IMPROVEMENTS IN THE MANUFACTURE OF SULPHURIC ACID AND THE APPARATUS EMPLOYED THEREIN, PARTS OF WHICH IMPROVEMENTS ARE APPLICABLE TO THE MANUFACTURE OF NITRIC, HYDRO- CHLORIC, AND OTHER ACIDS
Year: 1856

page_text: LETTERS PATENT to William l'etrie, of Woolwich, in the County of Kent
Civil Engineer, for the Invention of "IMPROVEMENTS IN THE MANUFACTURE
OF SULPHURIC ACID AND THE APPARATUS EMPLOYED THEREIN, PARTS OF WHICH
IMPROVEMENTS ARE APPLICABLE TO THE MANUFACTURE OF NITRIC, HYDRO-
CHLORIC, AND OTHER ACIDS."
Sealed the 3rd March 1857, and dated the 8th September 1856.
PROVISIONAL SPECIFICATION left by the said William Petric at the
Office of the Commissioners of Patents, with his Petition, on the 8th
September 1856.
I, WILLIAM PETRIE, of Woolwich, in the County of Kent, Civil Engineer,
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF SULPHURIC ACID AND THE APPARATUS EMPLOYED THEREIN,
PARTS OF WHICH IMPROVEMENTS ARE APPLICABLE TO THE MANUFACTURE OF NITRIC,
HYDROCHLORIC, AND OTHER ACIDS," to be as follows:-
My Invention refers principally to the mode of manufacturing sul-
phuric acid with columns, such for example, as the method for which I
obtained Letters Patent dated 1st November 1852. I transmit sulphur-
ous gas into the lower end of a column which I designate the denitrizing
column. The gas rises through this into the lower end of one which I call
is
the producing or condensing column, and the uncondensed or refuse gas
drawn from the upper end thereof by the power of inward draught or
suction by whatever means obtained, while liquor such as water or weak
acid is made to percolate through the condensing column into a reservoir,
and thence into the denitrizing column. The reservoir is charged with
nitrous or nitric liquor. In this reservoir is my improved equable flow

page_text: apparatus, consisting of a cylinder with the bottom of a coarse filtering
material, in which stands one leg of a glass syphon tube, the other leg
discharges the liquor into a filter which covers the top of the denitrizing
column. This syphon is so contrived as to be raised or lowered at
pleasure until the liquor flows through it so fast that the whole of the
nitric acid is worked out of the sulphuric liquor which runs out at the
bottom of the column. The diameter of the bore of the syphon is so small
in proportion to the flow of liquid through it, that any gas is immediately
carried away through it by the liquid, and the inlet end is contracted to
such a size that any rate of flow found desirable may be obtained by rais-
ing or lowering the syphon. Any surplus liquor that may run into the
reservoir passes off by a lip into a vessel, whence it may be removed to
another vessel fixed just above the level of the top of the condensing
column, and fitted with a similar equable flow apparatus as that last
described, but the inflow leg of the syphon and its cylinder descends lower
than the bottom of the vessel. A similar equable flow apparatus is also
employed in the reservoir of liquor to supply the uppermost column of the
apparatus already described and of that to be described. The liquor is
thus made to run again through the condensing column:
Instead of carrying away the gas by a vent pipe, I sometimes carry it
first through a supplementary condensing column, placed in some cases
so high that the liquor may run from it into the other condensing column,
water or weak liquor being supplied to the top of this column instead of
to the top of the other. In some cases steam instead of liquid is let into
the top of the first or of the supplementary condensing columns, and inlet
and outlet pipes, so arranged that the gases are drawn downwards through
it instead of upwards; or I supply liquor or steam to the condensing
column; and the liquor from the supplementary column passes into the
denitrizing column with that which flows into it from the condensing
column; or strong sulphuric acid may be supplied to the supplementary
column and led into the filter (at the top of the denitrizing column), which
should be covered over air-tight, the liquors being let through the covers
separately through "traps" (sufficiently deep to resist draught of suction);
an aperture is made in the filter, provided with a pipe extending through
the sand and liquid, which cover the filter, through which pipe the
nitrous gas disengaged passes down. For this mode I prefer to place the
two condensing columns on a level; I sometimes cover over the tops of all
the columns. When water, steam, or weak acid liquor is supplied to the
supplementary column, I sometimes carry the nitrous and nitric liquid
into a supplementary denitrizing column, and thence into the condensing
column, while sulphurous gas is conveyed into the top of the denitrizing
column, and thence into the condensing column, or a second pipe conveys

page_text: sulphurous gas (from a furnace) which passes through it and thence into
the condensing column. The supplementary condensing column, instead
of being supplied with water, steam, or weak acid, may be supplied with
some liquor, such a strong sulphuric acid, for simply absorbing (without
oxydizing) the nitrous gas; I then prefer to make the liquid pass into a
receiver, and so work round as long as its quality is suitable.
