5:6-Benzoquinaldinic acid as a colorimetric reagent

5:6-Benzoquinaldinic acid, like α-picolinic acid, has been utilised as a colorimetric reagent for iron (ous). Transmittancy measurements with the Lumetron 402 EF having a cell of capacity 16 ml and thickness 20 mm show that iron from 0.4 to 20 p.p.m. may be estimated, while that with Klett-Summerson photoelectric colorimeter, iron from 5 to 50 p.p.m. may be determined in a tube cell of capacity 15 ml and diam. 12 mm. The optimum range with the minimum error is from 2.4 to 14 p.p.m. The effect of diverse ions, reagent, reducing agent, cyanide and other physical conditions as temperature, time, etc. on the colour system has been investigated.