Several crystallographically non-equivalent structures of sodium disilicate are known to exist. Successive heat treatments of the sodium disilicate glasses show alpha-, beta-, gamma- and delta-Na2Si2O5 as the devitrification products, depending upon the nature of heat treatment. At higher temperatures and for longer treatment times, only alpha-Na2Si2O5 is observed but for intermediate temperature and time, alpha and beta forms of the polymorphs are produced. For shorter times, all the polymorphs are formed. The results are verified using magic angle spinning nuclear magnetic resonance as well as X-ray diffraction. A way of estimating the unknown Si-O-Si mean bond angle of the polymorphs, with the help of the known values of the angles, is also presented.