PRACTICAL CHEMISTRY, 

 MEDICAL AND PHARMACEUTICAL, 



I. 



CHEMICAL PHYSICS. 



BOTH sciences, chemistry and physics, have for their object the 

 study of all substances, or of all varieties of matter, and the changes 

 which they undergo. When these alterations affect the composition 

 of matter we have chemical changes, which are considered by chem- 

 istry ; when the composition is not affected Ve have physical changes, 

 considered by physics. But whenever chemical changes take place 

 they are accompanied by physical changes. Indeed, there exists such 

 a close relation, such a mutual dependency, between these two series 

 of phenomena that they cannot be studied altogether independently 

 of one another. Moreover, the chemist uses constantly in his opera- 

 tions instruments or appliances the construction of which is based on 

 physical principles. A knowledge of certain parts of physics is 

 therefore essential for the proper understanding of chemistry. It is 

 for this reason that a few chapters dealing with certain physical con- 

 ditions of matter precede the parts on chemistry. 



Physics is defined above as the study of those changes in matter which do 

 not involve an alteration of the composition or constitution of the matter. 

 The phenomena of light, heat, electricity, magnetism, sound, motion, attrac- 

 tion, etc., fall within its province. A few examples of physical changes may 

 help to make the subject clearer. A piece of iron heated sufficiently becomes 

 luminous, radiates heat, and increases in size. All these are physical changes, 

 because if the iron be cooled it will be found to be the same in character as 

 before it was heated. There has been no change in the substance iron. A 

 body in rapid motion is quite different from the same body at rest, as is evident 

 if the body hit an individual, yet the nature or composition of the body is not 

 altered. A wire through which an electric current is passing is different from 

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