52 INORGANIC CONSTITUENTS. 



§ III.— OF THE INORGANIC MATTERS CONTAINED IN 

 PLANTS— THEIR ORIGIN— OF THE CHEMICAL 

 NATURE OF SAP. 



When a plant is burned, there always remains a residue, which is 

 commonly designated as the ash. Every part of a plant gives a 

 residue of the same essential kind ; but it varies in its quantity 

 and somewhat also in its composition. Equal weights of dry 

 herbaceous plants leave more ashes than woody plants.* In a 

 tree, the trunk gives more ash than the branches, and these give 

 less than the leaves. f The residue left by the combustion is com- 

 monly composed of salts — alkaline chlorides, with bases of potash 

 and soda, earthy and metallic phosphates, caustic or carbonated lime 

 and magnesia, silica, and oxides of iron and of manganese. Seve- 

 ral other substances are also met with there, but in quantities so 

 small that they may be neglected. 



The principles usually met with in the ashes of vegetables are 

 always found in the soil which exercises the greatest influence upon 

 the nature and quantity of the saline and earthy matters which re- 

 main after the combustion of plants. Those which grow in a soil 

 derived from silicious rocks, yield ashes that are richer in silica than 

 those that are produced in a calcareous soil. But, according to M. 

 de Saussure, the quality of the manure has a still more decided in- 

 fluence on the nature of the ash than the geological constitution of 

 the soil ; according to this observer, plants of the same species, 

 which have grown upon a calcareous sand, and upon a granitic sand, 

 contain the same kind of ashes, if they have been manured with the 

 same dung ; and different species, although growing in the same 

 earth, do not contain the saline and earthy constituents of their 

 ashes in the same proportions.! 



 Kirwan, Memoirs of the Royal Irish Academy, voL T. 

 t Pertuis, Annales de Chiraie, l^e s6rie, t. xix. 

 i Saussure, Sechercbes chimiques, p. 283. 



