IMPROVEMENTS IN THE MEANS AND APPARATUS FOR EFFECTING THE PURIFICATION OR FILTRATION OF WATER, SEWAGE AND OTHER IMPURE LIQUIDS.”
Year: 1879

page_text: LETTERS PATENT to Gustav Bischof, of No. 1, Hart Street, Bloomsbury, in the
County of Middlesex, for the Invention of "IMPROVEMENTS IN THE MEANS
AND APPARATUS FOR EFFECTING THE PURIFICATION OR FILTRATION OF WATER,
SEWAGE AND OTHER IMPURE LIQUIDS.”
PROVISIONAL SPECIFICATION left by the said Gustav Bischof at the Office
of the Commissioners of Patents on the 29th May 1879.
GUSTAV BISCHOF, of No. 4, Hart Street, Bloomsbury, in the County of Middlesex.
"IMPROVEMENTS IN THE MEANS AND APPARATUS FOR EFFECTING THE PURIFICATION
OR FILTRATION OF WATER, SEWAGE, AND OTHER IMPURE LIQUIDS."
One part of iny Invention refers to the application of spongy iron for filtration
on a large scale, such as is required by waterworks, and for the purification of
sewage and similar impure liquids. The solid or suspended impurities contained in
sewage should preferably be separated by any of the known methods previous to
the filtration through the spongy iron filter hereinafter described.
In constructing filters on a large scale for the purposes mentioned above I first
form a proper substratum for the layer which is to contain the spongy iron. To
this end I place on the perforated bottom of an ordinary filter bed, such as is
commonly used in water works, a layer of moderately fine gravel, employing by
preference such as has been passed through a sieve with about four holes on the
square inch, or should the construction of the perforated bottom not permit of this
I place underneath such gravel and on to the perforated bottom one or more layers
of shells or gravel of larger size until a proper bed has been obtained on which the
gravel may rest which is to form the substratum to the layer containing spongy
iron. On the top of such substratum I place a layer, by preference about three
feet thick, of a mixture of about one volume of spongy iron to three volumes of
gravel; the latter material should preferably have been passed through a sieve
with about four holes on the square inch; the spongy iron may be slightly coarser.
Instead of mixing the spongy iron with gravel it may be mixed in the same
proportion and under similar conditions as to size with coke or any other inerţ

page_text: matter which is not affected or altered by the filtration of water. Finally, I place
on the top of the mixture of spongy iron and gravel or other material a layer of
fine sharp sand, such as the well known "Harwich" sand, or according to the
condition of the water to be filtered several layers of sand, gradually increasing in
fineness towards the top, may be employed.
Whenever the greatest possible purity and brightness is desired the water or
other liquid should after filtration through the spongy iron filter, as herein before
described, be subsequently passed through a sand filter arranged in a similar
manner as is usual in water works where filtration through sand is employed.
The object of the sand filter in connection with the filter which contains the spongy
iron is hereinafter explained.
Although I have stated herein before and shall state hereinafter several pro-
portions, dimensions, and sizes, and although these will generally answer the
purpose, I wish it to be understood that I do not limit myself to these, as they
are only given by way of example and may be varied as circumstances may
require.
In order that the nature of my improvements may be more readily understood,
and to enable any one conversant with such matters to introduce such variations as
may be required himself, I will proceed to state the considerations upon which the
before described arrangements are based.
1st. The object of using spongy iron as a purifier of water is to effect the
decomposition or otherwise separation by chemical affinities of those impurities in
water or other liquids which cannot be separated by ordinary mechanical means,
such as filtration through sand. Mechanical filtration being thus not the primary
nor the more important object of filtration through spongy iron, the layer containing
this medium should be so arranged as to allow the water to percolate comparatively
speaking freely, in order to prevent, as far as possible, any liability to choking.
As the spongy iron itself is apt to increase in bulk when water is passed through
it, owing to oxidation, I counteract the liability to choking which might thereby
arise by mixing the spongy iron with some such inert matter as gravel in the manner
hereinbefore explained. The proper contact between the spongy iron and the
liquid to be filtered should nevertheless be secured by regulation of the valves or
stopcocks in connection with the exit pipes from the filter or filters. A volume of
water equal to the bulk of spongy iron in a filter may be passed through in about
45 minutes, or if the sizes and dimensions hereinbefore explained be adhered to
150 gallons per square foot of filtoring area in 24 hours is about the proper yield of
the spongy iron filter when purifying a water of the quality of Thames water for
domestic uses. The valves should likewise be so regulated that the layer of spongy
iron after it has once been wetted remains as far as practicable always covered with
water, alternate exposure to air and water causing too rapid an oxidation of the
metallic spongy iron.
