He had been eight years upon a project for extracting sunbeams out of cucumbers, which were to be put into vials hermetically sealed, and let out to warm the air in raw, inclement summers. -Jonathan Swift.
Purpose
Several days ago this odd quote appeared in the node Whorehouse cucumber. Most took it for the satire that it was and dismissed it. I, recalling the potato clock I built many years ago, decided to see if it could be done. And since anything worth doing is worth doing right, I decided to follow the scientific method.
Of course, I have easy access to higher levels of technology than Mr. Swift or his fictional mad scientist, and a better understanding of electrolyte solutions, voltaic cells, and electronegativity. I also had access to lemons, having just made a cheesecake a few days ago.
Hypothesis
My hypothesis was that I could use lemons to power a small pocket flashlight bulb, thus extracting if not sunlight, then a reasonable facsimile thereof. I had a number of metals around the house with which I could try building my organic battery.
Materials
The materials I tested were:
- Coated sinker nail (I do not know what it was coated with)
- Bright finishing nail (material unknown)
- Treated exterior screw (surface material unknown)
- Brass doorstop (not used, too large to get the alligator clips attached)
- Machine screw (assuming zinc plated)
- U.S. quarter (copper-nickel alloy)
- U.S. nickel (copper-nickel alloy)
- U.S. dime (copper-nickel alloy)
- U.S. penny (copper plated zinc)
- Copper wire (from old telephone cord)
- Aluminum foil
I forgot until just now that I had pure gold and silver in the house, too, but I already threw away the lemons.
Other equipment:
- Workbench (particle board surface)
- Lemon (left over from cheesecake creation)
- Egg carton (also left over from cheesecake creation)
- (2) Alligator clips (1 red, 1 black)
- Digital multimeter
- (1) 1.5 Volt Mag-Lite Solitaire light bulb
- (1) Red LED
Procedure
First I cut the lemon in half, exposing the slightly acidic, highly electrolytic, deliciously lemony, sour, pulpy insides and jamed two dissimilar metals into it, making sure they didn't touch. The egg carton was used to hold the lemon halves upright. Then I hooked up my multimeter to the metals via alligator clips and took a voltage reading, making note of which one was the anode and which was the cathode in each setup. I tested every combination of materials in this way.
Depending on the specific setup, sometimes a metal would be the anode and sometimes it would be the cathode. Negative values in the below table show the left column is the cathode, not the anode, and is shown this way for readability. The results from the quarter, nickel, and dime were all very similar due to the fact that they were all made of a very similar copper-nickel alloy (these being recently minted coins selected for being bright and shiny).
Volts DC
Cathode| CS BF Ext Mach Cpr Alm
Anode | Nail Nail Screw Screw Quart Nickel Dime Penny Wire Foil
---------+-----------------------------------------------------------------------
CS Nail | X.XX
BF Nail |-0.21 X.XX
|
Ext Scrw |-0.46 -0.44 X.XX
Mac Scrw |-0.50 -0.47 0.01 X.XX
|
Quarter | 0.55 0.55 1.00 0.98 X.XX
Nickel | 0.53 0.53 0.97 0.97 0.05 X.XX
|
Dime | 0.54 0.55 0.98 0.98 -0.01 -0.10 X.XX
Penny | 0.50 0.54 0.96 0.90 0.35 -0.45 -0.18 X.XX
|
Cpr Wire | 0.50 0.51 0.93 0.93 0.10 0.01 -0.25 0.17 X.XX
Alm Foil |-0.50 -0.25 0.40 0.39 0.56 0.57 -0.57 -0.45 -0.55 X.XX
The quarter, nickel, and dime were all 0.1 Volt DC or less, because they are nearly the same material and not dissimilar enough for a large electronegative difference. The wire and penny were likewise made of similar materials and also supplied a low voltage. The machine screw showed excellent results with the quarter, nickel and dime. Although the exterior screw did as well, I have no idea what the exterior screw is coated with and I think the machine screw is zinc plated, so I went with that one.
Please bear in mind that these are the results of a single test, and some of the values may be inaccurate or even flat-out wrong due to contamination or other causes. Upon later reflection of this table, the negative value of aluminum foil with the dime is particularly suspect, considering it is positive with the similar quarter and nickel. This is probably a flaw in my note taking during experimentation.
The Pauling electronegativity of zinc is 1.65.
The Pauling electronegativity of copper and nickel are 1.90 and 1.91.
My next step was to determine which among the quarter, nickel and dime would provide the best current when used with the machine screw. The quarter was able to push 0.35mA (yes, less than half a milliAmpere) through my multimeter with no additional resistance, compared with the dime at 0.25mA and the penny at 0.02mA. I assume this is at least partially the result of the quarter's greater surface area.
Now that my cathode (possibly zinc plated machine screw) and anode (copper-nickel alloy quarter) were chosen, I conducted a few tests to see if I could increase the voltage by putting additional lemon batteries in series, or increase the current capacity by putting lemon batteries in parallel. Three lemon batteries in series provided 0.12mA at 2.8VDC, a substantial drop in current capacity but the expected rise in voltage. Three lemon batteries in parallel provided 0.45mA at 0.93VDC, no statistically significant voltage drop but far from the expected rise in current capacity.
So it was finally time to attempt to extract sunshine from lemons. I tried it with both setups, series and parallel, but was unable to make the filament in the bulb glow.
I decided to try something a little easier, and hooked up the lemon battery to an LED instead (although being red, the LED is less similar to true sunlight than a light bulb). Three lemon batteries in parallel still provided no result. The 0.93VDC provided by the battery probably didn't leave enough forward bias left over after the 0.7 Volt drop across the diode. In series, however, the LED did glow very, very faintly. The 2.8VDC appeared to be enough voltage, but the anemic 0.12mA was far too small to make the LED glow very brightly.
Conclusion
As three lemons batteries were completely unable to light a 1.5V light bulb, and only just barely able to make an LED glow, it appears to be impractical to extract sunlight from produce. Even if a larger array of lemon batteries could be used to create a glow in the filament, the efficiency is too low to be at all practical.
Ideas for Follow-up Experiments
Different produce could be used, and I never did test the cucumbers — as was the original idea provided by Jonathan Swift — because the lemons proved disappointing. Metals with a larger surface area might increase the available power of the battery. A larger array of lemon batteries might actually produce a glow in the filament. The experimental results of the lemon battery voltages were the result of only one run of tests under non-ideal conditions and can not be considered authoritative.
Interesting Notes
The machine screw tarnished where it was inserted into the lemon, probably a result of the acidity, the electric current, or both. Parallel connections of lemon batteries provided far less than the expected rise in current capacity.