JANUARY 19, 1912] 
stances, has placed this almost beyond the pale 
of doubt. The atoms with the largest atomic 
masses are certainly unstable, and it is 
highly probable that the atoms of all the ele- 
ments are undergoing devolutionary changes. 
In the light of these facts are we going to 
persist in teaching the stable atom, without 
qualification even to the beginner, and rely 
upon time, fate or the effort of some one else 
to correct, if possible, the evil that we have 
done ? It is perfectly true that the stable 
atom is simpler for the beginner than the un- 
stable atom, but here again it is simplicity vs. 
truth. 
In conelusion, there is one other matter 
which I can not leave untouched, because it 
lies at the very foundation of our science. 
I submit that no serious student of chemistry, 
and this is the class for which we must be 
most concerned, can study the subject for six 
months, learning that certain things react 
chemically with certain other things, and that 
certain things do not react with one another, 
without asking himself the question, why is 
this? Why do some substances react, and 
why do others not react? If this question is 
not raised by the student it certainly should 
be by the instructor. The question then is, 
why do chemical reactions take place at all? 
We might almost call this the most funda- 
mental question of chemical science. It is 
certainly so for the student, and that in the 
early part of his career. This brings me to 
the most heterodox position that I have yet 
ventured to take. 
Should we not introduce into our elemen- 
tary courses in chemistry something about the 
energy changes that take place in all chemical 
reactions, and which make those reactions pos- 
sible? In the evolution of chemistry the 
material changes were studied first, and this 
was natural. These changes were the most 
obvious, and the material products were often 
desired for one purpose or another. Again, 
these material changes were the easiest to 
study, and chemists, like other men, were 
inclined to follow the lines of least resistance. 
I believe the nineteenth century will go down 
SCIENCE 93 
in the history of chemistry primarily as the 
period of material chemistry. 
But even this is changed now. Without 
decrying in the least the study of matter, the 
chemist of to-day insists that we can no longer 
ignore the changes in energy that manifest 
themselves in every chemical reaction. In- 
deed, he would even go further, and point out 
again that whatever is easiest in science is 
relatively most superficial. 
We know to-day that all chemical reactions 
are really due to differences in the intensity, 
or quantity, or kind of the intrinsic energy 
present in the substances that are to react; 
and whether any two substances will or will 
not react is determined primarily by this dif- 
ference. We can, furthermore, form a phys- 
ical conception now of what is meant by in- 
trinsic energy, since we have the electron 
theory of the atom; it is primarily the kinetic 
energy of the moving electrons within the 
atom. 
But dare we venture even to refer to energy 
or energy changes in the early stages of the 
teaching of chemistry? J ask why not? The 
physicist does not hesitate to do so. Indeed, 
most of his subject has to deal very largely 
with changes in the different manifestations of 
energy. Why should we assume that the 
chemical student has less natural intelligence 
than the student of physics, especially when 
he is almost always the same student? (In 
my opinion no one should be allowed to begin 
the study of chemistry until he has had at 
least one year of physics. 
There is, of course, no reason for assuming 
that the beginning chemist is not as intelli- 
gent as the beginning physicist, and, there- 
fore, there is no more reason why a student of 
chemistry should not deal with changes in 
energy than a student in physics, especially 
when these energy changes are as fundamental 
for chemical science as they are for physics. 
Instead of teaching to-day that chemical 
reactions are accompanied by energy changes, 
why not teach the truth, which is, that it is 
these very energy changes that are the cause 
of all chemical reaction? Systems which 
alone are fairly stable, when brought together 
