| Anyone old enough to remember "ice boxes", will | | | | To make dry ice, liquid carbon dioxide is released |
| remember the daily deliveries of huge blocks of ice | | | | from a high pressure container, after which there is a |
| that kept their meat and food cool inside the icebox, | | | | rapid evaporation of some of the gas into the air, |
| a forerunner of the refrigerator. But those blocks | | | | which results in almost instantaneous cooling of the |
| were hugely messy when they melted, and turned to | | | | rest of the escaping liquid, to freezing point. The ice |
| liquid. | | | | foam like product is then subjected to compression, |
| That's one problem you don't have with dry ice. | | | | to create blocks of ice whose surface temperature |
| Because it is just what its name says- dry ice. And | | | | averages around -109F. |
| when it "melts", it is actually changing its state from a | | | | The very density, and the slow process of |
| solid to a gas. Dry ice is carbon dioxide gas that has | | | | evaporation after compression, makes dry ice the |
| been subjected to high pressure. | | | | perfect way to ship perishables over very long |
| Just as the nature of water changes according to | | | | distances. There are no messy puddles of water |
| the sea level, boiling at lower temperatures, at lower | | | | because any evaporation turns the dry ice to a gas |
| pressures, carbon dioxide also has a solid-liquid-gas | | | | released into the air. For this reason, dry ice should |
| transformation related to pressure. At normal | | | | never be carried in a closed vehicle, or kept in a |
| pressure, CO2 is not quite liquid, and not quite a gas. | | | | room without proper ventilation. When the CO2 |
| But when confined within the high-pressure chamber | | | | content in normal air rises about its standard 5% |
| of a fire extinguisher, it becomes a liquid. | | | | level, it becomes toxic. |