STATE GEOLOGIST. Ball 
been answered and we do not know whether the resulting hardness is 
due to the sum of the effects of the crystallization and the colloid harden- 
ing or of one of the two, just as we are in ignorance as to the cause 
of the plasticity of clay, in regard to which, however, the colloid theory 
is offering the most powerful evidence. 
On the other hand it has been shown that when cement is made up 
with water, its electrical conductivity is much greater if a current 
is conducted through it than if the latter were simply passed through 
the solution which was’ in contact with the cement, and in which 
the latter had been thoroughly shaken. At the moment of hardening 
the electric resistance increases enormously. ‘This thus offers some ad- 
ditional evidence in favor of the supersaturation theory. Whatever the 
results of the hydration may be, we know that the crystalline mass of 
the hydrolite breaks down by hydration to simpler compounds and cal- 
cium hydrate. We have hence a certain amount of water of hydration. 
At the same time a slight increase in temperatures 1s observed; that is, 
‘some heat of hydration is evolved. The amount of water of hydration 
found in Portland cement varies greatly and depends on the conditions 
of fineness, the amount of water added, etc. The writer, by heating 
hardened cement pats in a hard glass tube in an atmosphere of air freed 
from carbon dioxide and water, up to red heat, was unable to obtain 
consistent results. On using a little more or less water, making a larger 
or smaller pat, different amounts of water of hydration were found. 
Zulkowski takes 14.67 per cent. of water to be theoretically correct for 
ideal Portland cement. S. B. Newberry found from 10 to 27 per cent. 
of water, Feichtinger 11.56 per cent. Probably Zulkowski is nearest to 
the truth, especially since one of his assistants actually found in a Port- 
land cement 14.44 per cent. of water of hydration. 
In regard to the heat of hydration a number of commercial American 
Portland cements were taken and tested in the calorimeter already de- 
scribed, using from 5 to 10 grams in 100 cc. of distilled water. The 
results obtained were as follows: : 
Number. Calories per gram. Number. Calories per gram. 
1 | 1.79 | 8 BRB 
2 1.19 9 3.43 
3 0.47 10 6.41 
4 2.00 11 1.35 
5 0.50 12 3.98 
6 2.10 13 1.04 
i 2.20 14 1.19 
20 Se1G@ Bulls 3: 
