213 
Mr. Chenevix's Analysis of 
effervescence takes place; hydrogen gas is disengaged, and, in 
less than two minutes, the copper is so completely precipitated 
in the metallic state, that neither ammonia, nor even sulphu- 
rated hydrogen, can discover any vestige of its presence. 
It would appear from this, that hydrogen is, in this case, the 
real reductive and precipitant of the copper. Yet, how can 
we reconcile the evident contradiction that, in one case, zinc 
with muriatic acid will decompose water, that is, that zinc 
and muriatic acid will attract oxygen more strongly than hy- 
drogen can, yet that, in the other case, hydrogen, whose affinity 
for oxygen is weaker than that of zinc and muriatic acid, will 
be more speedy and powerful than zinc and muriatic acid, in 
attracting that oxygen from copper. Again, how is it pos- 
sible that zinc and muriatic acid will, in preference to taking 
oxygen immediately from the oxide of copper, decompose 
water, the hydrogen of which will unite with the oxygen of 
the oxide of copper, again to become water, which it originally 
was. All this appears to me, I confess, as contradictory as to 
say, one is less than two, two are less than three, yet three are 
much less than one. This opinion, that hydrogen is really the 
reductive, is the more extraordinary, as it is not founded on the 
single experiment above-mentioned. 
If a bit of zinc (or tin, or iron,) is thrown into a solution of 
oxide of arsenic in water, no change of any kind will be effected, 
even after a considerable time. But, the instant that muriatic 
acid is added, effervescence and precipitation commence ; a fetv 
minutes suffice to obtain all the arsenic in its metallic state. If 
maybe objected here, that muriatic acid, (as muriatic acid,) 
produces some hitherto unknown modification in the order of 
established affinities. This objection is not plausible ; and I can 
