To study the effect of heat on crystals.
Heat each of the salts listed above in a dry test tube carrying a delivery tube. Insert the delivery tube in another test tube cooled in a beaker of cold water. Collect the condensed liquid and identify it by placing a drop of it on white copper sulphate powder. The test for water is that it turns white anhydrous copper sulphate blue.
The clear liquid turns white anhydrous copper sulphate blue. A few of the salts do not give this liquid, most of them do. Salts that give out water of cystallisation on heating are copper sulphate, Epsom salt Glauber's salt, washing soda & cobalt chloride. Salts that do not give out water of crystallisation are common salt, potassium nitrate & potassium chlorate.
This clear liquid which certain crystals of salts contain and give out on heating is water. It is called water of crystallisation. Thus, there are two types of crystalline salts: those that contain water of rcystallisation and give it out on heating and others which do not.