Notes on Hydraulic Lime and Cement.— By Francis H. 

 Mason, F. C. S.. Mebdlurgist, Halifax. 



(Communicated by Dr. Poole, 11th April, I'JOlt ) 

 Setting of Hydraulic Limk axd Cemknt. 



It is generally accepted that the ingredients necessary to 

 form hydraulic lime and cement are lime, silicaj and alumina; 

 while in all probability oxides of iron, and manganese and 

 magnesia may, to a large extent, replace alumina without detri- 

 mental effect to the hydraulic properties of the lime or cement. 



That it is not essential that the silica, oxide of iron and 

 alumina shall be in chemical combination with the lime, is at 

 once evident from the fact that the old Roman cement, described 

 by Pliny, Vitruvius and others, consisted of a mixture of volcanic 

 scoria and fat lime. Volcanic scoria is composed principally of 

 silicates of peroxide of iron and alumina, with small quanti- 

 ties of magnesia, oxide of manganese and the alkalies. It is 

 necessary that the scoria and the lime shall be in a line state 

 of division and in intimate contact with each other. 



The initial setting of cement is undoubtedly due to hydra- 

 tion, while the hardening is, in all probability, due to chemical 

 action. 



Considerable attention has been given to the subject by a 

 number of able chemists, which has resulted in a very great 

 diversity of opinion The results of the researches of Le 

 Chatelier are probabh* the most generally accepted. 



His method of proeeedure, namel}^ that of examining thin 

 plates of cement, at different stages of setting, under the micro- 

 scope by the aid of polarized light, and then building up similar 

 crystals synthetically to match, so to speak, does not carry with 

 it that finality whicli analj'sis of those same crystals would have 



Proc, & Trans N. S. I.vst. Sci., Vol.XI Trvns. m. 



(179) 



