F Ol J ° 
WIL 
SOME SEDIMENTATION EXPERIMENTS AND THEORIES. 
IB? Vo POINT, IDISG, IslRsh, INES, 
Honorary Secretary R.D.S., Professor of Geology and Mineralogy, Trinity College, Dublin. 
[ Read, DrcremBrr 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,t 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 c.ms. in length and 1°3 c.ms. diameter; and 
12 c.cs. 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. R. D.S., 
vol. 1x., p. 325. 
+ Comptes Rendus de la vili® session, Deuxiéme fasciende, p. 710. (Note in the press.) 
+ Chemical Soc. Journ., vol. 67, 1895, p. 63. 
§ Proc. Roy. Soc., vol. 66, p. 110. 
|| Phil. Mag., v. 48, 1899, p. 74. 
TRANS, ROY. DUB. SOC., N.S., VOL. VII., PART XVI. 2M 