2nd. Although as hereinbefore explained mechanical filtration is not the object
of the employment of spongy iron provision must be made to remove also the solid
or suspended impurities. These, as far as they may not have been separated from
the water or other liquid by any previous treatment, such as subsidence, pre-
cipitation, or otherwise, should be retained by the layer of fine sand on the top of
the mixture of spongy iron and gravel, so as to prevent those impurites from mixing
with, contaminating, or choking the spongy iron itself. It will be understood that
the upper portion of the top layer of fine sand may be scraped off, washed, and
replaced, as is usual, whenever required.
3rd. On filtering water or other liquid through spongy iron a minute portion of
iron is dissolved, probably as ferrous hydrate or carbonate. Both these compounds
are readily oxidised when they come in contact with oxygen, as explained in my
Specification No. 2516 of 1870. The separation of the ferric hydrate then formed
has hitherto been a difficulty in applying the spongy iron process to large filters. If
water be passed through a layer of spongy iron even only a few inches in thick-
ɲess which is not mixed with gravel or similar material the oxygen dissolved in

page_text: the water may be completely abstracted by agency of the metallic spongy iron. If
this is the case the soluble proto-compounds of iron referred to above do not meet
with oxygen in the filtered water, nor can they be oxidised or rendered insoluble
until the water has again, after filtration through spongy iron, taken up oxygen by
exposure to the air, or by such artificial means as is explained in my Specification
No. 2080 of 1876. These soluble proto-compounds of iron would therefore in a
filter containing spongy iron without any admixture have to be subsequently
separated by subsidence or filtration, both of which are apt to interfere with the
regular working of the system of filtration.
However by mixing the spongy iron with gravel or other matter, essentially in
the manner hereinbefore explained, the effluent water from the spongy iron filter
may readily be made still to contain sufficient oxygen to more or less completely
oxidise the proto-compounds of iron herein before referred to, which are thus
retained more or less completely within the spongy iron filter itself. The deposit
of ferric hydrate thus formed in the spongy iron filter scarcely at all interferes, for
a long time at least, with the free percolation of the water; from time to time it
may be removed by washing in the ordinary way. Nevertheless whenever extreme
purity is an object I prefer passing the effluent water from the spongy iron filter or
filters through the sand filter hereinbefore referred to, so as to have an additional
surety that the iron shall be efficiently separated from the filtered water. In
combining such a system of filters containing spongy iron mixed, as berein before
explained, with another system of filters containing sand, the former should
preferably be on a higher level than the latter, so that the water may pass through
the two filters by gravitation. The uppermost portion of the sand filter requires
much less frequent renewal or washing if the spongy iron filter be constructed as
hereinbefore explained than if the effluent water from the spongy iron filter were
deprived of oxygen in solution, as in the former case very little ferric hydrate,
comparatively speaking, has to be retained by the sand filter. It will thus be
understood that in the manner indicated both the spongy iron filters and the sand
filters in connection therewith do not offer any such practical difficulties to their
application on a large scale as before the discovery of the improvements which form
the part of my Invention herein before explained.
Another part of my Invention refers to the application of spongy iron to smaller
portable filters, such as are commonly used for the purification of water in private
houses, hospitals, and the like.
When regulating the flow of water in the manner indicated in my Specification
No. 2243 of 1874, it sometimes happens, apparently if the water to be filtered be
very hard, that the small regulator hole n (see Drawing annexed to the Specification
I have
referred to) is choked and cannot, at least without some trouble, be cleared;
therefore improved the regulator arrangement explained in the above Specification
by making the pipe d of two separate pieces, one of which is screwed into the
other. Supposing the two pieces to be screwed together the inner end of the pipe
is cemented or otherwise made tight in the pocket 6', as shewn in the Drawing
referred to. The other end, which projects outside the filter case, is provided with
a flange corresponding to a neck on the filter. By placing between the flange and
neck an india rubber washer a water tight joint is made between the tube and the
filter case.
The joint in the pipe being in such a position that the opening n is on
that portion which can be withdrawn from the filter by unscrewing, it will be seen
that this opening is made readily accessible, and may be cleared whenever required
with a fine needle, after withdrawing it from the filter.
