762 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
determined by the chemical relation of all the other particles with which they are 
for the time being associated. Substances, the particles of which are to one another 
in this peculiar chemical relation, I term chemically polar. 
The electro-chemical theory was developed before even the true laws of the propa- 
gation of electricity had been discovered, and in the above propositions I have but 
transferred to chemical change some of the more exact ideas as to the nature of elec- 
tric action which have since arisen ; and we may transfer the ideas and mode of 
thought without making any hypothesis as to the mutual relation of the phenomena. 
This is not the place to enter fully on this question, and I shall confine myself to the 
application of these principles to explain certain phenomena of change in compound 
substances, to which I shall presently show the parallel in the case of the element. 
These phenomena are those which go under the name of the ‘‘ phenomena of the 
nascent state.” 
Silver cannot be oxidized by the direct action of oxygen on the metal, but oxide 
of silver is readily formed by boiling the chloride of this metal with potash. The 
particles of oxygen and silver have therefore acquired by this association with the 
chlorine and potassium a chemical relation or affinity which at other times they 
have not. This is the fact. The rational conception of the fact is given in the ex- 
pression 
+ — -i — 
AgClKO = AgO-i-KCl, 
in which I have indicated the polar relation of the substances. The chemical re- 
lation therefore between the oxygen and silver is essentially dependent on the che- 
mical relation betu^een the oxygen and potassium, in the same way as a negative 
and positive electricity are related to each other. The same is true of the relation 
between any other two particles of the system. Hence chemical decomposition is an 
essential condition of chemical combination ; so that when we see one of these events 
we may infer the other. 
On the other hand, where this polar division of the substance cannot take place, 
there is no chemical action, or at any rate it takes place with greater difficulty ; thus 
anhydrous sulphuric acid may (as has been shown by Millon) be distilled off carbo- 
nate of potash without alteration, and generally the so-called anhydrous acids have 
none of the combining properties of the hydrates to which they correspond. The 
reason of this being, that when these bodies combine they do not decompose, and 
that it is by the very fact alone of the decomposition of the substance that the com- 
bining power is developed in the particles of which they consist, so that in the che- 
mical change which is thus represented — 
-|- — H — 
IISO4 K0=H0-hS04K, 
} 
the two combinations which take place are not two combinations accidentally simul- 
