Year: 1888

page_text: I, EMILE MARIE HIPPOLYTE ANDREOLI, Journalist of 62 Loughborough Park
Brixton S.W. Surrey 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:—
The object of this invention is the bleaching of Pulp made of Esparto, Hemp, Flax,
Straw, Jute, Wood, Bamboo etc. etc. used for the manufacture of Paper, by means of
hypochlorite of sodium produced by electrolytical decomposition of a solution
of chloride of sodium in presence of two charcoal electrodes or other convenient carbon
electrodes.
Hypochlorite of sodium is an excellent substitute for Hypochlorite of Calcium which
is generally used for bleaching.
In carrying out this bleaching of paper pulp I use as an electrolyte, concentrated
or non-concentrated sea water, or a solution of Chloride of Sodium, the specific
gravity of which varies according to the quality and nature of the materials to be
treated.
Generally the solution to be electrolysed works better with a density of 8 to 12
Baumé but although salt is cheap and the solution when exhausted may be regenerated
by passing an electric current I always endeavour to have when possible a weak
solution, and with some kind of pulp an electrolyte having the density of sea water
(3° Baume) is sufficiently strong to bleach.
I may work with any conveniently size shaped tanks but the form I prefer is a long
high and narrow trough along the sides of which the two rows of electrodes are so
disposed that the liquid is rapidly decomposed by the electric current and hypochlorite
of sodium is formed.
When I electrolyse in several vats or tanks they are placed if convenient at slightly
different heights
so that the electrolyte runs from the first to the second and so on
down to the last where it acquires its maximum of bleaching power or to a reservoir
where it is stored.
The action of hypochlorite of sodium is more powerful at the moment of its formation
.e. when the liquid is used for bleaching immediately after the electrolysis has taken
place but as my electrolyte retains for a certain time its bleaching properties especially

page_text: when stored in closed vessels. It can be prepared in advance & kept in large
reservoirs and in case the materials to be treated are rebellious there is no difficulty in
refreshing or strengthening the liquid in an electrolytic tank from which directly
afterwards it will be sent to the bleaching tank.
My electrodes may be made of charcoal broken pieces retained between a network of
lead wire or any other convenient substance or of solid slabs, but common charcoal
will seldom answer my purpose because charcoal is not a good conductor of heat and
electricity unless the carbonization has taken place in retorts at a very high
temperature. I prefer to make plates, rods, cylinders &c. of pulverized wood charcoal
or any vegetable charcoal powder mixed with a suitable agglutinating substance, such
as sugar or its equivalents, readily transformable into pure carbon and then moulded,
compressed and baked until a carbon is produced which is highly conductive, homo-
genous & dense, and has the same strength throughout.
It is a very well known fact that in an electrolytic operation, the anode is attacked
and that even platinum at the positive pole is attacked corroded & little by little
destroyed under the action of chlorine and oxygen. This renders prohibitive the
commercial use of Platinum or any other expensive anode for bleaching in Paper
Mills where large quantities of Paper Pulp must be treated daily, which involves the
use of many plates having a large surface in vats of a considerable capacity and
therefore an enormous outlay.
I have found that charcoal resists, better than any other material, the action of
Chlorine and Oxygen and I use it indifferently as electrode at the positive pole and at
the negative and by reversing the current or by an alternating current dynamo, both
the electrodes act as positive and negative plates one after the other so that if chlorine
and oxygen were to act on the anode their action would be insignificant. But an
alternating current is extremely dangerous in itself and as I do not want so many
reversions per minute as are given by an alternating current machine I simply reverse
the current every 5 or 10 minutes or less by means of a switch so that if the electrode
which for the time being is a positive is even liable to be attacked even slightly by
chlorine and oxygen, no decomposition, no disintegration of the carbon and formation
of Mellic acid which blickens the electrolyte, takes place & both the electrodes which
already resist the chlorine & oxygen will be worn out equally and can be used for a
considerable time.
The mouldings and bakings of such charcoal electrodes are effected by some of the
well known processes for manufacturing gas retort or other carbons for electrical
purposes but I make it a point to have them several times submitted to the heat
of the retort or of the oven after they have been immersed in a bath of sugar syrup
or glucose so that this carbon of charcoal & sugar is dense, hard, very pure and
almost incorrodible.
.
The alternating or better reversing of the current allows me to use also carbons and
more especially carbons for electric are lamps which are hård highly conductive
and very little liable to deteriorate by chlorine and oxygen. I prefer to use electrodes
made of cylinders sticks or rods of which I make a kind of grid or grate in the
following manner
1st. I coat one end of the carbons with a galvanic deposit of copper on a length of
say one inch.
2nd. I tin this film of copper with common solder.
!
3rd. I place the required number of carbons wanted to make a plate between two
grooved boards of wood which are fastened together and which hold them firmly side
by side and having the tinned end emerging.
4th. I dip the emerging ends of the carbons in a bath of molten lead which when
cold keeps together all the heads of the carbons which now form an electrode.
5th. On the top of the lead which binds together all the sticks I solder and firmly
attach and fix a strong copper or brass rod one end of which will be connected with
a pole of the dynamo.
6th. I dip the whole of the upper ends of the electrode into a bath of insulating
substance to protect the copper & the tin.