To cause a stronger suction or draught, I employ an apparatus, which
I call a "pneumatic ram." It consists of a long tube, having one end con-
nected with the source of draught employed, and the other end furnished
with a light valve opening outwards, and so balanced that the inward
draught shall cause it to vibrate, so as to shut and open alternately, and
in this tube, near this valve, there are a set of smaller light valves, opening
inwards, and a pipe or air chamber connected with the seat of the valves
and with the vent of the apparatus for making the acid. Or, instead of
my "pneumatic ram," I employ another new apparatus, which consists of
a series of "venæ contractæ," each succeeding one being so much larger,
as that the end or large part of one may fit into and be fixed in the middle,
neck, or smallest part of the next concentrically, and in the same straight
axis, their relative sizes being such that a space is left all round the
internal one, where it terminates in the neck of the next. The pipe from
the vent is similarly fitted, and terminates in the axis of the first or
smallest "venæ contracta" of the series, while the last or largest is con-
nected with the source of draught employed.
In preference to many of the existing materials for filling the columns,
I use globules of sulphur or glass (glass containing but little alkali being
preferred), coated with a rough surface, made by the adhesion of suitable
powder, such as carbon dust or fine silicious sand. The mode I prefer to
adopt for attaching this powder and producing roundness in the globules
is, to take the coarsely crushed sulphur or glass, double sift it, mix the
product with a quantity of fine silicious sand or carbon dust, and heat it
slowly to a heat sufficient to fuse the sulphur or glass (as the case may be),
leave the mass to cool, and double sift it again. Or I form the globules
of carbon, either by long continued mechanical attrition of grains of
carbon, or by subjecting small nuclei, such as grains of carbon, or of
silicious sand, whether angular or rounded, to the action of very hot gas
charged with carbonaceous matter, and keeping the nuclei in motion
sufficiently to secure an equable concretion of hard carbon all round them,
until they become sufficiently rounded and of the required size. To
secure a suitable temperature, I employ columns of large diameter; if
small, they should be clothed and protected from cold air and near
together, and the pipes connecting them also well clothed, and as short
as may be, and the furnace gases should be admitted at a temperature to

page_text: supply sufficient heat to the lower part of the denitrizing process where
but little heat is developed spontaneously. Before the sulphurous gas
from the furnace passes into the columns I carry it through a chamber,
wherein any solid matter, as dust or sublimed sulphur, may be deposited
to preserve the porosity of the mass.
In some cases, as for example where the column is to be used between
the furnace and chamber, I compose the column or columns in the follow-
ing manner:-Instead of exposing a liquid surface on the irregular discon-
tinuous surfaces of grains of sand or divided matter, I expose it on plates
or continuous surfaces; they may be flat and rectangular, placed one
under another, so that the liquor shall fall from one to the other at alter-
nate sides or ends, but with a rough surface, and with the under side very
slightly sloping downwards from the end over which the liquor runs, so
that a film of liquor shall continue moving all over the under sides of the
plates as well as on their upper sides. I sometimes make the plates
circular, and so constructed that both the liquid and the
gas shall pass
from one plate to another, by radiating alternately to and from the centres
of the successive plates; and I so form the plates that they can be piled
together and cemented, so as to compose by themselves the column, and
the necessary air passages about them.
I sometimes substitute for the nitrous gas, nitrous liquor, or nitric acid
mentioned herein, nitrogen combined with other proportions of oxygen, or
any other volatile oxydator that may be desirable.
