Baghdad's National Museum in Iraq houses some of the world's finest treasures dating from the beginning of recorded civilisation. In 2003, during the chaos of war in Iraq, the National Museum was looted. The tragic loss may include more than just priceless vases, seals and statues however. Before the war started, BBC reported on the museum's unusual 2000-year-old artefacts known as the "Baghdad Batteries".
The "Baghdad Batteries" are 13cm high earthenware jars, one of which was first discovered by German archaeologist Wilhelm Konig in 1938. Up to a dozen of the jars are said to have been found. The function of the jars has been much debated, as there is no written record of them.
The jars contain a vertical cylinder made of sheet copper and an iron rod. The edges of the sheet copper were soldered together to make the cylinder, using 60/40 silver-lead solder similar to that used in electronics today. The top of the jar and both ends of the cylinder were sealed with asphalt. The iron rod was held in place at the centre of the cylinder by the asphalt.
Mr Konig found the iron rod was corroded, as if it had been etched by acid. Dissimilar metals such as iron and copper form an electrochemical couple when submerged in an electrolyte such as acid, producing electricity. Mr Konig concluded that the jars could have been filled with an electrolyte, and suggested they were used for gilding gold onto silver – a process today known as electroplating.
Following World War II many archaeologists around the world built replicas of the batteries and some attempted electroplating with them. Various attempts using grape juice, vinegar and modern electrolytes produced around 0.8 – 2 volts, similar to today's zinc-carbon batteries. Placed in series the batteries could produce higher voltage, although no wires have been found associated with jars.
Other suggestions as to the use of the batteries include medicinal uses. The early Greeks and Romans are known to have used electric eels to treat cases of gout, so scientists have suggested the batteries may have been used for a similar purpose. The batteries may also have been used to electrify acupuncture needles as is done by some acupuncturists today. Although acupuncture was practised in ancient China it is unknown whether it was practiced in ancient Iraq.
The age of the batteries is also debated. The jars were reputedly found at an archaeological site at Khujut Rabu, just outside Baghdad, which was a Parthian settlement around 200BC. Experts from the British Museum however say the jars are Sassanian style, dating back to 225-640AD. The Parthians were known as warriors, not for their scientific achievements, although the technology may have been handed down from their ancestors. Regardless of their precise age, the batteries are significantly older than the first modern batteries invented by Alessandro Volta in 1800.
Whilst many scientists believe they are batteries, others remain sceptical citing a number of problems with the design, and similarities to scroll storage jars found at nearby Seleucia on the Tigris. But the possibility that they are batteries is not unbelievable. The technology certainly isn't high-tech and they were made with materials available at the time. Understanding how something works is also not necessary to use it.
Who knows what other mysteries are hidden away in the basements of museums? Let's hope the "Baghdad Batteries" and the many other treasures turn up safe and sound.
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