Thellusson. Owing, however, to the heavy expenses, the amount
inherited was not much larger than that originally bequeathed.
To prevent such a disposition of property in the future, the
Accumulations Act 1800 (known also as the ``Thellusson Act'')
was passed, by which it was enacted that no property should
be accumulated for any longer term than either (1) the life
of the settlor; or (2) the term of twenty-one years from
his death; or (3) during the minority of any person living
or en ventre sa mere at the time of the death of the
grantor; or (4) during the minority of any person who, if
of full age, would be entitled to the income directed to be
accumulated. The act, however, did not extend to any provision
for payment of the debts of the grantor or of any other
person, nor to any provision for raising portions for the
children of the settlor, or any person interested under the
settlement, nor to any direction touching the produce of timber
or wood upon any lands or tenements. The act was extended
to heritable property in Scotland by the Entail Amendment Act
1848, but does not apply to property in Ireland. The act
was further amended by the Accumulations Act 1892, which
forbids accumulations for the purpose of the purchase of
land for any longer period than during the minority of any
person or persons who, if of full age, would be entitled to
receive the income. (See also TRUST and PERPETUITY.)
ACCUMULATOR, the term applied to a number of devices whose
function is to store energy in one form or another, as, for
example, the hydraulic accumulator of Lord Armstrong (see
HYDRAULICS, sec. 179). In the present article the term is
restricted to its use in electro-technology, in which it
describes a special type of battery. The ordinary voltaic
cell is made by bringing together certain chemicals, whose
reaction maintains the electric currents taken from the
cell. When exhausted, such cells can be restored by replacing
the spent materials, by a fresh ``charge'' of the original
substances. But in some cases it is not necessary to get rid
of the spent materials, because they can be brought back to
their original state by forcing a reverse current through the
cell. The reverse current reverses the chemical action and
re-establishes the original conditions, thus enabling the
cell to repeat its electrical work. Cells which can thus be
``re-charged'' by the action of a reverse current are called
accumulators because they ``accumulate'' the chemical work
of an electric current. An accumulator is also known as a
``reversible battery,'' ``storage battery'' or ``secondary
battery.'' The last name dates from the early days of
electrolysis. When a liquid like sulphuric acid was electrolysed
for a moment with the aid of platinum electrodes, it was
found that the electrodes could themselves produce a current
when detached from the primary battery. Such a current was
attributed to an ``electric polarization'' of the electrodes,
and was regarded as having a secondary nature, the implication
being that the phenomenon was almost equivalent to a storage
of electricity. It is now known that the platinum electrodes
stored, not electricity, but the products of electro-chemical
decomposition. Hence if the two names, secondary and storage
cells, are used, they are liable to be misunderstood
unless the interpretation now put on them be kept in mind.
``Reversible battery'' is an excellent name for accumulators.
Sir W. R. Grove first used ``polarization'' effects in his gas
battery, but R. L. G. Plante (1834-1889) laid the foundation
of modern methods. That he was clear as to the function
of an accumulator is obvious from his declaration that the
lead-sulphuric acid cell could retain its charge for a long
time, and had the power d'emmagasiner ainsi le travail chimique
de la pile voltaique: a phrase whose accuracy could not be
excelled. Plante began his work on electrolytic polarization
in 1859, his object being to investigate the conditions under
which its maximum effects can be produced. He found that the
greatest storage and the most useful electric effects were
obtained by using lead plates in dilute sulphuric acid. After
some ``forming'' operations described below, he obtained a
cell having a high electromotive force, a low resistance, a
large capacity and almost perfect freedom from polarization.
The practical value of the lead-peroxide-sulphuric-acid
cell arises largely from the fact that not only are the
active materials (lead and lead peroxide, PbO2) insoluble
in the dilute acid, but that the sulphate of lead formed
from them in the course of discharge is also insoluble.
Consequently, it remains fixed in the place where it is
formed; and on the passage of the charging current, the
original PbO2 and lead are reproduced in the places they
originally occupied. Thus there is no material change in
the distribution of masses of active material. Lastly,
the active materials are in a porous, spongy condition,
so that the acid is within reach of all parts of them.
Plante's cell.
Plante carefully studied the changes which occur in the
formation, charge and discharge of the cell. In forming,
he placed two sheets of lead in sulphuric acid, separating
them by narrow strips of caoutchouc (fig. 1). When a charging
current is sent through the cell, the hydrogen liberated
at one plate escapes, a small quantity possibly being spent
in reducing the surface film of oxide generally found on
lead. Some of the oxygen is always fixed on the other
(positive) plate, forming a surface film of peroxide. After
a few minutes the current is reversed so that the first
plate is peroxidized, and the peroxide previously formed
on the second plate is reduced to metallic lead in a spongy
state. By repeated reversals, the surface of each plate
is alternately peroxidized and reduced to metallic lead.
