IMPROVEMENTS IN THE PURIFICATION OF GAS, AND THE OBTENTION OF CERTAIN PRODUCTS DURING THE PROCESS OF SUCH PURIFICATION
Year: 1852

page_text: LETTERS PATENT to William Chisholm, of Holloway, in the County
of Middlesex, Chemist, for the Invention of "IMPROVEMENTS IN THE
PURIFICATION OF GAS, AND THE OBTENTION OF CERTAIN PRODUCTS
DURING THE PROCESS OF SUCH PURIFICATION."
COMPLETE SPECIFICATION filed by the said William Chisholm at
the Office of the Commissioners of Patents, with his Petition
and Declaration, on the 14th October 1852, pursuant to the 9th
section of the Patent Law Amendment Act, 1852.
I, WILLIAM CHISHOLM, of Holloway, in the County of Middlesex,
Chemist, do hereby declare the nature of the said Invention of "Iм-
PROVEMENTS IN THE PURIFICATION OF GAS, AND THE OBTENTION OF CERTAIN
PRODUCTS DURING THE PROCEES OF SUCH PURIFICATION," to be as follows:-
My process for purifying gas consists in using charcoal, either vege-
table, animal, or what is called mineral charcoal, from bituminous shale
combined with chemical agents, capable of decomposing and absorbing
the impurities contained in such gas. I use charcoal combined with
such chemical materials, that when the mixture thus composed has

page_text: fulfilled its office of purifying the gas used for illuminating purposes it
shall have attained a value as a rich manure, as hereafter described.
Charcoal may be used alone for purifying gas, or with acids combined
with alkalies, or acids or water only.
DESCRIPTION OF THE PROCESS OR PROCESSES.
Firstly. I take charcoal made from peat, or peat partially chared, or
charcoal made from algo (sea weed), either in blocks, or coarsely
powdered, or finely ground; in this first process I prefer to use peat
charcoal, to which I add chloride of sodium (common salt) and commer-
cial superphosphate of lime. This mixture will be placed in that vessel
well known in all gas works as the dry lime purifier, and the gas is to
be made to play through it in a similar manner, which being effected, a
decomposition takes place the chloride of sodium is decomposed by the
hydrosulphate of ammonia contained in the gas; a hydrochlorate of am-
monia and hydrosulphate of soda are formed; the hydrosulphate of soda
and phosphate of lime are taken up by another portion of the hydro-
sulphate of ammonia, and converted into phosphate of soda and lime;
the sulphate of lime contained in the commercial superphosphate of lime
is also decomposed by the ammonia of the gas being converted into sul-
phate of ammonia. The hydrogen of the hydrosulphuric acid (sulphu-
retted hydrogen) will be seized upon by the oxygen of the charcoal,
forming water, and setting the sulphur free, and the gas is thus purified.
The principal constituent parts of peat charcoal are carbon, iron, alumina,
silica, and alkalies. To the charcoal is added a superphosphate of lime
and chloride of sodium, the acids of which sieze upon the volatile am-
monia contained in the gas, forming a phosphate of lime and phosphate
of soda and ammonia, a hydrochlorate of ammonia, a sulphate of ammonia,
and a sulphate of lime, and a hydrosulphate and sulphate of soda and
lime, together with the other minor impurities in the gas, forms a com-
pound possessing in a high degree the elements necessary for promoting
the growth of plants. A variety of chemical compounds may be used
in combination with charcoal, such as are well known to fix or decom-
pose ammonia, as the oxy-salts, chlorides of calcium and magnesium,
potassa, and nitrates.

page_text: Proportions,
Superphosphate of lime
Algoe (sea weed) charcoal
Peat charcoal
294..
224..
422..
Instead of chloride of sodium, bisulphate of potassa may be used, or in
combination with the chloride of sodium and sulphate of magnesia;
when the gas has passed through this mixture the resulting compound
will be phosphate, sulphate, and carbonate of ammonia and potassa,
phosphate of lime, phosphate of magnesia and lime, a sulphate and a
carbonate of lime, oxyde of iron, alumina, chloride of potassium, carbon.
This process will produce a manure analogous to guano.
Superphosphate of lime
Bisulphate of potassa
Proportions,
Chloride of sodium
Sulphate of magnesia
Charcoal
Parts.
196.00
128..
60..
69..
547..
Secondly. When gas contains much hydrosulphuric acid it will be
desirable to have two purifying vessels, one to take up the ammonia,
and the other the hydrosulphuric acid. The peat charcoal for the
hydrosulphuric purifier should be selected so as to contain considerable
portions of mineral substances. The gas is passed, first, through the am-
monia purifier containing the ingredients as firstly described, and then
into the hydrosulphuric vessel (which contains the charcoal, as above
mentioned). On its passage through this latter the oxygen of the
charcoal will seize the hydrogen of the hydrosulphuric acid, forming
water, and depositing the sulphur. When the charcoal has become
exhausted; that is, when it ceases to decompose hydrosulphuric acid, the
gas should be turned off, and a column of air moistened with a jet of.
steam forced through it: until its properties are partially or wholly
restored. This process may be repeated until the deposit of sulphur
becomes inconveniently large. By this process the hydrosulphuric
purifier, even in the largest establishments, need be but rarely opened.
In passing the moist air through the hydrosulphuric purifier the com-

