Intelligence and Miscellaneous Articles. 319 



ON THE DETECTION OF LEAD IN THE PRESENCE OF BISMUTH 

 IN BLOWPIPE EXPERIMENTS. BY E. J. CHAPMAN, ESQ. 



It is well known that lead, bismuth and cadmium are the only- 

 metals which, when heated before the blowpipe, deposit a yellow 

 coating of oxide on the support. The areola formed by oxide of 

 cadmium is of a much deeper colour than that deposited by either 

 lead or bismuth ; and the metal itself is so rapidly volatilized, that 

 in these experiments it is never obtained in the metallic state. When, 

 therefore, in the examination of any substance, a yellow sublimate 

 takes place upon the charcoal with the production of a metallic glo- 

 bule, we have to determine whether this globule consist of lead or of 

 bismuth, or of the two combined. A malleable " button" is usually 

 presumed to consist of lead, and a brittle one of bismuth ; neverthe- 

 less a perfectly malleable globule may be obtained, containing an 

 admixture of bismuth ; and a brittle one, on the other hand, con- 

 taining a very considerable quantity of lead. For this reason the 

 assay should be examined further ; and in the reaction of bismuth 

 with microcosmic salt, as first noted by Berzelius, we possess a ready 

 method of detecting that metal, whether it be combined with lead 

 or not. For this purpose it must be treated with the reagent on 

 charcoal in the reducing-flame, with the addition of a minute par- 

 ticle of tin, Avhen the glass, which is colourless and quite trans- 

 parent whilst hot, becomes on cooling, if bismuth be present, grayish- 

 black and opake. The only metal which produces a similar reac- 

 tion is antimony; but this, if it chance to be present, can easily be 

 got rid of by Plattner's process, which consists in fusing the assay 

 matter with vitrified boracie acid in the oxidating flame, taking care 

 not to allow the globule to be entirely surrounded by the flux, by 

 which means the antimony is entirely driven off, whilst the lead and 

 bismuth are retained, as oxides, by the melted acid, and may be 

 again brought to the metallic state by fusion in the reducing-flame 

 with carbonate of soda. 



Thus far then the presence of bismuth is easily ascertained even 

 in a malleable globule consisting almost wholly of lead ; but the 

 detection of this latter metal in a globule rendered brittle by a large 

 proportion of bismuth, has been hitherto, in experiments with the 

 blowpipe, a much more troublesome affair. Plattner recommends 

 for this purpose a modification of one of the methods given in the 

 Manual of Professor Rose for the separation of lead from bismuth ; 

 but this method — which consists, as modified by Plattner, in fusing 

 the mixed metals with an excess of bisulphate of potash, and subse- 

 quently treating the fused mass, first with water, and afterwards with 

 nitric acid, to dissolve the sulphate of bismuth — is scarcely admissible 

 in these rapid experiments, in which the use of liquid acids and 

 other bulky reagents should, if possible, be avoided, in order not only 

 to render the operations as simple as accuracy will admit of, but 

 also to prevent the dimensions of the blowpipe-case from affecting 

 its portability. On this account I have endeavoured to discover 

 some other method for the detection of lead when combined in small 



