STATE GEOLOGIST. MSs (| 
2. The ratios of silica to alumina given on several occasions seem 
to be correct, for the safest cements in the boiling test, though not the 
highest in the tensile test, are those with a silica-alumina ratio of, from 
3:1 to 4:1. Aluminous cements are to be condemned. 
LOA 
CALORIES PER GRAM 
Cuan an CHS mmo OMn coma 4 uN ollr2 REmnSIONNS 210s aula Gulslell 410142 
¥% SILICA =% ALUMINA 
Fig. 28. Curves showing heats of hydration of three cements of varying silica-alumina 
ratios. 
Some of these cements were tested in the calorimeter by Mr. Edward 
Thomas, a former student of the writer. Ten grams oi the 
cements were taken and 100 cc. of distilled water. The results of these 
determinations are plotted in the accompanying curve, and show quite 
clearly that the silicious cements possess lower heats of hydration in spite 
