among the earths composed of two elements of aluminum and three of oxygen Al2O3
- any of different types of aluminum oxide occurring obviously as corundum
- One of the earths, comprising two parts of aluminium and three of oxygen, Al2O3.
(n.) Among earths, comprising two components of aluminium and three of air, Al2O3.
English hydraulic limes are of a different class; they contain a good deal of alumina and ferric oxide, and in composition resemble somewhat irregular Portland cement.