MR, W. CROOKES ON THE ATOMIC WEIGHT OE THALLIUM. 
309 
The spongy metal is washed, boiled in pure water, tied up in a linen cloth, and com- 
pressed between steel plates in a vice. The hard lump is broken up, put into a 
porcelain crucible and melted over a spirit-lamp, no flux being used other than the 
thallium oxide formed on heating. The metal is constantly stirred with a piece of 
unglazed porcelain and cast in a warm porcelain mould. With thallium prepared in 
this manner the synthetical operations E and F were performed. 
e. The peroxide of thallium obtained by the electrolysis of the carbonate (processes 
c and d) is dissolved in purified sulphuric acid, evaporated to dryness, and heated strongly 
to decompose any sulphate of peroxide ; it is then dissolved in water and recrystallized 
twice. The sulphate of thallium is then reduced to the metallic state by three of 
Grove’s cells, platinum terminals being employed. The metal is squeezed into a lump 
and melted under hydrogen in a porcelain crucible, and cast in a polished steel mould, 
the heat in this case being produced by the combustion of pure hydrogen gas. The 
thallium purified as above was used in the operation G. 
f. Chloride of thallium, as obtained by method a, is boiled in nitric acid till most of 
it is converted into sesquichloride. This is washed by decantation until it begins to 
decompose with separation of peroxide of thallium, and purified by twice recrystallizing. 
The purified sesquichloride of thallium is dissolved in boiling water and poured into 
dilute ammonia. The precipitated peroxide of thallium is washed by decantation till 
chlorine is no longer detected in the washings, and then boiled in a little water with 
pure sublimed oxalic acid till the whole is converted into oxalate of thallium. This is 
dried and heated in a crucible until the w'hole is decomposed into a mixture of metallic 
thallium and oxide of thallium ; the reduced metal is then cast in a mould of polished 
steel. The ingot was employed in the determination IT. 
g. Ordinary thallium is dissolved in nitric acid, and the excess of acid driven off by 
heat, the residue is dissolved in w r ater, and the solution saturated with sulphuretted 
hydrogen. A slight black precipitate is generally formed, the solution is filtered cold, 
and is then freed from sulphuretted hydrogen by boiling. Ammonia is then added, 
which generally produces a faint precipitate of sesquioxide of iron and peroxide of 
thallium ; it is then filtered, and the solution is mixed with oxalate of ammonium and 
concentrated till the oxalate of thallium crystallizes out. This is freed from nitrate of 
ammonium by recrystallizing, and the oxalate of thallium decomposed by heat, as in 
process f. The thallium thus obtained is again fused in a lime crucible, a blowpipe- 
flame being directed downwards on to the surface of the fused metal for about five 
minutes, till the slag of thallium oxide has united with the lime, forming a semifluid 
pasty mass. The metal is then cast in a lime mould, washed when cold, and kept under 
boiled distilled water or very dilute acetic acid. With metal purified in this manner 
the estimations I and K were performed. 
Purification of Thallium by Fusion in Lime. 
A piece of well burnt, very dense quick-lime, prepared from black marble, is cut out 
MDCCCLXXIII. 2 T 
