After seeing a neat YouTube video (everything starts this way, doesn't it?) showing a chemist removing the copper plating from a zinc-core penny to make a solid zinc penny, I decided to try the experiment myself. Upon further research, I saw that Theodore Gray the element collector also had a solid zinc penny, but he had used cyanide to remove the copper plating. Since I didn't feel like exposing myself to extremely toxic salts, I decided to go with the YouTube method.
The reaction uses calcium hydroxide and elemental sulfur to oxidize away the penny's copper plating but not the underlying zinc. If I remember correctly (I did this experiment some time ago), the reaction smells awful, so it is best performed outside. I didn't have any calcium hydroxide, so I substituted in sodium hydroxide drain cleaner and used gardening sulfur as my source of sulfur. After that, I simply followed the video's directions.
The pennies come out of the solution blackened with copper oxide, so I tried to remove it with a scrubbing pad. That got rid of the copper oxide, but it also scratched the zinc pennies, making them less shiny than they otherwise might have been. I would recommend going with the YouTube video's recommended cleaning method using ceramic cooktop cleaner. I suppose the dullness could also be because of my substitutions, but the reaction still worked well using sodium hydroxide, so I doubt that was the case. Nonetheless, I was really impressed that a reaction could remove only the copper on a penny while leaving the zinc untouched. After polishing the pennies with a Dremel wheel, I was left with ten solid zinc pennies.
Platings provide opportunities to observe the subtle differences in colors of transition metals. While nearly all transition metals are some color of gray, some have different hues. I had some pennies with a layer of zinc or nickel plated over the copper, so I put them together with the solid zinc penny for a nice comparison. Nickel definitely has a golden hue compared to zinc, which I find interesting.
I wanted to "see" nuclear radiation, so I looked online for experiments similar to making a Geiger counter. One of the ones I found was an alpha particle spark detector, which shows passing alpha particles as high-voltage sparks. A wire grid hovers a few millimeters above a plate charged to a high voltage, and when an alpha particle shoots by, it ionizes the air between the grid and the plate, which allows a spark to jump across. I enjoy this device because it helps me visualize alpha radiation emanating from a source.
I made extensive use of this tutorial, which was the only one at the time. To generate the high voltages required for this experiment, I powered a CCFL inverter with 12V from my lab power supply. While the inverter's 900V is high voltage, it isn't high enough for this experiment, so I fed the inverter output into a Cockcroft–Walton voltage multiplier, as per the tutorial. I used 0.01uF ceramic capacitors and 1N4007 diodes for my multiplier, which had four stages. When powered with my lab power supply, that increases the voltage about eight-fold, generating the approximately 10kV necessary for a successful spark detector. I also tried to round off the solder joints to minimize sharp edges that might cause performance-harming corona discharge.
When detecting alpha radiation, it is nice to have frequent small sparks that represent individual alpha particles, rather than one large spark every now and then. To achieve this affect, I placed a 10 mega-Ohm high voltage resistor (from Vishay) on the high voltage output of my voltage multiplier. This makes each spark smaller, but it also enables a greater number of sparks at a time. The resistor also limits the current--larger currents might burn out the extremely thin wire grid. A normal-voltage resistor might possibly work, but it could fail under 10kV.
Before building the wire grid and plate assembly, I picked out a case for my project. Previously, I had gotten a sleek enclosure from OKW Enclosures, so I decided to use it in this project. Because the enclosure was an oval, I picked an oval-shaped piece of aluminum for my high voltage plate. I needed a good electrical connection for the high voltage, so I tried soldering to the aluminum. After many failed attempts, I found online instructions that suggested scratching the aluminum under a pool of molten solder. This eventually made the solder wet the aluminum, and soldering a wire to the plate underside was simple with that done. After sanding the top to a near-mirror finish, I used four bolts and springs to attach the plate to the enclosure top. The wire grid sits a few millimeters above the plate, and the bolts and springs let me adjust this distance so that the spark detector does not spark while idle. I adjust the bolts until the detector only sparks in the presence of alpha radiation.
