continuous oxidation increases in weight.

I have preserved pure tin for many years without its changing
its silvery luster, while different alloys of this metal which
I have prepared for technical purposes have behaved quite
otherwise.

I have seen in the museum at Cortonne Etrusean inscriptions
upon plates of pure lead which are perfectly preserved to this
day' although they date from very ancient times; on the other
hand, I have found with astonishment in the gallery of Florence
that the so-called "piombi" or leaden medallions of different
popes, in which tin and possibly some arsenic have been mixed
to make them harder and more beautiful, have fallen completely
to white powder, or have changed to their oxides, though they
were wrapped in paper and preserved in drawers.

In the same way I have observed that the alloy which was used
for soldering the copper plates upon the movable roof of the
observatory at Florence has changed rapidly and in places of
contact with the copper plates has gone over into a white
oxide.

I have heard also in England that the iron nails which were
formerly used for fastening the copper plates of the sheathing
of ships were attacked on account of contact, and that the
holes became enlarged until they would slip over the heads of
the nails which held them in position.

It seems to me that this is sufficient to show that the metals