CHAPTER VI. 

 SALTS OF CHROMIUM. 



A comparatively large number of investigators have worked on salts 

 of chromium from the standpoint of absorption of light. We need only 

 mention the work of Talbot, 1 Brewster, 2 Croft, 3 Miiller, 4 Gladstone, 5 Melde, 6 

 the early work of Hartley, 7 Vierordt, 8 Vogel, 9 E. Wiedermann, 10 Soret, 11 

 Settegast, 12 Moissan, 13 Pulfrich, 14 Zimmermann, 15 Becquerel, 16 Liveing 

 and Dewar, 17 Schunck, 18 Recoura, 19 and Sabatier. 20 



Knoblauch, 21 in his interesting and important investigation on the ab- 

 sorption spectra of very dilute solutions, studied a number of chromium 

 compounds. These were the chloride, nitrate, sulphate, acetate, oxalate, 

 potassium chrom-oxalate, and chrom-alum. Knoblauch directed a part 

 of his work to testing the consequences of the then recently proposed 

 theory of electrolytic dissociation. According to this theory, the absorp- 

 tion spectrum of a concentrated solution must be different from that of 

 a very dilute solution; and at dilutions of complete dissociation, all of 

 the salts of an acid with a colored anion, having colorless cations, or all 

 of the salts of a metal having colorless anions, must have the same absorp- 

 tion spectrum. Knoblauch found that neither of these conclusions from 

 the theory was verified experimentally. 



Ostwald 22 showed a little later that the second consequence of the 

 theory is fully verified by experimental facts. 



Knoblauch also tested Beer's law, and found that it held for many 

 salts within wide limits of concentration. He concluded that the apparent 

 deviations from the law are to be explained as due to chemical or physical 

 changes in the solutions. 



1 Phil. Mag. (3), 4, 112 (1834). 



2 Phil. Trans., 1835, 1, 91, and Phi!. Mag. (4), 24, 441 (1862). 



3 Ibid. (3), 21, 197 (1842). 



4 Pogg. Ann., 72, 76 (1847), and 79, 344 (1850). 



s Phil. Mag. (4), 14, 418 (1857), and Journ. Chem. Soc., 10, 79 (1858). 

 Pogg. Ann., 124, 91 (1865). 



7 Proc. Roy. Soc., 21, 499 (1873). 



8 Ber. d. deutsch. chem. Gesell., 5, 34 (1872). 



9 Ibid., 11, 913, 1363 (1878). 

 10 Wied. Ann., 5, 500 (1878). 



11 Arch. Sci. Phys. et Nat. (2), 61, 322 (1878); (2), 63, 89 (1878). 



12 Wied. Ann., 7, 242 (1879). 

 13 Compt. rend., 93, 1079 (1881). 

 "Ztschr. f. Kryst., 6, 142 (1882). 

 15 Lieb. Ann., 213, 285 (1882). 



18 Ann. Chim. Phys. (5), 30, 5 (1883). 



17 Proc. Roy. Soc., 35, 71 (1883). 



18 Chem. News, 51, 152 (1885). 



19 Compt. rend., 102, 515 (1886), 112, 1439 (1891). 



20 Ibid., 103,49(1886). 



21 Wied. Ann., 43, 738 (1891). 

 "Ztschr. phys. Chem., 9, 579 (1892). 



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