Production of titanium dioxide

Claim 1

IN THE SULFURIC ACID DIGESTION OF TITANIFEROUS MATERIAL, SAID MATERIAL HAVING BEEN OBTAINED BY ELECTROTHERMAL SMELTING OF A TITANIFEROUS ORE IN THE PRESENCE OF A CARBONACEOUS REDUCING MATERIAL AND CONSEQUENTLY CONTAINING MORE THAN ONE PER CENT OF ITS TITANIUM IN A REDUCED STATE HAVING A VALENCE OF LESS THAN FOUR, WHEREIN THE TITANIFEROUS MATERIAL IS HEATED IN ADMIXTURE WITH CONCENTRATED SULFURIC ACID TO INITIATE EXOTHERMIC REACTION THEREBETWEEN, THE HOT REACTION MASS IS PERMITTED TO SET IN THE FORM OF A HARD POROUS CAKE, AND THE RESULTING HOT CAKE IS BAKED BY BEING RETAINED AT AN ELEVATED TEMPERATURE FOR A SUFFICIENT PERIOD OF TIME TO EFFECT MORE COMPLETE CONVERSION OF THE TITANIFEROUS MATERIAL TO TITANIUM SULFATE, THE IMPROVEMENT WHICH COMPRISES PASSING AN OXYGEN-CONTAINING GAS THROUGH THE POROUS CAKE DURING THE BAKING STAGE, AND MAINTAINING THE POROUS CAKE DURING THE PASSAGE OF SAID GAS THERETHROUGH AT AN ELEVATED TEMPERATURE WITHIN THE RANGE OF 150* TO 260* C. IN ORDER TO PROMOTE OXIDATION OF THE REDUCED TITANIUM TO THE TETRAVALENT STATE BY THE OXYGEN CONTENT OF SAID GAS PASSING THERETHROUGH.