430 TRANSACTIONS OF SECTION B. 
out the relation between isomorphism and molecular structure. When it is con- 
sidered how little is known of solid or liquid structure, and that our present 
knowledge of molecules is only of gaseous molecules, it is fortunate that these 
methods of study of solids are available The same may be said of the results 
of the work of Kopp and his successors on molecular volumes. Of other aids 
to fixing our conception of molecules and atoms I need only refer to the periodic 
law, the studies of the properties of dilute solutions, of electrolytic dissociation, 
and of surface tension of liquids. 
Liebig, in his first inquiry, begun before he went to Gay-Lussac in Paris, 
proved that silver fulminate and silver cyanate, though distinct substances, 
had exactly the same composition; thus was opened that great chapter in the 
history of chemistry which Berzelius named isomerism. Perhaps nothing in 
chemistry has given rise in recent years to more intellectual and practical 
activity than isomerism. Wohler’s classical synthesis of urea, by the meta- 
stasis of ammonium cyanate, added another instance of isomerism, and Berzelius 
soon afterwards announced the isomerism of tartaric and racemic acids. 
Wohler’s synthesis of urea, followed, as it was, by numerous other laboratory 
syntheses, showed that substances which occur in living organisms are not 
different from those which may be prepared artificially, and the old distinction 
between inorganic and organic chemistry disappeared—there is, of course, 
only one chemistry. The words, it is true, have survived, but only for reasons 
of practical convenience. 
After isomerism the next great step forward in the study of intra-molecular 
structure was the discovery of groups partially individualised which are capable 
of remaining intact through many reactions. Gay-Lussac had previously 
noticed the Cyanogen group as common to cyanides; but it was the celebrated 
paper by Wohler and Liebig on ‘The Radical of Benzoic Acid’ which finally 
established the existence of compound radicals or groups such as benzoyl, and 
obtained for the theory of compound radicals the position in chemistry it now 
holds. Bunsen followed somewhat later with the discovery of cacodyl, and now 
such groups are almost innumerable. In many respects, by the experimental 
skill which it shows, the clearness of its logical method, and the beauty of its 
form and diction, this memoir is a model of what a scientific communication 
should be. I will read the opening paragraph, using Hofmann’s translation : 
“When a chemist is fortunate enough to encounter, in the darksome field of 
organic nature, a bright point affording him guidance to the true path by follow- 
ing which he may hope to explore the unknown region he has good reason to con- 
gratulate himself, even though he may be conscious of being still far from the 
desired goal.’ Of this memoir Berzelius, in a letter quoted by Hofmann (Faraday 
lecture), says: ‘The facts put forward by you give rise to such considerations 
that they may well be regarded as the dawn of a new day in vegetal (organic) 
chemistry.’ 
The history of the advance of chemistry since the days of the Giessen 
jahoratory is bewildering in its extent. This has been largely due to the 
Giessen laboratory itself, which sent trained investigators, each carrying with 
him some touch of its master’s magic, into all civilised lands. I cannot attempt 
to even catalogue the results here. One thing may be said, that chemistry is 
not worked out, as some have thought; but rather the opportunities of dis- 
covery seem greater and more promising than at any previous period. 
Parr II. 
Whether in the light of recent researches it may become necessary to give 
up that portion of Dalton’s theory of atoms in which he regards them as 
undecomposable and indivisible; or whether we may consider them, 
Sub-atoms,- as Prout suggested a hundred years ago, as different aggregates 
atoms, mole- of sub-atoms of a uniform kind of matter; or whether they must 
cules, mole- be regarded as complexes built in the manner supposed by the 
cular aggre- electron hypothesis; also what should be our attitude towards the 
gates ; related problem of transmutation—all this I pass over, the more 
valency. willingly that these subjects were discussed so recently by so high 
an authority as Sir William Ramsay in his address to the Association 
last year at Portsmouth. 
I assume that we are fairly satisfied with our present atoms and their 
a 
