AN IMPROVED PROCESS FOR ECONOMIZING THE NITROUS PRODUCTS IN THE MANUFACTURE OF SULPHURIC ACID
Year: 1880

page_text: LETTERS PATENT to John Imray, of No. 28, Southampton Buildings, Chancery
Lane, in the County of Middlesex, for an Invention of "AN IMPROVED
PROCESS FOR ECONOMIZING THE NITROUS PRODUCTS IN THE MANUFACTURE
OF SULPHURIC ACID." A communication from abroad by Frederic Benker
and Henri Lasne, both of Paris, France.
PROVISIONAL SPECIFICATION left by the said John Inray at the Office
of the Commissioners of Patents on the 4th November 1880.
"
JOHN IMRAY, of No. 28, Southampton Buildings, Chancery Lane, in the County
of Middlesex. AN IMPROVED PROCESS FOR ECONOMIZING THE NITROUS
PRODUCTS IN THE MANUFACTURE OF SULPHURIC ACID." [A communication from
abroad by Frederic Benker and Henri Lasne, both of Paris, France.]
This Invention has for its object to economize the nitrous products, such as
nitrates, nitric acid, or other substances forming nitrous compounds in the
manufacture of sulphuric acid.
In the manufacture as at present carried out, a portion of these compounds is
retained in combination with the concentrated sulphuric acid which trickles down
the Gay Lussac tower situated at the end of the lead chambers. It has been
observed that the nitric peroxide (NO) which is always formed when the nitrous
products are in the presence of oxygen in excess, is only retained by the sulphuric
acid in a state of simple solution, and that this gas becomes disengaged like all
other gases in solution when it is brought in contact with a different gas. This
takes place in the Gay Lussac tower, the escaping gases having often a reddish tint,
this being certain indication of the presence of nitrous compounds which thus
escape into the atmosphere. On the other hand nitrous acid (NO) forms with
concentrated sulphuric acid a compound of a very stable nature, which is not
decomposed either by inert, reducing, or oxidising gases, nor even by a high
degree of heat.

page_text: According to the present Invention, by mixing with the gases that enter the
Gay Lussac tower any reducing gas in suitable proportion, the nitric peroxide
becomes converted into nitrous acid which combines with the concentrated
sulphuric acid. This acid being introduced into the first part of the apparatus
again, the nitrous compounds contained in it are utilized in the manufacture in the
ordinary manner.
Thus an economy is effected in the nitrous products to the extent of that
portion of the nitric peroxide which formerly escaped into the atmosphere.
The gas having reducing properties which can be suitably employed may,
according to circumstances, be either the sulphurous acid coming from the sulphur,
or pyrites furnaces, or it may be sulphurous acid specially manufactured for the
purpose, or any other gas capable of reducing the nitric peroxide, such as
hydrosulphuric acid or binoxide of nitrogen.
The quantity of reducing gas employed is determined by the proportion of nitric
peroxide to be converted into nitrous oxide.
Any suitable means may be employed for introducing the reducing gas at the
bottom of the Gay Lussac tower, such as a steam or air injector, or it may be
introduced directly from a closed chamber in which it is generated with or without
the aid of a pump.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Imray in the Great Seal Patent Office on the 3rd May
1881.
JOHN IMRAY, of No. 28, Southampton Buildings, Chancery Lane, in the County
of Middlesex. "AN IMPROVED PROCESS FOR ECONOMIZING THE NITROUS
PRODUCTS IN THE MANUFACTURE OF SULPHURIC ACID." A communication from
abroad by Frederick Benker and Henri Lasne, both of Paris, France.
This Invention relates to the absorption in what is known as the Gay Lussac
tower, of the nitrous compounds contained in the gases passing off from vitriol
chambers. It consists in mixing with the gases which pass from the vitriol
chambers into the Gay Lussac tower sulphurous acid gas, in proportions regulated
as will be explained below.
My correspondents who have communicated to me the present Invention, have
found that it is as nitric peroxide passing off from the Gay Lussac tower that the
greater part of the loss of nitre at present experienced by manufacturers of
sulphuric acid takes place, and that this source of loss of nitre may be avoided,
practically completely, by mixing the gases which pass from the vitriol chambers
into the Gay Lussac tower with a suitable proportion of sulphurous acid gas.
My correspondents account for this result as follows:-According to their
observation and experience, sulphuric acid of the strength ordinarily employed in
the Gay Lussac tower cannot combine chemically with nitric peroxide. It can
dissolve small quantities of nitric peroxide, but the quantity of nitric peroxide
which it can retain in solution under the conditions which have place in the Gay
Lussac tower is absolutely inappreciable. With nitrous acid, however, sulphuric
acid as concentrated as that employed in the Gay Lussac tower combines
chemically, forming therewith the very stable compound which some chemists call
nitrosulphonic acid, and which when in the solid state constitutes what are known
as "chamber crystals." The so-called "nitrous vitriol" which runs from the Gay
Lussac tower is simply a solution of this compound in excess of sulphuric acid,
and never contains more than traces of any oxide or oxides of nitrogen other than
the nitrous acid of this compound. In order then that the nitric peroxide contained
in the chamber gases shall be absorbed in the Gay Lussac tower, that nitric
peroxide must first be transformed, either into nitrous acid, or into such other
oxide of nitrogen as, with the help or not of the free oxygen contained in the
atmosphere of the Gay Lussac tower, can become nitrosulphonic acid on contact .
with the sulphuric acid of the Gay Lussac tower; and such transformation is
readily effected by sulphurous acid in presence of the necessary quantity of vapour
of water and of free oxygen.
The sulphurous acid gas, which is to be mixed with the gases from the vitriol
chambers for the purposes of the present Invention, may be taken from the pyrites
burners or from the sulphur burners, as the case may be; or it may be generated
by whatever method in special apparatus. It may be either forced or aspirated
by whatever means may be preferred in each particular case; but the method
employed, whether for forcing it or for drawing it, must be one which shall permit
that the quantity of sulphurous acid delivered per unit of time may be easily
varied and regulated at will.
In executing the present Invention in their own work my correspondents
employ what it will be convenient to speak of simply as sulphurous acid, but
what is of course a mixture of sulphurous acid gas and other gases taken from
pyrites burners. By a pipe having an internal diameter of about four inches the
sulphurous acid passes from the pyrites burners into the lower part of a closed

