By F. STOLBA.
Finely ground zircon is quickly rendered soluble if fused with a
mixture of potassium borofluoride and potassium carbonate. The author
takes two parts of the former to three of the latter, and prepares an
intimate, finely divided mixture, which is kept ready for use.
Of this mixture four parts are taken to one of zircon, thoroughly
mixed, and melted in a platinum crucible at a red heat. The mass fuses
readily, froths at first and gives off bubbles of gas, and flows then
quietly, forming a very fluid melt. If the zircon is finely ground, 15
minutes are sufficient for this operation. The loss of weight is 16
per cent., and is not notably increased on prolonged fusion. It
corresponds approximately to the weight of the carbonic anhydride
present in the potassium carbonate.
As pungent vapors are given off during fusion, the operation should be
conducted under a draught hood. The activity of the mixture in
attacking zircon appears from the following experiment: Two zircon
crystals, each weighing ½ grm., were introduced into the melted
mixture and subjected to prolonged heat. In a short time they
decreased perceptibly in size; each of them broke up into two
fragments, and within an hour they were entirely dissolved. The melted
mass is poured upon a dry metal plate, and when congealed is thrown
into water. It is at once intersected with a number of fissures, which
facilitate pulverization. This process is the more necessary as the
unbroken mass is very slowly attacked by water even on prolonged
boiling. The powder is boiled in a large quantity of water so as to
remove everything soluble. There is obtained a faintly alkaline
solution and a sediment insoluble in water. From the filtrate alkalies
throw down zirconium hydroxide, free from iron.
The portion insoluble in water is readily dissolved in hydrofluoric
acid, and is converted into zircon potassium fluoride. The chief bulk
of the zirconium is found in the aqueous solution in the state of
double fluorides. The platinum crucible is not in the least attacked
during melting. On the contrary, dirty platinum crucibles may be
advantageously cleaned by melting in them a little of the above
mentioned mixture.
If finely divided zircon is boiled for a long time with caustic lye,
it is perceptibly attacked. It is very probable that in this manner
zircon might be entirely dissolved under a pressure of 10 atmospheres.
Potassium borofluoride may be readily prepared from cryolite.
Crucibles of nickel seem especially well adapted for the fusion of
zircon in caustic alkalies.--_Ber. Boehm. Gesell. Wissenschaft;
Chem. News_.
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