INTRODUCTION. 13 



the atoms are united, as when a chemical compound is transformed into an 

 isomeric form. This dynamic isomerism is known to take place in many 

 chemical compounds in the presence of a catalytic agent or at high tem- 

 peratures. The case of acetylacetone and ethyl acetoacetate is cited as an 

 example. The absorption in this case is considered as being due to the reac- 

 tion changing the ketonic (1) to the enolic (2) form. 



H H 



I I 



_c c ^ c=c 



I II I 



HOD OH<2' 



It has been found that anything that changes the velocity of the above 

 reaction also changes the persistence of the absorption bands. 



The case of pyruvic ester is also given as a typical example of this kind 

 of a reaction which results in the absorption of light. 



CH 3 C C O C^ ?= CH 3 C=C OC 2 H 6 



II II II 



O O 00 



This oscillation of the carbonyl grouping Stewart and Baly call isor- 

 ropesis. 



On account of the large number of isomeric compounds that may exist 

 among the hydrocarbons, it is easily seen that a theory of this kind may 

 have very wide applicability. 



THEORY OF STARK. 



Stark considers that chemical valency can be explained as due to the 

 presence of negative electrons between the atoms, or rather the positively 

 charged ions that constitute atoms when they are combined with one or 

 more electrons. These valency electrons are considered as being "locked" 

 to the atoms in different degrees. Whenever a double chemical bond exists 

 in a compound it is considered that one or more of the valency electrons is 

 very loosely united with the atom. Under certain conditions, as, for example, 

 when ultra-violet light falls on a compound, some of the electrons may 

 absorb sufficient energy to be shot off from the molecule. In this way the 

 photoelectric is explained. When an electron is attracted back to a mole- 

 cule which has lost one, Stark supposes that light will be emitted, and in this 

 way fluorescence can be explained. The fluorescence of a large number of 

 organic compounds has been investigated by Stark and Steubing. 1 



COMPLEXITY OF THE PROBLEM OF THE SPECTRA OF COMPOUNDS. 



It is a fact that investigations on the spectral emission and absorption 

 of bodies have been far less fruitful in extending our knowledge of the 

 structure of the atom than had been expected. This is largely owing to the 

 almost infinite complexity of the structure of the atom and our general 

 ignorance of the forces that exist there. Probably the best known example 

 is that of the uranyl group which we shall describe. Let us consider the spec- 



1 Phys. Zeit.., 9, 661 (190S); 9, 4S1 (1908). 



