Either concentrated sulfuric acid or oleum absorbs the excess water. The oleum is then diluted with water to form concentrated sulfuric acid. It is produced by the sulfonation of benzene with sulfuric acid and oleum. Sulfuric acid itself is regenerated by dilution of part of the oleum. Hydroxylammonium sulfate is also used to generate hydroxylamine-O-sulfonic acid from oleum or chlorosulfuric acid. The nitric acid cuts carbon nanotubes while the oleum creates a channel. One important use of oleum as a reagent is the secondary nitration of nitrobenzene. Such compounds are prepared by treating CuPc with chlorine, bromine or oleum. Oleum is a harsh reagent, and is highly corrosive. The species name is derived from the Latin words "oleum" "oil" and "ferre" "to bear". The name derives from the Latin word "oleum", which means oil. Oleum is reacted with water to form concentrated HSO. George Fownes named this oil furfurol in 1845 (from "furfur" - bran, and "oleum"). The name is a contraction of "Oleum Basileum", "oil from Basel". Oleum is generally assessed according to the free SO content by mass.