LANTERNS OF THE DEAD  , the architectural name for the small towers in

stone, found chiefly in the centre and west of France, pierced with small openings at the top, where a light was exhibited at night to indicate the position of a cemetery . These towers were usually circular, with a small entrance in the lower part giving access to the interior, so as to raise the lamps by a pulley to the required height . One of the most perfect in France is that at Cellefrouin (Charente), which consists of a series of eight attached semicircular shafts, raised on a pedestal, and is crowned with a conical roof decorated with fir cones; it has only one aperture, towards the main road . Other examples exist at Ciron (Indre) and Antigny (Vienne) . 187 1: ;It 0muikTik I If ~f 'IC „', :1' I .~T h!C~ J , J 1j, Iy — in. u91 111111 iMiliBlbl lllp d ~, ~ `°°~1 Il t L I III IIItll96 Lantern of the Dead at Cellefrouin (Charente) . . LANTHANUM [symbol La, atomic weight 139•o (0=16)1 one of the metals of the cerium group of rare earths . Its name is derived from the Gr . XavOaveiv, to lie hidden . It was first isolated in 1839 by C . G . Mosander from the " cerium " of J . Berzelius .

It is found in the minerals gadolinite, cerite, samarskite and fergusonite, and is usually obtained from cerite . For details of the complex

process for the separation of the lanthanum salts from cerite, see R . Bunsen (Pogg . Ann., 1875, 155, p . 377); P . T . Cleve (Bull. de la sac. chim., 1874, 21, p . 196) ; and A. v . Welsbach (Monats. f . Chem., 1884, 5, p . 5o8) . The metal was obtained by Mosander on heating its chloride with potassium, and by W .

F .

Hillebrand and T . Norton (Pogg . Ann., 1875, 156, p . 466) on electrolysis of the fused chloride, while C . Winkler (Ber., 189o, 23, p . 78) prepared it by heating the oxide with a mixture of magnesium and magnesia . Muthmann and Weiss (Ann., 1904, 331, p . 1) obtained it by electrolysing the anhydrous chloride . It may be readily hammered, but cannot be drawn . Its specific gravity is 6.1545, and it melts at 81o° . It decomposes cold water slowly, but hot water violently .

It

burns in air, and also in chlorine and bromine, and is readily oxidized by nitric acid . Lanthanum oxide, La203, is a white powder obtained by burning the metal in oxygen, or by ignition of the carbonate, nitrate or sulphate . It combines with water with evolution of heat, and on heating with magnesium powder in an atmosphere of hydrogen forms a hydride of probable composition La2H3 (C . Winkler, Ber . 1891, 24, p . 890) . Lanthanum hydroxide, La(OH)3, is a white amorphous powder formed by precipitating lanthanum salts by potassium hydroxide . It decomposes ammonium salts . Lanthanum chloride, LaCl3, is obtained in the anhydrous condition by heating lanthanum ammonium chloride or, according to C . Matignon (Compt. rend., 1905, 40, p . 1181), by the action of chlorine or hydrochloric acid on the residue obtained by evaporating the oxide with hydrochloric acid . It forms a deliquescent crystalline mass .

By evaporation of a

solution of lanthanum oxide in hydrochloric acid to the consistency of a syrup, and allowing the solution to stand, large colourless crystals of a hydrated chloride of the composition 2LaC13.15H20 are obtained . Lanthanum sulphide, La2S3, is a yellow powder, obtained when the oxide is heated in the vapour of carbon bisulphide . It is decomposed by water, with evolution of sulphuretted hydrogen Lanthanum sulphate, La2(SO4)3.9H20, forms six-sided prisms, isomorphous with those of the corresponding cerium salt . By careful heating it may be made to yield the anhydrous salt . Lanthanum nitrate, La(NO3)3.6H20, is obtained by dissolving the oxide in nitric acid . It crystallizes in plates, and is soluble in water and alcohol . Lanthanum carbide, LaC2, is prepared by heating the oxide with carbon in the electric furnace (H . Moissan, Compt. rend., 1896, 123, p . 148) . It is decomposed by water with the formation of acetylene, methane, ethylene, &c . Lanthanum carbonate, La2CO3.8H20, occurs as the rare mineral lanthanite, forming greyish-white, pink or yellowish rhombic prisms . The atomic weight of lanthanum has been determined by B .

Brauner (Prot . Chem .

Soc., 1901, 17, p . 63) by ignition of lanthanum sulphate at 5oo° C., the value obtained being 139 (O =16) .