Several patents protect the use of rare earth compounds for flashlight powders. For most of the mixtures covered, it is claimed that the usual defects of fumes, slow firing, etc., are absent. The usual recipes[581] are for magnesium or aluminium powder with chromates, nitrates, or similar salts of thorium, cerium, etc.; in one case[582] the rare earth metals, alloyed with barium, silicon, uranium, or titanium, are to be used with ‘an oxidising agent which leaves a non-volatile residue.’ None of these mixtures appears to have been successful. [581] _Vide_, _e.g._ _E._ 14692, 1908; _D. R. P._ 158215. [582] _F._ 403722, October, 1909. Cerium compounds have also been proposed for use in arc-lamp electrodes; it is claimed that they give a very intense light, one patent[583] adding that the presence of cerium peroxide and a little fluorspar causes the arc to burn evenly and quietly. In another, the use of a mixture of tungstates or molybdates of the alkaline earths, with fluorides of the rare earth elements is protected;[584] the use of pyrophoric alloys, either entirely, or for the core of the electrode, has also been suggested.[585] [583] _E._ 414707, June, 1910. [584] _F._ 431040, August, 1911; also _E._ 21374, 1909. [585] _E._ 8150, 1909. ~The Nernst Lamp.~--The first efforts which were made for the employment of electricity in illumination endeavoured to utilize the heat produced, when a current traverses a very thin metallic filament, to raise the conductor to incandescence. Numerous efforts were made to adapt platinum to this purpose, but its melting-point was finally admitted to be too low; at length it was found possible to produce carbon filaments, and the well-known carbon lamps came into use. Numerous attempts were made to effect improvements;[586] one plan was to coat the carbon filament, after its production, with a skin of metallic conductor, and zirconium and thorium were among the metals proposed in this connection.[587] The first really important advance, however, was effected by Nernst, who took up the study of ‘conductors of the second order,’ and within a few months succeeded in adapting these to the purposes of illumination (1897-1898). The Nernst lamps gave a very intense white light with considerably less consumption of electricity than the carbon filament lamps; they enjoyed a very considerable vogue for some years, but have been almost entirely displaced by the cheaper metal filament lamps, which were occupying the attention of Auer von Welsbach at the time Nernst perfected his invention.[588] [586] The reader is recommended to consult the _Jahresberichte über die Leistungen der Chemischen Technologie_ of Fischer, Section ‘Beleuchtung,’ for the years 1898-1901 inclusive, from which some idea may be obtained of the innumerable proposals and suggestions, usually protected by patent, which were put forward at this time. [587] _Vide_, _e.g._ _D. R. P._ 153959.