As soon as I need to heat up the stove for something else more important (i.e. cookies, bread, roast etc.) I am going to try this baking soda-into-washing soda experiment.
Now, there is another site, http://candleandsoap.about.com/od/tipstricks/ht/How-To-Convert-Baking-Soda-To-Washing-Soda.htm
I usually don't trust ehow or about.com, so this truly is an experiement. Both sites vary in the directions, and how do you really know if you baked the soda long enough? It's not like it will change colors or look different. Hmmm . . . .will let you know.