The methods which I have described for producing an increased draft
by my "pneumatic ram," and arrangements of "venæ contractæ," as also
the globules of sulphur, glass, and carbon, whether manufactured as I
have described or otherwise, and which I employ for filling the columns
for condensing the gases, may be employed in the manufacture of other
acids than sulphuric, as for example, in manufacturing nitric, hydro-
chloric, and other acids. The contrivance for obtaining an equable flow,
herein-before described, may also be applied in the manufacture of nitric,
hydrochoric, and other acids.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Petrie in the Great Seal Patent Office on the
7th March 1857.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
PETRIE, of Woolwich, in the County of Kent, Civil Engineer, send greet-
ing.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eighth day of September, in the year of our
Lord One thousand eight hundred and fifty-six, in the twentieth year of
Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said William Petrie, Her special licence that I, the said
William Petrie, my executors, administrators, and assigns, or such others
as I, the said William Petrie, 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 MANUFACTURE OF SULPHURIC ACID AND THE APPARATUS
EMPLOYED THEREIN, PARTS OF WHICH IMPROVEMENTS ARE APPLICABLE TO THE
MANUFACTURE OF NITRIC, HYDROCHLORIC, AND OTHER ACIDS," upon the condition
(amongst others) that I, the said William Petrie, my executors or ad-
ministrators, by an instrument in writing under my, 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 Petrie, 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 thereof, reference being had to the Drawings here-
unto annexed, that is to say:-
My improvements relates to an apparatus and process in the manu-
facture of sulphuric acid, consisting of columns arranged together with
their contents in a particular manner, to be described hereafter, and
which improvements are applicable to the manufacture of other acids.
I obtained a Patent on 1st November 1852, a material part of which was
for improvements in the old "coke columns," namely, to use in stoneware
columns fine granular matter, as small pebbles or sand, instead of using
large stones or lumps of coke. By this means I get a much more extensive
surface of action. I avoid the difficulty of its obstructing the draught
too much by having the grains of equal size and rounded form, and by
using a much more powerful draught than has usually been employed.
The equal size of the grains and their rounded form are important points,
which have been neglected by previous manufacturers. Some other of
my improvements were for the means of dispersing the liquid equably
over the top of the column of sand, and for means of supporting the sand

page_text: at the bottom of the column, so as to admit of a free draught through it
without the usual grating, and of clearing it out, if obstructed by sublimed
sulphur, &c. These columns I described as working in modes, which
I have now greatly modified and improved, as will be seen by the
description of my present Invention, which relates to further improve-
ments in the construction of these columns, and in the materials with
which they may be filled, and to particular arrangements or combinations
of several of these columns together, and to the mode of arranging the flow
of different liquids in each part and to and from the several columns,
and in the means of improving the draught.
My apparatus are constructed as follows, reference being had to the
accompanying Figures. A number of stoneware pipes placed upright,
one upon another, and cemented together, form one of the columns which
I use.
The cement which I find most suitable to be employed in the
construction of the columns is that for which Letters Patent were granted
to me for Great Britain on the 12th day of July 1856. Other parts of
this apparatus, its pipes for the gases, and shoots and vessels for the acids
and porous materials K and k, are best made according to the same
Patent.
Referring to Figure 1, the lowest pipe has a bottom, with a hole at one
side, into which a small elbow pipe E is fitted, to carry off the liquor; this
pipe is trapped, in the manner well known in similar cases, that is to say,
it dips under the surface of liquor in a vessel or shoot below, and the
pipe is so long that the weight of the liquor in it prevents air from being
drawn up it by the power of suction within the column. A stoneware
cylindrical ring G, G, of the form shewn in section in Figure 1, is sup-
ported at a little height above the bottom, as shewn. I prefer to effect
this by making its flange to rest on an internal flange F, F, at the lower
end of the next pipe, which stands upon the lowest pipe or cylinder already
described, so that an annular space is left between the outside of the
ring and the upper part of the lowest stoneware pipe. The column is
nearly filled with the siliceous or granular matter, to be hereafter
described, which spreads so as to form a conical heap beyond the under
side of the ring, but does not rise so as to fill the annular
space. There
are holes H, H, as heretofore recommended by me, five are preferred, in
the sides of the column, where the annular space is. Into one of these a
pipe is fitted, to lead the sulphurous or other gases into the column; the
rest of the holes are closed by stoppers, which I prefer to make of the
same material as the column, and which are fitted closely into them. By
removing these stoppers some of the conical surface of sand can be raked
out if it becomes clogged with sublimed sulphur or dust, which might

page_text: prevent the gas from passing freely through it. In the upper pipe or
cylinder, just above the surface of the sand, I prefer to have a similar set
of holes I, I, into which plate glass may be cemented, so that the gases
which are drawn through the sand may be seen, and from one of these
holes there is a pipe J, whereby the gases are drawn out of the column.
