Introduction: Building a "Baghdad Battery"
The intent of this instructable is to provide ideas for experimenting with battery chemistry in general, and to summarize my experience producing a replica of what is often referred to as the Baghdad Battery. In my version of a replica I argue the artifacts have been misinterpreted in replicas previously built by other investigators. The replica I've created yields not only a better performing cell (capable of 5x the capacity), but one that is rechargeable.
This is not a great cell, and our cars and homes will likely never employ the design, but it is curious that ~2000 years ago people may have been experimenting with electricity. What they were using this electricity for is subject to as much speculation as the actual construction of the "battery" (Perhaps it was not a battery, that is for you to decide).
To keep the interest of the reader and focus on the construction aspects of the replica I will try not to write too much about the history and interpretation by others of the artifacts. Several of the sources listed in Step 10 have already done a wonderful job discussing these details.
A few notes:
>Several of the listed artifact photos were found on Wikipedia or widely used on the web, so I am assuming there are no copyright infringements.
>Since this is my first instructable, and it has been a while since I've had to explain anything to someone through writing, I welcome all criticism and suggestions for improvement.
>I would like to reference photos and figures inline with the text since I presume it would be easier for the reader to follow, but I am unsure if there is a way to do this through the instructable editor interface and wiki markup (?) - so for now I am just listing relevant images at the bottom of a step. Also, I'm unsure how to apply subscripts in the editor to write chemical formulas, I'd like to include the half cell reactions - otherwise I can take a screenshot and post it as an image.
Step 1: Construction Overview an Materials
I did not create a true replica, since I could not find a porous jar with the correct geometry. However, jar geometry should not have much effect on the battery performance. Also, a clear vessel - such as the mason jar I used - is helpful for observing the chemistry. If you want a replica that is similar in form to the artifacts, use an unglazed jar with the geometry seen in the photos, and substitute asphalt for the rubber tape I used as a sealant.
Nothing is precise here, so feel free to substitute similar materials. For example, I used bundles of nails before I could find a large iron nail. Just be careful what you use is uncoated iron, many iron objects in the hardware store will be coated with a polymer or zinc (galvanized). Regardless of where you find the metals, ensure your copper and iron have the oxidation layers cleaned off - I used Al2O3 abrasive to clean the copper, and HCL acid for the iron.
- sheet of copper, it can be found in craft stores -copper pipe found in the hardware store will work too, but the slit seen in the side of the copper tube (in photos) does improve performance, so try to emulate this construction detail (use a saw or mill)
- piece of iron with an Fe3O4 coating - I used a large iron nail and created my own Fe3O4 coating, see step 2 for details on creating Fe3O4
- mason jar or similar non reactive container for holding the electrolyte and electrodes - if you have a porous clay jar, try this instead
- stranded and solid wire
- rubber stopper
- rubber mastic tape, or if more adventurous, try asphalt
- rubber gloves
- an alkaline electrolyte - Potassium Hydroxide (KOH), also known as Potash, or an alkaline urine should work. Note: Be careful with retailers of KOH, since there is some paranoia of KOH in certain areas. My first attempt at purchase was a bad experience and waste of time. I believe the first company I contacted was under investigation for supplying methamphetamine manufacture - I'm not quite sure who the owner thought I was. Anyway, stay away from any companies that rhyme with "Spinner Chemical" and are based in Michigan. I won't advertise the company I did have success with, but if you can read the label in one of the photos, my experience was completely painless with this company.
Step 2: Making Fe3O4 for the Iron Electrode
The best option is to heat the iron until orange (temperature of decalescence 475 F to 525 F), either in a forge or with a torch, it will oxidise and leave behind Fe3O4.
If you live near an ocean, leaving iron in seawater for an extended period should create a coating of Fe3O4. Or, you might scavenge for some Fe3O4 coated iron near the shorelines - I found some last time I was near the ocean.
