Black deposits in the kettle that just will not get of? Grease the inside of the kettle all over with lemon juice from such a vial and let it stand for half an hour. Then fill the jug with water and apply all this with an extra dash of lemon juice to a boil. Leave for half an hour to cool and repeat all this again if necessary. Discard water and the kettle inside with a clean tea towel. A few more times with only water to boil to the dirt and the aftertaste. The effect is stunning, it looks like new.