556 
POPULAR SCIENCE REVIEW. 
obtained an additional supply of material, lie was enabled to precipitate 
the substance from solution, by means of zinc, in the form of a black 
powder, and to obtain it in distinct metallic crystals by voltaic deposition, 
which removed all doubt as to its metallic nature. It may be as well to 
remark, in vindication of Mr. Crookes’s claim to the priority in the dis- 
covery of this metal, that he obtained these metallic crystals in September, 
1861. 
To obtain the metal in a coherent form, it is only necessary to squeeze 
the precipitated mass together, and fuse it under cyanide of potassium, or 
simply to submit it to powerful pressure, when, from its great softness, it 
will unite into one mass. 
Spectrum analysis furnishing an easy method for the detection of the 
new metal, Mr. Crookes has discovered its existence in varying proportions 
in many specimens of pyrites, sulphur, sulphide of cadmium, metallic 
cadmium, and zinc; also in copper and in bismuth ores. A specimen of 
native sulphur from Lipari was found to contain so much thallium that it 
might almost be classed as a new mineral. 
Thallium is extracted from pyrites by distilling the sulphur from it, the 
thallium passing away at the same time; the thalliferous sulphur is then 
boiled with potash, and the black residue heated with sulphuric acid ; the 
solution is then filtered, and hydrochloric acid added to the filtrate, when 
the difficultly-soluble protochloride of thallium is precipitated ; this is 
filtered off, washed, and converted into sulphate ; the solution of the sulphate 
is then decomposed by means of the voltaic battery. 
The chief characteristics of thallium are as follows : It is a white 
opaque metal, with a perfect metallic lustre ; its specific gravity is 11*19 ; it 
is very malleable, and may be rolled into leaves as thin as tissue-paper ; it 
is not very ductile, and can only with difficulty be drawn into wire, but, 
by means of pressure, thallium-wire can be made with great ease. The 
metal also possesses the singular property of compressibility, and it is the 
softest known heavy metal, being exceeded in this respect only by the metals 
of the alkalies. Thallium marks paper like plumbago ; the mark fades 
out from oxidation in a short time, but it may be again rendered visible 
by moistening the paper with a solution of sulphide of ammonium ; with 
the exception of bismuth it is the most diamagnetic metal known. Thal- 
lium melts at 550° Fahrenheit ; at a full red heat it may be distilled ; it 
burns in oxygen, and tarnishes very quickly in the air, becoming coated 
with an oxide which is tolerably soluble in water ; the oxide may be 
rendered anhydrous at the ordinary temperature in a vacuum. The metal 
dissolves in acids, the proper solvent being nitric acid ; it forms at least two 
basic oxides ; the protochloride, like chloride of lead, is slightly’soluble in 
water ; bichloride of platinum produces an insoluble double salt with 
chloride of thallium ; sulphuretted hydrogen produces no precipitate in 
an acid solution ; sulphide of ammonium, a black precipitate of sulphide 
of thallium ; on adding ammonia to a solution of the sesquichloride, a 
brown peroxide is produced, together with protochloride of thallium. In 
one or two of the properties here alluded to, thallium approaches the 
metals of the alkalies, but the great majority of its characteristics point 
out that its true position is by the side of silver and lead. 
