B.—CHEMISTRY. 35 
ray method of analysis. It was the chemical work of Soddy, Russell, 
_ Fleck and Fajans, establishing the fact that two or more elements, differing 
in atomic weight but identical in chemical properties, could occupy the 
same position in the periodic classification, which opened up this new and 
extraordinarily important and interesting field of research. 
Two physical doctrines, originating outside of chemistry, have had and 
are having a profound influence in the science—the ionic hypothesis and 
Bohr’s hypothesis as to the internal structure of the atom. The former has 
had its opponents among chemists, although it has been generally accepted. 
One can understand the uneasy feeling of the chemist habituated to dealing 
with real things, when presented with formule which are only strictly 
valid for infinitely dilute solutions, and are apt to break down when the 
solution reaches the concentrations at which he is accustomed to work in 
the laboratory. The modern work on the hydration of ions has made it 
more possible to reconcile the theory with the facts, but at the expense of 
additional complications. Invaluable as the conception is to the physical 
chemist, therefore, I venture to think that it should be used sparingly in 
the elementary teaching of chemical reactions. [ have in view more 
particularly the teaching of analytical chemistry. A text-book of that 
subject, written entirely in the language of ions, is apt to lead the student 
to believe that the truth of the statements he is reading is bound up with 
that of the hypothesis, and to obscure the fact that the analytical reactions 
were firmly established by experiment without reference to any hypo- 
thesis, whilst they are carried out in solutions so concentrated that a 
strict application of the formule is practically impossible. This view may 
be somewhat heretical, but I submit it for the serious consideration of 
teachers, particularly of those who have to train professional analysts, 
in whom skill and accuracy are all-important. 
The development of the theory of atomic structure, due mainly to 
Bohr, has necessarily affected modern views of chemistry. The theory 
was devised to explain the phenomena of radiation, and later proved to 
accommodate itself in a wonderful manner to those of chemical union, 
making use for the purpose of Werner’s doctrine of co-ordination, another 
successful chemical theory which I have passed over in the foregoing 
sketch. In its new form it promises to do much to reduce to order the facts 
_ of inorganic chemistry, still so far behind the organic part of the science 
in the perfection of its logic. The static atom of Langmuir, now abandoned, 
played an important part in bridging over the gap between the planetary 
arrangement, chiefly suited to the explanation of spectra, and the present 
highly developed system. Whilst recognising the immense value of the new 
ideas, may I once more venture to utter a word of warning? The modern 
tudent, in these days of higher certificates and honours degrees, tends to 
‘Specialise in his scientific studies at a very early stage, and, if introduced in 
detail to the new conceptions while still engaged in learning the elementary 
facts of chemistry, is likely to suppose that the facts depend on the theory, 
‘instead of the opposite being true. In place of describing the facts deter- 
_ mined by analysis, a student in such a position will first give an account 
of the electronic arrangement of the atoms in question, and then proceed 
_ to deduce the formation of a compound, the existence of which had been 
_ proved a century or so ago. The danger may seem to be exaggerated, 
but it is nevertheless real. I would submit that the facts should be known 
to the student before he applies to them this interpretation, which may 
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