Category Archives: Science fair ideas

Fun With Arsenic: 1927


What could possibly go wrong here?

Ninety years ago, the September 1927 issue of Science and Invention magazine carried this article for aspiring young chemists with some educational and fun experiments they could do with arsenic. After a brief historical introduction ot the element, the article jumped right in with some practical experiments the young chemist could do at home.

For example, the amateur chemist could take some arsenic, presumably procured from the friendly neighborhood pharmacist, and reduce it at home to produce a purer oxide of the element. This was done by placing it over a porous plug of asbestos (also presumably readily available from the local hardware store), putting it in a test tube with some charcoal, and then placing it over a bunsen burner. This produced a vapor of arsenic trioxide, which was captured in another test tube. “When cool, the arsenic can be shaken out upon a piece of paper.”

The article also showed how to conduct a test for arsenic, with which “amounts of arsenic as small as a fraction of a milligram can easily be detected.” Perhaps the author included this bit of information as a warning, lest the young chemist allow a fraction of a milligram to “accidentally” be ingested by someone.

It also showed how to make a lovely green dye, known as Scheele’s green. Apparently, political correctness had already made a foothold by 1927, since the article pointed out that this green dye had previously been used in wallpaper. According to the article, “this caused a great deal of unnecessary excitement, for it was thought that you could be poisoned from it.” But this concern was entirely unwarranted, since “unless some was rubbed off accidentally and eaten, there is absolutely no danger.”

The article did caution, however, that the young chemist should “be very careful with it, as it is very poisonous.”

Warning:  This article is from 90 years ago.  You can’t buy arsenic from your local pharmacist any more.  Even if you could, the experiments described in this article sound very dangerous, and I would not recommend attempting any of them.  Those arsenic vapors sound like a really bad idea.  Besides, you can’t get asbestos either.  So even though the only category I had to put this article under was “Science Fair Ideas,” I don’t think this is a good choice.  But for more science fair ideas, some of which are just dangerous enough to be fun, you can see them all at this link.

Science Fair Idea: How to Weigh Smoke


Sir Walter Ralegh by 'H' monogrammist.jpg

Sir Walter Raleigh. Wikipedia image.

Sir Walter Raleigh is reputed to have won a bet with Queen Elizabeth that he would be able to weigh the smoke coming from his pipe. After she accepted the bet, he weighed a pinch of tobacco, smoked it, and then weighed the resulting ashes. He convinced the Queen that the difference in weight was the weight of the smoke.

Of course, the Queen could have won the bet by pointing out that the combustion products contained oxygen, and most of that oxygen originated not in the tobacco, but in the air. But she didn’t think of that, and instead paid the bet.

This little experiment, from 80 years ago, takes into account the amount of oxygen, and proves that the total mass doesn’t change during the combustion process. You do this by placing some matches inside a sealed glass flask. You carefully place it on a balance. Since the matches are sealed inside, you’re not able to strike them. To ignite them, you heat up the outside of the glass. Eventually, the matches will burst into flame and burn until all of the oxygen in the flask is consumed.

The balance won’t move, since the weight inside the container remains exactly the same. The weight of the matches plus the oxygen will exactly equal the weight of the burnt matches plus the weight of the smoke. Since it’s all sealed inside the same container, that weight won’t change.

If you wanted, you could take it a step further and repeat the experiment with the flask open.  In this case, the matches would burn longer.  Oxygen would be able to go in, and the smoke would be able to go out.  Therefore, the weight would change.  Would it go up or down?

You can easily adapt this idea to your next science fair assignment with a hypothesis along the lines of, “mass is conserved during combustion.”  While that other kid is busy fumbling with the paper mache volcano, the teacher will be suitably impressed that you’re smarter than Sir Walter Raleigh, and you’ll undoubtedly go home with the first prize.

The photo and experiment appeared in the August 1937 issue of Popular Science.

Sciene Fair Idea: Measuring Wind Resistance

1937MayPSWindIf Junior just remembered that the Science Fair project is due tomorrow, and he hasn’t even started, there’s no need to panic. The little project shown here can easily be whipped up in an evening, and the teacher will be none the wiser about your haste. He or she will assume that the little scientist has been working on it for weeks.

