[642] Guay, U. S. P. 1039522, September, 1912.
In arc lamps in which pencils containing titanium compounds are used, the anode is generally made of copper, and is placed below the cathode, the reverse being the case where carbon electrodes are employed. The copper is inactive, and contributes nothing to the light; if the anode be of suitable dimensions, it wears away very slowly, whereas the cathode, containing the titanium compound, is rapidly consumed. In lamps in which carbon electrodes are used, the light is emitted chiefly from the extremities of the electrodes, the path of the arc being comparatively non-luminous; the light has the familiar reddish-yellow colour characteristic of the earlier forms of arc lamps. Where titanium pencils are employed, however, the light is emitted almost entirely from the arc itself, the electrodes contributing very little, and is of a pure white colour, very different from that of the carbon lamp.
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.