page_text: vertical cylindrical dust-chamber, constructed of lead, this chamber being about
six feet high and having an internal diameter of about sixteen inches. The lower
half of this chamber is immersed in a vessel, through which cold water is kept
running. In this chamber the sulphurous acid deposits any dust which it may
have carried over from the pyrites burners, and is at the same time cooled. The
sulphurous acid passes from the upper part of this chamber by a pipe, also of about
four inches internal diameter, in which pipe, at a distance of a few feet from the dust-
chamber, is fixed an injector on the principle of the Körting injector, but made of
an alloy of lead and antimony. Steam is supplied to the injector by a pipe of
about half an inch bore. The injector draws the sulphurous acid from the pyrites
burners through the dust-chamber, and forces it into a closed vertical annular
cylindrical vessel, immersed in an open vessel, through which last a current of cold
water continually passes. The closed annular vessel is about three feet high; the
diameter of the cylinder constituting its outer side is about twenty inches, and the
diameter of the cylinder constituting its inner side is about sixteen inches,
the annular space between the inner and outer cylinders being thus about two
inches across. The water which condenses in this annular vessel passes off from it
by a tube curved after the fashion of a swan's neck. The sulphurous acid having
entered this annular vessel at the top, passes from near the bottom of it again by
a pipe of about four inches internal diameter into the lower part of a small tower
packed with coke, down which sulphuric acid is kept trickling. This tower is of
lead, is about ten feet high, and is of about two feet internal diameter. From the
upper part of this tower the sulphurous acid finally passes by a pipe of about two
inches internal diameter into the pipe, by which the gases from the chambers enter
the Gay Lussac tower. The apparatus which I have thus described has been
found amply sufficient for the application of my correspondents' Invention to a set
of vitriol chambers, having a total capacity of about one hundred and forty
thousand cubic feet, and producing vitriol equal to about fifteen tons of mono-
hydrated sulphuric acid per twenty-four hours. My correspondents believe that
in the case of sets of vitriol chambers of greater capacity than their own, the
proportion of the dimensions of the apparatus for the application of their Invention
to the capacity of the vitriol chambers may be a little smaller than that
proportion actually is in their own case. The apparatus however should always be
capable of delivering, to be mixed with the gases from the chambers, a quantity of
sulphurous acid equal to about three per cent. of the quantity supplied to the
chambers themselves. It will only be very rarely that it will be necessary to mix
with the exit gases from the chambers so much sulphurous acid as the quantity
corresponding to three per cent. of the quantity of sulphurous acid going into the
chambers. It will indeed only be occasionally that it will be desirable to mix
with the gases from the chambers more than half that quantity of sulphurous acid.
But to meet the extreme cases which sometimes occur it will be well to be able
to mix with the exit gases a quantity of sulphurous acid, equal to three per cent.
of the quantity entering the chambers in the same time.
The regulation of the quantity of sulphurous acid to be added to and mixed with
the gases passing from the chambers to the Gay Lussac tower must be governed
by tests of the gases passing from the Gay Lussac tower. It is possible so to
regulate the proportion of sulphurous acid added to the chamber gases that the
gases passing from the Gay Lussac tower shall contain neither sulphurous acid nor
nitric peroxide. To enable the process to be conducted however by an ordinary
workman, without which it would not be practicable industrially, my correspondents
at present employ a method based on there being always permitted to be contained
in the gases passing from the Gay Lussac tower a trace, though barely more than a
trace, of sulphurous acid. The foreman over the chambers is supplied with
peroxide of lead paper, made by dipping filter-paper first into a dilute solution of
acetate of lead and then into a dilute solution of bleaching-powder. Paper
impregnated by these means with peroxide of lead, if the solutions used have not
been too strong, and if the paper be never allowed to dry, but the stock of it

