AT THE MOMENT OF CHEMICAL CHANGE. 
771 
the element is obvious, it being plain that the reduction of oxide of silver* into 
oxygen gas and the metal, differs only from the spontaneous decomposition of the 
chloride of nitrogen in the temperature at which it takes place. 
In the preceding statement, I have used the word polar to express that alternate 
difference of the condition of the particles by which I conceive chemical action to be 
propagated. It is no objection to the use of this word that it is undefined, and that 
I have not pointed out in what this difference consists. It may be a real difference, 
which we can use for purposes of thought and inquiry, and yet an unknown difference, 
to which we cannot at present assign a true value. A more serious objection lies in 
the way in which this word has been misused, and the false associations which, in 
some minds, are connected with it. It is, however, not difficult for those who must 
ultimately fix the meaning of this term, to draw the distinctions necessary to its right 
application ; and as I myself have found the word very useful, and also found that 
through the associations which are rightly connected with it, it conveyed to some 
persons, whose opinion was well worth considering, an idea which could not other- 
wise have been so simply given, I have here used it. At the same time let me ob- 
serve, that that to which I wish to direct the attention of chemists, is to a new ana- 
logy between certain chemical changes and to the correlation of phenomena which 
have not before been grouped together, and, provided that analogy and relation be 
recognized, the word by which it is expressed is of less importance-^. I now pro- 
ceed to an experimental inquiry which originated in the considerations I have here 
given. 
The discoverer of the peroxide of hydrogen, Thenard, observed certain singular 
and remarkable properties of this compound, of a kind altogether new and calculated 
to fix the interest and attention of chemists. To prepare the peroxide of hydrogen, 
according to his directions, is a process so troublesome and tedious, that it may 
have deterred chemists from the further and full investigation of these pheno- 
mena. It is at any rate to Thenard alone that we owe whatever knowledge we 
possess of this singular body. Since his investigation, which dates from the year 
* In certain cases we can trace the very mode in which this decomposition hy heat takes place. Thus in the 
decomposition of chlorate of potash by heat, the true way in which this substance is decomposed is, as disco- 
vered by Serullas, the decomposition of one particle by the next. The chlorate is first oxidized to perchlo- 
rate, and this perchlorate, as shown hy Millon, again reduced to chlorate with evolution of oxygen. Thus the 
action proceeds by a continual oxidation and reduction of the substance, the phenomena being very similar to 
the oxidation of the chromic acid by the peroxide of hydrogen and the spontaneous decomposition of the com- 
pound formed. By mixing the chlorate of potash with oxide of copper, the formation of the perchlorate is en- 
tirely prevented, and the action converted into one of spontaneous decomposition. 
t The idea of polarity has been applied to the explanation of chemical phenomena by other chemists as well 
as myself. I may refer especially to Lowig’s Introduction to his Organic Chemistry (vol. i. p. 1. Edition 1845). 
Graham also has given, in the last edition of his Treatise on Chemistry, a chapter on Chemical Polarity. It 
would be out of place to enter here on any criticism of their views or comparison of them with my own, but I 
give the reference for those who may be desirous to see the way in which others have treated this subject. 
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