IMPROVEMENTS IN THE METHOD OF USING AND PRODUCING NITRIC ACID
Year: 1877

page_text: LETTERS PATENT to Bernard Charles Molloy, of The Temple, Barrister-at-
Law, and John Davis Warren, of South Kensington, in the County of
Middlesex, Scientist, for the Invention of "IMPROVEMENTS IN THE METHOD OF
USING AND PRODUCING NITRIC ACID."
Sealed the 31st July 1877, and dated the 18th May 1877.
PROVISIONAL SPECIFICATION left by the said Bernard Charles Molloy
and John Davis Warren at the Office of the Commissioners of Patents on the
18th May 1877.
"
BERNARD CHARLES MOLLOY, of The Temple, Barrister-at-Law, and JOHN DAVIS
WARRES, of South Kensington, in the County of Middlesex, Scientist. IMPROVE-
MENTS IN THE METHOD OF USING AND PRODUCING NITRIC ACID."
The object of our Invention is to employ nitric acid in connexion with apparatus
that enables what would otherwise be waste products to be recovered. and thereby
wo economise quantities of nitric acid employed in the usual manner in the various
metallurgical and other operations of various kinds wherein oxidising processes are
employed.
One mode of procedure is to collect the fumes of the lower oxides of
nitrogen arising from the decomposition of nitric acid, re-oxidise them back
again into nitric acid, absorb and collect the acid thus produced, so that it may
be again used.
.
In carrying out this Invention the details of manufacture will vary with the
purpose or purposes for which the nitric acid is used, but the general arrangement
for carrying out this Invention may be described as follows:-The tower, or other
convenient receptacle in which the lower oxides of nitrogen are to be oxidized,
should be constructed of materials not easily attacked by nitric acid. The height
and form of the tower or receptacle may of course vary, but one or more towers of
about 30 feet high and from 3 to 6 feet in diameter will answer most purposes.
The fumes, such as nitrous acid and peroxide of nitrogen, which have escaped
from the vessel when the nitric acid is being used as an oxidant or otherwise, ar

page_text: conveyed by a conduit to, preferably, the lower end of a tower or receptacle, there to
be re-oxidized into nitric acid and absorbed and collected.
Fitted to the upper portion of the tower are one or more jets through which
steam and water, preferably at about 100° centigrade, are forced and brought into
contact. These jets, whether used separately or combined, should be capable of
being easily and accurately adjusted. When properly adjusted the result is that
a cloud or spray of very finely divided water, of a temperature of about 100°
centigrade, falls slowly through the tower or receptacle. Atmospheric air or
oxygen is at the same tiine allowed to enter the tower or receptacle. This hot vapour,
cloud, or spray, in its descent comes into contact with the peroxide and the other
lower oxides of nitrogen, and the oxides become oxidised by the atmosphere or
oxygen admitted into the receptacle, and are so converted into the higher oxides of
nitrogen. The hot vapour, cloud, or spray decomposes the peroxide of nitrogen into
nitric acid and nitrous acid. The nitric acid thus formed is absorbed by the cloud
or spray, and is collected in a tank at the foot of the tower or receptaclo, while the
nitrous acid is re-oxidised by. the atmosphere or oxygen, as above mentioned, into
peroxide of nitrogen, which in turn is again decomposed and absorbed, as above
described.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Bernard Charles Molloy and John Davis Warren in the Great Seal
Patent Office on the 17th November 1877.
BERNARD CHARLES MOLLOY, of The Temple, Barrister-at-Law, and JOHN DAVIS
WARREN, of South Kensington, in the County of Middlesex. "IMPROVEMENTS IN
THE METHOD OF USING AND PRODUCING NITRIC ACID."
The object of our said Invention is to employ nitric acid in connection with
apparatus that enables what would otherwise be waste products to be recovered,
and thereby wo economise quantities of nitric acid employed in the usual manner
in various metallurgical and other operations wherein oxidising processes are
employed.
Our mode of procedure is to collect the fuines of the lower oxides of nitrogen
arising from the decomposition of nitric acid, and by treating them in the manner
herein-after described, again to form nitric acid capable of being used over again.
In carrying out the said Invention the details of the process will vary with the
purpose or purposes for which nitric acid is used, such, for example, as tho
production of chlorine from hydrochloric acid, the oxidation of ores, and the like;
but the following general arrangements for re-oxidation, absorption, and re-
production of the nitric acid are adopted.
When nitric acid is used in the ordinary way for oxydising various substances, it
parts with a portion of its oxygen, and the remainder passes off as funies or gases,
being peroxide of nitrogen, nitrous acid, and nitric oxide, or one or more of these
gases. These fuines represent the original nitric acid, less part of its oxygen and
the water of the acid. In order to reconvert these fumes or gases into nitric acid it
is necessary therefore to replace the lost or used-up atoms of oxygen and the water.
The former in our process we obtain from atmospheric air or from oxygen, and the
latter from the spray in the manner presently described.

