2. 2.75 gr. of sulphinide was sealed up in a tube with pure conc. HCl and heated two hours to 150°. On cooling nothing separated; the liquid was evaporated to dryness giving 3.2 gr of acid and ammonium chloride. The reaction taking place here may be represented thus: CO COOH ╱ ╲ ╱ C_{6}H_{4} NH + 2H_{2}O + HCl = C_{6}H_{4} + NH_{4}Cl. ╲ ╱ ╲ SO_{2} SO_{2}OH 3. A more convenient method for obtaining the acid than either of the above, is to heat the sulphinide with conc. HCl on the water bath for two days. Then evaporate to dryness and dissolve the residue in a small quantity of water. If the sulphinide contained any para-sulphamide, as is usually the case, this will be left undissolved and most of the NH_{4}Cl will crystallize on standing. This solution by slow evaporation deposits large colorless crystals of the free acid. This acid is soluble in about two parts of cold water, very difficultly soluble in absolute alcohol and almost completely insoluble in ether. It does not melt under 250° but considerably above that it melts, at first apparently without change and then with slight sublimation of a very deliquescent substance, probably the anhydride. Two determinations of the S. made by Mr. A. F. Linn, gave the following results. I ·1358 gr substance gave ·1855 gr BaSO_{4} representing 15·72% S. II ” ” ” ” ” ” COOH ╱ Calculated for the formula C_{6}H_{4} = 15·84% S. ╲ SO_{2}OH [Illustration] A crystallographic examination of the acid showed it to belong to the orthorhombic system. Axial ratio: a: b: c = ·8507: 1: ·8121. Planes. Ρ and αΡὰ. ┌─ ┌─ │ Edge X = 131° 8' │ Ρ ^ Ρ ─┤ ” Y = 82° 18' │ │ ” Z = 118° 40' Angles measured ─┤ └─ │ │ Ρ ^ αΡὰ = 114° 38' └─ The crystals are up to 8 mm in length. The pyramidal faces are generally etched so that the image is poor. Sulphonfluoresceïn.