IMPROVEMENTS IN THE PURIFICATION OF COAL GAS AND IN THE PREPARATION AND TREATMENT OF MATERIALS TO BE EMPLOYED THEREIN "
Year: 1883

page_text: LETTERS PATENT to James Thomas MoDougall of the firm of McDougall
Brothers of Manchester for an Invention of "IMPROVEMENTS IN THE
PURIFICATION OF COAL GAS AND IN THE PREPARATION AND TREATMENT OF
MATERIALS TO BE EMPLOYED THEREIN
"
PROVISIONAL SPECIFICATION left by the said James Thomas M⚫Dougall
at the Office of the Commissioners of Patents on the 23rd February 1883.
JAMES THOMAS M'DOUGALL of the firm of McDougall Brothers of Manchester
"IMPROVEMENTS IN THE PURIFICATION OF COAL GAS AND IN THE PREPARATION
AND TREATMENT OF MATERIALS TO BE EMPLOYED THEREIN
"
This Invention has for its object improved means of removing Sulphuretted
Hydrogen from Coal gas-In carrying out my Invention I employ any of the
following methods
I take iron in any form that will dissolve in Sulphuric Acid of any desired
strength as an example scrap wrought iron is suitable so as to produce a strong
solution of Sulphate of Iron into which I place sufficient Carbonate of Lime or
lime to unite with the whole of the Sulphuric Acid in the Solution-The Carbonate
of lime or the lime combines with the Acid causing the iron to be precipitated as
Hydrated Oxide which on exposure to the atmosphere are converted into Peroxide
of iron in which form it works actively in the absorption of Sulphuretted Hydrogen
from Coal Gas If the Acid has not been greatly diluted before use the resulting
mixture will become hot and must then be gradually cooled down-This I make
into a powder light and porous and very suitable for employment in Gas
Purifiers
According to another part of my Invention I take the Sulphate of Iron of
Commerce and reduce it into a strong solution or into a finely divided state, and
then I add to it sufficient Carbonate of lime or Lime also in a finely divided state
and then agitate or stir the mixture well together to ensure that all the Acid
present shall combine with the Alkali so converting the iron into a precipitated

page_text: Oxide of Iron-The mixture is then exposed to the air until dry or the drying is
hastened by simple artificial means. The product is well adapted for use in the
purification of gas also by a Process similar to that lastly above stated
I utilize
the waste solutions of Sulphate of Iron produced in the process of cleaning Iron
for galvanizing and tinning purposes
According to another part of my Invention I take any description of Iron that
will dissolve in Muriatic Acid I thereby produc a Solution of Muriate of Iron to
which I add sufficient Carbonate of Lime or Lime to precipitate the iron which
precipitate I separate from the resulting Solution of Muriate of Lime and then
wash the precipitate in water and make it sufficiently dry by any convenient
means for use in the Gas Purifiers-Or I take the Muriate of Iron or of Manganese
of Commerce and treat them with sufficient Carbonate of Lime or Lime to
precipitate the Iron, then I add water to wash the precipitate and to remove the
Muriate of Lime formed which if not removed would hinder the satisfactory
working of the precipitate in Gas purification-Also by a process similar to that
above stated the waste solutions of Muriate of Iron produced in the process of
cleaning Iron for galvanizing and tinning purposes or waste Muriate of Manganese
liquors of Chemical Works may be utilized and employed for the purposes of my
Invention.
When any Oxide of Iron used in the purification of Gas from Sulphur has
become charged with Sulphur it is known as spent Oxide and is then employed in
Sulphur furnaces where the Sulphur is burned off for the production of Sulphuric
Acid. Up to the present time there has been no means known of rendering the
burnt spent Oxide residue suitable for re-use-Also when Iron or Copper pyrites
also containing Sulphur are burned for the production of Sulphuric Acid a similar
residue is obtained. I find that these residues on testing have an Acid reaction
and in that state are not useful for the removal of Sulphuretted Hydrogen from
Coal Gas A further portion of my Invention consists in first rendering neutral
the burnt Spent Oxide residues by the addition of lime or other suitable Alkali;
whereby they develop a considerable power in removing Sulphuretted Hydrogen
from Coal Gas and this power is further much increased if in addition to their
treatment with an Alkali some active precipitated peroxide of Iron is mixed with
then It is sometimes found desirable to make the Oxides of Iron employed in
the purification of gas more porous so as to allow the gas to pass more freely by
the addition of Saw dust Tanners refuse or other light or fibrous material as it is
of great importance in the purification of gas to present as inuch active surface of
the purifying Agents with which the gas may be brought into contact as possible-
The above light and porous materials do not of themselves contain any power of
decomposing the Sulphuretted Hydrogen in Coal gas.
A further portion of my Invention consists in bringing the said materials when
intented to be used in conjunction with the Oxides of Iron as above mentioned
into close contact or impregnating them with any soluble Salts of Iron and then
treated with an alkali until neutral whereby they become saturated to a greater or
less degree with precipitated peroxide Iron and in that condition readily decompose
the Sulphuretted Hydrogen in Coal Gas in addition to making any other Oxide of
Iron they are mixed with, more porous