page_text: The fumes or gases, above referred to, as they escape from the oxidising tank are
conducted through a pipe or other convenient conduit into a tower or towers, there
to be re-oxidised and absorbed, as herein-after described. These towers consist of
closed chambers, which may be of any convenient size, but we prefer to make them
about thirty feet in height and three feet in diameter. Their form and material
may also be varied, but we construct them by preference of glazed earthenware
pipes (or slate or such other material as will not bo easily affected by acid), they are
built up and jointed with sulphato of lime (Paris plastor). Each tower rests in a
tank having a water joint, into which the reconverted acid falls, and from which it
may be drawn.
Into the sides of the pipes forming the tower we fix a suitable number (say, two
or three) glass bottles with ground stoppers, but with the bottoms cut out. Theso
bottles may be fitted in and luted with sulphate of lime.
To the upper portion of the tower is or are fitted one or more jets, through which
steam and water, preferably at about 100° centigrade, are forced, so as to be brought
into contact. These jets, whether used separately or combined, are so arranged as
to be capable of being easily and accurately adjusted, in order to cause a cloud or
spray of very finely divided water, of a temperature of, say, about 100° centigrade,
to fall slowly through the tower or receptacle. Atmospheric air or oxygen is at the
same time allowed to enter the tower or receptacle. The construction of the jet
may be varied, but it is so arranged that the quantity of air or oxygen, water, and
steam can be regulated at will. The tower should, as is obvious, be made
gas-tight.
When the fumes or gases coming from the nitric acid are evolved and enter the
tower, an approximate estimate may be formed of the quantity by the depth of the
color seen in the bottles, fixed, or through glazed or equivalent openings made in the
sides of the tower. When the tower is sufficiently charged, the jet comes into action.
Steam and hot water are turned on into the jet in such proportions and quantities
as that the steam shall strike and separate the water into a minutely divided spray,
the steam itself being to a very great extent condensed in the hot water, so that
the spray is a misty vapour of hot water slowly falling through the tower.
descent the particles of the spray come in contact with the peroxide of nitrogen and
the other oxides N₂ O3, and No 0₂, which may be present. The nitrous anhydride
(No 03) and nitric oxide (N₂ O₂,) are immediately oxidised by the air (adimitted
and drawn in through the air tube of the jet or through the other air holes) into
peroxide of nitrogen N₂ O, thus-
N, O, N, O, + 30 2 N, O,
===
In its
This peroxide of nitrogen (N, O.,) is quickly absorbed by the spray, and
decomposed by it into nitric oxido and nitric acid. The nitric acid is dissolved by
the hot water, and carried with it into the tank at the bottom of the tower, there
to be collected. The nitric oxide remains undissolved by the spray, becomes
oxidised eventually by the air admitted into peroxide, which in turn becomes split
up again into nitric oxide and nitric acid, the latter being collected as before in the
tank. The re-action may be-
6 N, 0, + 4 1 0
=
2 N, 0, +8 H NO.
Eventually therefore the lower oxides of nitrogen, becoming oxidised by contact
with the air into the higher peroxide, and this in turn being absorbed by the spray
and divided into nitric oxide and nitric acid, which is dissolved and carried down,
and the re-nctions being successively continuous, the whole of the nitric acid, when
operated or under perfect conditions, will be regained.
When necessary there may be two towers connected at the top by means of a pipe.
The egress into the second tower may be closed by a water joint (or other
convenient means), so that an excess of the fumes or gases in the first tower would
at a given pressure pass through the water joint into the second tower.
Where a large quantity of nitric acid is being used, or upon substances where
evolution is sudden and rapid, then to avoid any loss through forced leakage, wo

