thiosulfuric

adjective

thio·​sul·​fu·​ric

variants or chiefly British thiosulphuric

-ˌsəl-ˈfyu̇(ə)r-ik 

: of, relating to, or being an unstable acid H₂S₂O₃ derived from sulfuric acid by replacement of one oxygen atom by sulfur and known only in solution or in salts and esters