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How To: Make a cloud chamber

David Ng has a great guide to building your very own sub-atomic-particle-spotting device. Maggie

Fun family science project — electric lighting from trash

The Joule Thief is a way of producing enough electricity to run small, but useful, electric lights using cast-off trash like pop-can tabs and "dead" batteries. It's especially handy in the Himalayas, writes inventor and Google Science Fair judge T.H. Culhane. There, electricity is a precious resource. But the components needed to build a Joule Thief are abundant, thanks to climbers and tourists who leave behind all sorts of surprisingly useful litter.

Last week, Culhane joined a G+ hangout sponsored by National Geographic and Girlstart to talk about the value in things we throw away and walk viewers through the construction of their very own Joule Thief. You can watched the video of the event, or read the instructions for building a Joule Thief at Culhane's blog.

The fact that the Joule thief allows one to run a 3V LED from a 1.5 or 1.2 Volt battery would itself be astounding, because it means you only need half the number of batteries to get the same light.

Some of you are thinking "wait, maybe it enables you to use a single 1.5 volt battery to light a 3V LED instead of the usual two, but doesn't it just make that battery last half as long? Great question, but the answer is that the Joule Thief, which works by building up and collapsing a magnetic field around the torus (which acts as an electromagnetic inductor) actually is more efficient than using a battery directly because it PULSES the energy to the LED. You see the lightbulb shining brightly, but in fact it is turning on and off very rapidly as the magnetic field of the inductor builds up and discharges again and again. That means that though the light appears to be on all the time it is actually turning on and off and saving energy because it isn't on all the time.

It turns out that the Joule Thief enables the battery to keep supplying electrons to the light long after the battery is normally considered DEAD. So the battery actually lasts much much longer than a normal battery. I've observed "dead" batteries working down to about 0.5 Volts. Normally a 1.5 V battery is considered dead when it reaches 1.0 volts. But the Joule Thief can "steal" the remaining energy much below that. And that got me thinking -- could I use other sources of between 0.5 and 1.0 Volts to run a 3V LED?

T.H. Culhane's post on The Joule Thief (includes instructions for making a Joule Thief with batteries and alternative electricity sources)

Watch the video at National Geographic Newswatch

Growing mushrooms on old catalogs

I cleaned out the attic recently, throwing away several of my husband's old chemistry and jewelry making catalogs. Which reminded me of this video sent to by Bill Beatty, in which he talks about how you could use catalogs like that as a medium for growing oyster mushrooms (aka, one of the yummy mushrooms).

Bill includes a set of instructions for this on his website, but he admits, this is somewhat theoretical as he hasn't pulled it off himself, yet. What about you? Have any of you grown mushrooms on catalogs or other unique medium? What do you think of Bill's proposed system?


Old phone book or catalog (thick one)
small trash bags ("tall kitchen can bags")
Large 6qt boiling pot
Distilled water ($1 gallon jug from a drug store)
1 Tbs Baking soda
one pound of very fresh large oyster mushrooms


First need to somehow sterilize (pasteurize) your old catalog. I'll try baking mine for two or three hours at 300F on a foil-covered cookie sheet. Then I'll boil a couple of quarts of distilled water in my biggest pasta pot, add a teaspoon of baking soda, then dunk the catalog and let it soak and swell up. (Use less soda? How much water to swell up a catalog without saturating it?)

Add mushrooms to cooled catalog: I'll try slicing the mushrooms very thin, then adding slices to many places in the catalog. If that doesn't work, maybe I'll blender the mushrooms in cold distilled water and use it instead. Conventional instructions have you first make some mushroom+grain material in jars, then days later you mix this "spawn" into the damp chopped straw.

Grow: I'll store the swollen catalog in a white plastic garbage bag. Push the catalog sides so the damp paper opens up a lot. Probably we want lots of air gaps, and not a solid wet log? Tie it off, then poke ten or twenty holes in the bag with a pencil or nail.

Grow: Store it out of the way in a closet for one and a half to two weeks. See if the white mushroom stuff completely takes over the paper. Perhaps it will take longer, since paper catalog is denser than chopped straw. Fuzzy white = good. Colorful or dark is mold=bad.

Trigger mushroom growth: put the bag overnight in your refrigerator. Then store it in an undisturbed spot in basement or washroom. Freakin huge edible mushrooms push out of those nail holes.

Video Link