34 A BTUDY OF THE ABSORPTION SPECTRA. 



spectroscopic apparatus is not properly adapted. Examples of this kind 

 of absorption are given by the copper or nickel salts, the ferricyanides, 

 the chromates, etc. There is not the slightest indication of a finer structure 

 to these bands. 



The second kind of absorption spectra consists of diffuse bands that 

 are quite narrow in many cases and are usually very weak at ordinary 

 temperatures. These bands may be from 10 to several hundred Angstrom 

 units wide, and at very low temperatures may be broken up into finer and 

 sharper bands. Examples of this kind of bands are the cobalt, uranyl, or 

 uranous bands. In many cases these bands appear only under very special 

 conditions of concentration and depth of cell. If the amount of absorbing 

 material is large there is usually a wide absorption band in the region. 

 This is well illustrated by the uranyl bands and the blue-violet band of the 

 uranyl salts. If the amount of absorbing material is small the transmission 

 of light is so great that these faint bands are entirely obliterated. 



The third class of bands are sharp and appear over rather wide ranges 

 of concentration. They are exemplified by the neodymium and erbium 

 bands. This classification of bands is quite adequate for the present article 

 on account of the salts studied and the temperatures used. It is very 

 probable, however, that the latter two kinds of bands gradually merge into 

 each other. 



Glycerol Solutions of Cobalt Salts. 



A dilute solution of cobalt chloride was placed in the silica cell and 

 exposures were made at 10, 100, and 200 C. At 10 and 100 there was 

 practically complete transmission throughout the visible portion of the 

 spectrum. At 200 the whole shorter wave-length portion of the spectrum 

 was absorbed up to X 6200. No indications of any fine bands in the red 

 were to be noticed. A solution of normal cobalt bromide in glycerol was 

 exposed in the same way as the chloride, with practically no change in the 

 absorption with rise in temperature. A more concentrated solution of 

 cobalt bromide in glycerol was exposed in the silica cell at 10, 100, and 

 200. At 10 there was a very diffuse absorption band extending from 

 X 5000 to X 5300. At 100 this band had broadened so as to reach from 

 X 4900 to X 5400. At 200 the whole of the spectrum of wave-length less 

 than X 6200 was absorbed. No signs of the red bands appeared. Concen- 

 trated solutions of cobalt salts in glycerol become blue on being heated. 

 Unfortunately the length of the silica cell prevented the use of concentrated 

 solutions. 



Aqueous Solutions of Cobalt Salts. 



A spectrogram, Plate 13, A, of the absorption spectrum of an aqueous 

 solution of cobalt chloride was made for a 2.37 normal concentration and a 

 depth of cell of 1.3 mm. The current in the Nernst glower was 0.7 ampere, 

 slit-width 0.20 mm. and the time of exposure 3 minutes. No exposure was 

 made to the spark in this instance. The temperatures were 2, 14, 30, 

 45, 60, 70, and 81 C. 



At the lowest temperature there is an absorption band extending from 

 X 4800 to X 5100. As the temperature rises this band broadens, the broad- 



