IMPROVEMENTS IN THE PURIFICATION OF COAL GAS
Year: 1872

page_text: LETTERS PATENT to Robert Hogarth Patterson, of Hammersmith,
in the County of Middlesex, Gentleman, for the Invention of
"IMPROVEMENTS IN THE PURIFICATION OF COAL GAS."
Sealed the 28th May 1872, and dated the 9th March 1872.
PROVISIONAL SPECIFICATION left by the said Robert Hogarth
Patterson at the Office of the Commissioners of Patents, with his
Petition, on the 9th March 1872.
I, ROBERT HOGARTH PATTERSON, of Hammersmith, in the County of
Middlesex, Gentleman, do hereby declare the nature of my said Inven-
tion for "IMPROVEMENTS IN THE PURIFICATION OF COAL GAS," to be as
follows:-
This Invention relates to the purification of coal gas from sulphur in
other forms than sulphuretted hydrogen by means of sulphide of
calcium, while the carbonic acid is likewise reduced, with a correspond-
ing improvement in the illuminating power of the gas. Also the lime
on being emptied from the purifiers, having been mainly converted into

page_text: used.
It is proposed to use this process in the following ways, which may be
employed either together or separately.
(1.) A purifier (or purifiers) is used containing pure sulphide of
calcium, into which the gas is passed after being purified from sul-
phuretted hydrogen and carbonic acid. Thereafter a second purifier is
used containing fresh lime which is gradually converted into sulphide
of calcium by the overflow of sulphur compounds from the first
purifier.
(2.) At present the action of lime purifiers is greatly impaired and
sometimes wholly destroyed owing to the carbonic acid in the gas,
whereby the lime is converted into carbonate of lime which does not
absorb sulphur in any form. Accordingly I propose to eliminate car-
bonic acid from the gas in such manner that one or more of the said
purifiers shall contain lime as nearly as may be in the form of sulphide
of calcium.
One mode of applying this principle is by passing the gas through
the first purifier (or purifiers) of the series for such time that the car-
bonic acid shall (from its greater affinity for lime) have expelled the
sulphuretted hydrogen from the vessel, taking its place and driving
it (viz., the sulphuretted hydrogen) forward into the succeeding
purifiers. By this means the largest possible amount of carbonic acid
will be absorbed by the first purifier or purifiers, while the sulphuretted
hydrogen being thus driven forward converts the contents of the sub-
sequent purifiers into sulphide of calcium. The contents of the first
purifier being now mainly carbonate of lime are when emptied com-
paratively free from the offensive odour of ordinary gas lime.
Another method (which may be used in conjunction with either of the
above-described processes) is to make the gas pass through or otherwise
come in contact with a solution of soda or of potash, or of ammonia,
before entering the purifiers, in order to reduce the amount of carbonic
acid.
I also propose as an improvement in the purification of gas from
sulphur in other forms than sulphuretted hydrogen, to make the gas
pass through or otherwise come in contact with a solution of soda or of