This upper pipe of the column is covered with a plate K, K, pierced with
a number of large holes, into which pieces of porous material k, k, are
cemented; their under sides are conical, so as to carry off the drops of
liquid; or, instead of this filtering plate, the upper pipe, when not too
large, may be covered with a plate, as heretofore made by me, entirely
of porous material, and having on its under side small pyramidal pro-
jections to carry off the drops. By these means the liquid is made to fall
equally all over the surface of the sand. I make the filtering plate K, K,
just so porous that the liquor shall drop through as fast as may be re-
quired without accumulating on the upper surface. The upper side of
the filtering plate is covered in the usual way with very fine silicious sand,
to prevent any impurities in the liquor from choking the filter itself,
and to spread the liquor equally to all parts, and by its fineness and
quantity the porosity of the filter can be adjusted to the right degree.
There is a hole in the middle of the filtering plate, with a collar around it,
standing higher than the surface of this sand; through this hole the other
sand which fills the column can be poured in whenever needed. Over
the filtering plate is cemented a conical stoneware cover L, in the centre
of which is a hole, covered with a piece of plate glass M, ground to fit
it air-tight, and in the centre of this plate glass there is a hole, into which
a glass funnel N (with a tube extending downwards from it) is ground to
fit air-tight. These air-tight parts are preferred to be ground so as to
have what is known as the patent spherical surface, which fits closely, even
if it be not put on with accuracy. This funnel N is trapped by dipping
into a deep cup or tube which rests in another which hangs by a flange
upon the collar of the hole in the filter plate; the flange has its outer
edge sloping downwards, so that the liquor shall drip from it. The collar
is not quite flat around its upper edge, but notched, so that gas can pass
thereby from the upper side of the filter to its under side. These arrange-
ments will be better comprehended by my stating their object, namely,
to exclude atmospheric air from the upper surface of the filter, whence
it might be drawn through the pores of the filter, to prevent inequality
of atmospheric pressure on the upper and under surface of the filter, and
to cause to pass into the column the gases generated on the upper surface
of the filter; also to admit of liquor being supplied to the filter without
atmospheric air being drawn in through the same opening. All the

page_text: parts are arranged so that they can be removed and cleaned or repaired
without difficulty. 1 prefer to have these small articles made of glass.
I improve the granules with which the column is filled by giving them a
rough surface like ground glass in the course of manufacture; in other
respects they should be as I formerly used them, namely, of a quality not
acted on by the acids, the grains of a rounded form, of solid material,
as silex or solid carbon, such as that which concretes in gas retorts (not
porous, as ordinary coke or pumice), and of nearly equal size; that is, it
is desirable to have the larger grains not more than double the diameter
of the smaller; but the more equal they are the more porous the mass is,
and the better it is in other respects. The grains should be as small as
is compatible with their interstices, not being so much filled up with the
liquor which passes through them as to diminish materially the rate at
which the gases would be drawn through the sand by means of the same
force of suction if no liquor were percolating through the sand. The
actual size of the grains for this object will depend on the height of the
columns, and many other circumstances, but to of an inch in
diameter is the size I prefer for an apparatus of an ordinary size; silicious
sand having the above properties sufficiently may be found already exist-
ing in some places, and needing only washing, and sifting when dry;
but as an alternative, I use globules of sulphur or glass (glass containing
but little alkali being preferred) coated with a rough surface made by the
adhesion of suitable powder or grit, such as carbon dust, or fine silicious
sand.
