184 DISCUSSION OF EVIDENCE. 



intermediate systems or compounds is formed. These systems are for 

 the most part too unstable to be isolated, at least by the methods now 

 at our disposal; but the action of solutions on light makes their exist- 

 ence highly probable. 



Our chemical equations of to-day represent, in general, only the 

 beginning and end of chemical relations. They tell us little or nothing 

 about the intermediate stages of chemical reactions, and these are the 

 most interesting phases of the reaction. From our spectroscopic work 

 we are forced to conclude that at least some chemical reactions are 

 far more complex than would be indicated by the equations that we 

 ordinarily use to express them. When, for example, a nitrate is 

 transformed into a sulphate, there seems to be formed a series of inter- 

 mediate systems, sulphonitrates or nitrosulphates. We know nothing 

 about these substances chemically, but their existence is made highly 

 probable by a purely physical method the action of these substances 

 on light. 



This raises the question, are chemical reactions in general more com- 

 plex than we ordinarily represent them to be? Do these intermediate 

 systems exist in chemical reactions in general? It is impossible to 

 study all reactions by the spectroscopic method, if, for no other reason, 

 because many solutions do not have sharp and well-defined absorption. 

 The reactions, however, which can be studied directly by the spectro- 

 scopic method do not seem to differ in any fundamental manner from 

 those reactions which can not be so studied. They conform to the 

 same laws that are obeyed by other reactions and are in every respect 

 analogous to them. This leads to the conjecture that in those reac- 

 tions which can not be studied spectroscopically, there are also inter- 

 mediate systems or compounds which are too unstable to isolate; and 

 since they do not have characteristic spectra, their presence can not 

 even be detected. The formation of these intermediate systems is 

 strictly in accord with the action of mass in chemistry. Some such 

 intermediate compounds have in a number of reactions recently been 

 isolated by methods now at our disposal. As methods become more 

 refined, and we acquire better control of conditions, it seems not 

 improbable that many more intermediate compounds will be isolated. 



At present we can not isolate any large percentage of these inter- 

 mediate systems on account of their instability. The best we can do 

 is to study their properties in solution in the different solvents by 

 purely physical methods. It is obvious that these intermediate sys- 

 tems must be studied if we are ever to know the real mechanism of 

 chemical reactions, and not simply the conditions at the beginning and 

 end of reactions. Other suggestions which have been offered to explain 

 the gradual shift of the absorption bands as one salt is transformed into 

 another, appear to be entirely inadequate, if not meaningless. 



