ON ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION. 219 



Solutions were made of such a strength that 1 gramme-molecule was 

 contained in 1,000 litres of water. Photographs of the transmitted rays 

 were taken through a constant thickness with a constant exposure and 

 exactly the same development. The photographs reproduced in the paper 

 are explained in the text. They exhibit a luminous band in the red 

 which in respect to substances 1 and 2 is the same in intensity and posi- 

 tion. In substances 3 and 4 it is more luminous and slightly broader, 

 and the luminous band of No. 3 lies rather more towards the less re- 

 frangible rays than No. 4. Wave-length measurements are not given, 

 but numbers on an arbitrary scale are recorded. On diluting these 

 solutions, the change in the spectrum is seen to be a decrease of the 

 intensity of the absorption bands more on the side of the rays of greater 

 refrangibility than on the other. The author proposes to enunciate 

 definitely the law of auxochromes in a future paper. 



Note. — That there is apparently a decrease in the intensity of the 

 absorption bands more in the direction of the rays of shorter wave-length 

 is due undoubtedly in the first instance to the property of the prism, there 

 being greater dispersion of the more refrangible rays. 



Nouvelle methode permettant de cliaracteriser les matieres colorantes, 

 By MM. Camichel and Bayrac.'^ 



The absorption of light by solutions of indophenols in alcohol, ether 

 carbon disulphide, and chloroform has been studied by taking as abscissje 

 the wave-lengths and as ordinates the coefficients of transmission. 

 Curves have been obtained of parabolic form, of which the convexity is 

 turned from the side of the axis of the abscissse. That portion of the 

 curve corresponding to the transmitted red rays ascends much more 

 rapidly than that which corresponds to the green or the blue. The 

 minimum position of the ordinate lies between the wave-lengths 610 and 

 535 according to the nature of the indophenol and its solvent. In order 

 to characterise each of the substances studied, the lowest point of the 

 curve was determined — that is to say, its minimum of transmission or of 

 greatest absorption. This is determined with precision by cutting the 

 curve with a series of lines or chords lying parallel to the axis of the 

 abscissfe. The conjugate diameter of these chords, obtained by joining 

 points at the middle of each line, is rectilinear in a sufficiently large 

 interval lying between wave-lengths 670 and 510 ; in such a case, for 

 example, as that of an alcoholic solution of indophenol and of orthocresol 

 with two tertiary nitrogens. The minimum of transparency (maximum 

 of absorption) is independent of the concentration of the solution for all 

 substances of which the absorption coefficient is proportional to the degree 

 of concentration, according to the law of Beer. It varies with the solvent 

 according to a law which is not that indicated by Kundt. 



Two series of indophenols have been studied ; those of Series A have 

 two tertiary nitrogens, the simplest of which is indophenol of ordinary 

 phenol. 



0=/ \=N-CeH,-N(CH3),,. 



The others (Series B) have the second tertiary nitrogen replaced by 

 ' Covij)tes Rendus, cxsxii. p. 882, April 9, 1901. 



