Improvements in Voltaic Cells.
Year: 1891

page_text: Date of Application, 23rd Dec., 1891-Accepted, 6th Feb., 1892
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Voltaic Cells.
1. HENRY HARRIS LAKE of the firm of Haseltine, Lake & Co., Patent
Agents, 45 Southampton Buildings 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:—
This invention consists of a voltaic cell, the temperature co-efficient of which is
practically invariable, in other words, a cell which is free from temperature error,
or in which the electromotive force does not depend upon the temperature of the
cell. Such a cell has hitherto been unknown in the art.
In the
While a cell of this character may be applied to various uses, it will find its
principal employment and be of the highest utility as a standard of measurement
of electromotive force. There is, at the present time no absolute standard of the
unit of electromotive force, (the volt) but there is a variety of cells termed
"standard" with which comparisons are made. In all of these cells, the effect of
change of temperature is to change the value of the electromotive force.
improved Clark standard cell, for example, which contains amalgamated platinum
wire and a rod of pure zinc as elements, imbedded in a paste of pure mercurous
sulphate and a saturated solution of pure zinc sulphate, the effect of change of
temperature is to change the value of the electromotive force about 077 per degree
Centigrade. It will be apparent that such a cell cannot be called a "standard
cell in any proper sense of the term inasmuch as its indications depend, first,
upon constantly varying temperatures, and second, upon the recognition of these
variations through some other device, as for example a thermometer, which in
turn becomes the standard.
32
In cells containing a sulphate of zinc solution, the density of the solution is
dependent upon the temperature of the solvent (water) in which the zinc salt is
dissolved; and with every change of density, there is a corresponding change of
electromotive force; the latter rising to a marked extent as density diminishes.
Furthermore, in all so-called standard cells, there is a deposition on the zinc of
something which. like the copper in the Daniel cell, does not protect the zinc but
enters into local action with it, thus affecting the relation of one electrode to the
other. It will be apparent, therefore, that in order to adapt my discovery to the
purposes of a standard cell, I must not only devise a cell in which the value of
the electromotive force does not change with temperature, but also one which
contains such substances as will not cause local action to affect the electromotive
force.
I have discovered that the electromotive force of all cadmium salts is practically
independent of temperature changes. This appears to be due to the fact that such
salts are equally as soluble in hot as in cold water; the density of the solution
remaining substantially the same, so that there is no disturbance of electromotive
force due to changes in density. The chemical affinities in the cell are substantially
the same, no matter what the temperature of the cell may be, within reasonable
limits; and in fact, we have the very remarkable condition of the action of chemical
affinities being practically unhelped by heat. Any salt of cadmium may be used,
the acid of which forms a practically insoluble compound with mercury when the
salt is in the state of a saturated solution in water, or in a solution of the salt of
cadmium employed. Such salts, for example, are the sulphate, the chloride, the

