Leclanché Cell

Dissolve ammonium chloride in warm water until saturated, then let it cool.

The carbon rod carries the current; the manganese dioxide around it does the chemical work.

1. Mix manganese dioxide with a little powdered graphite to improve conductivity.
2. Pack the mixture tightly around the graphite electrode inside a porous bag or perforated tube.
3. Keep the top of the rod clean and dry for the connection.

Stand the packed carbon assembly and a zinc rod in the jar of electrolyte, not touching each other.

1. Zinc is the negative terminal.
2. Carbon is the positive terminal.
3. Both must stand clear of the bottom so debris cannot bridge them.

Read the open-circuit voltage, then watch what a heavy load does.

1. Expect about 1.5 V unloaded.
2. Connect a low-value resistor and watch the voltage sag within a minute or two.
3. Disconnect, wait ten minutes, and read again — it will have largely recovered.

Georges Leclanché, a French engineer, patented this cell in 1866, and the Belgian telegraph service adopted it soon after. Its combination of cheap materials, no acid to spill and no porous pot to maintain beat the Daniell cell for anything that did not need a continuous draw.

Its real descendant arrived when the liquid was replaced by a paste and the zinc became the container itself. That is the dry cell — Carl Gassner patented a version in 1886 — and the ordinary zinc-carbon battery on sale today is still recognisably Leclanché's chemistry: zinc, manganese dioxide, carbon, ammonium chloride.

Being careful with the claim: the modern alkaline cell is not a Leclanché cell. It shares the zinc and manganese dioxide but uses potassium hydroxide, which is what lets it sustain the heavy continuous currents this one cannot.