page_text: munication with the ammonia purifier must be kept open, because the
moist air forced through the charcoal, which has been exhausted of its
oxygen to decompose the hydrogen of the hydrosulphuric acid, is in its
turn decomposed, the oxygen of the water combining with the charcoal,
while its hydrogen combines with the nitrogen of the air. Ammonia is
thus formed and fixed in its passage through the ammonia purifier. The
re-oxydising process may be applied to any material now in use at gas
works for depriving the gas of its hydrosulphuric acid and produce am-
monia; it may be used with or without the steam, but I prefer it with.
Thirdly. Charcoal, when saturated with a solution of hydrochloric,
sulphuric, or nitric acids, more or less diluted, will purify illuminating
gas, converting its ammonia into a hydrochlorate, sulphate, or nitrate of
ammonia. The application of diluted acids in the purification of gas is
well known and been long practised, but its combination with peat
charcoal has never hitherto been used. It is always an objection to pass
gas through liquids, as washing injures its illuminating power. It was
also found that the gas in passing through the acidulated mixture carried
along with it free acid, which was very objectionable; all this is avoided
by the peat charcoal, for although it absorbs nearly four times its own
weight of the acid solution, still the gas passes through it as if it were a
dry substance, not depriving the charcoal of its moisture, but rendering
up to it all its ammonia. If animal charcoal is used with the acid
solution instead of vegetable, a very rich manure will be the product.
The water in the hydraulic main, and through which gas flows in its
passage from the retorts, and known by the name of gas or ammoniacal
liquor, contains, as is well known, a considerable quantity of ammonia
in a state of carbonate and hydrosulphate; this liquor may be entirely
absorbed, either by the charcoal alone, or by any of the combinations
with the chemicals, as before described, for the purification of gas. It
will require about three pounds weight of charcoal, or the mixture of
charcoal and chemical compounds, for each gallon of gas or ammonical
liquor. The superabundant water may be thrown off either by exposure
to the air, or by passing a current of hot air through it, or by any arti-
ficial means; when dried it may be employed again by absorbing another
quantity of the gas or ammonical liquor, and this may be repeated until

page_text: such time as the charcoal and chemicals have absorbed any given quan-
tity of ammonia required. The quantity of ammoniacal salts obtained
from each gallon of gas or ammoniacal liquor may be estimated at about.
8 ounces.
Care must therefore be taken that the quantity of chemicals-
are in sufficient quantity to decompose or fix the ammonia. For instance,.
in drying the charcoal mixture that has been saturated with gas or.
ammoniacal liquor, if the vapour thrown off stains turmeric paper brown
it shews that ammonia is escaping; there must be added therefore to
the mixture superphosphate of lime, or chloride of sodium, or bisulphate
of potassa, or any of the chemicals before mentioned, to fix or decom-
pose the ammonia. The gas or ammoniacal liquor has an exceedingly
offensive smell, but when the charcoal mixture has been added to it it is
deodorized; its hydrosalphuric acid is decomposed, its volatile ammonia
is fixed, and in drying the simple vapour of water escapes, having no
disagreeable odour whatever.
In the various modes I have stated for purifying gases I recommend
the use of peat charcoal from its great abundance, from its cheapness,
and because it can always be produced with such natural combinations
as are requisite to purify or deprive gas of its impurities; for instance,
for depriving gas of ammonia I would use a peat charcoal, rich in
phosphates and alkalies; if for hydrosulphuric acid, the charcoal should
contain by analysis peroxide of iron and other substances capable of
decomposing that acid.
In explaining the chemical changes that take place, as in the first of
my Invention, where I have stated "the oxygen of the charcoal" I mean
a charcoal containing substances capable of parting with a portion of
their oxygen.
Having now described the nature of my Invention, and the mode or
modes of carrying it into practical effect, and given such proportions of
substances as I consider will be found to effect success in the operations
of purifying gas, and producing by means of such processes manures of
highly fertilizing properties, I would nevertheless remark that I do not
confine myself to the use of the proportions only as given, as they may,
and in some instances must, be varied to suit particular operations, and
also in consequence of the varying properties in the articles used in my

page_text: combinations. But I claim the sole use (in the combinations shewn) of
the various ingredients mentioned in the first, second, and third divisions
of this my Specification in the process or processes, mode or modes,
herein-before fully described, for improvements in the purification of
gas, and the obtention of certain products during the process of such
purification.
In witness whereof, I, William Chisholm, have hereunto set my
hand and seal, this Twelfth day of October, One thousand eight
hundred and fifty-two.
WM CHISHOLM. (L.S.)