For my wire grid, I bolted small strips of copper-clad PCB stock to the enclosure top on each side of the aluminum plate. I used the bolts protruding through the enclosure top's underside as my feedthroughs for the ground connection. (The wires are ground and the aluminum plate is high voltage.) I made multiple small cuts in the PCB strips to make individual (but still connected) pads to solder my wire grid to. I didn't cut all the way through the fiberglass, nor did I separate the pads completely. They still have copper connecting them in the back, but they are more thermally isolated, which makes soldering easier. After tinning each pad and using soldering flux, I soldered 10 strands of flexible copper alligator clip lead wire from one pad to its corresponding pad across the aluminum plate. I tried to make each wire tight so that it would not sag closer to the aluminum plate and create sparks without alpha particles present. The distance between each wire was 4mm, and the distance from the wires to the aluminum plate was 3mm. Each wire had a diameter of 0.08mm; such a small diameter is necessary to create the concentrated electric fields which make the spark effect.
As I put everything inside the enclosure, I tried to be sure that none of the high voltage (900V or 10kV) wire were close together or overlapping. When I finally applied power, I found out that the aluminum plate was too close to the copper pads. I sanded the plate's sides using 80 grit sandpaper, and eventually, I stopped the continuous sparking that had been I had noticed. Some of the wires had low spots that sparked even without alpha particles, so I gently pushed those up with a q-tip.
Eventually, I got all the bugs worked out and tested the spark detector using an Am-241 source from a smoke detector. It worked wonderfully, making a beautiful storm of sparks and small pinging sounds. If you open the picture on the right and look closely, you can see small sparks on the finished detector as I hold the Am-241 source above it. Because uranium undergoes primarily alpha decay, this detector also works with uranium ore, although not quite as vigorously, since the source material is more spread out. This project is one of my favorites because I can "see" radiation with it. Each spark happens at the actual location of an alpha particle, thus showing me the distribution of the radioactivity, which I think is really neat.
A while ago, I saw a YouTube video showing someone smelting gold from ore using a common household microwave. Intrigued, I researched microwave furnaces further. Amazingly, the microwave found in nearly any kitchen can melt metals like gold, copper, and aluminum! Microwave furnaces work by surrounding the crucible or the metal to be melted with something that absorbs microwaves (a susceptor) and turns them into heat. Some common microwave susceptors are charcoal and silicon carbide, as well as water--food gets hot in a microwave because of its water content.
To make my microwave furnace, I grabbed the alumina-silica light-density firebrick that was my arc furnace body and cleaned the metal residue from its inside. The furnace body is simply one brick with a 2" diameter hole 1.5" deep in it and another brick as the lid. Each brick is about 4" by 4" by 2.5", so this leaves a 1" thick bottom on the furnace body.
I added a 1/8" layer of crushed lump charcoal to the bottom of the furnace's inside and put my soup can crucible on top of that. Then, I added some aluminum TIG welding filler rod scraps and set the furnace in an experiments-only microwave. With everything in place, I nuked my furnace for six minutes on high heat. Amazingly, the aluminum was completely molten and glowed bright orange! I was quite impressed, so I tried zinc in the microwave furnace. After four minutes, it was a mere puddle.
I read on a forum somewhere that charcoal can heat things to at least 1000°C as a microwave susceptor, so I suppose I shouldn't be surprised that the furnace works so well. With a simple soup can as its crucible, though, it has limitations. I tried melting copper, and while the copper melted (around 20 minutes on high), it also ate through the steel and leaked out everywhere. A graphite crucible might be a better choice. However, I am still impressed that a common microwave can melt a metal like aluminum in less than ten minutes!
I had an old (possibly from the 1960s) Hoover vacuum cleaner motor lying around, so I decided to turn it onto a lab centrifuge for chemistry experiments. The motor was enormous and spun with such ferocity that I thought it would might go airborne and kill me, which scared me thoroughly. For that reason, I used large bolts to attach it to a thick plastic/wood board, which I clamp to a table when I use the centrifuge.