Another improvement refers also to the construction of portable filters. The
spongy iron after it has once been wetted should as far as practicable always remain
covered with water. In the portable filters herein before referred to this is mostly
provided for by some such arrangement of an inner vessel with overflow pipe as is
described in my Specification No. 38 of 1873. In some instances I find it however
preferable to accomplish this by the following arrangement, which at the same time
is a novel and improved way of effecting the regulation of the passage of water

page_text: through the filter. The filter case of stone-ware or other material is provided at a
convenient distance above its bottom with a perforated bottom, the space between
the two bottoms serving as a receptacle for the filtered water. On the top of the per-
forated bottom I place the several materials, gravel, sand, pyrolusite, and spongy iron,
referred to in my Specification No. 2080 of 1876. At a certain distance below the
top of the filter case and on a level with the top of the spongy iron I provide the
filter case with an inner rim fitted watertight to the sides of the case, so as to leave
in the centre an opening of convenient size, through which the hand may be
introduced; when charging, discharging, or cleansing the filter this opening can be
closed air and water tight by a plug covered by an india rubber ring or by other
means. The space in the filter case above the rim should be of such capacity as to
allow a sufficient storage of unfiltered water. The rim hereinbefore referred to is pro-
vided about an inch from the filter case with a small hole bored through the material
which forms the ring. Supposing the plug has been made airtight this hole would
form the only communication between the receptacle for unfiltered water and the
parts of the filter below the rim. Into this hole I cement a tube of glass or metal of a
regulated diameter, the upper projecting end of which should be perfectly smooth.
A lever turning with one end in suitable bearings and provided at the other end
with a float of glass or other material is so arranged as to press an india rubber
valve against the upper end of the tube, and thus shut off the communication
whenever the unfiltered water above the rim is becoming exhausted by the passage
through the filter, the communication being opened again by the rising of the float
as soon as fresh unfiltered water is introduced; it is therefore evident that after
once starting a filter the spongy iron must always in this way remain covered with
water. Further, with a view of regulating the flow of water when there is a
sufficiency of unfiltered water in the top part of the filter I attach to the lever
above referred to, on the principle of a ball and socket joint, a small metallic rod or
wire, so situated that its lower end may slide up and down in the tube as the float
rises or falls. The annular space between the rod or wire and the tube is so
regulated as to allow under the condition of prossure and friction in the filter only
the passage of a certain quantity of water within a given time, thus regulating the
flow of water through the filter. Should that annular space become choked by sus-
pended impurities in the water it is at once readily cleansed by depressing the lever
a few times, so as to move the rod up and down in the tube.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Gustav Bischof in the Great Seal Patent Office on tho 28th November
1879.
GUSTAV BISCHOF, of No. 4, Hart Street, Bloomsbury, in the County of Middlesex,
"IMPROVEMENTS IN THE MEANS AND APPARATUS FOR EFFECTING THE PURIFICATION
OR FILTRATION OF WATER, SEWAGE, AND OTHER IMPURE LIQUIDS."
One part of my Invention refers to the application of spongy iron for filtration
on a large scale, such as is required by water-works, and for the purification of
sewage and similar impure liquids. The difficulty of applying spongy iron to those
purposes has hitherto been twofold; first, the liability of spongy iron to choking,
owing mainly to the increase in bulk when the spongy (metallic) irou is oxidised
by agency of the atmospheric oxygen dissolved in the water to be filtered; and,
second, the separation of the ferric hydrate, which is formed by oxydation of the
ferrous hydrate or carbonate, both of which are mostly dissolved by water when
passing through spongy iron. These difficulties I remove in the following way :-
In constructing filters on a large scale, for the purposes mentioned above, I first
forn a proper substratum for the layer which is to contain the spongy iron; to this
end I place on the perforated hottom of an ordinary filter bed, such as is commonly
used in water-works, a layer of moderately fine gravel, employing by peference
such as has been passed through a sieve with about four holes on the square inch,
or should the construction of the perforated bottom not permit of this, I place
underneath such gravel, and on to the perforated bottom, one or more layers of
shells or gravel of larger size until a proper bed has been obtained on which the
gravel may rest which is to form the substratum to the layer containing the spongy
iron. On the top of such substratum I place a layer, by preference about three feet
thick, of a mixture of about one volume of spongy iron to three volumes of gravel.
The latter material should preferably have been passed through a sieve with about
four holes on the squaro inch; the spongy iron may be slightly coarser. Instead of
mixing the spongy iron with gravel, it may be mixed in the same proportion and
under similar conditions as to size with coke or any other inert matter which is
not materially affected or altered by the filtration of water. Finally, I place on
the top of the mixture of spongy iron and gravel or other material a layer of fine
sharp sand, such as the well known "Harwich" sand; or, according to the condition
of the water to be filtered, several layers of sand, gradually increasing in finensss
towards the top, may be employed.
