178 DISCUSSION OF EVIDENCE. 



It has already been pointed out that salts of neodymium are espe- 

 cially well adapted to the study of " solvent" bands, on account of the 

 sharpness of the neodymium lines and bands, and the accuracy with 

 which they can be measured. Neodymium salts were studied in a 

 number of solvents, and a few of the results obtained are given below. 1 



ABSORPTION SPECTRA OF NEODYMIUM SALTS. 



The following nomenclature will be used in describing the neodym- 

 ium absorption spectra: 



a group in the region X3400 to X3600. 



|8 "at about X4300. 



7 " from X4600 to X4800. 



5 " from X5000 to X5400. 



"in the region X5800. 



In designating the neodymium spectra we start from the violet end 

 of the spectrum. This is the natural method when a grating is used. 

 It is doubtful whether, in the near future, the ultra-violet spectrum 

 of neodymium can be studied much farther than we have done, so that 

 this is the natural end of the spectrum at which to begin. It is, on 

 the other hand, probable that there are many neodymium bands 

 farther down in the infra-red than we have gone ; and when these have 

 been worked out they can then be named in the natural order. 



The change in the absorption spectrum of neodymium chloride as 

 the solvent is changed can best be seen by expressing the results in 

 the following form: The abbreviations used are "d. " diffuse, "fa." 

 faint, "fi." fine, "h." hazy, "i." intense, "n." narrow, "sh." sharp, "st." 

 strong, "we." weak, "wi." wide. 



The following results obtained with neodymium chloride show the 

 effect of the solvent on the absorption spectra of solutions of this 

 compound. The bands of the different solvents have different wave- 

 lengths and different relative intensities. 



Having found that the solvent played an important part in deter- 

 mining the absorption of light by the dissolved substances, Jones and 

 Strong used isomeric organic solvents, to see whether such closely related 

 compounds would affect differently the power of substances dissolved 

 in them to absorb light. They prepared solutions of neodymium 

 chloride in propyl and isopropyl alcohols, and in butyl and isobutyl 

 alcohols, and photographed the absorption spectra of this salt in these 

 isomeric solvents. The results show different absorption lines and 

 bands in the isomeric solvents. 



If we compare carefully the spectra of neodymium chloride in butyl 

 and isobutyl alcohols, we find that the bands are weak and diffuse 

 in isobutyl alcohol, and have different relative intensities from what 

 they have in the butyl alcohol. The bands in butyl alcohol are very 



'See Phil. Mag. May 1912, p. 737, from which the few following pages are taken; also, Journ. 

 Franklin Inst. Dec. 1913, p. 531. 