The vacuum cleaner creates suction by spinning a cast aluminum turbine. The aluminum turbine blades were relatively flat on top, so I decided to make this the centrifuge top. I cut some plywood into a disc with a hole it in to go around the motor output shaft. If the disc ever flew off in operation, someone could get seriously hurt, so I cut some scrap sheet steel into a large washer to go between the end nut of the motor output shaft and the plywood. Once everything was assembled, I tightened the nut until everything was snugly in place.
Previously, I had requested and received free samples of 2mL plastic centrifuge tubes from a laboratory supply company, so I designed my tube holders around those. I cut and drilled six wood cubes with holes sized for my centrifuge tubes and then glued these around the plywood disc. Centrifuges can self-destruct if they are off-balance, so I carefully measured 60° increments around the circle so that the disc would be balanced. To finish off the centrifuge, I added a cord and on/off switch salvaged from the old vacuum cleaner.
For being made from a vacuum cleaner, this centrifuge works surprisingly well. I have successfully separated oil from mayonnaise, although mustard does not separate. This centrifuge is extremely useful for settling precipitates out of solutions. If I mix copper sulfate and sodium carbonate solutions, I get clear sodium sulfate in solution and blue copper carbonate precipitate. By placing a sample of solution in the centrifuge, I can settle all the blue precipitate out and see the true color of the solution--it should be clear if I have used enough sodium carbonate. One thing this centrifuge can't do is enrich uranium, but if that's the only complaint, I would say it works pretty well!
A very long time ago, one of my friends introduced me to The King of Random's videos on YouTube. I was impressed, and it wasn't long before I found his video on making a solar death ray using a Fresnel lens from a rear projection TV and some cheap wood boards. I had to try it!
After finding a rear projection TV on craigslist for free and just barely managing to compress it into a minivan for transport, I began searching for its Fresnel lens. The TV was absolutely enormous, and it was really heavy as well. I eventually found out how to take off the lens and carefully set it aside so it wouldn't get scratched. Other useful things I found in the TV were castor wheels (used in my ball mill), mirrors (CO2 laser, perhaps?), and various circuit boards and lenses that I haven't used yet.
The Fresnel lens itself is quite floppy, and it is also large and unwieldy, which isn't good. The King of Random's video showed how to build a nice frame for the lens that held it rigidly but still allowed for easy rotation to follow the sun. I followed his instructions closely, and the frame turned out to be inexpensive and very helpful. I also used this Instructable to find the lens focal length so I knew where to put objects for best burning performance. My death ray's focal length is about 35". I put a board across the two cross-pieces on the frame so that objects can rest there at a fixed distance from the lens (instead of me holding them in midair). Finally, I scratched each lens side with my fingernail to find out which side had grooves on it. The grooves should face the sun for best performance. In use, I also try to line the lens up so that it is perpendicular to the sun's rays that are hitting it.
Concentrating over a square yard of sunlight into a square inch makes a very bright spot of light, which can be problematic for unprotected eyeballs. I bought some #10 shade cheap-o welding goggles from Harbor Freight and use them every time I play with the death ray. It is impossible to see what is happening otherwise, although my iPad can see details inside the bright spot.
I love using my Fresnel lens. It creates a searing-hot spot of intensely focused sunlight, capable of melting or burning many things. Over the years, I have melted over a quarter's worth of zinc pennies using this Fresnel lens. Yes, melting metal with sunlight! While this lens cannot melt iron or rocks as some videos show, I have melted and compressed HDPE milk jug shreds into a usable billet by placing them in a soup can "oven" under the death ray spot. My Fresnel lens has even burnt all the way through inch-thick wood boards! This death ray cost less than $20 to make and uses freely available energy to do incredibly destructive things, which is exactly why I love it!
Next on my list of thermite reactions I want to try is copper. For that, I will need copper (II) oxide to react with my homemade ball-milled aluminum powder. I saw a nice video by zhmapper on YouTube about making copper (II) oxide, so I decided to try his method myself.