When filtering sewage or similar impure liquids, the solid or suspended im-
purities contained in then should preferably be separated by any of the known
methods previous to the filtration through the spongy iron filter hereinbefore
described.
Whenever the greatest possible purity and brightness is desired, the water or
other liquid should, after filtration through the spongy iron filter, as hereinbefore
described, be subsequently passed through a sand filter arranged in a similar
manner as is usual in water-works where filtration through sand is employed.
Although I have stated herein before and shall state hereinafter several propor-
tions, dimensions, and sizes, and although these will generally answer the purpose,
I wish it to be understood that I do not limit myself to these, as they are only
given by way of example, and may be varied as circumstances require.
In order that the nature of my improvements may be more readily understood,
and to enable any one conversant with such matters to introduce such variations as
may be required himself, I will proceed to state the considerations upon which the
beforedescribed arrangements are based.
1st. The object of using spongy iron as a purifier of water is to effect the
decomposition or separation, by chemical affinities, of those impurities in water or

page_text: other liquids which are either in a state of solution or too minuto in size to be
separated by ordinary mechanical means, such as filtration through sand, ordinary
mechanical filtration being thus not the primary nor the more important object of
filtration through spongy iron; the layer containing this medium should be
so arranged as to allow the water to percolate, comparatively speaking, freely, in
order to prevent as far as possible any liability to choking. As the spongy iron
itself is apt to increase in bulk, as hereinbefore explained, I counteract the liability
to choking which might thereby arise by mixing the spongy iron with some such
inert matter as gravel in the manner herein before explained. The proper contact
between the spongy iron and the liquid to be filtered, upon which contact the
chemical action of the spongy iron depends, should be secured by regulating the
valves or stopcocks in connection with the exit pipes from the filter or filters. A
volume of water equal to the bulk of spongy iron in a filter may be passed through
in about 45 minutes, or, if the sizes and dimensions hereinbefore explained be
adhered to, 150 gallons per square foot of filtering area in 24 hours is about the
yield of the spongy iron filter when purifying a water of the quality of Thames
water for domestic use. The valves should likewise be so regulated that the layer
of spongy iron, after it has once been wetted, remains, as far as practicable, always
covered with water, alternate exposure to air and water causing too rapid an
oxydation of the metallic spongy iron.
2nd. Although, as hereinbefore explained, mechanical filtration is not the object
of the employment of spongy iron, provision must be made to remove also the solid
or suspended impurities. Thesc, as far as they may not have been separated from
the water or other liquid by any previous treatment, such as subsidence, precipita-
tion, or otherwise, should be retained by the layer of fine sand on the top of the
mixture of spongy iron and gravel, so as to prevent those impurities from mixing
with, contaminating, or choking the spongy iron itself. It will be understood that
the upper portion of the top layer of fine sand may be scraped off, washed, and
replaced, as is usual in the case of ordinary sand filters, whenever required.
3rd. On filtering water or other liquid through spongy iron, a minute quantity of
iron is dissolved, probably as ferrous hydrate or carbonate. Both these compounds
are readily oxydised when they come in contact with oxygen. The separation of
the ferric hydrate then formed has, as above referred to, hitherto been a difficulty
in applying the spongy iron process to large filters. If water be passed through a
layer of spongy iron, even only a few inches in thickness, which is not mixed with
gravel or similar material, the oxygen dissolved in the water may be completely
abstracted by agency of the metallic spongy iron. If this is the case, the soluble
proto-compounds of iron referred to above do not meet with oxygen in the filtered
water, nor can they be oxydised or rendered insoluble until the water has again,
after filtration through the spongy iron, taken up oxygen by exposure to the air,
or by artificial means. These soluble proto-compounds of iron would, therefore, in
a filter containing spongy iron without any admixture, have to be subsequently
separated by subsidence or filtration, both of which are apt to interfere with the
regular working of the system of filtration, as the ferric hydrate is very fine and
slimy, and therefore does not subside readily, and if to be separated by filtration
greatly chokes the filter or filters used for that purpose.
However, by mixing the spongy iron with gravel or other matter, essentially in
the manner hereinbefore explained, the effluent water from the spongy iron filter
may readily be made to contain sufficient oxygen to more or less completely
oxydise the proto-compounds of iron herein before referred to, and the ferric hydrate
thus formed is then retained, more or less completely, within the spongy iron filter
itself, forming a coating over the porous material of which this filter is composed,
without interfering, for a long time at least, with the free percolation of the water.
