ever, is less precise than the potentiometric end point (±0.05 ml. vs. ±0.01 ml.).There is one class of aminoethylthiosulfates which cannot be acid-titrated in ethylene glycol. The N-acetyl and N-formyl derivatives of aminoethylthiosulfates were neutral salts in ethylene glycol, and hence could not be assayed by titration.These titrations are now performed on a routine basis in this laboratory to assay research quantities of these compounds. Amperometric TitrationSir: In an earlier paper (2) a method was