Baghdad Battery

Austrian archaeologist Wilhelm König's description of the find, translated into English, included: In a vase-like container of bright yellow clay, the neck of which had been removed, a copper cylinder was stuck, held in place by asphalt. The vase was about 15cm high; the cylindrical tube with a closed bottom made from sheet copper had a diameter of 26 mm and a height of 9 cm. In the latter a completely oxidized rod of iron was found, held in place by a sort of stopper of asphalt... 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 clay vessels were excavated at Seleucia in 1930 under the archaeological direction of Leroy Waterman, University of Michigan. All four were common unglazed ceramic, sealed with bitumen stoppers and between 6 and 8 inches (15 to 20cm) tall. Three of these finds were lying horizontal, held in place by up to four metal rods at the ends and sides. The rods were six to ten inches (15 to 25cm) long, one iron rod per jar and the rest bronze. Each contained a bronze cylinder, sealed at both ends, all three the same size: 1¼ inches (3cm) in diameter and 3 inches (7½cm) long. All three cylinders contained plant matter, one decomposed to flakes, one just a small closely-wrapped core and the other appearing to be a papyrus roll folded over at the ends. The fourth jar was found upright and contained fragments of a small broken glass bottle. Silver coins found in context imply a Sasanian date. 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. These finds were also dated to the late Sasanian period. == Electric battery theory ==

Its origin and purpose remain unclear. offering the hypothesis that the Khujut Rabu jar may have formed a galvanic cell, perhaps used for electroplating gold onto silver objects. This interpretation is rejected by archaeologists and scientists. Two media reports (in 2003 and 2004) stated that corrosion of the metal and tests both indicated that an acidic agent such as wine or vinegar was present in the jar, without giving sources for that information. In 1993, Paul T. Keyser had speculated that "the asphalt seal indicates the presence of liquid" and that because most liquids known at the time were acidic, except for vegetable and mineral oils, that the hypothetical 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. == Experiments ==

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.” 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. 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. 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. == See also ==