My method of attaching this powder, and of producing roundness in the
globules, is to take the coarsely crushed sulphur or glass, double sift it to
get rid of all the grains that are too large or too small, mix the product
with so much of the said powder that the grains shall be well separated
by it, and heat it slowly to a heat sufficient to fuse the grains, let the mass
cool, and double sift it again. Or I use globules of solid carbon, formed
by long continued mechanical attrition, (by means which, being publicly
known, need not be described,) of grains of crushed carbon (such as that
which concretes in gas retorts); or they may be formed by subjecting
small nuclei, such as grains of carbon, or of silicious sand, whether angular
or rounded, to the action of very hot gas charged with carboniferous
matter, in the manner in which it often is in gas retorts, and keeping
the nuclei in motion, as, for instance, by stirring or by shaking them, or
raising them and letting them fall repeatedly, so as to secure an equable
concretion of hard carbon all around them, until they have become
sufficiently rounded and of the required size.
In some cases, instead of exposing a liquid surface on the irregular and
discontinuous surfaces of grains of sand or divided matter, as in the

page_text: columns just described, I expose it on planes or continuous surfaces, such
as have hitherto been slightly used, but improved, as hereafter explained.
They may be flat and rectangular, placed one under another, so that the
liquor shall fall from one to the other of alternate ends or sides, as already
practised, but with a rough though flat surface, similar to a surface of fine
sand, and with the under side slightly sloping downwards from the end
over which the liquor runs, so that a film of liquor shall continue gliding
all over the under sides of the plates as well as on their upper sides. But
I improve this arrangement yet further by making the plates O, O, and
P, P, circular, as in Figure 2, and so constructed that both the liquid and
the
gas shall pass
from one plate to another by radiating alternately from
and to the centres of the successive plates, (as shewn by the arrows; those
indicating an upwards direction represent the course of the gas, and the
others the liquor.) These plates are fixed as closely one over another as
will only allow sufficient room for the liquor and gas to pass freely, and
they are formed (as will be understood by examining Figure 2) so that
the rim around the edges of alternate plates P, P, resting upon the blocks
p, p, shall form by themselves the exterior of the column, and leave the
necessary air passages between the rims of these plates and the smaller
rims of the intermediate plates. The holes in the centre of those plates
O, O, through which the gases do not pass, I prefer to make of equal size
with the centre holes in the other plates, and to place stoppers or discs
Q, Q, notched in such manner around their edges that the liquor can
pass down around them.
Either form of column already described, Figure 1 or Figure 2, may be
used in many ways to produce sulphuric acid either with or without
connection with the ordinary leaden chambers; but where the draught or
power of suction at the vent is weak, as may be the case where the gases
are made to pass through leaden chambers after leaving the column, the
column shewn in Figure 2 is preferable.
Where the chambers act a subordinate part, or where the columns are
used without connection with chambers, in the making of sulphuric acid,
I prefer to use such columns and their contents as are described in Figure
1, and I arrange them in the following manner:-The sulphurous gas
(from the furnace or other source) is led through a small leaden chamber
of the ordinary construction, and so arranged as to facilitate the deposition
of
any sublimed sulphur or dust. The gas is made to pass thence through
the columns in the following manner (see Figure 3) by suitable pipes R, R,
of stoneware or such material into the lower parts of the columns D, d.
In passing through these the gas becomes nitro-sulphurous, and is united
from the upper parts of D and d, and led similarly through the columns
C, C, and thence as nitrous gas almost without sulphurous through the

page_text: column B, and thence as air only feebly nitrous through the column b
upwards, whence it is drawn as mere air partly exhausted of its oxygen,
and passes into the atmosphere by a strong power of suction, which may
be produced in various ways, which are publicly known, such as a strong
chimney draft, or by a fall of broken water spray down a shaft or tube,
or by air bells moved by power, or by other means, herein-after described;
at the same time liquors percolate through the columns in the following
manner: From a reservoir strong sulphuric acid about 1'65 (specific
gravity) is made to percolate slowly through b, whence it issues charged
with a little nitrous gas, and is led by a shoot S to percolate through d,
whence it is led as denitrized acid into a reservoir, whence it is carried
back (by any of the means well known in manufactories of acid) into the
reservoir which runs into b, again mixed, if necessary, with a little of other
acid to keep it of the proper strength. A register or tap is fixed in the
pipe leading into or out of d, to regulate the proportion in which the gas
is divided between D and d, so that only just so much gas shall pass
through das will suffice to eliminate nearly all the nitrous gas from it.
