Baghdad Battery

The Baghdad Battery is the name given to a set of three artifacts which were found together: a ceramic pot, a tube of copper, and a rod of iron. It was discovered in present-day Khujut Rabu, Iraq in 1936, close to the metropolis of Ctesiphon, the capital of the Parthian (150 BC – 223 AD) and Sasanian (224–650 AD) empires, and it is believed to date from either of these periods.

Its origin and purpose remain unclear. It was hypothesized by Wilhelm König, at the time director of the National Museum of Iraq, that the object functioned as a galvanic cell, possibly used for electroplating, or some kind of electrotherapy, but there is no electroplated object known from this period, and the claims are universally rejected by archaeologists. An alternative explanation is that it functioned as a storage vessel for sacred scrolls.

Ten similar clay vessels had been found earlier. Four were found in 1930 in Seleucia dating to the Sassanid period. Three were sealed with bitumen and contained a bronze cylinder, again sealed, with a pressed-in papyrus wrapper containing decomposed fiber rolls. They had been staked out with up to four metal rods made of bronze and iron sunk into the ground and their cult meaning and use are inferred. Six other clay vessles were found nearby. Some had bronze wrappers with badly decomposed cellulose fibers. Others had iron nails or lead plates.

The artifact disappeared in 2003 during the US-led invasion of Iraq.

Physical description and dating
The artifacts consist of a terracotta pot approximately 140 mm tall, with a 38 mm mouth, containing a cylinder made of a rolled copper sheet, which houses a single iron rod. At the top, the iron rod is isolated from the copper by bitumen, with plugs or stoppers, and both rod and cylinder fit snugly inside the opening of the jar. The copper cylinder is not watertight, so if the jar were filled with a liquid, this would surround the iron rod as well. The artifact had been exposed to the weather and had suffered corrosion.

Austrian archeologist Wilhelm König thought the objects might date to the Parthian period, between 250 BC and AD 224. However, according to St John Simpson of the Near Eastern department of the British Museum, their original excavation and context were not well-recorded, and evidence for this date range is very weak. Furthermore, the style of the pottery is Sasanian (224–640).

Albert Al-Haik noted original reports from the 1936 dig at Khuyut Rabbou'a giving the location as an area northeast of Baghdad, "some two miles off the Baghdad eastern bund." W. B. Hafford gives context to the discovery of the artifacts in his reaction video to Milo Rossi's video on the subject.

Comparable finds
Similar vessels, which can be distinguished primarily by their contents, had previously been found and examined more closely:

Four sealed clay vessels were excavated at Seleucia in 1930 under the archaeological direction of Leroy Waterman, University of Michigan. Three of these finds, dated to the late Sassanid period (5th to 6th centuries AD), were sealed with bitumen. These vessels contained a bronze cylinder, again sealed, with a pressed-in papyrus wrapper. Although writing could not be found on any of these largely decomposed fiber rolls, on the other hand these clay containers had been staked out with up to four metal rods made of bronze and iron sunk into the ground, their cult meaning and use are inferred. The fourth jar, also sealed, contained broken glass.

In 1931, a German-American excavation expedition led by Ernst Kühnel found six more clay vessels in the immediately neighboring Ctesiphon, including three sealed find objects, each with one, three and ten wrapped and sealed bronze rolls. Inside these bronze wraps were already badly decomposed cellulose fibers. Another clay vessel contained three sealed bronze cylinders. In the other two vessels, which were also sealed, there were plates of originally pure lead coated with lead carbonate in a find specimen; in the other ten heavily corroded iron nails, on which traces of a wrapped organic fiber material could be detected. Although a round coil of metal foil and paper is reminiscent of the construction-typical feature of an electrolytic capacitor constructed, for example, with soaked paper, there is no immediately tangible electrophysical functional basis for this or the finds excavated at Seleucia due to the obviously missing counter-electrode.

Theories concerning operation
Its origin and purpose remain unclear. Wilhelm König was an assistant at the Iraq Museum in the 1930s. He had observed a number of very fine silver objects from ancient Iraq, plated with very thin layers of gold, and speculated that they were electroplated. In 1938 he authored a paper offering the hypothesis that they may have formed a galvanic cell, perhaps used for electroplating gold onto silver objects. This interpretation is rejected by archeologists and scientists.

Corrosion of the metal and tests both indicate that an acidic agent such as wine or vinegar was present in the jar. This led to speculation that the liquid was used as an acidic electrolyte solution to generate an electric current from the difference between the electrode potentials of the copper and iron electrodes.

Supporting experiments
After the Second World War, Willard Gray demonstrated current production by a reconstruction of the inferred battery design when filled with grape juice. W. Jansen experimented with benzoquinone (some beetles produce quinones) and vinegar in a cell and got satisfactory performance.

In 1978, Arne Eggebrecht, a past director of the Roemer- und Pelizaeus-Museum Hildesheim reportedly reproduced the electroplating of gold onto a small statue. There are no (direct) written or photographic records of this experiment. In an article from the BBC, Dr 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."

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.

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".

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 Eggebrecht used a more efficient, modern electrolyte, and that using only vinegar, or other electrolytes available at the time assumed, the battery would be very feeble, and for that and other reasons concludes 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.

Alternative hypothesis
The artifacts are similar to other objects believed to be storage vessels for sacred scrolls from nearby Seleucia on the Tigris. The object was looted along with thousands of other artifacts from the National Museum during the 2003 invasion of Iraq.

In March 2012, Professor Elizabeth Stone of Stony Brook University, an expert on Iraqi archaeology, returning from the first archaeological expedition in Iraq after 20 years, stated that she does not know a single archaeologist who believed that these were batteries.

MythBusters TV program
The Discovery Channel program  MythBusters built replicas of the jars to see if it was possible for them to have been used for electroplating or electrostimulation. On MythBusters' 29th episode (23 March 2005), ten hand-made terracotta jars were fitted to act as batteries. Lemon juice was chosen as the electrolyte to activate the electrochemical reaction between the copper and iron. Connected in series, the battery produced 4 volts of electricity. When linked in series, the cells had sufficient power to electroplate a small token and to deliver current to acupuncture type needles for therapeutic purposes, but not enough to deliver an electric shock to MythBusters co-host Adam Savage who was instead pranked by co-hosts who hooked him up to a 10,000 volt cattle fence shock generator. 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.