Improvements in or relating to the Manufacture of Salt (Chloride of Sodium).
Year: 1892

page_text: Date of Application, 24th May, 1892-Accepted, 25th June, 1892
COMPLETE SPECIFICATION,
Improvements in or relating to the Manufacture of Salt (Chloride
of Sodium).
A communication by ALBERT L. LAWTON, of Rochester, in the County of Monroe
and State of New York, Chemist, and WALTER S. DODGE, of Washington, in
the District of Columbia, United States of America, Attorney.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6 Bank Street, Man-
chester, both in the County of Lancaster, and 323 High Holborn in the County of
Middlesex, Civil Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :--
This invention relates to the manufacture of salt (chloride of sodium), and has
reference more particularly to a process for the purification and whitening thereof.
Briefly stated, the first part of the invention consists in the process of providing
a furnace, chamber or other suitable receptacle with a protecting face or lining of
basic infusible material, placing salt therein, and subjecting the salt to a fusing
heat, advisably adding to the salt, before or after fusion, alkaline material.
The second part of this invention consists in changing the salt from a fused state
into spherical or globular bodies which may be either hollow or solid or more or
less fine.
The form of apparatus for carrying out the first part of the invention is, for the
purposes of illustration, shown in Figure 1 of the drawing, which is a vertical
sectional view of a furnace. This form gives good results; but it must be under-
stood that the invention is not limited to the construction shown or to any parti-
cular form, as many other forms of melting furnaces may be substituted with equally
good results.
The apparatus here shown in Figure 1 consists of a fire-place A ; a receptacle B
for the melted or fused salt; two flues or passages C and D, the former directly
over the latter, and inclined as shown, and a series of steps i, i, i, between the two
flues. Between these steps are openings through which the hot gases from the fire
pass and come in contact with the salt resting upon the steps, the gases also passing
around the lower end of the hopper C and finally up into the flue or chimney F.
The steps incline downward toward the furnace so as to cause the fused or
melted salt to run down into the receptacle B where the impurities settle to the
bottom with the purer salt in a state of fusion on the top.
In the side of the vessel B is a tap-hole, through which, from time to time, the
dross and the purified salt are separately drawn off into suitable receptacles or
moulds.
H is a tube through which a rod is occasionally thrust to see when the salt in
the receptacle is deep enough for drawing off. At the upper end of the flue D is
placed a valve or damper E, which, when closed, causes the heat to pass through
the spaces between the steps; but when opened (as, for instance, in starting a fire)
allows the products of combustion to pass directly to the chimney.
With the valve closed, salt is fed through the hopper on to the uppermost step,
and, as the body of salt works its way down the flue C from step to step, it
is subjected to the action of heat (varying from 900 to 1340 degrees Fahrenheit)
the degree of heat increasing as the salt continues its travel, so that, by the time
the salt reaches the lowermost step, it will run therefrom into the receptacle B
in a fused or molten condition. The crucible or receptacle B, being located in
proximity to the fire, is kept at a high temperature to prevent the cooling of the
fused salt therein.

page_text: The process just described is that which is employed in reducing comparatively
coarse mined or rock salt; but, where the salt to be melted is in the form of a
powder, the door of the ash-pit should be closed and an artificial but gentle air
blast injected under the grate so as to force the hot gases from the fire through
the powdered salt on the steps i.
An alkali or alkaline material may be mixed with the salt prior to its fusion or
subsequently thereto, and may also be applied in a hydrated or anhydrous state.
Or the alkalies may, before or at the time of using, be combined with weak acids
such as silica or carbonic acid. Some of the alkalies and their compounds that may
be used alone or two or more together are lime, magnesia, strontian, soda and
potash their silicates, carbonates and hydrates, or such substances in an anhydrous
caustic state.
In practice, caustic lime, either hydrated or anhydrous, has been found as good
as anything else, and the quantity required is from one-half of one per cent. to two
per cent. of lime to ninety-nine and one-half to ninety-eight per cent. of salt. These
proportions may, however, be varied somewhat.
In using the silicate or the carbonate of lime, more time is required to produce
the proper effect upon the salt than is required in using lime in the caustic state.
Dolomitic or magnesian lime made from magnesian limestone, a natural rock com-
posed of lime and magnesia carbonates, is found to answer quite as well as the pure
lime.
Pure magnesia, magnesia carbonate, soda and potash also work well in purifying
and whitening salt, but their cost far exceeds that of the lime.
In using the alkali, or materials of an alkaline nature, they may be sprinkled
over or distributed through the salt before it is fused; or the powdered alkali may
be thrown on to or stirred into the salt after fusion. After the salt containing the
alkali is fused and run into a large infusible crucible or receptacle, it is allowed to
stand from five to thirty minutes to give time for the alkali to act on the salt. The
dregs or impurities which had previously settled to the bottom are then drawn off
and then the purified salt is drawn off from the bottom of the receptacle containing
it. When a smaller percentage of alkali is used, it is necessary for the fused
salt to stand a longer time to settle the impurities and to give the desired
effect.
Instead of sprinkling the salt with a powdered alkali, or mixing the alkali with
the previously fused salt, the alkali may be worked into the basic material or
lining of the furnace and crucible in larger proportion than would otherwise be
used, and this extra strongly basic lining and material will of itself whiten the
salt, but it takes more time than when the powdered alkali is mixed with the
salt direct.
When the proportion of lime or magnesia in this lining mortar is very large, the
composition will not readily fuse by contact with the melted salt and at the same
time will cohere sufficiently not to break down.
To save fuel, it is preferable to conduct the hot gases from the fire into direct
contact with the salt to be melted, such dust or soot as gets into the melted salt
settling with the other impurities in the bottom of the fused-salt-crucible or
receptacle.
A furnace, which would produce carbonic-oxide or carbon monoxide gas and
hydrogen, can be substituted for the furnace shown; the heat escaping from the
furnace, after passing through and over the salt, being recovered as in a Siemen's
regenerative furnace.
Natural gas and petroleum may also be employed; but, if petroleum is used, it
would be preferable to convert it into vapour before bringing it to the place of
combustion.
It may also be mentioned that, while the alkaline matters are preferably used
prior to the removal of the fused salt from the receptacle or crucible, such a
course is not essential, as it can obviously be applied afterwards by thoroughly
mixing it with the melted salt, or coating the moulds into which it is poured.

