In a recent paper' reference to the use of the reagent 5 :W>enzoquinaldinic acid for the estimation of mercury has been made. This paper provides the procedure for the determination of mercury, the I)H regions of its complete precipitation and the method of its separation from other elements.
From a study of the pyrolysis curves of the mercury complexes with the organic reagents, DUVAL~ recommended the adoption of the methods based on precipitation as dipy~dinomercury bichromate 3, bis-(propylene-diamino)-copper iodomercurateq, bis-(biguanido)-copper iodomercurateh, and thionalide5. Of the methods, the first requires precipitation in a neutral medium and a complicated wash liquid, the second, though applicable only in the neutral or faintly ammoniacal medium, is ineffective in presence of copper, cobalt, zinc, chromium and ammonium salts.
The method based on biguanide requires strictly controlfed conditions and even then for satisfactory results the mercury solution should be free from other ions except those of halogens and be kept overnight.
The dipyridine complex has a very short range of stability and requires complicated wash liquids.
The thionalide method requires conversion of mercuric nitrate to chloride and a three-fold excess of the reagent for complete precipitation. Recently SEKXVEC~ utilized Bismuthiol II for the gravimetric estimation of mercury at a high prr in presence of Complexone III, without which the precipitates showed to have variable composition. This method gives quite satisfactory results in presence of a number of elements.
5:6-Benzoquinaldinic acid, the subject of this paper, effects the complete precipitation of mercury at PH r,g to 6.0 and its separation from ammonium salts, salts of alkalis, alkaline earths, rare earths, magnesium, chromium, iron, aluminium, thorium, titanium, zirconium, uranium (UOs+2), lead, bismuth, sulphate, nitrate, molybdate, vanadate, tungstate, arsenate and phosphate.
The mercury complex is anhydrous at 100% and stable up to r50Β°C and is insoluble in dilute acids and in organic solvents. 1refcvcMccs p, 5r3