AS MEASURED BY MEANS OF THE RADIOMlCROMETER. 



81 



region does the curve representing the transmission reach complete absorp- 

 tion. Maxima in transmission appear near X5400 and X9000 and minima 

 of about 8 per cent at X6900 and XI 1000. Readings were not made at 

 greater wave-lengths with any of the nickel salts, on account of the intense 

 water absorption slightly beyond this region. 



No striking or characteristic difference is noted in the absorption as shown 

 by the three curves representing the three salts of nickel studied. Each of 

 them shows maxima and minima in about the same region of the spectrum. 



O.B,a 



Fig. 38. 



SALTS OF COBALT. 



The photographic plate shows that in the visible region salts of cobalt 

 have a strong ultra-violet absorption, a band in the orange near X5000, and 

 increasing transmission from the center of this band toward the longer 

 wave-lengths. It was interesting to see whether solutions of cobalt salts 

 were completely transparent beyond the limit of sensibility of the photo- 

 graphic plate, or if such solutions again showed absorption bands in the 

 infra-red. It was also of interest to know whether equal concentrations of 

 the different salts showed the same or different absorption bands. With this 

 idea in view, the solutions of five salts of cobalt were studied. In each case 

 the concentration was 0.347 normal, and the depth of absorbing layer 10 mm. 



The results are given in table 19. Beginning at the left are given, in their 

 respective order, the observed transmissions for 10 mm. of solution of the 

 following salts: cobalt chloride, cobalt bromide, cobalt nitrate, cobalt sul- 

 phate, and cobalt acetate. 



The results of table 19 are plotted as transmission curves in figs. 39 to 43, 

 inclusive. A study of these curves shows that they are very similar, all 

 having maxima of transmission at the following points : X5950, X7800, X91 00, 

 and X10,600. In general, for all the salts of cobalt studied, the transmission 

 curves rise rapidly from X5000 to X5900, where the transmission reaches 

 about 65 per cent. The curves show a broad but slight absorption over the 



