11--12] 



SOLUTION AND EVAPORATION 



substance is in a fine powder. Heating and shaking also 

 promote solution. 



Solution may be of two kinds : (i) simple, when the 

 body dissolved does not change in its chemical composition, 

 and is therefore left behind on evaporating off the liquid ; 

 (2) chemical, when a body of different composition is left 

 on evaporating off the liquid. 



a. Simple Solution. — Place a little alum in a 3-in. 

 evaporating- dish, nearly fill the dish with water. Heat over 

 the Bunsen burner until the solid dissolves. Reserve the 

 solution for future use. 



Fig. 11 



b. Chemical Solution.— Place a few pieces of marble in 

 a test-tube, add a little dilute hydrochloric acid (HC1). 

 The marble, which is insoluble in water, will gradually 

 dissolve, carbon dioxide gas being given off (paragraph 39). 



12. Evaporation. — On heating a solution of a sub- 

 stance the liquid portion is driven off— evaporated— the solid 

 being left behind. 



Experiment— Heat the liquid from paragraph 1 1 b, in 

 a small evaporating dish until the liquid is all expelled ; 

 white solid calcium chloride 6CaCl 2 ) will be left behind. 



