One of the general methods for the preparation of the metallic filaments may be illustrated by a patent taken out in 1902 by Sander,[594] for the preparation of filaments of zirconium, with or without addition of zirconium carbide. The metal, or a compound which on heating will yield the metal and a volatile substance which can be removed, is prepared in a finely divided condition, and made into a paste with some organic binding material; the paste is then forced through a tiny aperture, and the resulting thread is shaped and heated to a high temperature _in vacuo_ or in an inert atmosphere. If an organic substance be used to form a paste with metallic zirconium, the final process of heating results in the formation of the carbide; the same compound is also obtained by another process protected by Sander (_loc. cit._) in which the hydride of zirconium, prepared by the reduction of the oxide by means of powdered magnesium in an atmosphere of hydrogen, is mixed with a cellulose solution, and the liquid treated as in the manufacture of artificial silk, the threads obtained being then heated to remove all organic matter as far as possible. [594] _D. R. P._ 133701, July, 1902. The carbide is also probably obtained by the process of the British Thomson-Houston Company, in which advantage is taken of the fact that zirconium oxalate is a pasty gelatinous substance, which can be forced through a die to form a thread without addition of any agglutinating agent. The oxalate, precipitated by addition of ammonium oxalate to a solution of a zirconium salt, is mixed with finely divided carbon, and the threads obtained from the pasty mass heated to a very high temperature in a furnace.[595] Zirconium oxalate is also proposed as a binding material for powdered tungsten, in the preparation of filaments from that metal.[596] [595] _E._ 5415, 1908. [596] _E._ 10590, 1908. The compounds of zirconium and thorium with elements of group VB, according to two German patents,[597] are suitable for the preparation of metallic filaments in much the same way. Thorium, titanium, and zirconium are also among the metals which, it is claimed, can be obtained in the pure fused state by heating in an electric arc _in vacuo_, so that filaments can be drawn directly.[598] [597] _D. R. P._ 153958 and 154299, September, 1904. [598] _Ibid._ 169928, April, 1906.