Notice that Si02 is the basis of an acid, while CAO is essentially a base, and the union of the two forms a salt.
"An Introduction to Chemical Science"
R.P. Williams
CAO forms with SiO2 just the flux needed.
"An Introduction to Chemical Science"
R.P. Williams
Five per cent more can be removed by distilling with CAO, which has a strong affinity for water.
"An Introduction to Chemical Science"
R.P. Williams