sulphion

from The Century Dictionary.

• noun A hypothetical body consisting of one equivalent of sulphur and four of oxygen: so called in referenee to the binary theory of salts.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A hypothetical radical, SO4, regarded as forming the acid or negative constituent of sulphuric acid and the sulphates in electrolytic decomposition; -- so called in accordance with the binary theory of salts.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry A hypothetical radical, SO4, regarded as forming the acid or negative constituent of sulphuric acid and the sulphates in electrolytic decomposition.