IMPROVEMENTS. IN THE MANUFACTURE OF SODA
Year: 1870

page_text: LETTERS PATENT to Edward Andrew Parnell, of Swansea, in the
County of Glamorgan, Manufacturing Chemist, for the Invention
"
COMPLETE SPECIFICATION filed by the said Edward Andrew Parnell
at the Office of the Commissioners of Patents, with his Petition
and Declaration, on the 2nd September 1870, pursuant to the
9th Section of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
ANDREW PARNELL, of Swansea, in the County of Glamorgan, Manu-
facturing Chemist, send greeting.
WHEREAS I am in possession of an Invention for "IMPROVEMENTS.
IN THE MANUFACTURE OF SODA," and have petitioned Her most Excellent
Majesty Queen Victoria to grant unto me, my executors, administrators,
and assigns, Her Royal Letters Patent for the same, and have made.
solemn Declaration that I am the first and true Inventor thereof.
NOW KNOW YE, that I, the said Edward Andrew Parnell, do hereby
declare the nature of the said Invention, to be as follows:-
My improvements relate in the first place to a process for the puri-
fication of crude soda liquors such as are produced in the ordinary

page_text: manufacture of soda from the sulphate of soda, and commonly known as
"black ash liquor." The principal impurity in this liquor is, sulphide
of sodium, the presence of which is not only a loss of soda, but of great
inconvenience from its solvent power over sulphide of iron, thereby
deteriorating the colour of the subsequent products. To overcome this
inconvenience the method commonly pursued is to oxidize the sodium
sulphide by exposure to air. It is thereby converted into sulphite of
soda and becomes therefore of no value as an alkaline material.
0
By my improvement herein described, which is applicable to all
alkaline liquors containing sodium sulphide, tliis impurity is decomposed,
the sulphur contained therein is separated from the liquor, and the
soda is liberated in an available state. To effect this decomposition of
sodium sulphide I add to the black ash liquor or other alkaline liquor
precipitated carbonate or mixed oxide and carbonate of zinc prepared
as herein-after described. I use this material in the moist state as pre-
cipitated, washed, but not dessicated. The application of dry oxide of
zinc has already been proposed for the purification of black ash liquor,
but the slowness of the action of this material has prevented its adoption.
In the form, however, of moist precipitated sub-carbonate, it instantly
decomposes the alkaline sulphide with formation on the one hand of
zinc sulphide, which is insoluble and soon subsides, and on the other
hand of carbonate of soda and caustic soda. For the purification of a
quantity of alkaline liquor containing 16 parts of sulphur in the state
of sodium sulphide, I introduce a quantity of the zine precipitate which
contains 32 parts of metallic zinc. The zinc precipitate may be supplied
with agitation so long as the presence of sodium sulphide is indicated
by the coloration of paper impregnated with lead solution. If used in
slight excess the zinc is dissolved by the caustic alkali present in the
liquor, but this excess is immediately separated by the admixture of
more black ash liquor. A very slight agitation suffices to ensure com-
plete decomposition of the alkaline sulphide. As a convenient method
of mixing I cause continuous streams of black ash liquor and washed
zinc precipitate in the state of thin mud to flow into a well from which
the mixture is forced through a pipe by a pump or "blower" into a
higher reservoir or settler, where the zinc sulphide is allowed to subside.
The agitation thus effected is sufficient. The application of heat to the
mixture is unnecessary; I employ the black ash liquor of its usual
strength, namely, from 30° to 40° of Twaddell's hydrometer. If speedy

page_text: subsidence of the zinc sulphide is desirable I use liquor of from 30° to
35 Twaddle. The clear alkaline liquor thus purified is then ready for
subsequent treatment according to the usual methods for the production
of either caustic soda, white soda ash, or soda crystals. If the purified
liquor is converted by the ordinary way into caustic soda a white
product is obtained of high per-centage (70 to 74 p. c.) as it is not
diluted by the presence of sulphite of soda, which is always the case.
when the usual method is pursued of oxidizing the sodium sulphide by
the injection of atmospheric air.
My next improvement relates to the preparation of the precipitated
sub-carbonate of zinc for the preceding operation. The materials I
employ for this purpose are solution of sulphate of zinc (obtained as
herein-after described), and the inferior "salts" deposited from caustic
soda liquor during its evaporation. These "salts" consist chiefly of
sulphate of soda mixed with more or less carbonate of soda and
caustic soda. I make use of "salts" containing in the dry state from
20 to 30 per cent. of available soda, in which this soda is of no more
value than the total sulphate. The precipitated sub-carbonate of zinc
when washed is ready for usc. I concentrate the supernatant liquors
for the recovery of the sulphate of soda, for which I make use of the
waste heat of a black ash furnace. For commencing the preceding
operation the sulphate of zinc may be obtained by adding sulphuric
acid to calcined blende, calamine, or silicate of zinc. The material I
prefer as most economical is inferior blende (so poor in zinc as to be
of little value for smelting purposes). This is first calcined at a
moderate heat, not sufficient to decompose all the sulphate of zinc
thus formed, and afterwards mixed with sufficient sulphuric acid to
convert all the oxide of zinc into neutral sulphate. But for a continuous
supply of zinc material I make use of the precipitated zinc sulphide
obtained in the purification of the alkaline liquors already described,
this precipitate having been washed with water until free from alkali,
and then allowed to drain on a porous bed. I convert this material into
sulphate of zinc by admixture of ordinary chamber sulphuric acid,
either with or without previous drying and roasting according to the
proportion of iron which may be present. If the proportion of iron
amounts to one-fourth or upwards of that of the zinc, I first dry and calcine
this material. For this purpose I heat it in an ordinary reverberatory
furnace, at first moderately, afterwards to dull redness, the heat not

page_text: being raised sufficient to decompose sulphate of zinc thus formed. This
product, which consists for the most part of oxide of zinc and peroxidė
of iron I then mix in a fine state with sufficient sulphuric acid to
combine with the zine. I calcine this mixture with sulphuric acid in a
reverberatory furnace, the heat being moderate at first, but increased
towards the end to dull redness, whereby the sulphate of iron is de-
composed and the iron rendered insoluble, while the zinc remains as
soluble sulphate. If the precipitated zinc sulphide is mixed with a
smaller proportion of iron than above specified (less than one-fourth
the amount of zinc) I add sulphuric acid to the washed sulphide without
previous drying or calcining: The product, which-is-a-mixture-of
sulphate of zinc with more or less protosulphate. of iron; I calcine in a
roverberatory furnace in the manner above described. The sulphate of
zinc obtained by either of the preceding methods affords on lixiviation
with water a solution adapted for the preparation of the precipitated sub-
carbonate of zinc with the caustic "salts," as-before described.
Having thus described the nature of my said Invention, and the
manner of performing the same, I would have it understood that I do
not confine myself to the exact details described, but I claim the purifi-
cation of alkaline liquors containing sulphide of sodium by means of
the precipitate of carbonate or mixed oxide and carbonate of zinc pre-
pared from sulphate of zinc and the "salts" obtained in the manufacture
of caustic soda.
I also claim the treatment, substantially as described of the zinc
sulphide precipitate resulting from the purification of alkaline liquors.
in such manner as to bring it back to the state of a carbonate or mixed
oxide and carbonate precipitate fit to be again used for the purification of
alkaline liquors.
In witness whereof I, the said Edward Andrew Parnell, have here-
unto set my hand and seal, this Twenty-ninth day of August, in
the year of our Lord One thousand cight hundred and seventy.
EDWARD ANDREW PARNELL. (L.S.)