350 
NATURE 
[March 2, 1871 

A CONSTANT FORM OF DANIELL’S 
BATTER Y* 
RAHAM’S discovery of the extreme slowness with which 
one liquid diffuses into another, and Fick’s mathematical 
theory of diffusion, cannot fail to suggest that diffusion alone, 
without intervention of a porous cell or membrane, might be ad- 
vantageously used for keeping the two liquids of a Daniell’s 
battery separate. Hitherto, however, no galvanic clement with- 
out some form of porous cell, membrane, or other porous solid 
for separator, has been found satisfactory in practice. : 
The first idea of dispensing with a porous cell, and keeping 
the two liquids separate by gravity, is due to Mr. C. F. Varley, 
who proposed to put the copper-plate in the bottom of a jar; 
resting on it a saturated solution of sulphate of copper ; rest- 
ing on this a less dense solution of sulphate of zinc ; and im- 
mersed in the sulphate of zinc, the metal zinc-plate fixed 
near the top of the jar. But he tells me that batteries on this 
plan, called ‘gravity batteries,” were carefully tried in the late 
Electric and International Telegraph Company's establishments, 
and found wanting in economy. ‘The waste of zinc and of sul- 
phate of copper was found to be more in them than in the or- 
dinary porous-cell batteries. Daniell’s batteries without porous 
cells have also been tried in France, and found unsatisfactory 
on account of the too free access of sulphate of copper to the 
zinc, which they permit. Still, Graham’s and Fick’s measure- 
ments leave no room to doubt but that the access of sulphate of 
copper to the zinc would be much less rapid if by true diffusion 
alone, than it cannot but be in any form of porous-cell battery 
with vertical plates of copper and zinc opposed to one‘another, 

GROUND PLAN OF NEW BATTERY 
as are the ordinary telegraphic Daniell’s batteries which Mr. 
Varley finds superior to his own “‘ gravity battery.” The com 
parative failure of the latter, therefore, must have arisen from 
mixing by currents of the liquids, All that seems necessary, 
therefore, to make the gravity battery much superior instead of 
somewhat inferior to the porous-cell battery, is to secure that the 
lower part of the liquid shall always remain denser than the 
upper part. In seeking how to realise this condition, it first 
occurred to me to take advantage of the fact that saturated solu- 
tion of sulphate of zinc is much denser than saturated solution of 
sulphate of copper. It seemst that, at 15° temperature, saturated 
aqueous solution of sulphate of copper is of 17186 sp. gr., and 
contains in every 100 parts of water 331 parts of the crystalline 
salt ; and that at 15° the saturated solution of sulphate of zinc is 
of sp. gr. 1°44, and contains in every 100 parts of water 140°5 
parts of sulphate of zinc, both results being from Michel and 
Krafft’s experiments.{ tence I made an element with the zinc 
below; next it saturated solution of sulphate of zinc, gradually 
diminishing to half strength through a few centimetres upwards ; 
saturated sulphate of copper resting on this; and the copper-plate 
fixed above in the sulphate of copper solution. In the be- 
ginning, and for some time after, it is clear that the sulphate of 
copper can have no access to the zinc otherwise than by true dif- 
fusion. I have found this anticipation thoroughly realised in 
trials continued for several weeks ; but the ultimate fate of such 
a battery is that the sulphate of zinc must penetrate through 
the whole liquid, and then it will be impossible to keep sulphate 
of copper separate in the upper part, because saturated solution 
of sulphate of zinc certainly becomes denser on the introduction 
of sulphate of copper toit. To escape this chaotic termination, 
I have introduced a siphon of glass with a piece of cotton wick 
* From the Proceedings of the Royal Society. 
+ Storer’s Dictionary of Solubilities of Chemical Substances, 
Massachusetts : Sever and Francis, 1864. 
t Ann, Ch, et Phys. (3) vol. xli. pp. 478, 482, 1854. 
Cambridge, 


along its length inside it, so placed as to draw off liquor very 
gradually from a level somewhat nearer the copper than the zinc ; 
and a glass funnel, also providet with a core of cotton 
wick, by which water semisaturated with sulphate of zinc may 
be continually introduced at a somewhat lower level. A galvanic 
element thus arranged will undoubtedly continue remarkably 
constant for many months ; but it has one defect, which prevents 
me from expecting permanence for years. The zinc being below, 
must sooner or later, according to the less or greater vertical 
dimensions of the cell, become covered with precipitated 
copper from the sulphate of copper which finds its way (however 
slowly) to the zinc. On the other hand, if the zine be above, 
the greater part of the deposited copper falls off incoherently 
from the zinc through the liquid to the copper below, where it does 
no mischief, provided always that the zinc be not amalgamated, 
—a most important condition for permanent batteries, pointed 
out to me many years ago by Mr. Varley. Placing the zinc 
above has also the great practical advantage. that, even when 
after a very long time it becomes so much coated with metallic 
copper as to seriously injure the electrical effect, it may be removed, 
cleaned, and replaced, without otherwise disturbing the cell ; 
whereas if the zinc be below, it cannot be cleaned without empty- 
ing the cell and mixing the solutions, which will entail a renewal of 
fresh separate solutions in setting up the cellagain. I have therefore 
planned the following form of element, which cannot but last 
until the zinc is eaten away so much as to fall to pieces, and 
which must, I think, as long as it lasts, have a very satisfactory 
degree of constancy. 
The cell is of glass, in order that the condition of the solu- 
tions and metals which it contains may be easily seen at any 
time. It is simply a cylindrical or rectangular jar with a flat 
bottom. It need not be more than ten centimetres deep ; but it 


SECTION 
may be much deeper, with advantage in respect to permanence 
and ease of management, when very small internal resistance is 
not desired. A disc of thin sheet copper is laid at its bottom, 
A properly shaped mass of zinc is supported in the upper part 
of the jar. A glass tube (which for brevity will be called the 
charging-tube) of a centimetre or more internal diameter, ending 
in a wide saucer or funnel above, passes through the centre of 
the zinc, and is supported so as to rest with its lower open end 
about a centimetre above the copper. A glass siphon with 
cotton-wick core is placed so as to draw liquid gradually 
from a level about a centimetre and a half above the copper. 
The jar is then filled with semisaturated sulphate of zine 
solution. A copper wire or stout ribbon of copper coated with 
india-rubber or gutta percha passes vertically down through the 
liquid to the copper plate below, to which itis riveted or soldered 
to secure metallic communication. Another suitable electrode 
is kept in metallic communication with the zinc above. To put 
the cell in action, fragments of sulphate of copper, small enough 
to fall down through the charging tube, are placed in the funnel 
above. In the course of a very short time the whole liquid below 
the lower end of the charging tube becomes saturated with 
sulphate of copper, and the cell is ready for use. It may be 
kept always ready by occasionally (once a week for instance) 
pouring in enough of fresh water, or of water quarter saturated 
with sulphate of zinc at the top of the cell, to replace the liquid 
drawn off by the syphon from near the bottom. A cover may be 
advantageously added above, to prevent evaporation. When 
the cell is much used, so that zinc enough is dissolved, the liquid 
added above may be pure water ; or if large internal resistance is 
‘not objected to, the hquid added may be pure water, whether 
the cell has been much used or not ; but after an interval, during 
which the battery has not been much in use, the liquid added 
ought to be quarter saturated, or even stronger solution of sul- 
phate of zinc, when it is desired to keep down the internal 
resistance. It is probable that one or more specific gravity beads 
kept constantly floating between top and bottom of the hetero- 
geneous fluid will be found a useful adjunct, to guide in judging 
whether to fill up with pure water or with sulphate of zinc solu- 