Water is made to percolate through B, whence it issues as weak nitric
acid, and is led by shoots to percolate in equal quantities through C, C,
which are similar in their structure and in the chemical actions within
them, only there are two of them by preference, because a portion of the
liquor which flows from them is carried back and made continually to
return through them, as will be described, and therefore a double
sectional area of sand is desirable to prevent so much liquor from choking
the draught of the gas through the sand. From C, C, the liquor issues
as nitro-sulphuric acid, and a portion of it (equal in bulk to what comes
from B into C, C,) percolates through D, whence it issues as sulphuric
acid, (free from nitric acid, or its lower degrees of oxidation.) This
sulphuric acid is then concentrated, if wanted stronger, by means of the
usual apparatus, or by a process likewise known, the percolating of it
through a suitable column (made like those above described, only in a
manner that will not be injured by the heat,) with sufficiently heated air
or other suitable hot gases drawn upwards through it. The water made
to run into B has, by preference, a little acid from C, C, mixed with it,
just sufficient to prevent the gases drawn through it from evaporating it
so much as to make the acid in b to become too weak, also to prevent the
said water from freezing in cold weather. This water is made to run so
slowly into B, that the sulphuric acid shall come from D of a sufficient
strength and properly denitrized, but the flow of water must not be so
restricted as to hinder the proper condensation of the gases in C, C, and
B. The desirable specific gravity for the sulphuric acid produced from D

page_text: is 1'4 to 15, but a greater gravity may be obtained by diminishing the flow
of water, and keeping the draught of gas so moderated as to ensure its
condensation.
The liquor from each of the columns C flows from the outflow pipe E
(Figure 1) into a cup or hollow formed in the end of a shoot T (Figure 4),
as described in speaking of Figure 1. These shoots from each of the
columns C lead the liquor into a reservoir or stock of liquor, whence it
flows into column D; but I contrive the reservoir and its appurtenances
so that the liquor which enters it is made to displace other liquor already
in it, instead of the entering liquor passing into D more directly through
or over the stock in the reservoir. By this arrangement I preserve the
nitrous character of the liquor in the upper part of D and lower part of C,
and I am able to examine and to increase or renew the nitric acid there,
so that the section of maximum chemical action shall not be able to shift
its position, as it would tend to do by degrees, either by rising or falling
in the columnar mass.
I sometimes divide the stream of liquor from a column acting as C into
two branches, the one running into a column acting as D and the other
into a reservoir, and to be returned into a column above, so that the
proportion passing into D can be regulated to produce the best result;
while any desirable rate of flow can be maintained through C without
disturbing the proper action of D.
The means which I usually adopt for effecting these two several objects
are as follows:-The liquor from C, C, is led into a shelf or circular
trough U, U, U, (Figure 4 and Figure 4*,) formed around the internal
upper part of the vessel or reservoir V. An overflow lip W is made in the
side of the vessel close to where the liquor falls into the trough U, and
the liquor from the lip is led into the reservoir (not shewn), whence it
is carried back into a reservoir placed so high that the liquor can run
from it into C, C, again. The shelf U is pierced with fine holes over parts
not near to where the liquor falls into it, and sand is placed in the trough
to form a coarse filter. There is a circular hole X through the shelf or
bottom of this trougn, with a collar around it, to keep the sand in the
trough. Into this hole is put a tube Y, extending half way down the
reservoir V, or else having holes pierced at the level of the middle part
of the reservoir. Into this tube is put one leg of a syphon Z, arranged
so that it can be moved up and down, and made to stand at any desired
height within the limits of a few inches, so that the rate of flow of liquid
through it can be properly adjusted. This may be effected by various
means, for instance, the syphon may pass through a cork fixed on the top
of the tube Y. The syphon is preferred to be of glass tube; it is of so

page_text: small a bore that any air bubbles that may come into it may be carried
out of it again by the velocity of the liquid flowing through it, and its
inlet end is contracted slightly to prevent any solid matter from entering
which will not be carried out of it by the flow of liquid, and its outlet end
is bent up and terminates at a little higher level than its inlet, and drops
its liquor into a shoot which carries it into the top of column D.