Since I am not near an ocean at the moment, don't know any blacksmiths, and wanted to speed up the process, I used the following recipe:
- First you will need to create Fe2O3 (red rust). If your iron already has a good coating of red rust, you may skip this part. If you need to make your own red rust, it is a little trickier since you will need to handle a few chemicals, but not bad. My recipe is not optimal, if you have Nitric acid and washing soda you can do better, but neither of these chemicals can be easily found at a hardware store - so, for most people, this recipe should be easier to implement. Near the concrete section of the hardware store, you will likely find something labeled as 'Muriatic Acid' - it is actually 30% HCL. Use your rubber gloves when handling any chemicals. Dip your iron nail in a mason jar of this acid and you will be left with a clean piece of iron ready to be oxidized. Now, pour another jar full of household Clorox bleach (or generic) and dip the cleaned iron into this solution. Allow the iron to dry in a glass dish - and you should have a nice coat of Fe2O3 (red rust).
- Now that we have a good coat of Fe2O3, we will convert this to Fe3O4. The Fe3O4 will appear as a black coating over the iron, where the red rust was formerly. Heat a pot of water on the stove until it is boiling and place the red rust coated piece of iron you created in the boiling water, after a few minutes it should turn black, now you have Fe3O4.
Step 3: Constructing the Electrode Pairs
The photos should be more explanatory, but roughly:
- Drill a hole in the mason jar lid and slide the Fe3O4 coated iron nail through it
- Drill a hole in the rubber stopper so the Fe3O4 coated iron nail can fit snugly through it with the head of the nail protruding an inch or so from the top - you may want to put a single wrap of rubber tape around the upper exposed portion of where the nail interfaces with the stopper to seal it
- Form a piece of copper sheet into a cylinder around the rubber stopper so there is a slight opening (as seen in photos) still visible along the side, now wrap the top portion with rubber tape and attach the stranded wire to the side of the copper and then wrap again to seal the copper against the stopper, also put a single wrap of tape at the bottom to help hold the slotted cylindrical form
- now, slide the wire through the hole drilled in the jar lid and put a wrap of rubber tape to secure the wire to the nail at the point where you would like to interface with the mason jar lid, force the lid down on to this wrap of rubber tape and you should have a tight seal - it should look like photo 1
- now, fill your mason jar with 20% KOH or other alkaline electrolyte and place the mason jar lid assembly you just created into the solution and seal the jar - it should look like photo 3
Step 4: Containment of Electrochemical Cells an Other Notes
Although we are primarily concerned with the Baghdad battery in the instructable, this step addresses the containment and construction of any electrochemical cell. I've not arrived at a 'best' cell construction method for quickly evaluating different chemistries, but to provide ideas, I listed photos of various permutations I have attempted - including some earlier versions of my Baghdad cell replica.
I only selected a mason jar as my container because I needed to fit the electrode dimensions of a Baghdad battery. To save time and materials, use much smaller containers and electrode dimensions when evaluating other cells.
Find any sturdy non reactive sealed container that allows for external electrical contact with the electrodes, and if you will be pushing the cell hard, a means to vent any gases that might accumulate (this does not apply to the Baghdad cell).
Materials I have found useful when constructing cells (generally, just use what you have on hand): rubber tape (my new duct tape), rubber stoppers, spice jars, condoms, mason jars, film cannisters, toothbrush holders (also work well for simple voltaic piles), stranded wire to ensure good contact with the electrode surface, emery board or plumber's sand cloth for cleaning metals, liquid tape
One of my current projects is to build a battery monitoring chamber that can run several experiments in parallel and monitor temperature, gas pressures in the cells, etc.. The cells I've constructed for this project are small jars (roughly the size of spice jars) with rubber stoppers that have two slits in them to seal the electrodes, a tube to monitor pressure, and a thermowell contact for temperature - perhaps I'll turn that into an Instructable too.
To Experiment with other chemistries:
As you've likely realized, there is not much to experimenting with electrochemistry, place two dissimilar metals in a jar with some fluid. This table should give some ideas when considering different cell potentials.
To learn about batteries in general, the web is fertile ground. I've also found this book to be very helpful (and affordable relative to other battery books). This book is another well regarded alternative, and I highly recommend it if you want a more comprehensive understanding of batteries. I wasted considerable time in some of my experiments by not purchasing it sooner - it contains lots of data on many different chemistries. It will run ~$100 new, but I'm told it can be found for ~$20 used.
