294 THE ATOMIC WEIGHTS. 



Dumas'* determinations of the two atomic, weights were made with 

 the chlorides of nickel and cobalt. The pure metals were dissolved in 

 aqua regia, the solutions were repeatedly evaporated to dryness, and the 

 residual chlorides were ignited in dry hydrochloric acid gas. The last 

 two estimations in the nickel series were made upon NiClj formed by 

 heating the spongy metal in pure chlorine. In the third column I give 

 the NiCl^ or CoCl,^ equivalent to 100 parts of silver : 



.9123 grm. NiClj =1.515 grm. Ag. 60.218 



2.295 " 3-8115 " 60.212 



3.290 " 5.464 " 60.212 



1.830 " 3.041 " 60.178 



3.001 " 4.987 " 60.176 



Mean, 60.1992, =b .0062 



2.352 grm. CoCI.^ = 3.9035 grm. Ag. 60.254 



4.210 " 6.990 " 60.229 



3.592 " 5. 960 " 60.268 



2.492 " 4.1405 " 60.186 



4.2295 " 7.0255 " 60.202 



Mean, 60.2278, zb.oil 



These results give values for Co and Ni differing by less than a tenth 

 of a unit; here, as elsewhere, the figure for Ni being a trifle the lower. 

 Combining these data with Marignac's, we have — 



Ag-i •■ NiCl-i : : 100 : X. 



Marignac 60.139, rt .0310 



Dumas 60.199,^.0062 



General mean 60.194, +: .0061 



Ag.^ : CoCl.^ : : lOO : X. 



Marignac 60. 118, zb .0192 



Dumas 60 228, ± .0110 



General mean 60.200, ± .0095 



In 1863 1 the idea that nickel and cobalt have equal atomic weights 

 was strengthened by the researches of Russell. He found that the black 

 oxide of cobalt, by intense heating in an atmosphere of carbon dioxide, 

 becamjC converted into a brown monoxide of constant composition. The 

 ordinary oxide of nickel, on the other hand, was shown to be convert- 

 ible into a definite monoxide by simple heating over the blast lamp. 

 The pure oxides of the two metals, thus obtained, were reduced by 

 ignition in hydrogen, and their exact composition thus ascertained. 



*Ann. Chem. Pharm., 113, 25. i860. 

 t Journ. Chem. Soc. (2), i, 51. 1863. 



