Improvements in the Manufacture of Sulphide of Zinc and the Obtainment of Sulphuretted Hydrogen and Sulphurous Acid as Products of the said Manufacture.
Year: 1884

page_text: Improvements in the Manufacture of Sulphide of Zinc and the
Obtainment of Sulphuretted Hydrogen and Sulphurous Acid
as Products of the said Manufacture.
PROVISIONAL SPECIFICATION.
I JOHN HENRY JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of said Invention for "IMPROVEMENTS
IN THE MANUFACTURE OF Sulphide oF ZINC AND THE OBTAINMENT OF SUL-
PIIURETTED HYDROGEN AND SULPHUROUS ACID AS PRODUCTS OF THE SAID
MANUFACTURE," which Invention has been communicated to me from abroad by
Thomas Macfarlane of Montreal in the Province of Quebec and Dominion of
Canada, Chemist, to be as follows :-
According to this Invention a solution containing a hydrosulphate of lime is
prepared which may be effected according to one or other of the following methods.
I. Two parts of quick lime are slaked mixed with one part of ground sulphur
and boiled together with water for about two hours. After subsidence the
resulting solution is drawn off which contains hydrosulphate and hyposulphite of
line together with some pentasulphide of calcium. This may be designated as
sulphur liquor N° 1.
II. One part of quick lime is slaked, mixed with one part of the spent iron oxide
produced in making illuminating gas (which contains about 50 per cent sulphur)
and boiled together with water for about two hours. The resulting solution is of
the same nature as described in the foregoing paragraph and may be termed
sulphur liquor Nº 2.
III. Ordinary tank waste from the alkali manufacture consisting mainly of
Calcium Sulphide, is taken and exposed in loose heaps on inclined watertight floors
to the action of the atmosphere, for three or four weeks, until it has acquired in
the interior, a greenish yellow colour and has absorbed sufficient oxygen and
Carbonic acid for the formation, in conjunction with moisture of considerable
quantities of carbonate of lime and bihydrosulphate of lime. Should the heap of
tank waste in thus weathering, become heated to such an extent as to cause
ignition and loss of sulphur, this is to be stopped by heating down the heap to
excludo air, or cooling it down with water. The bihydrosulphate of lime being
soluble, is leached out with water and fresh quantities of weathered tank waste

page_text: treated with it, until it attains a strength of 10° to 20° Twaddell. In this case it
contains from two and a quarter to two and a half equivalents of sulphur for each
equivalent of calcium in the liquor. Besides the bihydrosulphate of lime, there
is therefore, likewise present more or less bisulphide of calcium. The solution thus
produced may be called sulphur liquor N° 3, and, like the others is to be made use
of in the manner hereinafter to be described.
A perfectly pure solution of Chloride of Zinc is then prepared. This is done by
dissolving metallic zinc impure zinc oxide calcined zinc blende, or ores, either raw
or calcined, containing carbonate or oxide of zinc in hydro-chloric acid presenting
these substances in excess to the acid until the latter is completely neutralized.
The resulting solution is then evaporated in lead or cast iron pans, until it attains
a specific gravity of at least 1.6. During this evaporation, the manganese iron and
other impurity, which the solution may contain is, for the most part, rendered
insoluble, and separated. The evaporation may be continued until the solution is
of such a strength that it solidifies on cooling in which case it is ladled into sheet
iron alkali drums and stored for use. When redissolved it yields an almost pure
solution of chloride of zinc. Any trace of iron which it may contain is precipitated
by the addition of a small quantity of solution of chloride of lime.
