Mix with water, add ammonia drops until precipitation stops, and filter the lump of coke with a handkerchief, squeezing out all of the ammonia water, and drying.
Make sure it is ALL dissolved, not just mixed with water. Also don't squeeze it, it will get too much stuck in the filter especially if it is only a small amount. After the percipitate is filtered once, it can be dumped back into a fresh bowl of distilled water to wash off any remaining ammonia and refiltered to get clean rock.