98 JUNIOR GRADE SCIENCE 



low temperature, whereas in alum it exists at ordinary temperatures 

 in a permanent form. When this water is removed from the alum 

 the latter loses its crystalline appearance. 



Water of crystallisation is the water contained in certain crystals in 

 solid form. It seems to have something to do with their appearance and 

 shape. 



The white solid which remains after the water has been removed 

 is said to be anhydrous (Greek without water). 



39. EXAMINATION OF BLUE VITRIOL. 



i. Examine as described in Chapter XVII. 



ii. Effect of heating. When heated it is noticed that blue vitriol changes 

 colour and that a liquid is given off. Allow the test-tube to cool, then add 

 a few drops of water to the residue and note the etf< 



iti. Estimation of water of crystallisation in blue vitriol. Grind some 

 blue vitriol in a mortar, and take about two grams of the powder in a v 

 crucible with a cover; place the crucible on a pipe clay triangle on a tripod 



. Heat gently -with a -mall 

 flame. Note the appearance from time 

 to time, and continue heating till the 

 solid ceases to change colour. Allow to 

 cool and weigh. IN- h< at. cool and wci'_ r h. 

 The weight should not have changed 

 further; if it has, the process must be 

 continued till a constant wi^ht is 

 obtained. Calculate the loss of weight 

 for 100 grams. Add a little \vater to 

 the residue. Note the change of tem- 

 perature. 



Blue vitriol. Blue vitrol is usually 

 supplied in the form of blue transparent 

 crystals. When powdered the sub- 

 FIQ. 75.- How to^heat blue vitriol In stance fc a p& i eT blue . J t dissolves in 



water formimg a blue solution. 



When heated the solid becomes white, and a vapour is given off 

 resembling steam. As the addition of a drop of water restores the 

 colour we may assume that blue vitriol contains " water of crystal- 

 lisation." When a weighed quantity of powdered blue vitriol is 

 heated carefully in a crucible it is found that it loses weight, and when 

 the class results are collected they show that the weight of anhydrous 

 blue vitriol remaining is the same in every case. Assuming that the 

 loss of weight is due to the water given off, it can be stated that blue 

 vitriol contains a definite percentage of water of crystallisation. This 

 is an important fact. 





