@Julia M. Usher posted:Just to be clear - so the 10g is the weight of the egg white powder, and the 135g is the weight of the powder plus water??
No, not directly. I only wanted to refer to Pat`s 10 g ...
So I think my answer was wrong because of that !! Sorry!!
At that time I googled for a long time and found a note on some protein powder can (I no longer know the brand) how much fresh protein the content corresponds to. Then I weighed an average egg and came to 30g. From these hints, I calculated and applied this composition for half the amount, which worked well for me.
At that time I came to 9 raw egg whites with 6 tablespoons of meringue powder plus 5 oz of water. That corresponded to (at 30g per egg white) 270g. Since I have given half the amount, the 135g came together, which in this case either means the powder and the water together or the clear egg white, as stated in the calculated recipe.
I googled again today and approached the bill differently. I looked on the Internet to find out how many grams of powder and how many g / ml of water make exactly one egg white. I came across a statement from:
4 g powder + 28 ml water = 1 fresh egg white = 32 ml / g mass
6 tbsp meringue powder (approx. 90 ml) + 150 ml (5 oz) water results in a mass of 240 ml / g. If you divide that by the 32 ml / g that an egg weighs, you get 7.5 clear egg white. Half the amount = 3.75 egg whites
3.75 egg white x 32 ml / g per egg white results in a mass of 120 g this time.
So I think that the quantities of the various protein powders are not the same everywhere? Or, of course that can also be, I have a huge calculation error somewhere?!? 
The new calculation (with half the amount):
- 500 g of powdered sugar
- 120 g of fresh egg whites
- 0.375 teaspoons of tartar
- 1/2 teaspoon butter flavor
- 1 teaspoon lemon flavor
- 1/2 tbsp light corn syrup
Maybe someone who uses meringue powder knows whether the package says how many raw eggs it contains?
I hope it helps and my english is understood ??...