The deposit of ferric hydrate may from time to time be removed in the ordinary
way by washing. Nevertheless, whenever extreme purity is an object, I prefer
passing the effluent water from the spongy iron filter or filters through the sand
filter hereinbefore referred to, so as to have an additional surety that the iron shall

page_text: be efficiently separated from the filtered water. In combining such a system of filters
containing spongy iron mixed as hereinbefore explained with another system of filters
containing sand, the former should preferably be on a higher level than the latter, so
that the water may pass through the two filters by gravitation. The uppermost
portion of the sand filter requires much less frequent renewal or washing if the
spongy iron filter be constructed as herein before explained, than if the effluent
water from the spongy iron filter were deprived of oxygen in solution, as in the
former case very little ferric hydrate, comparatively speaking, has to be retained by
the sand filter. It will thus be understood that in the manner indicated both the
spongy iron filters and the sand filters in connection therewith do not offer any
such practical difficulties to their application on a large scale as before the discovery
of the improvements which form the part of my Invention hereinbefore explained.
Another part of my Invention refers to the application of spongy iron to smaller
portable filters, such as are commonly used for the purification of water in private
houses, hospitals, and the like.
When regulating the flow of water in the manner indicated in my Specification
N° 2243 of 1874, it sometimes happens, apparently if the water to be filtered be
very hard, that the small regulator hole n (see Drawing annexed to the Specifica-
tion referred to) is choked, and cannot, at least without some trouble, be cleared;
I have therefore improved the regulator arrangement explained in the above
Specification, by making the pipe d of two separate pieces, one of which is screwed
into the other. Supposing the two picces to be screwed together, the inner end of
the pipe is cemented or otherwise made tight in the pocket b¹, as shewn in the
Drawing referred to. The other end, which projects outside the filter case, is
provided with a flange corresponding to a neck on the filter; by placing between
the flange and neck an india rubber washer, a water tight joint is made between
the tube and the filter case. The joint in the pipe being in such a position that
the opening is on that portion which can be withdrawn from the filter by
unscrewing, it will be seen that this opening is made readily accesible, and may be
cleared whenever required with a fine needle, after withdrawing it from the
filter.
Another improvement refers also to the construction of portable filters. The
spongy iron, after it has once been wetted, should, as far as practicable, always
remain covered with water. In the portable filters hereinbefore referred to this is
mostly provided for by some such arrangement of an inner vessel with overflow
pipe as is described in iny Specification No 38 of 1873. In some instances I find
it, however, preferable to accomplish this by the following arrangement, which, at
the same time, is a novel and improved way of effecting the regulation of the
passage of water through the filter:-The filter case of stoneware or other material
is provided at a convenient distance above its bottom with a perforated bottom,
the space between the two bottoms serving as a receptacle for the filtered water.
On the top of the perforated bottom I place the several materials, gravel, sand,
pyrolusite, and spongy iron, referred to in my Specification No 2080 of 1876. At
a certain distance below the top of the filter case, and on a level with the top of
the spongy iron, I provide the filter case with an inner rim fitted watertight to the
sides of the case, so as to leave in the centre an opening of convenient size, through
which the hand may be introduced when charging, discharging, or cleansing the
filter. This opening can be closed air and water tight by a plug covered by an
india rubber ring or by other means.
The space in the filter case above the rim should be of such capacity as to allow
a sufficient storage of unfiltered water. The rim hereinbefore referred to is provided
about an inch from the filter case with a small hole bored through the material
which forms the ring. Supposing the plug has been made air tight, this hole
would form the only communication between the receptacle for unfiltered water
and the parts of the filter below the rim. Into this hole I cement a tube of glass
or metal of a regulated diameter, the upper projecting end of which should be
perfectly smooth. A lever, turning with one end in suitable bearings, and provided

page_text: at the other end with a float of glass or other material, is so arranged as to press
an india rubber valve against the upper end of the tube, and thus shut off the
communication whenever the unfiltered water above the rim is becoming exhausted
by the passage through the filter, the communication being opened again by the
rising of the float as soon as fresh unfiltered water is introduced. It is therefore
evident that after once starting a filter the spongy iron must always in this way
remain covered with water.
