On Wednesday, January 14, 2015 at 10:07:57 AM UTC-5, Danny D. wrote:
Stormin Mormon wrote, on Wed, 14 Jan 2015 09:11:28 -0500:

By the time you endure the expense of the ingredients,
you'd have been better tt go buy baking powder at your
grocery.

Baking powder, at the store, is about $6 per pound.

Baking soda, alone, is five cents a pound.

IDK where that price came from. Best pricing I've seen
is Costco, where for a big back it's probably more like
50 centa a pound



Cream of tartar is seven dollars a pound.
Corn starch, if used, is two dollars a pound.

So, it would seem that the entire expense of the baking
powder is in the cream of tartar.

Because of that, one would expect grocery store suppliers
to skimp on that particular ingredient, substituting
something cheaper instead.

Do they?

Given that the ingredinet that the OP listed for making
baking powder apparently isn't cream of tartar, I'd say yes.
I think there is more to it than that though, as the other ingredient
that is the acid part is likely what gives it the double
acting ability, where cream of tartar wouldn't.