Orthotolidine1 was first proposed by E. B. Phelps2 in 1909 as a qualitative test for minute amounts of free chlorine or hypochlorites in water. It is a crystalline basic body of the aromatic series obtained by reduction from orthonitrotoluene. It has a melting point of 129-130 centigrade and is quite insoluble in distilled water. It is quite soluble in acid solutions and in alcohol and ether. Ruttan and Hardisty3 in 1912 described the use of orthotolidine as a test for the detection of blood. They used a 4 per cent solution in glacial acetic acid and added a small amount of perhydrol (Merck) as an oxidizing agent to obtain a blue color in the presence of blood. They stated that the solution would detect hemoglobin in a dilution of one part in 7,000,000 parts of water, in a dilution of one part in 24,000 parts of urine,