Supposing the glass or metal tube above referred to be of such diameter as to
allow, under the conditions of pressure and friction in the filter, the passage of the
proper quantity of water within a given time, this would in itself be an efficient
regulation when there is a sufficiency of unfiltered water in the top part of the
filter, or, with the same object of regulating the flow of water, I attach in some
instances to the lever above referred to, on the principle of a ball and socket joint,
a small metallic rod or wire, so situated that its lower end may slide up and down
in the tube as the float rises or falls. The annular space between the rod or wire
and the tube is in this case so regulated as to allow, under the conditions of pressure
and friction in the filter, only the passage of a certain quantity of water within a
given time, thus regulating the flow of water through the filter. Should that
annular space become choked by suspended impurities in the water, it is at once
readily cleansed by depressing the lever a few times, so as to move the rod up and
down in the tube.
Having thus described the nature of the said Invention, and in what manner the
same is to be performed, I claim,—
First. The use for filter beds of a layer of filtering material composed of spongy
iron mixed with gravel or similar matter of a nature hereinbefore explained,
whereby the deposit of the whole or nearly the whole of the ferric hydrate is
effected in the filter containing the spongy iron itself, substantially as herein
described.
Second. The use, in combination with the layer of filtering medium referred to
in the preceding claim, of a superstratum of one or more layers of sand, substantially
as herein described.
Third. In domestic or portable spongy iron filters, constructing the pipe
containing the regulating hole through which the filtered water flows into the
reservoir in two parts, so arranged that the part containing the regulating hole can
be withdrawn from the filter for the purpose of clearing the hole, substantially as
herein described.
Fourth. In domestic or portable spongy iron filters, providing at the top of the
filtering medium a diaphragm or partition having a small tube or channel through
which the water to be filtered passes from the space above the diaphragm to the
space below it, such tube or channel having a valve connected to a float, so arranged
that when the unfiltered water sinks to a certain level above the partition or dia-
phragin the tube is closed, substantially as and for the purpose herein described.
In witness whereof, I, the said Gustav Bischof, have hereunto set my hand
and seal, this Twentyeighth day of November, in the year of our Lord One
thousand eight hundred and seventy nine.
ATISLAV DISCON
01

page_text: DISCLAIMER AND MEMORANDUM OF ALTERATION as proposed to
be entered by Gustav Bischof, Professor of Chemistry, of No. 4, Hart Street,
Bloomsbury, in the County of Middlesex, pursuant to the statutes in that case
made and provided.
WHEREAS Her Majesty Queen Victoria, by Her Letters Patent, under the
Great Seal of the United Kingdom of Great Britain and Ireland, bearing date at
Westminster the Twenty ninth day of May 1879, in the Forty-third year of Her
reign, did give and grant unto the said Gustav Bischof, his executors, admini-
strators, and assigns, the sole privilege for the term of fourteen years thence next
ensuing, of making, using, exercising, and vending within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Mann, the said Invention
of "IMPROVEMENTS IN THE MEANS AND APPARATUS FOR EFFECTING THE PURIFI-
CATION OR FILTRATION OF WATER, SEWAGE, AND OTHER IMPURE LIQUIDS":
And whereas in pursuance of a proviso in the said Letters Patent contained, the
said Gustav Bischof did, within six calendar months next after the date of the said
Letters Patent, cause a Specification or instrument in writing under his hand and
seal, purporting to describe and ascertain the nature of the said Invention and in
what manner the same was to be performed, to be duly filed in the Great Seal
Patent Office:
And whereas, since the filing of the said Specification, I, the said Gustaf Bischof,
have ascertained that the first claiming clause may be understood to include more
than was or is intended to be included therein, and that the second, third, and
fourth claiming clauses might be objected to as being of doubtful validity, as
claiming what at the date of the said Letters Patent was not proper subject-matter
for the grant thereof, and I do not wish to retain any claim in respect of the parts
of the Invention to which these clauses relate.

page_text: And I desire to disclaim and alter the said Specification in manner following,
that is to say :-
Referring to the Queen's Printers' copy, at page 5, line 7, I omit the words "one
part of;" at page 5, line 19, for "peference" I substitute "preference;" at page 6,
line 48, I omit the word "effluent," and for "from" I substitute "in;" at page 6,
line 49, for "contain " I substitute "retain; " at page 7, line 12, I omit the words
"the part of." I omit the whole of the passages beginning at page 7, line 13, with
the words "another part of," and ending at page 8, line 21, with the words "in the
tube;" at page 8, line 23, for the words "I claim," I substitute the following words,
"I hereby declare that I make no general claim to the use of gravel or like sub-
stances, or to the use of spongy iron, which was claimed under a former Patent
granted to me, and dated the 19th September 1870, No. 2156, but I claim in
respect of filters, where the use of spongy iron would otherwise be attended with
a liability to choking and difficulty in the separation of ferric hydrate from the
"water;" at page 8, line 24, I omit the word "First;" at page 8, line 25, between
the words "iron" and "mixed" I insert "so;" at page 8, line 26, for "whereby "I
substitute "that." I omit the whole of the passages beginning at page 8, line 29,
with the words "Second. The use," and ending at page 8, line 42, with the words
"herein described."
