In Gadgetzan, you talk to Mux Manascrambler who gives you the quest The Ectoplasmic Distiller. He wants to build an "Ectoplasmic Distiller" for his newest project, an "Extra-Dimensional Ghost Revealer". He requests 1 Delicate Arcanite Converter, 4 Greater Eternal Essence, 10 Stonescale Oil, and 40File:Gold.png, as well as 25 Volcanic Ash, which can be found in piles near lava streams in Burning Steppes (map). The volcanic ash piles look just like dirt piles found in Un'Goro Crater (when looking for these ash piles look for the red lava pools on the map). You get 1-4 Volcanic Ash per pile, and it is a Quest Item (soulbound, only lootable if on the quest and not in a raid). Collecting these won't take long, maybe 15 minutes.