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Lll. Researches in Adino- Chemistry. — Memoir Second. On the 

 Distribution of Chemical Force in the Spectrum, By John 

 William Draper^ M.D., LL.D., President of the Faculties 

 of Science and Medicine in the University of New York^. 



WITH scarcely an exception, the most recent works on the 

 chemical action of radiations and spectrum-analysis de- 

 scribe a tripartite arrangement of the spectrum, illustrated by 

 an engraving of three curves, exhibiting the supposed relations 

 of the calorific, the luminous, and the chemical spectra. This 

 view, which by a mass of evidence may be shown to be erroneous, 

 is exerting a very prejudicial efi'ect on the progress of actino- 

 chemistry. 



I propose now to present certain facts which may aid in cor- 

 recting this error. For this purpose it is necessary to show 

 that chemical effects (decompositions and combustions) may 

 take place in any part of the spectrum. The points to be 

 established may be thus distinctly stated : — 



1st. That so far from chemical influences being restricted to 

 the more refrangible rays, every part of the spectrum, visible 

 and invisible, can give rise to chemical changes, or modify the 

 molecular arrangement of bodies. 



2nd. That the ray effective in producing chemical or molecular 

 changes in any special substance is determined by the absorp- 

 tive property of that substance. 



I may here remark that both these propositions were main- 

 tained by me many years ago ; an example of the first will be 

 found in the Philosophical Magazine (Dec. 1842), and of the 

 second in a paper in the same journal, ^' On some Analogies 

 between the Phenomena of the Chemical Rays and those of 

 Radiant Heat^' (Sept. 1841). 



The opinion commonly held respecting the distribution of 

 chemical force in the spectrum is mainly founded on the be- 

 haviour of some of the compounds of silver. These darken 

 when exposed to the more refrangible rays, and, unless correct 

 methods of examination be resorted to, seem to be unaffected 

 by the less refrangible. Hence it has been supposed that in the 

 higher parts of the spectrum a special principle prevails, to 

 which the designation of " actinic rays ^^ is often applied — an 

 inappropriate iteration. In these pages I use the derivatives of 

 afcrU, not in this restricted sense, but as expressive of radiations 

 of every kind. This is their proper signification. 



Every part of the spectrum^ no matter what its refrangibility 

 may be, can produce chemical changes; and therefore there is 

 no special localization of force in any limited region. Out of a 



* Communicated by the Author. 



