Abstract:
At present the method of determination of nickel in widest use is based on precipitation with dimethylglyoxime. Its advantages art that direct separation obtainable from most metals and, where the method is finished by weighing as nickel dimethylglyoxime, the precipitate contains a low percentage of nickel. A point often not fully appreciated is that the procedure as described by Brunck (1907, 1914) must be followed closely to overcome difficulties arising from the very slight solubility of the reagent in water or dilute alcohol and also from the solubility of the precipitate in too great a concentration of alcohol in the solution. If the nickel present in the solution is of the order 0.1 gm. the voluminous precipitate is difficult to transfer and filter. while other oximes. have been found to give more compact precipitates, the decreased solubility of such reagents in aqueous alcohol prohibits their general adoption, with the exception of the expensive α -furilglyoxime which requires a difficult preparation.
In 1923 G. Spacu and Ripan (1922, 1923) proposed a method of precipitation of nickel using as reagent pyridine in the presence of ammonium thiocyanate. Precipitation is carried out by the addition of pyridine to the solution of nickel containing ammonium or potassium thiocyanate. This promising method makes use of the co-ordination compound [N (C5 H5 N)4] (CNS)2 which precipitates rapidly and is easily filtered. After washing the precipitate with 5% pyridine and drying at 130°C, the method is completed by incinerating and finally subjecting to the blast as in Carnot's method (1889).The nickel is then weighed as nickel oxide.
