When washing soda is heated

when washing soda was strongly heated, it loses all water of crystallization and become anhydrous sodium carbonate. The following reaction takes place: 

${\mathrm{Na}}_2{\mathrm{CO}}_3.2{\mathrm{H}}_2\mathrm{O} \underset{∆}{\overset{-9{\mathrm{H}}_2\mathrm{O}}{\to }} {\mathrm{Na}}_2{\mathrm{CO}}_3.{\mathrm{H}}_2\mathrm{O} \underset{∆}{\overset{-{\mathrm{H}}_2\mathrm{O}}{\to }} {\mathrm{Na}}_2{\mathrm{CO}}_3$

Thus when washing soda is heated it loses water vapour.