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III. 



SOME EXPEEIMENTS ON DENUDATION BY SOLUTION IN 

 FEESH AND SALT WATER. By J. JOLY, D.Sc, F.R.S., 

 F.G.S., Professor of Geology and Mineralogy in tlie University 

 of Dublin, 



[Read February 24, 1901.] 



The following experiments are directed to throw light on the much- 

 neglected question of the solvent effects of sea- water on rocks and 

 rock-forming silicates. 



Materials dealt with. — Four substances are dealt with in these 

 preliminary experiments — basalt, hornblende, obsidian, and orthoclase. 

 The basalt is a typical specimen, black, fine-grained, compact, with 

 specks of olivine, from the Giant's Causeway, Ireland. The hornblende 

 is the dark-green aluminous variety, well crystallized, cleavable, from 

 Friedrickshaabe. The obsidian is a typical rhyolite glass from Monte 

 Pelato, Lipari. The orthoclase is highly cleavable, fresh, pale pink in 

 colour. 



Mode of Experiment. — The experiments are all comparative, equal 

 amounts being exposed to solution in distilled water and in sea-water 

 under like conditions. The sea-water used was taken fi'om the rocky 

 coast of Killiney, County Dublin, a part of the coast sufficiently far 

 removed from any stream or river discharge. 



The experiments are of two distinct types. In the one it was 

 sought to secure to the full the effects of aeration upon the rate of 

 solution. 



To this end ten grammes of the mineral, finely powdered, are 

 placed along with 1000 c.cs. of the solvent in a Jena-glass flask of 

 the conical Erlenmeyer shape, the flask having a capacity of 

 1100 c.cs. A continuous stream of air is directed by a Jena-glass 

 tube to the bottom of the flask, the air escaping in bubbles which rise 

 through the liquid, and with the help of occasional shaking preserve 

 the sediment in suspension. The entering air is filtered from dust by 

 passage through cotton wool, and damped by passage through towers 



R.I. A. PROC, VOL. VIII., SEC. A.] C 



