From one of my recent favourite sites (the homopolar motor's a classic), there's now this response to the subject of yesterday's post:
Dry ice can be had from various places. The Evil Mad Scientists apparently got theirs at the grocery store, but industrial gas suppliers, catering joints, ice cream wholesalers and so on can be useful if your grocery store ain't that hip.
Hit the phone book - suppliers of water ice may sell dry ice too, and should know where you can get it if they don't. It'll keep for a while if you put it in an unsealed (that's important) cooler/Esky in your domestic freezer (and probably save you some electricity, since it'll keep the freezer cool all by itself - dry ice is a useful emergency measure if you've got a broken fridge full of valuable food, or there's a lengthy power outage, and aberrant cables are not an option).
All the dry ice is for, in this case, is the creation of a blanket of cold carbon dioxide. So it's conceivable that you could substitute in some other CO2 source. A welding CO2 tank set to just trickle the gas out, for instance, or a similarly restricted fire extinguisher (CO2 extinguishers can also be used to very wastefully make a little pile of dry ice, as can be seen in one of the Secret Life of Machines episodes).
Or even, possibly, ye olde bicarbonate of soda and vinegar.
Don't expect a little soda and vinegar to make enough CO2 to be useful for this trick. But a whole kilo box of bicarb in the bottom of a bucket, with a couple of litres of the supermarket's finest, cheapest white vinegar dumped on it, might do the trick. Ice cubes to cool the gas and encourage it to make an orderly layer may or may not help further.
The soda-vinegar reaction can also be used as a pressure source to power rockets.
Add a giant wobbly solar bag (which is filled with air, not CO2), and you've got a grand day out.
16 January 2007 at 6:42 pm
Question concerning the photo of the kids blowing bubbles into a cylinder with dry ice at the bottom:
Is the concentration of CO2 in that cylinder high enough that you'd asphyxiate if you fell into it?
To be honest, I was thinking the same thing about the esky of dry-ice in the chest freezer - you lean in to get something out...
17 January 2007 at 2:56 am
If you put your toddler in the cylinder (ignoring the cries of pain as it sat on the dry ice) and went away, then yes, that kid would probably die.
[strokes beard] In time.
Any kid who could climb out, and chose to do so rather than sit there for the at-least-most-of-a-minute it'd take for them to pass out, would be fine (except for the abovementioned freeze burns). Even if they did pass out, you could resuscitate them if you got to them fast enough.
A chest freezer would fill up with CO2 if you put a decent amount of dry ice in it; the lid would "burp" a bit from time to time if the freezer didn't have any leaks anywhere else - it'd probably be likely to leak a little around the drain plug, though. But it's not as if one lungful of even 100% CO2 is a death sentence. It only takes several per cent CO2 in air to eventually kill you, but the stuff is heavy and dissipates rapidly in normal rooms, so it's pretty difficult to kill yourself with dry ice.
This is just as well, of course, or people would be dropping dead all over the place when they used things like kerosene heaters. People do asphyxiate when using combustion heaters in inadequately ventilated premises, but it's the carbon monoxide that does them in, since that'll be lethal over a few hours in concentrations below 0.2%.
As far as exposure for a few seconds goes, neither carbon dioxide nor the much more toxic carbon monoxide are a danger in any concentration.
Which, again, is just as well, or the hilarious practice of substituting someone's nitrous oxide bulb for a CO2 one at a hippie crack party would leave a trail of corpses, rather than just people with a mild headache, a strange tingly feeling in their mouth, and a totally harshed buzz, man.