IMPROVEMENTS IN THE PURIFICATION OF COAL. GAS AND OF COAL OILS
Year: 1860

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LETTERS PATENT to William Renwick Bowditch, Clerk, of Saint Andrew's,
Wakefield, in the County of York, for the Invention of "IMPROVEMENTS IN
THE PURIFICATION OF COAL. GAS AND OF COAL OILS."
PROVISIONAL SPECIFICATION left by the said William Renwick Bowditch
at the Office of the Commissioners of Patents, with his Petition, on the
31st May 1860.
I, WILLIAM RENWICK BOWDITCH, Clerk, of Saint Andrews, Wakefield, in
the County of York, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE PURIFICATION OF COAL, GAS AND. OF COAL OILS," to beras
follows
H
Pulverized clay, slightly damp,is placed in the ordinary dry lime purifiers
of gasworks, and the gas is passed through layers of the said clay, in
addition. to being passed, "through layers of slaked lime, or hydrated
metallic oxides, or salts or acids used in the ordinary and known methods of
purification of gas. The clay is used as supplementary to the other materials,
and the combination of the use of clay, with the said other materials. is the
subject of this portion of my 'Patent.
...
..
To carry out my Invention, purifiers, containing clay alteriiated with the
other materials are to be used at the gasworks; & a smaller one may be
employed on the premises of the consumers of gas to remove iinpurities which

page_text: have escaped purification at the gasworks. The foul clay, when no longer fit
for use in the purification of gas, is employed as manure. I also pass gas
through clay, slaked lime, or hydrated oxide of iron heated below redness, &
subsequently through purifierscontaining the ordinary cold materialsemployed
in the purification of gas to remove impurities not removable by processes at
present in use. I also pass oils obtained by the distillation of coal or coal tar
through vessels filled with heated purifying materials, as is above specified,
for purifying gas.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Renwick Bowditch in the Great Seal Patent Office
on the 29th November 1860.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
RENWICK BOWDITCH, of Saint Andrew's, Wakefield, in the County of York,
Clerk send, greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirty-first day of May, in the year of our Lord
One thousand eight hundred and sixty, in the twenty-third year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said William Renwick Bowditch, Her special licence that I, the said
William Renwick Bowditch, my executors, administrators, and assigns, or
such others as I, the said William Renwick Bowditch my executors,
administrators, 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 PURIFICATION OF
COAL GAS AND OF COAL OILS," upon the condition. (amongst others) that I, the
said William Renwick Bowditch, my executors or administrators, by an instru-
ment in writing under my, or his, 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.
NOW KNOW YE, that I, the said William Renwick Bowditch, 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:-

page_text: To carry out my Invention I proceed as follows:-As much pulverized
damp clay as there is room for is spread upon one of the trays of each ordinary
dry lime purifier, which contains upon the other trays slaked lime or hydrated
peroxide of iron. Gas is passed through the purifiers in the ordinary way.
When a purifier is emptied the partially foul clay is to be spread so that the air
may act upon it. After exposure it is used again in combination with the other
materials, and the best mode of using it is this:-A leading purifier is used:
through which the gas is made to pass on its way from the condenser to the
ordinary purifiers. This leading purifier should have four tiers of riddles.
The two tiers nearest to the inlet should be charged with clay which has been
employed in the ordinary purifiers, and subsequently exposed to the air; the
next tier should be charged with sawdust saturated with an acid or a solution
of a metallic salt suitable for removing ammonia; and the fourth tier should
be charged with clay, like the first and second. The gas then passes on to the
ordinary purifiers, which should contain in each, as above stated, one tier of
fresh clay, and the remaining tiers of lime or hydrated peroxide of iron. By
the combination of the use of clay with the other materials, as directed, gas,
is better purified from sulphur compounds (other than sulpheretted hydrogen,
than it can be by any other known method of cold purification. Where the
purifiers are differently arranged other arrangements of the purifying materials
may be made, while the principle of my Invention is preserved. The leading
purifier should be emptied and refilled whenever there is a sufficient quantity
of partially foul clay which has been taken from the ordinary purifiers to
fill it.
I do not claim the use of any of the materials here specified for purifying
gas, as they are all in use, but I claim the use of clay alternated with acids
or metallic salts, and used in addition to lime or hydrated peroxide of iron.
The foul clay forms a valuable manure, and the sawdust when removed
from the purifiers, is used to obtain salts of ammonia.
Another part of my Invention consists in passing coal gas through
pounded clay, hydrated peroxide of irou, or, preferably, slaked lime heated
below redness, as herein after described, and subsequently through the
ordinary cold purifying materials, and thereby removing impurities not
removable by processes at present in use.
To prepare the clay, hydrated peroxide or iron, of slaked lime, herein-after
called purifying materials, for use in hot purifiers, I prefer to sift out from
them such fine matter as will pass through wire gauze of forty-nine meshes to
a square inch, I prefer to have the purifying materials in small pieces from
about an eighth of an inch to three-eighths of an inch in diameter. Lime is.

