[649] _Vide_ _D. R. P._ 139059 and 139060 of February, 1903, and 139838 of March, 1903. The titanium salts specified in these patents are salts of the element in the tetravalent condition, prepared from rutile by the action of strong mineral acids. As early as 1902, the technical preparation of salts of trivalent titanium for reducing purposes was patented by Spence and Spence, of Manchester.[650] The process is an electrolytic one, and is effected in a cell divided into two compartments by a porous partition, one electrode being introduced into each compartment; an electromotive force of 3-4 volts is required. A 20-25 per cent. titanium tetrachloride solution is introduced into the cathode compartment, and dilute hydrochloric acid into the anode compartment; on electrolysing, chlorine is evolved at the anode, and may be utilised as usual in the preparation of bleaching powder, etc., whilst the tetrachloride in the cathode compartment is reduced to trichloride. The solution is then concentrated at 65°-70°C. under reduced pressure, and the crystalline trichloride separated. In the preparation of the corresponding sulphate, sodium sulphate must be present in the cathode compartment, and a double salt is obtained; the process is carried out in lead-lined cells, in presence of excess of sulphuric acid. The preparation of the sesquioxide, Ti₂O₃, free from compounds of aluminium and iron, was also suggested by Dreher[651] by reduction of the acid solution of the impure or mixed salts with zinc or sodium amalgam, and approximate neutralisation; the sesquioxide differs from the dioxide in that it separates while the solution is still somewhat acid, which the hydrated oxides of iron and aluminium will not do. Dreher suggested that the strong reducing properties of the sesquioxide and its salts should make these valuable for bleaching, colour-printing, and similar purposes. [650] _E._ 16238 and 18108 of 1902. [651] _E._ 1835, 1903. More recently[652] the reduction of titanium salts by means of aluminium powder has been suggested; in the case of the sulphate, the aluminium salt formed may be partly eliminated as alum, in the ordinary way, if desired, but it is claimed that its effect is beneficial rather than harmful. The preparation of organic double basic salts of trivalent titanium,[653] which hydrolyse very readily, suggested the use of such compounds as mordants and for reducing purposes. These salts may be prepared fairly easily[654] by adding concentrated solutions of the appropriate potassium, sodium, or ammonium salts in excess to concentrated solutions of the trichloride, in absence of air. The double salts separate, and are washed and dried; in this condition they are fairly stable, but the solutions hydrolyse at once on merely warming, with separation of the hydrated sesquioxide. On this account, and also because of the strong reducing action, these compounds are likely to prove valuable as mordants, and for other purposes.