In the following reaction (unbalanced), equivalent weight of As2S3 is related to molecular weight M byAs2S3 + H+ + NO3- →  NO + H2O + AsO43- + SO42-

As+32S-23  →  As+5O43- + 3S+6O42-Change in ox. state of ‘As’ = 2(2) = 4Change in Ox. state of  ‘S’ = 3(8) = 24Net change in Oxidation state = 28 Thus, equivalent mass of  As2S3 = M28