Pub. 4 2014 Issue 2

8 AT THE CENTER OF UTAH INDUSTRY BATTERIES WERE INVENTED EARLIER THAN YOU THINK T he National Museum of Iraq has an interesting bright yellow Sassanid clay jar as part of its collection. It’s about 5.5 inches tall, has a three-inch diameter at its widest point, and has been sealed with pitch (asphalt) at the top. An iron rod sticks up a little from the center of the blocked opening at the top. The iron rod is held inside a thin copper tube, but the tube and the copper don’t touch each other. The copper tube is sealed at the bottom by another asphalt seal. The rod’s diameter is a little more than 1.5 inches, and its length is almost 4.75 inches. The jar could be 2000 years old. What is its purpose? It’s a battery. More than that, it probably isn’t even the first one. It’s just the first one that has survived long enough to be identified. A German painter-turned-archeologist named Dr. Wilhelm Konig studied and identified the jar in 1938. By 1940, when he published a paper about it, he was the director. His timing was unfortunate because of World War II. It’s also possible he got at least part of his analysis wrong. Dr. Paul Craddock of the British Museum has identified the Baghdad battery as Sassanian, meaning either the age of the jar or the place it was found have not been identified correctly. However, Dr. Craddock does think that it is a battery, along with about a dozen other jars that are much like it. Nobody knows exactly how many are still around. If you build a similar jar and fill it with something acid, like wine or vinegar, a jar like this can create between 1.5 V and 2 V of electrical current. The Baghdad battery’s rod, in fact, does show some corrosion, as if fromacid, and when it was tested, the jar showed some evidence of having held either wine or vinegar. It is the earliest version of a battery that has