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

evidence is presented to substantiate the olefin and aromatic calibration data on the basis that wide changes in composition do not cause appreciable differences between results from two different sources.Comparisons of saturate percentages are also made in Table VI. There is a significant discrepancy in the four higher boiling fractions. This may be caused by the influence of dicycloparaffins on the percentage of naphthenes by refractivitv intercept.Table VII shows aromatic and olefin data for a variety of commercial motor fuels. The close agreement indicates that a good approximation of the right compound distribution was achieved.The composition of the commercial fuels was largely unknown but was assumed to be mostly catalytically cracked material. Since ASTM Method D1019 was used to relate total saturated and unsaturated hydrocarbons as percentages of the stabilized original, the precision of the distribution between these two types is dependent on the precision of D1019. Although this is 2% or better (3) the MS does provide compari-son data from the peak height ratios.