213 
the Arseniates of Copper , and cf Iron. 
adduce so clear an answer to it, as to shew that it is of very 
little moment. If aqueous arsenic acid is used, instead of the 
above solution, the same phenomena of effervescence and pre- 
cipitation ensue, as when muriatic acid had been used in the 
former case ; and that precise quantity of metallic arsenic is 
thrown down, which can yield sufficient oxygen to the zinc to 
combine with the remaining acid undecomposed. The precipi- 
tate which is formed, is a mixture of metallic arsenic with arse- 
niate of zinc ; and these may be separated by muriatic acid, 
which will dissolve the metallic salt, without acting upon the 
arsenic. 
If, instead of muriatic acid, sulphuric acid is used, the same 
phenomena take place, in a less degree. But, if the experiment 
is tried with nitric acid, there is no disengagement of hydrogen 
gas ; and the metals effect a precipitation with much less rapi- 
dity and certainty than in the former case. 
It is very true, that hydrogen, in its nascent state, may have 
properties with which we are yet unacquainted; and may 
determine combinations, which it can in no other state produce. 
But the decomposition of water, in the first instance, in order 
that a new recomposition may, at that moment, be effected by 
the same agents, is in itself sufficiently paradoxical. 
The facts last mentioned, are somewhat analogous to, and 
seem even confirmative of, a theory proposed some time past 
by Mrs. Fulhame; but I shall withhold my full assent, both 
to her explanation and to any I could give, until these evident 
contradictions can in some way be further elucidated. 
In the analysis of every ore in which the metal is combined 
with sulphur, I have found much variation in the quantity of the 
latter which may be obtained, even in experiments upon the 