page_text: potash, or of ammonia, after all the other purifying processes (whether
by lime, by oxide of iron, or otherwise) with a view to absorb the sulphur
in the gas in other forms than sulphuretted hydrogen, after the gas has
been purified from sulphuretted hydrogen and carbonic acid.
I also propose to attain the same object (viz., the purification of gas
from sulphur, in other forms than sulphuretted hydrogen) by means of
pure sulphur, used either by itself or mixed with lime, soda, or ammonia,
these substances being used either in solid or in solution.
filed by the said Robert Hogarth Patterson in the Great Seal Patent
Office on the 9th September 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
HOGARTH PATTERSON, of Hammersmith, in the County of Middlesex,
Gentleman, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Ninth day of March, in the year
of our Lord One thousand eight hundred and seventy-two, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Robert Hogarth Patterson, Her special
license that I, the said Robert Hogarth Patterson, my executors, adminis-
trators, and assigns, or such others as I, the said Robert Hogarth Patterson,
my executors, administrators, or 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 PURIFICATION OF COAL GAS," upon the condition (amongst others)
that I, the said Robert Hogarth Patterson, my executors or adminis-
trators, by an instrument in writing under my hand and seal, 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 Robert Hogarth Patterson, 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, reference being had to the accompanying
Drawings, and to the letters and figures marked thereon, that is to
say:
This Invention relates to the purification of coal gas from sulphur in
other forms than that of sulphuretted hydrogen by means of sulphides
of calcium (as distinct from the material called "gas lime" or "foul
lime," which may be, and under the existing methods of working lime
purifiers is always partly carbonate of lime) employed in separate
purifiers.
It also relates to a principle and process of working lime purifiers,
whereby the carbonic acid in the gas is eliminated by the action of the
first purifier or purifiers of the series in such manner that the lime in
the subsequent purifiers is converted either wholly or to any extent that
may be desired into sulphides of calcium.
It also relates to the use of washers or scrubbers containing a solution
of caustic soda, or of potash, or of ammonia, by the employment of
which vessels the carbonic acid is eliminated from the gas in such
manner that when the said washers or scrubbers are placed before
ordinary lime purifiers, the contents of these purifiers can be converted
into sulphides of calcium, and thereafter maintained in that form; and
when the said washers or scrubbers are placed before purifying vessels
containing sulphides of calcium or sulphides of sodium, the contents of
those vessels can be maintained in the form of sulphides.
It also relates to the purification of coal gas from sulphur existing in
other forms than that of sulphuretted hydrogen by means of washers or
scrubbers containing a solution of caustic soda or of potash, through
which vessels the gas is passed after it has been purified from sul-
phuretted hydrogen and carbonic acid.
It also relates to the purification of coal gas from sulphur, existing in
other forms than that of sulphuretted hydrogen, by means of sulphur in
a fine state of division, and in conjunction with an inert substance, or in
combination with soda or with lime, or with lime and soda together in
solution or otherwise.

page_text: I propose to employ these processes as follows :-
-
1. Sulphide of Calcium Purifiers. A purifier (or purifiers) is used
containing pure sulphides of calcium, into which the gas is passed after
being purified from sulphuretted hydrogen and carbonic acid for the
purpose of absorbing the sulpho-carbons, i.c., the sulphur in other forms.
than sulphuretted hydrogen. A second purifier should be used con-
taining fresh lime or oxide of iron to arrest any sulphur compounds
passing forward from the previous vessel containing the sulphides of
calcium. When the first purifier has become saturated to such an extent
as to be no longer capable of efficiently absorbing the sulpho-carbons it
is to be charged anew with fresh sulphide of calcium. The easiest and
most economical manner of making or producing the sulphide of calcium
to any required extent is described infra, § II.
It is not indispensable that the whole of the carbonic acid or of the
sulphuretted hydrogen shall be eliminated from the gas before it enters
these sulphide of calcium purifiers, but the less carbonic acid and
sulphuretted hydrogen enters the said purifiers the longer will their
contents remain in an efficient condition for purifying the gas from
sulphur in other forms than sulphuretted hydrogen. When the gas (by
processes described in this Specification or otherwise) has previously
been completely purified from carbonic acid and from sulphuretted
hydrogen the contents of the sulphide of calcium purifiers will remain
efficient for a long time, seeing that the only "fouling" element which
enters is the small amount of sulphur which exists in the gas in other
forms than sulphuretted hydrogen. If any carbonic acid or sulphuretted
hydrogen enters the said purifiers the fresh lime in the subsequent
purifier will quickly be converted into sulphide of calcium by an over-
flow of sulphur compounds expelled from the anterior purifiers by the
carbonic acid.
This process may be advantageously employed in addition and sub-
sequent to the purifying processes, by oxide of iron or otherwise, at
present used in gas works.
II. New Principle and Process of Employing Lime Purifiers.-At
present the action of lime purifiers is greatly impaired owing to the
carbonic acid in the gas which enters them, whereby the lime in those
vessels is converted into carbonate of lime, which does not absorb
sulphur in any form. Indeed (as the principle for employing lime

