306 ME. Tv. CEOOKES ON THE ATOMIC WEIGHT OE THALLIUM. 
time, is then placed in the dish, and water poured over to cover the salt. Heat is applied, 
and in the course of a few hours the whole of the thallium will be reduced to the state 
of a metallic sponge, which readily separates from the plates of zinc on slight agitation. 
The liquid is poured off, the zinc removed, and the spongy thallium washed several 
times. It is then strongly compressed between the fingers, and preserved under water 
until it is ready for fusion. 
The metal is readily obtained in the coherent form by fusing the sponge. This is 
most conveniently performed under cyanide of potassium on the small scale, and under 
coal-gas when working with large quantities. In the former case the sponge, strongly 
compressed and quite dry, is broken into small pieces, which are dropped one by one 
into cyanide of potassium kept fused in a porcelain crucible. They rapidly melt, forming 
a brilliant metallic button at the bottom. When cold, the cyanide of potassium may be 
dissolved in water, when the thallium will be left in the form of an irregular lump, 
owing to its remaining liquid and contracting after the cyanide has solidified. 
On the large scale, the fusion is best effected in an iron crucible. This 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 appreciably acted upon by the melted 
thallium. 
1). From Iron Pyrites . — The richest pyrites which I have yet met with comes from 
Oneux, near Theux; it contains about 1 part of thallium in 4000. Two tons of this 
ore were worked in the following manner: — 
The pyrites, broken up into pieces of the size of a walnut, is distilled in hexagonal 
cast-iron pipes, closed at one end, and arranged in a reverberatory furnace. Conical 
sheet-iron tubes are luted on to the open ends, and the retorts are kept at a bright red 
heat for about four hours. At the end of the operation the receivers are found to 
contain from 14 lbs. to 17 lbs. of dark green or grey-coloured sulphur for every 100 lbs. 
of ore used. The whole of the thallium originally in the pyrites will be found in this 
sulphur, from which it has now to be separated. The sulphur may be dissolved out by 
means of bisulphide of carbon, which leaves the sulphide of thallium behind ; or it may 
be extracted by boiling with caustic soda. The former plan occasions less loss of 
thallium, but, owing to the inconvenience of working with large bulks of bisulphide of 
carbon, the soda process is preferable. 12 lbs. of canstic soda, 18 lbs. of the thalliferous 
sulphur, and li gallon of water are boiled together till the sulphur has dissolved; 6 
gallons of water are added, and the clear liquid, when cool, is decanted from a voluminous 
black precipitate, which has been separated from the sulphur. The precipitate is then 
collected on a calico filter and washed. It contains the greater portion of the thallium 
in the form of sulphide, together with iron, copper, mercury, zinc, &c. Some thallium, 
