The _carbide_, ThC₂, is obtained by the action of carbon on the oxide in the electric furnace; it is a yellow crystalline mass, decomposed slowly by water, energetically by dilute acids in the cold, with evolution of a complex mixture of hydrogen and hydrocarbons, in which many members of the paraffin, olefine and acetylene series have been observed.[482] Hydrogen constitutes over 50 per cent. of the mixture, the next most important constituents being the acetylenic hydrocarbons, followed by ethane. [482] Lebeau and Damiens, _Compt. rend._ 1913, ~156~, 1987. _Thorium fluoride_, ThF₄, is obtained anhydrous by passing hydrogen fluoride over the anhydrous chloride or bromide at a temperature of 350°-400°. The tetrahydrate, ThF₄,4H₂O, is precipitated by addition of hydrofluoric acid to a solution of a thorium salt, or by the action of the acid on the hydroxide. Hydrofluosilicic acid also throws down the fluoride, even in the cold, from solutions of thorium salts. The fluoride is insoluble in water and mineral acids, as well as in excess of precipitant; this behaviour allows of a complete and easy separation of thorium from titanium and zirconium. The rare earth fluorides are also much more easily soluble in concentrated mineral acids than thorium fluoride, so that this compound may also be used in the separation from the rare earths. When heated in a stream of the acid to 800°, the hydrated salt yields the oxyfluoride, ThOF₂; ignited in the air, it leaves the dioxide. Precipitation with potassium fluoride gives the _double fluoride_, KThF₅,H₂O, which may be obtained anhydrous by fusion of the mixed fluorides; it is insoluble. An amorphous insoluble compound, K₂ThF₆,4H₂O, is obtained by boiling the hydroxide with a mixture of potassium hydrogen fluoride and hydrofluoric acid. Sodium and ammonium fluorides throw down the simple fluoride. _Thorium chloride_, ThCl₄, is obtained in the anhydrous form by all the usual methods, the most convenient being perhaps the action of chlorine and sulphur monochloride on the heated dioxide. It almost invariably contains small quantities of oxychloride. When pure, it forms colourless needles fairly stable in dry air; the impure product gradually darkens in colour. It dissolves in water with considerable evolution of heat, and is soluble also in alcohol and moist ether. It melts at about 820°, and sublimes unchanged at somewhat higher temperatures; the vapour begins to dissociate at about 1050°, the dissociation increasing rapidly as the temperature rises. It resembles zirconium chloride in the ease with which it forms additive compounds with ammonia and organic bases, and addition and condensation products with organic oxygen-compounds; many _double_ and _complex chlorides_ are also known, among which the platinum compounds ThPtCl₈,12H₂O and Th₂Pt₃Cl₁₄,24H₂O, and the pyridine salt (C₅H₅NH)₂ThCl₆ may be mentioned.