Step 5: Monitoring Performance of Cells
To produce charge and discharge curves for your cells you can either log by hand the readings on your meter, or invest in a DAQ or microcontroller to automate data logging. A spreadsheet or similar application is helpful for plotting data. I am rather fond of the Labjack products (seen in some of my photos) - I used their DAQ+software and opamp. DAQFactory is the software that comes with Labjack's measurement devices and it's a good alternative to Labview. Although I am using the scaled down version of DAQFactory that ships with Labjack's products, it can be upgraded to enable some very sophisticated process control applications, but at a fraction of Labview's cost. The Arduino (Atmega) and Parallax Propeller microcontrollers are good choices too, but will require additional setup time - I am using them for other projects where cost is more of a concern. Labjack + DAQFactory is nice for speed of setup, plus they have a great support staff, but so does Parallax, and arduino has a huge volunteer support community.
Besides a measuring device, consider:
- Your measuring device may already have high input impedance (>100Mohm), but if not, use an operational amplifier (opamp), otherwise cells with high internal resistance (such as the Baghdad Battery chemistry) will create problems in your measurements. Opamp's are also helpful to amplify the voltage drop across the current shunt resistor, which is low. Opamps allow differential measurements too, so it is easier to read the voltage drop across the shunt resistor.
- If not using an ammeter, a small resistor provides a voltage drop for calculating current - ideally around 1 ohm (for the voltage/current of the Baghdad cell) although mine was 0.33 ohm. Using ohm's law simply measure the voltage drop across the resistor (dV) and solve for current I=dV/R, in my case R=0.33 ohm, Watts are calculated as P=I*V
- A small resistor or other device to act as a load, I used a 330 ohm resistor for the Baghdad battery, which seemed to be an appropriate load for the cell. The resistor value will differ depending on the battery.
- A terminal block for wiring connections - I find the European style blocks (shown in the photos) easier to use, but stick to the 20A rated blocks since the larger block size is easier to work with and only costs a few cents more
- To charge the battery, a constant voltage source such as another battery (e.g. earth battery) or in my case a digital to analog converter (DAC) on the DAQ works fine for the Baghdad Battery chemistry, but keep in mind that to properly charge some cell chemistries you will need a constant current source or a mix of both at different time intervals. I generally charged at 1.5 V and limited current to 20 mA - again, similar to what an Earth Battery might provide.
Step 6: Performance of This "Baghdad Battery" Replica
The photos below should tell most of the story, but in summary:
- charge at 1.1 to 1.5 V and a few milliamps of current
- discharge with a 330 ohm load
- repeat 1-2 times if you like, your cell should be providing about 7 mA-h of capacity. Then let sit for 3 days and you will see the 5x increase in capacity I note below
This cell likes to take a charge slowly and give it up slowly - it will take three days to discharge with the 330 ohm load, and 1-2 days to charge, I actually never fully charged or discharged the cell since I did not have the patience, and have several other experiments that are in neglect at the moment. The cell seems ideally suited to take a charge from the voltage/current characteristics of telluric currents present in the Earth, or earth battery as some have labeled it. I tested other voltages and currents and they do not seem to work as well. The slow release of current seen in this cell would likely work well to run a homopolar motor but since I have not created a well enough balanced piece of copper or bronze wire yet, I have been unable to fully test this theory. Also, if you attempt to discharge the cell too rapidly (too large of a load) it seems to ruin the cell.
One additional curiosity of the alkaline cell chemistry is that either the Fe or Cu can serve as the anode, although with Fe as the anode it is a better cell. With an Fe anode the electrolyte turns blue upon charge (indicative of Cu ions), and becomes clear on discharge. With Cu as the anode the solution is clear on charge and discharge and the metals actually appear polished.
It should be noted that all of my experiments (and cell performance curves) were done without careful attention to ambient temperature, usually around 55-65 deg. F. We keep our house relatively cool and try to minimize furnace use. Temperature is the most important environmental factor when evaluating electrochemistry, and 80-90 deg. F would likely produce better results, and provide a more accurate recreation of the 'Baghdad Battery' since temperatures were likely much warmer in Mesopotamia. I tested the temperature dependence of the chemistry by allowing a minor ~5 deg rise in temperature and observed a 10% increase in rate of charge current and release of the current on discharge. The increase in charge/discharge rate is a function of what is commonly called internal resistance. Most battery chemistries have a lower internal resistance as temperature increases. As most batteries are cycled, their internal resistance will increase with time - in addition to self discharge rate, and a decline in capacity. I am developing a reaction chamber to control environmental parameters and further automate my other electrochemistry experiments - this will allow a more precise characterization, but the results I've presented will have to suffice for now.
