Making culinary foams for cocktails
I suspect that if you are using egg whites, you won't need to add the lecithin. The egg whites are more than capable of creating a protein-based foam on their own. Using CO2 will give you residual carbonation. I would just use the NO2 (unless you want the foam to be somewhat sparkling). Oh, in fact here is a recipe confirming that just the egg whites are sufficient: http://www.smallscreennetwork.com/video/476/raising_the_bar_how_to_make_foam_for_a_cocktail/