THE ASH OF PLANTS. 143 



Combined with water, as manganite. It is a substance having a red or 

 black-brown color. It dissolves in cold acids, forming salts of an in- 

 tensely red color. These are, however, easily decomposed by heat, or 

 by organic bodies, into oxygen and manganous salts. 



RED OXIDE OF MANGANESE, Mn s O 4 , or MnO . Mn a O 8 . This oxide re- 

 mains when manganese or any of its other oxides are subjected to & 

 high temperature with access of air. The metal and the protoxide 

 gain oxygen by this treatment, the higher oxides lose oxygen until 

 this compound oxide is formed, which, as its symbol shows, corres- 

 ponds to the magnetic oxide of iron. It is found in the ashes of plants. 



BLACK OXIDE OF MANGANESE, MnO a . This body is found extensively 

 in nature. It is employed in the preparation of oxygen and chlorine 

 (bleaching powder), and is an article of commerce. 



Some other metals occur as oxides or salts in ashes, though not in 

 such quantity or in such plants as to possess any agricultural signifi- 

 cance in this respect. 



ALUMINA, Al a O 3 , the oxide of the metal Aluminium, is found in 

 considerable quantity (20 to 50 per cent) in the ashes of the ground pine 

 (Lycopodlum). It is united with an organic acid (tartaric, according to 

 Berzelius ; malic, according to Ritthausen) in the plant itself. It is 

 often found in small quantity in the ashes 6'f agricultural plants, but 

 whether an ingredient, of the plant or due to particles of adhering clay 

 is not in all cases clear. 



ZINO has been found in a variety of yellow violet that grows about 

 the zinc mines of Aix-la-Chapelle. 



COPPER is frequently present in minute quantity in the ash of plants, 

 especially of such as grow in the vicinity of manufacturing establish- 

 ments, where dilute solutions containing copper are thrown to waste. 



The Salts or Compounds of Metals with Non- 

 metals found in the ashes of plants or in the unburned 

 plant remain to be considered. 



Of the elements, acids and oxides, that have been 

 noticed as constituting the ash of plants, it must be re- 

 marked that with the exception of silica, magnesia, oxide 

 of iron, ajid oxide of manganese, they all exist in the 

 ash in the form of salts (compounds of acids and bases). 

 In the living agricultural plant it is probable that, of 

 them all, only silica occurs in the uncombined state. 



We shall notice in the first place the salts which may 

 occur in the ash of plants, and shall consider them under 

 the following heads, viz. : Carbonates, Sulphates, Phos- 

 phates, and Chlorides. As to the Silicates, it is unnec- 

 essary to add anything here to what has been already 

 mentioned. 



