Right, Panfusine, but we're talking about literally a pinch.

I thought Proteins tend to precipitate out when acid is added to them as in milk curdling in the presence of vinegar.I Cream of tartar probably works in strengthening the protein in albumin so that they hold up & create a 'scaffolding' to hold up the whipped air,

Also known as tartaric acid. Have you ever pulled the cork from a bottle of wine and seen small crystals attached? That's tartaric acid. It's used as a bittering agent in some biscuits, and in a pinch if you don't have baking powder, you can also make a single-acting baking powder by mixing equal quantities of cream of tartar and baking soda. It's prime use, though is in strengthening egg whites for a meringue or an angel food cake. In acid, it causes the ovalbumen in egg whites to relax and be more easily manipulated by whipping. Happy baking!

Cream of tartar is derived as a byproduct from the winemaking process, wikipedia has a good informative article. Hope this helps!
http://en.wikipedia.org/wiki/Cream_of_tartar