To find the leak, first see that no burners have been left accidentally turned on. This is often the case where the cock has no stop, and is caused by the cock being partially turned around again so as to open the vent. Imperfect stop-cocks for this reason are dangerous, and should be promptly repaired. Try all the joints of the gas-fittings, by bringing a lighted match near them, to ignite the escaping gas if any there be. In case it is found by the sense of smell that the gas is escaping either within the floor or walls, do not on any account apply a match near a crevice. Turn off the gas at the metre, and send for a gas-fitter at once. In ordinary leaks, the burner or joint should be unscrewed, and white lead or common bar-soap rubbed in the threads before screwing home again.