NOTES ON HYDRAULIC LIME AND CEMENT.— MASON. 181 



and magnesia. It is well known that highly silicious magnesian 

 limestones almost invariably possess hydraulic properties, and if 

 we examine the analyses of natural cements and hydraulic limes, 

 we shall find that while the percentage of alumina is erratic, 

 with certain notable exceptions the percentage of oxide of iron, 

 alumina and magnesia together are a much more constant 

 quantity. 



Take four analysis by Knauss given in Thorpe's " Dictionary 

 of Applied Chemistry " : — 



Peroxide of iron . 9.2] 12.41 7.1 j 3.0] 



Alumina 7.3 19.2 4.0 20.7 9.8 -18.5 5.6 18.6 



Magnesia 2.7 I 3.7j J. 61 9.2] 



Lime 48.2^ 46.1 49.2^ 47.1 



All these are reported to be good natural cements. 



If, then, these substances only act as conveyors of silica to 

 the lime, the question at once arises, would it not be possible to 

 supply the silica in such a form, without the presence of these 

 substances, that the lime would combine with it readily ? 



Landrin, in his researches, throws some light upon this 

 point. He found that while pure lime intimately mixed with 

 fine sand or powdered quartz possessed no hydraulic properties, 

 it did set when mixed wath precipitated gelatinous or dialized 

 silica and in time attained a strength equal to the best Portlanid 

 cement. He further found that 30 parts of silica would take 

 up 38 parts of lime, corresponding to the formula 4 Ca O 

 3 Si O2 111 this we have a cement without alumina, oxide of iron 

 or magnesia. If then, alumina, oxide of iron and magnesia act 

 only as agents for holding the silica in a form in which it is 

 readily attacked by the hydrate of lime, when that reaction has 

 taken place they become inert and act as diluents and tend to 

 weaken the final product, so that if it is possible to comuiercially 

 prepare a cement free from these substances, pound for pound 

 it should be of better quality than the highest grade Portland 

 cement. 



