Leavening agents...

I used to think Baking soda and Baking Powder were one and the same -
how wrong !

Baking soda is an alkali. When mixed with an acid ( Buttermilk, Yogurt ,
lemon juice/ vinegar), it gives off carbon di oxide. Baking soda will
not work without an acidic ingredient.

Baking powder is a blend of acid and alkali. So it does not depend on
external acid for rising dough.

Double acting baking powder( the most commonly used version) releases
gas on contact with water and again on heating. ( That is why you should
sift baking soda with flour well before adding water). Good baking
powder should bubble as soon as water is added to it. If ti does not,
toss it out. ( Similarly good yeast should start bubbling in 5-10
minutes when added to some water - sugar mixture. Adding salt reduces
the growth of yeast)

As baking powder has an inbuilt acid,avoid adding more acid ( buttermilk
etc). More acid reduces the gas produced.

At high altitudes, gas expands more and so less baking powder is enough.

Whipped egg whites trap air in bubbles, which expand on heating, thus
mimicking the action of other leavening agents. Crushed ice serves the
same purpose.