THE INTERPEETATION OF CEMENT ANALYSES. 



273 



of carbon di-oxide taken up by the free lime was found to be 4*4 

 per cent. The theoretical quantity of lime that will unite with 

 4*4% carbon di-oxide is 5*6%, which nearly coincides with the 

 remainder 6'1%, the difference being only half a per cent, and 

 within the personal error of the experimenter. 



The 5*6% of lime will, I have said, form hydrate, and in making 

 concrete will unite at the surfaces of clean sharp sand to form 

 calcium metasilicate CaHo 2 + Si0 2 = CaSi0 2 + OH 2 ,* thus the 

 free lime within due limits in a properly constituted cement must 

 act as a cementing agent and prove a good feature in a sound 

 cement, the danger lies in the presence of free lime and free 

 magnesia together, exerting differing degrees of hydration and 

 causing the cement or concrete to bulge, swell, and crack. Com- 

 pared with the ideal type analysis, this good sample furnished by 

 Mr. Roberts stands as follows : — 





(Orthosilicates . 



.. 62-16 





Essentials - 



Alumina... 

 Ferrite ... 



.. 20-12 

 .. 3-25 







.Hydrate... 



. 7-40 



= 92-93 



L-Essentials 





7-07f 





100-00 



It is interesting to compare these results with those obtained 

 from a cement that had failed to pass the usual tests. The 

 chemical analysis of this cement was as follows : — 

 CaO 58-96 



Si0 2 



23-72 



A1 2 3 



9-17 



Fe 2 3 



1-98 



MgO 



-40 



K 2 ) 



Na 2 0/ - 



2-41 



* The water of course gradually disappearing as the age of the concrete^ 

 increases. 



f Objectionable compounds - 1-99. 

 R— Sept. 5, 1894. 



