450 



CAROLINE W. BALDWIN. 



[Vol. hi. 



Potassiiivi Chloride. 



Potassium easily gives a long arc which is homogeneous and 

 very clear, so as to be hardly visible between the carbons. It is of 

 a less intense color than the arc of sodium or of lithium, and seems 

 to be surrounded by a considerable mass of cooler vapor. The 

 carbons are not at a very high temperature. The band spectrum 

 is absent except very near the positive carbon. The strong me- 

 tallic lines from the original arc are present. The metallic lines 

 appear much as when sodium and lithium are used. 



Potassium lines photographed. 



Calciiivi Chloride. 



When calcium is in the carbons, they are as highly incandescent 

 as carbons which contain no metallic salt. The heat of the arc 

 does not seem to be so much diminished as in the preceding 

 cases. The arc shows a more varied formation. There is a blue- 

 violet center, which is decidedly blue near each carbon. This is 



» 



surrounded by a dark part, while the outer sheath is of an orange 

 tint. The dark part diminishes as the carbons become heated. 



In the spectrum the strength of the bands is less affected than 

 by the other metals yet studied ; but their hazy appearance is 

 removed, and the fine lines arc more sharp. As soon as we pass 

 into the outer sheath, the bands disappear with the exception of a 

 slight indication of the one which terminates at X. = 3885. The cal- 

 cium lines remain exceedingly sharp and brilliant in the outer sheath. 



As in the ordinary arc, the calcium lines 4581.66 and 4586.12, 

 also lines of unknown origin near 4603., 4586., and 4581., are 

 clearly seen at the negative carbon only, while lines at 4604. and 

 4576. are visible only at the positive carbon. Line 4226.91 was 

 strongly reversed. 