The chief use of the reservoir V is to steady the action, so that any tem-
porary want of nitric acid in the liquor from C, C, shall not alter the
processes in D; any change in the character of the liquor flowing into V
will not be felt in D until at least half of the contents of V have flowed
out, and if, after that interval of time, any deficiency of nitric acid is
discovered on testing the liquor, the requisite quantity of strong nitric
acid can be poured into V; the liquor displaced will flow off by the lip,
and then the whole body of liquor in V can be mixed together by stirring.
Without these arrangements the sites or strata of the various chemical
actions along the whole course of the gas through D, C, C, and B, how-
ever perfectly they might continue to go on, would be liable to shift
en masse slowly to a higher or a lower level in the columns, and thus
at last cause either nitrous gas to appear at the vent, or nitrous liquor at
the outflow of the sulphuric acid
If the overflow of liquor by the lip W is fully kept up, equal, for
instance, to the regular flow into D, then the reservoir V need not be
larger than is necessary to contain the syphon and some sort of strainer
or filter, and any nitric acid needed may be supplied to the reservoir
which receives the overflow; or if the reservoir V be made, as previously
described, full sized, then the overflow may be dispensed with, but in
this case the apparatus will not be able to produce acid quite so fast.
Whenever in this apparatus liquor has to flow from a reservoir into the
top of any of the columns, I use the arrangement of a syphon constructed
as I have described, and marked Z, and capable of being raised or
lowered to adjust the flow of liquor, and a filter or strainer for the liquid
before it enters the syphon. In all the reservoirs I prefer to make the
strainer in the bottom of a small tube like Y, and I make in the bottom
of the reservoir a pocket, into which the tube containing the leg of the
syphon is placed, so that the increased hydrostatic pressure so obtained
will prevent the rate of flow from being much affected by variations in
the height of the liquor in the reservoir.
As it is of great importance to have the proper temperatures in the
several parts of my apparatus, I place the columns in such positions as
to make the pipes between them to be as short as may be to prevent
undue cooling of the gases, and for the same reason I clothe the pipes

page_text: and the columns to such extent as their size and position and the weather
render needful to keep their parts at those temperatures which are known
to promote best the desired chemical actions; and, on the other hand,
in apparatus of large size and working actively; it will sometimes be
desirable to prevent undue accumulation of heat at some parts (especially
in C, C), this may be done in many ways, as by leaving parts of the
columns and pipes unclothed and by lengthening the pipes.
It will be seen that the operation of the above is to keep up a con-
tinuous and uniform action, maintaining the nitric acid chiefly in the
middle or producing columns C, C, by the sulphurous gas carrying it
upwards in a gaseous state, it being changed into nitrous and other
nitrogenous gases as fast as it percolates in a liquid form into the lower
column D, and, on the other hand, making the aqueous liquid (in the
upper column B) condense and bring downwards back into C, C, in a
liquid state as nitric acid that which has risen in a gaseous form out of
the upper part of the nitrous or condensing columns C, C, so that the
nitric acid is retained in the middle portion of the apparatus in as great
abundance as may be so as to act catalytically as an oxydator to the
sulphurous gas, without its being wasted (and needing replenishing) by
escaping in a liquid form along with the sulphuric acid produced, and
which flows out at the bottom of the lower column, or escaping in a
gaseous form along with the nitrogen and carbonic acid of the atmosphere
which are drawn out at the vent of the upper part of the apparatus.
The apparatus already described is susceptible of various modifications;
thus, any of the columns which I have described as being placed one above
another may be placed at any other relative levels, and the liquor from
one may then be raised up again to flow in the other; but this is dis-
advantageous in several ways.
In column 6 other liquids or solutions (such as a solution of sulphate of
iron) may be used instead of strong sulphuric acid; I do not limit myself
to the use of sulphuric acid in 6 and d. Water or weak acid may be
introduced into the top of d through an additional trap to hasten the
disengagement of the nitrous gas, and the liquor flowing from d will then
need to be concentrated again before it returns to b.
Column d may be dispensed with, and the liquor from 6 may be led into
D by an additional trap; column B may be supplied with steam instead
of water, and in this case the gases must be worked downwards through
B instead of upwards; this ensures the requisite warmth to promote the
chemical action in B, and the gases leaving the lower part of B (where
there is acid in its liquor) do not carry moisture into b.