page_text: purifiers now described has not hitherto been known or applied), in gas
works where oxide of iron purifiers are used after the lime purifiers the
contents of these last named vessels under the present mode of working
them sometimes exist almost entirely in the form of carbonate of lime,
the lime having become desulphuretted by the carbonic acid in the gas,
and the sulphur compounds driven forward into the subsequent oxide of
iron purifiers. Under this Patent I propose to eliminate carbonic acid
from the gas in such manner that in any required number of the said
purifiers the lime shall be converted into and (so far as required) main-
tained in the form of sulphides of calcium. And in doing so I turn to
account the superior affinity which carbonic acid has for lime, for soda,
for potash, and for ammonia, compared with sulphuretted hydrogen
:-
(1.) One process of applying the above described principle is by
passing the gas through the first lime purifier or purifiers of the series
for such time that the carbonic acid, from its greater affinity for lime,
shall have expelled sulphuretted hydrogen from the said purifier or
purifiers, taking its place, and driving it (namely, the sulphuretted
hydrogen) forward into the succeeding purifiers. By this means the
carbonic acid can be wholly eliminated from the gas by the first purifier
or purifier, while sulphuretted hydrogen being driven forward converts
the contents of the succeeding purifier or purifiers into sulphide of
calcium, which is a highly efficient material for purifying the gas from
sulphur in other forms than sulphuretted hydrogen. Thereupon these
latter mentioned purifiers, now containing sulphides of calcium, may be
used first in the series, and the gas passed through them into subsequent
purifiers containing fresh lime, whereby the contents of these subsequent
purifiers, or of any one of them, can be converted in turn into sulphides
of calcium. Or the first purifier or purifiers of the series may be
constantly employed, chiefly for the purpose of eliminating the carbonic
acid from the gas, while sulphur in all forms is eliminated from the gas
in the succeeding purifiers.
In devising this process of working lime purifiers I have been the first
to see the importance of and to have practically carried into effect the
principle of excluding carbonic acid from lime purifiers, or from any
required number of these vessels, as a means of obtaining steady and
perfect results in the purification of gas from sulphur. And in applying
this principle I have also been the first to turn to account and practi-

page_text: cally apply the greater affinity which carbonic acid has for lime, for
soda, for potash, and for ammonia than sulphuretted hydrogen has.
The process of working lime purifiers on this principle must vary
according to the number of those vessels employed, and also according
to the relative proportions in which carbonic acid and sulphuretted
hydrogen exist in the gas which enters the said purifiers. It is also to
be observed that the displacement of SH, from lime by CO, depends to
a considerable extent upon the rapidity with which the gas (containing
CO,) is passed through the sulphuretted lime. For example, when CO₂
is brought slowly in contact with lime in the form of sulphide of
calcium nearly the whole of the SH, will be expelled from the lime in
any purifier before CO, appears in the issuing gas, whereas if the CO₂ is
brought more rapidly in contact with lime in the form of sulphide of
calcium a larger portion of the SH, will remain unexpelled from the
purifier when CO, first appears in the gas issuing from the said purifier.
Hitherto no means have been employed by which the condition of the
lime in purifiers could be or has been ascertained save by testing the gas
at the outlet of the said purifiers (or of some of them) for SH2, a testing
which of itself, and as hitherto employed, gives no indication whatever
of the efficiency of the contents of the purifiers for absorbing sulphur
in other forms than sulphuretted hydrogen, for when SH, appears in the
issuing gas this only shows that the lime can no longer absorb the SH,
and affords no indication as to whether the contents of the purifiers are
in the state of carbonate of lime (which is wholly useless for gas
purification of any kind) or in the state of sulphides of calcium.
In connection with the system described in this Specification a series
of simple testings may advantageously be employed, by which the
condition of the lime in each purifier can be adequately ascertained. In
the first place it is desirable that the gas should be tested for CO₂ and
for SH, (by the eudiometer or otherwise) at the inlet of the first purifier,
for by knowing the relative proportions of CO, and of SH, in the
entering gas (which proportions do not greatly vary in any given gas
work) the condition of the lime in the first purifier, and approximately
also in the subsequent purifiers, can be known in advance. For example,
if the gas as it enters the purifiers contains (as it usually does) 3 volumes
of CO, to 1 volume of SH₂, then the first or immediate effect is that
three-fourths of the lime in the first purifier are converted into carbonate
and one-fourth into sulphides of calcium.

