CHAPTER X 

 SOLUTION 



THE property that many substances have of dissolving in others 

 is a most interesting and valuable one. The value lies chiefly in 

 the fact that some substances are easily soluble in a given liquid 

 and others are, practically, not soluble in it at all. These differ- 

 ences in solubility enable us to accomplish, both in the laboratory 

 and in chemical industry, many things otherwise impossible. 

 Thus, we separated sulphur from iron (p. 13), by using carbon 

 disulphide (082) to dissolve the former. In the same way the 

 refining of silver (its separation from the lead in which it is con- 

 tained) is carried out on a large scale in actual practice by the use 

 of molten zinc as a solvent. We must first learn precisely what is 

 meant by a solution, and then we shall be ready to understand 

 the uses and properties of solvents and solutions. 



Solution. We distinguish carefully between a solution and 

 a mere mixture, also between a solution and a compound. 



A mechanical mixture, such as that of iron and sulphur, can 

 never be perfect, as will be evident from what has been said in an 

 earlier chapter (p. 84) regarding the size of molecules. However 

 finely we may powder up such a mixture, we cannot possibly 

 bring about a sufficiently intimate dispersion of the particles of 

 its components among one another to justify us in believing that 

 the whole mass has become homogeneous in its ultimate structure. 

 In any true solution, however, intermingling of the particles of the 

 separate components down to molecular magnitudes has actually 

 been accomplished. In a solution of salt in water, for example, 

 the dissolved substance is completely and permanently dissipated 

 throughout the liquid. However long the solution is allowed to 



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