To start, I made concentrated solutions of copper sulfate (root killer) and sodium carbonate (washing soda). I used about a 2:1 mass ratio of these solids and completely dissolved each. Baking soda (sodium hydrogen carbonate) would work just as well, but the ratio might be different. With my solutions prepared, I mixed them thoroughly together. This made a lot of bubbles, so I had to quickly transfer my experiment to a larger container. When the solutions mix, they make copper carbonate, which can be decomposed into copper (II) oxide. I knew that I had added enough sodium carbonate because the blue color of the solution became clear (once the blue copper carbonate had settled out).
The byproduct of the reaction is sodium sulfate, so I filtered this off, along with the excess water, using simple coffee filters. When the copper carbonate dried, I was left with a robin's-egg-blue powder. To transform the copper carbonate into copper (II) oxide by releasing CO2 gas, I heated the powder in a soup can. My hot plate wasn't hot enough, so I put the can in a bonfire for 15 minutes. When everything had cooled, I was left with a dark black powder--the copper (II) oxide. I also noticed some pink inside the can, so I wonder if the fire was somehow reducing some of the copper oxide back into copper metal.
Untouched, the copper oxide would probably work. I have heard that copper thermite is very energetic, so it probably doesn't require extra fine ingredients. However, I want the best performance from this reaction, so I milled the powder by hand using some steel ball bearings in a plastic jar. Shaken enough, the bearings break up any clumps. I also ran a magnet in a plastic bag over the powder to remove magnetic particles that came from the soup can. I was left with 55 grams of fine copper (II) oxide powder for an exciting thermite reaction.
For a very long time, I have been fascinated with crystals of pure metals. Many people have grown crystals of copper sulfate, but crystals of metallic copper are a rare thing. After seeing The Backyard Scientist's video as well as this more crystalline crystal, I had to try it myself.
The basic principle of copper crystal growing is to very slowly electrolyze a solution of copper sulfate with two copper electrodes. I used a normal copper wire as my cathode (-) and a flat spiral of thick copper wire as my anode (+). The cathode just poked into the solution ~5mm, and the anode rested on the bottom of my glass jar electrolysis cell, connected to my breadboard via a soldered-on insulated wire. In a Sciencemadness forum post, The Backyard Scientist says he used 100g/L copper sulfate and 60ppm chloride ions to prevent spindly dendrites from forming (thick crystals are more impressive). I initially thought dilute copper sulfate would conduct less electricity and thus grow the crystals more slowly, thus helping to form larger crystals. It turns out that if the solution is too dilute, the growing crystal will "use up" all the Cu2+ ions in the immediate vicinity and will get weird polyp-like black growths instead of shiny crystalline copper. I ended up using 40g/L of copper sulfate for the final iteration of my experiment; concentrated solutions (or frequent stirring) are key to success. My chloride ion source was simply table salt, and I used tap water for my electrolyte bath. There was some gunk in the root killer copper sulfate, so I filtered my solution before use.
While a dilute solution is actually not good for making beautiful crystals, very low currents and voltages are. My electrodes were spaced about 7cm apart, and my voltage varied throughout the experiment‐it was usually around 0.28V. The key is to keep the current very low. I never let the current exceed 10mA for the entire experiment. To achieve the very low voltages necessary for low currents, I made an LM317 constant voltage circuit and put five 1N4007 diodes in series on the positive output of the circuit to drop the voltage down lower. Basically, the LM317 can only regulate down to an output voltage of 1.25V, but I wanted the ability to go to around 0.25V, so I put a bunch of diodes on the output so that each of them dropped the voltage down a little bit.constant voltage circuit. Oh well!
Turning the potentiometer on the circuit still changes the voltage, only everything is shifted down a volt. I used a 7.5V wall wart power supply to power the LM317; anything within the specified input voltage will do fine. One odd thing I noticed was that while reading the voltage between the two electrodes, if I connected the ammeter, the measured voltage would increase. I have no idea why this happened, since my circuit should have been a
With everything connected and my electrolyte prepared (filled to ~1/2" of top of glass jar), I turned on the power and adjusted the potentiometer until my multimeter read less than 10mA on the output. I recorded the voltage and nearly everything I did in an experiment log which may be viewed here. If you would like to repeat this experiment, definitely read it through. With my electrolysis power on, I just had to wait. Every few days, I checked on the experiment. At times, I had to gently swirl the solution to mix the Cu2+ ions up again. When I swirled the solution, the current would increase and the voltage would decrease. I could tell when the solution was becoming depleted around the crystal because it would be a lighter blue than the rest of my electrolysis cell. I also covered the jar to prevent dust from entering and added water to balance evaporation. After waiting for six weeks (yes, 42 days), I pulled out an unbelievably shiny bloom of huge copper crystals!
