on the fixed Alkalies. 
33 
been uniformly adopted, yet the motive for employing it has 
been rather a sense of its beauty and precision, than a convic- 
tion of its permanency and truth. 
The discovery of the agencies of the gasses destroyed the 
hypothesis of Stahl. The knowledge of the powers and 
effects of the etherial substances may at a future time possibly 
act a similar part with regard to the more refined and inge- 
nious hypothesis of Lavoisier ; but in the present state of our 
knowledge, it appears the best approximation that has been 
made to a perfect logic of chemistry. 
Whatever future changes may take place in theory, there 
seems however every reason to believe that the metallic bases 
of the alkalies, and the common metals, will stand in the same 
arrangement of substances ; and as yet we have no good 
reasons for assuming the compound nature of this class of 
bodies.* 
The experiments in which it is said that alkalies, metallic 
oxides, and earths may be formed from air and water alone, 
in processes of vegetation, have been always made in an in- 
conclusive manner ;*f- for distilled water, as I have endeavoured 
* A phlogistic chemical theory might certainly by defended, on the idea that the 
metals are compounds of certain unknown bases with the same matter as that exist- 
ing in hydrogene; and the metallic oxides, alkalies and acids compounds of the same 
bases with water but in this theory more unknown principles would be assumed 
than in the generally received theory. It would be less elegant and less distinct. 
In my first experiments on the distillation of the basis of potash finding hydrogene 
generally produced, I was led to compare the phlogistic hypothesis with the new facts, 
and I found it fully adequate to the explanation. More delicate researches however 
afterwards proved that in the cases when inflammable gasses appeared, water, or 
some body in which hydrogene is admitted to exist, was present. 
f The explanation of Van Helmokt of his fact of the production of earth in the 
growth of the willow, was completely overturned by the researches of Woodward, 
Phil. Trans. Vol. XXI. page. 193. 
MDCCCVIII. F 
