Determination of Copper and Nickel. 131 



and south, parallel with the sun's change of declination, but 

 has rather a kind of oscillatory movement, in which the West 

 Indies represent the fixed point ; and the greatest amplitude 

 of oscillation is on the side of India. The northern excursion 

 is much greater in the northern hemisphere than is the 

 southern excursion on the side of the southern hemisphere. 

 The European atmospheric relations, especially in summer, 

 are therefore essentially of a secondary nature ; and we must 

 regard the little alteration in the atmospheric pressure in the 

 course of the year in Europe as a secondary result, of which 

 the explanation would not have been possible without the 

 observations from Asia and Australia. 



H. W. Dove. 



Berlin, January 5, 1853. 



On the Determination of Copper and Nickel in quantita- 

 tive analysis. By David Forbes, F.G.S., Ass. Inst. C.E., 

 Espedalen, Norway. Communicated by the Author through 

 Dr George Wilson, F.R.S.E., &c. 



Although the determination of these metals by the present 

 methods, when properly conducted, must be considered quite 

 accurate, still they are tedious, and are likewise attended 

 with several sources of error, so as to render it desirable to 

 endeavour by some simpler process to shorten the manipula- 

 tion generally employed, as well as, if possible, to diminish 

 the chances of incorrectness. 



Both copper and nickel are usually weighed in the state of 

 oxide procured by precipitating their respective solutions by 

 potash. This precipitation, if not conducted with great care, 

 is liable to errors so considerable as completely to vitiate 

 the results obtained, from the tendency which potash has to 

 precipitate basic salts ; so that the precipitate produced is 

 not the oxide itself, but a compound of the oxide with potash, 

 generally retaining in addition some of the solvent acid. 



This compound, in the case of nickel and copper, is however 

 decomposable by boiling water, and this property affords the 

 means of obtaining the oxides in a pure state previous to 

 ignition ; it is however evident that some risk always exists 

 of a portion not being perfectly decomposed by this washing, 



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