SCIENCE OF COMMON THINGS. 193 



What is a solution ? Why water dissolves sugar. 



IS 7*3 When salt is mixed with water and disappears in the liquid, 

 what is said to have taken place ? 



The salt is said to have dissolved in the water, and 

 .the liquid is now a solution of salt. 



IS 73 What, then, w a solution f 



A solution is the result of an attraction or affinity 

 between a solid and a fluid ; and when a solid disap- 

 pears in a liquid, if the compound exhibits perfect 

 transparency, we have an example of a perfect solution. 



1374 When is a solution said to be saturated f 



When the fluid has dissolved as much of the solid as 

 it is capable of doing, it is said to be saturated ; or, in 

 other words, the affinity or attraction of the fluid for 

 the solid continues to operate to a certain point, where 

 it is overbalanced by the cohesion of the solid ; it then 

 ceases, and the fluid, is said to be saturated. 



1S75 What is the difference between a solution and a mixture f 



A solution is a chemical union / a mixture is a mere 

 mechanical union of bodies. 



IS 70 Why will water dissolve sugar f 



Because there is attraction or affinity between the 

 particles of the water and the particles of the sugar. 



1S77 What do we mean by affinity f 



Affinity is that kind of attraction in virtue of which 

 bodies of a dissimilar character combine together into 

 a whole, which appears perfectly uniform to the senses, 

 even when assisted by powerful magnifying instruments. 



1S7S Why will not water dissolve granite or metallic iron f 



Because there is not sufficient affinity or attraction 

 between the particles of the water and those of the iron 

 or granite. 



1379 Are there any liquids that have sufficient affinity to dissolve iron 

 and granite ? 



Yes ; certain acids have so great an affinity for the 

 iron and granite that they are enabled to dissolve them. 



1S8O Why will not water dissolve oil? 



Because there is no affinity or attraction between the 

 particles of the two substances. 



