ME. AY. CROOKES OK TIIE ATOMIC WEIGHT OF THALLIUM. 
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however, remains dissolved in the alkaline liquid, and is lost. The black precipitate is 
then dissolved in hot dilute sulphuric acid, to which a little nitric acid is added, and the 
liquid is diluted with water and filtered. Hydrochloric acid and a reducing agent, such 
as sulphite of sodium, will now throw down the nearly insoluble white protochloride of 
thallium, which is to be filtered off and washed. 
c. From Sulphur or Pyrites in the Wet Wccy. — The material is boiled in nitro-hydro- 
chloric acid until nothing but bright yellow sulphur is left ; water is then added, and 
the filtrate is evaporated with sulphuric acid until it is nearly dry, and sulphuric vapours 
are copiously evolved. The residue is dissolved in a large excess of hot water, and car- 
bonate of sodium is added to alkaline reaction, and then cyanide of potassium (free from 
sulphide of potassium). The liquid is then heated gently for some time, and filtered. 
The precipitate contains the whole of the lead and bismuth which may be present, as 
carbonates, whilst the thallium is in solution. A current of sulphuretted hydrogen 
being now passed through the alkaline liquid precipitates all the thallium, whilst the 
copper, antimony, tin, and arsenic remain dissolved. The precipitated sulphide is filtered 
off, washed, and dissolved in dilute sulphuric acid, and the thallium is precipitated by 
means of hydrochloric acid as chloride, from which the metal is extracted in the way 
previously described. 
cl. From the Saline Residues of the Scdt-ivorJes at Nauheim. — Dr. Bottger adds an 
insufficient quantity of bichloride of platinum to the strong solution, and boils the pre- 
cipitate five or six times with three times its weight of water. The insoluble residue 
consists of the platinum-salts of caesium, rubidium, and thallium. Upon boiling these 
with a weak solution of potash and a little hyposulphite of sodium, the solution soon 
becomes clear, whereupon cyanide of potassium and sulphuretted hydrogen are added. 
This precipitates the thallium as sulphide. The liquid is then to be filtered, the residue 
washed and dissolved in sulphuric acid, and the metal precipitated by metallic zinc. 
e. From Commercial Hydrochloric Acid. — Many samples of yellow hydrochloric acid 
contain thallium. It may be separated by neutralizing with an alkali and adding sul- 
phide of ammonium. The black precipitate contains the thallium, together with iron 
and some other metallic impurities of the acid. It is to be dissolved in sulphuric acid, 
and the thallium precipitated with hydrochloric acid as protochloride. This is after- 
wards reduced as already described. 
f. From the Mother-liquors of the Sidphate-of-Zinc Works at Goslccr. — Each kilo- 
gramme of these liquors is said to yield as much as half a gramme of chloride of thallium. 
A sheet of zinc is plunged into the liquid, whereby the thallium, copper, and cadmium 
are precipitated. The metallic sponge is then removed from the zinc, washed, and 
treated with cold dilute sulphuric acid, which dissolves the cadmium and thallium with 
disengagement of hydrogen, whilst the copper is left behind. The filtrate from the 
copper is then mixed with hydrochloric acid, which precipitates the nearly insoluble 
chloride of thallium. If only a small quantity of thallium is present, iodide of potassium 
may be used as a precipitant, as the iodide of thallium is insoluble in water. 
