Kiing—The Suspension of Solids in Fluids. 277 
tilled water in which, with continuous stirring it remained 
during three minutes, when the solution was drained away and 
the content of nitric acid determined. To the same sample of 
sand was added a second 100 cubic centimeter of distilled water 
in which it was washed by continuous stirring during three 
minutes and the solution drained away. This operation was 
repeated 10 times, after which the sand was dried and treated 
directly with disulphonic acid for the recovery of any nitrates 
which might have been retained. The first washing recovered, 
stating the results in round numbers, 3 milligrams, the second 
..3 milligram and the last four, when the rate of removal had 
become constant, carried away with each washing only .01 
milligram. But on drying the sand, after the 10th washing, 
and treating it with disulphonic acid in the same manner that 
the nitric acid would be taken up from the evaporating dish 
itself in an ordinary determination, there was recovered nearly 
.8 of a milligram of nitrates, or nearly 3 times the amount 
which was recovered from the sand in the second washing and 
more than one quarter of that recovered with the first 100 cubic 
centimeters of solution. 
It appears clear that, in this case, each individual sand grain 
must have appropriated to itself a certain amount of the first 
100 cubic centimeters of distilled water added; that this amount 
of water took into solution the nitrates carried by the respec¬ 
tive grains; that the identical molecules of water first appro¬ 
priated by the individual sand grains remained with them 
throughout all of the agitation incident to the stirring asso¬ 
ciated with the 10 washings; that it was only by slow diffusion 
into rather than by a mechanical mixture of the retained water 
with the successive 100 cubic centimeters of distilled water 
added during the 10 washings that nitrate recovered from the 
sand found its way into the water drained away; and, hence, 
that through a mutual specific attraction of the sand grains 
and the water, a portion of the first 100 cubic centimeters was 
differentiated from the mass but a small portion, if any, of 
which was drained away in the succeeding washings, this water 
thus shielding from removal the nitrates retained about the 
sand grains except as influenced by diffusion. 
