ON THE REFRACTIVE INDICES OF GASEOUS POTASSIUM, ETC. ISO 



Cadmium. (Atomic Weight 112.) 



For experiments with this element the purest metal to be obtained from KAHI.BAUM 

 used. The arrangement described alxwe acted very well. At a temperature 

 l>etween 600 C. and 700 C. enough cadmium evaporated to give a shift of 20 or 

 30 bands. There was no marked absorption. The principal difficulty in obtaining 

 concordant results lay in the reading of the bands, which were unsteady owing to the 

 mirage caused by currents of unequally heated air, and in many cases were badly 

 illuminated. It was never possible to read to less than a quarter of a band ; and if 

 the conditions were bad, it was exceedingly easy to miss a whole bund, or even two, 

 or to count one twice. It was for this reason that the number of readings recorded 

 is so large. 



Table I. exhibits the results obtained. Those readings which appear obviously 

 incorrect are enclosed in brackets. Four different charges of cadmium were used and 

 numerous readings were made with each. The results obtained with the second 

 charge may be neglected. In this case the bands were observed by the old method, 

 while the whole furnace was heated in a single operation, and the correction for 

 "end effects" was found to l)e of the order of 25 per cent, of the reading, and was 

 not trustworthy. The other three charges gave fairly consistent results, as will be 

 seen from the summary. 



Zinc. (Atomic Weight 65.) 



The next element dealt with was zinc, in the hope that the completion of the series 

 zinc, cadmium, mercury might afford useful information. Again, in this case, the 

 pure metal supplied by KAHLBAUM was used. Only two charges of zinc were used, 

 and much trouble was experienced in overcoming the effects of air convection currents. 

 No absorption l>and was oliserved. It is to be regretted that the number of bands 

 read was so small ; but the furnace was not adapted for reaching a higher temperature 

 than about 850 C., and it was not possible to evaporate a larger quantity at this 

 temperature. 



Table II. exhibits the results. 



Arsenic. (Atomic Weight 75.) 



Arsenic, free from iron, was obtained from two sources, and a series of determinations 

 was made with each specimen. 



This element proved the easiest of all those attempted, and concordant results were 

 quickly obtained (see Table III.). 



Selenium. (Atomic Weight 79.) 



Experiments were made with two charges of this element. In the first series the 

 readings were somewhat uncertain, and the result may be neglected. The second 



T 2 



