On the Deportment of Bismuth during Solidification. 19 



in raw bismuth, a portion of the silver accompanies the metal 

 protruded during solidification. 



3. To the metals already mentioned lead may be added as an 

 associate of commercial bismuth. 50 grammes of pure bismuth 

 melted with 2 per cent, of lead gave out no spheres on solidifica- 

 tion ; this immediately took place when 2 per cent, of sulphur 

 was added to the mixture. The spheres protruded to the amount 

 of 20 per cent. ; when melted and cooled they showed an even 

 surface, and mere traces only of sulphur and lead were to be 

 found in them. 



4. From a mixture of 80 per cent, bismuth, containing sonie 

 silver, and 20 per cent, sulphide of bismuth, some large metallic 

 globules were protruded during solidification. These were found 

 to contain 99-69 per cent, of bismuth, and 0-11 per cent, of 

 silver. Sulphur could not be detected in the globules, although 

 the original mass contained almost 4 per cent, of the substance. 



5. Chemically pure bismuth, which, when melted by itself 

 yielded no spheres, was melted with 5 per cent, of tersulphide of 

 bismuth (containing therefore nearly 1 per cent, sulphur) ; at the 

 moment of solidification bismuth spheres free from sulphur made 

 their appearance. 



These experiments show that the phsenomenon of globules 

 making their appearance on solidification, is not exhibited by 

 pure bismuth, but only by such as contains foreign ingredients. 

 Of the latter sulphur appears to be the chief cause of the phseno- 

 menon ; at least I have never observed it when the bismuth was 

 rendered impure by the heavier metals alone ; but always when, 

 together with such, sulphur was present, or when it alone was 

 the cause of impurity. These experiments show further that the 

 protruded metal possesses a high degree of purity ; it may, in- 

 deed, be regarded as almost chemically pure. 



These effects may be simply explained in the following manner. 

 The binary compounds of bismuth with the foreign substances, 

 particularly the sulphide of bismuth, solidify sooner than the 

 bismuth itself; and inasmuch as those compounds, without doubt, 

 expand [contract ?] by solidification, a portion of the still liquid 

 bismuth must be squeezed out of the mass. That this displaced 

 metal possesses a high degree of purity naturally follows from 

 the fact, that the foreign ingredients being already solidified 

 cannot accompany the protruded globules. 



Perhaps the deportment here desci-ibed might be taken ad- 

 vantage of to effect a preliminary purification of the raw metal, 

 particularly where an opportunity exists of working on a large 

 scale. The quantity squeezed out during one solidification 

 amounted in weight to from 2'5 to 3 per cent, of the total quantity 

 of the metal made use of. In the foregoing experiments I have 



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