Over six weeks, my crystal grew to 14 grams and a nick in the anode wire insulation allowed the wire to corrode almost through. In a previous run of this experiment, I had noticed that the crystal dulled and darkened after exposure to air. I wanted to preserve the extremely shiny pink color of my new crystal, so I cut the cathode wire ~1/2" from the crystal and hot-glued this to the inside of a small spice jar lid. One note on cutting thick wire with side cutters-be careful to hold the crystal at all times! My first crystal shot a yard away and smashed against the wall when the cutters made it through the wire. My new crystal had already darkened some, so I dipped it in plain vinegar, which restored its ultra-shiny pink color well. I then filled the spice jar with mineral oil and sealed the crystal in to keep its shine.
For photography, I brought the crystal display outside for the bright sunlight and set it on a microwave turntable motor connected to 120VAC. The motor was an AC motor rated for 3rpm, so it slowly rotated the crystal for the video. The effect was rather nice, and I was exuberantly happy to be the new owner of such a rare and amazingly beautiful crystal.
Nitrocellulose is simply cotton that has had its hydroxide groups replaced with nitrate groups. This simple substitution makes it highly flammable and even explosive. After seeing some YouTube videos demonstrating its highly combustible properties, I decided to make some.
First, I selected some 100% cotton string, a piece of white paper towel, and some cotton balls as my sources of cellulose. I very carefully made a 2:1 volume mixture of concentrated sulfuric and nitric acid in a small glass beaker. After stirring gently, I placed this beaker in a bucket of snow to cool the nitration. I nitrated my three sources of cotton separately, one after the other. To nitrate each batch, I placed it in the acid mixture for 15 minutes. After the time was up, I transferred the now-nitrocellulose to a saturated baking soda solution to neutralize remaining acid. Finally, I thoroughly washed the nitrocellulose with plain water and let it dry.
One interesting thing I noticed was that the cotton balls almost seemed to freeze in the mixture. It was quite cold when I did the experiment, but the stiffening could also have been caused by close packing. I had just enough acid to cover three cotton balls at a time, so they were squished.
The homemade nitrocellulose is quite inflammable. I have even held pieces in my hand and lit them without hurting myself. While the paper towel and the cotton seem to burn extremely quickly without any residue, the string burns slower and leaves some charred material behind. A cotton ball that I nitrated at the end of the run also left some residue--perhaps the acid was nearly used up. The best cotton burns so quickly that it can detonate under the right conditions.
I created these "right conditions" by compressing the nitrated cotton balls in a spent brass shell casing and initiating detonation with a homemade bridgewire detonator. I first made an insulating sleeve out of a straw to go on the inside of the shell; this protected the bridgewire from shorting on the casing. Then, I packed the shell half full with nitrocellulose. I inserted the bridgewire (also stuffed with nitrocellulose) and then packed the shell the rest of the way. I left 3/8" at the top and crimped this over with some pliers to seal the shell, creating containment for the combustion gasses.
I put the device in a cardboard box with a polycarbonate viewing window and set it off from another room using my flash capacitor bank. I was wearing hearing protection (a must for explosions), but from family member accounts, the ensuing explosion was frighteningly loud. The shell casing was completely blown to pieces, with brass shrapnel flying through the cardboard box and also embedding itself a centimeter into a nearby block of wood. I was quite impressed by the detonation-it was much more powerful than I had expected.
If you read the preceding two paragraphs, please don't do anything stupid. While exploding bridgewire detonators are incredibly safe (as they contain no primary explosives), shrapnel is much more dangerous than a simple fireball. If you repeat this experiment, make sure you will be protected from potential shrapnel.
