STATE GEOLOGIST. Ball 
1S 192, Or um ACAOSIO),((Ca,SiO),)) wate wre ohayexen ein (OI) is 2343 
Ow Tite 
Thus in the case of slag compositions showing an oxygen ratio of 
1:1, the resulting slags will be found to be stony in character, melting 
suddenly and being very liquid, while a blast furnace slag with a ratio 
of 1:2 is of a more vitreous character and softens gradually. 
Roman cements in general correspond to 2CaOSiO, or an O.R. 
of 1:1, while Portland cement approaches closely to 3CaOSiO, with an 
Ow IR, Ot Be. 
We see thus that the character of the many silicates which it 1s 
possible to produce depends on whether the composition is placed at one 
or the other end or the middle of the silicic acid series, giving us clays, 
glasses, slags or cements. 
Although the hydrous silicic acids, given in the table above, lose 
their chemical water at red heat, being converted back into silica (SiO,), 
as shown by the reaction: 
H,si0, +heat=S10,+H,0O. 
the silica under the action of heat will form, according to the amount, 
number and character of bases and the temperature, salts corresponding 
to the many possible silicic acids. This fact is repeatedly stated in order 
to bring out its importance. 
As has been said above, the chemical energy of hydrous silicic acid 
is greater the more water it holds chemically. After the water is ex- 
pelled, the chemical activity of the acid at the ordinary temperature 1s 
practically zero, excepting for extremely active bases like potash 
and soda. It may be said to have become like so much finely ground 
quartz. 
Silica, in the amorphous form, both anhydrous and hydrous, occurs in 
nature, though not with the abundance and universal distribution which 
characterizes the crystalline forms. Illustrations of rocks which are used 
as sources of amorphous silica are chalcedony (which is a mixture of silica 
and silicic acid), opal, infusorial earth, trass, santorin earth, volcanic ash 
and pozzuolane. ‘Though not giving rise to cements proper in the modern 
sense, they furnish an excellent raw material for the manufacture of 
cements and are especially valuable when used as sand in concrete 
exposed to sea water, since they unite readily with any uncombined lime. 
It is in this respect that they have assumed their modern importance in 
connection with pozzuolane cements. 
Combined Silica,_While the elements forming a chemical com- 
pound, whether it be a salt of silicic or some other acid, are not viewed by 
chemists as existing in molecular groups, like SiO, or Al,O,, and in that 
sense it is, therefore, improper to speak of silicates as containing silica, 
still when these substances are used as the raw materials for new combi- 
nations like cements or slags, the latter may be attained with as much cer- 
tainty and ease as if the silica had been supplied in the form of a pure and 
separate substance. In fact, silicates are exceptionally valuable for form- 