Step 7: How This 'replica' Differs From Other Attempts
Presuming it is a battery, the reproductions I have seen always assumed the following: an acidic electrolyte (lemon juice, red wine vinegar, etc.) with an iron|copper electrode pair contained in a porous unglazed jar. Because the jars and electrodes are present as artifacts, we can assume most aspects of previous reconstructions are accurate, but the evidence for an acid electrolyte or uncoated iron electrode is weaker.
7 mm diameter by 75 mm length iron rod with an Fe3O4 coating instead of uncoated iron
The assumption of an uncoated Iron electrode is perhaps not correct. The artifacts (as I understand from written accounts and a few low resolution photos) show a mixture of black and red colored iron - which I assume is Fe3O4 ('black rust') and Fe2O3 ('red rust'), two of the more common oxidation states for iron. I am far from an expert on Iron Oxides, but from what I understand, Fe3O4 does not typically form over Fe2O3 unless placed in boiling water. As an example, I have not seen black rust (Fe3O4) form on an old car covered with red rust (Fe2O3), but that does not mean it is not possible, I've never buried an iron artifact for 2000 years either. However, Fe2O3 (red rust) can work its way into a layer of Fe3O4. Since photos of the artifacts I have seen show a mixture of Fe2O3 and Fe3O4 on the artifact, in my mind's eye, it implies there was originally a layer of Fe3O4 that was later infiltrated by Fe2O3.
So, I presume the electrodes were Fe3O4 and not plain iron - it certainly was not Fe2O3, since this does not produce a viable cell. Additionally, as shown in Step 6, Fe3O4 produces a better electrode than plain iron, and if this was a rechargeable battery being used for extended periods, the Fe3O4 coating would provide some protection from the formation of Fe2O3. However, the strongest piece of evidence is that iron of this time and shape would have been forged under a high temperature that exceeded the point of decalescence for low carbon iron 425 F-525 F. Beyond the decalescence point, iron will readily form a coating of Fe3O4. So, by choosing an iron rod without Fe3O4, previous replica creators would need to assume that the Fe3O4 was purposefully removed from the iron rod - but we know that most forged objects of this time retained their Fe3O4 coating.
Plain iron would likely oxidize to Fe2O3 (red rust) and this oxidation state does not work well as an electrode. As Fe3O4, the iron is actually protected from the elements and produces a better cell than plain iron, and significantly better than Fe2O3.
As discussed in step 2, iron is easily converted to the Fe3O4 oxidation state - likely through the forging process, but a piece of already rusted iron can also be boiled in water for a few minutes, or iron can simply be immersed in seawater, all methods work fine, and would have been accessible to civilizations 2000 years ago.
A non acid electrolyte and thus a rechargeable cell
The copper electrode is completely oxidized during discharge in the acid chemistry, making for quite a mess (see photo). If an acid electrolyte, the artifacts should show substantial corrosion on the electrodes and in the jar, but none of the archaeological evidence or published accounts I have seen indicated this level of telltale corrosion. The BBC article listed in step 10 mentions corrosion and a test indicating acid, but does not provide any further detail. The corrosion shown in the artifact photographs, actually closely resembles the corrosion patterns I've seen after removing the copper from an alkaline electrolyte (see photo).
If it was an acid chemistry, cider vinegar seems more likely than the lemon juice or red wine vinegar used by some investigators - my understanding is that red wine vinegar was not used in earlier times. Perhaps mashed grapes were used instead, as seen in Arne Eggebrecht's replica demonstration, this would provide tartaric acid, but since acetic acid and citric acid were both known to the Parthians, these are equally possible too. However, an alkaline electrolyte seems just as likely to me, and as I've explained, creates a very interesting battery.
The available construction details also seem to support the possibility of this being an alkaline chemistry. Most investigators, including myself, have wondered why the copper electrode is sealed in the clay jar, since completing a circuit to extract the current is much more difficult - this is puzzling since concealment of the copper electrode does not appear to be necessary with an acid electrolyte. However, with an alkaline electrolyte, the copper electrode is quickly oxidized even when partially exposed to air. Since the artifacts found indicate that the copper was sealed in the vessel with only the iron electrode exposed - this construction detail seems to support the argument for an alkaline electrolyte, not an acid electrolyte, since exposed portions of the copper electrode are less prone to oxidation with an acid electrolyte (see photo).
