The effects of hydrogen chloride (hcl) concentration and temperature on the solubility and hydration state of the alkali chlorides licl, nacl, and kcl and the alkaline-earth chlorides, mgcl2, and cacl2 were investigated by the Bureau of Mines. Saturated aqueous solutions of the chlorides were sparged with hcl gas at temperatures of 20 deg, 40 deg, and 60 deg c. Increased hcl concentration caused decreased salt solubility because of the common ion effect. Aqueous solubilities for the chlorides of ca, li, mg, k, and na ranged from 42.6, 45.2, 35.2, 25.5, and 26.1 pct, respectively, at 20 deg c to 56.9, 49.4, 37.6, 31.0, and 27.0 pct, respectively, at 60 deg c. In solutions sparged to hcl saturation, solubilities for these chlorides ranged from 22.4, 26.5, 3.0, 1.3, and 0.05 pct, respectively, at 20 deg c to 53.2, 48.8, 28.3, 2.6, and 0.8 pct, respectively, at 60 deg c. The solubilities of licl and cacl2 in hcl solution were high because hcl solubility is low in these solutions. The chloride salts of ca, li, and mg formed hydrates, which depended on temperature and hcl concentration. Monohydrates for licl, tetrahydrates and hexahydrates for mgcl2, and dihydrates, tetrahydrates, and hexahydrates for cacl2 were obtained.