MAPPING ABSORPTION SPECTRA OF VARIOUS SALTS. 35 



from which to begin naming the groups of bands. On the other hand, it is 

 very probable that there are many more neodymium bands in the infra-red, 

 and if these occur in groups, these groups can then be named in their proper 

 order. The reason that the uranyl series of absorption bands was named in the 

 opposite direction was on account of the fact that the strongest of these bands 

 are at the red end of the series, while the weak bands are in the ultra-violet, 

 the weaker ones of the series in many cases still remaining to be photographed. 



Neodymium Chloride in Water. 



Some of the weak and fine bands of neodymium and uranium are extremely 

 difficult to obtain clearly on a photographic plate, and it has sometimes seemed 

 to us that the presence of absorption bands of some wave-lengths might be 

 due to some absorber that was not always present in the solution. For in- 

 stance, the presence or absence of foreign nuclei might be a determining factor 

 in the constitution of the aggregates. It might also be possible that aggregates 

 in solution are quite stable as far as their inner constitution is concerned, so 

 that an aqueous solution of neodymium chloride, for instance, might show 

 different absorption bands depending upon what the species of neodymium 

 chloride aggregates was before the salt was dissolved. It might be possible 

 to detect phenomena of this kind. It would also be very interesting to find 

 whether there is any relation between the kinds of spectral aggregates of a 

 salt in solution, and the ionic and nucleating centers produced by spraying 

 or bubbling the solution. Nuclei of various salts have been investigated in 

 this manner by Broglie and others. The spray from solutions of the same salt 

 in two or more solvents could be taken up. Samarium and uranous salts could 

 be studied in the same manner. 



Plate 60, B, in the original film shows bands at XX 4000, 4180, 4271, 4280, 

 4295, 4330, 4650, 4695, 4805, 5330, etc. So far as we remember, this is the 

 first plate of ah aqueous solution on which the very narrow and faint band 

 at X 4280 has clearly appeared. The band X4805 is also a very weak one. In 

 the first strip of the original film, the band X 4271 possessed very sharp edges 

 and was about 8 Angstrom units in width. The band X 4280 was very weak 

 and was not more than 1.5 or 2 Angstrom units wide. The band X4295, on 

 the other hand, was about 8 Angstrom units wide and very weak. X 4650 is 

 very weak and is seldom seen. 



An attempt will be made to compare as much in detail as possible the 

 bands at X4280, X5200, and X5800 for the various solvents, since it is these 

 bands that give evidences of the existence of solvates and the various aggregates. 



Neodymium Chloride as a Methyl Alcoholate. 



A solution of neodymium chloride in methyl alcohol, that had been 

 allowed to stand over the summer, was found to contain a gelatinous precipi- 

 tate. The absorption spectrum was found to show the neodymium bands quite 

 sharply, these bands having a somewhat different appearance from those in 

 an ordinary methyl alcohol solution. 



A sharp band appears at X 4270, a weaker band about 8 Angstrom units 

 wide at X4295; a wide weak band at X3440; the triplets at XX 4700, 4760, and 

 4830; a very weak band at X5100; a wide hazy band at X5140; two strong, 

 sharp bands at X 5220 and X 5235 ; a wide and weak band at X 5260, and bands 

 more or less blurred together at XX 5704, 5780, 5815, and 5860. It will be noticed 



