PRESIDENT’S ADDRESS—SECTION B. 5D. 
The following are amongst the most striking of the relations 
observed between the equivalents of the elements and their other 
properties. 
In 1832 Faraday showed that when an electric current is 
passed through an electrolyte, the quantity of the electrolyte 
decomposed is proportional to the intensity of the current. This 
is known as the law of electrolytic equivalence, and its further 
development will be dealt with later. 
Mitscherlich (1819) discovered the existence of a similarity in 
crystalline structure between substances of similar chemical con- 
stitution. From this is derived the law of isomorphism, which 
states that substances having the same number of atoms com- 
bined in the same way give rise to the same crystalline form. 
The application of this law, though limited, is of enormous im- 
portance, and is of special significance in organic chemistry. 
Dulong and Petit (1819) observed also a relationship between 
the combining weights of the elements and another physical pro- 
perty, namely, their capacity for heat, which they found to be 
inversely proportional to their atomic weights. 
It is notably Berzelius who made use of these equivalents 
in the first determinations of the atomic weights of the elements. 
The recognition of the hypothesis of Avogadro (1811) enabled 
us to determine the relative molecular weights for all gases. 
Avogadro’s hypothesis states that equal volumes of all gases 
contain the same number of molecules. It was announced by him 
in 1811, but its full significance was not recognised until the 
question of the determination of the atomic weights was in a 
more advanced state, and it was reintroduced by Cannizaro in 
1858. This far-reaching and important hypothesis is a direct 
corollary to the Daltonian theory of atoms. To attempt to trace 
its influence on our conception of the nature of matter is quite 
beyond my present task. 
Amongst its important developments were the proof of the 
mechanical theory of heat, upon which is based the now-accepted 
kinetic theory of gases advanced by Joule and Prescott, 1850, 
and the explanation of gaseous diffusion discovered by Graham, 
1831. 
The exact determination of the Stoechiometric values has 
engaged the attention of chemists, amongst the most notable of 
whom have been Berzelius and Stas, whose determination of the 
atomic weights of a number of the elements will always be 
models of exact and painstaking research. Of recent years, and 
especially since the acceptance of the periodic classification 
based on the atomic weights of the elements, the exact deter- 
mination of these weights has been undertaken afresh. Of 
recent workers may be mentioned T. E. Thorpe, G. W. Morley, 
Scott, Cooke, Kaiser and Noyes, &e. 
In 1864, Newlands first drew attention to a remarkable con- 
