12 THE FOOD OF PLANTS CHAP. 



in the next some whiting, and then add some water 

 to each and warm them gently over a spirit-lamp. 

 The salt, the sugar, and the sulphate of copper dis- 

 appear from sight ; the sand lies at the bottom un- 

 changed ; and the whiting mixes with the water, 

 but the water does not become clear. Now taste 

 the sugar water and the salt water. Evidently 

 from the taste the sugar and salt are still there, and 

 the blue colour of the sulphate of copper water shows 

 that the sulphate of copper also is still there. These 

 three substances have dissolved in the water. The 

 sand and whiting have not done so. 



Now place five glass funnels in 

 a row, and fit a piece of filter-paper 

 into each, and empty the flasks, 

 each into a separate funnel. 



The water comes through clear 

 in each case; but on tasting the 

 sugar water and salt water, we find 

 that the sugar and salt have passed 

 through the paper with the water. 

 The sulphate of copper water is still 

 blue in colour, showing that the 

 sulphate of copper has passed through. 

 But the sand and the whiting have been left behind on 

 the paper. It is now clear what we mean when we 

 say a substance dissolves or is soluble in water. 



