172 



Trans. Acad. Sci. of St. Louis. 



minutes. In the case of the monocalcium aluminate the per- 

 centage of water taken up shows a hydration of the alumina 

 as well as of the lime. It is our intention to make a further 

 study of this part of the subject. In determining free lime, 

 therefore, by this method in substances containing calcium 

 aluminates this fact must be borne in mind and the lime in 

 combination with the alumina must be deducted from the total 

 lime found. 



BEHAVIOR OF CEMENTS. 



As in commercial cements the proportion of alumina usually 

 varies from 5 to 9 per cent we have prepared several cements 

 by fusing with the oxy-coal gas blowpipe pure alumina, lime 

 and silica in definite proportions and have then hydrated the 

 resulting cements by our method. The following results were 

 obtained : — 



We see from this that as the proportion of alumina increases 

 the percentage of water taken up increases, but if the per- 

 centage of alumina does not exceed 10 per cent, as is the rule 

 in commercial cements, then the amount of water taken up 

 does not exceed 3 per cent. 



A number of the best known varieties of commercial cements 

 were then examined by our method. In each case the sample 

 was weighed in a platinum crucible, then ignited for a few 

 minutes over the blast lamp and after cooling in the desiccator 

 it was weighed. The cement was then moistened with a few 

 drops of water, the crucible put into the protector and warmed 



