38 ABSORPTION SPECTRA OF AQUEOUS SOLUTIONS OP CERTAIN SALTS 



The remaining bands of neodyniium nitrate, however, show the same rela- 

 tions that have been pointed out for the chloride and bromide ; with increas- 

 ing dilution the intensities of the bands increase and the centers seem to be 

 displaced somewhat towards the longer wave-lengths. 



We then have three salts, neodymium chloride, neodymium bromide, and 

 neodymium nitrate, all of which show a marked increase in the intensity of 

 the absorption bands with increase in dilution, when the product of con- 

 centration and depth of layer is kept constant, i. e., when the conditions 

 demanded by Beer's law are fulfilled. 



POSSIBLE EXPLANATION. 



It is well known that a resonator vibrates more strongly if excited by the 

 vibrations from one single vibrating resonator of the same pitch than when 

 set into vibration by a large number of resonators, one of which has the same 

 period as its own, and the others slightly different periods. In other words, 

 if several vibrators are near one another, every one exerts a certain influence 

 on its neighbors. The result is that no one of them has exactly the same 

 period as the original resonator. 



The presence of one vibrator seems to exercise a damping influence on the 

 other, and causes it to vibrate with a period slightly different from its normal 

 period. We thus have less perfect resonance. 



The absorption of light by solutions appears to be a resonance phenomenon. 

 In a concentrated solution the vibrators are relatively close to one another 

 and mutually affect one another. The result is an imperfect resonance, and 

 consequently the absorption bands are less intense in the more concentrated 

 solution. 



The vibrators are farther removed from one another in the more dilute 

 solutions, and in most cases are probably surrounded by large amounts of 

 water of hydration. The damping effect would not be so pronounced, and 

 a resonator would have greater freedom to vibrate in its own period. In 

 such cases we would have a more nearly perfect resonance, and the resulting 

 absorption bands would be more intense. This tentative explanation seems 

 to account for the observed facts. Subsequent work has shown that a part 

 of this effect can be explained as due to the fact that the slit width was not 

 infinitesimal. Fig. 10 is plotted from the results for neodymium sulphate, 

 and fig. 11 from those for neodymium acetate. The concentration of the 

 sulphate is 0.118 normal, and of the acetate 0.84 normal. The length of the 

 solution of the sulphate is 10 mm., and of the acetate 2.5 mm. 



The absorption of the acetate, for a given concentration, is much greater 

 than that of any other neodymium salt thus far studied. This agrees with 

 the results obtained photographically. 



The absorption of water beyond lju is very great, as has already been 

 stated. If we are working with very concentrated solutions and use a 

 "water" vessel of the same thickness as the "solution" vessel, it is obvious 

 that the results would not be comparable. Take the 3.43 normal solution 