page_text: It is likewise advantageous to make testings for CO, and for SH, at
the outlets of the purifiers, by which means the condition of the lime in
each of those vessels can be ascertained with sufficient accuracy for
practical purposes, thereby enabling the engineer to know and regulate
the condition of his lime purifiers in such manner as to obtain steady
results as regards the purification of gas, from sulphur, thereby obviating
the well-known excessive and hitherto unaccountable variations in the
action of lime purifiers. After the said testings for CO, and for SH,
have been made for a short time, the engineer will be able to ascertain
the right mode of working his lime purifiers upon this new principle
with sufficient accuracy by simply noting the quantity of gas passing
through his purifiers.
As a means of detecting the presence of carbonic acid in the gas
issuing from the purifiers (whereby the condition of the lime in each
purifier can be ascertained), I propose to employ an apparatus like that
to be now described; but the same object may be attained by simply
bubbling a portion of the gas at intervals through fresh lime water in
any other manner. And in order that the said apparatus may be fully
understood I shall now proceed more particularly to describe the same,
and for that purpose shall refer to the annexed Sheet of Drawings.
Figures 1 and 2 represent the mains (with valves A and B) connecting
the purifiers. At inlet of each purifier a short length of three-quarter
inch pipe is tapped into the main, and furnished with a three-eighth or
half-inch main cock. From this cock a half-inch pipe (D) is laid up to
the metal box (C) about six inches square, and four inches deep, which
has two or more glass sides, and is at each testing to be half filled with
freshly prepared and clear lime or baryta water, through which the gas
is made to bubble. A second service (E) conducts the gas from the box
back again into the main at outlet of purifier. A small plug is screwed
into the top of the box for the convenience of filling it, and another
Whenever the
such plug is fitted into the bottom for emptying it.
liquid in the metal box assumes a milky hue, this shows that carbonic
acid is contained in the gas issuing from the preceding purifier.
I may remark that lime which is to be used in gas purification ought
not to be slaked until immediately before being placed in the purifiers,
for slaked lime absorbs carbonic acid from the air, whereby its purifying
action upon gas is impaired.

