The chloride dissolves in fuming hydrochloric acid, forming a deep yellow solution, which becomes colourless when diluted. The solution appears to contain the unstable complex acid H₂TiCl₆, or its ions; by addition of ammonia, or organic bases, salts of the type (NH₄)₂TiCl₆ can be obtained as yellow crystalline solids. An interesting property of the chloride is its ability to form stable additive compounds with the chlorides of negative elements. A long series of these are known, of which the compounds TiCl₄,PCl₃, TiCl₄,PCl₅, TiCl₄,POCl₃, and TiCl₄,2POCl₃ may be considered examples; for the most part, they can be distilled without decomposition. A very long series of compounds, partly additive and partly condensation products, with all kinds of organic substances, is also known. A series of _oxychlorides_, or _basic chlorides_, TiCl₃(OH), TiCl₂(OH)₂, and TiCl(OH)₃, has been obtained by addition of hydrochloric acid, in certain quantities and concentrations, to the chloride; they are amorphous solids, of which little is known. The _tetrabromide_, TiBr₄, is a yellow crystalline solid, melting at 39° and boiling at 230°. Its solutions in concentrated hydrobromic acid are of a blood-red colour, and by treatment with ammonia and organic bases yield deep red crystalline salts of the type (NH₄)₂TiBr₆. The _tetraiodide_, TiI₄, is a reddish-brown metallic-looking solid, melting at 150°, and boiling at 360°; no complex salts are known. _The sulphates._--Many compounds of doubtful composition and individuality have been described as titanium sulphates, but relatively little is known with certainty of this class of derivatives. The most stable seems to be the _titanyl sulphate_, TiOSO₄, obtained as a white powder, which is slowly hydrolysed by water, by evaporating a solution of the dioxide in concentrated sulphuric acid. Under suitable conditions, _e.g._ when separated from acid or alcoholic solutions, it is said to form hydrated compounds; the mono-, di- and penta-hydrate have been described. When solutions of this compound in concentrated sulphuric acid are treated with concentrated aqueous solutions of alkali sulphates, salts of the formulæ (NH₄)₂TiO(SO₄)₂,H₂O and K₄(TiO)₃(SO₄)₅,10H₂O, are obtained. By treating solutions of the dioxide in a large excess of concentrated acid with solutions of calcium or strontium sulphate in sulphuric acid, salts of the type R´´Ti(SO₄)₃ are obtained; the barium salt has the formula 3Ti(SO₄)₂,2BaSO₄. All these compounds are rapidly hydrolysed by water. _Phosphoric Acid Derivatives._--Solutions of titanium compounds are completely precipitated by the addition of phosphoric acid, or soluble phosphates, even in presence of a large excess of mineral acid, but the composition of the precipitate obtained is unknown. By heating the oxide with orthophosphoric acid, a crystalline compound, TiO₂,P₂O₅, is obtained, and various alkali double phosphates may be prepared by suitable fusions.