76 THE ABSORPTION SPECTRA OF SOLUTIONS. 



For the methods of preparation see 0. Dammer's Handbuch der anor- 

 ganischen Chemie, vol. 3. 



The pentamine purpureo salts [RCo(NH 3 ) 5 ]X>, where A r may be CI, 

 Br, N0 3 , N0 2 , 3^S0 4 , etc. The pentamine nitrito salts are known as the 

 xanthocobalt salts, and have the general formula [NOvCo(NH 3 ).]X 2 . The 

 pentamine roseo salts can be obtained by the action of concentrated acids in 

 the cold on oxidized solutions of cobaltous salts. They are of a reddish 

 color. On heating with concentrated acids they become purpureo salts. 



The hexamine or luteo series has the composition [Co(NH 3 ) 6 ]X,. These 

 salts form yellow or bronze-colored crystals which decompose on boiling. The 

 above examples are cited because the cobalt salts give an absorption band 

 spectrum in some cases similar to the uranyl bands. It is very probable that 

 uranium, neodymium, erbium, etc., give rise to much more complex com- 

 pounds than even cobalt. 



It will be assumed that the absorption bands are due to compounds that 

 represent the average condition of the given dissolved salt. It may be that 

 only a few of the particles of the absorbing salt may be active at any one 

 instant. For instance, Becquerel 1 considers that only a very small number 

 of the neodymium atoms are taking part in the absorption of light at any 

 moment. It may be that the absorption only takes place when the compound 

 is in a special condition. For example, in the case of the uranyl salts we may 

 think of the absorption as being due to the valency electrons in the UOo 

 group. The absorption may take place when one of these electrons leaves 

 the uranium or oxygen atoms, or when it returns. Whatever the mechanism 

 may be, it will be assumed that the frequency of the absorber is determined 

 by the nature of the compound in which it is located, and that this compound 

 is typical of the average of all the possible compounds in the solution. Accord- 

 ingly, if the "methyl alcohol" and "water" bands of uranous bromide dis- 

 solved in methyl alcohol and water are of approximately the same intensity, 

 it follows that there are equal amounts of the uranous bromide existing as 

 the "methyl alcoholate" and as the "hydrate." 



In the case of neodymium chloride or neodymium bromide Jones and 

 Anderson 2 have shown that the "water" and "alcohol" bands are of about 

 equal intensity when the solution consists of 8 per cent of water and 92 per 

 cent of alcohol. In the case of uranous bromide or uranous chloride in water 

 and methyl alcohol, it is found that the "water" and "methyl alcohol" bands 

 are of about equal intensity when there are approximately 2 parts of water 

 to 3 parts of methyl alcohol in the solution. In the case of the neodymium 

 salts it would seem that the "water" bands are the more "persistent." The 

 less "persistence" of the "hydrate" of uranous chloride or uranous bromide 

 may be due to the presence of the zinc salts formed during the reduction of 

 the uranyl salts. It is found that the presence of free hydrochloric acid in 

 a solution containing the "hydrate" and "methyl alcoholate" of uranous 

 chloride causes the "water" bands to decrease in intensity with reference to 

 the "methyl alcohol" bands. The action of any chloride would probably be 

 the same. In the case of neutral salts of neodymium and uranium the "water " 



1 Becquerel: Le Radium, Sept. (1907). ; Phys. Rev., 26, 520 (1908). 



