150 
the linear inch) is sufficiently fine for chemical reaction. 
ANNUAL REPORT, 
But we must 
not lose sight of the fact that, though reaction by virtue of a higher heat 
or more lime might be made to take place with particles close to 150 mesh 
size, after all the most important role is played by much finer grains 
which cannot be differentiated by mere sieving. 
The real cement pro- 
ducing magma of Portland cement is formed from the-very finest particles 
of the clay which on vitrification draw the coarser grains into combina- 
tion. 
When the potter melts his fritt for a glaze in a crucible, the fine 
and more fusible portions melt first and gradually bring the coarser and 
more refractory material into fusion. 
select clays which contain the greatest amount of fine grained matter. 
The Ohio Geological Survey has undertaken to study this matter 
from the practical standpoint. 
It becomes important, therefore, to 
was first made the subject of an examination. 
carbonate and heated to 1100°C, it showed on treatment with hydrochlo- 
ric acid and sodium carbonate solutions, a residue of 28.83 per cent., 71.17 
per cent. having gone into solution. 
The first thing to do was the carrying out of the sieve analysis, 
but owing to the fact that sieves differ widely in mesh it was thought 
necessary to make measurements of the mesh of the different sieves, which 
are given in the following table: 
Potter’s flint, or finely ground quartzite, 
When mixed with calcium 
‘in inches 
Remarks. . 
No. of Sieve. 40 80 
Space between wires, 
Ries a ET eee 0.0087 | 0.0074 
Se te eet Slightly | Regular 
irregular 
The spaces given are the averages of 50 micrometer readings. 
100 120 150 
0.0060 0.0051 | 0.0038 
Regular | Somewhat | Regular 
irregular 
200 
0.0031 
Regular 
In 
the sieve analysis of the flint the following results were obtained: 
Left on 120 mesh sieve 
Left on 150 mesh sieve 
Left on 200 mesh sieve 
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Per cents. 
1.40 
In considering the results of a sieve analysis it must be remembered 
that the particles passing through the sieve are not necessarily round 
or symmetrical in shape, but may often be needle-like in form, and 
though they pass through the sieves they are apt to be larger in bulk 
than particles retained which approach the more ideal spherical shape. 
The portion of the flint washed through the 200 mesh sieve was trans- 
ferred to a 250 cc. beaker and enough water added to make 200 cc. of 
liquid. 
The water was now stirred and allowed to settle for one minute 
