The Bubbling Cauldron
Want a real witches´ brew? Mix soap-bubble solution with dry ice, or use liquid nitrogen for bubbles that release fog when they pop. In the following video, PopSci´s contributing mad scientist, Theodore Gray, uses the help of a few young assistants to create cauldrons of toil and trouble.
Here´s how it´s done:
There are many ways to make a bubbling cauldron of witch's brew. As with all magic, some preparation is required for the spell to work properly. The three most practical methods for creating a bubbling cauldron are:
- Liquid nitrogen
- Dry ice
- Mechanical injection of compressed air or, preferably, helium
- All magic potions begin with hot water. If you don't have a fire under your cauldron, it's OK to just fill it with hot water from the tap-the hotter the better. To this, add magic-potion ingredients such as chili powder (for its blood-red color), cayenne pepper (for its strong magical smell) and any other spices, herbs, dried leaves, sticks, bones, wolfsbane or eyes of newt you may have lying around. Bulk chili powder, etc., can be purchased at warehouse clubs quite inexpensively.
- If you want overflowing bubbles, add several good squirts of dishwashing liquid. For some reason, regular (non-Ultra) Dawn is renowned in the bubble industry as the best for producing suds.
- A note on cauldrons: Cast iron is the proper material for cauldrons, but for the potions discussed here, pretty much anything will do. Plastic buckets, cooking pots-anything that will hold at least a few gallons of water is fine. Your cauldron should be about half full (or half empty, depending on how you look at it).
- After mixing up the stock (cragged sticks and 6- to 10-year-olds are best for mixing), you´re ready to add the magic.
- Liquid nitrogen, available from any welding-supply shop (provided you have a certified transportation Dewar to carry it in), is by far the most dramatic bubble maker. A few quarts of it dumped rapidly into a cauldron of hot, soapy water can create a billowing tower of bubbles several feet high in an instant (stand back). Much fun is had by all, but it doesn't last very long.
- Dry ice is much easier to get. Some larger grocery stores and supermarkets actually sell dry ice from chests just like the ones selling regular ice. Call around to find a place that sells it. I don't know if it's unique to my town, but where I live, you can also buy dry ice at the blood bank, which is particularly appropriate for Halloween. Ten or 15 pounds should be plenty, and it costs about $1 per pound. Bring it home in a cooler, and use within a day. (Do not try to store dry ice in a freezer. Your freezer is boiling hot compared to the dry ice, which will last longer left alone in a Styrofoam cooler.) Do not lick the dry ice, and handle it with gloves at all times.
- Use a hammer to break up the block of dry ice, and add about five pounds at a time to the cauldron. It will bubble gently for quite a while, the bubbles full of spooky smoke. If you have soap in the brew, it will slowly bubble over and spill out in a most satisfying way. If the water gets cold, add hot water.
- The last, and most complicated, method of bubbling a cauldron involves injecting compressed air or other gas using a coil of copper pipe with small holes drilled in it. Air from a compressor works great if you want a basically unending stream of bubbles overflowing the cauldron and making a gigantic mess (which is, I should remind you, a good thing if you're six).
- But the ne plus ultra of bubbling cauldrons is, without a doubt, the helium-bubble cauldron. The same copper-pipe bubbler can be connected to a regulator attached to a commercial helium cylinder (available at the same welding-supply shops you get liquid nitrogen from, and from party-supply stores, though they will not have the right regulator). Turn the helium on just fast enough for the bubbles to rise about one or two inches per second.
- Any child who has not seen this before will be absolutely floored by it, as will many adults. Do note: It does not work very well in high winds, and the more you stir or otherwise mess with the bubbles, the less well they float. It's best to leave them alone or just slice them off when you think they are ready to go free. (Just try to enforce that rule once the kids get involved.)
- Also note that this is an expensive hobby: A full 240-cubic-foot tank (the largest commonly available size) will last about 15 minutes and cost about $80 to fill.
Visit periodictabletable.com for more on Theodore Gray´s scientific pursuits.
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