The elements of Group IVA are distinguished from the rare earth elements by their much less strongly marked electropositive character. This is apparent not only in the amphoteric nature of the oxides, and in the ease with which the salts are hydrolysed in solution, but in the more pronounced tendency to the formation of complex salts. The complex fluorides of the type K₂RF₆ are peculiarly characteristic, and in the case of titanium and zirconium have been very important for purposes of analysis and atomic weight determination. The solubility of zirconium and thorium salts in excess of alkali oxalate or carbonate is also in harmony with the less pronounced electropositive character of these elements. The sulphates of titanium and zirconium appear to be of complex constitution, whilst their neutral chlorides cannot be obtained from solution. As is to be expected from its high atomic weight, thorium approaches most nearly to the rare earths in chemical properties; thus it forms stable double nitrates of the type R₂Th(NO₃)₆ and its salts, especially the sulphate, resemble those of the rare earth elements in their solubility relations. The elements titanium, zirconium, and thorium are distinguished also by the fact that they form no definite hydroxides. The precipitates thrown down from solutions of the salts, on addition of alkali, are hydrated oxides, which lose water continuously when dried, giving rise to no definite chemical individuals until constant weight is reached with the anhydrous oxides. The hydroxides have the further characteristic, common also to the other members of Group IV, of readily forming colloidal solutions and gels, a property possessed to some extent also by the elements themselves, and particularly by zirconium, which, when reduced from its compounds, shows a great tendency to go into colloidal solution merely on washing. Highly characteristic also is the property of forming ‘meta’-oxides (acids) and ‘meta’-salts, which is common to all the Group IV elements which have solid oxides. In presence of hydrogen peroxide, alkalies throw down characteristic hydrated peroxides, which have definite acidic properties in the case of titanium: the zirconium compound is less strongly acidic, the cerium compound shows no tendency to salt formation, whilst if hydrogen peroxide be added to a neutral or faintly acid solution of a thorium salt, the precipitate is a peroxy-salt, containing some acid grouping, _e.g._ SO₄,NO₃.