PROGRESS OP CHEMISTRY. 
623 
metals, most remote'in their properties from those volatile 
and unstable substances of organic chemistry, have been got 
in many instances to combine together, and the organic 
metallic bodies thus formed have not only proved most 
valuable and powerful agents of decomposition, but they have 
served as a connecting link between the two branches of 
chemical science. A system of classification of elements is 
now coming into use, in which the heavy metals arrange 
themselves harmoniously with the elements of organic bodies, 
and in accordance wfith the principles w’hich were discovered 
b}^ a study of organic compounds. It is now many years 
since the attention of chemists was directed by a French 
professor to some inconsistencies which had crept into our 
system of atomic weights. Gerhardt showed that the prin¬ 
ciples which were adopted in fixing the atomic weight of 
elementary bodies generally required us to adopt for oxygen, 
carbon, and sulphur, numbers twice as great as those gene¬ 
rally in use for those elements. The logic of his arguments 
was unanswerable, and yet GerhardFs conclusions gained 
but fe\v adherents. It is to be observed that for some years 
Gerhardt represented chemical reactions by so-called synoptic 
formulae, which took no account of the existence of organic 
radicles. These synoptic formulae represent in the simplest 
terms the result of a chemical reaction, but they give no phy¬ 
sical image of the progress by which the reaction is brought 
about. The introduction, in this country, of the water type 
in connection with poly-atomic as well as mon-atomic 
radicles, was found to satisfy the requirements of the synoptic 
formulae. Gerhardt was the first to adopt them from us. 
He gave, in his admirable ‘Traite de Chimie Organique,^ a 
system of organic chemistry on that plan, and his book has 
been of immense service to the development of our science. 
The extension of these principles to mineral chemistry had 
been commenced in the cases of the commonest acids and 
bases, but their general introduction met with difficulties, 
and sometimes seemed wanting to their complete success. I 
must now travel southward for a short time, and ask you to 
accompany me to that sunny land of glorious memories, and 
to its southern dependency—the island of Sicily. It was 
reserved for Professor Cannizzaro, of the University of 
Palermo, to show us how the remainder of the knot could be 
untied. He argued, upon physical as well as chemical 
grounds, that the atomic weight of many metals ought to be 
doubled, as well as those of oxygen, sulphur, and carbon. 
His conclusions are confirmed by the constitution of those 
*r 
organo-metallic bodies which I mentioned just now, and it 
