The Disulphate of Quinine (or Quina) is the preparation of the alkaloid which is most commonly used.
The Action of Medicines in the System|Frederick William Headland
Cinchonine may be prepared from its sulphate or disulphate in the same way as quinine.
Cooley's Cyclopdia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades..., Sixth Edition, Volume I|Arnold Cooley