more complete if the tin had been again separated from 
the gold by muriatic acid, and the gold had been weigh- 
ed before and after the operation, but if this statement is 
accurate (which there is no apparent reason to doubt) it is 
a curious fact, and one for which in addition to M. Gado- 
lin’s explanation, we must probably refer to the late dis- 
covered experiments in Galvanism. This is confirmed 
by the circumstance that in every one of the experiments 
on tinning above related, the presence of two dissimilar 
metals in the reguline state is required, so that the mo- 
ment the metallic tin is withdrawn from the tartareous 
solution the precipitation of tin upon copper ceases** 
though we can hardly suppose that any immediate change 
in the state of oxygenation of the solution takes place. 
With respect to the circumstance of no copper being 
found in the solution of tartar after common tinning, we 
may observe however that the failure of the usual test of 
the volatile alkali is no certain proof of the absence of this 
metal in this instance, as the later discoveries of Proust 
on this subject (which are detailed under the article Cop- 
per J shew that when copper is in solution with tin in a 
low state of oxydation, it is so far deprived of oxygen by 
the tin, as not to turn blue with ammonia. 
The experiments in which iron, copper, and tin were 
immersed into a solution of tin, are complicated, and the 
exact operation of all the affinities between the respective 
substances is not easily made out. The order of preci- 
pitation with a single metal, and a single metallic solution, 
is copper, tin, iron ; that is to say, iron immersed into a 
solution of tin displaces the tin, and precipitates it most- 
ly in the metallic form ; and tin immersed into a solu- 
tion of copper precipitates the latter metal. But in the 
above complicated case both the iron and copper be- 
come tinned, so that the tinning of the iron may be ef- 
fected by simple and direct affinity, but that of the cop- 
