Baghdad Battery

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The Baghdad Battery is the common name for a number of artifacts apparently discovered in the village of Khuyut Rabbou'a (near Baghdad, Iraq) in 1936. 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, and (in 1940, having returned to Berlin due to illness) published a paper speculating that they may have been galvanic cells, perhaps used for electroplating gold onto silver objects.

1 Description and dating
2 Speculations on function
- 2.1 Electrical
- 2.2 Nonelectrical
3 Controversy and comparisons
- 3.1 MythBusters
4 See also
5 References
6 External articles, references, resources

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 asphalt plugs or stoppers, and both rod and cylinder fit snugly inside the opening of the jar which bulges outward towards the middle (reverse hourglass shape). 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 jumpstart the electrochemical reaction with the two metals.

König thought the objects might be Parthian (between 250 BC and 224 AD) because the village where they were excavated was Parthian. 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), so they are probably much more recent than König thought.

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 peoples 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 myths.

Nonelectrical

Skeptical 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 asphalt 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 (though controversial stone reliefs depicting arc lights have been suggested);
an asphalt 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.

Controversy and comparisons

Some have claimed that these artifacts provide evidence of ancient knowledge of electricity, millennia before the conventional dates given for its discovery. However 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. Any basic understanding of electrical theory of these cultures did not allow them to render more robust designs. The facts that using the electrodes in the electrolyte to produce the voltage, and using larger vessels gives a larger current is obvious to us today; but it is unclear if the ancient civilizations realised this.

Whoever made the Baghdad batteries, assuming they were in fact galvanic cells, may not have fully understood the principles. For example, it is well known that the Ancient Greeks were aware of electrostatic electrical phenomena produced by amber, but they regarded it as a mere curiosity or toy and developed no electrical theory or functional devices. For evidence of ancient Parthian knowledge of the ideas of electricity, records of its use await discovery in more concrete terms, such as seeing it discussed in their writings (though they may not have stated it as 'electricity', relating instead a mystical connotation) or gaining a better perception that their "batteries" were designed with a knowledge of electrical theory. A controversy also exists as to whether the Ancient Egyptians could have used such devices.

As electrical generators, the "Baghdad batteries" would be inefficient when compared to modern devices. However, if placed in appropriate network arrays, these artifacts could produce a qualitative power output. 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 (but Volta's devices 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.

MythBusters

On MythBusters' 29th episode (which aired on March 23, 2005), the Baghdad battery "myth" was put to the test. 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, they produced upwards of 4 volts. Then, the major question was, “What were these ancient batteries used for?”

The show’s research staff discovered three possible reasons: electroplating, medical pain relief (through acupuncture), and religious experience. It was discovered that the “linked” batteries 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 angels. Instead of linking the angels’ 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.

References

Dubpernell, G., "Evidence of the use of primitive batteries in antiquity". Selected Topics in the History of Electrochemistry, The Electrochemical Society, I-22 Princetn, NJ. 1978.
Eggert, G., "The Enigma of the 'Battery of Baghdad". Proceedings 7th European Skeptics Conference. 1995.
Eggert, G., "The enigmatic 'battery of Baghdad". Skeptical Inquirer, May-June 1996 V20 N3 PG31(4).
MacKechnie, J. C. "An Early Electric cell?" Journal of the Institute of Electrical Engineers, 6:356-57. 1960.
Paszthory E., "Electricity generation or Magic? The analysis of an unusual group of finds from Mesopotamia". MASCA Research Papers in Science and Technology 6:31-8. 1989.
Zymet, Matthew, "Electric Artifact". The Learning Channel.