I had someone comment on that post that they bought the baking soda from the laundry aisle and if it were possible to make it with this. I initially wanted to say since they aren't the same thing (washing soda = sodium carbonate, baking soda = sodium bicarbonate) that it wouldn't work.
(Be careful of price; at my store, the huge box of baking soda in the laundry aisle was actually more per ounce then the medium off-brand box of baking soda in the baking aisle.)
But I looked it up, found these sites:
Baking Soda or Washing Soda
or Baking soda vs. Washing soda
Plus looking around on other threads, I have seen comments on turning baking soda into washing soda by baking it (although the cost of electricity here may not be worth it), and a few who makes the detergent with baking soda and believe it to be fine as follows:
"If you are unable to find washing soda (sodium carbonate), you can make washing soda from baking soda (sodium bicarbonate) by heating baking soda in baking dish in the oven. Heat the baking soda in an ordinary oven at 300°F for 1-2 hours. Overheating is not a problem, either with higher temperatures or baking times. Be sure to NOT use baking powder. Baking powder is a different than baking soda."
"I have used baking soda instead, because sometimes washing soda is hard to find in my area. It seems to work really well."
UPDATE: Had a lady with a Chemist hubby explain that simply baking baking soda would not work, I am not a chemist (the only class I purposely avoided in school!), so here is what she said:
"I was curious about the suggestion to heat baking soda in the oven in order to turn it into washing soda. I checked it out with my husband (a chemist), and he said that won't work... you'd have to add lye to force a reaction in which a hydrogen atom is driven off the sodium bicarbonate. So, heating baking soda in the oven won't change it at all (really, if it did, the baked goods we use it in would end up inedible). Just thought I'd share to save people the electricity!"
UPDATE #2: From the Comments.Hmmm... that chemistry is incorrect. When heated to 70 degrees celsius and above, sodium bicarbonate(baking soda) decomposes to sodium carbonate(washing soda),carbon dioxide and water. By 200 degrees it has been fully decomposed to sodium carbonate. Putting baking soda into a 200 degree celsius oven WILL decompose it to washing soda.
So, baking soda is decomposed by heat and no, baked goods it is used in do not end up inedible because in the recipe an acid ingredient is included for the baking soda to react with. Baking soda reacts with acids to produce a salt, carbon dioxide and water(it also reacts with bases as it is amphoteric). So in baking, it reacts with the acid present to produce a salt, and this reaction produces the carbon dioxide needed to rise the baked good.
Plus, my mom always used Borax with a bit of detergent when I was a kid, perhaps you can just forgo the washing soda since borax and washing soda's purposes are similar or replace it with baking soda?
So, I just put one of my toughest laundry loads in the washer and put in this detergent (I eyeballed these measurements since I wasn't ready to make another batch of soap): 1/4 T grated soap, 1/4 T baking soda, 1/2 T borax. Seems clean to me! If I ever have another kid, I might consider doing this for cloth diaper washing.
You know, I am always put off by or leery of any company or person that says "You must use this, there is no other way or dun dun dun something terrible will happen!!" Sometimes the wisdom of old is wrong (not washing hands with soap in hospitals created high death rates) but sometimes it isn't. How many companies would be bankrupt if they let people know that their items are not the best way to go? They spend millions of advertising dollars to convince you that said product is the only way you want to go; it is needed. They are not going to advertise even in tiny print that instead of using said product you can just mix water, vinegar and soap and use that since that is what their product basically is anyway. They couldn't sell you the $3 bottle it comes in. (And is it just me or have others found that when they've bought cleaning spray bottle products, the silly squirt mechanism died before I ran out of the product?) So if you can't find washing soda, try baking soda out in the mix for awhile (I'd increase the borax amount I think) and see how it goes, it isn't that expensive.
All right, I am stepping off my soap box now. :P