20 AGRICULTURAL CHEMISTRY. 



31. Iron and manganese are metals proper, as dis- 

 tinguished from the alkaline and earthy metals. 



32. Potassium and sodium are metals of alkalies; cal- 

 cium and magnesium, of alkaline earths ; and alumi- 

 num, of the eai'th^ alumina (clay). 



33. Carbon^ hydrogen^ oxygen^ and nitrogen are called 

 organic elements, because they constitute by far the 

 larger part of all organized substances, whether ani- 

 mal or vegetable. 



TABULAR VIEWS OF ELEMENTS, COMPOUNDS, 

 AND SALTS. 



34. The 15 elements, above described, will now be 

 presented in tabular view, together with some of the 

 more important compounds and salts derived from 

 them. (See Table I.) 



35. It will be noticed that there is a capital letter, 

 or a capital and a small letter, placed after each ele- 

 ment. These are' called symbols. It is little else than 

 a short-hand, and very convenient way of writing the 

 words before them ; as 0, for Oxygen ; CI, for Chlo- 

 rine; S, for Sulphur, &c. With three exceptions, 

 these are the initials of the names. The exceptions 

 are that K, stands for Potassium, Na, for Sodium, and 

 Fe, for Iron. It is important that these symbols 

 should be well fixed in the memory. 



36. It will be seen also that after each symbol there 



