170 
Proceedings of the Royal Irish Aeadeniy. 
To specify, or enter too fully into these niceties, would needlessly 
encnmber my report witli extraneous matter ; and I have therefore 
determined to leave such points to the reader's discrimination, except 
in a few special cases. 
We may have various phases of decomposition, according to the 
force with which the molecular fragments of a compound are held 
together; and it is immaterial whether we consider such bodies as 
built up by the direct addition of molecules or by substitution. Com- 
pounds of a complex nature must be viewed as an aggregation of 
perfect entities, capable of having an individual existence ; but these 
component molecules cannot be taken into account when we are con- 
sidering the more complicated molecule — e.g., morphia splits up, on 
the application of heat, into apomorphia and water — no one could for 
a moment' suppose that the molecule H2O existed as water in the mor- 
phia, as its removal radically changes all the properties of the resulting 
compound. The more complex molecule has peculiarities which are 
not common to its factors, and vice versa. 
The importance of a study of such points in connexion with che- 
mical geology is almost self-evident ; but I may as well state that in 
this report the subject has been merely considered from a chemical 
point of view. The surface of the earth has been, and is, undergoing 
superficially a rapid change from its primitive condition of igneous 
construction. This change is continuously going on, and growing 
more and more profound. In this metamorphosis, water may be consi- 
dered as the prime mover towards the ultimate results of the chemical 
as well as the physical arrangement of our earth's surface. Such a 
line of study is as invaluable as it is difficult ; and it will be my en- 
deavour, more to open up this line of research than attempt to master 
even a moiety of such knowledge. 
Compound molecules exist as solids, liquids, and gases, provided 
that the temperature necessary to convert them into these physical 
modifications is not above the temperature at which their components 
are dissociated. The application of heat to a molecule may be graphi- 
cally, although perhaps rather fancifully represented by the annexed 
figure : — 
Solid. I a 
Liquid. 
l^ow, we can easily conceive that a substance A may be of sufficient 
structural stability to pass through all the increasing vibratory action 
without dissociation of its component molecules, until it has passed 
through the solid, liquid, and far into the vaporous condition, whilst a 
substance B has, what I will call, a thermanalytic point, or the point 
where the equilibrium upon such a line is broken. If it lies between 
a or /3, we have dissociation in the liquid condition. A great number 
of compounds are dissociated above the point /3 (e.g., anomalous 
1/3 
Gaseous. 
