STATE GEOLOGIST. MOI 
It is quite evident from the results obtained in this work as well as 
from other considerations that the heat of hydration of the calcium oxide 
present in these silicates cannot be used to approximate the amount 
of uncombined lime. Jn some manner the lime becomes “dead” burnt and 
does not hydrate as we should expect, analogous to the “dead” burnt 
limes in which a few per cent. of silica seem to take away from the 
time its tendency to slake rapidly. ‘The modus operandi of this process 
cannot be followed without further investigation. “The method proposed 
by some to determine the lime content of a limestone by igniting it 
and determining its hydration value hence does not promise to be a 
satisfactory test. In this connection it might be noted that cements with 
a silicious clay base, though very high in lime, show but a low heat of 
hydration. One fact, at least, was brought out quite clearly, namely, 
that silica does lower the temperature of the decomposition of calcium 
carbonate quite decidedly. 
For purposes of comparison it might be well to quote the heats of 
hydration obtained by heating a crystalline limestone, 99.5 per cent. 
calcium carbonate, at different temperatures : 
Temperature. 800° C. | 900° C. | 950° C. | 1000° c.|1050° C.;1100° C. 1200° C. 
Calories per gram...| 34 | 175 | 257 | 260 | 252 | 254 | 247 
In addition, these silicates were made up in water and allowed to 
harden in moist air for forty days, but practically all of them possessed 
but slight cementing qualities. In water most of them showed but a 
superficial hardness. Another experiment was decided upon in endeavy- 
oring to ascertain something in regard to the attack of lime on free silica. 
This was carried out by grinding together finely ground quartz, the 
same which was used in the preceding experiments in the proportion of 
0.25CaOSiO., = 18.9 parts of calcium. oxide, and 81 parts of silica, 
igniting the mixture at different temperatures, and determining the 
residue, insoluble in hydrochloric acid and sodium carbonate solution. It 
was thought that in this way the lime was bound to come in contact with 
all the silica it could combine with at the different temperatures. ‘These 
results are shown in the following tabulation: 
