292 JONES AND ANDERSON— ABSORPTION SPECTRA OF [April 25, 



tint. The negative for a does, in fact, show pretty strong general 

 absorption from A 7100 to the end of the red, but no doubt a spectro- 

 photometric study of the solutions would show general absorption 

 much farther down into the red. The negative for h shows no sign 

 of this absorption for very obvious reasons. 



Praseodymium Chloride in Mixtures of the Alcohols and 



Water. 

 (See plate 6.) 



The concentrations of the praseodymium chloride was constant 

 throughout and equal to 0.5 normal. The percentages of water in 

 the solutions, beginning with the one whose spectrum is adjacent 

 to the numbered scale, were o, 2^, 5§, 8, lof, 13^ and 16. The 

 depth of absorbing layer was i.o cm. 



Methyl alcohol was the chief solvent in the solutions pertaining 

 to a, while ethyl alcohol was used in the solutions used in making 

 the negative for h. The two spectrograms are identical, except for 

 a little greater general absorption in the ultra-violet with the ethyl 

 alcohol. 



The most striking feature of the spectrograms is the appearance 

 of the intense absorption band near A 3000 as the percentage of 

 water is gradually decreased. Only a faint trace of this band is 

 visible with 16 per cent, of water in the solution, and the band is 

 comparatively weak even with only 8 per cent, of water. From 

 this point it increases very rapidly in width and intensity with 

 decrease in the amount of water, until in the pure alcohol solutions 

 its limits (transmission) are A 2970 and A 3230, being by far the 

 most intense band in the whole spectrum. 



The bands in the violet and blue apparently shift somewhat 

 towards the red, this being, however, due to the fact that the alco- 

 hol bands are a little nearer the red end of the spctrum, and that 

 when the percentage of water changes from 16 to o, the two sets 

 of bands coexist, but are far from being separated. The change is 

 exactly the same in character as the one described in detail in dis- 

 cussing the A 4760 band in mixtures of alcohol and water for 

 neodymium chloride. The positions of the bands in the solution, 

 containing 16 per cent, of water, are as follows: A 4390 to A 4470, 



