CHAPTER VII. 



CHROMIUM SALTS. 



Introduction. Chromium chloride. Chromium nitrate. Chromium sulphate. 

 Chromium acetate. Chrome alum. Conductivity data. 



INTRODUCTION. 



A fairly large number of investigators have worked on the absorption 

 spectra of compounds of chromium. Some of these have studied the effect 

 on absorption spectra of temperature, concentration, nature of the solvent, 

 etc. In the following introduction to this chapter, a brief discussion of the 

 work of Hartley, of Jones and Anderson, and of Bois and Elias is given. 



Hartley found for the green chromium chloride that at 20 the bands 

 were at A 7040 to A 6850, and A 6730 to A 5380. For chromium sulphate he 

 found an absorption at A 6000 at 100, and at A 5880 at 20. 



Violet chromium sulphate at 16 gave a band at A 5430 (A 5620 to A 5250), 

 and at 100 the band was at A 5510 (A 5770 to A 5260). 



Chromium nitrate, a violet-colored salt, at 16 gave an absorption 

 band at A 5920 (A 6270 to A 5570), and at 50 the position of the band did not 

 change. Practically all of the light was absorbed at 100. 



A more dilute solution of chromium nitrate at 20 gave a band extend- 

 ing from A 5880 to A 5570. The position of this band did not change at 100. 



Chromium oxalate was found to give a band extending from A 7060 

 to A 6850 at 20, and blue potassium chromoxalate (K 6 Cr 2 ) (G 2 4 ) 6 .6H 2 0, a 

 band extending from A 6270 to A 4970 at 20, and from A 6310 to A 5030 

 at 100. 



Red potassium chromoxalate K 2 Gr 2 (C 2 O 4 ) 4 .10H 2 O gave narrow bands 

 at A 6940 and A 6850, and a band extending from A 6330 to A 4780 at 20, 

 and A 5880 to A 3570 at 100. 



Jones and Anderson l have photographed the absorption spectra of 

 chromium chloride and nitrate in water. For chromium chloride they 

 find large hazy bands at A 4200 and A 5900, and a much finer band at A 6690. 

 Chromium nitrate gives very similar bands at A 4100, A 5700, and A 6690. 

 It will be noticed that the wide nitrate bands have shorter wave-lengths 

 than the corresponding chloride bands.* The wave-lengths given by them 

 for the wide cobalt bands bring out the same result. The cobalt chloride 

 bands fall at A 3300 and A 5200, whereas for the nitrate the latter band lies 

 at about A 5100. The fact seems to be that the presence of the N0 3 group 

 in some way causes the absorption bands to be shoved towards the violet. 

 This is in accord with a paper by one of the authors, 2 where it was shown 

 that the uranyl nitrate bands have shorter wave-lengths than the other 

 uranyl bands. The same law was shown to hold for uranous bands and 

 also for the phosphorescent bands of uranyl salts. The presence of free 



1 Absorption Spectra of Solutions, Carnegie Institution of Washington Pub. No. 110. 



2 Phys. Rev., 29, 6, 555, Dec. (1909). 



4 49 



