the Electrical Resistance of Bismuth. 337 



commercially. It has been supplied to us by the well- 

 known chemical works of Herr Brommsdorff at Erfurt, who 

 has taken all possible care in its preparation. We have so 

 named this product to distinguish it from Herr Brommsdorff's 

 other bismuths, which we treated of in our " Preliminary 

 Communication." 



The qualitative analysis of this metal, made by Prof. 

 Classen, showed that it contains several impurities, princi- 

 pally copper. 



The four following bismuths are products as pure as can be 

 obtained by chemical methods of precipitation ; they were 

 prepared by Prof. Classen, who used every precaution. The 

 metals Classen L, II., and III. w r ere obtained by reduction 

 from bismuth oxychloride, Classen IV. by reduction from 

 bismuth nitrate. 



Bismuth nitrate is a pharmaceutical product which, it 

 appears, can be obtained in a very pure state in commerce. 



These different samples were subjected to a minute spectral 

 analysis, the results of which we will point out later, but we may 

 mention here that they all contained lead. Small quantities 

 of lead were always carried down with the precipitated bis- 

 muth; this experiment repeated even 13 times never resulted 

 in a pure product. It appears then that bismuth eamiot be 

 obtained absolutely pure by jwecipitation. 



The last bismuth which we examined, and which we have 

 called " pure electrolyzed bismuth," was prepared by elec- 

 trolysis. During the electrolysis of a solution of bismuth 

 containing traces of lead, pure bismuth was deposited at the 

 negative pole ; and lead, in the form of peroxide of lead, at 

 the positive pole. 



As to the lead or tin which were used in the alloys, they 

 came from Herr Brommsdorff's chemical works, and were 

 sold to me as pure. Besides, they were introduced into the 

 alloys in such small quantities that there was no occasion 

 to take account of any impurities they might have contained. 



Purification of Commercial Bismuth. 

 First Method. 

 About 250 grams of the metal were dissolved in HN0 3 ; 

 the solution was brought to the boiling-point in a porcelain 

 dish into which concentrated HC1 had been poured. In 

 order to transform all the bismuth nitrate into the chlo- 

 ride, the operation was repeated until the presence of HN0 3 

 could no longer be detected. The residue was then dis- 

 solved in HC1, and alcohol added in successive small quan- 

 tities. Most of the lead was precipitated in the form 



