28 DECOMPOSITION. 



thus, in the mixture of sand and sugar, we may easily 

 recognize both substances, for the characters of 

 neither are altered by being brought together. 



7. Another common case of affinity is observed 

 •when we slake quicklime. Quicklime has a strong 

 affinity for water, and when it is wetted, it becomes 

 very hot; the lime combines with a quantity of water, 

 and when is has cooled, we find that the lime is much 

 altered, having to a great extent lost its strong 

 caustic properties, and become slaked, as it is termed. 

 Here again we observe that the properties of the com- 

 pound differ remarkably from its components. Dry 

 caustic lime, in combining with water, forms a dry 

 compound of lime and water, the water becomes solid, 



'entering into the composition of a dry solid powder, 

 whilst the lime no longer possesses the power of heat- 

 ing when water is poured over it, and has become less 

 caustic (235). 



8. It may perhaps seem as if these two examples 

 of the change produced by attraction or affinity were 

 processes of Art, and not of Nature. They will, how- 

 ever, serve as examples of what is going on in a great 

 many natural operations ; and as we proceed with the 

 subject, it will be evident that this kind of change, 

 by which two or more different substances unite and 

 form one new substance, is exceedingly common 

 throughout Nature. 



9. The second kind of change which we shall have 

 to consider, is that which goes on whenever anything 

 decays. This change is quite opposite in its nature 



