The gas evolved is carbon dioxide and the method of testing this gas is lime water test.in this test carbondioxide is passed through a test in to the lime water.Make lime water. Add a small amount of calcium hydroxide to a test tube and add water. Add bung and shake. Allow to settle. Decant the clear solution into a beaker: lime water.
Turn the lime water cloudy. Add about 2 cm lime water to a test tube. Blow through a drinking straw to bubble CO2 through the lime water solution until it goes cloudy (20-30 seconds).
Turn the lime water clear again. Continue to bubble CO2 through the solution until the precipitate just disappears.