Chalk was added to the solution to precipitate the H_{2}SO_{4} and form a calcium salt of toluene-o-sulphonic acid. From this the sodium salt was made by adding a slight excess of Na_{2}SO_{3} and evaporating to dryness. The salt is very soluble being deliquescent in the air while the corresponding potassium salt is not. From 1538 gr. of para-nitro-toluene, 655 gr. of toluene ortho-sodium sulphonate were obtained. Having thus obtained the toluene ortho-sulphonic acid the next step in the problem was to find a convenient method for converting this into ortho-sulph-benzoic acid. Two ways present themselves for accomplishing this end. (1) direct oxidation of this salt and (2) conversion into benzoic sulphinide from which the acid may be obtained. Both of these methods were tried. Oxidation of toluene-o-sodium sulphonate. ┌─ C_{6}H_{4}─┤CH_{3} │SO_{2}ONa └─ The sodium salt of toluene-o-sulphonic acid is oxidized to ortho-sulphobenzoic acid with considerable difficulty by KMnO_{4} in neutral solution. Thus two experiments showed that the oxidation was not complete after 24 hours boiling with excess of permanganate. If the solution be made alkaline however, the oxidation is completed in a few hours, yet the greatest difficulty still remains in the separation of the free acid from the products of oxidation in the solution. If HCl be added to the solution the acid salt COOH ╱ C_{6}H_{4} ╲ SO_{2}OK is formed and this has nearly the same solubility as the KCl also present. A better method therefore is to add a slight excess of H_{2}SO_{4} and evaporate nearly to dryness. In this way are formed sulphates and the free acid presumably. The mixture is heated with alcohol (95%) which extracts the acid leaving the greater part of the manganese salts. This extract is evaporated and reextracted with alcohol. To this solution BaCO_{3} is added to precipitate the H_{2}SO_{4} and form the Barium salt of the o-sulphobenzoic acid. The solution is filtered from the BaSO_{4} and just enough H_{2}SO_{4} is added to exactly precipitate the barium. The solution should thus contain only the free acid sought, which crystallizes out on evaporating to a small volume. While the method is theoretically possible it presents so many difficulties that it is practically useless. The yield is extremely small; only enough acid being obtained in this way to show that it was possible. Formation of Sulphinide from toluene-o-sodium sulphonate. The second method for obtaining free o-sulphobenzoic acid from toluene-ortho-sulphonic acid is by the conversion of the latter first into benzoic sulphinide and then into the free acid. The sulphinide was made essentially as described by Remsen (Am. Ch. Jour. Vol. I. p. 428) with a few changes in the details as follows.