"
"
And the Specification when thus disclaimed and altered will read as follows:-
-
My Invention refers to the application of spongy iron for filtration on a large
scale, such as is required by water works and for the purification of sewage and
similar impure liquids. The difficulty of applying spongy iron to those purposes
has hitherto been twofold; first, the liability of spongy iron to choking, owing
mainly to the increase in bulk when the spongy (metallic) iron is oxidised by
agency of the atmospheric oxygen dissolved in the water to be filtered; and, second,
the separation of the ferric hydrate which is formed by oxydation of the ferrous
'bydrate or carbonate, both of which are mostly dissolved by water when passing
through spongy iron. These difficulties I remove in the following way:-
In constructing filters on a large scale for the purposes mentioned above, I first
form a proper substratum for the layer which is to contain the spongy iron; to this
end I place on the perforated bottom of an ordinary filter bed, such as is commonly
used in waterworks, a layer of moderately fine gravel, employing by preference such as
has been passed through a sieve with about four holes on the square inch, or should the
construction of the perforated bottom not permit of this, I place underneath such
gravel and on to the perforated bottom one or more layers of shells or gravel of
larger size, until a proper bed has been obtained on which the gravel inay rest
which is to form the substratum to the layer containing the spongy iron. On the
top of such substratum I place a layer, by preference about three feet thick of a
mixture of about one volume of spongy iron to three volumes of gravel. The latter
material should preferably have been passed through a sieve with about four holes
on the square inch; the spongy iron may be slightly coarser. Instead of mixing the
spongy iron with gravel, it may be mixed in the same proportion and under similar
conditions as to size with coke or any other inert matter which is not materially
affected or altered by the filtration of water. Finally, I place on the top of the
mixture of spongy iron and gravel or other material a layer of fine sharp sand, such
as the well known "Harwich" sand; or, according to the condition of the water to
be filtered, several layers of sand gradually increasing in fineness towards the top
may be employed.
When filtering sewage or similar impure liquids the solid or suspended
impurities contained in them should preferably be separated by any of the known
methods, previous to the filtration through the spongy iron filter hereinbefore
described.

page_text: Whenever the greatest possible purity and brightness is desired, the water or
other liquid should after filtration through the spongy iron filter, as herein before
described, be subsequently passed through a sand filter arranged in a similar
manner as is usual in waterworks where filtration through sand is employed.
Although I have stated hereinbefore and shall state hereinafter several pro-
portions, dimensions, and sizes, and although these will generally answer the
purpose, I wish it to be understood that I do not limit myself to these, as they are
only given by way of example, and may be variod as circumstances require.
In order that the nature of my improvements may be more readily understood,
and to enable any one conversant with such matters to introduce such variations as
may be required himself, I will proceed to state the considerations upon which the
before described arrangements are based.
1st. The object of using spongy iron as a purifier of water is to effect the
decomposition or separation by chemical affinities of those impurities in water or
other liquids, which are either in a state of solution or too minute in sizo to bo
separated by ordinary mechanical means, such as filtration through sand, ordinary
mechanical filtration being thus not the primary nor the more important object
of filtration through spongy iron; tho layer containing this medium should be so
arranged as to allow the water to porcolate, comparatively speaking, freely, in
order to prevent as far as possible any liability to choking. As the spongy iron
itself is apt to increase in bulk, as herein before explained, I counteract the liability
to choking, which might thereby arise, by mixing the spongy iron with some such
inert matter as gravel, in the manner hereinbefore explained. The proper contact
between the spongy iron and the liquid to be filtored, upon which contact the
chemical action of the spongy iron depends, should be secured by regulating the
valves or stop coks in connection with the exit pipes from the filter or filters. A
volume of water equal to the bulk of spongy iron in a filter may be passed through
in about 45 minutes, or if the sizes and dimensions hereinbefore explained be
adhered to 150 gallons per square foot of filtering area in 24 hours is about the
yield of the spongy iron filter when purifying a water of the quality of Thames
water for domestic use. The valves should likewise be so regulated that the layer
of spongy iron after it has once been wetted remains, as far as practicable, always
covered with water, alternate exposure to air and water causing too rapid an
oxydation of the metallic spongy iron.
