<s>
A	O
mercury	B-Algorithm
battery	I-Algorithm
(	O
also	O
called	O
mercuric	O
oxide	O
battery	O
,	O
mercury	B-Algorithm
cell	I-Algorithm
,	O
button	B-Algorithm
cell	I-Algorithm
,	O
or	O
Ruben-Mallory	O
)	O
is	O
a	O
non-rechargeable	O
electrochemical	O
battery	O
,	O
a	O
primary	B-Algorithm
cell	I-Algorithm
.	O
</s>
<s>
Mercury	B-Algorithm
batteries	I-Algorithm
use	O
a	O
reaction	O
between	O
mercuric	O
oxide	O
and	O
zinc	B-Application
electrodes	O
in	O
an	O
alkaline	O
electrolyte	O
.	O
</s>
<s>
The	O
voltage	O
during	O
discharge	O
remains	O
practically	O
constant	O
at	O
1.35volts	O
,	O
and	O
the	O
capacity	O
is	O
much	O
greater	O
than	O
that	O
of	O
a	O
similarly	O
sized	O
zinc-carbon	B-Algorithm
battery	I-Algorithm
.	O
</s>
<s>
Mercury	B-Algorithm
batteries	I-Algorithm
were	O
used	O
in	O
the	O
shape	O
of	O
button	B-Algorithm
cells	I-Algorithm
for	O
watches	O
,	O
hearing	O
aids	O
,	O
cameras	O
and	O
calculators	B-Application
,	O
and	O
in	O
larger	O
forms	O
for	O
other	O
applications	O
.	O
</s>
<s>
Due	O
to	O
the	O
content	O
of	O
toxic	O
mercury	O
and	O
environmental	O
concerns	O
about	O
its	O
disposal	O
,	O
the	O
sale	O
of	O
mercury	B-Algorithm
batteries	I-Algorithm
is	O
now	O
banned	O
in	O
many	O
countries	O
.	O
</s>
<s>
Both	O
ANSI	O
and	O
IEC	O
have	O
withdrawn	O
their	O
standards	O
for	O
mercury	B-Algorithm
batteries	I-Algorithm
.	O
</s>
<s>
The	O
mercury	O
oxide-zinc	O
battery	O
system	O
was	O
known	O
since	O
the	O
19th	O
century	O
,	O
but	O
did	O
not	O
become	O
widely	O
used	O
until	O
1942	O
,	O
when	O
Samuel	O
Ruben	O
developed	O
a	O
balanced	O
mercury	B-Algorithm
cell	I-Algorithm
which	O
was	O
useful	O
for	O
military	O
applications	O
such	O
as	O
metal	O
detectors	O
,	O
munitions	O
,	O
and	O
walkie-talkies	B-Application
.	O
</s>
<s>
Mercury	O
oxide	O
batteries	O
were	O
made	O
in	O
a	O
range	O
of	O
sizes	O
from	O
miniature	O
button	B-Algorithm
cells	I-Algorithm
used	O
for	O
hearing	O
aids	O
and	O
electric	O
wrist	O
watches	O
,	O
cylindrical	O
types	O
used	O
for	O
portable	O
electronic	O
apparatus	O
,	O
rectangular	O
batteries	O
used	O
for	O
transistor	O
radios	O
,	O
and	O
large	O
multicell	O
packs	O
used	O
for	O
industrial	O
applications	O
such	O
as	O
radio	O
remote	B-Protocol
control	I-Protocol
for	O
overhead	O
crane	O
systems	O
.	O
</s>
<s>
Mercury	B-Algorithm
batteries	I-Algorithm
use	O
either	O
pure	O
mercury(II )	O
oxide	O
(	O
HgO	O
)	O
—	O
also	O
called	O
mercuric	O
oxide	O
—	O
or	O
a	O
mixture	O
of	O
HgO	O
with	O
manganese	O
dioxide	O
(	O
MnO2	O
)	O
as	O
the	O
cathode	O
.	O
</s>
<s>
Mercuric	O
oxide	O
is	O
a	O
non-conductor	O
,	O
so	O
some	O
graphite	B-Application
is	O
mixed	O
with	O
it	O
;	O
the	O
graphite	B-Application
also	O
helps	O
prevent	O
collection	O
of	O
mercury	O
into	O
large	O
droplets	O
.	O
</s>
<s>
The	O
anode	O
is	O
made	O
of	O
zinc	B-Application
(	O
Zn	O
)	O
and	O
separated	O
from	O
the	O
cathode	O
with	O
a	O
layer	O
of	O
paper	O
or	O
other	O
porous	O
material	O
soaked	O
with	O
electrolyte	O
;	O
this	O
is	O
known	O
as	O
a	O
salt	O
bridge	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
during	O
discharge	O
,	O
zinc	B-Application
is	O
oxidized	O
(	O
loses	O
electrons	O
)	O
to	O
become	O
zinc	B-Application
oxide	O
(	O
ZnO	O
)	O
while	O
the	O
mercuric	O
oxide	O
gets	O
reduced	B-Operating_System
(	O
gains	O
electrons	O
)	O
to	O
form	O
elemental	O
mercury	O
.	O
</s>
<s>
Sodium	O
hydroxide	O
cells	O
have	O
nearly	O
constant	O
voltage	O
at	O
low	O
discharge	O
currents	O
,	O
making	O
them	O
ideal	O
for	O
hearing	O
aids	O
,	O
calculators	B-Application
,	O
and	O
electronic	O
watches	O
.	O
</s>
<s>
Mercury	B-Algorithm
