some Copper Salts in Aqueous Solution. 319 



It would appear, therefore, that the absorption-spectrum 

 of a substance in solution is, as a rule, variable to a greater 

 or smaller extent with the concentration. 



The second question which received attention was the con- 

 nexion between the spectra of the salts of the same acid or 

 base in aqueous solution. 



Gladstone*, in 1857, said that " a particular base or acid 

 has the same effect on the rays of light, with whatever it may 

 be combined in aqueous solution/' This law, he found, held 

 good generally though not invariably ; and this conclusion 

 was afterwards confirmed by the researches of Bahr and 

 Bunsenf, Bunsen J, Landauer §, Morton and Bolton ||, 

 Eussel and Lapraik H, Soret**, Russelff, Knoblauch, and 

 others. 



A discussion of a number of these papers is to be found in 

 a Report on Spectrum Analysis by Dr. Schuster in the 

 British Association Reports, 1882. I will therefore content 

 myself by referring to it. Morton and Bolton found that a 

 large group of double acetates of uranium possess the same 

 absorption-spectrum. Knoblauch found in one experiment 

 that the bands of the nitrate and acetate of uranium occupied 

 the same position in dilute solutions, while in stronger 

 solutions they had different positions. The chloride and 

 acetate had the same spectrum. Russel and Lapraik found 

 that the nature of the acid had no influence on the spectrum 

 of uranic salts ; while Oeffinger (Dissertation quoted by 

 Knoblauch) apparently found no two salts of uranium with 

 the absorption-bands in exactly the same position. The dis- 

 crepancies are perhaps due to the different observers using 

 solutions of different concentrations. 



Knoblauch has shown that, even in the most dilute solu- 

 tions, the spectra of the copper and potassium salts of eosin 

 are not identical. 



The photometric researches bearing on this question are 

 very few in number. The work of Settegast ft and of 

 Sabatier § § shows that potassium and ammonium bichromates 



* Gladstone, Phil. Mag. (4) xiv. p. 418 (1857), and Journ. Chem. Soc. 

 x. p. 79 (1858). 



t Bahr and Bunsen, Liebig's Ann. cxxxvii. p. 20 (1866). 



X Bunsen, Pogg. Ann. cxxviii. p. 100 (1866). 



§ Landauer, Berliner Ber. xi. p. 1772 (1872). 



|| Morton and Bolton, Chem. News, xxviii. p. 47 (1873). 



If Russel and Lapraik, Nature, xxxiv. p. 510 (1886). 



** Soret, Compt. Bend, lxxxvi. p. 708 (1878). 



tt Russel, Proc. Roy. Soc. xxxii. p. 258 (1881). 



Jt Settegast, Wied. Ann. vii. p. 242 (1879). / See also Ostwald, Zeit. Fhys 



§§ Sabatier, Compt. Bend. ciii. p. 49 (1886). \ Chem. ii. p. 78 (1886>. 



Z2 



