Attempts have been made to employ titanium in the manufacture of metal filaments for glow lamps. The metal would be very suitable for this purpose, by reason of its high melting-point and low conductivity, but the difficulty of obtaining it in the pure state, and the remarkable susceptibility of the filament to traces of impurity, have so far proved insuperable. For the sake of illustration, a proposal put forward in 1908 may be briefly referred to.[643] Pure titanium dioxide is heated in a stream of ammonia; the nitride obtained is decomposed at 1200° _in vacuo_, and after cooling, the metal is powdered and made into a paste with a solution of albumen in ammonia. The threads obtained from this in the usual manner are heated to 1200° in an electric furnace; the carbon deposited from the albumen forms the cyanide by reaction with the trace of nitride which has escaped decomposition, or which has been formed by further action of ammonia. The cyanide is volatile, and can be removed at high temperatures _in vacuo_, leaving a sintered filament of the metal. So susceptible is the filament to impurity, that the trace of carbon deposited from the vapour of the oil of the pump which diffuses into the vacuum is sufficient to render it so fragile as to be useless.[644] [643] Trenzen and Pope, _E._ 14852, 1908. [644] _Vide_ _Bull. Imp. Inst._ 1911, ~9~, 134. ~Titanium Compounds in Dyeing and Colouring.~--The use of titanium compounds as mordants in the dyeing of leather and textile goods has been known for a considerable time.[645] As early as 1896, a patent was taken out by Barnes[646] for the treatment of prepared animal skins by immersion in a bath of a titanium salt. Subsequent boiling or steaming causes hydrolysis, with precipitation in the skin of hydrated titanium dioxide, which forms lasting dye-lakes when the fabric is immersed in the dye-bath. Whilst this treatment has been found satisfactory with some classes of leather goods,[647] more delicate kinds are liable to be injured by the mineral acid set free, and numerous patents protecting the preparation and employment of organic salts of the element have been taken out by Dreher.[648] The same investigator[649] has discovered that excellent results can be obtained in the cold by the addition of various ‘Hülfsalze,’ which are chiefly acetates or formates of the alkaline earth metals, chromium, or aluminium, or basic salts of the last two. Double decomposition of these with the titanium salt forms basic or highly hydrolysed salts of the latter, so that the hydrated oxide or a basic compound is formed on the fabric. [645] A good account of some of the earlier work in this connection is given by Erban, _Chem. Zeitg._ 1906, ~30~, 145. [646] _E._ 5712, 1896. [647] _Vide_ Dreher, _D. R. P._ 142464, June, 1903. [648] _Vide_ _E._ 22629 and 23188 of 1901, 14921 and 27597 of 1902, and 5211 of 1903.