154: THE PRINCIPLES INVOLVED IN EOCK-WEATHERING 



addition, attributed a part of the decomposition to the action 

 of deconxposing organic matter carried into the ground by ants, 

 and also to the acid secretions of the ants themselves. 



The chemical changes involved in the process of decompo- 

 sition received attention from several of the earlier workers, 

 among whom the names of Berthier, Forschammer, .Brongniart, 

 Gustav Bischof, and Ebelmen stand out in greater prominence. 

 More recently the name of Sterry Hunt becomes conspicuous, 

 while the purely geological side of the question has been ably 

 set forth in numerous papers by L. Agassiz, E. Pumpelly, N. S. 

 Shaler, 0. A. Derby, E. Irving, J. C. Branner, and others, to 

 which reference is frequently made in these pages. 



1. ACTION" OF THE ATMOSPHERE 



Atmospheric air consists in its normal state of a mechanical 

 admixture of free nitrogen and oxygen in the proportion of 

 four volumes of the former to one of the latter. In addition are 

 small and comparatively insignificant amounts of various com- 

 bined gases and salts, of which carbonic acid is by far the most 

 abundant, constant, and, from the present standpoint, important. 

 Still smaller quantities of ammoniacal vapors exist, and in vol- 

 canic regions there have been detected appreciable but variable 

 quantities of sulphuric and hydrochloric acids as well. With 

 rare exceptions these last exist in combination as sulphates, chlo- 

 rides, and nitrates and with the exception of the last-named need 

 little consideration. 



(1) Nitrogen, Nitric Acid, and Ammonia. — Nitrogen, by it- 

 self, is believed to be wholly inoperative in promoting rock 

 decomposition. In works on agricultural chemistry, much has, 

 however, been written concerning the presence in the atmosphere 

 of the compounds of nitrogen, nitric acid, and ammonia, and it 

 will be well to devote a little space to a consideration of the 

 facts as known, and their possible application to the subject 

 under consideration. 



The well-known experiments of Cloez, Boussingault, De Luca, 



Kletzinsky, and Way, as well as the more recent ones of G. H. 



Failyer,^ prove conclusively the existence of ammonia and rarely 



of nitric acid in the air, from whence they are brought to the 



surface of the earth in the water of rainfalls, 



^ Ammonia and Nitric Acid in Atmospherie Vy^aters, 2d Ann. Bep. Kansas 

 Experiment Station, 1889, 



