ACIDS OF THE ATMOSPHERE. OO 



tity has not been determined, but we know from experiment 

 that it must be considerable. A succession of electric shocks, 

 through common air or ammonia, is attended with the forma- 

 tion of nitric acid ; Liebig found this aci*d in the rain, which 

 fell during seventeen thunder storms, generally combined with 

 lime and ammonia. 



Nitric acid, as we have seen, p. 48, is composed of fourteen 

 parts of nitrogen, and forty parts of oxygen. It is, therefore, 

 capable of yielding to plants one or both of these organic con- 

 stituents. Whether it can be absorbed by the leaves, and de- 

 composed like ammonia and carbonic acid, is not yet fully set- 

 tled ; the fact that it readily dissolves in water, renders it proba- 

 ble, that its influence is confined, mostly, to the liquid state ; 

 and that, although there must be a small quantity thrown up- 

 on the leaves of plants in dew and rain, and consequently ab- 

 sorbed, yet it mostly enters the roots of plants, in the form of 

 some of its salts, and is decomposed either in the stem, or in 

 the leaves by the agency of light. (See chapter 3.) 



V. Light carbureted Hydrogen is found also in the atmos- 

 phere in very small quantities. It is given off in the fermen- 

 tation of compost heaps, and of other vegetable matter. It is 

 found in marshes, and rises up from the bottom of ponds ; coal 

 mines also furnish it. It is a colorless, tasteless and inodorous 

 gas, highly inflammable and explosive when mixed with air or 

 oxygen gas, and is fatal to life. This gas is sparingly soluble 

 in water, and must enter the organs of plants. It is composed 

 of one equivalent of carbon and two of hydrogen, and may be 

 represented by CH^. Its agency in vegetation is not well 

 knowTi. It may yield carbon or hydrogen or both to plants. 



VI. Injiuenceof the Carbonic Acid of the Atmosphere. Car-, 

 bonic acid is a constant ingredient of the atmosphere, but in 

 very variable proportions ; generally, less than one tenth per 

 cent, or one thousandth part by weight, and, as the acid is 

 more than twice as heavy as air, a very much less quantity by 

 volume. According to Saussure only 0,000415 of the vol- 