page_text: provide an escape chamber, into which any fumes which may not have been
absorbed, or any nitric acid which may have passed away as spray, may be
conducted. We construct this chamber of glazed brick, or slate, or other suitable
material. It may be in the form of a chimney at a slight incline, and with alternato
baffle plates or projections, so that the vapour and gases, if any will pass up slowly
from right to left, and then from left to right, and so on, following a zig-zag course.
The gases,
if any, will be absorbed, as before described, by the vapour spray, which
will in turn condense and flow back into a tank.
The size, form, and number of the towers, tanks, and their appurtances will of
necessity vary according to the work to be done. The towers should be gas-tight,
and arranged as above indicated, so that no escape of fumes can take place, except
as described; with moderate care and attention, practically, there should be no loss
whatever.
In order to give a further exemplification of our method of using and reproducing
the nitric acid, we will describe an operation with an auriferous iron pyrites. The
pyrites, being well ground and roasted, is placed in a slate or other convenient tank.
The nitric acid is added to the pyrites by simply turning a tap fixed in the foot
of the tower, and to the nitric acid so introduced there is added hydrochloric acid,
sufficient for acting on the metal. The remaining oxidisable matter in the ore is
oxidised, and the hydrochloric acid splits up, and gives chlorine to combino with tho
gold and with the silver, if any be present. The affinity of the chlorine for the
metals is greatest when the chlorine, as in this case, is nascent.
The contents of the tank may be maintained in a heated state by a steam jacket
or other suitable means. When after the lapse of about from two to six hours, tho
operation is completed, the contents without being exposed are discharged through
a sluico door, and run down a slight incline into another or settling tank, also con-
structed of slate or other suitable material. The first tank or converter (as we
term it) is closed everywhere during the operation, so that the fumes may not escape,
except into the tower. At the end of the operation in the converter, steam is
injected into the mass through an earthenware pipe, in order to blow off any of
the lower oxides which may remain absorbed in the solution.
When after the lapse of several hours the mass has settled down in the settling
tank, the solution is drawn off by taps into a precipitating tank, the residue is
washed, and in the same manner tho washings are drawn off into the precipitating
tank. Now in this solution will properly be found some nitric acid; this tank
therefore, like the others, is closed, and we connect it with the tower. In order to
precipitate the gold we added ferrous salt, or sulphurous acid or other known
reducing agent. This in the first place decomposes the nitric acid, if any, by
becoming oxidised into ferric salt. The fumes or gases of all the remaining nitric
acid then pass over into the tower, and are there reconverted and absorbed, as
described. The ferrous salt then precipitates all the gold which is collected and
fused. The whole of the gold will be thus extracted from the ore without any
manipulation, the mass falls down the slight inclino into the settling tank, whence
by turning a tap the solution and washing in turn also fall into the settling tank,
where the gold is precipitated, as described, assisted by a jet of steam, and the
solution runs off, leaving the gold. There being no escape, all the nitric acid is
recovered, the small quantity of hydrochloric acid, given for the gold or other metal,
is all that is consumed. If there be any copper it will be found in solution with
the gold, after precipitating which it is run over iron scrap in the usual manner.
If there be silver it will be found as an insoluble chloride in the magma in the
settling tank. It is dissolved out by a hot solution of salt, which in the same
manner as with the gold is run off after settling into another precipitating tank,
where the silver is precipitated by a bar of zinc. This salt solution is used over
and over again. The magma is then taken out.
Having now described and particularly ascertained the nature of our said Inven-
tion, and the manner in which the same is or may be used or carried into effect, we

page_text: would observe in conclusion that what we consider to be novel and original, and
therefore claim as the Invention secured to us by the herein-before in part recited
Letters Patent is,-
First. The use of hot water spray for absorbing peroxide of nitrogen and recovering
nitric acid from its lower oxides, as herein-beforo described.
Second. The use of hot water spray, in combination with atmospheric air or
oxygen, for re-oxidising and absorbing the lower oxides of nitrogen, and regaining
the nitric acid, as herein-before described.
Third. The application of this process of using and recovering nitric acid to the
treatinent of metals and metallic ores, and to other industrial purposes, sub-
stantially as herein-before described.
In witness whereof, we, the said Bernard Charles Molloy and John Davis
Warren, have to this our Specification set our hands and seals, this Sixteenth
day of November, Ono thousand eight hundred and seventy-soven.
BERNARD C. MOLLOY.
(L.S.)
JOHN DAVIS WARREN. (L.S.