STATE GEOLOGIST. 151 
and the supernatant liquid was syphoned off carefully. This operation 
was repeated till the washings were clear. The residue in the beaker was 
removed, dried and weighed. Then the washings that had been removed 
were boiled down to 200 cc., stirred as before and allowed to settle for 
three minutes and syphoned off. This was continued until finally after 
three minutes the supernatant liquid was clear. The residue was dried 
and weighed as before. The third washing was collected, stirred, allowed 
to settle for nine minutes, syphoned and washed as before. The same 
operation was repeated for 27 and 81 minutes’ settling. 
The syphon, with rack and pinion for adjusting its level above the - 
bottom of the beaker, and glass stop cock for controlling the rate of flow 
together with the sieves, microscope, etc., used in this method of analysis 
are shown in Fig. 12. 
The sediments in each case were carefully examined under the micro- 
scope and measurements made of the grains. In the table marked A on 
page 153 the measurements of particles found in two samples of flint are 
given. The average dimensions represent 45 measurements. 
Since in cement clays the question of the fineness of the quartz grains 
is the most important question, and since practically everything else offers 
no difficulty to the chemical combination, this table should prove of some 
assistance to the cement chemist in making use of the suspension method 
of mechanical analysis. 
The flint samples pienbioneel: when analyzed mechanically as given 
in the method above, showed the average results given in Table B, 
page 153. 
This mechanical analysis represents probably the greatest fineness 
practiced in commercial dry grinding for the clay industries at the pres- 
ent time. 
The fact remains, however, that the cement chemist has but little 
time at his disposal in the daily rush of his routine work, and the 
mechanical analysis, if made‘at all, must be carried out rapidly. It is 
possible to obtain results sufficiently valuable by making only one sedi- 
mentation, with one minute settling, obtaining the amount of all particles 
finer than this sediment, 0.0021 inch, by difference. : 
Thus the process might be carried out as follows: Weigh out 5 
grams of the sample, make up into a thin slurry,and wash cleanly through 
the 40, 100, 150 and 200 mesh sieves The washings from the last sieve 
are caught in a 250 cc. tall, narrow beaker, stirred, allowed to settle for 
one minute and the supernatant liquid syphoned off. Fresh distilled water 
is now added to the sediment in the beaker, thoroughly stirred, allowed 
to settle for one minute and syphoned off as before. This is repeated till 
the water added to the sediment no longer is turbid. After the last de- 
cantation the residue is transferred to a weighed porcelain or metal dish 
and weighed. The sum of the weight of the residues on the four sieves 
