For a good quality cement what should be the ratio of  following 
I. Silica to alumina 
II. CaO to the total of oxides of ${\mathrm{SiO}}_2,{\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{Fe}}_2{\mathrm{O}}_3$

For a good quality cement, the ratio of silica $\left({\mathrm{SiO}}_2\right)$to alumina $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$should be between 2.5 and 4 and the ratio of lime (CaO) to the total of the oxides of silicon $\left({\mathrm{SiO}}_2\right)$ aluminium $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$and iron $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$should be as close as possible to 2.