IMPROVEMENTS IN PURIFYING GAS, AND IN THE TREATMENT OF PRODUCTS OF GAS- WORKS
Year: 1845

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
ROBERT JOHNSON, of Nelson Square, in the County of Surrey, Chemist, send
greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Twentieth day of December, in the ninth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
John Robert Johnson, my exors, adiñors, and assigns, Her especial licence,
full power, sole privilege and authority, that I, the said John Robert Johnson,
my exors, admors, and assigns, or such others as I, the said John Robert
Johnson, my exors, admors, or assigns, should at any time agree with, and no
others, from time to time and at all times during the term of years therein
expressed, should and lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, my Invention of
"IMPROVEMENTS IN PURIFYING GAS, AND IN THE TREATMENT OF PRODUCTS OF GAS-
WORKS;" in which said Letters Patent is contained a proviso, that I, the said
John Robert Johnson, shall cause a particular description of the nature of my
said Invention, and in what manner the same is to be performed, to be inrolled

page_text: in Her said Majesty's High Court of Chancery within six calendar months
next and immediately after the date of the said in part recited Letters Patent,
as in and by the same, reference being thereunto had, will more fully and at
large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
John Robert Johnson, do hereby declare that the nature of my said Invention,
and the manner in which the same is to be performed, are fully described and
ascertained in and by the following statement thereof, reference being had
to the Drawings hereunto annexed, and to the figures and letters marked
thereon, that is to say:-
My Invention consists, first, in a new mode of purifying gas used for the
purpose of illumination from those impurities which consist of ammonia and
its compounds. Ammonia exists in gas after it has passed the condensers and
before entering the lime purifyer, in combination with several volatile acids, for
example, the hydrosulphuric, hydrocyanic or prussic, and carbonic acid. When
the gas has passed the lime purifier, these compounds have become decom-
posed, the lime combining with the acids before mentioned and liberating the
ammonia, which is then found in the gas in the uncombined or so-called
caustic state. Various plans have been proposed, and some used, to effect the
separation of the ammoniacal compounds; dilute acids have been employed,
and likewise solutions of metallic salts, such as the chloride of manganese.
All these plans have the disadvantage to require a considerable increase of
pressure to force the gas through the fluid, and some require the use of motive
power to render the operation successful, in addition to the increase of pres-
sure. Now, I obviate these inconveniences, and completely effect the separa-
tion of the ammonia, by using the substances possessing the property of
absorbing ammonia or its compounds in the dry, or, more properly speaking,
solid state, instead of in the state of solution as has hitherto been practised.
All the substances I have tried which absorb ammonia and its compounds when
in solution possess the same property when employed in the solid state, pro-
vided they are used in a divided or pulverulent form, and that they contain
sufficient water of crystallization or hygrometric moisture to bring the gas and
solid matter within the sphere of affinity. The substances which possess this
property may be divided into two classes; first, those substances which act on
the compounds of ammonia in the manner of the acids, that is to say, which
absorb the ammonia only, and which liberate or only partially absorb the
acids with which it was previously in combination. Among this class of
substances are comprised the solid acids, such as the phosphoric, boracic,

page_text: and other acids; the salts with excess of acid, as the bisulphates of potash,
of soda, and of ammonia; the biphosphates of these bases, and other salts of
this class; the salts of allumina and of some other earths. Second, those
substances which absorb the compounds of ammonia entirely, acid as well as
base entering into combination with the components of. the substance used.
The metallic salts containing the requisite quantity of water are comprised in
this class, and will serve more or less perfectly for the purpose required, but
the salts of iron and manganese from their cheapness will be found preferable
to others.
For the purpose of facilitating the carrying out of this part of my In-
vention, I proceed to describe more particularly the mode which I adopt. I
take, as an example, one of the substances included in the second class,
videlicit, the sulphate of iron, or common green copperas of commerce.
As
usually found in commerce it is in the state of crystals, dry to the touch, but
containing a large quantity of combined water or water of crystallization. I
reduce this salt to powder by any of the known modes of effecting that object.
The finer the powder the more complete will be the decomposition of the salt
by the ammoniacal compounds. I take this powder and use it precisely as
the moistened lime is used in what are called dry lime purifiers; that is to
say, I spread it upon the shelves of a purifier constructed like that used for
the dry lime, only I prefer that the bars of which these shelves are formed
should be placed closer than is necessary for lime. When thus spread, the
subsequent part of the process is the same as with dry lime; that is to say,
the cover is lowered and sealed, and the gas is allowed to pass until the
application of a piece of turmeric or other test paper shews that the material
ceases to absorb the ammonia. When this point is arrived at, the gas is
turned into another purifier similarly prepared, and the one just saturated is
emptied. I have here only spoken of one purifying vessel in use at a time,
but it should be understood that the operation is more perfectly effected when
a series is employed, as in the lime purifyers, and as is well understood. I
prefer to employ the purifier or series of purifiers containing the substance
used for absorbing the ammonia when placed so as to receive the gas before
it enters the lime purifiers, as the acids in combination with the ammonia are
then absorbed by the substance (when belonging to class second), the quantity
of time required for the purification of the gas is diminished, and the union of
one of these acids (the hydrocyanic) with the salt of iron gives rise to a useful.
product.
When employed subsequently to the passage through the lime purifiers,
one of the substances of class 1 will, I believe, be found most advantageous.

