obtained. Thorium dioxide, ThO,, does not decompose Na,CO when heated with this salt, nor does it form salts by fusion with solid potash or soda. The fact that when hydrated cerium dioxide, CeO,.xH,O, is precipitated by adding potash to a solution of ceric sulphate, Ce(SO4)2, the whole of the potash cannot be removed from the precipitate by washing with water indicates the possible formation of an unstable potassium cerate. Carbon monoxide, CO, is obtained by heating the dioxide with carbon (CO, + C = 2CO), or by the interaction of (1) formic acid, or (2) oxalic acid, with concentrated hot sulphuric acid; (1) H,CO,+H,SO = CO + H,O.H,SO4, (2) H,C,O,+ H,SO, = CO + CO,+ H,O. H,SO,. 2 This oxide is a poisonous gas; salts of formic acid H,CO2 can be obtained from it, and as the oxide is produced from the acid, the oxide is sometimes called formic anhydride. The sesquioxides TiO and CeO are obtained by reducing the higher oxides MO; in the case of titanium this is done by heating TiO, to redness in dry hydrogen, in the case of cerium it is better to heat cerous oxalate, Ce(C2O4)39 in hydrogen. TiO, is oxidised to TiO, by continued heating in air; Ce2O, is very easily oxidised by mere exposure to air. Both oxides dissolve in acids forming salts; a large series of cerous salts Ce,. 3X is known; only titanous sulphate, Ti2(SO),. 8H2O, seems to have been obtained as a definite solid. The sulphides, with the exception of CS2, have not 470 been much examined. Titanium disulphide, TiS,, is a dark coloured stable solid, obtained by the interaction of titanium tetrachloride and sulphuretted hydrogen at high temperatures. Thorium disulphide, ThS,, resembles TiS,; it is obtained by passing hydrogen mixed with hydrogen sulphide over heated Tho. Cerium sesquisulphide, Ce,S,, is a golden coloured solid formed by passing sulphuretted hydrogen over hot CeO2. None of these sulphides exhibits any tendency to form thiosalts by interacting with alkali sulphides, or by fusion with alkalis. Carbon disulphide is a mobile, very refractive, liquid, boiling at 47°; its vapour is very inflammable. It is obtained by the direct union of its elements at high temperatures. This sulphide is the anhydride of thio-carbonic acid H,CS,; when CS, interacts with concentrated Na,SAq sodium thio-carbonate Na,CS, is formed; the acid H,CS, is obtained as a dark M. E. C. 22 471 472 yellow oily liquid by decomposing one of its alkaline salts by dilute HClAq. Thio-carbonic acid and its salts are very easily decomposed, to CS, and HS in the case of the acid, and to HS and carbonates in the case of the salts. The haloid compounds of the carbon family of the form MX, where X = Cl or Br, are prepared, except in the case of the carbon compounds, by strongly heating an intimate mixture of the oxides MO, and carbon in a stream of chlorine, or bromine; tetrachloride of cerium has not yet been prepared. TiCl, is a liquid boiling at 136°, the other tetrachlorides are solids; they have all been gasified without decomposition. These tetrachlorides all combine with various other chlorides, and in some cases with other compounds, to form double compounds; e.g. TiCl PC1; 3Tic. 4NOCI; TiC1⁄4.4NH ̧; ZrCI,. 2NaCl; 2ThCl,. 8NH,CI. The tetrafluorides MF, M = Ti, Zr, Ce, or Th, are obtained by dissolving the hydrated dioxides MO,.xH2O in aqueous hydrofluoric acid and evaporating. The tetrafluorides of titanium, zirconium, and thorium form compounds with potassium fluoride of the form 2KF. MF,; as in some cases the corresponding hydrogen compounds 2HF. MF, have been isolated and the potassium compounds have been obtained by neutralising aqueous solutions of these hydrogen compounds, it seems better to regard the compounds in question as the potassium salts of fluotitanic, fluozirconic, and Auothoric acids, H,MF, (M = Ti, Zr, Th). A double fluoride of cerium and potassium is known, but its composition is different from that of the K,MF, salts; it is represented by the formula 2CeF. 3KF.2H2O. Cerous chloride, or cerium sesquichloride, Ce,Cl, is obtained by heating in chlorine a mixture of the corresponding oxide, Ce,O,, and carbon. Carbon forms several haloid compounds; CX, CX, CX1, where X Cl or Br; and CI. Carbon tetrachloride CC, trichloride C,Cl, and dichloride C,Cl,, have been gasified without decomposition. The first of these compounds is obtained by the interaction of chlorine and chloroform, CHCI,; the second by the interaction of chlorine and ethylene dichloride, CHCI,; and the third by reducing C,Cl, by means of hydrogen evolved in contact with the carbon trichloride. 4 2 Salts. Salts of carbon, i.e. compounds obtained by replacing the hydrogen of acids by carbon, are unknown. Titanium forms two series of salts; titanous salts represented by the sulphate Ti,(SO), which is obtained by dissolving the corresponding oxide Ti,O, in concentrated sulphuric acid and evaporating; and titanic salts obtained by dissolving the dioxide, TiO2, in acids. Most of the titanic salts are basic salts, e.g. TiO. SO,; 5TiO2. N2O.жH2O; 2TiO1⁄2. P ̧О.жH2O; &c.; a few normal salts are known, e.g. Ti(SO4)2. 3H2O. Zirconium forms one series of salts, the zirconic salts, represented by the sulphate Zr(SO4)2, and one or two others. Most of the zirconium salts are basic salts, e.g. 3ZrO2.SO; 3ZrO,. 