i would like to see MERV implemented. Mercury vapor is very useful. It aids in making florescent light, it helps with a lot of electronics, ect. i have it in my mod but it is kinda glitchy because of spark storms.
Chlorine, for distilling water and reacting with metal into salt It was going to be in my mod, before it failed, but I'll update a working version from an old source with it in! :)