page_text: (2.) Another process of applying this new principle in the employ-
ment of lime purifiers is to eliminate the carbonic acid from the gas by
the soda washers or scrubbers to be next described (vide § III. 2), in
which case the lime in all the purifiers can be converted into sulphides
of calcium, and thereafter maintained in that form.
III. Soda Washers or Scrubbers.-In connection with the purification
of gas from sulphur I also propose to make the gas pass through or
otherwise come in contact with a solution of caustic soda, or of
potash, or of ammonia. The solution may be used in one or more
washers or scrubbers. I prefer to use soda for this purpose, and I shall
describe the process in connection with soda, but the process is the same
if potash or ammonia be used.
+
(1). When employed in connection with the purifiers charged with
sulphide of calcium, described in § I., or with the sulphide of sodium
vessels to be afterwards described (vide § IV.), the soda washers or
scrubbers should be used next before the said vessels, thereby the whole
of the carbonic acid can be and ought to be eliminated from the gas
before it enters the said vessels, the sulphuretted hydrogen as above
mentioned having been previously eliminated either by oxide of iron or
otherwise.
The fouled or carbonated liquor withdrawn from the soda washers or
scrubbers may be converted back into caustic soda by treating it with
fresh lime in the ordinary manner employed in alkali works (i.e., raise
the liquor to the boiling point and thereafter allow the carbonated lime
to settle), whereupon the liquor can be again employed in the said
washers or scrubbers.
(2).. When employed in connection with the ordinary lime purifiers,
these soda washers or scrubbers will be used between the ordinary
washers or scrubbers (i.e., those employed for eliminating ammonia) and
the lime purifiers. So placed these soda vessels will act alike as decar-
bonators and as a means of converting the lime in the purifiers into
sulphide of calcium, as follows:-The soda solution will absorb both the
carbonic acid and the sulphuretted hydrogen contained in the gas at
this stage of purification, and will at first take them up simultaneously,
but as carbonic acid has a greater affinity for soda than sulphuretted
hydrogen has, after the soda solution has become saturated with these
two gas impurities the carbonic acid will proceed to displace the sulphu-
retted hydrogen, the result being that the carbonic acid can be wholly

page_text: arrested in the soda washers or scrubbers, while the sulphuretted
hydrogen displaced by the carbonic acid will pass forward into the
lime purifiers, converting their contents into sulphide of calcium. When
it is desired to eliminate the whole of the carbonic acid from the gas
before it enters the lime purifiers, the solution in the soda washers or
scrubbers is to be withdrawn, and fresh (i.e., caustic) liquor supplied to
the said washers or scrubbers as soon as the gas which issues from
them shows traces of carbonic acid.
The fouled liquor withdrawn from the said washers or scrubbers may
be treated with fresh lime, whereupon the liquor can be again used in
the said washers or scrubbers.
moreover
Note. Lime is a dirty material to use in gas works;
however used it is objectionable on account of the nuisance which it
occasions to the neighbourhood; accordingly it is desirable to reduce the
quantity of lime used in gasworks to the smallest amount necessary.
As hitherto employed, lime has been used to purify gas from sulphur in
all forms, namely, both from sulphuretted hydrogen and from the sulpho-
carbons indiscriminately, and also with so little knowledge of the correct
principles for using this material (now for the first time set forth in this
Patent) that it has been impossible to prevent great fluctuations in the
action of lime purifiers upon the sulphur, especially in other forms
than sulphuretted hydrogen.
My soda washers or scrubbers afford a means of confining the use of
lime in gasworks to the elimination of the sulphur in other forms than
sulphuretted bydrogen, by employing the said material (namely, lime)
only in the form of sulphides of calcium. For example, suppose it is
desired to use sulphide of calcium purifiers, as described in § I., then
the soda washers or scrubbers may be employed first of all and tem-
porarily to make or produce the sulphide of calcium to any required
amount. This is done by using these washers or scrubbers immediately
before a purifier or purifiers containing fresh lime, and passing the gas
into the said washers or scrubbers before it has been purified from
sulphuretted bydrogen. Then owing to the power of carbonic acid
(contained in the entering gas) to displace sulphuretted hydrogen from
the soda solution, the sulphuretted hydrogen can be driven forward
from the said washers or scrubbers in any quantity (by changing the
soda solution as soon as carbonic acid appears in the issuing gas),
thereby converting the lime in the purifier or purifiers into sulphides of

