41 
sent state of chemical knowledge. It is probable, 
that as yet we are not acquainted with any of the 
true elements of matter ; many substances, for- 
merly supposed to be simple, have been lately de- 
compounded, and the chemical arrangement of 
bodies must be considered as a mere expression 
of facts, the results of accurate statical experi- 
ments. 
Vegetable substances in general are of a very 
compound nature, and consist of a great number 
of elements, most of which belong likewise to the 
other kingdoms of nature, and are found in vari- 
ous forms. Their more complicated arrangements 
are best understood after their simpler forms of 
combination have been examined. 
The number of bodies which I shall consider 
as at present undecomposed, are, as was stated in 
the introductory lecture, five acidifying or solvent 
substances, eight inflammable bodies, and forty 
metals. 
In most of the inorganic compounds, the na- 
ture of which is well known, into which these 
elements enter, they are combined in definite pro- 
portions ; so that, if the elements be represented by 
numbers, the proportions in which they combine 
are expressed either by those numbers, or by some 
simple multiples of them. 
I shall mention, in a few words, the character- 
istic properties of the most important simple sub- 
stances, and the numbers representing the propor- 
tions in which they combine in those cases, where 
they have been accurately ascertained. 
1. Oocygene forms about one-fifth of the air of 
