Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/551

Rh ARSENIC GROUP.] CHEMISTRY 539 warm hydrochloric acid, which converts it into stannous chloride, Sn 2 Cl 4, but is rapidly acted on by moderately concentrated nitric acid ; chlorine acts readily on the melted metal, converting it into stannic chloride, SnCl 4. Two chlorides of titanium are known, Ti 2 Cl 6 and TiCl 4, but only one chloride of zirconium, ZrCl 4. Titanium and tin tetrachlorides are colourless liquids, which byil respectively at 135 and 115 C. ; their lower chlorides are solids, and are powerful reducing agents. Zirconium chloride is a white, crystalline solid ; its vapour density corresponds with the formula ZrCl 4. When titanium and tin tetrachlorides are mixed with a small quantity of water, much heat is developed, and they dissolve, probably forming chlorhydrins; but a large quantity of water causes their conversion into the corresponding hydroxides, which separate as white gelatinous precipitates. Zirconium chloride is dissolved even by a large quantity of water, but the hydroxide Zr(OH) 4 separates as a gelatinous, bulky, white precipitate on the addition of alkalies. Titanium, zirconium, and tin tetrafluoride unite with metallic fluorides, forming crystalline salts which correspond in composition to the silcofluorides or fluosilicates (p. 522), with which they are isotnorphous; thus : K 2 SiF 6 Potassium fluosilicate. K 2 TiF 6 Potassium fluotitanate. K 2 ZrF 6 Potassium fluozirconate. K 2 SnF 6. Potassium fiuostannate. Titanic oxide, Ti0 2, has a reddish-brown colour ; stannic oxide, Sn0 2, is white or yellowish-white, but assumes a transient dark yellow or brown colour when heated; zirconic oxide, ZrO 2, is white. They may be obtained in crystals which are isomorphous. Zirconic oxide is infusible, and titanic oxide melts only at the heat of the oxyhydrogen blowpipe ; stannic oxide is somewhat more fusible, although very difficult to fuse. Titanic oxide is reduced by charcoal at a white heat, and stannic oxide at a full red heat; zirconic oxide, however, appears entirely to resist reduc tion ; by ignition with charcoal in an atmosphere of chlorine they are converted into the corresponding chlorides. After ignition they are insoluble in acids, except con centrated sulphuric acid ; they are dissolved on fusion with alkalies. By dissolving the oxides or the corresponding hydroxides in acids, salts such as stannic sulphate, Sn(S0 4 ) 2 , are produced ; the titanium and tin salts are so unstable, however, that their solutions are decomposed by boiling ; the zirconium salts are somewhat more stable. Stannic hydroxide readily dissolves in alkaline solutions, but titanic and zirconic hydroxides are insoluble. The salts which are formed from the hydroxides or oxides by the action of alkalies are mostly analogous to the silicates of the form MVSiOo ; thus : Na 2 SiO 3 Na 2 TiO 3 Na,ZrO 3 Sodium silicate. Sodium titanate. Sodium zirconate. Sodium starmate. Na 2 SnO 3. When tin is heated with concentrated nitric acid it is converted into white, insoluble, metastannic acid ; the air-dry substance has the composition Sn 5 O 10, 10H 2 0, but on drying at 100 C. it is converted into the compound H IO Sn 5 15 ; metastannic acid has feeble acid properties, and furnishes salts which all correspond in composition to potassium metastannate, K. 2 H 8 S 5 15. On loiling a solution of titanic hydroxide in hydrochloric acid an apparently similar compound is precipitated. Stannous hydroxide, Sn 2 (OH) 4, like stannic hydroxide, exhibits both basic and acid properties, dissolving in acids and also in alkalies; it gradually absorbs oxygen on exposure to the air. When a solution of titanic hydroxide in hydrochloric acid is digested with metallic copper, it becomes violet-blue, and on the addition of an alkali a dark brown precipitate separates, which probably is the hydroxide corresponding to the chloride TLCL. Tin is the only element of this group which may be precipitated sulphide by hydrogen sulphide. VANADIUM ARSENIC NIOBIUM : ANTIMONY TANTALUM BISMUTH. as Name. Symbol. At. -wt. Sp. gr. At. vol. Vanadium V 51-2 5-5 9-3 A rsenic As 74-9 57 13-9 Niobium Nb 94 (?) 6-3 14-9 Antimony Sb 122 67 18-1 Tantalum Ta 182 (?) 10-8 16-8 Bismuth Bi 207-5 9-8 21-1 These elements belong to the same group as nitrogen and phosphorus, but the relation between them is in a marked degree periodic, the resemblance being greatest in many respects between arsenic, antimony, and bismuth, and between vanadium, niobium, and tantalum. Vanadium is the only member of the group, excepting niobium and, perhaps, tantalum, which furnishes coloured compounds, and in this respect resembles titanium and chromium, to both of which it is about equally related. Relationship may also be traced between arsenic and selenium ; between niobium and zirconium, and niobium and molybdenum ; between antimony and tin, and antimony and tellurium ; and between tantalum and tungsten. The following chlorides and oxides of the elements of this group are known : Chlorides. Bi,Cl 4 N,0 (?) NCI, PC1 3 vA AsCl 3 SbC 1, Bici 3 NO vlb. (?) VC1 Oxides. V S 0, (As 2 3 ) 2 (Sb,b s ) a PCI, NbCl B SbCl 5 TaCl 5 N 2 4 v,o, As0 Sb 2 5 Ta.,0 4 Ta 2 5 Bi 2 3 ... Bi 2 5 Arsenic, antimony, and bismuth are readily reduced from their oxides, but the oxides of vanadium, niobium, and tantalum are not reduced to the metallic state by ignition with charcoal ; vanadium may be obtained by the reduc tion of its dichloride in hydrogen at a bright-red heat. Arsenic has a brilliant, dark steel-grey lustre ; antimony has a bluish-white, and bismuth a reddish-white colour ; they are hard, and extremely brittle, and bad conductors of electricity. Arsenic begins to volatilize at 180 C. without fusing ; antimony fuses at about 450 C., and bismuth at about 265 C. They are but little altered on exposure to the air at ordinary temperatures, but readily oxidize when heated. They are readily acted upon by moderately concentrated nitric acid, but are only very slowly dissolved by boiling hydrochloric acid. Vanadium has been obtained as a whitish-grey powder which under the microscope appears as a brilliant, crystal line, metallic mass possessing a silver-white lustre. It does not oxidize at ordinary temperatures, but when heated in air it rapidly absorbs oxygen, and is finally converted into the pentoxide. It is not attacked by boiling hydrochloric acid, but nitric acid of all strengths readily dissolves it. It is converted into a mononitride when heated in nitrogen gas. Niobium and tantalum have been obtained only in an impure state as black powders. Like vanadium, these