Edison Storage Battery

He wants an element usable "in an alkaline electrolyte" whose oxide has a heat of formation as low or lower than mercury oxide. That is a materials search written as a sentence.

The electrolyte is caustic: it attacks skin and eyes and does not hurt at first. Glasses and gloves on, water to hand, work over a tray.

Cut two plates about 40 x 60 mm — one iron, one nickel-plated steel. Iron is the negative, nickel the positive.

Abrade and degrease both. Oxide and grease from handling add resistance and make the cell look worse than it is.

Dissolve 20 g of sodium hydroxide in 200 ml of water, adding alkali to water, never the reverse. It warms as it dissolves; let it cool.

Edison specifies potassium hydroxide. Sodium hydroxide is the safer, cheaper stand-in and behaves the same way here — record the change rather than pretending it is the original.

Suspend both plates in the electrolyte, parallel, about 20 mm apart, not touching. Keep the top edges dry for the leads.

Read the voltage. It is small — near zero. A storage cell holds nothing until you put it there. That is the difference from the dry cell.

Apply about 2 V with the nickel plate positive. Bubbles form on both plates. Charge for ten minutes, then disconnect.

Read it again with nothing connected. The cell now holds a voltage of its own. Compare with step 8 — you stored energy chemically.

Connect a small lamp and time how long a useful voltage lasts. Record it — this is the cell's capacity in the crudest honest terms.

Charge and discharge three times, recording each. The figures should hold up rather than collapse. Edison's claim was permanence — test it.

Lift both plates and look for sediment. An alkaline nickel-iron cell sheds very little, which is exactly why Edison chose the chemistry.

The patent. US 678,722, "Reversible Galvanic Battery", Case No. 1,060, filed 20 June 1901 and granted 16 July 1901 to Thomas A. Edison of Llewellyn Park, Essex County, New Jersey. Note the pace: filed and granted inside a month, which happened when an examiner had a clear, well-drafted case in front of him.

⚠ The grant date is not the date Google Patents shows first. The metadata date on this patent is 20 June 1901, which is the filing date; the printed sheet says "Patented July 16, 1901". This trips people up constantly on twentieth-century patents, and the rule is simple — read the "Patented" line on the document.

This patent is one move in a series, and it says so. Edison refers to his earlier application of 31 October 1900 (Serial No. 34,994) in which "the metals, cadmium, and copper are employed as the elements in an alkaline electrolyte", giving a cell "wherein the initial and final states of the electrolyte are the same". That last phrase is the whole design philosophy: in a lead-acid cell the electrolyte is consumed and regenerated, so its state tells you the charge and its chemistry attacks the plates. In an alkaline cell the electrolyte is a spectator — it carries ions and is not used up. The present patent's contribution is to replace copper as "the oxygen-furnishing element" with something lighter and more energetic, and the element he lands on is nickel.

Why he cared so much about weight. The target was the electric car, in an era when electric, steam and petrol vehicles were genuinely competing. Battery mass is the whole problem for an electric vehicle, because every kilogram of battery is a kilogram the battery must also move. Edison's own words are "remarkably light weight per unit of energy" and "deliver the energy to the exterior circuit at a higher rate" — energy density and power density, named in 1901 in almost the terms an engineer would use now.

He was right about the chemistry and wrong about the market. The nickel-iron cell turned out to be phenomenally durable — cells from the 1910s have been recovered still working, because there is no sulphation and very little shedding. But it is inefficient, it self-discharges noticeably, it performs poorly in cold, and it was expensive. Meanwhile the electric starter motor arrived in 1912 and removed the hand crank, which was the petrol car's worst feature, and the electric car market largely evaporated. Edison's battery found its long life instead in mine locomotives, railway signalling, standby power and lighting — places where nothing may fail for twenty years and nobody minds the weight. A technology that misses its intended market and thrives in another is a normal outcome, not a failure, and it is worth saying so plainly.