MEMOIU XX.] THE ALLOTROPISM OF CHLORINE. 307 



from tlu- mode of grouping of their constituent atoms as 

 from the qualities of those atoms themselves. 



But, if it be admitted that the experiments related in 

 this Memoir establish the allotropism of chlorine, then it 

 is plain that a very different and perhaps satisfactory 

 account of the phenomena of substitution may be given. 



As has been already said, no difficulty can arise in 

 accounting for the removal of hydrogen from organic 

 bodies, or for the first fact just alluded to. This remov- 

 al will ensue whenever processes are resorted to which 

 bring the chlorine into an active state. When we ex- 

 pose acetic acid and chlorine to the sun, the latter be- 

 comes active, gains the quality of uniting with hydrogen, 

 and chlor-acetic acid forms. Probably the same change 

 could be brought about by the aid of spongy platinum 

 and heat. 



Upon the second fact the similarity of function dis- 

 charged by the chlorine which has replaced the hydro- 

 gen atoms with the function of those atoms themselves 

 a flood of light is thrown by other phenomena of allot- 

 ropism. If a piece of iron be dipped in hydrated nitric 

 acid, though it may be acted on for a few moments, it 

 rapidly becomes passive. And so with the chlorine 

 atoms which have substituted the hydrogen. In the 

 circumstances in which they are placed they rapidly re- 

 vert from the active to the passive state. They are no 

 longer endued with an intense electro-negative quality 

 they have assumed the condition of inactivity. The 

 fact that chlorine in chlor-acetic acid simulates the func- 

 tions of hydrogen in acetic acid is not more remarkable 

 than that iron touched by platinum under nitric acid 

 simulates the properties of that noble metal. 



Do not, therefore, these circumstances seem to point 

 out that if we admit the fact that simple substances can 

 exist in different states, in a passive and an active form, 



