092 Hartley — The Action of Heat on the Absorption Spectra and 



quantities of tliese salts which Mr. Hugh Ramage was so good as to lend me, I here- 

 with submit photographs taken with the 4-prism spectrograph. The dispersion of 

 this instrument is considerable as may be understood by the measurements between 

 the D' and D^ lines being 0-045 and 0-05 mm. on different occasions ; in wave- 

 length the difference is only four tenth-metres, so that, at this part of the spectrum, 



Q-Ol mm. of linear measurement is equivalent to a difference of ' th of 



a millimetre in wave-length. 



Neodym-amnionium Nitrate. — Solution was made by dissolving 2'8 grs. in 2-2 c.c. 

 of water. It was placed in a thin wedge-shaped cell to be photographed. 



Praseodym-ammonium Nitrate. — Solution was made by dissolving 1-9 grs. of the 

 salt in 2 '3 c.c. of water. It was photographed in a similar cell. 



The position of the solar lines and of the absorption bands in cold and hot 

 solutions is shown ; and it will be observed how the bands in the hot solutions are 

 widened out ; also how the absorption increases at the end in the ultra-violet near 

 the lines N and 0, PI. XXII. I beg to express my thanks to Mr. Hugh Ramage 

 for the assistance he gave me, by the loan of these salts, and in other ways when 

 photographing their spectra. 



In a recently published paper,* Muthmann and Stutzel remark upon the great 

 difference between the spectra of the nitrate, chloride, and carbonate of neodym. 

 This last compound differs from the others, and possesses a somewhat intense blue 

 colour. The intensity of the absorption was greatly increased ; the band in the 

 violet, X 432-434 was no longer visible, and that in the green was stronger than in 

 the nitrate. There was a marked alteration in the wave-lengths of the bands, 

 which showed a shifting towards the red end of the sjDCctrum, the maximum of 

 absorption in the bands being altered to the extent of 7'5 millionths of a 

 millimetre of wave-length in the yellow and green. The neodym carbonate 

 showed, in addition, a fine well-marked dark line in the orangef at X 600'5, which 

 disappeared when the carbonate was converted into salts with mineral acids, but 

 in the acetate, though much weaker, it was visible at X 6970. The relative 

 intensities of the bands in praseodym carbonate, also the order in which the lines 

 disappear upon dilution, are quite different from the nitrate and chloride. For 

 instance, while in the nitrate solution the blue line is the most persistent, that in 

 the yellow about X596"5 is the last to disappear from the carbonate. As I have 

 explained with regard to the absorption bands in organic compounds, the most 

 persistent bands are those corresponding with the greatest amj)Iitude of vibration. 



The authors connect these alterations in the spectra with the state of electro- 

 lytic dissociation of the solutions, but meet with a difficulty in accounting for the 



* " Beitragc zur Speotralanalyse von Neodym unci Piaseodym," Berichte der Deutsch. Chem. Ges., vol. 

 32, p. 2653, 1899. 



■j- Compare the didymium potassium nitrate and didymium acetate spectra already described. 



