PRESIDENTS ADDRESS—SEOTION B. 53 
planation of them had been attempted, and in these instances 
the explanations advanced were vague, or even, as in the case 
of phlogiston, calculated to retard rather than advance chemical 
progress. It is Lavoisier’s supreme merit to have grasped the 
full significance of the discoveries of Black, Priestley, and 
Cavendish, and to have evolved order out of all this confusion. 
We owe more than this to Lavoisier. To him is due the proof by 
quantitative methods of the indestructibility of matter. To him 
also we owe the definition of an element as the simplest form of 
matter. He also establish®@ a rigid system of nomenclature for 
chemical substances, the principles of which are retained to this 
day. 
It is the establishment of these three luminous generalisations, 
the indestructibility of matter, the explanation of the phenomena 
attending combustion, and the definition of an element, that has 
rendered possible the later development of the atomic and mole- 
cular theories, and the science of modern chemistry may be fairly 
said to date from Lavoisier. 
To Boyle is to be assigned the supreme merit of pointing the 
direction along which chemical science should progress, and the 
methods which should be adopted. To Black, Cavendish, and 
Priestley we owe the great experimental first fruits of this new 
method of investigation ; to Lavoisier, the explanation of these 
discoveries and the establishment of chemistry as a science. 
Since Lavoisier’s time, the history of chemical progress has 
been of almost bewildering rapidity, and instead of finding our 
landmarks scattered and ‘separated by hundreds of years from 
each other, they crowd so quickly on each other’s heels that the 
difficulty is to pick out the salient features in the ever-accumulat- 
ing mass of fact and theory. 
I shall be able in the limited time allowed to do little more 
than mention them, and attempt to show their proper position 
in the general advance, and their connection with prior and 
later discoveries. 
We shall have to leave the strictly chronological order which 
I have hitherto attempted to follow, and trace the development 
of discovery along one or two of the numerous branches of 
research. 
STOECHIOMETRY. 
The introduction of quantitative methods, and the clear under- 
standing of what was meant by the terms, elements and chemical 
compounds, paved the way for the study of the quantitative com- 
position of compounds, or stoechiometry. The fundamental 
stoechiometrical laws are the following :—Proust’s (1806) law 
that chemical compounds consist invariably of the same ele- 
ments by the same proportion of weight; Berzelius’ law of 
