the Electrical Resistance of Bismuth. 339 



Third Method. 

 The metal, after having been purified by the preceding 

 methods, was subjected to electrolysis to take away com- 

 pletely any trace of lead. Prof. Classen, who is at present 

 engaged in determining the atomic weight of bismuth, intends 

 to describe this electrolytic method in detail. 



Researches with the Spectrum. 



To produce the bismuth spectrum a large Ruhmkorff's coil 

 with a Leyden jar intercalated was used, and the spark ob- 

 tained between rods of the metal. The spectrometer employed 

 was one of Meyerstein's with a Schroeder direct- vision prism 

 composed of five separate prisms. The slit was made rather 

 open so as to give a very bright spectrum. 



With a smaller dispersion, produced by a fine Merz 

 prism, the spectrum was still more luminous. It was inter- 

 esting to compare the method of observation which we have 

 just described with that which consists in sending an elec- 

 tric discharge between platinum electrodes, in a tube con- 

 taining a solution of a salt of the metal. This method was 

 also used, the rest of the apparatus remaining the same. 



It can thus be proved experimentally, and this is of some 

 importance to chemists, that the first method is much more 

 sure and exact than the other. 



On examining the bismuth "Latest Brommsdorff" in the 

 spectroscope, sodium and copper were found to be present. 

 The two characteristic lines Dj D 2 of sodium remained, even 

 when the surface of the bismuth rods had been well cleaned 

 by long immersion in nitric acid. The metal contained only 

 traces of lead. 



The other bismuths contained no copper and no sodium. 

 The traces of lead, which were found in the bismuths Classen 

 I., II., III., IV., and in the " Latest Brommsdorff," were all 

 very faint ; indeed we were not able to establish them with 

 certainty, except by the following process : — 



After having substituted, for the original rods of bismuth, 

 other rods of lead, so as to produce a good spectrum of this 

 latter metal, the point of cross section of the micrometer wires 

 of the spectroscope was placed upon the most visible line of 

 the lead spectrum, and then the rods of lead were replaced 

 by those of bismuth. 



The bismuth Classen I. showed the very characteristic 

 line of lead, of wave-length 5610'4. 



The same line was found in Classen II. and Latest 

 Brommsdorff ; but it was much more feeble. Classen III. 

 and Classen IV. also contained lead. 



