$\begin{array}{1 1}\text{Glass has no fixed melting point}\\\text{Ordinary glass is a mixture of sodium and calcium silicates and may be represented as }Na_2SiO_3,CaSiO_3\\\text{Small amounts of Co(II),Cr(III),Fe(III) and Mn(IV) compounds impart respectively blue,green,brown,violet colours to the glass}\\\text{Flint glass has a low refractive index}\end{array} $
