834 =F. W. Hilgard—Silt analysis of Soils and Clays. 
The pure clay, when dry, adheres to the tongue so tenaciously 
as to render its separation painful. hen moistened an 
worked into the plastic condition, it is exceedingly tenacious 
and “sticky,” adhering to everything it touches. 
Under a magnifying power of 850 diameters, no definite 
particles can be discovered in the vpalescent clay water remain- 
ing after several weeks’ subsidence. The precipitate formed 
by saline solutions then appears as an indefinite cloud (mostly 
of a yellowish tint), for which one vainly seeks a better focus. 
In stronger clay water one can discern a great number of in- 
definite, punctiform bodies, very uniformly diffused through- 
out the liquid, and apparently opaque; the precipitate then 
formed by brine also shows a faintly dotted structure of its 
clouds. 
Doubtless the fine silt obtained in the 24 hours’ subsidence, 
the diameter of whose quartz particles varies from 0-001 to 0°02 
of a millimeter, is not entirely free from adherent clay, as 18 
indicated by its deeper tint, compared with that of the coarser 
sediments. The extent to which this contamination exists, the 
possible means of further separation, and the distribution 
of the important soil ingredients among the several sediments, 
I reserve for future discussion. 
Separation of the Coarser Sediments.—The mixed sediments 
remaining after the separation of the clay, and silts of less than 
0-25" hydraulic value (< 0-25), by decantation, are transferred 
to the elutriator, after separating by means of a sieve, such as, 
being of more than 0°8™™ diameter, would fail to pass through 
the wire screen, and thus interfere with the operation. he 
water should previously have been let on, so far as to stand 
above the screen; otherwise some sediment may be force 
back into the rubber connecting tube. ; 
e Fine S-diments.—The operation is best begun by running 
up the column rapidly nearly to the cork, allowimg 4 few 
seconds’ subsidence, and then setting the index to the prope? 
velocity of 0-25™" per second at the beginning. At first be 
sediment passes off rapidly and the column remains obviously 
and evenly turbid, from the point where the agitation cause 
by the churner ceases, to the top. But this obvious turbidity 
generally exhausts itself in the course of a few hours, an 
then requires some attention to determine the progress of the 
operation. I have never known the 0:25™™ sediment to becomé 
exhausted in less than 15 hours, and in one case it, has re 
wired 90. The more rigorously the process of prea 
isintegration, above described, has been carried out, bg 
shorter the time required for running off the fine sediments, 
which otherwise tax the operator’s patience severely. ‘ina 
matter of fact, they never do give out entirely ; doub ae 
for the reason that the stirrer contiaues to disinteg 
Serta Pr or ee MOA ae a eS 
Coa he en poe 
