TERRANEANTS IN THE MANUFACTURE OF CAUSTIC ALKALIES
Year: 1859

page_text: LETTERS PATENT to Frederick Collier Bakewell, of No. 6, Haverstock
Terrace, Hampstead, in the County of Middlesex, for the Invention of
TERRANEANTS IN THE MANUFACTURE OF CAUSTIC ALKALIES."-A communi-
Sealed the 2nd December 1859, and dated the 5th September 1859.
PROVISIONAL SPECIFICATION left by the said Frederick Collier Bakewell
at the Office of the Commissioners of Patents, with his Petition, on the
5th September 1859..
I. FREDERICK COLLIER BAKEWELL, of No. 6, Haverstock Terrace, Hamp-
stead, in the County of Middlesex, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN THE MANUFACTURE OF CAUSTIO ALKALIES,' .
to be as follows:-
This Invention consists in a method of separating caustic alkalies from the
lime or other precipitate used in the process of their manufacture by means of
filtration through fire-bricks or other solid porous substance capable of resisting
the action of the alkaline liquid. A shallow tank of suitable dimensions made
of stone, brick, or other material not corrodible by alkalies is constructed with
a false bottom composed of a solid porous substance laid upon joists that will
In
allow the fluid to flow through a single pipe at the bottom of the tank.
conducting this improved process, the caustic alkali is first prepared as usual
by mixing carbonated alkali with hydrate of lime in excess, whereby the car-
bonic acid in the alkali is transferred to the lime. The line is allowed to
Price Sd.1

page_text: precipitate, and the clear alkaline liquor having been drawn off, the remaining
portion is thrown into the filtering tank, through the porous bottom of which
the alkali percolates. When the filtration ceases, the portion of alkali that
remains in the lime is extracted mechanically by pouring water carefully over
the lime to the height of a few inches. That stratum of water then forces the
remaining alkali through the porous floor without diluting it. By this means
nearly the whole of the caustic alkali is liberated in a state of strong solution,
and it can be much more readily evaporated to form a solid mass than when
the alkali is extracted from the precipitated, lime by repeated dilution with
water and precipitation.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Frederick Collier Bakewell in the Great Seal Patent Office
on the 2nd February 1860.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FREDERICK
COLLIER BAKEWELL, of No. 6, Haverstock Terrace, Hampstead, in the County
of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifth day of September, in the year of our
Lord One thousand cight hundred and fifty-nine, in the twenty-third year
of Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said Frederick Collier Bakewell, Her special licence that I, the
said Frederick Collier Bakewell, my executors, administrators, and assigns,
or such others as I, the said Frederick Collier Bakewell, iny executors, admi-
nistrators, and assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle of Man,
an Invention for "IMPROVEMENTS IN THE MANUFACTURE OF CAUSTIC ALKALIES,"
(a communication from abroad from Henry Pemberton, of East Tarentum,
U. S., North America,) upon the condition (amongst others) that I, the
said Frederick Collier Bakewell, my executors or administrators, by an
instrument in writing under my, or their, or one of their hands and seals,
should particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the same
to be filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.

page_text: NOW KNOW YE, that I, the said Frederick Collier Bakewell, do hereby
declare the nature of the said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement:-
This Invention consists in a method of separating caustic alkalies from the
lime or other precipitate used in the process of their manufacture by means of
filtration through fire-bricks or other solid porous substance capable of resisting
the caustic action of the alkaline liquid, whereby a more perfect separation is
effected than by the processes heretofore known and practised combined with
a great saving in time and fuel. In describing this Invention, so as to enable
others skilled in the art to practise it, I will take for example the process as
applied to the manufacture of caustic soda. A solution of carbonate of soda
is treated with hydrate of lime in excess in the usual manner, whereby the
carbonic acid is separated from the soda, and uniting with the lime in the form
of insoluble carbonate, the lime is precipitated, and the soda solution is left in
a caustic state. This solution of caustic soda is decanted from the precipitated
carbonate of lime, and is reduced by evaporation to a solid mass. After as
much as possible of the solution of caustic soda has been decanted from the
precipitate, there remains a large quantity of the solution mixed with the lime,
forming a pulpy mass which requires further treatment to extract the soda
from it. By the ordinary process of manufacture this remaining portion of the
soda solution is separated from the insoluble lime by the addition of a quantity
of water which is mixed thoroughly with the lime, and the latter is allowed to
settle. The diluted solution of soda thus produced is then decanted from the
lime, and the process of washing and decanting is repeated ten or twelve times
until nearly all the caustic soda is removed from the lime. By this process
the quantity of liquid to be evaporated becomes very great before the caustic
soda is obtained in a solid state. The filtration of the solution through matting
or other fabric might in some degree overcome this difficulty, were it not that
the corrosive property of the caustic soda rapidly destroys any vegetable or
animal textile fabrics, and even a filter made of sand or other similar substance
would require renewal after each operation, would be difficult to construct and
to keep in order, and a large quantity of the alkaline solution would be retained
by capillary attraction among the particles of the lime. The obstacles to the
ordinary use of filtration for the separation of the caustic soda from the
residuum of carbonate of lime are entirely removed in this Invention by
causing the solution of soda, after it has been mixed with the hydrate of time,
to pass through a filter composed of porous bricks or tiles, or other similar

