Dr Thomson on the atomic weight of NicJcel. 155 



Art. XXXIII. — On the Atomic Weight of Nickel. By Tho- 

 mas Thomson, M.D. F. R.S. L. andE. Professor of Chemis- 

 try in Glasgow. Communicated by the Author. 



I HAVE been induced to draw up a few remarks on the atomic 

 weight of Nickel from meeting with the following paragraph 

 in Dr Turner's Elements of Chemistry, p. 418 : — 



" Nickel is susceptible of two stages of oxidation. The 

 composition of its oxides is stated very differently by different 

 chemists. According to the experiments of RothofF and 

 Tupputi 29.5 is the atomic weight of nickel. Thomson esti- 

 mates it at 26, and Lassaigne at 40. (Ann. de Chim. et de 

 Phys. tom. 21.) Lassaigne, whose analyses are the most re- 

 cent, attributes this discordance to the presence of cobalt in 

 the nickel employed by preceding chemists, a supposition 

 which is by no means improbable. According to his experi- 

 ments, the two oxides are thus constituted. 



Nickel. Oxygen. 



Protoxide, 40 -f- 8 



Peroxide, 40 -t- 16" 



Had Dr Turner attended to the experiments on nickel and 

 cobalt pubhshed by Berzelius, Berthier, and myself, he would 

 have seen that the atomic weights of the two metals are iden- 

 tical, and consequently that'the presence of cobalt in the nickel 

 employed by preceding chemists could have had no influence 

 whatever in altering the atomic weight. 



The experiments of Lassaigne were shown to be inaccu- 

 rate by Berthier in a paper published about two years ago. 

 (Ann. de Chim. et de Phys. 25, 94.) His results are nearly 

 a mean between those of Berzelius and my own. He employ- 

 ed an oxide of nickel which he had carefully freed from every 

 trace of cobalt and from every other impurity. 



Berzelius's number for the atom of nickel, (when divided 

 by two to bring it into accordance with the simple atomic 

 doctrine of the British chemists,) is 3.69755. 



Berthier reduced 1000 parts of protoxide of nickel to the 

 metallic state by exposure to a sufficient heat in a charcoal cru- 

 cible. In two experiments he got 775 parts of metallic nickel ; 