page_text: calcium. After the contents of the purifiers have thus been converted
into sulphides of calcium, the gas is to be passed into the soda washer
or scrubbers after it has been purified from sulphuretted hydrogen (say
by oxide of iron), the said washers or scrubbers being then used simply
as decarbonators, i.e., to eliminate the carbonic acid from the gas,
thereby maintaining the sulphide of calcium in the purifiers in an
efficient condition for purifying gas from sulphur in other forms than
sulphuretted hydrogen.
(3). I also propose to employ washers or scrubbers containing a
solution of caustic soda or potash as a direct means of purifying the
gas from sulphur in other forms than sulphuretted hydrogen. In this
case these washers or scrubbers are used after all the other purifying
processes (whether by lime, by oxide of iron, or otherwise), and after
the gas has been purified from sulphuretted hydrogen and from
carbonic acid.
IV. (1). I also propose to attain the same object (viz., the purifi-
cation of gas from sulphur in other forms than sulphuretted hydrogen)
by means of sulphur in a state of fine division used along with sawdust
or such like substance as, together with the sulphur, will form a porous
material through which the gas can pass freely. This material may be
used in the ordinary purifiers in gas works.
(2). I also propose to use sulphur mixed with soda or with lime,
or with lime and soda together, in solution or otherwise; I prefer to
use the sulphur with soda, and I will describe the process accordingly.
Sulphide of Sodium Washers or Scrubbers.-Sulphur is mixed with
caustic soda in a solution, and the proportions which I prefer (although
others may be used) are 1 lb. of sulphur and 2 lb. of soda to each
gallon of water. This mixture (which may be placed in a tank to
which steam is conducted) is to be raised to or nearly to the boiling
point, whereby the sulphur and soda will be dissolved, uniting in the
solution. The liquor is then to be used in washers or scrubbers
through which the gas is passed after having been purified from
sulphuretted hydrogen and carbonic acid. The liquor is to be retained
in the washers, or repassed through the scrubbers until it becomes so
charged with sulphur as to be incapable of acting efficiently as an
absorbent of the sulphur compounds remaining in the gas, whereupon
it is to be withdrawn from those vessels and fresh liquor employed.

page_text: The fouled liquor so withdrawn being highly charged with sulphur and
soda, is an article of commercial value.
A similar solution of sulphur and soda may be made by procuring
sulphide of sodium from chemical works. This material is to be used
in a solution; the strength which I prefer (although the solution may
be of other strength) being 3 lb. of the material, or thereabouts, to
each gallon of water.
A similar solution may also be formed more conveniently in gas
works by passing the gas containing sulphuretted hydrogen through
a solution of soda until the sulphuretted hydrogen is no longer absorbed.
This can be done by employing the soda washers or scrubbers in the
manner already described for making or producing sulphide of calcium
in lime purifiers, namely, by using these washers or scrubbers im-
mediately before other vessels of the same kind (viz., containing a
solution of caustic soda), and passing the gas into the said vessels
before it has been purified from sulphuretted hydrogen. Then owing
to the power of carbonic acid (contained in the entering gas) to displace
sulphuretted hydrogen from the soda solution, the sulphuretted hydro-
gen can be driven forward from the first soda washers or scrubbers of
the series in any quantity (by changing the soda solution as soon as
carbonic acid appears in the issuing gas), thereby converting the soda
solution in the subsequent vessels into sulphides of sodium.
Note. The best manner of employing the processes above described
(other than those which relate to purification by lime) appears to me
to be as follows:-After condensing, scrubbing, and eliminating
sulphuretted hydrogen by oxide of iron purifiers, as at present practised,
pass the gas through soda washers or scrubbers, thereby eleminating all
the carbonic acid, and thereafter pass the gas into washers or scrubbers
containing a solution of sulphide of sodium (produced in any of the
above mentioned ways) to purify the gas from sulphur in other forms
than sulphuretted hydrogen. Or, purifiers (whether containing lime or
oxide of iron) may be entirely dispensed with and the purification of
gas from carbonic acid and from sulphur in all forms be effected by
means of the soda washers or scrubbers. In this case these vessels will
be worked on the same principle as that devised and above described for
the working of lime purifiers (vide § II.), the chief portion of the
process for applying which principle may for the sake of ready intelli-
gence be repeated here, reference being made to soda washers or

