ATOMIC WEIGHTS 433 



NICKEL AND COBALT. 



On account of the close similarity of these metals to each other, their 

 atomic weights, approximately if not actually identical, have received 

 of late years much attention. 



The first determinations, and the only ones up to 1853, were made by 

 Eothhoff,^ each with but a single experiment. For nickel 188 parts of 

 the monoxide were dissolved in hydrochloric acid ; the solution was 

 evaporated to dryness, the residue was dissolved in water, and precipi- 

 tated by silver nitrate. 718.2 parts of silver chloride were thus formed; 

 whence Ni = 59.05. The same process was applied also to cobalt, 269.2 

 parts of the oxide being fovmd equivalent to 1029.9 of AgCl; hence Co=: 

 58.93. These values are so nearly equal that their diiHerences were 

 naturally ascribed to experimental errors. They are, however, entitled 

 to no special weight at present, since it cannot be certain from any evi- 

 dence recorded that the oxide of either metal was absolutely free from 

 traces of the other. 



In 1852 Erdmann and Marchand '^ published some figures, but without 

 details, concerning the atomic weight of nickel. They reduced the oxide 

 by heating in a current of hydrogen, and obtained values ranging from 

 58.2 to 58.6, when = 16. 



In 1856, incidentally to other work, Deville ' found that 100 parts of 

 pure metallic nickel yielded 262 of sulphate; whence Ni = 59.26. 



To none of the foregoing estimations can any importance now be at- 

 tached. The modern discussion of the atomic weights under considera- 

 tion began with the researches of Schneider' in 1857. This chemist 

 examined the oxalates of both metals, determining carbon by the com- 

 bustion of the salts with copper oxide in a stream of dry air. The carbon 

 dioxide thus formed was collected as usual in a potash bulb, which, in 

 weighing, was counterpoised by a similar bulb, so as to eliminate errors 

 due to the hygroscopic character of the glass. The metal in each oxalate 

 was estimated, first by ignition in a stream of dry air, followed by intense 

 heating in hydrogen. Pure nickel or cobalt was left behind in good con- 

 dition for weighing. Four analyses of each oxalate were made, with the 



1 Cited by Berzelius. Poggend. Annalen, S, 1S4. 1S2G. 

 = Journ. prakt. Chem., 55, 202. 1852. 

 3 Ann. Chim. Phys. (3), 46, 182. 1856. 

 *Poggend. Annalen, 101, 387. 1857. 



