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. Ortho-sulpho-benzoic acid: Methods for its preparation. 1. From toluene and H_{2}SO_{4}. A method employed by Remsen and Fahlberg (Am. Ch. Jour. Vol. 1. p __ ) for getting the sulphonic acid group in the ortho position to methyl was; (a) treat toluene with fuming H_{2}SO_{4} forming thus ortho- and para- toluene sulphonic acids, (b) make the calcium salt of the sulphonic acids thus formed and from this the potassium salt. (c) treat this mixture of potassium toluene sulphonates with phosphorous penta-chloride forming the corresponding sulphonchlorides. One of these (para) being a solid and the other (ortho) an oily liquid a nearly complete separation could be effected. The difficulty with this method is however that the larger part of the product is the para and only a comparatively small proportion of the ortho compound is formed. 2. From p-nitro-toluene and H_{2}SO_{4}. A second method employed consists in starting with p-nitro-toluene. This when treated with H_{2}SO_{4} forms toluene p-nitro o-sulphonic acid. If now a method could be obtained for removing the nitro group the desired result would be attained. The attempt was made by Remsen and Palmer (A.G.) to accomplish this by (a) reducing the nitro compound to the amide, (b) making the diazo compound and (c) boiling this with absolute alcohol. According to generally accepted views this should effect the removal of the diazo group and its replacement by hydrogen. Experiments however showed that the replacement was made not by hydrogen but by the ethoxy group -OC_{2}H_{5}. This method was therefore impracticable. A modification of this method was suggested by an observation of Baeyer and Liebermann that if phenyl hydrazine be boiled with a dilute solution of copper sulphate the hydrazine group is replaced by hydrogen and benzene thus formed. Hence it was believed that if the hydrazine compound should be made from diazo compound mentioned above, the corresponding hydrocarbon, i.e. toluene o-sulphonic acid could be obtained. The results of experiments showed that this afforded a practicable method of preparing toluene ortho-sulphonic acid. After experimenting with various modifications of the method the following was found to be the best adapted to the purpose.