While Mom and Dad race to the dollar store before it closes to buy the poster board and markers, Junior can start building this instrument for measuring wind resistance for objects of various sizes. Unless someone sticks their fingers into the moving fan blades, this experiment should be completely safe. It appeared 80 years ago this month in the May 1937 issue of Popular Science.

Of course, the teacher expects the students to come up with things like a hypothesis, which should be pretty easy.  All Junior needs to do is come up with a sentence such as “a ______ shaped object has more wind resistance than a ______ shaped object.”  The blanks can be filled in with whatever objects are easier to construct, for example, a cube and a sphere.

The instrument shown here is pretty self-explanatory.  The object being tested is mounted on top of a rigid wire, with a counterweight at the bottom.  To make it look fancy, you can make the pointer and scale.  Then, you balance the wire and blow a fan at it.  The object that deflects the furthest has the greater wind resistance.

As can be seen here, the fan has an “egg box partition” in front of it to straighten out the air currents.  Apparently, in 1937, most households had egg boxes lying around with cardboard partitions.  A modern egg carton probably won’t work, but Junior can retrieve some cardboard from the recycling bin and simply make a grate consisting of square openings.

When you get home with the poster board, Junior can copy down some interesting facts from the Wikipedia article about drag, and the result will probably be a blue ribbon.

Science Fair Idea: How Lightning Rods Work


For today’s science fair idea, we go back 80 years to find this idea from the May 1937 issue of Popular Science. Junior can demonstrate how lightning rods protect a building from fire caused by lightning. If the teacher insists that Junior answer a question, then he can use the experiment to answer the question, “do lightning rods protect buildings from fire?” Hopefully, Junior will discover that they do. But in the process, he gets to set fire to a paper model of a house using high voltage electricity.

The pictures should be self-explanatory.  At the left, the spark is being applied directly to the model house, which quickly bursts into flame after the simulated lightning bolt strikes.  At right, the structure is protected by a lightning rod, which safely carries the current to ground.

To generate the spark, the magazine recommends a “neon-sign transformer or a spark coil.”  If you don’t have a spark generating device around the house, the Internet is full of plans.  If you’re in a hurry, you can just purchase this Tesla coil at Amazon, and get the best of both worlds.  Junior doesn’t have to build the coil, but he did build the lightning rod, so he did the work to prove his hypothesis.  As a bonus, he gets sparks, flames, and smoke.  The teacher will certainly be impressed, and Junior will come home with a blue ribbon.

The decorations on the house are a nice touch, but are optional.

1967 Homemade Galvanometer

1947AprRTVExpStudents looking for a simple but meaningful science fair project involving electricity won’t go wrong in constructing a simple galvanometer. The instrument can easily be constructed in an evening at little or no cost, and will prove to be very sensitive in detecting even small electrical currents.

The plans shown here appeared fifty years ago in the April-May issue of Radio TV Experimenter.  The plans are very straightforward, and most students can probably figure it out simply by looking at the diagram here.  It consists of a normal compass (even the most inexpensive toy version will work just fine) surrounded by a coil of wire.  When hooked to a battery, the compass will immediately deflect.

The sensitivity of the instrument is illustrated by using it to test a “dead” battery.  Even though an old battery is incapable of putting out enough current to run anything, it will still show a deflection if hooked to the galvanometer.

For students wanting to do something a bit more extraordinary, the homemade galvanometer can be paired up with one of the homemade batteries we previously profiled.  Most of the parts can be found around the house or at the closest dollar store.  Just about any type of insulated wire will work just fine.  If you can’t find any wire at the dollar store, you should be able to find some donor electronic device at the dollar store and you can scavenge the wire from it.  They’re not really necessary for the project, but if you want to match the design of the one shown here, the two “Fahnestock Clips” for hooking up the battery are available at Amazon.

