Industrial gases are compressed and cooled until they condense into liquid. The type of regulator determines if the liquid will quickly expand and evaporate. CO2 as well as Nitrogen are also used as a liquid coolants to shrink materials, such as metallic tubing and fittings, in order to temporarily reduce their dimensions so that they can be inserted or mated to create an "interference fit" when they warm up and expand. On those types of bottles the regulator does not allow the liquid to quickly expand.
Gaseous (vapor) systems are used to carbonate liquids and of course, to evacuate Oxygen from a target area in order to arrest flames.
Gas only systems, where the CO2 is stored as a compressed gas, are only used as inflation devices or where only small volumes are required. It's the weight of the product that counts. Liquids are more dense, therefore a greater amount of the gas can be stored in the cylinder when it is in liquid form.
When cooled further (or compressed further) the liquid becomes solid according to the chart depicted below. That product is called Dry Ice, which is much cooler than H20 Ice, and does not melt into liquid at room temperature/pressure. It simply vaporizes directly from solid making it a very tidy cooler for packages and in areas where moisture is unwanted.
The numbers shown on the left (vertical axis)is the value you can read on the first dial of your twin gauge regulator. The temperature reading on the horizontal axis is in Kelvin (K = C + 273).
Cheers,
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