page_text: material. The construction of such a filter is shown in the accompanying
Drawing.
.
In Figure 1 the letter a represents a shallow tank constructed of stone,
brick, or other suitable material about eighteen inches in depth, and of any
required length and width, twenty-five feet by forty being a convenient size..
This tank is made water-tight, and is supported on a wall or on props; the
bottom of the tank is made to incline from the sides towards a hole in the
centre, or in some other point from which a pipe b conducts the filtered liquid
to a cistern or other receptacle.. On the bottom of the tank are placed
joists c, c, c, parallel to each other about twelve inches apart; these joists need
not be more than one inch thick, and two or three inches in height, and should
have a number of openings close to their lower edge to allow the liquid to pass
through to the exit pipe b. Across these joists are placed supports d, d, of
suitable material, about one inch square, and distant from centre to centre the
length of the bricks or tiles to be laid upon them. The bricks or tiles e, e, e,
to be used for the filter are made of fire-clay or other suitable material con-
sisting essentially of a difficultly fusible siliceous clay, or clay, and sand united
into a mass by partial vitrification, or the reciprocate action of the silicates on
each other. These bricks or tiles are laid flat, side by side, care being taken to
cover the ends of them, wherever they touch each other, or the sides of the
tank; with a thin mortar of hydraulic cement mixed with water to the consis-
lence of cream, with or without sand, so as to leave no interstices between- the
bricks or tiles themselves, nor the sides of the tank, through which any liquid
could pass.
When the mortar has set, the bricks or tiles form a firm floor
which can be walked upon without injuring it. The solution of caustic soda
having been prepared by treating carbonate of soda with hydrate of lime in
excess, the lime is allowed to precipitate, and as much clear liquor as possible
is drawn off. The solution of soda that remains mingled with the lime is after-
wards filtered through the porous floor of the tank, and escapes by the pipe i,
The lime left on the
being thus separated from the lime without dilution.
floor of the tank is about three or four inches deep, and of the consistence of
thick mortar. The portion of caustic soda that still remains mingled with the
lime is then removed without diluting the solution by the gradual addition of
pure water poured gently over the lime to a depth of two or three inches, care
being taken not to wash away the lime from any part so as to uncover the
floor of the tank. The water, which thus forms a stratum above the lime,
then gradually displaces the alkali from the lime by forcing it through the
porous floor into the space below, whence it runs through the pipe b. This

page_text: operation is performed by the mechanical pressure of the water, which forces
the alkaline solution through the porous floor, and occupies the place of the
caustic soda without mixing with and diluting it. Nearly the whole quantity
of soda in solution is thus extracted from the precipitated carbonate of lime,
which is left in nearly a dry state, and may be used for other purposes. By
this method of extracting the solution of caustic soda from the lime, the quantity
of liquor to be evaporated is at least two-thirds less than by the ordinary mode
of washing the precipitate with water, and it thereby effects a great saving in
time, in labour, and in fuel, the economy of fuel in a manufactory making
twenty-five tons of soda per week being not less than ten tons of coal per diem.
After the filters have been used for some time, the porous bricks become
partially choked, so that the filtration becomes less rapid. When this is
observed, the bricks or tiles may be replaced with new ones, laid as before.
The old bricks are not at all injured by the filtration, and after being washed,
may be used for the purposes for which fire-bricks are usually employed.
Having thus described the improvements in the manufacture of caustic soda
and other caustic alkalies, what I claim and desire to secure by Letters Patent
is, the mode herein-before described of separating the solution of caustic soda
or other caustic alkaline liquids from an insoluble precipitate by the use of a
filter constructed substantially in the manner herein-before described. .
In witness whereof, I, the said Frederick Collier Bakewell, have here-
unto, set my hand and seal, this Second day of February, in the year
of our Lord 1860.
(L.s.) FRED. COLLIER BAKEWELL.