RESULTS. 1 7 



RESULTS. 



INTERPRETATION OF THE CURVES. 



If the distances from the edge of a positive which is adjacent to the 

 comparison spectrum (which edge therefore corresponds to zero depth of 

 liquid in the cell) to arbitrary points on the boundary of a sharply-defined 

 absorption curve be called ordinates, and if wave-lengths be considered as 

 abscissa?, we may say that the absorption constants* associated with any 

 two chosen wave-lengths are inversely proportional to the ordinates belong- 

 ing to these wave-lengths. This statement involves certain assumptions, 

 about emission curves and sensibility curves, a discussion of which will not 

 be given here. 



If the edge of an absorption band is a straight line at right angles to the 

 length of the picture it means that the position of this side of the band 

 will not appreciably change with wide variations in the concentration of the 

 solution; in other words, the limit of absorption will remain at the same 

 wave-length regardless of the concentration. This is roughly the case in 

 figs. 4 and 15 of plates i and 4 at the respective wave-lengths o. 29/i and 

 0.515,^, and for most of the narrow bands of figs. 96, 100, and loi. If this 

 condition holds for all the bands of a given substance, which are within or 

 near the confines of the visible spectrum, the color of the light transmitted 

 by the solution will be the same no matter how much the concentration be 

 varied. This is well illustrated by solutions of the salts of neodymium and 

 praseodymium. 



When the boundary of an absorption band is a straight line inclined to 

 the axis of wave-lengths it may be inferred that the limit of the band will be 

 displaced in proportion to the change of concentration, and that the factor of 

 proportionality depends upon the angle which the line makes with the axis of 

 abscissae. This is exemplified in fig. 45, plate 12, by the portions of the 

 band, at wave-length 0.47,". corresponding to the thicker layers of liquid. 



In like manner, the general relation between the displacements of the 

 limits of absorption and the associated changes in concentration may be 

 easily inferred when the confines of the absorption bands are curved either 

 convex or concave. 



EXPLANATION OF THE TABLES. 



Two plans suggest themselves for the sequence of the experimental data, 

 viz : {a) To classify the material on the basis of the characteristics of the 

 absorption spectra, i. e., the succession, intensity, etc., of the bands and 

 regions of absorption ; (d) to arrange the results according to the chemical 



r/ r fv^ 



