Allow me to quote one of my previous posts on the subject:
West-en wrote:A little tip from me if you can't find Sodium Carbonate (Na2CO3, Washing soda):
1. Buy Sodium Bicarbonate (NaHCO3, Baking soda).
2. Put it in a wide heatresistant container, and place it in oven at 250°C/500°F.
3. Stir occasionally and observe carbon dioxide escape as the bicarbonate decompose into the hydrogenfree carbonate of sodium instead.
(2 NaHCO3 + Heat → Na2CO3 + CO2 + H2O)
4. When the carbon dioxide stops flowing, wait a little further.
5. Take it out, let it cool and you're done. You now have sodium carbonate!
It works just fine, and if you're patient enough you will get almost a complete conversion. Happy heating!
There's a clear difference between what I say I do and what I actually do perform.