Hydrogen, in excess of track yields, and thiol are found in acidic cystamine sulfate solutions exposed, in air, to x-rays. These products are not found in basic solutions. Earlier work had shown that alkaline air-saturated cystamine solutions give sulfonic acid (taurine) in amounts of numerically close to$G_{{\rm OH}}$. Hydrogen peroxide in excess of track yields by amounts equal to 1/2$G_{{\rm H}}$ was also found. Acidic solutions, however, give considerably more sulfonic acid at intermediate disulfide concentrations and no excess peroxide. The present results indicate the extra sulfonic acid, above$G_{{\rm OH}}$, to arise from oxidation by H, in part directly (possibly as${\rm H}_{2}{}^{+}$) and in part via HO2. The latter part decreases steadily at higher disulfide concentrations as H are scavenged by disulfide, giving thiol, rather than by O2. Cystine, in neutral or acidic solution, gives sulfonic acid yields no greater than$G_{{\rm OH}}$ Concomitant hydrogen peroxide yields are near 1/2$G_{{\rm H}}$. Accordingly, no hydrogen (except track yields) and little thiol are found even in acidic air-saturated cystine solutions after irradiation. Cystine, it seems, is not oxidized by H$({\rm H}_{2}{}^{+})$ or HO2 and scavenges H, giving thiol, relatively poorly. At high cystamine concentrations, in basic solution, sulfonic acid yields fall and a new species, possibly sulfenate (R-S-O-), is produced. A novel procedure for determining radiolytic hydrogen is described.

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