Dry Cell Battery

Gassner writes that his invention "consists in the intermixture and employment of oxide of zinc". Not the battery — an additive. That is the whole claim.

Ammonium chloride and zinc chloride irritate eyes and skin. Glasses on, wash your hands afterwards.

Roll a piece of zinc sheet into a cylinder about 40 mm across and close the bottom tightly. The cup is container and electrode at the same time.

Place a graphite rod exactly in the middle without touching the zinc. Contact means a short circuit.

In a second jar dissolve 25 g of ammonium chloride in 100 ml of water — liquid, no additive. That is the Leclanché arrangement, as your control.

Note the voltage, then tilt the jar. It leaks. That behaviour alone makes a torch impossible.

Combine 20 g of manganese dioxide with 4 g of graphite powder dry. The graphite makes the mixture conductive.

Stir 10 g of ammonium chloride, 5 g of zinc oxide and a little water into a stiff paste, then fold it into the manganese dioxide mixture. The zinc oxide is Gassner's addition.

Pack the paste tightly between the zinc cup and the carbon rod with no voids. Air bubbles break the ionic path.

Close the top of the cup and leave it for two hours until the paste sets. Only then is it a dry cell.

Note the voltage, then invert the finished cell and shake it. Nothing leaks. Compare with step 6 — that is the entire advance.

Connect a small lamp and read the voltage every two minutes for ten minutes. The slow decline shows the manganese dioxide absorbing hydrogen.

Zinc of one to carbon of the other. The voltage doubles — that is how cells become a battery.

The patent. US 373,064, "Galvanic Battery", filed 20 May 1887, granted 15 November 1887 to Carl Gassner Jr. of Mainz. Important for the dating: the American specification lists the earlier foreign patents itself — Germany, 8 April 1886, No. 37,758, together with Belgium (16 July 1886, No. 73,872), France (17 July 1886, No. 177,465) and Austria. Priority therefore lies in Germany in 1886, not in the United States in 1887. Citing only the US number moves the invention eighteen months later than it belongs.

🔴 The claim is narrower than almost every account suggests. Gassner does not claim "the dry battery". He writes that the invention "relates to galvanic elements; and it consists in the intermixture and employment of oxide of zinc as an addition to the exciting agent". He states explicitly that he does not confine himself "to the precise ingredients or proportions" so long as the zinc oxide is present in the exciting agent. The claim is an additive, not a device.

Why zinc oxide specifically. A zinc–ammonium chloride cell has a quiet problem: the zinc is attacked even when no current flows. This "local action" discharges the cell on the shelf and eventually eats holes in the cup, which is also the container — a leaking cell is not merely flat, it is a mess. Zinc oxide in the electrolyte shifts the chemical equilibrium so that the zinc is attacked far more slowly. Only then does a thick paste become a storable product. Others had already tried thickening the electrolyte; the shelf life is Gassner's contribution.

What "dry" actually means. Nothing about a dry cell is dry. Without water no ions move, and without ions no current flows. The paste contains water — it simply no longer flows. That is why a dried-out battery really is dead, and why the name is a marketing term rather than a chemical state.

What came of it. The dry cell is what made portable electricity possible at all: the torch, the doorbell, the field telephone, later the portable radio. Today's zinc–carbon cell keeps the same construction — zinc cup outside, carbon rod in the centre, manganese dioxide mass between. Cut open a cheap zinc–carbon battery and you find Gassner's 1886 arrangement, and the alkaline cell merely turns it inside out.