136 HOW CEOPS GROW. 



Chloride of Sodium, Na CI, 58.5 — This substance is 

 common or culinary salt. It was formerly termed muriate 

 of soda. It is scai-cely necessary to speak of its occur- 

 rence in immense quantities in the water of the ocean, in 

 saline springs, and in the solid form as rock-salt, in the 

 earth. Its properties are so familiar as to require no de- 

 scription. It is rarely absent from the ash of plants. 



Besides the salts and compounds just described, there 

 occur in the living plant other substances, most of which 

 have been indeed already alluded to, but may be noticed 

 again connectedly in this place. 



These compounds, being destructible by heat, do not 

 appear in the analysis of the ash of a plant. 



Nitrates : Nitric acid — the compound by which nitro- 

 gen is chiefly furnished to plants for the elaboration of the 

 albuminoid principles — is not unfrequently present as a 

 nitrate in the tissues of the plant. It usually occurs there 

 as Nitrate of Potash, (niter, saltpeter.) 



The properties of this salt scarcely need description. It 

 is a white, crystalline body, readily soluble in water, and 

 has a cooling, saline taste. When heated with carbonaceous 

 matters, it yields oxygen to them, and a deflagration, or 

 rapid and explosive combustion, results. Touch-paper is 

 paper soaked in solution of niter, and dried. The leaves 

 of the sugar-beet, sun-flower, tobacco, and some other 

 plants, have been found to contain this salt. When such 

 vegetables are burned, the nitric acid is decomposed, often 

 with slight deflagration, or glowing like touch-paper, and 

 the alkali remains in the ash as carbonate. The characters 

 of nitric acid and the nitrates will be noticed at length in 

 another volume, " How Crops Feed." 



Oxalates, Citrates, Maiates, Taeteates, and salts of 

 other less common organic acids, are generally to be found 

 in the tissues of living plants. On burning, the bases with 

 which they were in combination — potash and lime in most 

 cases — remain as carbonates. 



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