If 3 unmarked refrigeration cylinders containing R12, R-22, and R-500 are all about 1/2 full and have been in the same room for several days at a temperature of 80 degrees F, which one contains R-22?

If 3 unmarked refrigeration cylinders containing R12, R-22, and R-500 are all about 1/2 full and have been in the same room for several days at a temperature of 80 degrees F, which one contains R-22?