364 Prof. Draper on the Allotropism of Chlorine 
ative than it was before, and the acid can no longer oxydize it. 
The contact of the very same substance, platina, determines an 
analogous change in chlorine,—giving it at once the capacity of 
uniting with hydrogen. 'The porous condition of spongy platina 
is not essential to the result, for clean platina foil exhibits the 
same phenomenon. 
In the case of iron, the action of a high temperature or the 
contact of platina, throws the metal from the active to the passive 
state ; in the case of chlorine the same causes apparently produce 
the opposite result, throwing the gas from the passive to the active 
state. But the difference is rather in appearance than in reality. 
In both cases it amounts to the same thing, and is an exaltation 
of the electro-negative qualities of either substance respectively. 
The same causes, therefore, which produce allotropic changes 
in other bodies, produce analogous changes in chlorine. 
Now, among the physical facts connected with the theory of 
types and substitutions, two are prominent; Ist. The union of 
chlorine with hydrogen, giving rise to the removal of that hydro- 
gen as chlorohydric acid. 2d. The subsequent function dis- 
charged by the chlorine, which has entered as an integrant por- 
tion of the molecules, and occupies the place of the hydrogen 
removed. ‘This function is in many instances that of the hydro- 
gen itself, and it is this fact which is the remarkable point in the 
phenomena of substitution,—that an intensely electro-negative 
body can act the part of a positive body. It is this fact which is 
leading chemists to the conclusion that the properties of compound 
bodies arise as much from the mode of grouping of their constitu- 
ent atoms as from the qualities of those atoms themselves. 
But, if it be admitted that the experiments related in this me- 
moir 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 removal will ensue whenever processes 
are resorted to which bring the chlorine into an active state. 
When we expose acetic acid and chlorine to the sun, the latter 
becomes active, gains the quality of uniting with hydrogen, and 
chloroacetic acid forms. Probably the same change could be 
brought about by the aid of spongy platina and heat. 