An acid chemistry means the electrodes are only good for one use. An alkaline electrolyte allows for a rechargeable cell. The cell chemistry is also much less robust with an acid electrolyte, and provides a cell with only 1/5 the capacity of a single charge cycle of the alkaline electrolyte rechargeable cell.
So, maybe I've convinced you this is a rechargeable cell, but how was it charged? Perhaps an earth battery - stick two conductors (Copper, Iron, Carbon, etc. all work fine) into the Earth and you will get around a 1.2 V potential with a few mA of current. I charged my replicas using voltage/current that simulates an earth battery.
KOH, an alkaline urine, or perhaps another alkaline substance, are all possible, but my experiments only used KOH. A diet rich in citrus fruits, legumes, and vegetables is known to raise pH and produce urine that is more alkaline - this would have been close to the diet of this time. I've been eating a lot of citrus and legumes lately, so maybe I will retest my urine pH and give it another go. Soap production is claimed to have been present during this time, so it is possible there was familiarity with alkaline chemistries. In my wife's DIY soap book, common lore states that soap was discovered when ash from fire pits drained with the fat from animal renderings into the nearby stream where people washed clothing and other items, and it was noticed clothes were easier to clean - whether this account is true or not, I do not know. However, mixing ash with water is not rocket science. Even today, most KOH is commercially produced by taking the ash form burned wood, soaking in water, and then evaporating the water off to leave KOH crystals. It might make sense to have a pit of water near your night fire, if the ash was raked into the water you should get an alkaline solution that would work well as an electrolyte. Since the Copper sheet was not exposed, the jars may have been placed into a reservoir of this solution (e.g. a hole dug in the Earth filled with urine or ash water) with the iron rod connected to another conductor in the Earth, now you should have an Earth Battery charging station with a ready source of electrolyte replenishment. I'm stretching a little here, but this explanation still seems more plausible than an acid electrolyte. After playing with several replica permutations, I'll reemphasize the electrodes are protected in an alkaline electrolyte, and are oxidized with an acidic electrolyte - furthermore, that the artifacts indicate the copper was isolated in the container, only really matters with an alkaline electrolyte.
Step 8: Interpretation of the Artifacts
Some say the "battery" is actually nothing more than a scroll holder, others have said it is a Leyden jar.
So what might a battery have been used for during this time?
- some speculate it was used as a current source to electrify various objects, either for curiosity or "religious experience" statues controlled by a crafty priest - this does seem nifty, but it would take several batteries to generate a noticeable jolt through the unsuspecting worshiper
- others have speculated it was used for electroplating gold and that many of the artifacts collected in museums are falsely assumed to be solid gold, although I am unaware of evidence for plated artifacts to support this argument - one researcher claims to have successfully used the batteries to electroplate gold, but other investigators have disputed the veracity of Arne Eggebrecht's claims - despite this dispute (disputes and name calling being all too common in certain academic circles), there are two videos (one with Arne) indicating that electroplating is indeed possible with this battery: 1, 2. I believe that someone could use the battery (or several) to plate gold, but there should also be plated artifacts in existence to support the argument.
- others speculate that it may have been used in medicine
- I think there is a possibility that it may have been used to run a homopolar motor. Homopolar motors have a very simple design, consisting of only a current source (the battery), a strip of copper or bronze, and a magnet (e.g. lodestone) - all readily accessible objects. A Homopolar motor was actually the first electric motor built (by Faraday) - but this would imply Faraday was actually late by several hundred years. Copper and Bronze were already being manipulated into various shapes (as seen in the artifacts) and lodestones (naturally magnetized rocks) were likely common and sacred to people of this time for their use as a navigational aid. I've not been able to find any photos or drawings of the bronze and iron artifacts that resembled wires (referenced in the sources listed below), so my argument for a homopolar motor is perhaps stretching, but if the 'wires' are bent properly it may support it. One perplexing aspect of the battery argument is the uncertainty of how the copper electrode was accessed to complete a circuit. According to the sources listed below, the Sassanid style pottery that the electrodes were suspended in with the asphalt seal/stopper was porous not glazed. Part of my reasoning for how a circuit is completed with the battery, depends on a porous shell that allows the electrolyte to seep in during a charge in a pool of electrolyte, and then sweat out during discharge (perhaps, to complete a circuit with a lodestone placed on the bottom of the pot to drive a homopolar motor, as described below, or some other unknown use). If I had access to the 'wire' and other artifacts found near the batteries, or photos of the dig sites, etc. it may be easier to support my claims for a homopolar motor. Until then, I am admittedly stretching to explain how the batteries were actually used, based on the limited puzzle pieces I have available. simple homopolar motor video 1, 2
Step 9: History
A better name would actually be "Mesopotamia Battery" since Baghdad was not in use at the time, furthermore, the battery was actually not found in Baghdad, but instead near it in an area called Khujut-Rabua in Parthian times, or Salman Pak in modern day Iraq. However, I will stick with Baghdad since this is how the artifacts are now commonly referenced. I also believe the name Baghdad is important since it would be nice if we identified this region of the world with the hope and centers of learning and science that it once embodied, instead of the cauldron of violence that has plagued its more recent chapters in history.
