STATE GEOLOGIST. 17a 
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type, called a “cracker,” which consists essentially of a ribbed, steel-faced 
or chilled iron cone, revolving within a conical space, the cone being 
rotated by means of a vertical shaft. ‘rom this machine the crushed ma- 
terial is conveyed to screens,which separate the cement which is fine enough 
to be packed. The coarser particles go on to the fine grinding machines, 
which in most plants are ordinary mill-stones or emery-faced stones. 
As a rule the cement is packed at once on coming from the mills. 
INVESTIGATIONS ON THE BURNING PROCESS. 
We know from the examination of the cement-rock analyses that we 
must distinguish between calcareous and magnesian rocks, that is, stones 
high in lime and low in magnesia and those containing more than 5 per 
cent. of magnesia. The typical Roman cement formula we have found 
WO [DO2 LGORO, CAVALLO, SiO. 
Mineralogically, we are here dealing with an intimate mixture of 
carbonates with clay, and mineral detritus of various origin, quartz, 
hornblende, augite and mica. In burning, the first stage must neces- 
sarily be the expulsion of the carbon dioxide; with the production of 
calcium oxide, the reaction between it and the accessory silicates and 
silica will begin. It is but natural to suppose that the clay should be at- 
attacked first by the calcium oxide, followed by the silicates, and finally 
by the free silica. 
Work of Nauss. —R. W. Nauss investigated this question of the 
action of calcium oxide on clay and quartz to some extent in his thesis 
for graduation at the Ohio State University, by making up a mixture 
of whiting, pure kaolin and quartz (between 120 and 150 mesh) of the 
following composition in the unburnt condition: 
Per Cents. 
Cal erumyearHomalersrrcveew rosea sie eke ee CNet ane hs are ts ERY NOB22 
Hany lira ese p en ey oat et GR ea eT at ruse aac lam base ides NO 
(ONUUEW READ aie, Ae rey ach el at, ea oa ulin test aisha Re che iene a ME 18.66 
99.93 
which would correspond in the burnt condition to: 
Per Cents. 
@alciumakox Gd Cae, latate ae ema es ey ctlee es, Doel Geil 58.45 
ANNU TOW NOE 053 5 Ol BSS Regrets CRN ULE ta ai ae cere GBS) 
SU GCa mre a Smee en AE Ne eho vr aer hw Bat ween. 35.30 
100.10 
This mixture was made up into briquettes, which were weighed 
when dry, heated in a kiln to different temperatures, and drawn at inter- 
vals above 500° C. ‘The briquettes were then cooled in a dessicator and 
again weighed. In addition, determinations of the insoluble silica were 
made by treatment with hydrochloric acid and sodium carbonate solution . 
