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Baghdad Battery
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The Baghdad Battery, sometimes referred to as the Parthian Battery, is the common name for a number of artifacts created in Mesopotamia, possibly during the Parthian or Sassanid period (the early centuries AD). These jars were probably discovered in 1936 in the village of Khuyut Rabbou'a, near Baghdad, Iraq. These artifacts came to wider attention in 1938 when Wilhelm König, the German director of the National Museum of Iraq, found the objects in the museum's collections.
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The Baghdad Battery, sometimes referred to as the Parthian Battery, is the common name for a number of artifacts created in Mesopotamia, possibly during the Parthian or Sassanid period (the early centuries AD). These jars were probably discovered in 1936 in the village of Khuyut Rabbou'a, near Baghdad, Iraq. These artifacts came to wider attention in 1938 when Wilhelm König, the German director of the National Museum of Iraq, found the objects in the museum's collections. In 1940 König published a paper speculating that they may have been galvanic cells, perhaps used for electroplating gold onto silver objects.
This interpretation continues to be considered as at least a hypothetical possibility. If correct, the artifacts would predate Alessandro Volta's 1800 invention of the electrochemical cell by more than a millennium.
Description and dating
The artifacts consist of ~130mm (~5 inch) tall terracotta jars (with a one and a half inch mouth) containing a copper cylinder made of a rolled-up copper sheet, which houses a single iron rod. At the top, the iron rod is isolated from the copper by bitumen plugs or stoppers, and both rod and cylinder fit snugly inside the opening of the jar which bulges outward towards the middle. The copper cylinder is not watertight, so when the jar was filled with a liquid, this would surround the iron rod as well. The artifact had been exposed to the weather and had suffered corrosion, although mild given the presence of an electrochemical couple. This has led some scholars to believe lemon juice, grape juice, or vinegar was used as an acidic agent to jump-start the electrochemical reaction with the two metals.
König thought the objects might date to the Parthian period (between 250 BC and AD 224).
However according to Dr. St. John Simpson of the Near Eastern department of the British Museum, their original excavation and context were not well recorded (see stratigraphy), so evidence for this date range is very weak. Furthermore, the style of the pottery (see typology) is Sassanid (224-640).
Most of the components of the objects are not particularly amenable to advanced dating methods. The ceramic pots could be analysed by thermoluminescence dating, but this has apparently not yet been done; in any case, it would only date the firing of the pots, which is not necessarily the same as when the complete artifact was assembled. Another possibility would be ion diffusion analysis, which could indicate how long the objects were buried.
Speculations on function
Electrical
Copper and iron form an electrochemical couple, so that in the presence of any electrolyte, an electric potential (voltage) will be produced. König had observed a number of very fine silver objects from ancient Iraq which were plated with very thin layers of gold, and speculated that they were electroplated using batteries of these "cells". 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.
However, even among those who believe the artifacts were electrical devices, electroplating as a use is not well regarded today. The gilded objects which König thought might be electroplated are now believed to have been fire-gilded (with mercury). Reproduction experiments of electroplating by Dr. Arne Eggebrecht consumed "many" reproduction cells to achieve a plated layer just one micrometre thick. Other scientists noted that Dr. Eggebrecht used a more efficient, modern electrolyte; using only vinegar, the "battery" is very feeble.
An alternative, but still electrical explanation was offered by Paul Keyser. It was suggested that a priest or healer, using an iron spatula to compound a vinegar based potion in a copper vessel, may have felt an electrical tingle, and used the phenomenon either for electro-acupuncture, or to amaze supplicants by electrifying a metal statue.
The Discovery Channel program MythBusters determined that it was indeed plausible for ancient people to have used the Baghdad Battery for electroplating or electrostimulation. However, the batteries which they reproduced did not produce a substantial amount of energy and had to be connected in series in order to test the theories.
Nonelectrical
Sceptical archaeologists see the electrical experiments as embodying a key problem with experimental archaeology; such experiments can only show that something was physically possible, they say nothing about whether it actually occurred. Further, there are many difficulties with the interpretation of these artifacts as galvanic cells:
- the bitumen completely covers the copper cylinder, electrically insulating it, so no current can be drawn without modifying the design;
- there are not any wires or conductors with them;
- no widely accepted electrical equipment is associated with them. (Controversial stone reliefs depicting arc lights have been suggested, however the voltages obtained are orders of magnitude below what would be needed to produce arc lighting);
- a bitumen seal, being thermoplastic, is excellent for forming a hermetic seal for long term storage. It would be extremely inconvenient however for a galvanic cell, which would require frequent topping up of the electrolyte (if they were intended for extended use).
Some observe that the artifacts strongly resemble another type of object with a known purpose – namely, storage vessels for sacred scrolls from nearby Seleucia on the Tigris. Those vessels do not have the outermost clay jar, but are otherwise almost identical. Since it is claimed these vessels were exposed to the elements, it would not be at all surprising if any papyrus or parchment inside had completely rotted away, perhaps leaving a trace of slightly acidic organic residue.
Interpretation as electrical device
Even if it is accepted that the "Baghdad batteries" were in fact electrical devices, this provides no evidence of any real knowledge of electrical phenomena. Thales of Miletus was aware of electrostatic phenomena produced by amber, without possessing any theoretical explanation.
As electrical power supplies, the "Baghdad batteries" would be inefficient when compared to modern devices. Luigi Galvani formulated a similar electrochemical couple experiment in the 1780s and, 20 years later, Alessandro Volta developed enough theory to convert Galvani's simple experiment into the efficient voltaic pile, producing around 30 volts of continuous current using devices which were much larger than known Baghdad relics. Within two or three more years Sir Humphry Davy was using voltaic piles that produced 1,000 volts and enough current to run an arc lamp.
The idea that the battery could have produced usable levels of electricity has been put to the test at least twice.
On the 1980 British Television series Arthur C. Clarke's Mysterious World, Egyptogist Dr Arne Eggebrecht used a recreation of the battery, filled with grape juice, to produce half a volt of electricity, demonstrating for the programme that the battery could electroplate a silver statuette in two hours, using a gold cyanide solution. Dr Eggebrecht speculated that museums could contain many mislabelled "golden" items that are merely electroplated.. However, doubt has recently been cast on the validity of these experiments
On MythBusters' 29th episode (which aired on March 23, 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. (Oddly enough, it was discovered that a single lemon produced more voltage than one of the batteries). When all of the batteries were linked together in series, they produced upwards of 4 volts. Then, the major question was, "What were these ancient batteries used for?"
The show's research staff proposed three possible uses: electroplating, medical pain relief (through acupuncture), and religious experience. It was discovered that when linked in series the cells indeed had sufficient power to electroplate a small token. For acupuncture, the batteries produced a "random" pulse that could be felt through the needles; however, it began to produce a painful burning sensation when the batteries were grounded to two needles at once. For the religious experience aspect of the batteries, a replica of the Ark of the Covenant was constructed, complete with two cherubim. Instead of linking the cherubim's golden wings to the low power batteries, an electric fence generator was connected. When touched, the wings produced a strong feeling of tightness in the chest. Although the batteries themselves had not been used, it was surmised that, due to the apparent lack of knowledge of electricity, any form of electrical sensation from them could equate to the "divine presence" in the eyes of ancient people. In the end, the Baghdad battery myth was found "plausible" on all three accounts.
See also
Further reading
- Von Handorf, D E., The Baghdad battery - myth or reality?. Plating and Surface Finishing (USA). Vol. 89, no. 5, pp. 84-87. May 2002
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