Dry ice is actually
manufactured much the same way as described with the "fire extinguisher spraying into a bag" comment above. Liquid carbon dioxide, stored at 1073
psi is sprayed into a
porous bag, causing rapid
evaporation to absorb enough
heat that the rest of the CO
2 freezes at -109°
F (-78°
C). The frozen carbon dioxide is gathered and then
compressed by machines into
blocks.
Dry ice was first made commercially in 1925 by the Prest-Air Devices Company in Long Island, NY to keep ice cream from melting. Those ice cream carts you see at theme parks are loaded with dry ice. I was "backstage" once and saw their huge liquid CO2 tanks.