Mr. Spitspury on a Single Galvanic Combination. 81 
pieces of pure platina foil were subjected to examination; but 
whatever was the difference of surface between the two plates (and 
in some experiments this was very considerable), or whether the 
acid was nitric or nitro-muriatic, assisted by heat, in neither case 
was the slightest action on the instrument to be detected. Coarse 
silver (which is finer than standard) gave evidence of magnetism, 
yet pure silver had no such effect. May we not then justly con- 
clude, that, in those cases where magnetism is produced by two 
bars of the same metal, it arises from that metal containing other 
substances in combination with it?) This conjecture is further sup- 
ported by this fact; the copper of commerce is incapable of acting 
upon the galvanoscope, except when the surfaces under oxidation 
are very extensive, or at least when one surface very materially 
exceeds the other in extent. The grain-tin of commerce also re- 
quires a similar extension of surface; though not in so great a 
degree as copper. Upon chemical examination this tin was found 
to contain a minute portion of zinc and manganese, both metals 
highly electro-negative to tin. The copper was not examined ; 
the most probable impurity would be antimony, arsenic, or lead, 
neither certainly very electro-negative metals. If this supposition 
be correct, the different degrees of intensity in the two may be 
easily accounted for. 
Should future experiments confirm the truth of these views, 
we nay probably have it in our power to construct an mstrument, 
by which the relative quantities of two metals in any alloys shall be 
discovered ; without having recourse to the more laborious method 
of humid analysis. The infinite service this would be in many 
departments of the arts, particularly in that of assaying, is evident. 
Also by submitting in turn each of the known metals, to the action 
of this test, very possibly we shall have it in our power to shew, 
as far as analogy can shew, the compound nature of some, which 
have hitherto been considered simple undecomposed bodies. It is 
Vol. VI. Part I. L 
