While trying to make a microbial fuel cell apparently I stumbled upon how to make an Earth battery, which is something whose existence I really had no clue about until I made one. While the current it generates is pretty much non-existent I've found that several of these in series are capable of dimly lighting a 3 volt LED for weeks, which I still think is pretty good for what amounts to a jar of mud.
To make this "mud battery" you'll need:
Aluminum Foil
An Empty Container
Insulated Copper Wire
At Least 5 cm of Graphite (taken from a pencil)
Dirt
Water
A Digital Multimeter
A Hand Shovel
To make this "mud battery" you'll need:
Aluminum Foil
An Empty Container
Insulated Copper Wire
At Least 5 cm of Graphite (taken from a pencil)
Dirt
Water
A Digital Multimeter
A Hand Shovel
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Signing UpStep 1: Obtain and Insert the Dirt
For this step, just go outside and find a spot where you can dig up some dirt. Though I've yet to experiment with how various types of dirt affect the mud battery's function, I've found while making the some dozen cells I've tried that the blackish-brown sort of topsoil pictured works well. If I had to guess, I'd say the dirt I use is towards the "loamy" side of things because it retains water well without holding it up so much that it prevents the diffusion of ions between the electrodes
Besides finding the right kind of soil to use, this step really is easy as just filling up your container with dirt.
Besides finding the right kind of soil to use, this step really is easy as just filling up your container with dirt.
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http://en.wikipedia.org/wiki/Earth_battery
Basically, if you stick two electrodes, of different materials, into most anything moist, you will read a voltage. Unfortunately, there is hardly any current to do much of anything with. Hope this helps some.
Though I'm a bit bummed that I completely missed the mark here, I'd still like to thank both of you for pointing it out and for providing sources for further research into this and for explaining how this thing is probably working.
Now, knowing that, you can factor that first volt in to you investigations. If you can double it, you know you are really onto something spectacular. Like I said, I don't know much about bacteria, but some can do fascinating things, like glow in the dark. They are some amazing chemical factories, you should continue your research.
That first volt will most likely be found anywhere, but you might find a way to get more. A red LED, needs about 2 volts to light, the brightness is determined by the current. White or blue take over 3 volts. Even if you can't get a higher voltage, maybe you can get a boost in current.
Being a biologist, I'm sure you have your own microscope, but you might be interest in one the hooks up to your USB port, around $30 surplus. Have one in a box some place, a little more magnification than I expect from a cheap piece of equipment. Work surprisingly well, but not sure if it's good enough for bacteria. Figure if you can see individual blood cells, probably close though.
I don't mean for this to sound like I'm trying to shoot down your suggestion, but unfortunately my own personal microscope is a bit old: not only am I not sure if it works, but I also don't know that it'd be able to differentiate much between types of bacteria even with a good one. But from what I can gather from the link you gave me, an earth battery's voltage is due to differences in electric potential between the metals used for the electrodes, and from how it seems they used to be used I'm guessing that (beyond the tapping into the telluric currents) it doesn't matter where in a "unit" of soil they're placed so long as they're placed within the same "unit". Now this differs from how the electrodes in the type of soil-based microbial fuel cell I'm going for need to be placed, where (since the voltage is due to the fact that redox potential decreases as one gets deeper in the soil due to the activity of certain bacteria) the anode needs to be placed at least several inches in the soil beneath the cathode for it to work.
Now if I'm correct in this difference, I was wondering if I'd be right to assume the following: I presently have set up a "mud battery" series with the electrodes set up in such a way that they only should work to generate voltage as an earth battery does, so if the increase in voltage following incubation is due to microbial activity then it'd be expected that letting the whole thing sit out overnight shouldn't alter the voltage any because it isn't set up to take advantage of the microbes. But if the voltage does go up then it's likely due to some inorganic process, right?
Also, you can get USB microscopes for $30 surplus? Do you know if you can take pictures with the one you have? I mean I guess one could always just do a print screen of whatever one was looking at, but being able to take microscope pictures would be pretty neat. A female lab tech I know took a bunch of pictures of molds with a microscope in the lab she works in for a research project and they all turned out really pretty.
It would be interesting to try this with a sample of soil, bake it to kill off the microbes, then re-hydrate and compare the voltage.
But like I said, my experience lies more on the "microbial" bits of things than the "fuel cell" bits. Since you pointed out that the temperature thing doesn't really lend any support that it is microbes, however, I'm going to go stick one of these cells I have contained in a glass jar into the oven for 35 minutes at 350 degrees to see if it alters anything. And well, even if it proves this isn't an MCF I'd have to say that generating a bit of voltage with a bit of mud is still pretty cool.
It would be cool if you could charge batteries by hammering a couple of electrodes into damp ground. Maybe a set of specially-designed tent-pegs could keep your mobile topped up...
But yeah, the people who made the MudWatt actually intended their experimental version for something like that; the soil-based MCF they designed was meant to be used as a kind of thing to get power for sensors and transmitters out in places where it'd be awkward to have batteries or normal generators.