302 
MR, W. CROOKES ON THE ATOMIC WEIGHT OE THALLIUM. 
portions of water, and is condensed in a receiver cooled with ice. The temperature of 
the liquid in the retort is not allowed to rise to the point of ebullition, and the operation 
is stopped when one fourth of the liquid in the retort has distilled over. 
2. Ammonia is also prepared by a method recommended by Professor Stas. Nitrite 
of potassium is mixed with strong solution of caustic potash, and the liquid poured into 
a large glass balloon containing a mixture of zinc (free from carbon*') and iron wire 
which has been first oxidized by heating in the air and then reduced by hydrogen. After 
standing for seventy-two hours, the liquid is decanted from the residue into a retort, 
which is then gently heated on a sand-bath. The arrangement for condensing the 
ammonia consists of two flasks fitted up as Woulfe’s bottles containing pure water. 
The distillation is effected very slowly below the boiling-point of the liquid, and the con- 
densers are cooled with ice. 
Hydrogen. 
The method pursued in the preparation of pure hydrogen is as follows : — The gas 
is generated in one of a series of Woulfe’s bottles by pouring warm caustic potash over 
a mixture of granulated zinc and iron scraps. The gas thus generated (the method is 
due to Runge, Pogg. Ann. xvi. p. 130) is inodorous. It is next passed into another 
Woulfe’s bottle containing protochloride of tin ; then through tubes containing pumice- 
stone moistened with a concentrated solution of pyrogallic acid in caustic potash, and 
again through tubes containing pumice moistened with sulphuric acid, the object in 
passing the gas through the protochloride of tin and through the pyrogallic acid being 
io remove the oxygen diffused into the apparatus from the atmosphere. 
Thallium. 
It may not be out of place here to note the most usual sources of thallium as it is 
ordinarily prepared. 
Thallium is a very widely distributed constituent of iron and copper pyrites. Upon 
examining a large collection of pyrites from different parts of the world, it was found 
present in more than one eighth. It is not confined to any particular locality. Amongst 
those ores in which it occurs most abundantly (although in these cases it does not con- 
stitute more than from the 100,000th to the 4000th of the bulk of the ore), may be 
mentioned iron pyrites from Theux, near Spa in Belgium, from Namur, Philipville, 
Alais, the south of Spain, France, Ireland, Cornwall, Cumberland, and different parts of 
North and South America; in copper pyrites from Spain, as well as in crude sulphur 
prepared from this ore ; in blende and calamine from Theux ; in blende, calamine, 
metallic zinc, sulphide of cadmium, metallic cadmium, and cake sulphur from Nouvelle- 
Montagne ; in native sulphur from Lipari and Spain ; in bismuth, mercury, and anti- 
mony ores, as well as in the manufactured products from these minerals (frequently in 
so-called pure medicinal preparations of these metals) ; in commercial selenium and 
tellurium (probably as selenide and telluride). 
Zinc -is obtained free from carbon by fusing it with a mixture of carbonate of sodium and nitre. 
