THE ASH OF PLANTS. 113 
either are acids in the ordinary sense of being sour to the 
taste, or enact the part of acids by uniting to metals or 
metallic oxides, to form salts. We may, therefore, desig: 
nate them as the acid elements. They are Oxygen, Sulphur, 
Phosphorus, Carbon, Silicon, and Chlorine. (Less com: 
mon are Arsenic, Titanium, Iodine, Bromine, and Fluorine.) 
With the exception of Silicon, (and Titanium,) and the 
denser forms of Carbon, these elements by themselves are 
readily volatile. Their compounds with each other, which 
may occur in vegetation, are also volatile, with two ex- 
ceptions, vizi, Silicic and Phosphoric acids. 
In order that they may resist the high temperature at 
which ashes are formed, they must be combined with the 
metallic elements or their oxides as salts. 
Oxygen, Symbol O, atomic weight 16, is an ingredient 
cf the ash, since it unites with nearly all the other elements 
of vegetation, either during the life of the plant, or in the 
act of combustion. It unites with Carbon, Sulphur, Phos- 
phorus, and Silicon, forming acid bodies; while with the 
metals it produces oxides, which have the characters of 
bases. Chlorine alone of the elements of the plant does 
not unite with oxygen, either in the living plant, or during 
its combustion. 
CAREON AND ITS COMPOUNDS. 
Carbon, Sym. C, at. wt. 12, has been noticed already 
with sufficient fulness, (p. 31.) It is often contained as 
charcoal in the ashes of the plant, owing to its being en- 
veloped in a coating of fused saline matters, which shield 
it from the action of oxygen. 
Carbonic acid, Sym. C O,, molecular weight, 44, is the 
colorless gas which causes the sparkling or effervescence 
of beer and soda water, and the frothing of yeast. 
It is formed by the oxidation of carbon, when vegetable 
matter is burned, (Exp. 6.) It is, therefore, found in the 
agh of plants, combined with those bases which in the liv- 
