248 THE POPULAR SCIENCE MONTHLY 



might be cited are >C = C<; = C0; >C — NH, — N = 0; 

 = 1ST = ; = C = S, etc. A bathochrome introduced into an organic 

 compound causes the absorption band to become wider. An auxo- 

 chrome causes the intensity of the absorption to be greater. 



Dynamic Isomeeism 



Baly and many others have supported the view that the absorption 

 of many organic compounds is due to a change in the valency linking 

 of a compound. This dynamic isomerism is known to take place in 

 many chemical compounds in the presence of a catalytic agent or at 

 high temperatures. Take the case of acetylacetone and ethyl aceto- 

 acetate. The absorption in this case may be due to a reaction changing 

 the ketonic (1) into the enolic (2) form and some experimental evi- 

 dence favors this view. 



H H 



I I 



_c_c— <± — c=c— 



I II I 



H (1) OH (2) 



Eesume 



From the above brief account of our knowledge concerning the 

 nature of the absorption and emission centers of light and heat radia- 

 tions it will be noted that many advances have been made toward the 

 solution of this problem in recent years. The existence of " electron " 

 atmospheres in many solids, liquids and gases has explained the emission 

 and absorption of spectra that are ordinarily described as continuous; 

 the existence of negative electrons serves to explain many phenomena 

 such as those of the Zeeman effect, etc. ; models containing elementary 

 magnets arranged in various ways have been used by Eitz to explain the 

 series classification of spectrum lines ; the various phenomena of ioniza- 

 tion are being found to be intimately correlated with the phenomena 

 of light emission and much evidence is being accumulated to show that 

 light and heat centers may ultimately be identified as consisting of cer- 

 tain kinds of ions; a very large amount of experimental data has been 

 accumulated concerning absorption spectra of solutions of organic and 

 inorganic compounds and the centers of this absorption seem to consist 

 in certain " aggregates/' " chromophores," etc., which can be studied 

 from other points of view ; much evidence is found to point to the view 

 that light and heat centers depend upon certain dynamic conditions and 

 are not stable systems such as we usually conceive atoms and molecules 

 to be. 



