330 J. Trowbridge — Carbon and Oxygen in the Sun. 



posite photograph, and the iron and carbon can also be regarded 

 as a composite photograph. It was speedily seen that from 

 twenty-eight to thirty per cent of iron in combination with 

 seventy-two to seventy per cent of carbon almost completely 

 obliterated the peculiar banded spectrum of carbon. This 

 proportion therefore of iron in the atmosphere of the sun, 

 were there no other vapors of metals present, would be suffi- 

 cient to prevent our seeing the full spectrum of carbon. 



The iron in the carbon terminals which I employed greatly 

 increased the conductivity, as will be seen from Table I, which 

 was obtained in the following manner. 



The carbons were separated by means of a micrometer 

 screw and the current and difference of potential were meas- 

 ured with different lengths of arc. Table I gives the results 

 for pure carbon. Table II for twenty- eight per cent of iron 

 and seventy-two per cent of carbon. 





Table I. 





Length of arc in mm. 



Amperes. 



Volts. 



1 



27 



25 



2 



23 



24 



3 



22'5 



20 



4 



20 



18 



5 



16-5 

 Table II. 



15 



Length of arc in mm. 



Amperes. 



Volts. 



1 ■ 



30"5 



30 



2 



29 



30 



3 



27-5 



28 



4 



24 



25 



5 



22 



20 



6 



20 



20 



7 



18 



19 



8 



16 



18 



The length of the arc could be nearly doubled with the same 

 current and the same voltage by the admixture of 28 per cent 

 of iron. The light was apparently greatly increased, but the 

 difference in color between the pure carbon light and the iron 

 carbon light made measurements unreliable. 



Moissan* has shown that the carbon in an electric oven 

 through which powerful electric currents have flowed is free 

 from foreign admixtures. Deslandres has confirmed this and 

 finds only a trace of calcium present. The purification comes 

 from a species of distillation of the volatile impurities. The 

 purest carbon is found at the negative pole. The light of the 



* Comptes Rendus, cxx, pp. 1259-1260, 1895. 



