Improvements in Filtering Materials and Filters.
Year: 1891

page_text: Date of Application, 16th May, 1891-Accepted, 27th June, 1891
COMPLETE SPECIFICATION.
Improvements in Filtering Materials and Filters.
A communication to me from OTTO ARLT, of Goerlitz, in the Empire of
Germany.
I, EDMUND EDWARDS, of the firm of Edwards and Co., Patent Agents and
Engineers, of 35, Southampton Buildings, Chancery Lane, in the County of
Middlesex, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement and accompanying drawing, that is to say :-
The filtering materials ordinarily heretofore used have many disadvantages
which detract more or less from their value. The filtering material nearly
always consists of a single substance of uniform porousness, so that naturally
the heaviest and coarsest deposit from the filtered liquid settles in the lowest
part of the mass and quickly stops it up whilst the upper part of the filter,
often as much as three-fourths of the entire thickness, has not properly come
into operation, so that a very uneconomical application of the filtering material
results.
The filtering material almost always is of organic origin or of a vegetable
character, which after using for a short time is liable to become decomposed and
slimy and the filtered liquid then naturally acquires more or less of an offensive
smell and taste.
In many filtering materials moreover, the cleansing after use causes much
trouble, inasmuch as they do not deposit their impurities in the water in which they
are washed, and must therefore be subjected to pressure.
All these objections have been considered and removed in the filtering materials
which form the subject of the present invention.
These filtering materials consist of inorganic substances of various densities and
quality, which are arranged in layers above one another in such a way that the
lowest, loosest, and largest layer, is surmounted by a finer layer and so on to the
uppermost which is the finest of all. The raw materials for the filtering beds are
as follows;
1. Slag wool or silicate cotton,
2. Clean white long-fibred asbestos,
3. Ordinary asbestos in the form of the finest fibre.
None of these materials would be of use alone and in its raw state, as a filtering
material.
Material is not sufficiently reliable for a filtering bed, as it is not by itself
sufficiently compact and does not settle free from dirt and impurity in the water
when being washed, unless it is suspended therein in loose flocks. The raw
material 2 is also not dense enough by itself to retain all the impurities from the
liquid passing through it, whilst the raw material 3 is so dense that filtration does
not take place through it at all. Moreover it has not like 1 and 2 the required
rigidity of fibre.
Many experiments have led to the result that by the suitable preparation
and mixing of the raw materials mentioned, arranged in layers above one another
a superior and effective filter is obtained.
From the raw material 1 a substance 1 is prepared by cutting up the slag wool
fibres. The raw material 2, consisting of asbestos fibres adhering together in wood
like form, is cut up into pieces about one centimêtre long, and is then treated for
thirty six hours with a mineral acid (concentrated hydrochloric acid) heated to
about seventy five degrees Celsius, washed and boiled with alkali (ammonia or soda