Carbon Button Microphone Amplifier


While they were rarely used in radio applications, the diagram here shows how a carbon button microphone amplifier could be used to drive a loudspeaker from a crystal set. This diagram is from 90 years ago, and appeared in the 1927 British Radio Year-Book.  The diagram actually appears in the advertisement for a book entitled Successful Crystal and One Valve Circuits by J.H. Watkins, who according to the ad was the wireless correspondent for the Daily Express.

The principle behind the circuit is very simple and almost self-explanatory.  The audio from the crystal set or other low-level source is fed to the traditional earphone.  A carbon button microphone is in physical contact with the earphone, and produces a stronger AF signal.  In this case, this stage is able to drive a loudspeaker.

This idea was rarely used in radio, since a vacuum tube amplifier provided better results and little additional cost.  The carbon button amplifier was more commonly used in telephone circuits, where they were the only method of amplification available prior to the vacuum tube.  They made long distance telephony possible.  They did have the advantage of a smaller size than a vacuum tube, and required less battery power.  Therefore, they did remain in use in hearing aids until the advent of the transistor three decades later.  You can read more about the carbon button amplifier at this site.

The advantage for the home constructor was probably cost, since driving a speaker this way would not require an expensive vacuum tube.  In fact, the carbon button amplifier could probably be constructed at home, which would be impossible in the case of a vacuum tube.  Students looking for a very novel science fair project might consider making one, since it would be possible to produce loudspeaker volume with entirely homemade components.

Science Fair Idea: Lens Simulator Made With Sand


We admit that our ideas for science fair projects, even though they are extremely interesting, sometimes get a little bit complicated. And occasionally they could be a little bit dangerous if the student isn’t paying attention.  Even though I know you’ll be careful, your parents and teachers might get nervous if you’re using toxic chemicals or playing around with lethal high voltages.

So today we present an idea that is extremely simple to carry out and should have no safety objections. Almost any student should be able to put the whole project together in a single evening. And the only materials you need are a piece of paper, some sand, and a couple of wheels connected together with an axle. If you rummage through your toybox, you probably have a toy car that you can borrow the wheels from. If you don’t, there’s probably a suitable donor as close as the nearest dollar store.

With these supplies, you can do a demonstration of how light is affected by a lens. You put a layer of sand on the paper in the same shape as the lens you want to examine. Then, you put the paper on a slight slope and roll the wheels straight down into the “lens” made of sand. Just like light waves hitting a real lens, the path of the wheels will bend. They will start out going straight down, but upon hitting the “lens,” they will turn toward the focal point. If set up correctly, all of the “light rays” will converge on the focal point, no matter where they originate.

Your science teacher, of course, demands more than simply coming up with some clever demonstration. You also are expected to come up with things like a hypothesis and conclusion. There are many possibilities here. For example, if the lens is more convex (in other words, if it’s “fatter”), then it will cause more of a bend, and the focal point will be closer.

Or, you can compare two lenses: A convex lens and a concave one. Your hypothesis could be that the convex lens will bend them in, and the concave one will bend them out. Your experiment will prove that this is correct.

It’s late, and you need to finish the science project by tomorrow morning. I understand. Almost all of the information you need can be found at Wikipedia, including the two diagrams below, which you will be able to duplicate with your “lens”.  The red lines will duplicate the path of your wheel.  The left side of the picture is the uphill side.

Biconvex lens

Biconcave lens

And if you really want to impress your teacher, you can include two “lenses” and make a telescope, again, simply by following the Wikipedia diagram:

The photo at the top of the page comes from Popular Science, February 1937.



1916 Homemade Flashlight

1916decelectexpflashlightIf you’re looking for a good inexpensive flashlight, I recommend the modern one shown at the left.  For just a few dollars, you get a reliable light with a long lasting battery, and replacement batteries will only set you back a few cents.

But a hundred years ago, while handheld flashlights were available, they were more expensive and less reliable.  So the economy minded handyman might consider the idea of just making his own, battery and all.  The self-explanatory diagram shown at the top of the page, taken from the December 1916 issue of Electrical Experimenter, shows exactly how it can be done.  The great advantage of this do-it-yourself model was that it didn’t even require a switch.  You just set the light on its side, all of the electrolyte would slosh to the compartment on the left, and the light would extinguish.