page_text: 7. The lower ends of the rods rest in the holes of a piece of wood which on both
sides is attached to two other pieces of wood which are fastened to the copper rod on
the upper part of the plate & therefore form a strong frame which protects the carbons
and prevents them from breaking.
The copper rods of the plates are longer than the electrode and one of the ends is
bent so as to enter into a barrel terminal vertically soldered on a copper bar fixed on
the outside of the tank on both sides so that if for instance all the bent rods on one
side are the anodes those on the other side will be the cathodes, while the other ends
of the rods rest on horizontally in grooves on the top of the tank, so that the plates
are all equi-distant and no short circuit can take place. The two copper bars fixed on
the tanks are connected with a dynamo so that each time at equal intervals the
current is reversed, the bars are connected with the positive and the negative of a
dynamo or other source of electricity alternately and at equal intervals.
It is obvious that continuous currents are the basis of this electrolytic process and
that in alternating or in reversing the current my object is to protect the charcoal
plates in the long run of the process against a possible corrosion and disintegration
and also to be able to utilize the electric carbons of ordinary quality and more
particularly the carbons for electric arc lamps.
When a chloride of sodium solution is electrolysed in presence of an anode made
of per oxide of lead & manganese and of a cathode made of chloride of lead or spongy
lead, or even of other electrodes such as of carbon or charcoal for instance, the liquid
turns green and a strong smell of chlorine is evolved. Such liquid cannot but have
very valuable properties for bleaching certain vegetable substances but as long as it
remains neutral there is almost no action on the paper pulp and when it becomes acid
its chlorometrical strength is not even then sufficiently great its bleaching power is
slow and is soon exhausted.
I find it far more advantageous to use a chloride of sodium solution which before I
subject it to electrolysis is rendered alkaline by adding a small quantity of common
soda crystals in the proportion of about half a pound per 100 gallons of solution;
other alkalies will give the same results, but I prefer a carbonate because its carbonic
acid assists the formation of hypochlorous acid which is fixed by the alkali. I do not
confine myself to such proportions as they may be varied according to the density of
the electrolyte and to the inore or less difficulty the pulp offers for bleaching. The
alkaline solution of chloride of sodium when electrolysed and transformed into
hypochlorite of sodium has instead of a strong smell of chlorine, a faint & not unpleasant
odour. Its colour is whitish and its bleaching action can only be compared to that of
the best chloride of lime solution.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is-
1st. The production of hypochlorite of sodium as a substitute for chloride of lime in
the bleaching of paper pulp by decomposing electrolytically an alkaline chloride of
sodium solution in presence of electrodes made of charcoal powder constructed as
herein before described or of carbons for electric arc lamps or other electric carbons
as aforesaid, used either with a continuous current dynamo or as the case may
be, alternately as anodes & cathodes by means of an apparatus for reversing the
current.
2nd. The whole process for generating hypochlorite of sodium in an electrolytic
tank substantially as hereinbefore described.
Dated this Eleventh day of September 1888.