218 ANNUAL REPORT 
3. At about 1000° C. lime combines with the fine grained free silica, 
leaving, however, much free lime in excess. The mass now is porous, 
and when made up with water takes up the latter eagerly by capillary 
attraction, so that the hydration takes place easily. We now have vir- 
tually a Roman cement, setting rapidly and corresponding to the first 
hydraulic maximum of the natural cement curve. This reaction is essen- 
tially pozzuolanic in character. 
4. Rising beyond 1000° up to 1100° or higher, the fluxing constitu- 
ents begin to act, consolidating the mass, more free silica is taken up by 
the lime, so that we have probably compounds corresponding to the bi- 
calcium silicates. The hydraulicity has been largely destroyed; second 
minimum of Roman cement curve. 
5. As the temperature rises still higher between 1200° and 1450°, 
depending on the amount of fluxing materials present, vitrification takes 
place rapidly within a short temperature interval and an exothermic 
reaction takes place, corresponding to the production of the subsilicate. 
We may represent this process to ourselves by supposing the. fusion of 
an iron—alumina—calcium silicate which dissolves more and more lime 
until the basic silicate crystallizes out on cooling. Like all calcareous 
bodies the magma fuses with great rapidity, accounting thus for the 
short time required for the operation. The amount of heat evolved in 
the reaction has as yet not been calculated accurately, which may be 
readily understood considering the great experimental difficulties. We 
can, readily understand that the clay substance and feldspathic matter 
enter readily into the reaction, but the combination between the quartz 
and lime is not so easily accomplished. 
RESEARCHES MADE BY THE WRITER. 
For the purpose of observing just how the lime combines with the 
quartz, and at what temperatures, mixtures of silica and calcium carbonate 
were ground together intimately, burnt in a dental furnace, fired with 
gasoline gas and the temperature measured by means of the Chatelier 
pyrometer. The resulting products were sealed in perfectly dry bottles 
and the heats of hydration determined by means of the calorimeter. This 
instrument, as shown by the cut (Figure 21), was made at the laboratory 
and served the purpose for which it was intended quite well. The ther- 
mometer, divided into 1-50tn of a degree Centigrade, could be read without 
difficulty accurate to 1-100th by means of a small telescope. The 
thermometer was calibrated and the water equivalent of the instrument 
calculated repeatedly. The stirrer consisted of a thick copper wire with 
a ring at the lower end, a vertical motion being imparted to it by means 
of a string running over a pulley. Though the construction of the 
apparatus is open to several criticisms, it nevertheless, on testing, gave 
close results with standard thermal determinations, showing an accuracy 
beyond that really needed in this work, inasmuch as the influences tending 
to produce irregularities during the burning were far more numerous. 
The corrections made for radiation were carried out. according to the 
