ATOMIC WEIGHTS 425 



The percentages given above will be discussed at the end of this chapter 

 in connection with all the other data relative to the constants in question. 

 The next chemist to take up the discussion of these atomic weights 

 was Marignac, in 1858/ He worked with the chlorides and sulphates 

 of nickel and cobalt, using various methods, but publishing few details, 

 as he did not consider the determinations final. The sulphates, taken 

 as anhydrous, were calcined to oxides. From the ratio NiSO^rlSTiO, he 

 found Ni = 58.4 to 59.0, and from five measurements of the ratio CoSO^ : 

 Co, Co = 58.64 to 58.76. If oxygen is taken as 16, these give for the 

 percentages of oxide in sulphate : 



CoO in CoSOi. NiO in NiSOf 



48.267 48.187 



48.307 48.387 



Mean, 48.287, ± .0135 Mean, 48.287, ± .0675 



Hence Co = 58.706. Hence Xi = 58.706. 



The chlorides were dried at 100°, but found to retain water; and in 

 most cases were then either fused in a stream of chlorine or of dry, 

 gaseous hydrochloric acid, or else calcined gently with ammonium 

 chloride. The determinations were then made by titration with a 

 standard solution of silver in nitric acid. Five experiments with an- 

 hydrous CoCL gave Co = 58.72 to 58.84. Three more with CoCL dried 

 at 100° gave Co = 58.84 to 59.02. Three with anhydrous NiCL gave 

 ]Sri = 58.80 to 59.00. If the calculations were made with Ag=108 and 

 Cl = 35.5, then these data give as proportional to 100 parts of silver: 



mCL. CoCL. 



60.093 60.056 



60.185 60.111 



— 60.111 



Mean, 60.139, ± .0310 60.194 



Mean, 60.118, ± .0192 



Hence M = 58.84. Hence Co = 58.79. 



In one more experiment NiCU was precipitated with a known qtiantity 

 of silver. The filtrate was calcined, yielding NiO ; hence the ratio 

 2Ag:!N"iO, giving Ni = 59.29. This experiment needs no farther atten- 

 tion. 



In short, according to Marignac, and contrary to Schneider's views, 

 the two atomic weights are approximately the same. Marignac criticises 

 Schneider's earlier paper, holding that the nickel oxalate may have con- 



' Arch. Sci. Phys. Nat. (nouv. sSrie), 1, 372. 1858. Oeuvres Completes, 1, .575. 



