STATE GEOLOGIST. 147 
the Ohio Geological Survey comprises the 20, 40, 60, 80, 100, 120, 150 
and 200 mesh sieves, these being small copper frame affairs conical in 
shape, 314 inches in diameter at the top and 2% inches at the bottom. 
These sieves are readily put together, telescope-like in a vertical arrange- 
ment, so that the coarsest sieve, No. 20, is at the top, the finest at the 
bottom. By making a weighed amount of materials up into a thin slurry 
with water, using, say, 10 grams, the separation is effected by pouring 
the liquid mixture through the top sieve, washing out the beaker and play- 
ing a fine stream of water from a water bottle on the sieve until no more 
can be washed through. It is then placed on a watch glass and dried in 
a laboratory drying oven. When dry and cooled the sieve and its con- 
tents are weighed. The weight of the dry sieve alone has been previously 
determined. The difference between the gross and the net weights of 
the sieve will, of course, give the weight of the residue. Similarly, the 
weights of the residues on the remaining sieves are determined readily 
and quickly. 
If it is desired to make a sieve analysis of a cement, water evidently 
cannot be used, but it is necessary to work with alcohol, redistilled over 
caustic lime. The separation is effected just as in the case of the clay 
mixtures. 
Analysis by Sedimentation.—For the separation of grains passing 
through the 200 mesh sieve we must employ another means of differentia- 
tion. Two principles are commonly used in the classifying of fine par- 
ticles, suspension and elutriation. 
The first is obviously the simplest mode of separation, the practical 
difficulties being in securing perfect separation of the particles, in pre- 
venting flocculation and in avoiding currents. The particles may be pre- 
vented to a large extent from flocculation by boiling and the addition of 
a little ammonia. | 
In regard to the theory governing the fall of small grains while in 
suspension in a liquid, Rittinger has given a formula, the equation of a 
parabola, which expresses the relation between the velocity in meters, V, 
the diameter of the particles, D, and the specific gravity, d, for average 
particles as follows: | 
V 
—=2.44(d-1) 
D 
Wagoner, on the other hand, has found that the parabolic formula 
does not apply, but has derived a formula for fine grains expressing the 
relation between the diameter and rate of fall, viz.: 
D3? 
== Aa Oun il 
aD?--b 
where V is the velocity in mm. per second; D is the diameter of the 
particle in mm. and a, b and c are constants. 
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