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ME. V. CEOOKE3 ON THE ATOMIC WEIGHT OE THALLIUM. 
PREPARATION OF CHEMICALLY PURE THALLIUM. 
a. Commercial sulphate of thallium is dissolved in water, and the cold solution 
deluged with sulphuretted hydrogen. It is then filtered, heated to ebullition, and 
poured into boiling dilute hydrochloric acid. The solution is filtered whilst hot and 
then allowed to cool. The chloride of thallium which crystallizes out on cooling is 
washed by decantation until the washings are free from sulphuric acid, and further 
purified by recrystallizing twice from water. The chloride of thallium thus obtained is 
dried, mixed with pure carbonate of sodium, and projected by small portions at a time 
into pure cyanide of potassium kept in a state of fusion in a white unglazed crucible. 
The chloride is rapidly reduced to the metallic state ; the crucible is then allowed to 
cool, and the contents exhausted with water. The resulting ingot of metal is well boiled 
in water, dried and fused over a spirit-lamp* in an unglazed porcelain crucible with free 
access of air, stirred with a porcelain rod to facilitate oxidation, and finally cast in a 
porcelain mould. It may be preserved under water which has been boiled to expel the 
air. This metal was used in the determinations A and B. 
b. Ordinary metallic thallium is fused in contact with the air, in an iron crucible 
made nearly red-hot, and then poured into water. The granulated metal is then 
exposed to a warm atmosphere to facilitate oxidation, the oxide being frequently 
removed by boiling out with water. When a considerable quantity of oxide (mixed 
with carbonate) has been obtained, the solution is heated to ebullition, and a rapid 
current of carbonic-acid gas passed through until the liquid is quite cold, and the excess 
of carbonate of thallium has crystallized out. The resulting salt is recrystallized and 
projected into pure cyanide of potassium kept in a state of fusion in a porcelain crucible 
at a dull red heat ; carbonic acid escapes with effervescence, and the metal is reduced to 
the metallic state. The whole is then allowed to cool, the soluble salts boiled out with 
water, and the lump of thallium fused over an alcohol-lamp in a lime crucible and cast 
in a lime mould as described further on. With this iimot of thallium the determina- 
tion C was effected. 
c. Carbonate of thallium, obtained as in process b, is covered with a small quantity 
of water, and decomposed by the current from six Grove’s cells. Much peroxide of 
thallium is deposited, which is removed f and preserved for the preparation of thallium 
by another method. The reduced thallium is then squeezed into a hard cake, melted 
in a lime crucible heated by means of a spirit-lamp, and cast in a lime mould. This 
metal was employed in the determination D. 
d. A third portion of carbonate of thallium, obtained as in process b, is crystallized 
several times from water, carbonic acid being passed through during the cooling of the 
solution. After six crystallizations the carbonate is perfectly white. It is then placed 
in a porcelain dish, covered with a little water, and decomposed by four Grove’s cells. 
* A spirit-flame is preferable to one of coal-gas, as the latter contains sulphur. 
t The operation requires this peroxide of thallium to be constantly removed from the positive pole, or the 
passage of the current will be retarded and ultimately stopped. 
