Are you looking for an item named Neutral Essence?
Or, do you mean Essentia the power system?
Problems with essentia might be the following:
Are you using an Obelisk?
Did you use a Crystal Wrench to connect it to anything?
Does it have Liquid Essence in it?
Let me know if these solve the issue.
EDIT: This isn't thaumcraft, pom. Essentia isn't a thing.
IT DIDNT WORK!!!! ;-;
In what way did it not work. Is it generating essence? Is it not sending it to the altar?