VEGETABLE ALKALIS, 165 
Morpaia. Quina. STRYCHNIA. 
Oxygen, 48 16 2 
Carbon, 204 120 180 
Hydrogen, 18 12 16 
Nitrogen, 14 14 14 
284 162 234 
617. Besides these, the common alkalis, potassa and soda, 
_ are found in considerable quantities in vegetables. They are 
generally in combination with the acetic and carbonic acids ; 
_ and in small quantities with the sulphuric and muriatic acids. 
Potassa may be obtained from some plants by burning them, 
washing the ashes, filtering them, and evaporating to dryness. 
It is the most common alkali in vegetables. Soda is found 
in all plants growing in or very near the sea. There are 
only four of the earths found in vegetables—lime, magnesia, 
alumina, and silica (239). They are procured by incinerat- 
ing the plant. The lime is usually in combination with car-_ 
bonic acid ; and small portions of the sulphate and phosphate 
of lime are sometimes present. Lime and silica exist in 
much larger quantity in the vegetable kingdom than magne- 
sia and alumina ; and of these two the former is the more 
abundant. These alkalis and earths form the ashes which 
Temain after the burning of vegetables; and the insoluble 
_ Matter of the ashes consists principally of the earths. The 
only other metallic oxides found in plants are those of iron 
and manganese. They are in very minute quantities. When 
the ashes are brownish-red, they contain iron ; when purple 
or blackish, manganese. Herbs give more ashes than shrubs 
and shrubs more than trees. The leaves of trees afford more 
than the branches, and the branches more than the trunk. — 
