224 



KEPORT — 1901. 

 Aurine. 



Thick- 

 ness 



Bays transmitted 



A 



Mean 



MM. 



60 



30 



15 



10 



5 



4 



3 



2 



1 



5 

 4 

 3 

 2 

 1 



0'29 ffT. or 1 Milligramme-molecxde in 100 c.c. of Water. 



659-5 



624-5 



1 Milligramme-molecule in 500 ex. 



139 to 188 

 to 192 

 to 193 

 to 195 



139 to 198 



719 to 530 

 to 520 

 to 516 

 to 511 



719 to 504 



611-5 



1 MiUigramvie-molecule in 2,500 c.c. 



601-5 



It may here be remarked that in the diagram given in the ' Trans. 

 Chem. Soc' vol. li. 1887, pp. 152-202, of benzene and its derivatives (ij 

 the relationship of the absorption curves to the chemical constitution of 

 these substances is fully described ; (2) the band in the red is indicated 

 on the less refrangible side as not being the termination of the transmitted 

 rays, but as the 'extreme limit of the visible spectrum,' and on p. 20 L 

 it is pointed out that ' instances -where the light is almost entirely absorbed 

 are indicated by the curve being continued by a dotted line, as in 

 rosaniline hydrochloride,' and also that ' iodine green appeared to transmit 

 more of the least refrangible red rays than the other rosaniline derivatives. 

 This may have been due to the colour being favourable to viewing this 

 end of the spectrum, the more brilliant rays being absorbed, and those 

 that are feeble thus rendered visible.' This observation has been verified 

 by MM. Bayrac and Camichel's examination of other substances of a similar 

 character. 



It should, however, be distinctly understood that it is the absorption 

 bands which are of prime importance in the study of spectra. 



It is the position and width of these which determine those of the 

 transmittent rays, and therefore greater attention should be paid to 

 measurements of the bands of absorption. Comparisons of spectra 

 measured on an arbitrary scale are liable to be very misleadin"- when 

 deductions are drawn from them. 



The apparent shifting of the band of transmitted rays in the red 

 observed by Lemoult is satisfactorily shown by Bayrac and Camichel 

 to be only apparent, and not a real alteration in .position. 



