In the U.S., Red Devil lye comes in 12-oz containers. If your container is not this size, then scale the recipe up or down accordingly. Leftover lye is a serious disposal problem. What I find I have to do is reserve it, because they normally don't keep the fat after they've cut up their cow. The recipe will work equally well with other animal fats to produce a similar result.
Coconut oil yields a softer, quick-lathering soap.
Olive oil and other vegetable cooking oils yield a very soft soap that never completely hardens. Unfortunately, these oils are sensitive to air and light, and soap made from cooking oils will spoil in a few weeks unless it is refrigerated. Volatile fragrance oils, also called essential oils, are highly concentrated scent ingredients. The amount that you should use depends on how fragrant you want the soap to be. Let this mixture sit for a few weeks, stirring it every day, then heat in a double boiler for 10 minutes, then cool and strain the oil.