Is it safe for me to turn a lecture bottle of CO2 upside down and release it into a pillow-case so as to get some dry ice out of it? I know the technique works with fire-extinguishers but I wonder if the same things apply

should be as safe as using a fire extinguisher for the task.

 

just wear some gloves to prevent cold burns and take the usual safety precautions when dealing with high pressure and very cold temperatures and it should be fine.

I didn't know you could even do that...although getting CO2 at those temperatures on your hands would be bad...

 

I did some searching, and at http://hypertextbook.com/facts/2005/VictoriaPoon.shtml they claim that CO2 fire extinguishers can reach up to 5861 kPa. Searching around for lecture bottles of CO2, I found http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=295108|ALDRICH&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC that says CO2 lecture bottles are filled at 56.5 atm (5724.86 kPa). So it should be just as safe as a fire extinguisher when it comes to pressure.

Yeah, and you may want some ventilation as well.

Yeah, and you may want some ventilation as well.

 

my lab is extremely well designed for ventilation... one side is windows... so if anything goes boom, one side of the lab becomes ventilation :0)

The ventilation is also needed if your experiment proceeds without "boom".

You'll release a significant amount of CO2 into the room, and CO2 is already toxic at concentrations of >1%vol.

 

The CO2 is (probably) in a liquid form in the gas cylinder. That means that the volume expands significantly when the CO2 is released. (And that means that the concentration is significant). If there is 227 g of CO2 in the cylinder, this will become 126 liters of pure CO2 gas when released. If you have a bigger cylinder (like most fire extinguishers), the CO2 concentrations can easily become dangerous.

 

But I have a feeling that you know that already. Still, I've added it for other people.

thanks for doing the calculation for me... there is slightly less than 227g, so my lab would have to be 12,600L to stay safe. My front room is approximately 24,000L and my lab is easily four times that. Should be OK... but I might do it outside anyway :0)

You're not going to make much dry ice that way, especially since that is a very small amount of CO2 and a lot of it is wasted cooling down the remainder to freezing temps. As a demo, you're in the clear though. You're probably better off with a small sewn felt bag than a pillowcase.

apparently if it's all kept in the same place, about one-third of the CO2 will solidify

i wouldn't have said the yield was a third, maybe a tenth. but you should get enough for a demonstration.

you think i'll have enough for this?

could do. i'd give it a shot before trying it in class to make sure there won't be any embarassment over some decidedly nonicy icecream.

I've learned the lesson never to try a demo for the first time in front of an audience.