By G.S. NEWTH.
This method is a synthetical one, and consists in passing a stream of
hydrogen and bromine vapor over a spiral of platinum wire heated to
bright redness by means of an electric current. A glass tube, about 7
inches long and 5/8 of an inch bore, is fitted at each end with a cork
carrying a short straight piece of small tube; through each cork is
also fixed a stout wire, and these two wires are joined by means of a
short spiral of platinum wire, the spiral being about 1 inch long. One
end of this apparatus is connected to a small wash bottle containing
bromine, through which a stream of hydrogen can be bubbled. The other
end is attached to a tube dipping into a vessel of water for the
absorption of the gas, or, if a large quantity of the solution is
required, to a series of Woulf's bottles containing water. Hydrogen is
first slowly passed through the tube until the air is displaced, when
the platinum spiral is heated to bright redness by the passage of a
suitable electric current. Complete combination takes place in contact
with the hot wire, and the color imparted to the ingoing gases by the
bromine vapor is entirely removed, and the contents of the tube beyond
the platinum are perfectly colorless. The vessel containing the
bromine may be heated to a temperature of about 60° C. in a water
bath, at which temperature the hydrogen will be mixed with nearly the
requisite amount of bromine to combine with the whole of it. So long
as even a slight excess of hydrogen is passing, which is readily seen
by the escape of bubbles through the water in the absorbing vessels,
the issuing hydrobromic acid will remain perfectly colorless, and
therefore free from bromine; so that it is not necessary to adopt any
of the usual methods for scrubbing the gas through vessels containing
phosphorus. When the operation is proceeding very rapidly a lambent
flame occasionally appears in the tube just before the platinum wire,
but this flame is never propagated back through the narrow tube into
the bromine bottle. The precaution may be taken, however, of plugging
this narrow tube with a little glass wool, which renders any
inconvenience from this cause quite impossible. By this method a large
quantity of bromine may be rapidly converted into hydrobromic acid
without any loss of bromine, and the operation when once started can
be allowed to proceed without any further attention.--_Chemical News._
* * * * *