SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 99 



the nitrate, which we have found shows a considerable variation in its 

 spectrum with change in dissociation, and her solvents being water and 

 acetone, the change in the dissociation would be very considerable. For 

 this reason, she found a continuous change in the spectrum as more and 

 more acetone was added, which was just what she expected. Had she 

 worked with the chloride or bromide she would have found practically no 

 change until the proportion of the non-aqueous solvent in the mixture 

 had become very great, and in this event her conclusions would have 

 been quite different. 



In the second case her salts were not dehydrated (if they were she 

 makes no mention of the fact), and hence even in the solution in pure 

 acetone she probably had from 6 to 10 molecules of water per molecule of 

 the dissolved salt, which we have found would give the spectrum character- 

 istic of the non-aqueous solvent with only about half its normal intensity. 

 It is not very surprising, therefore, that she failed to discover the coexist- 

 ence of the two sets of bands, which would have given a perfectly simple 

 explanation of all the phenomena that she observed. 



