438 Action of the Atmosj^here upon newly-deepened Soil. 



more than sufficient, Avith the available mineral constituents pre- 

 sent in the soil, to obtain the maximum of produce for each soil. 

 This of course does not exclude the feasibility of attaining a still 

 higher produce, if we increase the proportion of mineral and 

 atmospheric constituents in the soil." {Principles of Ar/ricultural 

 Chemistry, p. 45.) 



Ammonia is produced in many cases where nitrogen at the 

 moment of its liberation from compounds containing it is met by 

 hydrogen. 



Water. — The action of the watery vapour and rains of the 

 atmosphere still remains for consideration. Without the pre- 

 sence of water little chemical action would take place, and the 

 oxidation of minerals would probably not be effected. Perfectly- 

 dry air has little combining power, and has no effect whatever 

 upon iron ; the extreme slowness with which even the moderately 

 dry air of the higher regions of the atmosphere influences bodies 

 exposed to it is evidenced by an experiment of M. Zumbstein, 

 who fixed a polished iron cross on the summit of Monte Rosa, 

 in the Alps, in August, 1820 ; on visiting it again in August, 

 1821, he found it neither rusted nor corroded, but with merely 

 a tarnish the colour of bronze. The temperature of the air was 

 21' F. ; barometer 16 inches 42 lines ; and height above the sea 

 14,086 feet. Neither does pure water deprived of all air, ac- 

 cording to Marshall Hall, act upon iron at any temperature be- 

 low 212° F., and at that but slowly. 



Air and water, therefore, at ordinary temperatures, taken 

 separately, are quite neutral in respect to iron, and to many other 

 bodies, but taken together the case is widely different ; the con- 

 ditions most favourable for the rapid oxidation of iron consisting 

 in its exposure to alternations of w'et and dry, or to air covered 

 with an indefinitely thin film of water constantly renewed. {Mallet, 

 Brit. Association Report for 1840, p. 256.) 



Water, owing partly to its own extensive affinities, and also to 

 its elements, the oxygen and hydrogen of which it is composed, 

 is itself a chemical agent of great power, and in consequence of 

 its great solvent action it is never quite pure in nature : even 

 rain-water before reaching the ground contains, as we have seen, 

 atmospheric air, ammonia, nitric acid, and carbonic acid ; it 

 also frequently contains sea-salt, found more abundantly during 

 or immediately after a gale off the ocean. The air found in 

 water from newly-fallen snow melted is much richer in oxygen 

 than atmospheric air ; according to Gay Lussac and Humboldt it 

 contains 34"8 per cent of oxygen, and the air in rain-water con- 

 tains 32 per cent, of that gas. Air or oxygen dissolved in water 

 is in a condensed state, and hence in a condition highly apt for 

 combination. Rain-water, when newly fallen, frequently con- 



