THE ASH OF PLANTS. 129 



salts of manganese. Its hydrate, prepared by decompos- 

 ing protosulphate of manganese by lime-water, is a white 

 substance, which, on exposure to the air, shortly becomes 

 brown and iinally black from absorption of oxygen. The 

 salts of protoxide of manganese are mostly pale rose-red 

 in color. 



Sesquioxide of IVlang'anose, Mnj O3, occurs native as the 

 mineral braunile, or, combined with water, as manganite. It is a sub- 

 stance having a red or black-brown color. It dissolves in cold acids, 

 forming salts of an intensely red color. These are, however, easily de- 

 composed by heat, or by organic bodies, into oxygen and ijrotosalts. 



Red. Oxide of Manganese, Muj Oj, or Mn O, Muj O3. — This 

 oxide remains when manganese or any of its other oxides are subjected 

 to a 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, corresponds to 

 the magnetic oxide of iron. It is found lu the ashes of plants. 



Blade Oxide of Manganese, Mn O2. — 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 significance 

 in this respect. 



Alumina, the sesquioxide of the metal Aluminum, is found in con- 

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

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

 Berzelius ; malic, according to Eitthausen) in the plant itself It is often 

 found in small quantity in the ashes of agricultural plants, but whether 

 an ingi'edient of the plant or due to particles of adhering clay is not iu 

 all eases clear. 



Zinc has been found in a variety of yellow violet that grows in the 

 zinc mines of Aix la Chapelle. 



Copper is frequently present in minute quantity in the ash of trees, 

 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 



fonnd in the ashes of plants or in the nnburned plant re- 

 main to be considered. 



Of the elements, acids, and oxides, that have been no- 

 ticed as constituting the ash of plants, it must be remark- 

 ed that with the exception of silica, magnesia, oxide of 

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