12 AGRICULTURAL CHEMISTRY. 



5. There are three forms in which bodies may exist 

 — the gaseous^ the liquid^ and the solid. A body that 

 is elastic, like air, is called a gas ; one that is inelastic^ 

 like water, a liguid ; and one in which the particles dc 

 not readily move among each other, as iron, wood,"^ 

 straw, feathers, a solid, 



6. Some bodies are capable of assuming all these 

 forms at different temperatures, as water, for instance, 

 is gaseous above 212°, liquid from that down to 82°, 

 and solid below that point. 



7. Bodies which will combine with each other when 

 brought into contact, are said to have an affinity for 

 each other ; those which will not, are said to have no 

 such affinity. Chemical affinity is a tendency existing 

 between certain bodies to combine and form com- 

 pounds. It is of three kinds — simple^ single elective^ 

 and dovhle elective — simple^ when two substances com- 

 bine, no other body being present, as oxygen and hy- 

 drogen, to form water ; single elective^ when One sub- 

 stance decomposes another to combine with one of its 

 ingredients, as when vinegar decomposes chalk, com- 

 bining with its lime, and setting its acid free; and 

 double elective^ when two compounds exchange partners 

 with each other. 



8. We must distinguish between a compound and a 

 mixture. When two substances combine of their own 

 accord, as if self- moved, the result is a compound. If 

 they are only put together by mechanical force, it is a 

 rnucture In the first case, the properties of the ingre- 



