46 BIOLOGY OF PLANTS. 



their pure state are gaseous bodies ; Carbon C — 6.12, Silicon 

 Si — 22.5, Phosphorus P — 15.7, and Sulphur S — 16.1, which are 

 called non-metallic combustibles, (and for which Dr. Dana has 

 proposed the term wrefs) ; Potassium K — 39.15, Sodium Na — 

 23.3, Magnesium Mg — 12.17, Calcium Ca — 20.5, Aluminium 

 A\ — 13.7, Iron Fe — 28, and Manganese Mn — 27.7, which are 

 metals. 



10. Compound Bodies. A compound body is one which is 

 composed, or made up of two or more simple bodies. The 

 number of compound bodies is unknown. They are represen- 

 ted by adding the symbols of the simple substances, which en- 

 ter into their composition; thus, HO represents a compound 

 formed by the union of oxygen and hydrogen (water). The 

 equivalent is the sum of the equivalents of the simple bodies 

 thus combined, HO=l-|-8=9, which is the equivalent for wa- 

 ter. 



11. When oxygen combines with any other substance, the 

 compound is called an alkali, an alkaline earth, an oxide or an 

 acid; thus potassa, soda and lithia are compounds of oxy- 

 gen with metals, and are alkalies. Ahunina, lime and magne- 

 sia are alkaline earths, and oxide of iron and of manganese are 

 oxides. Oxygen combined with nitrogen forms nitric acid ; 

 with sulphur, silicon and carbon, sulphuric, silicic and carbon- 

 ic acids. 



12. When acids unite with the alkalies, alkaline earths or 

 metallic oxides, the class of bodies formed are called salts. 

 When the nuniber of the equivalents of an acid and an al- 

 kali are equal, the salt is called neutral. When the alkali is in 

 excess, the salts are called by some sub-salts, and when the 

 acid is in excess they are sometimes called super-salts. The 

 name of the salt terminates in ate, as phosphates, carbonates, 

 nitrates. When carbon, phosphorus, silicon and sulphur unite 

 with each other or with the metals, they are termed carburets, 

 phosphurets, siliciurets and sulphurets. 



13. An acid and an alkali unite in definite proportions, and 

 mutually neutralize each other. TJuis, 40 parts of sulpliuric 

 acid is neutralized by 48 of potash, or 20 of magnesia, or 28 of 

 lime, or 32 of soda, or 17 of ammonia ; hence these alkalies may 

 be substituted for each other, whatever acid is used ; and the 

 same is true of acids — hence the term equivalent, because they 

 may be substituted for each other, and form neutral salts. 



14. Almost the entire mass of every vegetable may be resol- 

 ved into two or more of four simple bodies, viz., oxygen, hydro- 



