6G 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[July 27, 1872. 
known metal potassium, thallium can hardly he said 
even at the present time, to be definitely and generally 
recognized by chemists as the analogue of any particular 
.metal, or as a member of any particular family of ele¬ 
ments. With each of such differently characterized 
elements as potassium, lead, aluminum, silver and gold, 
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 
_ r _ 7 _ 7 _ 7 __ i melting-point, namely, 176° C., indium occupies, an ex¬ 
it is associated by certain marked points of resemblance; treme position among the metals permanent in air ; the 
while from each of them it is distinguished by equally next most fusible of these metals, namely tin and cad- 
’well-marked points of difference. Hence the necessity | minm. mhltino- at 228°: bismuth at 264 L ; thallium at 
for subjecting thallium and its salts to a thorough che¬ 
mical examination, so as to accumulate a well ascer 
tained store of facts with regard to it. And thanks to 
the careful labours of many chemists, more particularly 
of Mr. Crookes in London, and of Messrs. Lamy and 
Willm in Paris, our knowledge of the properties of 
thallium and of its salts may compare not unfavourably 
with our similar knowledge in relation to even the 
longest known of the metallic elements. Still it was 
not until our knowledge of indium had culminated in 
the determination of its specific heat only last year, that 
the position of thallium as an analogue of indium, and a 
member of the aluminum family of elements became 
unmistakably evident. 
Indium was first recognized in 1863, by Drs. Reich 
and Richter, in the zinc blende of Freiberg in Saxony, 
and by reason of the very characteristic spectrum 
afforded,—consisting of two bright blue or indigo bands; 
mium, melting at zzcr; bismuth at 264 
294°; and lead at 235°. Though so readily fusible, in¬ 
dium is not an especially volatile metal. It is appre¬ 
ciably less volatile than the zinc in which it occurs, and 
far less volatile than cadmium. Heated as far as prac¬ 
ticable 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. 
Indium resists oxidation up to a temperature some¬ 
what beyond its melting-point, but at much higher tem¬ 
perature it oxidizes freely ; and at a red heat it takes 
fire in the air, burning w T ith a characteristic blue flame 
and abundant brownish smoke. It is readily attacked 
by nitric acid, and by strong sulphuric and muriatic 
acids. In diluted sulphuric and muriatic acids, however, 
it dissolves but slowly, with evolution of hydrogen. 
Oxide of indium is a pale yellow powder, becoming darker 
when heated, and dissolving in acids with evolution of 
heat. The hydrated oxide is thrown down from indium 
the brightest of them somewhat more refrangible than 1 solutions by ammonia, as a white, gelatinous, alumina- 
the blue line of strontium, and the other of them some- like precipitate, drying up into a horny mass. The 
w r hat less refrangible than the indigo line of potassium. : sulphide is thrown down by sulphuretted hydrogen as an 
♦Since its first discovery, indium has been recognized in orange-yellow precipitate, insoluble in acetic but.soluble 
one or two varieties of wolfram, and as a not unfrequent in mineral acids. The hydrate and sulphate of indium, 
constituent of zinc ores, and of the metal obtained there¬ 
from, but always in a very minute proportion. Indeed, 
indium would appear to be an exceedingly rare element, 
far more rare than its immediate predecessors in period 
of discovery. Its chief source is metallic zinc,—that of 
Freiberg, smelted from the ore in w T hich indium was first 
discovered, containing very nearly one half part of in¬ 
dium per 1000 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 
in their relations to fixed alkali solutions more particu¬ 
larly, seemed to manifest a feebly-marked acidulous 
character. Chloride of indium, obtained by combustion 
of the metal in chlorine gas, occurs as a white micaceous 
sublimate ; and is volatile at a red heat without previous 
fusion. The chloride itself undergoes decomposition when 
heated in free air, and the solution of the chloride upon 
brisk evaporation, with formation in both cases of an 
oxichloride. 
But the chief point of chemical interest with regard 
Museum, weighing 200 grammes, or over 7 ounces, has to any newly discovered element, and consequently with 
within the last few days been kindly forwarded by Dr. regard to indium, is the establishment of its atomic 
Richter himself, for inspection on the present occasion, weight; which, in the case of a metallic element, is based 
To Dr. Schuchardt, of Goerlitz, also, the members of the primarily upon the determination of the ratio in which 
Institution are indebted for his loan of nearly 60 grammes it combines with oxygen and chlorine. Now the quan- 
of metallic indium; and of fine specimens of other rare ! tity of indium w r hich unites with 8 parts by weight of 
chemical products, prepared with his well-known skill, oxygen and with 35‘5 parts by weight of chlorine, has 
in a state of great purity and beauty. been found by Winkler to be 37’9, and by Bunsen to be 
When zinc containing indium is dissolved not quite com- 37*8 parts. But this determination of combining ratio 
pletely in dilute sulphuric or muriatic acid, the whole of the falls far short of the definite establishment of the atomic 
indium originally present in the zinc is left in the black weight of the metal. For example, the quantities of 
spongy or flocculent residue of undissolved metal, with silver, mercury, bismuth, tin and tantalum, which exist 
which every one who has prepared hydrogen gas by in the best-known chlorides of these metals combined 
means .of zinc and acid is so well acquainted. Besides with 35*5 parts of chlorine, are 108, 100, 70, 29, and 37 
some zinc, this black residue is found to contain lead, parts respectively. Nevertheless, the atomic weights of 
cadmium, iron and arsenic, less frequently copper and these metals are taken to be not 108, 100, 70, 29 and 37, 
thallium, and in some cases, as that of the Freiberg zinc, but 108, 200, 210, 118, and 184 respectively, the chlorides 
a small proportion of indium. From the solution of this of the several metals being expressed by the formulae 
residue in nitric acid, the indium is separated by ordinary Ag Clj, Hg Cl 2 , Bi Cl 3 , Sn Cl 4 , and Ta Cl 5 , respectively, 
analytical processes, based chiefly on the precipitability Accordingly, in order to deduce the atomic weight of 
of its sulphide by sulphuretted hydrogen from solutions indium from the ascertained composition of its chloride, 
acidulated only with acetic acid; and on the precipita- we require first to know whether its chloride is a 
bility of its hydrate both by ammonia and carbonate of mono-, di-, tri-, tetra- or penta-chloride. Now, in 
barium. From its soluble salts, metallic indium is the case of a metal forming only one definite chloride, 
readily thrown down in the spongy state by means of the constitution of the chloride as a mono- or poly¬ 
zinc. The washed sponge of metal is then pressed to- chloride, may frequently be determinated by a conside- 
gether between filtering paper, by aid of a screw press, ration of the analogies presented by the metal and its 
and finally melted under a flux of cyanide of potassium, compounds to some other metal and its compounds, of 
Thus obtained, indium is a metal of an almost silver- which the atomic weight and molecular formulae re- 
white colour, apt to become faintly bismuth-tinted. It spectively are well established. But it is obvious that 
tarnishes slowly on exposure to air, and thereby acquires analogy can afford but little help in the case of a newly - 
very much the appearance of ordinary lead. Like lead, it; discovered element, of which the analogies have still 
is compact and seemingly devoid of crystalline structure, to be determined. 
Moreover, like lead and thallium, it is exceedingly soft, [ Failing analogy, a more sure guide to the establish- 
