1 8 ATLAS OF ABSORPTION SPECTRA. 



nature of the absorbing media. Because the first method conforms more 

 closel}^ to the professed object of the present research than the second, every 

 scheme consistent with it was tried which suggested itself. The great num- 

 ber of combinations on the negatives of the effects of weak, general absorp- 

 tion with definite, intense bands, combined with more or less uncertaint}' as 

 to the interpretation of the negatives in the region for which the source of 

 the discontinuous spectrum had to be used, made it impossible to find a 

 satisfactory permutation of the photographic records. Consequently the 

 second plan suggested above was followed as far as the text is concerned. 

 The spectrograms, on the contrary, are arranged, as far as possible, so as 

 not to have widely different absorption spectra succeed one another on the 

 same plate.* The organic coloring matters succeed one another in the same 

 order as is given to them in the English translation by A. G. Green of a 

 book by G. Schultz and P. Julius entitled "A Systematic Survey of the 

 Organic Colouring Matters" (Macmillan & Co., London, 1904). This con- 

 nection between the contents of the volume just named and the material 

 recorded below has the advantage of making it easy to find out many things 

 about the dyes which can not be appropriately given here, such as the names 

 of their discoverers, their literature, patents, methods of preparation, their 

 behavior with various reagents, chemical constitution, etc. 



The descriptive tables following this explanatory section present the 

 experimental results in the following order: 



(i) The absorption of a small number of interesting intermediate prod- 

 ucts, so-called, arranged according to the alphabetical order of their names. 



(2) The absorption of such dyes as were studied and were capable of 

 identification with the dyes discussed in the book by Schultz & Julius. 



(3) The absorption of such dyes as were not unquestionably the same 

 as any given in the reference volume. The accounts of these dyes follow 

 the alphabetical order of their comvicrcial names. 



(4) The absorption of certain miscellaneous objects of more or less 

 interest, in alphabetical order. 



Whenever a number without qualification is given to a substance it 

 refers to the present account, but when a number is quoted from the volume 

 by Schultz & Julius attention is called to the fact by the abbreviation S. & J. 



In the brief account of any one dye the details are presented in the 

 sequence explained by the following sentences: 



First. The arbitrary number of the substance in the present list is given. 



Second. The commercial name of each substance is recorded precisely 

 as it was labeled by the firm which furnished the coloring matter. When 



*Plate 2 is an exception to this statement. 