The date range commonly cited for the artifacts spans 600 years - 300 B.C. to 300 A.D., although I suspect the date of origin might be even earlier. During this time, it was common to conquer people in one region and then move the population (particularly skilled workers) to another, so the artifacts may have originated elsewhere and the people producing them simply enslaved and forced into Mesopotamia. In one famous example, the Babylonians conquered and enslaved people inhabiting what is now Israel (in addition to other regions) and brought them to Mesopotamia to compile bits and pieces of religious text from the area to create the Old Testament - it is likely that technology from the conquered societies came too. Or, perhaps a group that inhabited Mesopotamia even earlier in the timeline is the origin of inspiration (e.g. during the Sumerian reign).
The Assyrians (1200 BC to 612 BC) preceded the Babylonians in Mesopotamia, then the Persians conquered the Babylonians, followed by the rise of Macedonian and Seleucid rule over the Persians, then came Parthian rule (Iran), and then Sasanian rule (also Iranian). In the 7th century, Mesopotamia was conquered by Arab armies and under the Abbasid caliphate became known as Baghdad and Iraq - the cultural and commercial center of the Islamic world. Most of my understanding of the regional history was derived from the Metropolitan Museum of Art summaries e.g. 1, 2, 3 - clearly from the works of art referenced from their site, the inhabitants were highly skilled craftspeople. The Parthians, who conquered Mesopotamia in 138 B.C. ruled over the region until 224 A.D., and whether right or wrong, is the group often credited with creation of the artifacts in many of the archaeological interpretations - perhaps because their rule sits in the middle of the 600 year span (300 B.C. - 300 A.D.) listed as the artifacts' origin date. However, 600 years is quite a margin of error, and I'd like to better understand the reasoning behind this often quoted range. To further complicate matters, the pottery geometry is thought to be of Sassanid origin (224 to 637 A.D.). Pottery geometry could simply be enforced by whom ever is wielding the biggest stick at the time, with the more relevant construction details being conceived/refined earlier in the timeline.
Who's responsible for creating the artifacts? I don't know, but the history certainly seems rather messy. I would guess the inspiration for the artifacts could have arrived along a number of vectors (e.g. conquered populations external to Mesopotamia, or earlier inhabitants), and it would be presumptuous to give credit to any one group (sociopolitical, ethnic, etc.). I feel inclined to give some attention to the history of the "Baghdad battery" since during my research I observed some rather ignorant comments on Youtube and other locations hosting information regarding the artifacts. Ignoring all the complications with pinpointing the origin of these artifacts, in my understanding of the continuous flux of sociopolitical dynamics and population migrations, I find nationalistic pride rather humorous. Let me know if I misstated any of the history.
Step 10: On Other Published Accounts
- Wikipedia - Baghdad Battery
- Mythbusters did a show on this battery but I am unaware of a URL pointing to the video footage - it was shown in episode #29, March 23, 2005. Wikipedia summary of the show: "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 in series, 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 cherubim. Instead of linking the cherubim's 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."
- "Discovery Channel: The Baghdad battery" video excerpt posted to YouTube (from the 90's?), starts 5 minutes into the video. This cell appears to be a fraudulent replica - the presenter demonstrates a 4.2V cell, but I do not believe these claims. I used a similar experiment setup, and was not able to replicate the results. I found it on this site and they state the following about the presenter: "In this video Jason Martell founder of Godtube and CEO of BooyaMedia performs an on-camera experiment for the Discovery Channel where he is able to consistently generate a positive full 4 volts using a replica he made of the Baghdad battery."
