The reagent, 5 : 6-bcnzocluinaldinic acid, m.1,. 187~ C, is highly solul~le in alcohol and in acetic acid, less soluble in hot water and sparingly so in cold water. Under controlled per conditions, it can be used to precipitate completely almost all the metals, Of them, copper gives a green precipitate; zinc, magnesium, calcium, strontium, barium, silver, mercury, lead and cadmium, white precipitates; cobalt, cream coloured; nickel, grecnisb ancl mangttnesc, yellow.
The copper complex which is sparingly soluble in dilute mineral acids or acetic acid, is soluble in a. large excess of ammonia and in solutions of alkali cyanide, All other complexes arc more or less soluble in dilute acids. Such solubility in dilute a.cids is also shown by the complexes of iron(III), aluminium, antimony(III), bismuth, uranium ( U0,"2)f zirconium, thorium, beryllium, rare earths and tin(1 I), which arc not precipitated from ammoniacal tartrate solutions. The chromic complex though soluble in ammoniacal tartrate medium is sparingly soluble even in fairly strong acicls. Zinc, manganese, nickel, cobalt, silver, mercury and cadmium complexes arc soluble in solutions of alkali cyanide and those due to lead and mercury also dissolve in an excess of ammonium acetate. The zinc complex is soluble also in an excess of ammonia, as is cadmium, and in alkali. Cobalt, nickel and manganese, on the other hand, are insoluble in ammonia. In moderately strong caustic soda solution both the nickel and tnanganese complexes are decomposed to their hydroxides, but tltzit of cobalt, dissolves on heating and reappears on cooling. The lithium and thullous complexes arc soluble in dilute acids and in hot water as arc the complexes of beryllium, barium, calcium and strontium. Vanadatc, molybdate and tungstatc arc not precipitated by the reagent from an alkaline solution, but in the presence OF acid they give yellowish white precipitates which are sparingly soluble in excess of &lute acids. All the metal complexes, except that of beryllium, have been found to be insoluble in organic solvents such as ethyl and amyl alcohols, ether, chloroform, ethyl acetate, benzene, carbon disulphide and carbon tetrachloride, The beryllium complcs on the other hand is fairly soluble in ethyl acetate and acetone and slightly so in ethyl alcohol and chloroform.
The pri regions for complete precipitation of copper, cadmium, zinc, manganese, nickel and cobalt are respectively at and over 0.82, 3.r2, 2.85, 2.90, 3.00 and 3.24. Even at a p~lr value of about -IO they may be accurately determined. Copper is com-Hcf~rewcss $3. 3x0