page_text: best got into this state by drying it artificially after it has been slaked; natural
oxide of iron in lumps and clay should be pounded, precipitated oxide and
the dust of the natural oxide should be moistened till they will aggregate
into lumps, and then be dried artificially. This is done in order that the
gas may pass through without much pressure.
The purifying materials are to be heated to the proper temperature before
the gas is passed through them, during which heating a little steam will be
driven off. Water which is contained in the hot purifying materials, but is
removable as steam at the temperature employed in purification, must be
driven off before the materials are in a proper state for purifying the gas.
The temperature required in the hot purifying materials may vary in some
measure with the kind of coal and with the temperature which is employed in
the production of the gas. For gas made at the ordinary temperature I find
the best temperature for the purifying materials to be 280° to 300° F. Gas
made at higher than ordinary temperatures may require the purifying materials
to be heated above 300 F., and greater heat still may be required where
removal of the last traces of sulphur from the gas is of more importance than
a loss of illuminating power. Care must be taken not to raise the tempera-
ture of the purifying materials too high, as, from the melting point of lead
upwards there is considerable deposition of light-giving matter upon the hot
purifying materials; and with the purifying material at a red heat the gas is
almost spoilt. The rule should be to employ the purifying material at the
lowest temperature consistent with efficiency. The limits will generally be
found to be between 24° and 420° F. The proportion of impurity
removable by using the purifying materials at a lower temperature than
240° F. is less than when they are heated so that point, though I find that
slaked lime which has been properly dried liberates in the form of sul-
phuretted hydrogen, sulphur from sulphur compounds now generally found
in purified gas, even at 108° F.
The vessels employed to hold the hot purifying material may be of any
form, size, or material found convenient. I prefer to have them cylindrical
and of cast iron, with a door at each end. Each vessel should have an outer
metallic casing or jacket made steam-tight, so that steam may be employed as
the source of heat to the purifying materials, such steam being applied by
injecting it between the purifying vessel and its outer coating, or water may
be converted into steam within the space between the purifier and its jacket
by a direct application of heat to the outer jacket. I prefer to pass in steam
heated to the proper temperature, and should not use direct heat if steam were
available. The purifiers may be fixed vertically, or at any convenient angle