The aforesaid sulphur liquors and the chloride of zinc solution are mixed in
suitable vessels when a precipitate is formed by hydrated sulphide of zinc, mixed
with more or less free sulphur, while chloride of Calcium remains in solution. The
zinc chloride is added to the sulphur liquors until the mixture shews a slightly
acid reaction. The liquors N° 1 and 2 yield the precipitate without any evolution
of sulphuretted hydrogen, but this is not the case with sulphur liquor N° 3. When
this has a strength of 10° to 20° Twaddell and is mixed with the chloride of zinc
solution sulphuretted hydrogen is produced abundantly and may be collected, and
conducted away from the precipitating vat. In order to do this the latter must
be provided with a cover having an opening in the centre through which the
agitator shaft passes. The opening is furnished with a water lute in which an
airtight collar fastened on to the shaft works in order to prevent any escape of gas.
The latter is led off through a pipe in the cover and being uncontaminated with
other gases, may be ignited in a properly constructed furnace or flue and burnt to
sulphurous acid, which may be used for the manufacture of Sulphuric acid. The
precipitate of zinc sulphide and free sulphur is then passed through filter presses
in order to separate it from the solution of chloride of calcium accompanying it.
Pure bydrated sulphide of zinc is of a very finely divided or slimy nature and
difficult to filter even under great pressure but the presence of the precipitated
sulphur renders it more granular and easy of filtration. The cakes produced in the
filter presses are dried in a drying chamber of the usual construction in which the
temperature is not allowed to exceed 150° Fahrenheit.
The hydrated zinc sulphide dried as above indicated is then ignited. This is
performed in gas retorts or muffle furnaces at a red heat and under continuous
stirring of the charge. The water of hydration is thus expelled and the free
sulphur burnt off. When the charge has attained a low red heat, it is withdrawn
from the retort or furnace into water to prevent oxidation of the sulphide. After
washing, grinding in water and drying the zinc sulphide is ready for market as a
white pigment of great covering power. The free sulphur burnt off produces
sulphurous acid which may be conducted into leaden chambers and utilised in the
manufacture of sulphuric acid.

page_text: COMPLETE SPECIFICATION.
"
I, JOHN HENRY JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of this Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF SULPHIDE OF ŽINO AND THE OBTAINMENT OF SulphurETTED
HYDROGEN, AND SULPHUROUS ACID, AS PRODUCTS OF THE SAID MANUFACTURE
which Invention has been communicated to me from abroad by Thomas Macfarlane
of Montreal in the Province of Quebec and Dominion of Canada Chemist and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
According to this Invention a Solution containing Hydro Sulphate of lime is
prepared, which may be effected according to one or other of the following
methods.
I. Two parts of quicklime are slaked, mixed with one part of ground sulphur,
and boiled together with water for about two hours. After subsidence the resulting
solution is drawn off, which contains hydrosulphate and hypo-Sulphite of lime,
together with some penta-Sulphide of Calcium. This may be designated as Sulphur
liquor N° 1.
II. One part of Quicklime is slaked, mixed with one part of the spent iron oxide
produced in purifying illuminating gas, (which contains about fifty per cent
Sulphur) and boiled together with water for about two hours. The resulting
solution is of the same nature as described in the foregoing paragraph and may be
termed Sulphur Liquor N° 2.
III. Ordinary tank waste from the Alkali manufacture, consisting mainly of
Calcium Sulphide, is taken and exposed in loose heaps on inclined water-tight
floors, to the action of the Atmosphere for 3 or 4 weeks, until it has acquired in
the interior a greenish yellow colour, and has absorbed sufficient Oxygen and
Carbonic acid for the formation in conjunction with moisture, of considerable.
quantities of Carbonate of lime and bi-hydrosulphato of lime.. Should the heap of
tank waste in thus weathering become heated to such an extent as to cause ignition
and loss of Sulphur, this is to be stopped by beating down the heap to exclude air,
or cooling it down with water. The bihydrosulphate of lime being soluble, is
leached out with water and fresh quantities of weathered tank waste treated with
it until it attains a strength of 10° to 20° Twaddell. In this case it contains from.
two and a quarter to two and a half equivalents of Sulphur for each equivalent of
calcium in the liquor. Besides the bihydrosulphate of lime, there is therefore
likewise present more or less bi-Sulphide of Calcium. The Solution thus produced
may be called Sulphur liquor N° 3, and like the others, is to be made use of in the
manner hereinafter to be described.