2nd. Although, as hereinbefore explained, mechanical filtration is not the object
of the employment of spongy iron, provision must be made to remove also tho
solid or suspended impurities. These, as far as they may not have been separated
from the water or other liquid by any previous treatinent, such as subsidence,
precipitation, or otherwise, should be retained by the layer of fine sand on the top
of the mixture of spongy iron and gravel, so as to prevent those impurities from
mixing with, contaminating, or choking the spongy iron itself. It will be under-
stood that the upper portion of the top layer of fine sand may be scraped off,
washed, and replaced, as is usual in the elass case of ordinary sand filters whenever
required.
3rd. On filtering water or other liquid through spongy iron a minute quantity of
iron is dissolved, probably as ferrous hydrate or carbonate. Both these compounds
are readily oxydised when they come in contact with oxygen. The separation of
the ferric hydrate then formed has, as above referred to, hitherto been a difficulty
in applying the spongy, iron process to large filters. If water be passed through a
layer of spongy iron, even only a few inches in thickness, which is not mixed with
gravel or similar material, the oxygen dissolved in the water may be completely
abstracted by agency of the metallic spongy iron. If this is the case, the soluble
proto-compounds of iron referred to above do not meet with oxygen in the filtered
water, nor can they be oxydised or rendered insoluble until the water has again,
after filtration through spongy iron, taken up oxygen by exposure to the air, or
the

page_text: by artificial means. These soluble proto-compounds of iron would, therefore, in a
filter containing spongy iron without any admixture, have to be subsequently
separated by subsidence or filtration, both of which are apt to interfere with the
regular working of the system of filtration, as the ferric hydrate is very fine and
slimy, and therefore does not subside readily, and if to be separated by filtration
greatly chokes the filter or filters used for that purpose.
However by mixing the spongy iron with gravel or other matter, essentially in
the manner hereinbefore explained, the water in the spongy iron filter may readily
be made to retain sufficient oxygen to more or less completely oxydise the proto-
compounds of iron, herein before referred to, and the ferric bydrate thus formed is
then retained, more or less completely, within the spongy iron filter itself, thus
forming a coating over the porous material of which this filter is composed, without
interfering, for a long time at least, with the free percolation of the water. The
deposit of ferric hydrate may from time to time be removed in the ordinary way
by washing. Nevertheless, whenever extreme purity is an object, I prefer passing
the effluent water from the spongy iron filter or filters through the sand filter
herein before referred to, so as to have an additional surety that the iron shall be
efficiently separated from the filtered water. In combining such a system of filters
containing spongy iron mixed as hereinbefore explained with another system of
filters containing sand, the former should preferably be on a higher level than the
latter, so that the water may pass through the two filters by gravitation. The
uppermost portion of the sand filter requires much less frequent renewal or
washing, if the spongy iron filter be constructed as herein before explained, than if
the effluent water from the spongy iron filter were deprived of oxygen in solution,
as in the former case very little ferric hydrate comparatively speaking has to be
retained by the sand filter. It will thus be understood that in the manner
indicated both the spongy iron filters and the sand filters in connection therewith
do not offer any such practical diffiel difficulties to their application on a large scale
as before the discovery of the improvements which form my Invention herein before
explained.
Having thus described the nature of the said Invention and in what manner
the same is to be performed, I hereby declare that I make no general claim to the
use of gravel or like substances, or to the use of spongy iron, which was claimed
under a former Patent granted me, and dated the 19th September, 1870, No. 2156,
but I claim in respect of filters where the use of spongy iron would otherwise be
attended with liability to choking and difficulty in the separation of ferric hydrate
from the water,―
The use for filter beds of a layer of filtering material composed of spongy iron,
so mixed with gravel or similar matter of a nature herein before explained, that the
deposit of the whole, & of the ferric hydrate is effected in the filter containing the
spongy iron itself, substantially as herein described.
or nearly the whole,
A
In witness whereof, I, the said Gustav Bischof, have hereunto set my hand
and seal this Twenty eighth day of November, in the year of our Lord One
thousand eight hundred and seventy nine.
GUSTAV BISCHOF. (L.S.)
Witness,
OLIVER IMRAY,
28, Southampton Buildings,
London, W.C.
GUSTAV BISCHOF. (L.S.)

page_text: To the Commissioners of Patents for Inventions.
I hereby grant my fiat, giving leave to the within named Gustav Bischof to file
in the Office of the Commissioners of Patents for Inventions, with the Specification
to which the same relates, the within writton Disclaimer and Memorandum of
5 Alteration.
Dated this Nineteenth day of Jannare One thousand night hundund and