page_text: bromide and the iodide: I may use a single salt or I may use combinations of
these various salts with any insoluble salt and mercury. The ingredients of the
cell will depend upon the use to which it is to be put. If, for example, it is to be
employed as an absolute standard, then it should be so made as to be absolutely
permanent and in such condition, it may be supplied to the market as a completed
article of manufacture; or the cells may be put together by the user an intended
only for an hour or two's employment. In that case, it is immaterial if the
compounds become impaired in efficiency at the end of that time, since they may be
thrown aside and be replaced on the next occasion for use.
I may arrange the ingredients of the cell in either of three ways. First, I may
use an electrolyte composed of a saturated solution of cadmium salt with electrodes
of other material. Second, I may use an electrode containing cadmium opposed to
an electrode of mercury and an electrolyte of material other than cadmium salt.
Third, and this is the best arrangement for an absolute standard cell, which I now
know I may use as an electrolyte a saturated solution of cadmium salt in water, and
as electrodes an amalgam of cadmium and mercury opposed to an electrode of pure
mercury and proto-sulphate of mercury.
Thus, to illustrate case 1, I may substitute a solution of cadmium sulphate for
the mercurous sulphate and saturated solution of pure zinc sulphate employed in the
Clark cell; the electrodes being zinc and amalgamated platinum. In such event,
however, while the cell on first construction will show much less variation of
electromotive force dependent upon change of temperature than does the Clark
cell, nevertheless, in time its errors will approach that of the Clark cell, because
by the reduction of the mercury salts, the solution becomes more and more near to
the sulphate of zinc, or Clark's cell.
Under the second case, I may employ electrodes such as described in case 3 with
a saturated solution of zinc sulphate. Here, while the change in electromotive
force due to variation in temperature will be less than is common in standard cells,
still the best conditions for an efficient cell will not be realized.
The construction described in case 3, is, as I have stated, the best means which I
now know for carrying the discovery into practical effect, both broadly and generi-
cally, and specifically in the form of a standard cell. I have already stated that such
a cell must not only be independent of temperature changes and free from local
action, but it must also be free from what may be termed differential action
dependent upon the difference in the conditions surrounding or affecting the
electrodes. To illustrate my meaning in this last statement, if a cell be composed
of two zinc electrodes, both immersed in a solution of zinc sulphate, and oue elec-
trode be heated more than another, there will be a current and the equilibrium
will be disturbed. Or if two zinc electrodes, each chemically pure, be immersed
in separate solutions of zinc sulphate, one of which is more dense or stronger than
the other, again the equilibrium will be disturbed, and there will be a difference
of potential between the terminals of the cell. Now with a cell composed as before
stated of electrodes respectively of an amalgam of cadmium and mercury and of
pure mercury and sulphate of inercury with a saturated solution of a cadmium salt
as an electrolyte, there will be, first no variation of electromotive force due to
changes of temperature, second, no disturbing currents due to local action, third,
no potential differences due to greater or less density of solution as affecting one
electrode or the other, or to differences of temperature of one electrode or the
other.
In stating that these effects are totally absent, I do not wish to be understood as
asserting that fact with mathematical precision, but in the sense that the cell shows
no disturbance from these causes within all reasonable and practicable limits. This
I have determined by the most delicate electrical tests known in the art. I have
for example, submitted the cell to temperature changes over
a range of
200 degrees Fah., under which conditions I have been unable to detect a variation
of electromotive force in excess of one one-hundredth of one per cent. In order to
adapt my discovery to practical use as a standard cell, I have embodied it in the

page_text: construction which is represented in the annexed drawings, Figures 1, 2, 3, wherein
similar letters of reference indicate like parts.
Figure 1 is a vertical section of the line 1, 1, of Figure 3.
Figure 2 is a vertical section on the line 2, 2, of Figure 3.
Figure 3 is a top view.
A is an outer shell or casing made preferably of sheet brass and elliptical in
form. In the bottom of this shell is inserted a wooden block B containing cavities
or recesses to receive the glass cell CC. The said glass cell consists of two
cylindrical vessels C C₁, connected by a transverse tube D. The lower ends of the
Within one
said vessels are rounded and their mouths are flared, as shown.
vessel as C, I place an amalgam of cadmium and mercury. In the other vessel !
I then insert in
place a mixture of pure mercury and proto-sulphate of mercury.
each vessel above the electrode, a piece of muslin or other suitable cloth E, the
edges of which turn upwards. In the cup-shaped piece of cloth thus introduced, I
insert a cork F pierced with apertures G. This arrangement of corks and muslin
serves to hold the materials of the electrodes in place and prevent their becoming
commingled with the solution when the cell is moved about. At the same time, the
openings in the corks F allow of free contact of the solution with the electrodes.
I then place in each cell C C' a saturated solution of cadmium sulphate. Lastly,
I insert in the mouths of the cell suitable stoppers M, and secure them in place with
cement. The connecting wires H pass through the bottoms of the cells C C¹ and
communicate electrically with the electrodes. They are connected to copper
wires I, which are received in suitable binding posts J. These binding posts J
are carried by the cover K of the shell A, which cover is made of rubber. The
binding posts J are provided with covering caps L, as shown. After the cells are
in place, the space in the shell A above the block B is filled up with a composition
preferably composed of bees wax, rosin and linseed oil. The cover K is then
adjusted and the cell permanently closed. The electromotive force of the elements
described approximates 1.019 volt.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is :-
1. A voltaic cell, the electromotive force of which is practically independent
of temperature changes and constructed and arranged substantially as hereinbefore
described.
2. A voltaic cell having an electrode containing cadmium and an electrolyte
containing a cadmium salt, combined substantially as hereinbefore set forth, so
that the electromotive force of said cell is practically independent of temperature
changes.
1001
red dais 23rd day of December 1901.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.