Combine the flour, sugar, salt, and baking soda in a mixing bowl; mix well.
Using an electric or hand rotary beater, beat the eggs; add milk, melted butter, orange peel and juice, and rum.
Combine egg mixture with dry ingredients and continue beating until smooth.
(Batter should be consistency of heavy cream.
Add more orange juice, if necessary.) Heat and lightly butter the bottom of a 6- or 8-inch skillet.
Pour in about 2 tablespoons of the batter and tilt skillet to spread batter evenly.
Cook over medium heat until small bubbles form in the batter.
Turn over and brown crepe very lightly on second side.
Repeat process using all the batter.
Keep crepes warm by placing them in a pan over simmering water.