science, (3), 46. 107, 1893; (3), 47. 451, 1894; A. de Gramont, Bull. Soc. Min., 18. 241, 1895; G. T. Prior and L. J. Spencer, Min. Mag., 12. 5, 1898; O. Pufahl, Metall Erz, 19. 324, 1922; E. T. Wherry, Amer. Min., 10. 28, 1925; A. Weisbach, Jahrb. Berg. Hütt. Sachsen, 89. 163, 1886; Chem. News, 53. 257, 1886; Neues Jahrb. Min., ii, 67, 1886; i, 98, 1894.

3 C. Winkler, Journ. prakt. Chem., (2), 34. 177, 1886; (2), 36. 177, 1887.

CHAPTER XLVI

TIN

§ 1. The History of Tin

Ir is generally believed that tin is one of the metals which has been known since very ancient times, and that this metal was employed in the arts at the time of Herodotus, Homer, and Moses. The proof of the great antiquity of tin, however, is not so convincing as in the case of copper, silver, gold, mercury, lead, and iron. The metal tin was not found native by the ancients, and they could have obtained it only by extraction from its ore. It is true, however, that the ore is found near the surface of the earth, and that it gives up its metal more readily than some of the ores of the other metals. Thus, according to J. F. Reitemeyer,1 the early Britons smelted the ore by a very simple process:

They placed the ore in a hole dug in the ground, and laid wood between and around it. They then set fire to the wood. The fire smelted the ore. The slag was run from the molten metal through a pipe or furrow into a second hole. Many of these slag-hearths are still found in Cornwall. The whole smelting process was as effective as it was simple ; proof of this is found in the fact that the slag residues do not contain sufficient ore to warrant a second separation by more modern methods.

Tin ores occur in only a few countries which were not readily accessible to the Romans or Greeks, and accordingly, as J. Beckmann has pointed out, it appears probable that the metal would be scarce and costly among these people. Assuming that the metal believed to be tin was really such, it does not appear to have been accounted of much value. The few references to tin do not allude to objects made of this metal as being valued possessions. Again, although more durable than lead or copper, vessels of tin are very rarely found among Greek or Roman antiquities under conditions where vessels of lead and copper are comparatively

common.

There are good grounds for doubting whether the scholars have been always correct in translating the ancient terms by what is now connoted by the word "tin." Moses, in the book of Numbers (31. 22), gives a list of the metals then known, and his term bedil was translated κaσσíтe pos in the old Greek versions of the Hebrew books; and cassiteros in turn was translated stannum in the Latin versions. Stannum was rendered by tin in Low German and English; by tenn in Swedish ; by Zinn in High German; by estain in French; by estano in Spanish; and by stagno in Italian. Pliny, in his Historia naturalis (34. 47), regarded tin as a variety of lead. He said:

There are two kinds of plumbum-nigrum, and candidum or album, i.e. black lead, and shining or white lead. The plumbum candidum is the most valuable, and it was called cassiteros by the Greeks. There is a fabulous story told of their going in quest of it to the islands in the Atlantic Ocean, and of its being brought in boats made of osiers covered with hides. The plumbum candidum occurs as a black sand found on the surface of the earth, and is to be detected only by its weight; it is mingled with small pebbles, particularly in the dried beds of rivers. The miners wash the sand, which is then melted in the furnace and becomes converted into plumbum album.