IMPROVEMENTS IN PURIFYING GAB
Year: 1861

page_text: LETTERS PATENT to Robert Angus Smith, 20, Devonshire St., Manchester,
for the Invention, of "IMPROVEMENTS IN PURIFYING GAB."
Sealed the 5th November 1861, and dated the 6th July 1861.
PROVISIONAL SPECIFICATION left by the said Robert Angus Smith
at the Oflice of the Commissioners of Patents, with his Petition, on
the 6th July 1861.
I, ROBERT ANGUS SMITH, 20, Devonshire St., Manchester, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN PURIFYING
GAS," to be as follows:-
My improvements in the method of purifying gas are principally intended
for the removal of impurities which are difficult of removal by the means
commonly employed, and consist in so disposing a solution of a compound of
lead or other metal in caustic alkali as to present to the gas a sufficiently large
surface. When a metallic sulphide is formed, it is oxidised by exposure to the
air, and so fitted for repeated use.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Robert Angus Smith in the Great Seal Patent Office on the
4th January 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
ANGUS SMITH, of 90, Devonshire Street, Manchester, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent. bearing date the Sixth day of July, in the year of our Lord One
thousand eight hundred and sixty-one, in the twenty-fifth year of Her reign,
did, for Herself, Iler heirs and successors, give and grant unto me, the
said Robert Angus Smith, Her special licence that 1, the said Robert
Angus Smith, my executors, administrators, and assigns, or such others
as I, the said Robert Angus Smith, my executors, administrators, and
assigns, should at any time agree with, and no others, from time to time and
at all times hereafter 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 PURIFYING GAS." upon the condition (amongst others) that
I, the said Robert Angus Smith, 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 saune 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.
NOW KNOW YE, that I, the said Robert Angus Smith, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed to be particularly described and ascertained in and by the
following statement, that is to say:-
My Invention of an improved method in purifying gas is principally
intended for the removal of bisulphide of carbon, and consists in so disposing
of a solution of lead and certain other metals in caustic alkali as to present a
sufficiently large surface. The metallic sulphide formed is oxidised by
exposure to the air.
I pass the gas (which 1 prefer should be previously purified by some
ordinary means from its sulphuretted hydrogen and carbonic acid) through
sawdust or other convenient absorbent material presenting a large surface,
moistened with a solution of oxide of lead (or litharge) in caustic soda, and
arranged in thick layers in dry purifiers, after the manner of oxide of iron. 1
find that about four pounds of oxide of lead dissolved in one gallon of caustic

page_text: soda, having a specific gravity of 1250, will answer my purpose in ordinary
cases, but the more lead the better. I prefer to have two purifiers, and to
use them alternately, each being of the usual depth, and of such an area at
least that the gas shall not pass through it in larger quantity than one cubic
foot for each superficial square inch during an hour. This is about the pro-
portion of area generally in use in well-established works for oxide of iron:
but the greater it is the better. Gas so purified has been found entirely free
from sulphur, as well as the sulphuretted hydrogen, if not previously removed,
or any residue of it that may have escaped the previous ordinary process.
During the purification of gas from sulphur by means of my Invention, the
sulphur combines with the lead to form sulphide of lead. When the material
is spent, I recover the lead for further use by exposing the mixture for a few
hours to the air, either in the purifier or out of it; the black sulphide there-
upon changes into the white sulphate of lead, to which (as it contains oxide of
lead) I then add a fresh dose of alkaline ley to bring it again into solution,
and make it fit to repeat its former service. After several alternations of this
use and restoration, the sawdust becomes inconveniently full of sulphate of
soda when that is the case, I simply wash that salt out with water, and as
little or no lead is thereby removed. the metal and sawdust are again thus
made available for use. Instead of oxide of lead, a saturated solution of
sulphate of lead may be substituted in the first instance, and sometimes it is to
be obtained as a cheap residue of other manufacturing operations. Instead of
a compound of lead, oxide of zinc, antimony, arsenic, or tin may be dissolved
in the alkali, but I prefer the solution of lead, and instead of soda, caustic
potash may be substituted, but it is more costly. I find also that in place of
cither of the above chemicals, the sawdust may be usefully moistened with a
solution of copper in ammonia, or if iron, in either organic acids, or other
organic substances in which it is soluble, such as sugar, treacle, &c., all such
solutions being better the stronger they are; but in my estimation nothing is
altogether so desirable as the solution of oxide of lead in caustic soda.
Lastly, instead of using the several chemical reagents in dry purifiers, as 1
have recommended, the solutions without the sawdust may be brought into
contact with the gas by what is ordinarily understood as "scrubbing," but I
do not recommend that modification, on account of the precipitates that might
be found inconvenient, and for other reasons of a mechanical character that
will be well understood.
I do not propose to confine the use of my Invention to public manufactories
of gas, as every gas consumer who shall have the misfortune to be in a district
supplied with sulphureous gas, may, by means of a small box furnished under

page_text: my Patent, purify the gas for myself without his being put to the least trouble
or personal inconvenience.
Having thus described my Invention for improvements in the manufacture
of gas, and best means of performing the same, I claim as my Invention, the
purifying of gas from sulphur and its compounds, except sulpherretted
hydrogen, by treating it with alkaline solutions of the metals, and in the
manner herein-before particularly described.
In witness whereof, I, the said Robert Augus Smith, have hereunto set
my hand and seal, this Third day of January, One thousand eight
hundred and sixty-two.
ROBERT ANGUS SMITH. (L.S.)