In these experiments, except with the excessive quantities of acetate of soda and the insufficiency of potassium iodide in the cases of d and f, there was no difficulty with the after-blueing.
METHOD OF SEPARATING COBALT AND NICKEL.
The following method of separating and estimating cobalt and nickel has been described by Mr. James Hope,[125] with whom it has been in daily use for several years with completely satisfactory results.
The quantity of ore taken should contain about .5 gram of the mixed metals. It is dissolved in hydrochloric acid or aqua regia, and the solution evaporated to dryness. The residue is taken up with dilute hydrochloric acid and hot water. The solution is filtered off from the silica, freed from second group metals by treatment with sulphuretted hydrogen and filtered, and after oxidation with nitric acid is separated from iron and alumina by the basic acetate method (page 233). The precipitate is redissolved in a little hydrochloric acid, and again precipitated by sodium acetate. The two filtrates are mixed and treated with a little acetic acid, and the cobalt and nickel are then precipitated as sulphides by a current of sulphuretted hydrogen. The precipitate is filtered off, washed, dried, and calcined, and the resulting oxides are weighed to get an idea as to the quantity of the two metals present.
The calcined precipitate is dissolved in a small covered beaker in aqua regia with the help of a few drops of bromine to remove any separated sulphur, and the solution evaporated to dryness with a few drops of sulphuric acid. The residue is dissolved in hot water, diluted to about 50 c.c., and heated to boiling. About 2 grams (four times the quantity of mixed metals present) of ammonium phosphate (AmH2PO4) are weighed off, dissolved in the smallest possible quantity of water, and boiled for a minute or two with a few c.c. of dilute sulphuric acid. This is added to the boiling-hot solution of cobalt and nickel, which is then treated cautiously with dilute ammonia until the precipitate partially dissolves. The addition of the ammonia is continued drop by drop with constant stirring, until the cobalt comes down as a pink precipitate of ammonium cobalt phosphate (AmCoPO4). The beaker is placed on the top of a water bath with occasional stirring for five or ten minutes. The blue liquid containing the nickel is decanted through a small filter and the precipitate is dissolved with a few drops of dilute sulphuric acid. The resulting solution is treated with a small excess of ammonium phosphate and the cobalt again precipitated by the cautious addition of ammonia exactly as before. The precipitate containing the whole of the cobalt is filtered off and washed with small quantities of hot water. The filtrate is added to the previous one containing the greater part of the nickel.
The ammonium cobalt phosphate is dried, transferred to a platinum crucible, and ignited over a Bunsen flame for fifteen or twenty minutes. A purple coloured cobalt pyrophosphate (Co2P2O7) is thus formed, and is weighed. It contains 40.3 per cent. of cobalt.
The mixed filtrates containing the nickel are placed in a tall beaker, and dilated if necessary to about 200 c.c. Ten c.c. of strong ammonia are added, and the solution, heated to 70° C., is ready for electrolysis. A battery of two 1-1/2 pint Bunsen cells is used. This is found capable of depositing from .15 to .20 gram of nickel per hour, and from two to three hours is generally sufficient for the electrolysis. The electrode with the deposited nickel is washed with distilled water, afterwards with alcohol as described under copper, and is then dried and weighed.
The following results obtained with this method by Mr. Hope illustrate the accuracy of the method. They were obtained by working on solutions containing known weights of the two metals:
| Taken. | Found. | ||
| Cobalt. | Nickel. | Cobalt. | Nickel. |
| .1236 gram | .1155 gram | .1242 gram | .1155 gram |
| .1236 " | .0577 " | .1232 " | .0575 " |
| .2472 " | .0577 " | .2449 " | .0585 " |
| .3708 " | .0577 " | .3701 " | .0580 " |
| .0618 " | .3465 " | .0619 " | .3454 " |
| .0618 " | .2310 " | .0625 " | .2295 " |
| .0618 " | .1155 " | .0621 " | .1155 " |