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said James Thomas MoDougall in the Great Seal Patent Office on the
23rd August 1883.
JAMES THOMAS M'DOUGALL of the firm of McDougall Brothers of Manchester
and London IMPROVEMENTS IN THE PURIFICATION OF COAL GAS AND IN THE
PREPARATION AND TREATMENT OF MATERIALS TO BE EMPLOYED THEREIN
,,
This Invention has for its object an improved means of removing Sulphuretted
Hydrogen from Coal Gas. Hitherto it has been mainly effected by the use of
Lime or a native Oxide of Iron-The use of lime is attended with the great
advantages that it is costly that the Sulphur it combines with cannot afterwards
be utilized in the production of Sulphuric Acid and that it entails much labour-
The native Oxide of Iron has the great disadvantages that it rarely possesses much
active purifying power owing to the low per centage of hydrated peroxide of iron
it contains and its high percentage of water It is important here to note that
simple Oxide of Iron does not decompose Sulphuretted Hydrogen, and that to do
so the iron must be in the form of hydrated peroxide of Iron. The native Oxide
of Iron hardly absorbs any Sulphur until it has been placed in the purifiers and
gas passed through it two or three times and then it rarely takes up more than
one or two per cent of Sulphur each time it is employed in the purifiers until
at length when it contains thirty five per cent to forty per cent of Sulphur it often
practically ceases to absorb more Sulphur and has to be replaced with fresh
material This saturated or spent Oxide containing about thirty five per cent. to
forty per cent of Sulphur is utilized in the production of Sulphuric Acid but some
difficulty is experienced in burning it in the Sulphur Furnaces owing to its not
containing a higher percentage of Sulphur. In carrying out my Invention I
employ any of the following methods.
I take the Sulphate of Iron of Commerce and reduce it into a finely divided
state and then I add to it sufficient Carbonate of Lime or lime also in a finely
divided state and then stir the mixture well together to ensure that all the acid
present shall combine with the Alkali so converting the Iron into a precipitated
per oxide of iron. The product is well adapted for use in the purification of Gas-
It works well from the first time it is put into the purifiers and afterwards on
being exposed to the air revivifies rapidly-After it has been employed nine or
ten times in the purifiers it generally contains over sixty per cent of Sulphur a
strength at which it can be employed with great advantage in the production
of sulphuric acid-Also by a process somewhat similar. I utilize for these purposes
the waste solutions of Sulphate of Iron produced in the process of cleaning iron
previous to galvanizing or tinuing.
I add to them sufficient Carbonate of Lime or Lime to combine with the Acid
causing the Iron to be precipitated as hydrated Oxide which on exposure to the
atmosphere is converted into peroxide of Iron suitable for use in gas purification
I am aware that the Copperas of Commerce and Lime have been mixed together
and employed in the purification of Gas but hitherto a mixture of but slight
purifying power has been produced (which for distinction I call the old mixture)
owing to the two ingredients not having been thoroughly incorporated together
and in such proportions that the lime shall be sufficient to render neutral the
copperas When this old mixture is put into the purifiers it contains only a small
percentage of precipitated peroxide of Iron and much free Lime and free Copperas.
This free lime is speedily converted into Carbonate and Sulphide of Lime by the
Carbonic Acid and sulphuretted hydrogen in the Gas and therefore no longer exists