The lamp is built from nice thick pieces of hardwood, which securely contain the acid sloshing around inside.  What could possibly go wrong?  Well, what could go wrong is hinted at by this admonition in the instructions:

The next, and perhaps the most important step, to be taken in the construction of the portable battery lamp, is to seal up the battery jar so as to make it absolutely acid-proof.  To prevent the acid from leaking out of the jar the cracks can be filled up by applying a thin coat of molten pitch or asphalt around the inside walls of the jar, as indicated by the heavy black line.  This can be done very well by melting a few pounds of asphalt in a kettle and pouring a small quantity through the rubber tube holes at A, tilting the whole case so that it will run into all the corners; then permit it to cool.  Additional molten tar is added until every crevice and surface of the interior is thoroughly coated with the insulating and acid-proof material.

After this acid-proof container is thus constructed, the interior is filled with a solution of sulfuric acid.  When the lamp is set as shown in the diagram, the bulb should glow brightly.

This is presented as inspiration for a science fair project, but even I would recommend that aspiring scientists contemplating a similar project should make a few more concessions to safety.  The school janitor probably won’t be very pleased if some sulfuric acid leaks out of your wooden “jar” onto the floor of the school gymnasium.  And mom probably won’t appreciate it if you melt a few pounds of asphalt in one of her kettles.  But the general concept is sound.  It’s quite possible to make your own battery capable of generating honest to goodness electrical current.  For more ideas on other homemade batteries, you can visit my earlier post on the subject.  You can find other science fair ideas at this link.

Science Fair Idea: Eddy Currents


Eddy currents in solid core (left) and laminated core (right). Wikipedia image. This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.

This simple experiment from eighty years ago shows how to experimentally verify the existence of eddy currents in the core of an electromagnet or transformer.

A coil of wire through which house current is passing is wound over two cores. One half is a solid piece of iron, and the other half consists of pieces of wire bundled together. The magnetic field in the coil, which changes direction 60 times per second, sets up eddy currents in the solid core, and the result is that it becomes noticeably warm. In the core consisting of wire, the currents are broken up, and the effect is not noticed.

Of course, it goes without saying that the aspiring scientist should be careful using household current in an experiment. But as long as all of the connections are properly made and insulated wire is used, the experiment is perfectly safe, and would make a good science fair experiment.

The image is from the December 1936 issue of Popular Science.

In transformers, eddy currents are undesirable, since they cause unwanted heat and inefficiency.  However, they have some practical applications, such as levitation and braking.

Science Fair Idea: Homemade Cardboard Box Speaker


The young scientist or engineer looking for a relatively simple but interesting project for the science fair could construct the homemade permanent-magnet speaker shown here.  It appeared fifty years ago this month in the October-November 1966 issue of Radio-TV Experimenter.

The speaker is constructed inside a cardboard box, which also serves as the sounding board (which the article incorrectly calls a “cone,” which it would be in a normal speaker).

The only other components, aside from a few pieces of cardboard and glue, consist of a permanent magnet and wire. Just as in a commercially manufactured speaker, a coil of is mounted on a form surrounding the magnet. When an audio signal is applied to the coil, it and the top of the box are made to vibrate.

The 1965 plans call for a magnet from a burnt out speaker, and this would still be a possibility.  These days, a more prolific source of powerful magnets would be from the drives of defunct computers, as shown in this video:

Suitable magnets are also available from Amazon or many other sources.  These plans call for a coil of 75 turns of 30-gauge enamel wire, although the exact wire size is not critical. The original plans call for using the speaker with a radio or television. The simplest way to make the connection to a modern radio or MP3 player would be through the headphone jack. Another option would be to use an inexpensive audio amplifier such as the one shown below:

The use of an audio amplifier would also allow the use of a homemade microphone, such as one of those shown in an earlier post.  And for another somewhat more complex homemade speaker (or microphone), see this post.

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