<s>
The	O
Daniell	B-Algorithm
cell	I-Algorithm
is	O
a	O
type	O
of	O
electrochemical	O
cell	O
invented	O
in	O
1836	O
by	O
John	O
Frederic	O
Daniell	O
,	O
a	O
British	O
chemist	O
and	O
meteorologist	O
,	O
and	O
consists	O
of	O
a	O
copper	O
pot	O
filled	O
with	O
a	O
copper	O
(	O
II	O
)	O
sulfate	O
solution	O
,	O
in	O
which	O
is	O
immersed	O
an	O
unglazed	O
earthenware	O
container	O
filled	O
with	O
sulfuric	O
acid	O
and	O
a	O
zinc	B-Application
electrode	O
.	O
</s>
<s>
He	O
was	O
searching	O
for	O
a	O
way	O
to	O
eliminate	O
the	O
hydrogen	O
bubble	O
problem	O
found	O
in	O
the	O
voltaic	B-Architecture
pile	I-Architecture
,	O
and	O
his	O
solution	O
was	O
to	O
use	O
a	O
second	O
electrolyte	O
to	O
consume	O
the	O
hydrogen	O
produced	O
by	O
the	O
first	O
.	O
</s>
<s>
Zinc	B-Application
sulfate	O
may	O
be	O
substituted	O
for	O
the	O
sulfuric	O
acid	O
.	O
</s>
<s>
The	O
Daniell	B-Algorithm
cell	I-Algorithm
was	O
a	O
great	O
improvement	O
over	O
the	O
existing	O
technology	O
used	O
in	O
the	O
early	O
days	O
of	O
battery	O
development	O
.	O
</s>
<s>
A	O
later	O
variant	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
called	O
the	O
gravity	B-Algorithm
cell	I-Algorithm
or	O
crowfoot	O
cell	O
was	O
invented	O
in	O
the	O
1860s	O
by	O
a	O
Frenchman	O
named	O
Callaud	O
and	O
became	O
a	O
popular	O
choice	O
for	O
electrical	O
telegraphy	O
.	O
</s>
<s>
The	O
Daniell	B-Algorithm
cell	I-Algorithm
is	O
also	O
the	O
historical	O
basis	O
for	O
the	O
contemporary	O
definition	O
of	O
the	O
volt	O
,	O
which	O
is	O
the	O
unit	O
of	O
electromotive	O
force	O
in	O
the	O
International	O
System	O
of	O
Units	O
.	O
</s>
<s>
The	O
definitions	O
of	O
electrical	O
units	O
that	O
were	O
proposed	O
at	O
the	O
1881	O
International	O
Conference	O
of	O
Electricians	O
were	O
designed	O
so	O
that	O
the	O
electromotive	O
force	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
would	O
be	O
about	O
1.0	O
volts	O
.	O
</s>
<s>
With	O
contemporary	O
definitions	O
,	O
the	O
standard	O
potential	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
at	O
25°C	O
is	O
actually	O
1.10	O
V	O
.	O
</s>
<s>
In	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
,	O
copper	O
and	O
zinc	B-Application
electrodes	O
are	O
immersed	O
in	O
a	O
solution	O
of	O
copper(II )	O
sulfate	O
and	O
zinc	B-Application
sulfate	O
,	O
respectively	O
.	O
</s>
<s>
At	O
the	O
anode	O
(	O
negative	O
electrode	O
)	O
,	O
zinc	B-Application
is	O
oxidized	O
as	O
per	O
the	O
following	O
half	O
reaction	O
:	O
</s>
<s>
Note	O
that	O
positively	O
charged	O
copper	O
ions	O
move	O
towards	O
the	O
positive	O
electrode	O
,	O
driven	O
by	O
a	O
reduction	B-Operating_System
in	O
chemical	O
energy	O
.	O
</s>
<s>
These	O
processes	O
result	O
in	O
the	O
accumulation	O
of	O
solid	O
copper	O
at	O
the	O
cathode	O
and	O
the	O
corrosion	O
of	O
the	O
zinc	B-Application
electrode	O
into	O
the	O
solution	O
as	O
zinc	B-Application
cations	O
.	O
</s>
<s>
In	O
classroom	O
demonstrations	O
,	O
a	O
form	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
known	O
as	O
two	O
half	O
cells	O
is	O
often	O
used	O
due	O
to	O
its	O
simplicity	O
.	O
</s>
<s>
Excess	O
electrons	O
produced	O
by	O
the	O
oxidation	O
of	O
zinc	B-Application
metal	O
are	O
“	O
pushed	O
”	O
out	O
of	O
the	O
anode	O
,	O
which	O
is	O
therefore	O
the	O
negative	O
electrode	O
,	O
travel	O
through	O
the	O
wire	O
and	O
are	O
"	O
pulled	O
"	O
into	O
the	O
copper	O
cathode	O
where	O
they	O
are	O
consumed	O
by	O
the	O
reduction	B-Operating_System
of	O
copper	O
ions	O
.	O
</s>
<s>
In	O
the	O
above	O
wet-cell	O
during	O
discharge	O
,	O
nitrate	O
anions	O
in	O
the	O
salt	O
bridge	O
move	O
into	O
the	O
zinc	B-Application
half-cell	O
in	O
order	O
to	O
balance	O
the	O
increase	O
in	O
ions	O
.	O
</s>
<s>
Hence	O
