308 REPORT— 1 SOS. 



the reagents employed, the current density, ikc, but they led to no marked 

 improvement. It had been decided to adopt 5 grme. of ammonium 

 sulphate and 1'5 grme. of ammonia to 130 c.c. of liquid as the standard 

 solution, and the influence of otlier substances present was being investi- 

 gated as in the case of nickel, when, quite unexpectedly, a solution of the 

 problem was indicated. The influence of nitrates was being studied, 

 in the expectation that it would be at least as marked as with nickel, 

 probably more so. This was found to be the case, 1 grme. of ammonium 

 nitrate was suflicient to prevent the decolourisation of the solution even 

 when the current was passed for several hours longer than would other- 

 wise have been necessary. The experiment was continued overnight, and 

 in the morning the solution was found to be quite decoloui'ised, and on 

 decantation proved to be free from cobalt. The deposit was bright and 

 lustrous, much superior to any formerly obtained, but not so white as a 

 good nickel one. Most important of all, the percentage result, which in 

 former cases with complete precipitation varied mostly from 1505 to lo'lO, 

 had in this case fallen to 1490. 



Acting on this, experiments were conducted with varying quantities 

 of ammonium nitrate, when it was found that satisfactory results were 

 obtained with only 0'2 grme. of the salt, but that less was not of much 

 benefit. The presence of nitrate of course increases the time necessary for 

 complete deposition, but, if so desired, this can be counteracted by con- 

 ducting the electi'olysis at a higher temperature, say about 60° C. A 

 good deposit can still be secured when that is done, and the duration of 

 the experiment need not exceed about four hours. If time is no object 

 the electrolysis may still be conducted at the ordinary temperature, and 

 even a larger quantity of ammonium nitrate employed. 



Assuming that it is desired to keep the time limit fairly low, the 

 following may be taken as standard conditions for quantities of cobalt, 

 from 0*1 — 0'3 grme., the volume of solution, as usual, being about 130 c.c. 



Reagents added : 5 grme. of ammonium sulphate, 2 grme. of ammonia, 

 and 0'2 grme. of ammonium nitrate. 



Current : 0-5 — 0-8 ampere per 100 sq. cm. of cathode sui-face ; 3 — 3"5 

 volts. 



Temperature : About 60° C. 



Time : 4 liours. 



The deposits obtained under these conditions are generally fairly good, 

 but there is not the same regularity of results that is obtainable with 

 nickel. The metal in this case is much more readily altered by various 

 reagents, and greater care is necessary in the treatment of the deposit. 

 As already stated, it is advisable to remove the liquid and wash the 

 basin, in the first instance, by means of siphons without breaking the 

 circuit. 



As in the case of nickel, an excess of ammonium sulphate is com- 

 paratively unimportant, though in some of the earlier experiments, 

 conducted at ordinary temperature without nitrate, it seemed as if the 

 last traces were more difiicult to remove in presence of much of this 

 salt. 



The amount of ammonia is more important here than in the case of 

 nickel, as already indicated, the latter metal being apparently less liable to 

 attack by ammoniacal solutions than cobalt. The proportion of ammonia 

 should therefore be kept as low as possible, not only because the necessary 

 time is thereby diminished, but also because better and more regular 



