C. Bar us — Subsidence of ji/ne Particles in Liquids. 121 



rily less in water than in ether, being compact in the first in- 

 stance and of a microscopically arched or castellated internal 

 structure in the second instance, as I found ; that the effect of 

 a precipitant is particularly marked when the mixture is 

 densely turbid with relatively coarse particles, as I found ; 

 that finally the phenomena of sedimentation must be of a dis- 

 tinct and special kind, and by no means the immediate con- 

 verse of capillary viscous transpiration. The inferences are 

 thus based on equation (1) above, and follow at once when h 

 and p are nearly constant. In the Bulletin, I computed the 

 relative size (radii) of particle of tripoli subsiding in water, 

 alcohol, ether, to be 1, 19 and 24 respectively.* 



It is exceedingly curious to note in case of water, that despite 

 the phenomenally large surface energy of the liquid, subsidence 

 takes place in such a way that for a given mass of suspended 

 sediment, the surfaces of separation are a maximum. On the 

 other hand, in case of subsidence in ether, or in salt solutions, 

 the solid particles behave much like the capillary spherules of 

 a heavy liquid, shaken up in a lighter liquid with which it 

 does not mix. In other words the tendency here is to reduce 

 surfaces of separation to the least possible value, large particles 

 growing in mass and bulk mechanically at the expense of 

 smaller particles. Finally it is clear that the condition of 

 stratified sedimentation is very slow subsidence of a granular 

 precipitate. 



The experimental evidence adduced bears directly on the 

 size of the particles of any precipitate. A given mass of small 

 solid particles presupposed, the observations of the foregoing 

 paragraph make it probable that the potential energy of the 

 system of solid particles and liquid.increases with the radius of 

 the particle. These observations also show that the potential 

 energy of the system of solid particles alone, decreases as the 

 size of the particles increases, a state of things due both to the 

 immediate action between solid particles, and probably also to 

 the surface energy of the liquid in which suspension takes 



* This is the first of the hypotheses which I develop in detail in Bulletin Xo. 36, 

 pp. 34, 35, 37. In a re-calculation since made with more accurate values of h 

 (water 0° to 100°, Slotte in Wied. Ann., xx, p. 262. 1883; ethyl and methyl 

 alcohol, Graham in Phil. Mag, (4), xxiv, p. 238, 1861; ether, Landolt and 

 Boernstein's Tables, p. 153 ; glycerine estimated ^=10 g cm- 1 sec.- 1 ), the radii 

 of the particles in water, ethyl alcohol, methyl alcohol, ether and glycerine are 

 found to be r = 0-000009 cm , 0-00019 cm , 0-00018 cm , 0-00020< !m and 0-00005 cm re- 

 spectively. In case of bole suspended in water at 15° and 100°, the radii were 

 approximately < 0-000010 cm and > 0'000020 cm . § 6 points out, that whereas 

 these dimensions may be called in question when considered absolutely, the rela- 

 tive values of r are probably true. 



The fact that particles so extremely light descend at all is a result showing 

 the almost marvelous delicacy of these experiments. In case of tripoli-water, 

 for instance, the estimated weight of particle is only 1/10 11 milligrams; being in- 

 visible microscopically it must have weighed less than 1/10 10 milligram. 



