174 THE PEINGIPLES INYOLYED IX EOCK-WEATHERING- 



Daubree's experiments, noted on page 176, showed also 

 decomposition to be retarded hy the presence of sodium chloride 

 in solution. 



These results, however, do not at all agree with those obtained 

 in a carefully conducted series of experiments by Prof. Joly, 

 who showed^ that under the same conditions sea-water dissolved 

 from hornblende, orthoelase, obsidian and basalt from two to 

 fourteen times as much material as did the fresh water. 



It has in times past been very generally assumed that certain 

 complex, unstable, and little understood organic compounds, 

 known under such names as humic, ulmic, crenic, and apocrenic 

 acid were present in soils rich in organic matter, and that, fur- 

 ther, such might be of considerable geological significance.^ Re- 

 cent studies by Cameron and Bell,® however, throw a doubt on 

 the very existence of these acids. Even do they exist, their 

 solvent action is shown to be quite insignificant, and it is re- 

 garded as probable that results heretofore attributed to these 

 agencies are in reality due to carbonic acid.^ 



iProc. Royal Irish Academy, Yol. 24, 1902. 



2 See A. A. Julian, The Geological Action of Humus Acids, Proe. Am. 

 Assoc, for the Adv. of Science, 1879, p. 324. 



3 Bull. 30, Bureau of Soils, TJ. S. Bept, of Agr., 1905. 



^Berthelot and Andre (Comptes Eendus Academie de Paris, 114, 1802, 

 pp. 41-32) have shown that the brown substance of humus and analogous 

 compounds undergo direct oxidation under the influence of the air and sun- 

 light, forming carbonic acid. These reactions take place without the inter- 

 vention of microbes, and are accompanied by a change in color of the original 

 humus. The oxidation is rendered more active through the division and 

 mellowing of the humus by cultivation. Through chemical union of the 

 carbonic acid with certain bases, as lime, soda, and potash, there are formed 

 soluble carbonates which may be leached out by meteoric waters. 



The writer was shown not long since, by Professor Charles E. Munro, a 

 very practical illustration of the remarkable corrosive power of organic 

 acids. A highly ornate French clock, with case of black marble, was packed 

 for storage in excelsior which was a trifle damp. The clock remained in 

 storage from the last of May until about the first of October of the same 

 year. When the packing material was removed, the marble was found to 

 be so corroded as to need rehoning and polishing. The roughness could be 

 easily felt by passing the finger over the surface, and long lustreless lines 

 indicating the contact of excelsior fibres traversed the surface in every 

 direction. 



