Dry ice is the solid form of
carbon dioxide (CO2). At -78.5°C, it sublimates directly into CO2
gas instead of melting into a liquid, which makes it the perfect no-mess solution for cooling
a warm cryo in a pinch.
Why
does it vibrate inside the cryostat?
Compared to the ice, the metal of the
microtome is HOT. The rapid evaporation
of CO2 results in an audible vibration as the lump of dry ice hovers
above the layer of gas and then falls back to the metal surface.
Where can I buy some?
Dry ice can be purchased from some grocery stores in 8-10lb slabs (~$1-2/lb). Half a block should be enough, meaning you'll spend about $5-10. It’s a good idea to call your local store ahead
of time to make sure they carry it. While one Albertsons may
sell it, another may not, and you don’t want to find that out on the morning of
your cryo crisis.
For safety reasons, the dry ice is kept locked up, so make a
beeline to the checkout area and ask a cashier or manager-type person to get
some for you. You will need to break the block
into smaller pieces to place inside your cryo.
I would recommend doing this in the parking lot rather than inside the
office, since it can be rather noisy. Besides, if you do it outside, there’s no one
to witness you swinging the bag and yelling “HULK SMASH!” as the frozen block
hits the cement.
 |
| full slab of dry ice |
 |
| broken into chunks |
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