52^ Dr, Kidd’s Observations y &c, 
and all the component parts of these may be ultimately re- 
solved into the following elements — oxygen, nitrogen, hy- 
drogen, and carbon, together with iron and the metallic bases 
of some of the earths. 
The component parts of nitrate of potash, of which the 
saltpetre under consideration almost entirely consists, are 
nitric acid, water, and potash ; which may be resolved into 
the following elements — oxygen, nitrogen, hydrogen, and 
potassium : and all these elements are experimentally known 
to be present in the situations where saltpetre is formed, with 
the exception of potassium. 
In the supposition then that the saltpetre is a product and 
not an educt of the above process, since no potash can be 
detected either in the air or limestone, the potassium must 
either be contained in a free state in the atmosphere or in the 
limestone, which from its remarkable attraction for oxygen 
is inadmissible: or it must be a component principle of some 
one of the elements present; or lastly, it must be itself a com- 
pound of two or more of the principles of those elements, or 
of two or more of the elements themselves. 
« 
But I am aware that the saltpetre may be considered as an 
educt of the process, and that it may possibly exist already 
formed in the atmosphere in a state of minute division; yet, 
when we consider the comparatively fixed nature of that salt, 
and that no experiments have yet detected its presence in at-- 
mospherical air, or in the moisture precipitated from atmo- 
spherical air ; and lastly, when we reflect on the probability 
that the metals, of which potassium is one, are compound 
bodies, the former supposition seems upon the whole prefer- 
able to the latter. 
February, 1814. 
