hydrate of the composition TiO(OH)_{2}, and when heated it parts with a still larger proportion of water; at 100° the hydrate Ti_{2}O_{3}(OH)_{2} is obtained, and at 300° the anhydride itself. The higher hydrate, Ti(OH)_{4}, is soluble in dilute acid, and the solution may be diluted with water; but on boiling the sulphuric acid solution (though not the solution in hydrochloric acid), all the titanic acid separates in a modified form, which is, however, not only insoluble in dilute acids, but even in strong sulphuric acid. This hydrate has the composition Ti_{2}O_{3}(OH)_{2}, but shows different properties from those of the hydrate of the same composition described above, and therefore this modified hydrate is called _metatitanic acid_. It is most important to note the property of the ordinary gelatinous hydrate (that precipitated from acid solutions by ammonia) of dissolving in acids, the more so since silica does not show this property. In this property a transition apparently appears between the cases of common solution (based on a capacity for unstable combination) and the case of the formation of a hydrosol (the solubility of germanium oxide, GeO_{2}, perhaps presents another such instance). If titanium chloride be added drop by drop to a dilute solution of alcohol and hydrogen peroxide, and then ammonia be added to the resultant solution, a yellow precipitate of _titanium trioxide_, TiO_{3}H_{2}O, separates out, as Piccini, Weller, and Classen showed. This substance apparently belongs to the category of true peroxides.