In 1861 Sir William Crookes detected thallium (named from the Gr.
Rubidium, caesium, thallium, indium and gallium were first discovered by means of this instrument; the study of the rare earths is greatly facilitated, and the composition of the heavenly bodies alone determinable by it.
8 shows the variation of refractive index of mixed crystals of potash alum and thallium alum with variation in composition.
In 1861, while conducting a spectroscopic examination of the residue left in the manufacture of sulphuric acid, he observed a bright green line which had not been noticed previously, and by following up the indication thus given he succeeded in isolating a new element, thallium, a specimen of which was shown in public for the first time at the exhibition of 1862.
All carbonates, except those of the alkali metals and of thallium, are insoluble in water; and the majority decompose when heated strongly, carbon dioxide being liberated and a residue of an oxide of the metal left.
After these follow first thallium and then lead, the latter being the softest of the metals used in the arts.
By the joint action of water and air, thallium, lead, bismuth are oxidized, with formation of more or less sparingly soluble hydroxides (ThHO, PbH 2 O 2, BiH303), which, in the presence of carbonic acid, pass into still less soluble basic carbonates.
6, consisting of two downward sloping branches meeting in the eutectic point, and that of thallium and tin, the upper curve of fig.
7 gives the freezing-point curve of mercury and thallium; here A and E are the melting-points of pure mercury and pure thallium, and the branches AB and ED do not cut each other, but cut an intermediate rounded branch BCD.
The higher eutectic D may correspond to a complex of solid thallium and the compound; but the possible existence of solid solutions makes further investigation necessary here.
Silver-thallium nitrate, TIAg(N03)2, introduced by Retgers, melts at 75° to form a clear liquid of density 4.8; it may be diluted with water.
In a smaller degree these alkaline properties are shared by the less soluble hydrates of the "metals of the alkaline earths," calcium, barium and strontium, and by thallium hydrate.
We must refer to Kayser and Runge's Handbuch for further details, as well as for information on other spectra such as those of silver, thallium, indium and manganese, in which series lines have been found.
Traces of thallium, which are present in some pyrites, may be detected in the flues of the furnaces where the metal is roasted.
He concluded that the mineral contained a new element, to which he gave the name of thallium, from 9aXX6, a green twig.
Crookes presumed that his thallium was something of the order of sulphur, selenium or tellurium; but Lamy, who anticipated him in isolating the new element, found it to be a metal.
Our knowledge of the chemistry of thallium is based chiefly upon the labours of Crookes.
The chemical character of thallium presents striking peculiarities.
But the hydroxide of thallium, in most of its properties, comes very close to the alkali metals; it is strongly basic, forms an insoluble chloroplatinate, and an alum strikingly similar to the corresponding potassium compounds.
Traces of thallium exist in many kinds of pyrites, as used for vitriol-making.
The best raw materials for the preparation of thallium are the flue-dusts produced industrially in the roasting of thalliferous pyrites and the "chamber muds" accumulating in vitriol-chambers wrought with such pyrites; in both it is frequently associated with selenium.
Of thallium; that of the pyrites of Meggen, according to Carstanjen, as much as 3.5 per cent.; while that of the pyrites of Ruhrort yielded 1 per cent.
For the extraction of the metal from chamber mud, the latter is boiled with water, which extracts the thallium as the sulphate.
From the filtered solution the thallium is precipitated as the chloride by addition of hydrochloric acid, along, in general, with more or less of lead chloride.
The mixed chlorides are boiled down to dryness with sulphuric acid to convert them into sulphates, which are then separated by boiling water, which dissolves only the thallium salt.
From the filtered solution the thallium is recovered, as such, by means of pure metallic zinc, or by electrolysis.
Metallic thallium is bluish white; it is extremely soft and almost devoid of tenacity and elasticity.
Thallium forms two series of salts: thallous, in which the metal is monovalent; and thallic, in which it is trivalent.
The specific gravity of this "horn" thallium is 7.02.
All the thallium and selenium on the market is obtained from this source.
Traces of gold, silver, selenium or thallium are sometimes present, and the mineral is sometimes worked as an ore of gold or silver.
Many hydrated forms of the sulphate are known, as are also double salts of the sulphate with potassium, sodium, ammonium, thallium and cadmium sulphates.
On thallium sulphides see H.
Thallic oxide, T1203, is obtained as a dark reddish powder, insoluble in water and alkalis, by plunging molten thallium into oxygen, or by electrolysing water, using a thallium anode.
All thallium compounds volatile or liable to dissociation at the temperature of the flame of a Bunsen lamp impart to such flame an intense green colour.
Hawley employs sodium thiostannate which precipitates thallium as T1 2 SnS 4, insoluble in water, and which may be dried on a Gooch filter at 105°.
It may be noted that all thallium compounds are poisonous.
The atomic weight of thallium was determined very carefully by Crookes, who found T1=204.2 (0= 16); this figure was confirmed by Lepierre in 1893.