PRESIDENTIAL ADDRESS. 425 
The mineral world apparently owes its rigidity to the fact that the 
metals and certain other elements are so imperfectly capable of dominating 
oxygen that oxides generally polymerise with great readiness, giving rise 
to substances which do not even fuse easily. The organic, on the other 
hand, appears to be plastic by reason of the close approach to neutrality 
which is conditioned by association with carbon, 
Nothing is more striking than the remarkable diversity of properties 
manifest both in the materials which at present we are content to call 
elements and in the compounds formed by their interaction ; the range of 
variation met with in the case of the compounds of carbon with hydrogen 
and oxygen alone is almost infinite. We are almost compelled to attribute 
this diversity more to differences in the complexity and structure of the 
molecules than to differences in their material composition. The chemist, of 
necessity, must be a dreamer, knowing as he does that things are not as 
they seem to be. But this is not sufficiently remembered ; indeed, students 
are systematically trained up in an atmosphere of pretence. The beginner 
is allowed to regard elementary oxygen, for example, as a colourless gas 
which is generally harmless until things are presented to it in a more or 
less heated condition, whereat it takes umbrage and burns them up. He 
would regard elementary carbon as a soft black substance which if smeared 
on the face of the white man makes him look like a nigger, were it not 
that he also learns that at times it is the hardest and whitest substance 
known; of organic chemistry, which alone can give him honest ideas of 
carbon, he is not allowed to hear as I have said. The sting of awakening 
conscience is salved by the introduction of a long Greek word when he is told 
that the two substances, soot and diamond, are allotropic forms of the 
element carbon ; nevertheless he regards them both as elementary carbon. 
Gradually, perhaps, he awakens to a sense of the wrong that he has suffered 
at the hands of his teachers, as he realises that from no one substance can 
- he gather what the properties of an element are, that after all the elemen- 
tary substance is but an ideal—in other words, a mere concept. If appre- 
ciative, he then learns to think of the blandness of water, the sweetness 
of sugar, the sourness of vinegar, the causticity of soda, indeed of every 
distinctive property of every known oxygen compound as more or less 
a property of, more or less conditioned by, the element oxygen: he is 
brought back, in fact, to the position from which Lavoisier started, as he 
realises that the oxygen gas which he inhales is not elementary oxygen; 
he can then perhaps appreciate the wonderful acumen which this greatest 
of chemical philosophers displayed when he wrote: ‘Nous avons donné & 
la base de la portion respirable de l’air le nom d’oxygéne en le derivant de 
deux mots grecs d&vs, acide, yeivoua, j’engendre, parce qu’en effet une des 
propriétés les plus générales de cette base est de former des acides en se 
combinant avec la plupart des substances. Nous appellerons donc gaz 
oxygene la réunion de cette base avec le calorique.’ We have allowed a 
century to pass without recognising the wonderfully accurate powers of 
prevision displayed by Lavoisier ; what is worse, we have been so far led 
astray that instead of regarding oxygen as the characteristic and attractive 
element in acids, hydrogen has been allowed to usurp the position: the 
extent to which the cult of the hydrogen ion now dominates the text-books 
they not only grow when placed in solutions but determine the separation of 
solids from solutions at a degree of saturation which is often considerably below 
that at which the solution is actually saturated with the substance; and such 
surface affinity, moreover, is selective, as the determinative effect is exercised 
only upon the substance itself or substances isomorphous with it—although 
exception must be made in favour of water, which all surfaces appear to attract. 
Sir James Dewar’s observations on the condensation of gases by charcoal at low 
temperatures afford most striking illustrations of surface affinity. 
