An alternative procedure is described for the colorimetric determination of molybdenum in steel. Molybdenum(VI) is reduced to molybdenum(V) with ascorbic acid and titanium(III) before being caused to react with thiocyanate and extracting it with tetraphenylarsonium chloride into chloroform that contains quinol. The procedure is sensitive (εmax.= 17 400 l mol–1 cm–1 at 470 nm) and precise. A forty-fold excess of tungsten over molybdenum can be tolerated. Results for a series of low-alloy and tungsten tool steels are reported.

Liquid state membrane electrodes based on bis -tetraethylammonium pentathiocyanatooxomolybdate(V) dissolved in nitrobenzene: o-dichlorobenzene (2:3) have been prepared and assessed. Nernstian response (29.5 mV/pMo at 25°C) was obtained in the range 5×10−8 M to 10 M molybdenum. Several other metal ions which form thiocyanate complexes, namely those of iron, vanadium, tungsten, niobium and rhenium, interfere. DETERMINATION OF MOLYBDENUM BY MEANS OF AN ION-SELECTIVE ELECTRODE BASED ON BIS-TETRAETHYLAMMONIUM PENTATHIOCYANATOOXOMOLYBDATE(V) Key Words: molybdenumion-selective electrode

Mordant red 74 in its complexes with beryllium and lead is reduced at a potential 120 mV more negative than that at which the free dye is reduced. Either beryllium or lead can be determined in the presence of nickel, chromium(III) and iron(III) when these latter metals, which also give displaced waves with the dye, are masked with EDTA. Thorium(IV) interferes by forming a precipitate with the dye even in the presence of EDTA, and molybdate interferes by distorting the dye wave.

The basis of a method for the determination of beryllium by using the displaced polarographic wave obtained with Mordant red 74 (C.I. 16315) in the presence of beryllium ions is described. Aluminium ions do not give a displaced wave with this dye, and an amount of aluminium five times that of beryllium can be tolerated. Nickel and iron(III) give displaced waves and interfere with the determination.