CHEMISTRY. 



GENERAL OBSERVATIONS. 



Chemistry is the science which treats of the laws that relate to 

 chemical attraction. 



Chemical attraction or affinity may be defined to be " the attrac- 

 tion existing between heterogeneous particles." It is distinguished 

 from cohesion, which is " the attraction between homogeneous parti- 

 cles." Like cohesion, chemical attraction can only be exerted at 

 insensible distances. 



Material substances are divided by the chemist into simple or ele- 

 mentary, and compound. The simple bodies are such, as have as 

 yet resisted all efforts to decompose them. Compound bodies are 

 those that may be resolved into two or more elements. The number 

 of simple bodies recognised by chemists has varied very much at 

 different times ; at present it is about sixty. 



As material bodies are more or less constantly influenced by the 

 imponderable agents. Caloric, Light, and Electricity ; and as these 

 agents, no doubt, modify chemical attraction, it will be proper to com- 

 mence with a brief description of their properties and effects. 