page_text: I find the water of crystallization in sulphate of iron to be sufficient to bring
the salt into a fit state to effect the absorption of the ammoniacal compounds.
But I wish it to be understood that I do not confine myself to the use of salts
in their natural state. The salts may have a certain quantity, more or less,
according to their nature, of water added, beyond that which they naturally
contain. The powdered sulphate of iron, for instance, if slightly moistened,
so that it hangs together, acts equally as in the former case, and rests better
upon the shelves of the purifier. I am aware that substances have been used
in the dry form for increasing the illuminating and diminishing the heating
power of gas after it has left the distributing main, and before it enters the
burner, and I therefore disclaim the use of dry substances for such objects
when used under such circumstances.
I claim, as the first part of my Invention, the use of substances in the dry
or solid form and in a divided state, for the purpose of separating from gas
(used for illumination) those impurities which consist of ammonia and its
compounds; and in thus using the word dry, I mean it to be understood in
the sense in which that word is employed with reference to lime used in what
are called "dry purifiers," and in contradistinction to solution.
My Invention consists, secondly, in a new mode of treating the ammoniacal
liquor of the gasworks, for the purpose of preparing the salts of ammonia in
a purer state than they have been usually obtained, and without the noxious
exhalations which attend the ordinary mode of operating. In treating the
ammoniacal liquors by the ordinary process, a large quantity of highly offen-
sive and deleterious gas, sulphuret of hydrogen, is evolved. Attempts have
been made to remedy this inconvenience by distilling the liquor mixed with
a large quantity of lime, condensing the vapours, and passing the products of
condensation into an acid. Another plan is to evaporate the liquor with or
without lime, and to pass the vapours through acid without condensation. In
the former case, in carrying the operation into practice on a large scale, it has
been found that the lime incrusts or deposits, and the process is thereby
rendered dangerous and otherwise objectionable. In the second plan, unless lime
be used in the evaporation, the operation is unsuccessful, as the noxious gas is
generated when the vapours come into contact with the acid, and must be got rid
of, thus resembling the old process. I obviate these inconveniences by operating
in the following manner :-I place the liquor in a vessel A, similar to an ordinary
steam boiler, and apply heat through the furnace B. The liquor consists
principally of hydrosulphuret and carbonate of ammonia, with small quantities
of other salts of that base. As soon as the temperature rises, the bydro-
sulphuret of ammonia comes over, it being the most volatile product. I keep

page_text: a slow fire, so as to volatilize this product exclusively, and during its passage I
conduct it by the pipe a, a, into the vessel c, containing a solution of some
substance which has the property of absorbing the sulphuretted hydrogen, the
deleterious gas. The salts of iron and manganese possess this property, as has
been already said above, and alkalies or lime mixed with water will also effect
the same object. In the former case the product, after sufficient of the vapors
have passed to saturate the material employed, is a solution of a salt of
ammonia, holding in suspension the sulphuret of iron or manganese. In this
plan one vessel for holding the material through which the vapours are passed
is sufficient, but if more be employed they are charged with the same solution.
When lime or alkali is used to absorb the sulphuretted hydrogen the ammonia
is liberated, and must be conducted into a second vessel (D) charged with an
acid. At the end of this part of the operation, that is, when all the hydro-
sulphuret of ammonia has passed over, the products found in the first vessel
are sulphuret of lime and some free ammonia, and in the second a solution of
a salt of ammonia. If the acid was but slightly diluted, the solution may be
obtained saturated and fit to crystallize on cooling. The liquid remaining in
the boiler, and now consisting principally of carbonate of ammonia, may be
treated in the ordinary way for preparing the salts, that is, it may be neutralized
with an acid, and the resulting solution evaporated in lead vessels to obtain
the crystals of the ammoniacal salts, as is well understood; or the evaporation
may be continued in the boiler at a higher temperature in order to drive
over the other volatile salts, and the vapours passed through acid to absorb the
ammonia. In the latter case the apparatus just described may be used; the
cock E being opened, the vapours then pass through the pipe b and through
the acid in the vessel without entering the vessel (C) containing the lime,
and are then absorbed. The evaporation is continued until the volatile salts
of ammonia are all driven off, when the liquor in the boiler may be rejected,
unless it be found that the fixed salts remaining in the liquor are in sufficient
quantity to be worth extracting, which may be ascertained approximatively by
evaporating a drop of the liquor on a strip of glass, or accurately by evapo-
rating to nearly dryness a known quantity of the liquor, and by weighing the
resulting salt. These fixed salts may be obtained by entirely evaporating the
liquor in a lead vessel, or by adding to the liquor, while in the boiler A,
a certain quantity, more or less, according to the quantity of the fixed salts
present, of sulphuret of lime in solution. This substance may be obtained
from the first part of the operation when lime is used, or from the liquor of
the wet purifiers of the gasworks. The sulphuret of lime decomposes the
fixed salts of ammonia, liberating the latter substance in the state of hydro-

page_text: sulphuret, which may be treated in the same manner as that evolved in the
first stage of the process.
Secondly, I claim the mode of treating the ammoniacal liquors of gasworks,
as herein described..
In witness whereof, I, the said John Robert Johnson, have hereunto set
my hand and seal, this Twentieth day of June, in the year of our Lord
One thousand eight hundred and forty-six.