AN IMPROVED PROCESS FOR THE MANUFACTURE OF HYDRATE OF STRONTIA."
Year: 1881

page_text: LETTERS PATENT to Carl Friedrich Claus, of Mark Lane, in the City of
London, Chemist, for an Invention of "AN IMPROVED PROCESS FOR THE
MANUFACTURE OF HYDRATE OF STRONTIA."
PROVISIONAL SPECIFICATION left by the.said Carl Friedrich Claus at the
Office of the Commissioners of Patents on the 27th August 1881.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist.
IMPROVED PROCESS FOR THE MANUFACTURE OF HYDRATE OF STRONTIA."
«< AN
In the Specification of Letters Patent granted to me and dated 16th of August,
A.D. 1878 (No. 3246), I have described a process for the manufacture of a white
pigment consisting of sulphide of zinc, in which process I obtain hydrate of
baryta (caustic baryta), as a bye product.
In the said process oxide of zinc was dissolved either in caustic soda, caustic
potash, or caustic ammonia (preferably the latter), and precipitated by means of
sulphide of barium or otherwise. Now according to my present Invention I
dissolve the oxide of zinc (obtained from any source) by means of caustic soda,
caustic potash, or (preferably) caustic ammonia, but I precipitate the sulphide of
zinc by means of solutions of sulphide of strontium, and obtain caustic strontia
(hydrate of strontia), which is at present an article of great commercial value, and
for the manufacture of which from its sulphide no cheap and practicable process
has hitherto been known.
When ammonia is used I carry on the process of precipitation in closed vessels,
and I prefer to heat the contents of the precipitating vessel during such process by
means of steam or directly by fire. The ammonia evaporated is conveyed by a
suitable pipe to a condensing apparatus and there condensed, and is subsequently
used for dissolving fresh quantities of oxide of zinc in future operations. When
the precipitation is completed I filter the contents of the precipitating vessel while
hot in press filters, provided with removable air tight covers to prevent loss of
ammonia by volatilisation, and keep the filter hot during the filtration and thereby
obtain a highly concentrated solution of caustic strontia (hydrate of strontia). I
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page_text: may utilize this last described process when sulphide of barium has been used as
a precipitant according to the Specification of my said former Letters Patent, to
obtain a concentrated solution of caustic baryta.
The ammonia is separated from the hydrate of strontia solution by distillation
and condensed, and the hydrate of strontia is crystallised out in the ordinary well
known manner.
The precipitate of sulphide of zinc is heated to a dull red in retorts or muffles,
arranged to collect the ammonia evaporated from the press cakes. It is then
raked into water, finely ground, levigated, dried, and is then ready for use as a
pigment.
I also dissolve oxide of zinc in caustic potash or caustic soda, and when this is
done the above described process of distillation is unnecessary and all of the
operations may be conducted in open vessels.
To the solution of oxide of zinc in caustic soda or caustic potash I add a solution
of sulphide of strontium until a precipitate is no longer formed. Sulphide of zinc
is precipitated, and hydrate of strontia is formed at the same time, whilst the
caustic soda or potash is again rendered free.
The solutions should be heated during precipitation to keep all the hydrate of
, strontia formed in solution and to prevent its crystallising out.
The sulphide of zinc is filtered off hot from the solution and treated as above
specified for the manufacture of the pigment.
The filtrate being as above stated, a solution of hydrate of strontia and caustic
soda or caustic potash is now boiled down and the hydrate of strontia allowed to
crystallise out by cooling to separate the same from the caustic alkali or alkalies,
this operation being well understood by chemists.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Carl Friedrich Claus in the Great Seal Patent Office on the
27th February 1882.
CARL FRIEDRICH CLAUS, of Mark Lane, in the City of London, Chemist,
"AN IMPROVED PROCESS FOR THE MANUFACTURE OF HYDRATE OF STRONTIA."
The said Invention relates to the manufacture of hydrate of strontia by an
improved process which is carried into practice as follows, that is to say :-I take
a solution of sulphide of strontium prepared in the well known manner, viz., by
heating to a bright redness a mixture of sulphate of strontia and carbonaceous
matter (in a kiln or in a reverberatory furnace in a reducing flame), and by
lixiviating the product of such beating process in water (preferably hot). I also
dissolve oxide of zinc (obtained from any source) by means of caustic soda,
caustic potash, or caustic ammonia to form an alkaline solution, which by its
action on the said sulphide solution will produce hydrate of strontia, as hereinafter
described.