page_text: as free lime to decompose the Copperas. So small a proportion of the copperas in
the old mixture is converted into precipitated Peroxide of Iron the mixture hitherto
has been but of slight service in the purification of Gas and has only one fifth of
the purifying power each time it is placed in the purifiers as compared with the
mixture described in this Invention whilst at the same time by the employment
of my Invention labor is greatly economised-In fact the old mixture is simply a
mechanical mixture of Oopperas and Lime whereas by the method included in this
Invention a chemical combination of the Copperas and Lime is insured thus gaining
immensely better results in the power of the resulting product in the purification
of Gas.
According to another part of my Invention I take any description of Iron that
will dissolve in Muriatic acid and thereby produce a solution of Muriate of Iron to
which I add sufficient carbonate of Lime or Lime to precipitate the iron which
precipitate I separate from the resulting solution of Muriate of Lime and then
wash the precipitate in water and make it sufficiently dry by any convenient
means for use in the gas purifiers Or I take the muriate of Iron or Manganese
of Commerce and treat them with sufficient Carbonate of Lime or Lime to pre-
cipitate the Iron, then I add water to wash the precipitate and to remove the
Muriate of Lime formed which if not removed would hinder the satisfactory
working of the precipitate in Gas purification-Also by a process similar to to that
above stated the waste solutions of Muriate of Iron produced in the process of
-cleaning iron for galvanizing and tinning purposes or waste Muriate of Manganese
Liquors of Chemical works may be utilized and employed for the purposes of my
Invention.
When any oxide of iron used in the purification of Gas from Sulphur has become
charged with Sulphur it is known as spent oxide and is then employed in Sulphur
furnaces where the Sulphur is burned off for the production of Sulphuric Acid-
Up to the present time there has been no really efficient means known of rendering
the burnt spent Oxide residue-suitable for re-use-Also when iron or copper
pyrites also containing Sulphur are burned for the production of Sulphuric Acid a
similar residue is obtained These residues on testing have an acid reaction, and in-
that state are not useful for the removal of sulphuretted hydrogen from Coal Gas.
After these burnt residues have been rendered neutral by the addition of an
Alkali a further portion of my Invention consists in mixing with them some active
precipitated Peroxide of iron whereby their efficiency in removing Sulphuretted
Hydrogen from Coal Gas is greatly increased
It is sometimes found desirable to make the Oxides of Iron employed in the
purification of gas more porous so as to allow the gas to pass more freely by the
addition of Sawdust Tanners refuse or other light or fibrous material as it is of
great importance in the purification of gas to present as much active surface of the
purifying Agents with which the gas may be brought into contact as possible.
The above light and porous materials do not of themselves contain any power of
decomposing the Sulphuretted Hydrogen in Coal Gas. A further portion of my
Invention consists in bringing the said porous materials when intended to be used
in conjunction with the Oxides of Iron as above mentioned into close contact or
impregnating them with any soluble salts of iron or their solutions and then
treating them with an Alkali until neutral whereby they become saturated to a
greater or less degree with precipitated peroxide of Iron and in that condition
· readily decompose the Sulphuretted Hydrogen in Coal gas in addition to making
any other Oxide of Iron they are mixed with more porous.
At many Gas Works a large proportion of the lime employed in purification is
now converted into Carbonate of Lime which Carbonate may be employed for the
purposes under this Invention where Carbonate of Lime is used and where
economy in the cost of materials is a main consideration.
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

page_text: and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent is:-
First. The production of precipitated Peroxide of Iron in the manner hereinbefore
described and the employment of such precipitated Peroxide of Iron in the
purification of Coal Gas as hereinbefore described.
Second. The treatment of Solutions of Sulphate of Iron in the manner herein-
before described and the employment of the same in combination with Carbonate
of Lime or Lime in the purification of Coal Gas as hereinbefore described
Third. The treatment of Muriate of Iron or Muriate of Manganese or mixtures
of the said Muriates with Carbonate of Lime or Lime in the manner herein before
described and the employment of the precipitates arising from such treatment in
the purification of Coal Gas as hereinbefore described.
Fourth. The mode herein before described of treating burnt Spent Oxide residues
or the residues resulting from burning Pyrites and the employment of the residues
so treated in the purification of Coal Gas as hereinbefore described
Fifth. The treatment of Saw dust Tanners refuse or other light or porous
material in the manner herein before described and the application of the said
materials so treated to the purification of Coal Gas as hereinbefore described.
In witness whereof I the said James Thomas McDougall have to this my
Specification set my hand and seal this twenty first day of August One thousand
eight hundred and eighty three
JAMES. T. MŪDOUGALL (L.B.)