, is one of the most
annoying substances in the treatment that you can imagine, because it is
not volatile; and while the iron remains adhering to the platinum, the
platinum will not flow readily. It cannot be sent away by a high
temperature--sent into the atmosphere so as to leave the platinum behind.
Well, then, a hundred parts of ore and a hundred parts of sulphuret of
lead, with about fifty parts of metallic lead, being all mingled together
in a crucible, the sulphur of the sulphuret takes the iron, the copper,
and some of the other metals and impurities, and combines with them to
form a slag; and as it goes on boiling and oxidising, it carries off the
iron, and so a great cleansing takes place.

Now, you ought to know that these metals, such as platinum, iridium, and
palladium, have a strong affinity for such metals as lead and tin, and
upon this a great deal depends. Very much depends upon the platinum
throwing out its impurities of iron and so forth, by being taken up with
the lead present in it. That you may have a notion of the great power that
platinum has of combining with other metals, I will refer you to a little
of the chemist's experience--his bad experience. He knows very well that
if he takes a piece of platinum-foil, and heats a piece of lead upon it,
or if he takes a piece of platinum-foil, such as we have here, and heats
things upon it that have lead in them, his platinum is destroyed. I have
here a piece of platinum, and if I apply the heat of the spirit-lamp to
it, in consequence of the presence of this little piece of lead which I
will place on it, I shall make a hole in the metal. The heat of the lamp
itself would do no harm to the platinum, nor would other chemical means;
but because there is a little lead present, and there is an affinity
between the two substances, the bodies fuse together at once. You see the
hole I have made. It is large enough to put your finger in, though the
platinum itself was, as you saw, almost infusible, except by the voltaic
battery. For the purpose of shewing this fact in a more striking manner, I
have taken pieces of platinum-foil, tin-foil, and lead-foil, and rolled
them together; and if I apply the blowpipe to them, you will have, in
fact, a repetition on a larger scale of the experiment you saw just now
when the lead and platinum came together, and one spoiled the other. When
the metals are laid one upon the other, and folded together and heat
applied, you will n