EFFECT OF MOLECULAR WEIGHT. 



63 



four bands. As in the preceding, several readings of each ill-defined 

 band are plotted in order to get the limits between which it extends. It is 

 of interest to note that one of the H 2 S0 4 bands, at 8.62 /1, falls on the graph 

 of the second maximum. 



In fig. 45, the maxima of the absorption bands of the sulphates [(Mg, 

 Ca, Sr, Cd, Ba) S0 4 ] are plotted (see Part III, Carnegie Publication No. 

 65, for data). It will be noticed that the graph of the band at 4.5 fi is 

 much steeper (the horizontal scale is different for these bands) than are 

 the ones farther toward the infra-red. The maxima of the absorption 

 bands lie close to the graph drawn through them. 



Fb .,.Pb 



riMmc in Max 



45 46 4-.7/J. 45 4-.9 5.0 6.0 6.2 6.4 6.6 6.8/Z 



Fig. 45. Maxima of absorption bands of sulphates. 



The second and third maxima of the absorption bands at 6.2 and 6.5 jj. 

 are quite close to the graph, except SrS0 4 , which has but one maximum 

 lying midway between the two graphs. From this it would appear that 

 the SrS0 4 band may be the mean of two unresolved bands (see, however, 

 Part V, Chapter III). The slant of these graphs is less than in the pre- 

 ceding one. 



For a discussion of the graph at 45 jj. see Appendix III. 



Considered as a whole, the data presented demonstrate very conclu- 

 sively the influence of the molecular weight of the basic atom or "ion" 

 upon the position of the maximum. The results explain why the increase 

 in the number of the groups of atoms (see carbohydrates) had no effect 

 upon the position of the maximum. This is to be expected if the cause 

 of the band is due to the group of atoms; but the position of the band 