page_text: The formation of fusible silicates is prevented by constructing all those parts
of the furnace that come in contact with the salt of a strongly basic infusible
composition made of a mixture of four parts of lime to one part of good clay, as
free from iron as possible.
By the use of this mixture, the decomposition of the salt and the formation of
soda silicate are avoided by reason of the superior attraction of the lime for the
little silica in the clay with which it is mixed. The fused salt, not coming in
contact with any silica with which it can re-act, remains unchanged so far as the
formation of silicate of soda is concerned; all of which becomes a matter of the
utmost importance when it is considered that no other substance (except perhaps
some virulent poison) could be more injurions to the salt. When the quantity of
soda silicate is so small that it will form a heavy insoluble precipitate with the
impurities in the salt, no injury will result, because of the elimination of the
silicate through such precipitation.
The term lining is used throughout this Specification as meaning and
including a protecting face or surface for the exposed parts of the apparatus,
whether such protection be extended into or throughout the thickness or body of
the chamber, furnace or receptacle, or merely applied as a surface coating.
In the construction of furnaces, the lining is commonly made in the form of
bricks, and such a lining that is, a lining made of bricks of basic infusible material,
is comprehended in the present invention.
Within recent years, a basic infusible lining has been employed in a Bessemer
smelting furnace because of the chemical affinity which the basic lining has for
the phosphorus in the iron under treatment; and this is not claimed.
This invention resides, in great part, in the discovery that the chemical action of
fused salt and salt vapours upon a furnace or vessel may be prevented from taking
place by the employment of a furnace, vessel, or chamber, formed of or lined
with a basic infusible substance, which, by reason of its inert qualities, not only
preserves the furnace from destruction, but also precludes the formation of a
fusible silicate of soda, the presence of which would render the salt practically
useless and unmarketable.
By this process, a table salt is produced chemically pure and consequently non-
hygroscopic, and this too at a cost less than by the evaporation process now
universally used.
In practice, it is found advantageous to perform the operation of purifying salt
as a continuous process, the fire in such case being maintained for an indefinite
period, and additional charges of salt being placed in the reducing vessel or chamber
to replace the fused or purified salt drawn off.
The basic infusible lining once applied will last for a long period, and may last
indefinitely; hence, it is to be understood that the step in the process or the act
which consists in lining the furnace with a basic infusible material will not require
to be repeated with each batch of salt or with each tiring, but only when, if ever,
the lining deteriorates and becomes incapable of resisting the action of the salt
vapours.
In carrying out the second part of the invention, the fused or melted salt is
introduced into the vessel or receptacle B of the apparatus shown in Figure 2.
From this receptacle, B, which is provided with a valve or gate l and a spouts,
the fused or molten salt passes into an atomiser E, which, as shown in Figure 2, is
connected with a pump or air-forcing mechanism D by means of a pipe d and a
reducing pipe q. The pipes d and q are provided with a valve b by means of
which the air or gas current may be regulated. The atomiser is provided with a
discharge pipe h through which the salt is projected into the chamber A, which
latter is advisably divided into compartments C C¹ C² C³ C, each of which is
provided with a valve c.
Opening through the top wall of the chamber A is a pipe p which will advisably
be jacketed, and immediately below the mouth of the pipe is a screen or air
filter n, which, owing to the great heat in the chamber A, will advisably be made

page_text: of asbestos. The air drawn through the coil or pipe d tends to cool the salt in the
bins C C, etcetera, which salt is further cooled by the air passing around the conical
lower ends of the bins. The salt will assume the form shown in Figure 3, and
will be found to have automatically assorted itself, according to the size of the
globules, into the respective bins.
. Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me by
my foreign correspondents, I declare that what I claim is :-
1. The herein described method of purifying salt (chloride of sodium), which
consists in, first, lining a receptacle with a basic infusible material such as
described, next placing salt therein, and, finally, fusing the salt in said receptacle ;
whereby the salt is purified and the formation of silicates is prevented.
2. The method of purifying salt (chloride of sodium), which consists in the
following steps, namely, lining a receptacle with a basic infusible material, as lime
and clay, which will, by reason of its inert chemical qualities, prevent the formation
of soda silicate and the destruction of the receptacle; placing the salt in said
receptacle, fusing the salt therein and adding to the salt, before or after fusion,
an alkaline material.
3. The manufacture of salt in a globular form, substantially as described.
4. The apparatus substantially as shown in Figure 2, and for the purposes
described.
....
ננפה..
SM 100
WM. P. THOMPSON & Co.,
Agents for the Applicant.