732 EEPOET — 1900. 



In the final results the analyses of the salt- water solutions are compared with 

 the analyses of unused samples of the sea water. 



The "results in all cases ascribe to the sea water solvent effects greatly 

 exceeding those of fresh water, contrary to what is generally believed to be the 

 case. Although it was found impossible to estimate tbe alkali^-s and magnesia 

 taken up by the sea waters, the total estimated amount of material taken into 

 solution is from 2j to 14 times the mass determined in the fresh-water solutions, 

 the preponderance being specially marked in the lime. Complete analyses of 

 the sea water would, of course, ascribe a still greater preponderance to its 

 activity. Tlie preponderance of activity is most marked in the cases of orthoclase 

 and hornblende. Obsidian proved to be the most insoluble of the substances 

 dealt with. 



The consideration of the application of these experiments to the relative rates 

 of marine and atmospheric denudation is deferred till other experiments are com- 

 pleted, as this question also involves the conservative action of exhausted 

 materials precipitated or left in situ. But the experiments as they stand show 

 that the conclusion often drawn from Daubree'a well-known experiment with 

 orthoclase exposed to tbe solvent action of chloride of sodium solution is erroneous, 

 sea water in presence of the atmosphere being a much more active solvent of 

 rock materials than fresh water. 



5. The Inner Mechanism of Sedimentation. 

 By Prof J. Jolt, D.Sc, F.R.S. 



The precipitating effects of marine salts on suspended particles of clay, &c., 

 are responsible for geological effects of great magnitude. This paper is occupied 

 by an account of experimental work directed to the investigation of the inner 

 mechanism of these actions. 



It is shown that the precipitating effects of salts in solution in general vary with 

 the valency of the electro-positive ion and (within certain limits) according to the 

 same law as obtains in the case of the coagulative power exerted by electrolytes 

 on colloids. At very extreme dilutions a further remarkable activity of triad 

 salts is revealed. 



These actions are ascribed to the electrical effects of the ions which by their 

 free charges neutralise the repulsive 'electric layers 'of the immersed particles, 

 bringing about llocculation, when precipitation follows, the theory being similar 

 to that which has been applied to colloids. 



The extension of the theory to the larger particles involved in sedimentation is 

 considered. It is shown that larger particles, by diminishing the element of 

 chance entering into the encounters of ions with particles, will tend to conceal 

 the valency effects. Conformably with this it is found that the finer sediments 

 require more concentrated solutions than the coarser to produce equal effects. 

 Similarly' it is shown that at high concentrations the effects dependent on the 

 amount of charge carried by the ion (the valency effects) should be concealed. In 

 agreement with this it is observed that concentrations above about 5 gram 

 equivalents per litre produce floccuiative effects equal in degree in monad, diad, 

 and triad salts. 



The floccuiative effects of the constituents of sea water are compared, and it 

 is shown that, owing to its monad valency, the chloride of sodium, although so 

 largely preponderating, produces effects no greater than the separate effects of the 

 magnesium chloride and magnesium sulphate present, and rather inferior effects to 

 the calcium sulphate. 



Applications to geology follow. The compacting of marine sediments and the 

 deposition in bulk of the finer detrital sedimentary rocks are ascribed to the 

 ionjsation in the sea of the salts dissolved by denudation from the rocks. 