- An Arthur C. Clarke video with Dr. Arne Eggebrecht - this video has imagery of the actual artifacts and shows Arne electroplating gold to a silver statuette, the replicas produced in this video seem to be the most accurate relative to the others listed, including mine since I did not have access to the pottery, and did not include the copper disc at the bottom (to simplify construction)
- A History Channel review (?) through a show called "Ancient Technologies"
- Smith College Replica: I was not able to get the 1.1 Volts they indicate though
- Writeup summarizing several sources - I included this reference to show how much conjecture there is in the claims one can find on the web when researching this topic Indicates that Willard Grey produced a 2 Volt cell with grape juice, again, I was not able to reproduce this. The BBC numbers indicate Mr. Grey's experiments yielded 0.5V but with Copper Sulfate, and this seems more accurate.
- BBC article or here Indicates that Dr. Arne Eggebrecht used the cells to electroplate gold in 1978, although the article indicates some have disputed the accuracy of these claims and been unable to reproduce them. Article indicates Arne's cell was 0.87V with fresh grape juice, which is actually not far off from my numbers. Also indicates that Willard F.M. Gray produced a 0.5V cell in 1940 using Copper Sulfate. A notable quote: "The vessel showed signs of corrosion, and early tests revealed that an acidic agent, such as vinegar or wine had been present." but I was unable to find which tests were applied to test the veracity of the claim. Also, Dr Marjorie Senechal, professor of the history of science and technology, Smith College, US states that replicas have been produced that range from 0.8 to 2 Volts, but I am unsure of what electrolyte she is using to make this claim. My own experiments have not generated such high voltages.
- A recent research paper on the subject Title: "The Baghdad Battery: Myth or reality?" Author: VON HANDORF D. E. states: "unglazed ceramic vessels"
- Some references to how the history of the battery is currently recorded 1, 2
- Just as I was about to publish this instructable I did one last set of Google searches and discovered the most comprehensive summary I have seen on the artifacts - I almost decided to start my write up from scratch, and perhaps I should - it can be found here: I wish I had found this sooner, as the account told in this paper also loosely supports several of my assumptions. According to the listed chronology, artifacts have been found at multiple digs and evidence of bronze and iron wire objects were present at the sites. some notable excerpts: "To answer the first question, one needs to remember that thin wire-like bronze or iron rods were found next to the urns, as reported by the archaeologists. As a point of departure, one may assume that Parthian goldsmiths might have used them as connecting means between the iron rod and the copper cylinder. " Or, as the conductor for a simple homopolar motor? I'd really like to see photos of the artifacts, so if anyone is aware of any, please let me know. "Given the fact that acetic acid and citric acid were known to the Parthians, one may assume that they probably made use of them as electrolytes." In a 1950 dig "excavators had also found copper discs, short thin metal wires, and pieces " "The vase was, the report stated, 12 cm high and contained a copper cylinder of 7 cm height." "They postulated that in the case of the real battery, the entire clay jar was filled with electrolyte, and its porous walls would allow oxygen to diffuse into the cell leading to a continuous flow of current." Or, perhaps electrolyte would seep out and complete a circuit? "One serious flaw with Konigs gold plating hypothesis is the lack of gold-plated items stemming from the excavation site at Khujut Rabbou"
- Another source I recently found: claims the BBC article as their source, although several bits of information in their article either are not found in the BBC account, or are different, so I am unsure where some of the statements are derived, nevertheless the author makes some interesting claims "Konig also found copper vases plated with silver in the Baghdad Museum, excavated from Sumerian sites in southern Iraq, dating back to at least 2500 BCE. When the vases were lightly tapped, a blue patina or film separated from the surface, which is characteristic of silver electroplated onto copper base. It would appear then that the Parthians inherited their batteries from one of the earliest known civilizations." this would be very interesting, but I'd like to know the source "It also seems that the use of similar batteries can be safely placed into ancient Egypt, where several objects with traces of electroplated precious metals have been found at different locations" again, very interesting, but I'd like to know the source - but then, later in the article there is this statement "One serious flaw with the electroplating hypothesis is the lack of items from this place and time that have been treated in this way." so, I'm confused - they also cite different timelines than I have seen elsewhere "Parthian occupation between 248 BCE and 226 CE"