I was thinking about what Blast was saying about getting enough ice early, before a storm. We have a large chest cooler with all of our frozen food in it, and a generator to keep it going during a power outage. But if something happened -- freezer break, run out of gas, etc. -- to keep things cold we'd have to rely on the "don't open the door, fill all empty space with ice" rules.

So I was thinking, dry ice would be better. The local Safeway has a dry ice cooler and they sell it by the pound. Normally it looks like no one goes near it for long periods of time, but I can imagine the stock goes quick before a storm.

What are the problems with keeping a CO2 cylinder, a nozzle and some burlap bags just in case? I understand you can make your own dry ice by sticking the nozzle attached to the cylinder into an empty burlap bag and spraying away. About 46% of the CO2's volume will turn into dry ice snow in the bag, and the rest dissipates into the air. (Do this outside!) Then packing the snow in the bags on top of your food in the chest freezer to keep things cold. Depending on how tightly packed it is, and what its wrapped in, you'll lose 4-5lbs/24 hours. (Info from dryiceinfo.com.)

What the site doesn't say -- is it expensive to keep a CO2 cylinder and nozzle in your garage, say? How long would it last without needing maintenance or topping off? Am I completely nuts in being curious about it?

Another example at http://scientificsonline.com/product.asp?pn=3071533&bhcd2=1222911792.

I'm not completely sure about the C02, but we have oxygen/acetylene tanks in our garage for welding that have been there for a long time, at least a few years, (as we rarely do any welding ourselves anymore) and they still work just fine when we do occasionally use them. I know the cylinders/tanks are dated, as they have to be pressure tested every few years, but if you swapped it out for a new one every other year or so I don't think it would be a problem.

You can even get ~20oz CO2 tanks for paintball guns at a few stores now (lowes, walmart, ect). Not sure how much dry ice they would make, but they would probably be a lot easier to handle than a big tank (which would either need a siphon tube or be turned upside down to get the liquid), as well as probably being easier and safer to store. Then all you would need is an on/off paintball gun ASA (~$20) and a length of 1/8" npt steel-braided hose ($ depends on length). You just hold the bottle with a gloved hand, turn it valve-side down, and open the ASA for the liquid CO2 to come out the hose.

To add a bit more science to Izzy's response, the molecular structure of dry ice prevents you from packing the flakes you get from the tank/burlap bag into a solid slab of dry ice. When you put ice under pressure it converts to liquid a little bit then refreezes as a solid mass. That's what allows ice skates to slide across the ice. No other material acts in quite that same manner. The flakes will evaporate away much, much quicker than the solid slabs because the flakes have a much greater surface area from which to evaporate.

The idea of keeping a CO2 tank system to make dry ice on demand sounds doable, but I have to wonder about the economics. I think it'd be cheaper just to get the dry ice if a storm is coming. Of course, this only works if you know a storm is coming...

-Blast

I guess if you really wanted to you could always buy a dry ice machine that makes blocks, then all you would need is the tank with a siphon tube. They seem to be pretty expensive though. ($300-$500 on average?)

I wonder how hard it would be to make one. They don't seem very complicated.

Way back when ... After a good summer weekend hike, after we tied up the pack dinosaurs, my friend asked I could do with a beer. I figured he had socked a few away and it would be, at best, tepid.

Instead he pulled out a Styrofoam cooler holding a six-pack, a CO2 fire extinguished and a proceeded to discharge the cylinder into the cooler. In about a minute we had frosty cold beer. A grand way to end a long summer hike.

Now this isn't a very efficient or cost effective system for most people. He could do it because, as part of his job, he could refill the fire extinguisher for free.

We use CO2 in our lab and a number of years ago we thought it would be great to buy a dry ice maker (basically, the same unit shown in the link), since we only had sporadic need for dry ice. While the unit does produce small quantities of dry ice, it is very inefficient and not worth the bother for the small amount of dry ice produced. We got rid of the unit and pirate some dry ice from another building if we need any. Save your money.

Pete