The close analogy in composition and structure between phthalic acid and ortho-sulpho-benzoic acid suggests the possibility of obtaining from the latter, by its action on phenols, substances analogous to the phthaleÏns. If such compounds could be made they would afford a favorable opportunity of studying the effects produced in the properties of a compound by the replacement of CO by SO₂. It was with a view to such study that the following discussed work was undertaken at the suggestion of Prof. Remsen and carried on under his constant guidance.

Some experiments previously performed by Remsen and Palmer (A.G.) indicated the possibility of the formation of a fluorescent substance by the action of ortho-sulpho-benzoic acid on resorcin but they did not succeed in obtaining any definite crystallized compound from the reaction.

The chief obstacle to be overcome in the work is the difficulty in obtaining the o-sulpho-benzoic acid and a large proportion of the work here described was applied in that direction.