page_text: Columns b and d may be dispensed with, but in most cases it will be at
the risk of losing some nitrous gas.
B and C, C, may be united as one column, with or without returning
liquor C into the top of B.
Column B, with or without column b, may be very well used for con-
densing various gases, especially compounds of oxygen and nitrogen,
and for oxydizing them more highly, to make, for instance, nitric acid,
in the manufacture of nitric acid itself, or in any manufacturing process,
as that of refining gold, &c., in which nitrous or some other gases are
evolved and cause waste and nuisance.
The foregoing improvements in the columns, so far as they relate to
the construction of the fittings and contents of an individual column,
may be employed either singly or more or less unitedly in many ways
besides those which I have now described, for instance, as a substitute for
columns of inferior construction already in use, or known in particular
modes of manufacturing sulphuric acid; I employ them also in the con-
densation or manufacture of nitric, nitrous, and hydrochloric acids, how-
ever produced, either by making the gases to pass through one or more
of these improved columns, either kept cool or left to lose their
temperature by natural radiation and convection, so as to condense warm
nitric or hydrochloric vapours without further oxydation, or supplied or
not with water, acid liquor, or steam, according to the known require-
ments of the gases employed. I also employ them in the manufacture
of oxalic acid, by using them to oxydize and condense the waste nitrous
gas arising in that process, and bringing the nitric acid thus formed back
again to act as at first in the formation of a fresh lot of oxalic acid.
I obtain the requisite draught from the vent by any of the well-known
means, but when the ordinary means are not desirable or not powerful
enough, I use either of the following Inventions, which I also adapt when
desirable to the vent pipe of any columns or chambers (for condensing
or producing acids) other than the apparatus already herein described.
First, to increase the power of an existing draught, I make use of a
series of what are termed venæ contractæ, (Figure 5); that is to say, the
end of the vent pipes A is made as small as will admit the gases to pass
without materially checking the draught, and is inserted concentrically
into a short pipe B, called a vena contracta, being gradually contracted
from each end towards its middle, where the end of A is fixed. This
vena contracta is similarly inserted into another of larger dimensions C,
and so the series may be increased, and the largest pipe which encloses
all the others is fixed into the side of the chimney, or applied to whatever

page_text: draught is available, which is in this way made to produce a greatly in-
creased force of draught at the vent pipe A. Suitable proportion of the
parts are indicated in the Figure 5. The venæ contractæ here described
and pipes may of course be very much modified in form, square or round
in section, and contracted in one direction only, instead of, as I prefer,
in both dimensions of their cross section.
Or, second, I increase an existing draught by means of what I call a
pneumatic ram, Figure 6. This consists of a large pipe D, preferred to
be straight, having one end connected with the chimney, or whatever the
available means of draught may be, and the other end trumpet-mouthed,
having a very light valve E hung so as to cover it and to open outward,
and so balanced by a weight F placed close to the hinge as that the
draught shall cause it to beat continuously. Close to this end of the pipe
D there is a valve, which I prefer to make in its under side, and in the
following manner; a number of holes G, G, G, are made in the side of the
pipe D, and over them a thin sheet of vulcanised caoutchouc is fastened
by its opposite ends so as to form a valve, and a perforated plate H is fixed
over it so close to it as not to let it rise farther from the holes than is
useful to allow the air to pass moderately freely into the pipe D; these
holes communicate with a large air vessel I. The action of the ram will
cause the air to be drawn with greatly multiplied force out of the air
vessel, and the vent pipe from the columns is connected with the air vessel
I. A very suitable length for the pipe is 1000 times the height which
the available draught will raise water.
This sapparatus may be constructed with a great variety of modifications
without altering the essential properties of this part of my Invention;
and I would observe, that where I mentioned nitrous gas or nitric acid I
do not mean to limit myself to the improvements when that particular
gas is used, but to include the alternative of using nitrogen compounded
with other proportions of oxygen, or of using any other volatile oxydator
that may be desired.
In witness whereof, I, the said William Petrie, have hereunto set my
hand and seal, this Seventh day of March, One thousand eight
hundred and fifty-seven
WILLIAM PETRIE. (L.S.)