YS) ANNUAL REPORT 
This table shows quite strikingly the effect of size of grain upon 
the action of lime, and brings out two kinds of facts which have a direct 
bearing upon the cement industry. | 
It confirms the general statement that the coarser the grain, the smaller 
the effect of the lime. Free silica contained in clay, unless very fine, finer 
than that passing through a 150 mesh sieve, is rendered available only af- 
ter thorough grinding, which means a certain extra amount of wear and 
tear of machinery, and a decrease in efficiency corresponding with the 
coarseness of the quartz. 
The second fact is to a certain extent opposite in character to the 
first. It tells us that it is commercially possible to reduce free quartz to 
a fineness in which it 1s available for combination with lime. To be more 
clear, it may be said that of two clays available, one high in alumina 
and low in quartz, and one with a proper alumina content, but rather high 
in free silica, the results in regard to the quality of cement will certainly 
be better when the silicious material 1s MSEC, in spite of the fact that its 
grinding is more difficult. 
The tendency, only too common, is to work softer clays, which 
often bring in more alumina, and result in a tendency to “hot” cements, 
which must be toned down by gypsum. Granted that the presence of 
quartz makes it necessary to grind longer, yet the clay should not alto- 
gether be chosen with regard to its easy reduction, but also in regard to 
the ultimate quality of the cement. 
Similarly to the quartz series, the same process was carried through 
with the corresponding sizes of feldspar grains, which were obtained from 
several fine specimens of orthoclase crystals, that apparently had not been 
kaolinized perceptibly. | 
Sizes: pane 150-120] 120-100} 100-80} 80-60 | 60-40 | 40-20 
Per cent. residue..... BUD 5A Se VOIR OO  O45Z9 8 ORGS: BO oe ieee 
Per cent. taken in so- 
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These results show at once the great difference between quartz and 
feldspar in regard to being acted upon by lime. It becomes evident that 
feldspar is a desirable constituent of cement materials. Light-burning 
clays high in feldspar should therefore receive more attention with refer- 
ence to the manufacture of light-colored cement. 
In addition to these series, commercial potter’s kaolin of a good 
grade was treated by the same process, resulting in a residue of 3.07 per 
cent., 96.93 per cent. being taken into solution. This verifies the work 
of the German investigators, who found that okey substance was easily 
unlocked by lime. 
