THE DISCOVERY OF THE ELEMENTS. 481 



Freiberg, smelted from the ore in which indium was first discovered, 

 containing very nearly one-half part of indium, per one thousand parts 

 of zinc. A considerable quantity of indium extracted from this zinc, 

 was shown in the Paris Exhibition of 1867; and an ingot from the 

 Freiberg Museum, weighing two hundred grammes, or over seven 

 ounces, has within the last few days been kindly forwarded by Dr. 

 Richter himself, for inspection on the present occasion. To Dr. Schu- 

 chardt, of Goerlitz, also, the members of the Institution are indebted for 

 his loau of nearly sixty grammes of metallic indium ; and of fine speci- 

 mens of other rare chemical products, prepared with his well-known 

 skill, in a state of great purity and beauty. 



When zinc containing indium is dissolved not quite completely in 

 dilute sulphuric or muriatic acid, the whole of the indium originally 

 present in the zinc is left in the black spongy or flocculent residue of 

 undissolved metal, with which every one who has prepared hydrogen 

 gas by means of zinc and acid is so well acquainted. Besides some 

 zinc, this black residue is found to contain lead, cadmium, iron, and 

 arsenic, less frequently copper and thallium, and in some cases, as that 

 of the Freiberg zinc, a small proportion of indium. From the solution 

 of this residue in nitric acid, the indium is separated by ordinary ana- 

 lytical processes, based chiefly on the precipitability of its sulphide by 

 sulphuretted hydrogen from solutions acidulated only with acetic acid, 

 and on the precipitability of its hydrate both by ammonia and carbon- 

 ate of barium. From its soluble salts, metallic indium is readily thrown 

 down in the spongy state by means of zinc. The washed sponge of 

 metal is then pressed together between filtering-paper, by aid of a 

 screw press, and finally melted under a flux of cyanide of potas- 

 sium. 



Thus obtained, indium is a metal of an almost silver-white color, 

 apt to become faintly bismuth-tinted. It tarnishes slowly on exposure 

 to air, and thereby acquires very much the appearance of ordinary lead. 

 Like lead, it is compact and seemingly devoid of crystalline structure. 

 Moreover, like lead and thallium, it is exceedingly soft, and readily 

 capable of furnishing wire, by the process of " squirting " or forcing. 

 The specific gravity of indium, or 7.4, is very close to that of tin, or 

 7.2 ; and much above that of aluminum, 2.6, and below that of lead, 

 11.4, and that of thallium, 11.9. In the lowness of its melting-point, 

 namely, 176 C, indium occupies an extreme position among the metals 

 permanent in air ; the next most fusible of these metals, namely, tin 

 and cadmium, melting at 228; bismuth at 264; thallium at 294; 

 and lead at 235. Though so readily fusible, indium is not an especially 

 volatile metal. It is appreciably less volatile than the zinc in which it 

 occurs, and far less volatile than cadmium. Heated as far as practi- 

 cable in a glass tube, it is incapable of being raised to a temperature 

 sufficiently high to allow of its being vaporized, even in a current of 

 hydrogen. 



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