e Carbon dioxide Many reactions can be used to produce carbon dioxide gas Marble chips or other carbonate rock treated with dilute acid provides a good source The gas is not too soluble to be collected by water displacement as shown above for the preparation of hydrogen Alternatively carbon dioxide can be collected by displacing air from dry bottles To test if the bottle is full lower a lighted splint or taper into the top of the jar If the flame is extinguished at the entrance as at ii then the jar is full Put a cardboard cover over the top to prevent diffusion of the gas Check the density of the carbon dioxide by pouring the gas into another bottle either above or below the first bottle Find where the gas is by testing with a lighted splint Note The presence of carbon dioxide can be confirmed by the fact that limewater becomes milky when the gas is Passed through it