as connected with the Theory of Substitutions. 365 
Upon the second fact,—the similarity of function discharged 
by the chlorine which has replaced the hydrogen atoms with the 
function of those atoms themselves,—a flood of light is thrown 
by other phenomena of allotropism. Ifa piece of iron be dipped 
in hydrated nitric acid, though it may be acted on for a few mo- 
ments, it rapidly becomes passive. And so with the chlorine 
atoms which have substituted the hydrogen. In the circum- 
stances in which they are placed they rapidly revert from the 
active to the passive state. They are no longer endued with an 
intense electro-negative quality,—they have assumed the condi- 
tion of inactivity. The fact that chlorine in chloracetic acid 
simulates the functions of hydrogen in acetic acid, is not more 
remarkable than that iron touched by platina 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, the phenomena of substi- 
tution are deprived of much of their singularity. 
Thus, to recall once more the example to which I have before 
referred, and which has been so well illustrated by the researches 
of M. Dumas, the transmutation of acetic into chloracetic acid 
exhibits a double phenomenon. Ist. The existence of active 
chlorine, expressed by the removal of hydrogen, activity having 
been communicated by the rays of the sun, or by some other ap- 
propriate method. 2d. The existence of passive chlorine in the 
particles of chloracetic acid. 
I consider that were no other instances known, the two cases 
cited by Berzelius of the double forms of silicic acid and arse- 
nious acid establish the fact, that a given allotropic condition 
may be continued*by an elementary atom when it goes into union 
with other bodies. And I regard the various cases in which hy- 
drogen is replaced by iodine, bromine, &c., in which, in the re- 
sulting compound, those energetic electro-negative elements fail 
to give any expression of their presence and activity, as analogous 
to other common and too much overlooked facts. Chlorine which 
is in the dark, may be kept in contact with hydrogen without 
exhibiting any of its latent energies. Touched by an indigo ray, 
it instantly assumes the active state, and a violent explosion is the 
result. 
Vol. xt1x, No. 2.—July—Sept. 1845. 47 
