I 
ON THE METAL INDIUM. 335 
No less than four new elementary bodies have already been discovered by means of 
Spectrum Analysis: Caesium and Rubidium, by Bunsen; Thallium, by Mr. Crookes; 
and Indium, by Reich and Richter, of Freiberg ; whilst the foundations of Solar Che¬ 
mistry, laid by Kirchhoff, have been rendered more secure by the observations of Cooke, 
in America ; Donati, in Italy ; and Miller and Huggins, in England. 
Caesium and rubidium were at first only found in one or two mineral waters ; they 
have since been shown to be widely distributed in the vegetable as well as in the mine¬ 
ral kingdom; they have been obtained in considerable quantities from the beet-root 
salt, and found in the ashes of tea and coffee, thus proving that they occur commonly in 
oil; whilst, quite recently, M. Pisani has found that a mineral, called pollux, occurring 
in Elba, contains 34 per cent, of caesium : this metal having been mistaken for potash in 
the analyses which had previously been made of this substance. Thallium and its com¬ 
pounds have been obtained in large quantities, and their properties fully investigated by 
Crookes and Lamy; whilst this metal has not only been found in iron pyrites, but also 
in large quantities, by Schrotter, in the mica of Zinnwald, and in lepidolite, from Mora¬ 
via. Thallium has been shown byBoettgerto occur, together with caesium and rubidium, 
in the mineral water of Nauheim, near Frankfort. Boettger has, moreover, shown that 
thallium is contained in the vegetable kingdom : he has found it in the yeast of the vi¬ 
nous fermentation ; so that thallium exists in wine, also in treacle, tobacco, and chicory. 
If 4 lb. of any of these substances are employed, a sufficient quantity of thallium can 
be obtained as the double platinum-chloride to enable its presence to be easily detected. 
Professor Bunsen has informed the speaker that he has found a mother liquor from the 
Hartz, which contains so much thallium, that the iodide can be obtained by direct pre¬ 
cipitation at the rate of 10s. per lb. The speaker exhibited the spectrum of the Nauheim 
salt, which contains the three new elements ; the spectrum of each metal is well seen 
by placing the mixed platino-chlorides in the electric arc. 
Drs. Reich and Richter, of Freiberg, in Saxony, have lately discovered a fourth new 
metal in the Freiberg zinc blende.* This metal has been termed Indium, from the two 
splendid indigo-blue lines which characterize its spectrum. Through the kindness of 
Professor Richter, the speaker had been placed in possession of a few grains of this new 
metal, the spectrum of which was exhibited by the electric lamp. In its chemical rela¬ 
tions it resembles zinc, with which it is associated in nature ; the metal can be reduced 
before the blowpipe to a malleable bead, when it forms a soft, ductile bead, which im¬ 
parts streaks to paper on rubbing, and possesses a colour lighter than that of lead, being 
about the same as that of tin. The metallic bead dissolves in hydrochloric acid with 
the evolution of hydrogen. The oxide of indium is formed as a yellow fusible incrusta¬ 
tion when the metal is heated before the blowpipe on charcoal. Indium differs from 
zinc in the insolubility of the hydrated oxide in excess of both ammonia and caustic 
potash. This new element may be separated from all the known metals by precipita¬ 
ting its sulphide in alkaline solution, and by throwing down the hydrated oxide first 
with ammonia and then with caustic potash ; and, lastly, by precipitating the iron with 
dilute solution of bicarbonate of sodium. The hydrated oxide of indium then remains 
in solution in the pure state. Indium may be readily detected when present in its pure 
compounds by the deep purple tint which these impart to flame. The characteristic 
lines are, however, best seen when a small bead of indium salt is placed between two 
poles, from which an electric spark passes; the lines In a and In £ fall respectively upon 
divisions 107\5, and 140 of the photographic scale of the spectroscope, when Na = 50, 
and Sr 5 = 100'5. Up to the present time, indium has been only found in the very 
smallest quantity, and hence the atomic weight of the metal and the composition of its 
salts have not yet been determined; in fact, the speaker was led to infer that Professor 
Richter sent him nearly all the compound of the metal remaining from the investigation 
of its properties, for the purpose of illustrating this discourse. It has only as yet been 
detected in the zinc blende of Freiberg; but it will, doubtless, soon be discovered in 
larger quantities, and its compounds more closely studied. 
As regards the spectra of the well-known metals, our knowledge has been much in¬ 
creased by the publication of the second series of Kirchhoff’s maps of the solar spectrum 
and the spectra of the chemical elements (Macmillan and Co.). In these, Kirchhoff has 
marked the position of the bright lines of no less than thirty metals, and indicated those 
* Phil. Mag. for March, 1864, 4th ser. vol. xxvii. p. 199. 
