Baghdad Battery

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.

Description

The artifacts consist of ~130 mm (~5 inch) long clay jars containing a copper cylinder made of a rolled up copper sheet, capped at the bottom, in turn covering and protecting an iron rod. The iron rods are isolated from the copper by asphalt plugs or stoppers, and the cylinders fairly neatly fit the necks of the jars, which bulge toward the middle. The copper cylinders are not watertight, so that if the jars were filled with a liquid, this would surround the iron rod as well. The artifacts had been exposed to the weather and had suffered corrosion, although fairly mild given the presence of an electrochemical couple (which may lend evidence against an ancient date).

Dating

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 Sassanian (224-640 AD), 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 in fact 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 the ancients 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 artefacts 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

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 realise 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 awaits 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.

Comparisons

As electrical generators, the "Baghdad batteries" would be inefficient when compared to modern devices. If placed in appropriate network arrays, these artifacts though could produce a qualitative power output. The formulation of a similar electrochemical couple experiment by Luigi Galvani 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 continous 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.

External articles, references, resources

Web links

Battery, Baghdad, 250 BC : Museum of Ancient Inventions
Baghdad Battery : Unmuseum.org
Baghdad Battery : Strange Artifacts - World Mysteries
Electricity in ancient times. WUFOC and NÄRKONTAKT.

Other

Zymet, Matthew, "Electric Artifact". The Learning Channel.