Improvements in the Electrolysis of Fused Zinc Chloride.
Year: 1897

page_text: Date of Application, 5th May, 1897
Complete Specification Left, 3rd Feb., 1898-Accepted, 26th Mar.,
1898
Improvements in the Electrolysis of Fused Zinc Chloride.
FARNHAM MAXWELL LYTE, F.J.C., F.C.S., Chemical Engineer, of 60, Finborough
Road, South Kensington, S.W., do hereby declare the nature of this invention to
be as follows:-
The object of this invention is the avoidance of the small explosions and priming
which are liable to occur when the electrolysis of fused zinc chloride which has
been incompletely dehydrated is attempted using a carbon anode and a zinc
cathode.
It is necessary for this purpose that, before commencing this electrolysis, the zinc
chloride should be deprived as far as possible of all traces of water. This may be
done by digestion of the fused zinc chloride for a suflicient length of time in contact
with metallic zinc whether fused or not, but preferably the former.
The presence of zinc also tends to keep the salt pure.
With this end the dehydration may be performed in an electrolytic cell such as
has been described by me in Patent No. 7594-1893, or in some similarly arranged
vessel in which the fused zinc chloride may be digested in contact with the metallic
zinc, and in which, when dehydrated, it may be submitted to electrolysis under the
conditions above alluded to, or, what may perhaps be preferred, the operation may
be conducted in a separate cell adapted to the purpose.
The process, however, of dehydration may be greatly assisted and accellerated by
electrolysis performed under the following conditions.
The anode in this case is to be the zine whether solid or fused, and the cathode
may be carbon or some suitable conducting material which will not under the
circumstances be attacked. In these conditions, on passing the electric current,
the water of hydration is decomposed, its oxygen combining with the zine of the
anode, and the zine oxide formed partly dissolves in the fused zinc chloride, partly
remains suspended in it, while the hydiogen is evolved at the cathode, and, perhaps,
if the pressure is sufficient, zine is deposited on the cathode.
This latter, if fused, falling in drops through the fused zine chloride will still
further tend to decompose any water it may contain.
This action will continue till all the water is eliminated, and nothing but
anhydrous zinc chloride with zinc oxide is left.
This may then be electrolysed with a carbon anode and a zinc cathode, as
described in my British Patent No. 15,813-August 22nd-1895, when, first of
all the zinc oxide held in solution in the fused zinc chloride is electrolysed, then
that held in suspension dissolves, takes its place, and dissappears in its turn, &
so on.
With all this, according to the voltage used, perhaps more or less chlorine may
be evolved with the oxygen.
Finally only anhydrous zinc chloride remains to be electrolysed for the production
of chlorine and metallic zinc, no explosion or foaming being liable to occur.
Dated this Fourth day of May 1897.

page_text: Improvements in the Electrolysis of Fused Zinc Chloride.
I, FARNHAM MAXWELL LYTE, Chemical Engineer, of 60, Finborough Road,
South Kensington, in the County of London, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:
-
The object of this invention is the dehydration of zine chloride, with a view to
the prevention of the small explosions & foaming mentioned by Lorenz.
These are liable to occur during its electrolysis, where a carbon anode & a fused
zinc cathode are employed, if the said zinc chloride has not been completely deprived
of its water of hydration beforehand.
L
Zinc chloride has such an extreme affinity for water, that it is, nearly if not quite
impossible to dehydrate it completely by evaporation. Even at the temperature
of melting zinc, or above that, it still retains some water, & long before then the
water of hydration & the zine chloride begin mutually to decompose one another,
with production of zinc oxide & the evolution of disagreeable fumes of hydrochloric
acid. Zine chloride is said to be the most hygrometric substance known.
If such hydrated zinc chloride be attempted to be electrolysed when fused, with
a carbon anode &.a fused zinc cathode, the water, & perhaps also a portion of the
fused zinc chloride, become decomposed with an evolution of explosive gasses, &
these by their repeated re-combinations & decompositions within the liquid, cause
not only considerable loss of power, but also much inconvenient frothing.
This may be remedied by the digestion of the fused zinc chloride over fused
metallic zinc. Unless the zinc be fused its action is slower & less complete, on
account of the protective film of zinc oxide which forms upon it, though even solid
metallic zinc acts, but less perfectly. Zinc begins to decompose water at 100° C.
(its temperature of ebullition).
The dehydration by means of zinc may be performed in an electrolytic cell such
as has been described by me in Patent No. 7594-1893, or in some similarly
disposed vessel, in which, when dehydrated, it may be submitted to electrolysis.
It will probably, however, be preferred to conduct the dehydration in a separate
cell adapted to the purpose, from whence the dry fused salt may be drawn over into
the electrolytic cell, as required.
If the metallic zinc produced be intended for commercial purposes, it should be
kept as pure as possible, & should be protected from contact with the iron casing
of the cell, as is done in Germany, where the iron utensils sometimes employed for
the re-melting of zinc, are protected by means of a thin layer of baked fireclay,
plumbago, or other refractory material." The zinc, however, which is used in the
separate dehydration cell above mentioned, may be of the most ordinary kind;
indeed the presence of the foreign metals with which it may be contaminated tends
rather to increase its activity than otherwise, without in any way affecting the purity
of the zinc chloride.
The process of dehydration may further be greatly assisted by electrolysis under
the following peculiar conditions.
The direction of the current is this time to be reversed, the zine being made the
anode & the carbon the cathode of the arrangement, & as an oxidising action is
always produced at the anode, while a reducing action is exerted at the cathode,
the tendency of the zinc to become oxidised per se. & to decompose the water, is
intensified & assisted by the tendency of this same zinc to become oxidised at the
anode under the influence of the current, & thus the water is more rapidly decom-
posed than before with the production of zinc oxide, while the hydrogen passes off