,	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
is	O
reversible	O
,	O
if	O
the	O
current	O
drawn	O
from	O
(	O
or	O
fed	O
to	O
)	O
it	O
is	O
small	O
.	O
</s>
<s>
The	O
Daniell	B-Algorithm
cell	I-Algorithm
can	O
be	O
used	O
to	O
‘	O
generate’	O
electricity	O
,	O
by	O
consuming	O
an	O
electrode	O
,	O
or	O
to	O
store	O
electricity	O
.	O
</s>
<s>
A	O
0.5	O
inch	O
diameter	O
zinc	B-Application
rod	O
hung	O
inside	O
this	O
ox-gullet	O
tube	O
suspended	O
from	O
wooden	O
supports	O
.	O
</s>
<s>
The	O
porous	O
pot	O
cell	O
consists	O
of	O
a	O
central	O
zinc	B-Application
anode	O
dipped	O
into	O
a	O
porous	O
earthenware	O
pot	O
containing	O
a	O
zinc	B-Application
sulfate	O
solution	O
.	O
</s>
<s>
Without	O
this	O
barrier	O
,	O
when	O
no	O
current	O
is	O
drawn	O
the	O
copper	O
ions	O
will	O
drift	O
to	O
the	O
zinc	B-Application
anode	O
and	O
undergo	O
reduction	B-Operating_System
without	O
producing	O
a	O
current	O
,	O
which	O
will	O
shorten	O
the	O
battery	O
's	O
life	O
.	O
</s>
<s>
The	O
replacement	O
of	O
sulfuric	O
acid	O
with	O
zinc	B-Application
sulfate	O
was	O
the	O
innovation	O
of	O
J	O
.	O
F	O
.	O
Fuller	O
in	O
1853	O
.	O
</s>
<s>
Nevertheless	O
,	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
provides	O
a	O
longer	O
and	O
more	O
reliable	O
current	O
than	O
the	O
Voltaic	B-Architecture
pile	I-Architecture
because	O
the	O
electrolyte	O
deposited	O
copper	O
,	O
which	O
is	O
a	O
conductor	O
,	O
rather	O
than	O
hydrogen	O
,	O
which	O
is	O
an	O
insulator	O
,	O
on	O
the	O
cathode	O
.	O
</s>
<s>
With	O
an	O
operating	O
voltage	O
of	O
roughly	O
1.1	O
volts	O
,	O
it	O
saw	O
widespread	O
use	O
in	O
telegraph	O
networks	O
until	O
it	O
was	O
supplanted	O
by	O
the	O
Leclanché	B-Algorithm
cell	I-Algorithm
in	O
the	O
late	O
1860s	O
.	O
</s>
<s>
Sometime	O
during	O
the	O
1860s	O
,	O
a	O
Frenchman	O
by	O
the	O
name	O
of	O
Callaud	O
invented	O
a	O
variant	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
which	O
dispensed	O
with	O
the	O
porous	O
barrier	O
.	O
</s>
<s>
Instead	O
,	O
a	O
layer	O
of	O
zinc	B-Application
sulfate	O
sits	O
on	O
top	O
of	O
a	O
layer	O
of	O
copper	O
sulfate	O
,	O
the	O
two	O
liquids	O
are	O
kept	O
separate	O
by	O
their	O
differing	O
densities	O
,	O
often	O
with	O
a	O
layer	O
of	O
oil	O
added	O
on	O
top	O
to	O
prevent	O
evaporation	O
.	O
</s>
<s>
This	O
variant	O
,	O
called	O
a	O
gravity	B-Algorithm
cell	I-Algorithm
,	O
consists	O
of	O
a	O
glass	O
jar	O
in	O
which	O
a	O
copper	O
cathode	O
sat	O
on	O
the	O
bottom	O
and	O
a	O
zinc	B-Application
anode	O
is	O
suspended	O
beneath	O
the	O
rim	O
in	O
the	O
zinc	B-Application
sulfate	O
layer	O
.	O
</s>
<s>
As	O
the	O
current	O
is	O
drawn	O
,	O
a	O
layer	O
of	O
zinc	B-Application
sulfate	O
solution	O
forms	O
at	O
the	O
top	O
around	O
the	O
anode	O
.	O
</s>
<s>
A	O
disadvantage	O
of	O
the	O
gravity	B-Algorithm
cell	I-Algorithm
is	O
that	O
a	O
current	O
has	O
to	O
be	O
continually	O
drawn	O
to	O
keep	O
the	O
two	O
solutions	O
from	O
mixing	O
by	O
diffusion	O
,	O
so	O
it	O
is	O
unsuitable	O
for	O
intermittent	O
use	O
.	O
</s>
<s>
The	O
zinc	B-Application
sulfate	O
layer	O
is	O
clear	O
in	O
contrast	O
to	O
the	O
deep	O
blue	O
copper	O
sulfate	O
layer	O
,	O
which	O
allows	O
a	O
technician	O
to	O
determine	O
the	O
battery	O
life	O
with	O
a	O
glance	O
.	O
</s>
<s>
A	O
variant	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
was	O
invented	O
in	O
1837	O
by	O
the	O
Guy	O
's	O
hospital	O
physician	O
Golding	O
Bird	O
who	O
used	O
a	O
plaster	O
of	O
Paris	O
barrier	O
to	O
keep	O
the	O
solutions	O
separate	O
.	O
</s>
<s>
John	O
Dancer	O
,	O
a	O
Liverpool	O
instrument	O
maker	O
,	O
in	O
1838	O
was	O
the	O
first	O
to	O
take	O
commercial	O
advantage	O
of	O
the	O
unique	O
features	O
of	O
the	O
Daniell	B-Algorithm
cell	I-Algorithm
for	O
copper	O
plating	O
.	O
</s>