A while ago, my church did a silent auction to raise money for students going to a youth conference. I wanted to donate some laser art, so I found neat designs online and used Inkscape's "Trace Bitmap" and "Object to Path" tools to create a path from an image. Then, I used a laser engraver plugin to transform the path into g-code for my laser cutter. I tried cutting the design from black paper, but it didn't work! My laser cutter (PiKnife) messed up the movements and cut things out in wrong places, making the entire cutout worthless. I was quite disappointed, so I tried to figure out what the problem was.
One problem PiKnife had a lot was that the stepper motors would sometimes stick and jitter. Eventually, I noticed that pressing on the input and output wires plugged into the ribbon cable going to the Raspberry Pi would cause this problem, so I deduced that the issue must stem from bad connections. To fix the connections, I wrote down where everything was in the ribbon cable and then used male-to-female breadboard jumpers to wire each input and output directly into the Pi's GPIO header. This eliminated the uncertainty of plugging wires directly into a ribbon cable.
Amazingly, that fixed the problem entirely! I set a new piece of paper on the laser cutter, pressed enter to begin the program, and didn't have an issue again! While it took five and a half hours to complete the design, it showed the true capability of PiKnife. It can cut extremely complex shapes for a long duration without problems.
With mere hours to spare, I completed the laser art and entered it in the silent auction. I also made a sped-up video (above) of the laser cutter working, which turned out well. Perhaps now that PiKnife really works it is time to expand into the CO2 laser range...
Electric resistance furnaces differ from electric arc furnaces (like the one I made in Experiment 32) in that they use resistive heating (like a toaster) instead of giant lightning bolts to melt metal. I had a hotplate that died (because a container holding hot sodium hydroxide solution broke on it), so I decided to use its heating elements to make a small furnace.
First, I played with the resistance wire to see what sort of current made it glow. I found that 12 volts made a 7" piece glow red hot. However, it didn't melt the wire, which was good. I calculated the current using Ohm's law and determined how much wire I would need to use to get the same current at 120 volts. Actually, the math is pretty simple--I needed to use ten times as much, or 70".
I used a hollowed-out low density soft alumina-silica firebrick as the furnace body. It had seen previous service as an arc furnace, so it was fairly beat up and I didn't care if it broke. I also used another piece of firebrick as an insulating lid. Fitting 70" of resistance wire in a 2" diameter hole was difficult, but coiling the wire seemed to work well. For connecting the mains electricity to the ends of the wire, I made clamps using small nuts and bolts that sandwhiched the wire snugly.
My crucible was a cut-off soup can bottom, and my metal of choice was aluminum. Plugging the furnace into the outlet made the heating elements glow, but the really neat thing about this furnace was that it was silent. I even read a book while I waited for my metal to melt! An hour later, I checked on the melt, and the aluminum was undoubtedly molten! I wanted to grow aluminum crystals inside a blob, so I tried pouring the molten aluminum onto some glass to insulate it better. That was a rather bad idea, because the glass exploded, and molten aluminum was dispersed about the room. Oops!
Even though the crystal growing didn't work out, I was quite impressed that aluminum could be melted silently with just some electricity! Of all the metal-melting methods I have tried (there are at least 14 of them), this is one of the quietest.
After seeing a neat YouTube video (everything starts this way, doesn't it?) showing a chemist removing the copper plating from a zinc-core penny to make a solid zinc penny, I decided to try the experiment myself. Upon further research, I saw that Theodore Gray the element collector also had a solid zinc penny, but he had used cyanide to remove the copper plating. Since I didn't feel like exposing myself to extremely toxic salts, I decided to go with the YouTube method.
The reaction uses calcium hydroxide and elemental sulfur to oxidize away the penny's copper plating but not the underlying zinc. If I remember correctly (I did this experiment some time ago), the reaction smells awful, so it is best performed outside. I didn't have any calcium hydroxide, so I substituted in sodium hydroxide drain cleaner and used gardening sulfur as my source of sulfur. After that, I simply followed the video's directions.