page_text: at the carbon cathode. Here the cathode may be of copper or of any of the heavy
metals which is less fusible than zinc, instead of carbon.
In the ordinary electrolysis for the production of zinc & chlorine on the contrary,
where the zinc is the cathode & the carbon the anode, the decomposing action of
the zinc on the water from its tendency to oxidation, is opposed & more or less
neutralized, by the reducing action of the current at the cathode acting on it in the
opposite direction.
The existence of these two opposing influences accounts perhaps for the notable
fall of the potential requisite for the electrolysis of fused zine chloride, as soon as
all the water of hydration has been eliminated.
In the above mentioned conditions of reversed electrolysis, as it may be called,
the zinc oxide formed, partly dissolves in the fused zinc chloride, partly remains
suspended in it, while the hydrogen, as has been said, is evolved at the carbon
cathode instead of from the surface of the zinc as otherwise is the case.
Perhaps also, if the electrical pressure be sufficient zinc is deposited on the
carbon cathode, & this falling in drops through the fused zinc chloride, still further
tends to decompose any water present.
This action will continue till all the water of hydration has been eliminated from
the zinc chloride, & only the anhydrous salt with zinc oxide is left.
This may now safely be electrolysed with a carbon anode & a fused zinc cathode,
as has been described in my British Patent No. 15,813 August 22nd-1895, when
first of all the zine oxide held in solution in the fused zinc chloride is electrolysed,
the oxygen escaping & the zinc being deposited & blending with the fused cathode,
then that held in suspension dissolves, takes its place, & disappears in its turn,
& so on.
With all this, according to the voltage, more or less chlorine may be mixed with
the oxygen.
Finally only anhydrous zinc chloride is left to be electrolysed for the production
of chlorine & metallic zine, no explosive mixtures of gasses being formed, no foam-
ing arising from explosions within the liquid being liable to occur.
Having now particularly described & ascertained the nature of my said inven-
tion & in what manner the same is to be performed, I declare that what I
claim is:-
1 In the production of chlorine & zinc from fused zinc chloride by electrolysis,
with a carbon anode & a fused zinc cathode, after as much of the water as may be
has been expelled by evaporation & heating, the removal of any remaining water
of hydration which the zinc chloride still retains, by digestion over fused metallic
zinc, whereby the water is eliminated by being resolved into its elements, zinc oxide
being formed & hydrogen evolved, explosions & foaming being thus avoided
substantially as above described.
2-In the production of chlorine & zinc from fused zinc chloride by electrolysis,
as in the last Claim (1), the substitution of solid metallic zinc for the fused zinc
there employed for the dehydration of the said zinc chloride, whereby a like effect,
though more slow & less complete is obtained, substantially as above described.
3 In the production of chlorine & zinc from fused zinc chloride by electrolysis,
assisting the action of the zinc in eliminating the last traces of water from the said
zinc chloride by the so-called reversed electrolysis, in which the zinc is made the
anode, & the carbon or a suitable heavy metal, the cathode, substantially as above
described.
1
13
1
1000