To obtain a gravimetric determination of nickel using dimethylglyoxime:
- Weigh and measure a sample so that not over 100 mg. Of nickel present. Add 10 cc’s of nitric acid .5 to .1 grams of potassium chlorate and digest on the steam plate adding more potassium chlorate if necessary to effect solution. Evaporate to dryness.
- Cool slightly and add 5 cc’s of HCl. And again evaporate to dryness, add 10 cc’s HCL. And 100 cc’s of water and heat to boiling, to dissolve all the soluble salts into the solution.
- In case of black residue remain filter; transfer to a platinum crucible, ignite the residue in clay crucible, and fuse two or three grams of sodium carbonate.
- Add the fused mass to the filtrate from the acid treatment. Evaporate to dryness to dehydrate the silica, add 50 cc’s of dilute HC1, and Boil the filter. Was with hot water until total volume is 100 cc’s.
- Pass hydrogen sulphide into the acid treatment or fusion as the case may be. When all the second group minerals have been precipitated filter off the sulphides etc. and wash well. Boil the filtrate to expel the excess H2S and add 5 cc’s or nitric acid to oxidize the iron etc. Boil and filter if a precipitate of sulphur forms. Dilute to 250 cc’s. Add 2 grams tartaric acid and 5 to 10 cc’s ammonium chloride solution. Stir to dissolve the tartaric acid and then add ammonia until slightly alkaline. The solution should remain clear. If much iron is present it will assume a deep red color.
- Heat to boiling, add an excess of dimethylglyoxime solution and the ammonia until the solution has a slight odor of the reagent. Stir, allow to stand on the steam plate for 1 hr. or longer and filter in a weighed crucible. Wash six times with hot water, dry on steam plate for one hour; cool and weigh. Multiply the weight obtained by 0.2032 to obtain the weight of nickel.
Special Reagents:
- Ammonium chloride solution ¾ A 10% solution of the salt in water.
- Dimethylglyoxime solution – Dissolve one gram of the reagent in 100 cc’s of alcohol. Seven parts of the dimethylglyoxime are required to precipitate 1 part of nickel. The bright red precipitate obtained has the composition – C8H14N4O4N