5.5 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Baghdad Battery | 2/3 | https://en.wikipedia.org/wiki/Baghdad_Battery | reference | science, encyclopedia | 2026-05-05T09:17:17.899908+00:00 | kb-cron |
After the publication of a sensationalist article describing the jar in the March 1939 edition of Astounding Science-Fiction, electrical engineer Willard F. M. Gray at the General Electric plant in Pittsfield, Massachusetts made a reconstruction. Gray chose to test it with copper (II) sulphate solution as the electrolyte. He reported that this “worked quite well for a short time.” Arne Eggebrecht, a past director of the Roemer- und Pelizaeus-Museum Hildesheim, claimed to have electroplated silver onto an unspecified surface. Using many replicas of the jar connected together, with grape juice as the electrolyte, Eggebrecht only produced a layer of silver 100 nanometres thick. Speaking to a reporter for BBC News, Bettina Schmitz, a researcher based at the same museum, said, "There does not exist any written documentation of the experiments which took place here in 1978... The experiments weren't even documented by photos, which really is a pity...I have searched through the archives of this museum and I talked to everyone involved in 1978 with no results." In 1993, W. Jansen reported an experiment with an electrolyte of diluted acetic acid with some dissolved benzoquinone in a cell and got "good experimental results". On the 29th episode (23 March 2005) of Discovery Channel program MythBusters, the build team made ten hand-made replica terracotta jars fitted to act as batteries. Lemon juice was chosen as the electrolyte to allow the electrochemical reaction between the copper and iron. With all ten connected in series, the battery produced 4.33 volts of electricity. When linked in series, the ten cells had sufficient power to visibly electroplate a small copper token with zinc when left overnight. Five were sufficient to deliver a painful current through acupuncture type needles stuck in the skin, but ten were not enough to deliver an electric shock to dry skin. Archaeologist Ken Feder commented on the show noting that no archaeological evidence has been found either for connections between the jars (which would have been necessary to produce the required voltage) or for their use for electroplating.
== Problems with the electrical interpretation ==
=== Lack of electrical connections === Though the iron rod did project outside of the asphalt plug, the copper tube did not, making it impossible to connect a wire to this to complete a circuit.
=== Expected residues === A 2002 article in Plating & Surface Finishing addressed the expected results of the jar being used for electroplating. If used as an electrical cell, copper would have gone into solution in the liquid and copious amounts of copper salts would have been seen in the ceramic vessel and copper metal on the iron parts. This jar was theorised to be the battery but to effect electroplating another cell would be needed. Nothing resembling an electroplating cell with the associated gold or silver traces has been reported.
=== Electroplating hypothesis === König himself seems to have been mistaken on the nature of the objects he thought were electroplated. They were apparently fire-gilded (with mercury). Paul Craddock of the British Museum said, "The examples we see from this region and era are conventional gold plating and mercury gilding. There's never been any irrefutable evidence to support the electroplating theory". König had seen primitive gold electroplating using a ceramic pot being done in Baghdad in 1938. He proposed that the technique could have been passed down through the millennia as a secret of the local jewelers. Gerhard Eggert showed that the method used by the Baghdadi silversmiths in 1938 was almost exactly the same process as that invented in Birmingham, UK in 1839 by John Wright - using a ceramic flowerpot. David A. Scott, senior scientist at the Getty Conservation Institute and head of its Museum Research Laboratory, writes: "There is a natural tendency for writers dealing with chemical technology to envisage these unique ancient objects of two thousand years ago as electroplating accessories (Foley 1977), but this is clearly untenable, for there is absolutely no evidence for electroplating in this region at the time". Paul T. Keyser of the University of Alberta noted that using only vinegar, or other electrolytes available at the time the jar was made, the battery would be very feeble. For that and other reasons, Keyser concluded that even if this was in fact a battery, it could not have been used for electroplating. However, Keyser still supported the battery theory, but believed it was used for some kind of mild electrotherapy such as pain relief, possibly through electroacupuncture.
=== Bitumen as an insulator === A bitumen seal, being thermoplastic, would be extremely inconvenient for a galvanic cell, which would require frequent topping up of the electrolyte for extended use.
=== Oxygen needed to function === Tests run by Emmerich Paszthory showed that oxygen was a limiting factor for the cell to function when the electrolyte was water with salt and acetic or citric acids. Sealing the copper cylinders in the way seen in the archaeological finds brought electricity production to a stop at once.
=== Iron shape === Emmerich Paszthory found that when used as an electrode an iron rod erodes at the neck, so the tapered shape of the iron nail showed it had not been used as an electrode.