As to the actual nature of the effect produced, it is generally believed that titanium acts merely as a cleansing agent, freeing the metal from occluded or combined gases, and removing blow-holes, so producing a denser and more homogeneous structure, with consequent improvement in properties. The added titanium is usually found entirely in the slag, so that it appears certain that it does not alloy, but merely purifies. It certainly acts as a powerful and rapid deoxidiser, removing the last traces of the gas which have escaped the action of the manganese, silicon, etc., with which steels are now generally treated. Many authorities, on the ground of analyses, and of the known affinity of titanium for nitrogen, believe that it very largely reduces the nitrogen-content,[625] which is so harmful; this, however, is still an open question.[626] It is stated that if excess of titanium is used, so that small quantities--0·05-0·20 per cent.--remain in the finished steel, the toughness and durability are further increased;[627] but as a rule, manufacturers prefer to work with smaller quantities, so that no free titanium remains in the product. [625] _Vide_ von Maltitz, _loc. cit._ [626] _Vide_ Venator, _loc. cit._ [627] _Vide_ _Bull. Imp. Inst._ 1911, ~9~, 134. * * * * * The preparation of alloys of titanium with almost all the commoner metals is protected by patent, but few of these are of technical importance. Small quantities of titanium are said to improve very considerably the properties of copper and its alloys, the brasses, bronzes, etc., especially in castings. The addition is usually made in the form of an appropriate titanium alloy, prepared by reduction of the mixed oxides with carbon in an electric furnace, or treatment of the mixed oxides, together with the alloying metal, with aluminium under similar conditions.[628] The titanium-silver alloys obtained in this way[629] are said to improve greatly the structure of silver, by preventing the familiar ‘spitting’ as the fused metal cools. [628] _Vide_ Rossi, _U. S. P._ 986505, March, 1911; 935863, October, 1909, etc. [629] Rossi, _U. S. P._ 1024476 and 1025426, August, 1912. An interesting process, which has been patented by Rossi,[630] recalls the method of formation of cementation steels. He has found that if a metal be loosely covered with its alloy with titanium, in a finely powdered condition, and the whole heated, the titanium diffuses into the metal, to a depth and concentration which vary with the temperature and the time of heating. He suggests that in this way a metallic body may be toughened and strengthened at any desired point, _e.g._ steel for armour-plate at the surface. Whether the process will be of any technical value or not can only be shown by experiment. [630] _U. S. P._ 986504, March, 1911.