page_text: scrubbers instead of to lime purifiers. Pass the gas through the first
washers or scrubbers of the series for such time that the carbonic acid
from its greater affinity for soda shall have expelled sulphuretted
hydrogen from these first washers or scrubbers of the series, taking its
place and driving it (namely, the sulphuretted hydrogen) forward into
the succeeding vessels. By this means the carbonic acid can be wholly
eliminated from the gas by the first washers or scrubbers of the series,
while sulphuretted hydrogen being driven forward converts the contents
of the succeeding vessels into sulphide of sodium, which is a highly
efficient material for purifying the gas from sulphur in other forms than
sulphuretted hydrogen. Thereupon these latter mentioned washers or
scrubbers containing sulphide of sodium may be placed first in the series
and the gas passed through them into subsequent vessels containing
a caustic soda solution, whereby the contents of these subsequent vessels,
or of any of them, can be converted in turn into sulphide of sodium.
Or, the first vessels of the series may be constantly employed chiefly as
decarbonators (i.e., for eliminating the carbonic acid from the gas)
while the sulphur in all forms is eliminated from the gas in the

page_text: plan is to employ the following complete process of revivifying the
fouled soda solution in the gas works, whereby the sulphur is simul-
taneously obtained in an odourless and commercial form :-Chalk
(carbonate of lime) is burnt in a retort, and the carbonic acid evolved
from it is conducted into the tank containing the fouled liquor from the
whole series of soda washers or scrubbers, whereby the sulphur is
expelled from the liquor by the carbonic acid, and is then passed into a
vessel containing oxide of iron, where the sulphur is arrested and
obtained in a commercial form. Thereafter the caustic lime remaining
in the retort (or a little more than that quantity) is thrown into the
liquor in the tank, whereby the said lime will decarbonate the liquor,
converting it back into a solution of caustic soda ready to be used anew
in the washers or scrubbers, while the lime is withdrawn from the tank
in the form of carbonate of lime ready to be used over again in the
retort. In this way no nuisance is occasioned by the use of those
washers or scrubbers, so that this process can be used in any gas works,.
wherever situated, while the soda solution employed in them is revivified
in the gas works and the sulphur which it has absorbed from the gas is
simultaneously obtained in a commercial form.
Having now described and particularly ascertained the nature of my
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that what I consider
to be novel and original and therefore claim as the Invention secured to
me by the herein-before in part recited Letters Patent is,―
Firstly. The employment of sulphides of calcium in separate purifiers 2
as a means of purifying coal gas from sulphur existing in other forms
than that of sulphuretted hydrogen.
Secondly. A method or system of employing lime purifiers in the
manner herein-before described, whereby the contents of all of the said
purifiers, or of any required number of them, can be converted into 3
sulphides of calcium, and also (if required) be maintained in that
condition.
Thirdly. The employment of a solution of caustic soda, or of potash,
or of ammonia, used in washers or scrubbers in the manner herein-before
described in order to eliminate carbonic acid from coal gas, and in such 3
a manner as to convert the lime in purifiers, or the soda solution

page_text: contained in any required number of the said washers or scrubbers into
sulphides of calcium and sulphides of sodium respectively, and also, if
required, to maintain them in that condition.
Fourthly. The employment of the soda washers or scrubbers after the
gas has been purified from carbonic acid and sulphuretted hydrogen as a
means of purifying the gas from sulphur existing in other forms than
that of sulphuretted hydrogen.
Fifthly. The employment of sulphur in a fine state of division in
conjunction with an inert substance suitable to form a porous material
through which the gas may pass freely, or in combination with lime or
with soda (or with lime and soda together) in solution or otherwise, in
order to effect the purification of coal gas from sulphur existing therein
in other forms than that of sulphuretted hydrogen.
In witness whereof, I, the said Robert Hogarth Patterson, have
to this my Specification set my hand and seal, this Sixth day
of September One thousand eight hundred and seventy-two.