Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number. And by the time you get 100%, you should know this topic pretty well. All the best. Dr E.

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 Check 

Across: 1. Against. 4. Metal used to protect iron on the surface of cans of beans. 6. Substance in sea water which increases the rate of rusting. 8. Large objects made of steel which float on water. 12. See 18 across. 13. Substance used to lubricate moving metal parts which also prevents rust from forming by blocking out oxygen. 14. English town. 15. Smallest possible part of an element. 16. See 16 down. 18. and 12 across. Method of protecting iron from rusting where a reactive metal (such as magnesium or zinc) is connected to the iron object. 20. Mark on the skin caused by disease. 21. Method of protecting iron from rusting where the surface is coated with zinc. 22. Increase in size. 23. Liquid required to make rust. 25. Large object often made of iron designed to span rivers. 27. Substance produced when iron or steel is oxidised by air in the presence of water. 29. Gas which has the formula NH3. (Find it using a search engine.) 30. A group of tissues in the body which work together. Examples include the liver, the eye or the heart.

Down: 1. Place. 2. Part of the verb "to be". 3. Substance used to galvanise iron. 5. Main element present in all steels. 7. Type of material which forms when two or more metals are melted together and then cooled to a solid. 9. Creature with 8 legs. 10. Belonging to a colony (of an empire). 11. Method of lubricating and protecting iron from rusting. 12. see 19 down. 16. and 16 across. Alloy of iron which does not rust. 17. Element in air which causes rust to form. 19. and 12 down. Method of protecting iron from rusting which also gives a very bright shiny surface. 20. Method of protecting iron from rusting often used on gates. 24. Oil prevents this gas from reaching the surface of iron. 26. Iron object designed to fire bullets. 28. Prefix to an infinitive.