318 Dr. T. Ewan on the Absorption-Spectra of 



Lippich*, in 1876, observed that the absorption-spectrum 

 of didymium nitrate is different in strong and in dilute 

 solutions. This was subsequently confirmed by H. Becquerel f . 



In 1878 Glan J made a careful series of measurements on 

 aqueous solutions of several salts in different concentrations. 

 He found differences between the absorptions of strong and 

 dilute solutions of about the magnitude of the experimental 

 error. 



Settegast§,in 1879, found a small decrease in the absorption 

 of solutions of potassium chromate and potassium bichromate, 

 with increasing dilution. This was in agreement with the 

 observations of Glan; while Vierordt (loc. cit.), Sabatier ||, 

 and 0. Knoblauch IT found a small increase in the absorption 

 of the more dilute solutions. 



0. Hesse ** (1880) examined alcoholic solutions of cyanine, 

 and obtained numbers which did not agree with Beer's law. 

 His experimental error appears to have been rather large, 

 however ; and more recently Ketteler and Pulfrich ft have 

 shown that the law holds accurately for such solutions. 



The measurements of Pulfrich J J and of Kriiss §§ on 

 potassium permanganate, and of Marshall || || and C. Norden 1HI 

 on carbonyl haemoglobin and oxyhemoglobin respectively, 

 show that in these cases the extinction-coefficients are not 

 strictly proportional to the concentrations. 



The measurements of B. Walter*** on solutions of 

 fluorescein in ammonia show that Beer's law only holds 

 good up to a certain concentration, above which deviations 

 occur. 



Knoblauch f ft, finally, was unable to observe any difference 

 between the spectra of strong and dilute solutions of a number 

 of salts which he examined ; in a number of other cases 

 differences were observed. 



* Lippich, Wien. Akad. Anz. 1676, p. 93. 

 t Becquerel, Compt. Rend. cii. p. 106 (1886). 

 X Glan, Wied. Ann. iii. p. 54 (1878). 

 § Settegast, Wied. Ann. vii. p. 212 (1879). 

 || Sa"batier, Compt, Rend. ciii. p. 19 (1886). 

 II Knoblauch, Wied. Ann. xliii. p. 738 (1891). 

 ** Hesse, Wied. Ann. xi. p. 871 (1880). 

 tt Ketteler and Pulfrich, Wied. Ann. xv. p. 337 (1882). 

 it Pulfrich, Wied. Ami. xiv. p. 177 (1881). 



§§ Kri.ss, G. and H., Kolorimetrie u. Quantitative Spectralanalyse, p. 156 

 (1891). 



|| || J. Marshall, see Kriiss, loc. cit. p. 211. 



1111 C. Norden, see Kriiss, loc. cit. p. 210. 



*** B. Walter, Wied. Ann. xxxvi. p. 518 (1889) 



ttt Knoblauch, Wied. Ann. xliii. p. 738 (1891). 



