Observations 07i Liebig's " Organic Chemistry.'''' 113 



with common salt (chloride of sodium). Burnt clay containing 

 oxide of alumina, and ferruginous soils containing oxide of iron, 

 owe their fertility, he says, to all minerals containing alumina 

 and iron attracting the ammonia from the atmosphere. Oxide of 

 iron emits ammonia in great abundance, and so does pipeclay 

 when moistened with potash. The ammonia absorbed by the 

 clay or ferruginous oxide is again separated, he says, by every 

 shower of rain, and conveyed in solution to the soil. Powdered 

 burnt charcoal, he says, possesses a similar property, and con- 

 denses ammonia within its pores. It absorbs 90 times its 

 volume of ammonia ; decayed wood, or humus, 72 times its 

 volume. 



The humus and charcoal I should think the best sub- 

 stances to absorb ammonia from the atmosphere. Burning of 

 soil is more often found to do harm than good ; when it does 

 good, it is ascribed to its altering the mechanical structure 

 of the soil, and making a dense impervious cold clay soil more 

 open and warm. Ferruginous soils, so far from being fertile, 

 I have always heard rated as proverbially sterile. I have, in 

 my practice, seen soils of a very deep red colour with oxide 

 of iron, which, though heavily manured, did not yield a tenth 

 part of the crop of potatoes which was got alongside from soil 

 of a yellow brown loamy colour. The manure was exhausted 

 amongst the oxide of iron ; and the potatoes were not above the 

 size of peas. The iron appears to decompose the manures in- 

 troduced into the soil, from its great affinity for acids ; its prot- 

 oxide combines with most salts, and forms new compounds. 

 The sulphate, one of those compounds likely to be formed 

 when animal remains exist in the manure, is poisonous and 

 soluble. Carbonates of ammonia or potash, or humate of lime, 

 may thus be decomposed, the ammonia set free, and the car- 

 bonic acid lost in the form of carbonate of iron. Dr. Thomson 

 says that iron has a great affinity for acids in the state of prot- 

 oxide ; and, when exposed to the air and oxygen after combin- 

 ing, is apt to form peroxides, and lose the acids. Whatever is 

 the reason, the soils abounding in iron are proverbially barren 

 here. 



He concludes this article by stating that carbonic acid, 

 water, and ammonia are the elements necessary for the support 

 of animals and vegetables. The innumerable products of vitality 

 resume after their death the original form from which they 

 sprang ; and their death, the dissolution of one generation, is 

 the source of life to another. The conditions already con- 

 sidered, however, are not the only ones necessary, he says, for 

 the life of vegetables; and he next proceeds to examine the 

 inorganic constituents of plants. 



Other substances than carbonic acid, water, and ammonia, he 

 1841.— III. 3dSer. i 



