First note that liquid Carbon dioxide doesn't exist at normal atmospheric pressure - you need to compress it to at least 5.1 atmospheres for it to liquify, so you need to specify the conditions. read more
If dry ice were a lot denser, CO2 would tend to freeze as you compressed it, so the boundary would slope to the right on the way up indicating that to stop it freezing as you compress it you have to warm it. read more
Dry ice, sometimes referred to as"cardice" (chiefly by British chemists), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). read more