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www.GOALias.blogspot.comOh, that is why my friendRita is always complainingabout iron articles rusting sofast. She lives near the coast.This process of depositing a layer of zincon iron is called galvanisation. The ironpipes we use in our homes to carry waterare galvanised to prevent rusting.You know that ships are made of ironand a part of them remains under water.On the part above water also waterdrops keep clinging to the ship’s outersurface. Moreover, the water of the seacontains many salts. The salt watermakes the process of rust formationfaster. Therefore, ships suffer a lot ofdamage from rusting in spite of beingStainless steel is made by mixing ironwith carbon and metals likechromium, nickel and manganese. Itdoes not rust.painted. So much so, that a fraction ofship’s iron has to be replaced every year.Can you imagine the monetary loss tothe world?6.4 CRYSTALLISATIONIn Class VI you have learnt that salt canbe obtained by the evaporation of seawater. The salt obtained in this manneris not pure and its crystals are small.The shape of the crystals cannot be seenclearly. However, large crystals of puresubstances can be formed from theirsolutions. The process is calledcrystallisation. It is an example of aphysical change.Activity 6.9(To be performed in the presence ofthe teacher)CAUTIONUse only dilute sulphuric acid. Becareful while boiling water.Take a cupful of water in a beakerand add a few drops of dilute sulphuricacid. Heat the water. When it startsboiling add copper sulphate powderslowly while stirring continuously(Fig. 6.6). Continue adding coppersulphate powder till no more powder canbe dissolved. Filter the solution. Allowit to cool. Do not disturb the solutionwhen it is cooling. Look at the solutionafter some time. Can you see the crystalsof copper sulphate? If not, wait for somemore time.Copper sulphateCrystalsFig. 6.6 Crystals of copper sulphate64SCIENCE