STATE GEOLOGIST. 33 
two to three minutes and assumed an extraordinary hardness after beinz 
in water for three months. We see hence that the alumina-lime com- 
pounds play an important role in the economy of the cementing process. 
They accelerate the reaction and contribute strength. 
Thus the American investigators, 5. B. and W. B. Newberry”, ob- 
tained practically the same result. The mixture 2CaOAl,O,, when made 
to a mortar with water, set very rapidly in a few seconds and became 
extremely hard. 
The experimental work in the investigation of the alumina-lime com- 
pounds has been carried on by many chemists like Winkler, Chatelier, 
Michaelis, Newberry, Rebuffat and others. 
As we have seen, the most readily available source of silica for cement 
making is clay which invariably introduces a certain amount of alumina 
with every part of silica, it being, as we know, an aluminum silicate. 
If we were to take a pure clay, kaolinite, and mix it with enough lime to 
make, say, a bisilicate and a bicalcium aluminate we would obtain on burn- 
ing a hydraulic cement which would harden well, but too rapidly. The 
rapidity of setting of this cement is due to the high content of alumina and 
is a source of danger, as the cement in practical use would show a danger- 
ous tendency of cracking. We see thus plainly that the alumina must be 
kept low so as to keep the cement within safe limits, but it must always 
be present. : 
Zulkowski prepared a cement from Zettlitz kaol:n( Al,O,2510,2H.O) 
corresponding to the formula 2(2CaOSiO,) (2CaOAl,O,). On burning 
this mixture to vitrification a white porcelain-like body was produced 
which, when powdered and mixed with water, set in fifteen minutes. 
After ninety minutes the cement became extremely hard and after a few 
months it was found to be still harder. Zulkowsky did not test this 
cement for constancy of volume. By the addition of quartz he prepared 
other white cements with the same lime-silica ratio (2CaOSiO,), which 
were all excellent cements. 
These examples have thus shown clearly the necessity of having 
alumina present in cements. Just what the exact chemical function of 
alumina is cannot be discussed here at this stage, but the discussion must 
be postponed to a later part of this work. 
The Function of Ferric Oxide.—Chemically, iron is the natural 
substitute of aluminum, which is shown by the fact that it forms different 
hydrates corresponding to the various hydrates of aluminum. ‘The first 
conclusion would hence be that ferric oxide behaves similarly to alumina 
when combined with lme, or with lime and silica. Many investigators 
have searched into this relation with different results and conclusions. 
Zulkowsky again has made experiments in this direction in the most 
careful manner, and as his results check with those of the most noted 
as *The Constitution of Hydraulic Cements, Journal Society Chemical Industry, November 
7 
3—S. G. Bull. 3. 
