ON THE EXTRACTION OF THALLIUM. 
279 
rating amounts to about five tons, the whole of which lias been treated by the method 
I am about to describe. The process I now adopt is as follows :—The thalliferous dust 
is first treated in wooden tubs with an equal weight of boiling water, and is well stirred ; 
during this operation a considerable quantity of nitrous acid is evolved; after which the 
mixture is allowed to rest for four-and-twenty hours for the undissolved residue to de¬ 
posit. The liquid is then siphoned off, the residue is washed, and afterwards treated 
with a fresh quantity of boiling water. The collected liquors, which have been 
siphoned off from the deposit, are allowed to cool, and are precipitated by the addition 
of a considerable excess of strong hydrochloric acid ; and the precipitate, consisting of very 
impure chloride of thallium, is allowed to subside. The chloride obtained in this way 
is then well washed on a calico filter, and afterwards squeezed dry. I may mention 
that from three tons of the dust I obtained 68 lbs. of this rough chloride. The next 
step in the process with this large quantity is necessarily a tedious one. It consists in 
treating the crude chloride in a platinum dish with an equal weight of strong sulphuric 
acid, and afterwards heating the mixture to expel the whole of the hydrochloric acid. 
To make sure of this, the heat must be continued until the greater part of the excess 
of sulphuric acid is volatilized. After this the mass of sulphate of thallium is dissolved 
in about twenty times its weight of water, and the solution filtered. On the addition 
of hydrochloric acid to this solution, nearly pure chloride of thallium is thrown down ; 
this is collected on a filter, well washed, and then squeezed dry. The object of the pro¬ 
cess so far has been to obtain a tolerably pure chloride ; but as thallium is most easily 
reduced to the metallic state from the sulphate, it is now necessary again to convert the 
chloride into sulphate. For this purpose I add the dry chloride gradually to hot 
sulphuric acid, using four parts by weight of strong acid to six parts of the chloride. The 
mixture so obtained is heated strongly until all the hydrochloric acid is expelled, and the 
residue assumes the form of a dense liquid. This being set aside, gradually solidifies to 
a white crystalline mass. When this is dissolved in water an immense amount of heat 
is evolved, and great care must be taken to avoid breakage of the vessels. The best 
way of dissolving it is to add it slowly to ten times its weight of hot water. A solution 
is thus obtained, which must be filtered, and on being concentrated and set aside to cool, 
crystals of sulphate of thallium will be obtained, which may be rendered quite pure 
by re-crystallization. The final step in the process is the reduction of the metal from this 
sulphate. Many ways can be adopted for the reduction when only a few ounces are under 
experiment; but when the quantity of crystallized salt is from a quarter to half a hun¬ 
dredweight, a process must be devised which will admit of considerable quantities being 
reduced without too much expenditure of time or trouble. Experiments in the dry way 
were not very successful. No difficulty was experienced in partially reducing the metal 
by igniting the sulphate with black flux, or with cyanide of potassium, in a clay cru¬ 
cible ; but I could not remove all the sulphur in this way. When sulphate of thallium 
is projected into a crucible containing fused cyanide of potassium, there is an imme¬ 
diate reduction to the state of protosulphide, which forms a brittle, metallic-looking 
mass, of the lustre of plumbago, and fusing more readily than the metal. A few cells 
of Groves’s batteries offer a most ready means of reducing the sulphate, and in quan¬ 
tities less than half a pound nothing can be simpler than this process. The fusion of 
the metal is readily effected. An iron crucible is placed over a gas-burner, and a tube 
is arranged so that a constant stream of coal-gas may flow into the upper part of the 
crucible. Lumps of the compressed sponge are then introduced, one after the other as 
they melt, until the crucible is full of metal. It is then stirred up with an iron rod, and 
the thallium may either be poured into water and obtained in a granulated form, or 
cast into an ingot. Thirty or forty fusions have been performed in the same crucible 
without the iron being acted upon in the least by the melted thallium. It contracts 
strongly on cooling. The coating of tarnish which it acquires while hot is instantly 
removed by water, which renders the surface perfectly bright. The liquid metal in the 
crucible, when protected by the stream of coal-gas, can scarcely be distinguished from 
mercury. Thallium is not absolutely identical in colour with any other metal, but 
approaches nearest to cadmium and tin. It has perfect metallic lustre. Its specific 
gravity is 1T9. It is very malleable, but not very ductile. It can only be drawn into 
wire with great difficulty, but by the operation technically known as squirting, thal¬ 
lium wire may be formed most readily. Thallium is very soft, being only exceeded in 
this property by the alkali metals. A point of lead will scratch thallium with the 