In successive oxidations, the action penetrates farther
into the plate, furnishing each time a larger quantity
of spongy PbO2 on one plate and of spongy lead on the
other. It follows that the duration of the successive
charging currents also increases. At the beginning. a
few minutes suffice; at the end, many hours are required.
Fig. 1
After the first six or eight cycles, Plante allowed a
period of repose before reversing. He claimed that the
PbO2 formed by reversal after repose was more strongly
adherent, and also more crystalline than if no repose were
allowed. The following figures show the relative amounts of
oxygen absorbed by a given plate in successive charges (between
one charge and the next the plate stood in repose for the
time stated, then was reduced, and again charged as anode):-
Separate periods of Charge. Relative amount of
Repose. Peroxide formed.
. . First 1.0
18 hours Second 1.57
2 days Third 1.71
4 days Fourth 2.14
2 days Fifth 2.43
and so on for many days (Gladstone and Tribe, Chemistry
of Secondary Batteries). Seeing that each plate is in turn
oxidized and then reduced, it is evident that the spongy
lead will increase at the same rate on the other plate of the
cell. The process of ``forming'' thus briefly described
was not continued indefinitely, but only till a fair
proportion of the thickness of the plates was converted
into the spongy material, PbO2 and Pb respectively. After
this, reversal was not permitted, the cell being put into
use and always charged in a given direction. If the process
of forming by reversal be continued, the positive plate is
ultimately all converted into PbO, and falls to pieces.
Plante made excellent cells by this method, yet three
objections were urged against them. They required too much
time to ``form''; the spongy masses (PbO2 more especially)
fell off for want of mechanical supoort, and the separating
strips of caoutchouc were not likely to have a long life.
The first advance was made by C. A. Faure (1881), who greatly
shortened the time required for ``forming'' by giving the
plates a preliminary coating of red lead, whereby the slow
precess of biting into the metal was avoided. At the first
charging, the red lead on the + electrode is changed to
PbO2, while that on the - etectrode is reduced to spongy
lead. Thus one continuous operation, lasting perhaps
sixty hours, takes the place of many reversals, which,
with periods of repose, last as much as three months.
Fig. 2 Tudor positive plate.
Faure used felt as a separating membrane, but its use
was soon abolished by methods of construction due to E.
Volckmar, J. S. Sellon, J. W. Swan and others. These
inventors put the paste not on to plates of lead, but into
the holes of a grid, which, when carefully designed, affords
good mechanical support to the spongy masses, and does away
with the necessity for felt, &c. They are more satisfactory,
however, as supporters or spongy lead than of the peroxide,
since at the point of contact in the latter case the acid
gives rise to a local action, which slowly destroys the
grid. Disintegration follows sooner or later, though the
best makers are able to defer the failure for a fairly long
time. Efforts have been made by A. Tribe, D. G. Fitzgerald
and others to dispense whin a supporting grid for the positive
plate, but these attempts have not yet been successful
enough to enable them to compete with the other forms.
For many years the battle between the ``Plante'' type and the
Faure or ``pasted'' type has been one in which the issue was
doubtful, but the general tendency is towards a mixed type
at the present time. There are many good cells, the value of
all resting on the care exercised during the manufacture and
also in the choice of pure materials. Increasing emphasis is
laid on the purity of the water used to replace that lost by
evaporation, distilled water generally being specified. The
following descriptions will give a good idea of modern practice.
Chloride cell.
The ``chloride cell'' has a Plante positive with a pasted
negative. For the positive a lead casting is made, about 0.4
inch thick pierced by a number of circular holes about half
an inch in diameter. Into each of these holes is thrust a
roll or rosette of lead ribbon, which has been cut to the
right breadth (equal to the thickness of the plate), then
ribbed or gimped, and finally coiled into a rosette. The
rosettes have sufficient spring to fix themselves in the
holes of the lead plate, but are keyed in position by a
hydraulic press. The plates are then ``formed'' by passing
a current for a long time. In a later pattern a kind of
discontinuous longitudinal rib is put in the ribbon, and
increases the capacity and life by strengthening the mass
Fig. 3.--Tudor negative plate.
without interfering with the diffusion of acid. The
negative plate was formerly obtained by reducing pastilles
of lead chloride, but by a later mode of construction
it is made by casting a grid with thin vertical ribs,
connected horizontally by small bars of triangular
section. The bars on the two faces are ``staggered,''
that is, those on one face are not opposite those on the
other. The grid is pasted with a lead oxide paste and
afterwards reduced; this is known as the ``exide'' negative.
The larger sizes of negative plate are of a ``box'' type, formed
by riveting together two grids and filling the intervening space