page_text: be always kept in water, is an extremely delicate test for sulphurous acid. From
time to time the foreman immerses a wet piece of this peroxide of lead paper in
the gases passing from the Gay Lussac tower and observes the rate at which it
loses colour. He knows that if the right proportion of sulphurous acid gas is
being added to the gases from the chambers his test-paper will not become
decolourized to the degree with which he has become familiar by experience in
less than a certain definite period of time. If his test-paper loses colour more
rapidly than he thus knows that it should lose colour, too much sulphurous acid is
being added to the gases from the chambers, and he therefore diminishes the
supply of sulphurous acid; but if his test-paper loses colour more slowly than he
knows that it ought to do, the quantity of sulphurous acid which is being added to
the gases from the chambers is too small and he therefore increases it. To obtain
uniform results by this method of regulating the quantity of sulphurous acid gas
to be added to the gases from the chambers pains must of course be taken to use
always test-papers of the same depth of tint. Equally of course the rate at which
the test papers will become decolourized will depend partly upon their depth of tint
and partly upon the rate at which the gases from the Gay Lussac tower travel
through the conduit in which the test-papers are exposed to those gases. Both of
these conditions may differ in different works, so that the rate of decolourization
corresponding to good working may not be quite the same in any two cases, and
should be specially determined once for all in each particular case by regulating
for a time the supply of sulphurous acid to the gases passing from the chambers to
the Gay Lussac tower by means of quantitative analyses of samples of the gases
passing from the Gay Lussac tower; and when in this way the right rate of supply
of sulphurous acid gas to the gases passing from the chambers to the Gay Lussac
tower has been arrived at, and the composition of the gases passing from the Gay
Lussac tower has accordingly become. such as should thenceforward be constantly
maintained, then observing carefully the rate at which these gases decolourize such
peroxide of lead paper as that by which it is proposed that the working shall
thereafter be conducted. It is believed, however, that it will be found in most
cases that too much sulphurous acid is being supplied if the gases passing from the
Gay Lussac tower decolourize peroxide of lead paper in less than five or six
minutes, and that too little sulphurous acid is being supplied if the decolourization
of peroxide of lead paper by those gases requires more than that time.
It must always be borne in mind that water is essential to the reactions by
which the sulphurous acid supplied to the gases passing from the chambers to the
Gay Lussac tower is to determine the conversion into nitrosulphonic acid of the nitric
peroxide contained in those gases, and that if the requisite quantity of water be
not present those reactions cannot take place. As the degree of humidity of the
exit gases from the chambers varies with the state of the atmosphere and with other
circumstances, while it is desirable that the mixture of these gases with the
sulphurous acid added to them under the present Invention should always contain
per given quantities of nitric peroxide and sulphurous acid contained in them, the
same quantity of moisture within narrow limits, it may occasionally be necessary
to vary the degree of humidity of the sulphurous acid gas added to the chamber
gases by varying the strength of the sulphuric acid supplied to the small coke-
tower which the sulphurous acid gas traverses immediately before being added to
the gases from the chambers. In France, where the summer temperature is higher
and the winter temperature lower than in England, my correspondents have already
(although they have not yet practised their Invention at the hottest season of the
year) found it necessary that in hot weather the sulphuric acid supplied to the
little coke-tower for partially drying the sulphurous acid shall be so concentrated
that its specific gravity shall not be less than about 1.69 or 17, whereas in winter
they have found it essential that the specific gravity of the sulphuric acid supplied
to the little coke-tower should not exceed 1.42, and once during a few exceptionally
cold days, during which the exit gases from the chambers were almost absolutely
dry, they were obliged to cut off from that tower all supply of sulphuric acid

page_text: whatever. My correspondents are of opinion; however, that in Great Britain the
sulphuric acid supplied to the little coke-tower may nearly always be ordinary
chamber-acid. If there should ever be an insufficiency of moisture with the gases,
such insufficiency will be indicated by nitric peroxide passing off from the Gay
Lussac tower, notwithstanding that enough sulphurous acid has been supplied to
the gases entering it to secure the conversion, if enough moisture for that purpose
bad been present, of all their nitric peroxide into nitrosulphonic acid.
To obtain the best possible results by means of the present Invention my
correspondents are of opinion that the chambers should be so worked that the
gases issuing from them shall contain not less than five per cent. and not more
than seven per cent. of free oxygen.
Having thus described the nature of the said Invention, and in what manner the
same may be performed, as communicated to me by my foreign correspondents, I
claim as the Invention to be secured by the herein before in part recited Letters
Patent the method economizing nitrous compounds in the manufacture of
sulphuric acid, which consists in mixing sulphurous acid gas with the gases which
enter the Gay Lussac tower, substantially as is above described.
In witness whereof, I, the said John Imray, have hereunto set my hand and
seal, this Third day of May, in the year of our Lord One thousand eight
hundred and eighty one.
JOHN IMRAY. (L.S.)