cells	I-Algorithm
have	O
very	O
long	O
shelf	O
life	O
,	O
up	O
to	O
10	O
years	O
.	O
</s>
<s>
A	O
different	O
form	O
of	O
mercury	B-Algorithm
battery	I-Algorithm
uses	O
mercuric	O
oxide	O
and	O
cadmium	O
.	O
</s>
<s>
It	O
was	O
designed	O
as	O
a	O
series	O
stack	O
of	O
cells	O
,	O
where	O
one	O
cell	O
had	O
a	O
reduced	B-Operating_System
capacity	O
resulting	O
in	O
a	O
very	O
distinct	O
two-step	O
voltage	O
discharge	O
characteristic	O
.	O
</s>
<s>
Mercury	B-Algorithm
batteries	I-Algorithm
using	O
a	O
mercury(II )	O
oxide	O
cathode	O
have	O
a	O
very	O
flat	O
discharge	O
curve	O
,	O
holding	O
constant	O
1.35	O
V	O
(	O
open	O
circuit	O
)	O
voltage	O
until	O
about	O
the	O
last	O
5%	O
of	O
their	O
lifetime	O
,	O
when	O
their	O
voltage	O
drops	O
rapidly	O
.	O
</s>
<s>
The	O
voltage	O
remains	O
within	O
1%	O
for	O
several	O
years	O
at	O
light	O
load	O
,	O
and	O
over	O
a	O
wide	O
temperature	O
range	O
,	O
making	O
mercury	B-Algorithm
batteries	I-Algorithm
useful	O
as	O
a	O
voltage	O
reference	O
in	O
electronic	O
instruments	O
and	O
in	O
photographic	O
light	O
meters	O
.	O
</s>
<s>
Mercury	B-Algorithm
batteries	I-Algorithm
with	O
cathodes	O
made	O
of	O
a	O
mix	O
of	O
mercuric	O
oxide	O
and	O
manganese	O
dioxide	O
have	O
output	O
voltage	O
of	O
1.4	O
V	O
and	O
a	O
more	O
sloped	O
discharge	O
curve	O
.	O
</s>
<s>
The	O
1991	O
European	O
commission	O
directive	O
91/157	O
,	O
when	O
adopted	O
by	O
member	O
states	O
,	O
prohibited	O
the	O
marketing	O
of	O
certain	O
types	B-Algorithm
of	I-Algorithm
batteries	I-Algorithm
containing	O
more	O
than	O
25milligrams	O
of	O
mercury	O
,	O
or	O
,	O
in	O
the	O
case	O
of	O
alkaline	B-Algorithm
batteries	I-Algorithm
,	O
more	O
than	O
0.025	O
%	O
by	O
weight	O
of	O
mercury	O
.	O
</s>
<s>
In	O
1992	O
,	O
the	O
state	O
of	O
New	O
Jersey	O
prohibited	O
sales	O
of	O
mercury	B-Algorithm
batteries	I-Algorithm
.	O
</s>
<s>
In	O
1996	O
,	O
the	O
United	O
States	O
Congress	O
passed	O
the	O
Mercury-Containing	O
and	O
Rechargeable	O
Battery	O
Management	O
Act	O
that	O
prohibited	O
further	O
sale	O
of	O
mercury-containing	O
batteries	O
(	O
with	O
an	O
exception	O
for	O
up	O
to	O
25mg	O
of	O
mercury	O
per	O
button	B-Algorithm
cell	I-Algorithm
)	O
.	O
</s>
<s>
Alternatives	O
used	O
are	O
zinc-air	B-Algorithm
batteries	I-Algorithm
,	O
with	O
similar	O
discharge	O
curve	O
,	O
high	O
capacity	O
,	O
but	O
much	O
shorter	O
lifetime	O
(	O
a	O
few	O
months	O
)	O
,	O
and	O
poor	O
performance	O
in	O
dry	O
climates	O
;	O
alkaline	B-Algorithm
batteries	I-Algorithm
with	O
voltage	O
widely	O
varying	O
through	O
their	O
lifetime	O
;	O
and	O
silver-oxide	B-Device
batteries	I-Device
with	O
higher	O
voltage	O
(	O
1.55	O
V	O
)	O
and	O
very	O
flat	O
discharge	O
curve	O
,	O
which	O
makes	O
them	O
possibly	O
the	O
best	O
,	O
though	O
expensive	O
,	O
replacement	O
after	O
recalibrating	O
the	O
meter	O
to	O
the	O
new	O
voltage	O
.	O
</s>
<s>
Special	O
adapters	O
with	O
voltage	O
dropping	O
Schottky	O
or	O
germanium	O
diodes	O
allow	O
silver	B-Device
oxide	I-Device
batteries	I-Device
to	O
be	O
used	O
in	O
equipment	O
designed	O
for	O
mercury	B-Algorithm
batteries	I-Algorithm
.	O
</s>
<s>
Formerly	O
,	O
the	O
zinc	B-Application
anodes	O
of	O
dry	O
cells	O
were	O
amalgamated	O
with	O
mercury	O
,	O
to	O
prevent	O
side-reactions	O
of	O
the	O
zinc	B-Application
with	O
the	O
electrolyte	O
that	O
would	O
reduce	O
the	O
service	O
life	O
of	O
the	O
battery	O
.	O
</s>
<s>
Manufacturers	O
have	O
changed	O
to	O
a	O
purer	O
grade	O
of	O
zinc	B-Application
,	O
so	O
amalgamation	O
is	O
no	O
longer	O
required	O
and	O
mercury	O
is	O
eliminated	O
from	O
the	O
dry	O
cell	O
.	O
</s>
