TITANIUM (symbol Ti, atomic number 22, atomic weight 48-1). In a substantially pure state, titanium has a very restricted commercial application. The method adopted by Hunter is the standard one for the production of the pure element, but an im pure product may be obtained from the dioxide by the application of Goldschmidt's thermit reaction (see below) or by reduction with carbon in the electric furnace. Pure titanium is silver-white with a fracture similar to that of steel. It is hard and brittle when cold, but at a low red heat it is malleable and can be forged readily like iron. The specific gravity is 4.5 and the melting point, accord ing to Hunter, 1850°C. It is soluble in dilute sulphuric acid, in hot concentrated hydrochloric acid and in aqua regia, whilst hydro fluoric acid readily dissolves it. It combines with nitrogen with avidity. With oxygen and the halogens, compounds of quad rivalent titanium are produced.
The existence of the element known as titanium was dis covered in 1789 by the Rev. William Gregor during an investi gation of a peculiar black sand found at Menachan in Corn wall. This black mineral he called menachanite (or meccanite) and the new element he named menachite. Four or five years later, the German chemist, Klaproth, discovered a new metal whilst in vestigating the composition of the mineral rutile. On account of the strength of the chemical combination in which it was held, he gave to the new element the name titanium—an allusion to the Titans of Greek mythology, the incarnation of natural strength. In 1797 Klaproth investigated the mineral ilmenite—which was identical with menachanite—and recognized that titanium and the menachite of Gregor were identical. Nevertheless, titanium is the name which is now universally adopted for the element. Attempts to isolate titanium were first made by Lampadius in '797 and later by Berzelius and other investigators. The metallic-looking prod ucts isolated by early investigators were generally nitrides or car bides, for titanium has a pronounced affinity for oxygen, carbon, and nitrogen. In 1895, Moissan published an account of his ex periments on the reduction of titanium dioxide with carbon at the temperature of the electric furnace. His final product was free from nitrogen and silicon but contained about 2% of carbon, probably as the carbide. This was the purest titanium isolated till the work of Hunter in 191o, who adopted a method previously used, unsuccessfully, by Nilson and Petterssen. By heating titan ium tetrachloride with sodium in an air-tight steel cylinder, with exclusion of air, Hunter obtained titanium nearly i00% pure.
Although frequently regarded as one of the rare elements, titanium occupies the ninth place in Clarke's table of the esti mated abundance of the elements in the earth's crust. This table
discloses the interesting fact that titanium is more abundant than such common elements as carbon, phosphorus or sulphur, and much more abundant than the useful metals, lead, copper and zinc. There is, however, a distinctive difference between the mode of occurrence of titanium and that of these other metals, for whereas the greater part of the titanium is so widely diffused through the earth's crust as to make its recovery economically im possible, the less abundant metals are concentrated in segregated deposits (mineral veins, lodes, etc.) capable of satisfactory ex ploitation. Hence, of all the numerous titanium-bearing minerals, only three or, at most, five are entitled to be classed as possible ores of titanium. They are rutile ilmenite titaniferous magnetite (magnetite is Fe,0,), and possibly titanite and perovokite (Ca,Fe'') TiO3. Rutile occurs in igneous, in metamorphic, and in sedimentary rocks, and its mineral associates include a wide range of species. Although widespread in occurrence, deposits of commercial importance are few in number and, so far, restricted to certain localities in the United States, Canada, Norway and South Australia. Rutile crystallizes in the tetragonal system, commonly as short, stout prisms or elongated prisms frequently showing striated prism faces. It is normally reddish-brown to red, the specific gravity of the ordinary red variety being 4.18 to 4.25. Titanium dioxide contains 6o% of titanium and 40% of oxygen. Actually, the mineral usually contains from 54 to 59% of titanium with minute quantities of vanadium and iron. Rutile is infusible before the blowpipe and insoluble in acids, but fused alkalis and alkali carbonates bring it into solution. Ilmenite crystallizes in the hexagonal system as rhombohedra, but it is rarely seen as good megascopic crystals. Commonly it occurs as embedded grains and masses, whilst it may also be found as a sand. The mineral is iron-black with a metallic lustre. Although it is customary to assign to it the formula numerous analyses indicate the formula whilst others correspond to neither formulation. Ilmenite is both cheaper and more plentiful than rutile, and probably the most extensive deposits of the min eral are those of the province of Quebec, Canada, and the Eker sund-Soggendal district of Sweden. Other important deposits are found in the United States and South Australia, whilst ilmenite is a by-product from the crude monazite sands of Ceylon and Travancore, India. For industrial purposes the only distinction between ilmenite and titaniferous magnetite is in the titanium content. Ore, classed as ilmenite, has a titanium content of 18 to 24% or more, whilst titaniferous magnetite seldom carries more than 15% of titanium.