A perfectly pure solution of Chloride of Zinc is then prepared. This is done by
dissolving metallic zinc, impure zinc oxide, calcined zinc blende, or ores, either raw
or calcined, containing carbonate or Oxide of Zinc, in Hydrochloric acid, presenting
these substances in excess to the acid until the latter is completely neutralised. The
resulting Solution is then evaporated in lead or cast iron pans until it attains &
specific gravity of at least 1.6. During this evaporation, the manganese iron and
other impurity which the solution may contain, is for the most part rendered
insoluble aud separated. The evaporation may be continued until the solution is

page_text: of such a strength that it solidifies on cooling, in which case it is ladled into sheet
Iron alkali drums and stored for use. When re-dissolved it yields an almost pure
solution of Chloride of Zinc. Any trace of iron which it may contain is precipitated
by the addition of a small quantity of Solution of Chloride of lime.
The aforesaid Sulphur liquors and the Chloride of Zinc Solution are mixed in
suitable vessels, when a precipitate is formed of hydrated Sulphide of Zinc mixed
with more or less free sulphur, while chloride of Calcium remains in solution. The
Zinc chloride is added to the Sulphur liquors until the mixture shews a slightly acid
reaction. The liquors Nos 1 and 2 yield the precipitate without any evolution of
sulphuretted hydrogen, but this is not the case with sulphur liquor No 3. When
this has a strength of 10° to 20° Twaddell, and is mixed with the chloride of zinc
solution, sulphurotted hydrogen is produced abundantly and may be collected and
conducted away from the precipitating vat. In order to do this, the latter must be
provided with a cover having an opening in the centre through which the agitator
shaft passes. The opening is furnished with a water luto in which an air-tight
collar fastened on to the shaft works, in order to prevent any escape of gas. The
latter is led off through a pipe in the cover and being uncontaminated with other
gases may be ignited in a properly constructed furnace or flue and burnt to
sulphurous acid, which may be used for the manufacture of sulphuric acid. The
precipitate of Zinc Sulphide and free. Sulphur is then passed through filter presses
in order to separate it from the Solution of Chloride of Calcium accompanying it.
Pure bydrated Sulphide of Zinc is of a very finely divided or slimy nature, and
difficult to filter, oven under great pressure, but the presence of the precipitated
Sulphur renders it more granular and easy of filtration The cakes produced in
the filter presses are dried in a drying chamber of the usual construction, in which
the temperature is not allowed to exceed 150° Fahrenheit.
The hydrated Zinc Sulphide dried as above indicated is then ignited. This is
performed in gas retorts or mufile furnaces at a red heat, and under continuous
stirring of the chargo. The water of hydration is thus expelled and the free sulphur
burnt off. When the chargo has attained a low red heat, it is withdrawn from the
retort or furnace into water to prevent oxidation of the Sulphide; After washing,
grinding in water, and drying, the Zinc Sulphide is ready for market as a white
pigment of great covoring power. The free sulphur burnt off produces sulphurous
acid which may be conducted into leaden chambers and utilized in the manufacture
of Sulphuric acid.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
First: The application of Solutions of hydro-Sulphates of lime prepared as above
described for precipitating hydrated Sulphide of Zinc as above described.
Second The purification of Chloride of Zinc solution by concentrating it to a
specific gravity of 1.6 as above described.
Third: The production of pure Sulphuretted hydrogen gas by the action of
Chloride of Zinc on bihydrosulphate of lime as above described.
Fourth: The preparation of hydrated Sulphide of Zinc for filtration by the
introduction amongst it of precipitated Sulphur as above described.
Fifth The production of Sulphurous acid from the free Sulphur precipitated
along with the Sulphide of Zinc by igniting it as above described.