20 CHEMISTRY. 



that come to us in the rays of the sun, so that every ray is 

 a bundle of three forces united together an illuminating, a 

 calorific, and a chemical. The sun, therefore, with its light 

 diffused every where, is the greatest of all the chemical 

 agents in our earth. 



15. Summary. The chief characteristics by which chem- 

 ical changes are distinguished are briefly summed up in the 

 statement following : 



1st. Heat is evolved during chemical combination. 



2d. A more or less complete change of physical and chemical properties. 



3d. A chemical compound can not be broken up by simple mechanical 

 means. 



4th. No weight is lost in chemical combination. 



5th. Chemical combination takes place only in certain definite propor- 

 tions by weight. 



The significance of the fifth point will appear fully in 

 Chapter III. 



16. Analysis and Synthesis. When a substance is sepa- 

 rated into the parts of which it is composed by means of 

 physical or chemical forces brought to bear upon it, the op- 

 eration is called analysis, or a "loosening again," from two 

 Greek words ana, " again," and luein, " to loosen." Chem- 

 ical analysis forms an important branch of practical chem- 

 istry of immense value in determining the composition of 

 bodies. Synthesis, or a " putting together," also from the 

 Greek, is the opposite of analysis it is the basis of a large 

 portion of chemical manufactures, which, however, pertain 

 to both branches. 



17. Nomenclature. There is no science that has so ap- 

 propriate and accurate a nomenclature as chemistry has at 

 the present time. It is in direct contrast with that loose 

 and unscientific nomenclature which was in vogue before 

 the time of Priestley and Scheele and Lavoisier. The old 

 names were given from some quality of the substance, or 



