this invention relates to a novel chemical apparatus , the inner surfaces of which are constituted by titanium material . the invention solves the problems of crevice corrosion and embrittlement of the material by taking in hydrogen , and discloses a method of solving such problems . the prior art methods of preventing crevice corrosion in apparatus prepared from titanium metal and also preventing the titanium of such apparatus from becoming fragile due to absorption of hydrogen include a method , in which an element of the platinum group is deposited on the surface of the titanium material and diffused thereinto . alternatively , a ti - pd alloy is used as the material of the apparatus . such methods , however , complicate the manufacture of the apparatus and are also disadvantageous in view of the cost of the great quantity of the platinum group element such as palladium which is consumed . in accordance with the invention , a mixed oxide layer , composed of an oxide of a platinum group element and an oxide of an anti - corrosion metal is provided on the surface , particularly , in the crevices of the titanium material of apparatus to achieve satisfactory prevention of corrosion and also prevention of hydrogen absorption . this method is very economical compared to the prior - art methods because the required quantity of the platinum group element is very small .