King—The Suspension of Solids in Fluids . 285 
the same as that for water, and making no allowance for com¬ 
pression of air in the retained film, the effective specific gravity 
becomes 1.2336, or about one-fourth greater tihan that of an 
equal volume of air. According to this view the dust particle 
is wrapped in a sphere of air which increases its effective vol¬ 
ume, in this specific case, 9,261-fold; which increaes the sur¬ 
face upon which an upward current may act to maintain sus¬ 
pension 441-fold. The power of suspension which is developed 
by the surrounding film of the suspending fluid is very much 
greater than would result from simply reducing the specific 
gravity of the solid particle to the extent computed without 
at the same time altering its effective diameter. This is so 
because the resistance to falling through the suspending fluid 
and the lifting power of the fluid itself, as the result of as¬ 
cending currents, increases with the square of the diameter of 
the body held in suspension. Suppose a body having a specific 
gravity of 2 to be immersed in water. The water will buoy it 
up with a force of 1 and the residual power of gravity to pro¬ 
duce the displacement of water necessary to permit sinking is* 
1, while the cross-section of the column of water displaced by 
the body in sinking or rising must also be 1. Now suppose a 
second body similar in every way except that it possesses the 
power of fixing about itself a layer of water sufficient to in¬ 
crease its diameter 5-fold is also immersed in the same water.. 
Its ability to displace water, when moving, will be increased 
25-fold while its power of displacement remains as in the- 
other case. Hence, with 25 times the work to be done in dis¬ 
placing water while moving a given distance, there is only the 
same amount of unneutralized effective gravity with which to 
do it. It cannot, therefore, fall as rapidly, and a much less 
strong upward current would be required to sustain it. 
Influence of Filters on the Concentration of Solutions . 
It is a matter of common observation that when a colored 
solution, like some of the fluid inks, is dropped upon filter or 
bl’otting paper, the action of capillarity causes the ink to spread 
radially and in doing so the solvent of the ink travels faster 
20—S. & A. 