2N,O,; 5ZrO2. 4PO, &c. The salts of thorium are all thoric salts, e.g. Th(SO4)2; Th(NO),.xH2O; Th(PO),.xH2O, &c. The thoric salts are usually normal; a few basic salts are known, e.g. Cerium resembles titanium in that it forms two classes of salts. Ce,(SO).xH2O; Ce(NO).жH2O; CePO, &c. The chief representatives of the ceric salts are Ce(SO4)2.xH2O, and Ce(NO3) The salts of all the metals of the family form many double salts generally by combination with salts of the alkali, and alkaline earth, metals. Carbon is evidently separated from the other even series 473 members of Group IV. by its distinctly non-metallic character. The other elements are all metals in their physical properties; their oxides are basic, but most of them shew acidic functions. As the atomic weight increases the elements become more distinctly metallic in their chemical properties. In a few respects, e.g. existence of M2O, and corresponding salts, cerium is more closely related to titanium than to any other member of the family. The three elements titanium, zirconium, and thorium exhibit very marked similarities; the existence of the compounds K,MF, is characteristic. 471 472 yellow oily liquid by decomposing one of its alkaline salts by dilute HCIAq. Thio-carbonic acid and its salts are very easily decomposed, to CS, and H,S in the case of the acid, and to HS and carbonates in the case of the salts. The haloid compounds of the carbon family of the form MX, where X = Cl or Br, are prepared, except in the case of the carbon compounds, by strongly heating an intimate mixture of the oxides MO, and carbon in a stream of chlorine, or bromine; tetrachloride of cerium has not yet been prepared. TiCl, is a liquid boiling at 136°, the other tetrachlorides are solids; they have all been gasified without decomposition. These tetrachlorides all combine with various other chlorides, and in some cases with other compounds, to form double compounds; e.g. TiCl PCI,; 3TiC. 4NOCI; TiCl. 4NH,; ZrCi̟. 2NaCl; 2ThC1.8NHCl. The tetrafluorides MF, M = Ti, Zr, Ce, or Th, are obtained by dissolving the hydrated dioxides MO,. H2O in aqueous hydrofluoric acid and evaporating. The tetrafluorides of titanium, zirconium, and thorium form compounds with potassium fluoride of the form 2KF. MF,; as in some cases the corresponding hydrogen compounds 2HF. MF, have been isolated and the potassium compounds have been obtained by neutralising aqueous solutions of these hydrogen compounds, it seems better to regard the compounds in question as the potassium salts of fluotitanic, fluozirconic, and fluothoric acids, H,MF, (M = Ti, Zr, Th). A double fluoride of cerium and potassium is known, but its composition is different from that of the K,MF, salts; it is represented by the formula 2CeF. 3KF.2H2O. Cerous chloride, or cerium sesquichloride, Ce,Cl, is obtained by heating in chlorine a mixture of the corresponding oxide, Ce2O, and carbon. Carbon forms several haloid compounds; CX,, C2X ̧, C2X¡, where X = Cl or Br; and CI. Carbon tetrachloride CC1, trichloride CCl, and dichloride C,Cl, have been gasified without decomposition. The first of these compounds is obtained by the interaction of chlorine and chloroform, CHCl,; the second by the interaction of chlorine and ethylene dichloride, CHCI,; and the third by reducing C,Cl, by means of hydrogen evolved in contact with the carbon trichloride. Salts. Salts of carbon, i.e. compounds obtained by replacing the hydrogen of acids by carbon, are unknown. Titanium forms two series of salts; titanous salts represented by the sulphate Ti,(SO), which is obtained by dissolving the corresponding oxide Ti,O, in concentrated sulphuric acid and evaporating; and titanic salts obtained by dissolving the dioxide, TiO2, in acids. Most of the titanic salts are basic salts, e.g. TiO.SO.; 5TiO. NO.жH2O; 2тiО. P ̧О. îH2O ; &c.; a few normal salts are known, e.g. Ti(SO). 3H,O. 2 5. Zirconium forms one series of salts, the zirconic salts, represented by the sulphate Zr(SO4)2, and one or two others. Most of the zirconium salts are basic salts, e.g. 3ZrO,. SO1; 3ZrO2.2NO; 5ZrO,. 4P,O,, &c. The salts of thorium are all thoric salts, e.g. Th(SO4)2; Th(NO).жH2O; Th(PO).≈H2O, &c. The thoric salts are usually normal; 1; a few basic salts are known, e.g. Cerium resembles titanium in that it forms two classes of salts. Ce(SO);.xH2O; Ce(NO ̧).жH2O; CePO, &c. The chief representatives of the ceric salts are The salts of all the metals of the family form many double salts generally by combination with salts of the alkali, and alkaline earth, metals. Carbon is evidently separated from the other even series 473 members of Group IV. by its distinctly non-metallic character. The other elements are all metals in their physical properties; their oxides are basic, but most of them shew acidic functions. As the atomic weight increases the elements become more distinctly metallic in their chemical properties. In a few respects, e.g. existence of M,O, and corresponding salts, cerium is more closely related to titanium than to any other member of the family. The three elements titanium, zirconium, and thorium exhibit very marked similarities; the existence of the compounds K,MF, is characteristic. 6 |