ATLAS OF ABSORPTION SPECTRA. 



OBJECT OF THE PRESENT INVESTIGATION, 



If we look over the literature of the subject of absorption of light we 

 fail to find a collection of absorption spectra presented in such a manner as 

 to enable the observer to select at a glance a substance which produces 

 either general or selective absorption in any specihed part of the visible or 

 ultra-violet spectrum. The wave-lengths of the absorption bands and other 

 characteristics of the absorption exhibited by innumerable natural and arti- 

 ficial compounds and mixtures, both inorganic and organic, may be found 

 in a great many books, journals, memoirs, and dissertations. If all of these 

 results were reproduced and catalogued in one volume they would not satis- 

 factorily fulfil the requirements just mentioned, because the different experi- 

 menters have had various objects in view and hence they have worked in 

 various and limited parts of the spectrum, have used different numerical 

 dispersions, have employed optical systems of unlike dispersion curves, have 

 not made it possible even to reduce their results to graphical form much less 

 to a common basis of wave-lengths and normal dispersion, etc. The nearest 

 approach to a work of the kind under consideration is made by the publica- 

 tions of J. Formanek, especially the two volumes entitled respectively ' ' Die 

 Qualitative Spektralanalyse anorganischer Korper" and "Spektralanaly- 

 tischer Nachweis kiinstlicher organischer Farbstoffe ; " Berlin, 1900. For- 

 manek's investigations are very extensive and complete from the point of 

 view explicitly stated in the preface to the last-named volume. It was his 

 aim to develop a practical spectroscopic method of procedure by which any 

 given organic coloring matter could be unambiguously identified. He says: 



" Das Princip des hier beschreibenen neuen Verfahrens beruht auf der Kombina- 

 tion der spektralanalytischen Beobaclitung und der chemischen Untersuchuug ; dieses 

 Verfahreu liefert nicht nur sichere Resultate, sondern sein Vortheil liegt auch darin, 

 dass man mit Hilfe desselben alle eiuzelnen Farbstoffe von einander unterscheiden 

 kann." 



Formanek, in order to obtain his results, varied the concentrations of 

 his solutions until each absorption band of a given substance became in suc- 

 cession as well defined as possible, so that the wave-lengths of their maxima 

 might be read off with precision. This method is preeminently adapted to 

 locating maxima, but it gives very little, if any, information relative to the 

 absorption between and beyond the maxima, for bodies exhibiting marked 



