[ 391 ] 



XVI. 



SOME SEDIMENTATION EXPERIMENTS AND THEORIES. 



By J. JOLY, D.Sc, F.R.S., F.G.S., 



Honorary Secretary R.D.S., Professor of Geology and Mineralogy, Trinity College, Dublin. 



[Read, December 18, 1901.] 



In a Note read before this Society* and in a Paper read before the Geological 

 Congress of Paris, 1900 (which has not yet appeared),*]* I described experiments 

 upon very fine and attenuated sediments, such as remain suspended some eighteen 

 hours in distilled water. It appeared from the observations on the effects 

 of various ions in precipitating such suspensions that an approximately similar 

 connexion exists between the ionic valency and the precipitating effectiveness 

 as obtains in the case of colloidal particles, as determined by the experiments and 

 investigations of Messrs. Linder and Picton,J Hardy,§ and Whetham.|| 



There was, furthermore, a remarkable efficiency found to obtain in the case 

 of extremely dilute aluminium salts, not falling into line with previously 

 observed facts. An attempt to connect the experimental results with the double 

 electric layers supposed on other grounds to exist at the boundary of the particles 

 and the liquid is outlined in the same paper. 



The present experiments cover somewhat different ground. 



Five grammes of a fine silt (in the following experiments this was obtained 

 by reducing Welsh roofing-slate to powder), so fine that the largest particles 

 pass freely through meshes 0-0025 m.m. in dimension (edge of the square) 

 are placed in a test tube about 15 cms. in length and 1'3 cms. diameter; and 

 12 CCS. of a solution of a salt are poured in. After shaking so as to distribute the 



* "On the Inner Mechanism of Sedimentation" (Preliminary Note). — Scient. Proc. K. D. S., 

 vol. IX., p. 325. 



t Comptes Rendus de la viii' session, Deuxieme fasciende, p. 710. (Note in the press.) 



I Chemical Soc. Journ., vol. 67, 1895, p. 63. 

 § Proc. Eoy. Soc, vol. 66, p. 110. 



II Phil. Mag., V. 48, 1899, p. 74. 



TEAJTS, EOT. DUB. SOC, N.S., VOL. TU., PART XVI. 2 M 