I prefer to use caustic ammonia as the solvent for the oxide of zinc, for the
reason that it will not so readily take up impurities with which the zinc may be
associated, and consequently will form a purer solution of zinc than could be
obtained with the other caustic alkalies. Should however this solution contain
oxide of copper or of silver or other metallic oxides soluble in ammonia (or in the
other caustic alkalies), these metals may be precipitated as sulphides by the
addition of a solution of an alkaline sulphide before any of the zinc will be
precipitated. I therefore add sufficient alkaline sulpbide (preferably a solution of
sulphide of strontium) to precipitate all of such impurities, that is to say, until a
sample of the filtrate tested with a further quantity of alkaline sulphide will yield
a pure white precipitate of sulphide of zinc.
This treatment for the removal of the foreign metals is not strictly necessary for
the ultimate production of hydrate of strontia according to my Invention, but it is
advantageous for the reason that when it is employed the sulphide of zinc produced
in the subsequent operations is of greater purity and commercial value than when
such treatment is omitted. I find that the addition of a small quantity of cream
of lime (hydrate of lime) and of chloride of lime to the zinc solution (preferably
after heating the same slightly) facilitates the subsequent removal of the foreign
metals or impurities by the alkaline sulphide.
Having thus produced a pure alkaline solution of oxide of zinc, I filter the same
to render it perfectly clear or free from sediment; I then add to this alkaline
solution of oxide of zinc the solution of sulphide of strontium (which must also be
perfectly clear), continuing the addition until no longer a precipitate is formed.
The precipitation may be carried on with a hot and concentrated solution, but a
better result is obtained when the sulphide of strontium solution contains only
from ten (10) per cent. to twenty (20) per cent. of sulphide of strontium, and
the solution of oxide of zinc contains about the same proportion of oxide of zinc
by weight.
During the precipitation and subsequent operations the liquors should be heated
to near the boiling point, and when caustic ammonia is used as a solvent for the
oxide of zinc it is obvious that all of the operations should be carried on in closed
vessels.
The precipitate produced is sulphide of zinc and the liquid or filtrate contains
hydrate of strontia formed simultaneously with the sulphide of zinc, and it also
contains the alkali which has served as the solvent for the oxide of zinc.

page_text: .
The sulphide of zinc is now separated by filtration from the liquid, is washed and
dried, and may be converted by calcination and other known means into a white
pigment.
Any ammonia not washed out of and still adhering to the sulphide of zinc
becomes volatilized during the process of calcination in closed retorts, and may be
conveyed by pipes to a condensing apparatus.
Hydrate of strontia is only sparingly soluble in cold water, but is readily soluble
in hot water; it is therefore necessary (in order to prevent its crystallizing out and
becoming mixed with the precipitate of sulphide of zinc) that the filtering and
washing operations as well as the precipitation should be carried on with heated
liquids.
All of the operations (either cold or hot) are, as aforesaid, carried on in closed
vessels when ammonia is used as a solvent, and the vapours of ammonia are
conveyed from such vessels to a condensing apparatus, wherein they are condensed
into liquid ammonia which may be repeatedly recovered and used.
The ammonia is separated from the solution of hydrate of strontia by distillation
and condensed and used repeatedly or over and over again. The hydrate of strontia
solution is boiled down to the point of saturation, and then run into crystallizing
vessels and crystallized out.
When caustic soda or caustic potash solutions are used in my improved process
as a solvent for the oxide of zinc, most of the reactions are the same as when
ammonia is used in such process, but the various operations may be carried on in
open vessels because the caustic soda and caustic potash are not volatile; but for
the same reason their use is not so advantageous as that of the caustic ammonia,
that is to say, they remain associated with the hydrate of strontia produced and
have to be separated by a tedious process of crystallization and re-crystallization.
The liquors containing them have to be boiled down and the hydrate of strontia is
crystallized out in cooling. The mother liquor from the crystals is boiled down
again and further quantities of hydrate of strontia are crystallized out until the
mother liquor is practically exhausted of hydrate of strontia.
In this condition the mother liquor consists of caustic soda or caustic potash,
which may be used over and over again as a solvent for oxide of zinc.
Having thus fully described my said Invention, and the manner of performing
_the_same, I wish-it-understood-that-I-claim;--
The improved process for the production of hydrate of strontia by the action of
an alkaline solution of oxide of zinc upon a solution of sulphide of strontium, as
above set forth.
In witness whereof, I, the said Carl Friedrich Claus, have hereunto set my
hand and seal, this Twenty seventh day of February, in the year of our Lord
One thousand eight hundred and eighty two.