page_text: with the horizon which will allow the purifying material to occupy
the space
within in such a manner as that no gas can pass through without coming into
contact with and passing through the heated purifying material. They need
not be more than three or four feet in length, and should be of such breadth
as will allow a ready passage to the maximum quantity of gas made in a day.
As a guide to the quantity of hot purifying material required, I may remark
that in order to break up the sulphur compounds generally found in gas, and
to liberate their sulphur in the form of sulphuretted hydrogen, the gas con-
taining the sulphur compounds should be passed through about three feet
thickness of hot purifying material, prepared as I above direct.
To charge
the purifiers the door at the lower end is fastened, and the purifying material
is put in from the upper end, and the purifier is filled entirely full, so that gas
being passed through it must come into contact with the hot purifying
material. A simple test to ascertain whether the purifying material requires
changing in the application of lead paper to the gas which is passing imme-
diately from the hot purifier. If it blacken lead paper strongly and quickly
the purifying material may be considered in order; if it do not it should be
changed. Gas which has passed through the hot purifiers is to be cooled in
the ordinary manner, and to be passed through cold purifiers of the ordinary
kind containing materials suitable for the removal of sulphuretted hydrogen,
ammonia, and carbonic acid.
I prefer to subject the gas to the ordinary cold process of purification before
using the above processes, as then the hot purifying material will not become
clogged by tarand cooled by water which have passed the condenser, but these
will have been deposited in the cold purifiers. My process may, however, be
applied to gas as soon as it leaves the condenser, before it passes into the
ordinary purifier, but with less effect and more trouble than when the gas has
first been subjected to the cold process of purification.
My Invention may be applied to gas by consumers upon their own premises,
in which case the gas which leaves the meter is made to pass through a small
purifier containing hot slaked lime, pounded, clay, or hydrated peroxide of iron,
and subsequently through another purifier containing layers of ordinary cold
purifying materials after which it may be burnt. The pressure of gas upon
consumers' premises is not often enough to overcome much resistance, where-
fore the cold purifying material should have the dust sifted out, as above
advised for the hot, and then the gas will pass through the purifiers without
any perceptible loss of pressure.
Another part of my Invention consists of purifying coal oils by means of
heated slaked lime, pounded clay, or hydrated peroxide of iron.

page_text: To purify coal oils I proceed as in the purification of gas. A vessel is to
be employed similar to that above specified for gas, or of other convenient
form or size, which vessel is to contain sifted slaked lime, pounded clay, or
hydrated peroxide of iron, but preferably lime, heated to or slightly above the
boiling point of the oils to be purified. When the purifying material is at the
proper temperature the oils are to be sent into the lower part of and allowed
to pass upwards through the hot purifier, after which they are to be condensed
in the usual way.
Care must be taken not to send in the oils too rapidly.
The gas produced in the process should be allowed to escape into the atmo-
sphere, or, better, be absorbed into slaked lime. Care is required to prevent
the tar liberated by this process from passing over with and becoming dissolved
in the purified oils. The tar will not pass with the purified oils if the
purifying material be not saturated with oil, but it will pass if the purifying
material is saturated. It is requisite, therefore, to supply the hot purifier with
the coal oil slowly, so that the purifying material may not become saturated.
The purified oil will then be of good color. The oil passing from the purifier
and through the condenser should be received into a glass vessel at intervals,
and examined, and, if coloured, the quantity passing through the hot purifier
should be lessened. If with a slow current, the distilled oil be colored, the
hot purifier should be charged with fresh purifying material.
The purified oils dissolve some part of the gases produced in the
process of
purification, which gases evolve. more odour than the oils have naturally.
Such gas may be removed, and the smell of the oils improved by washing
them with a solution of caustic soda or potash, and subsequently with water.
The quantity of removable matter is so small that a weak solution of alkali is
sufficient. I mention this washing with alkali as an improvement, but the oils
without it are so good that probably the washing will not be thought neces-
sary, except where smell is of great importance. My experience shows that a
quantity of neated purifying material equal to about a fourth of the weight of
oil to be purified gives an excellent result.
I claim, first, the combination of the use of pounded clay with acids, or
with salts, and with slaked lime, or oxide of iron, as described.
Secondly, I claim as my Invention the passing of coal gas through slaked
lime, pounded clay, or hydrated peroxide of iron, heated below redness, as
described, by which sulphur compounds now generally found in what is
termed purified gas and water are decomposed, and liberated as sulphuretted
hydrogen and carbonic acid; the sulphuretted hydrogen so generated,
together with carbonic acid and ammonia, being afterwards removed by the
ordinary means of purification.

page_text: Thirdly, I claim the passing of coal oils through slaked lime, or pounded
clay, or hydrated peroxide of iron, heated above the distilling point of the
oils, as described, by which treatment tar and sulphur compounds are
removed, and the oils are rendered whiter and freer from disagreeable smell.
In witness whereof, I, the said William Renwick Bowditch, have here-
unto set my hand and seal, this Twenty-fourth day of November, in
the year of our Lord One thousand eight hundred and sixty.
W. R. BOWDITCH. (L.s.)