page_text: Iye) and then separated into three separate degrees of fineness so that a coarse, fine,
and finest, asbestos material 2", 2", and 2, are obtained.
The raw material 3 is also heated for thirty six hours in mineral acid at seventy
five degrees Celsius, then treated with lye, and cut up into, pieces about a quarter of
a centimetre long. The resulting product constitutes 3ª.
After the raw materials have been formed into the preparations 1", 2", 2º, 2º,
and 3a, the different layers are prepared by a mixture of the different preparations
as follows:-
For the preparation of the coarsest or lowest layer the preparation 1ª (cut up
slag wool) and 2" (the coarsest) asbestos, in the proportion of about three to two,
are mixed together and after washing this material in water a compound is obtained
which forms the lowest layer of filtering material and which can be very easily
cleaned in a few minutes by washing in water when required.
The lowest layer but one consists of the preparation 2" (fine asbestos,) the third
layer of the preparation 2 (the finest asbestos,) and the fourth or top layer consists
of a mixture of the preparations 3", and 2, in the proportion of about three to two.
The preparation 3" (of the finest asbestos) which by itself would be impenetrable if
in layers, gives in combination with the preparation 2° a filter layer very dense but
yet so porous that the liquid can pass through and which can be easily cleaned by
washing.
These four preparations, of which 1 may be replaced by 2 with a certain
diminution of the filtering capacity, are in the described order arranged in a
plastic state in the filtering vessel which is to, be used, after they have been first
cleaned by washing. A. less dense inorganic filtering material may also be made by
the mixture of the preparation 2 with the prepared and boiled wool or silky fibres
cut short.
The advantages of the improved filtering beds over those ordinarily used
consist especially in the avoidance of all organic fibres in the filter so that no
decomposition takes place in the latter, and the taste and smell of the filtered
liquid are in no way prejudicially affected, so that even wine preserves its bouquet
and beer its favour. By the varying degrees of density of the different filtering
beds the largest and roughest impurities are detained in the lowest bed and the
finer ones in the upper beds, so that a uniform utilization of all the filtering
material takes place, and consequently the durability of the filtering action is much
greater than in other ordinary filters. For purifying heavy liquids the filtering
beds may be increased.
The cleaning of the filtering material can be effected without trouble by washing
the mass in cold water and simply allowing it to settle. The dirty water can
easily be separated in a quarter of an hour so that the filtering material can be
cleaned and brought back into use again in one or two hours from its removal
from the filter.
For the use of the filtering materials described a filter should be used of the
kind illustrated in the accompanying drawing, in which
Figure 1 is a vertical section through a filter,
Figure 2 a vertical section through a modification of the first filter, and
Figure 3 a vertical section through a third form.
Figure 4 is a section through a filter support, and
Figure 5 a section through a modified form of support.
On the bottom of a cylindrical vessel B supported upon legs A. Figure 1, and
made of sheet copper or other metal, an inlet cock C is fixed above which a filter
support as shewn in Figure 4 is arranged; upon which the filtering material is
placed, and upon this filtering material a similar support is arranged, and so on
until the vessel B is full and it is then covered by a perforated plate and by a cover F
making a tight joint by means of the india rubber joint D and provided with an
outlet cock E, a space being left between the perforated plate and the cover.
The liquid to be filtered is admitted through the cock C and is discharged above
through the cock E.

page_text: The filter support Figure 4, consists of a horse hair sieve G or other coarsely
woven net and a perforated copper plate H under which muslin or silk gauze J is
stretched, and upon this rests a hollow porcelain plate K provided with ribs on
which rests the horsehair sieve or other net Z which in turn is entirely covered by
the silk or other gauze N.
The plate K may be made of wood, horn, glass, stoneware, metal, or other
suitable material.
The filtering vessel N (Figure 2) is shewn formed of corrugated sheet metal
with a sufficient number of iron stays to enable the vessel to resist internal
pressure. In the vessel a lower domed perforated metal plate P is arranged,
(Figure 5), whilst the other filter supports are the same as in Figure 4. The filter
vessel Q (Figure 3) is fitted with domed metal perforated plates P (Figure 5) with
plates R arranged between them for the purpose of at the same time distributing
and cleaning the liquid to be filtered which enters below.
In this filter the current of the liquid to be filtered is distributed so that the body
of the filtering material is utilized and the flow of the fluid, towards the sides of the
vessel prevented.
This is effected by means of the shape of the supports in which the height of
each layer of filtering material decreases from its outer side toward the centre.
The current of the liquid spreads out in every direction in its attempt to find the
easiest passage, and the filtering material is therefore made use of through all its
bulk.
By the use of a filtering vessel of corrugated plates (Figure 2), instead of the
method just described which aims at shortening the path of the liquid through
the centre of the filtering material, as compared with the side of the vessel,
the corrugated sides are themselves of much greater length and so cause a
longer path for the fluid.
Lastly it should be noticed that the filtering vessel may be provided with a press
by which the material may be compressed if desired..
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A filtering bed consisting of inorganic materials which are composed of long
fibred asbestos brought into the form of the finest fibre by treating it in a hot bath
of mineral acid, washing it, heating it with alkalis, and dividing it into different
degrees of fineness, by combining which together in proper proportions, or with
the addition of slag wool or silk reduced to short pieces, filtering beds of different
degrees of density are obtained, and are arranged in layers one above the other,
substantially as described and shewn.
2. For containing the layers of filtering material claimed in Claim 1, a filtering
vessel in which the path through the filtering material of the liquid to be filtered
is shorter at the centre than at the sides, either by making spaces in the centre of
the filtering material by means of perforated plates of such a shape as to reduce
the thickness of the filtering material at the centre, or by making the sides of the
filtering vessel corrugated, substantially as described and shewn.
7
r
1001
EDWARDS & Co.,
35, Southampton Buildings, London, Agents for the Applicant.