SUMMARY AND GENERAL DISCUSSION OF RESULTS. 93 



x { UBr 4 } a { H 2 } <= y { UBr 4 } b { CH 3 OH } 



The variables x and y may be equal and both may be very small. These 

 quantities will be taken up later in the treatment of aggregates. 



The fact that there is no gradual shifting of the "water" bands into the 

 "alcohol" bands indicates that the equation representing the equilibrium 

 is not of the type: 



a { UBr 4 } x { H 2 } y { CH 3 OH } 



where x and y are variable and depend on the amount of water and methyl 

 alcohol present. The above constancy of a and b must not be interpreted 

 too literally, however, as it may be that in the "atmosphere" of solvent 

 molecules only the inner molecules are effective. In this case the constancy 

 of a and b would indicate that only the number of molecules in the outer 

 region of this atmosphere could change, or could consist of a mixture of water 

 and alcohol molecules. Accordingly, the inner solvent atmosphere consists 

 of but a single kind of molecules. 



(1) The percentage of solvents for which each set of solvent bands has 

 the same intensity will be used as a measure of the "persistency" of the given 

 solvates. The "persistency" of any given solvate will vary inversely as the 

 proportion of that solvent that is necessary for the bands to appear of a given 

 intensity. Whether there is any relation between the persistency of solvate 

 bands and the absolute values of a and b is not known. 



(2) The persistency of the same solvate bands for different salts is quite 

 different. In the case of neodymium chloride in water and alcohol the bands 

 are of the same intensity when 8 per cent of water and 92 per cent of alcohol 

 are present. In the case of samarium chloride a smaller percentage of water 

 is required, the water bands of samarium chloride having a greater persistency 

 than the water bands of neodymium chloride. The persistency of the water 

 bands of neodymium nitrate is different from those of the chloride. In the 

 case of the uranous salts the water bands are much less persistent, the water 

 and alcohol spectra being of about the same intensity when there is about 

 40 per cent of water and 60 per cent of alcohol present. 



(3) The persistency of the bands of the same salt in different solvents is 

 very different. In general the "water" bcmds are the most persistent of all the 

 solvent bands at ordinary temperatures. 



(4) The persistency of solvent bands depends on the concentration of the 

 solution. Keeping the percentage of water and alcohol constant, it is found 

 that the alcohol bands of neodymium chloride and of the uranous salts are 

 relatively more persistent for the greater dilutions, i.e., Beer's law does not 

 hold for solutions containing two solvents. 



(5) Although it has not been shown that only two solvates exist in the 

 case of a neodymium salt in a mixture of two isomeric solvents, yet there are 

 several instances where the absorption spectra of the same salt in isomeric 

 solvents are very different. A marked example of this kind is that of neody- 

 mium chloride in isobutyl and butyl alcohols, the butyl alcohol bands having 

 the shorter wave-lengths. On the other hand, the corresponding propyl 

 alcohol bands are shifted to the red with reference to the isopropyl bands. 

 The absorption of neodymium nitrate in butyl and isobutyl alcohol is very 

 much the same. 



