really do not see how they could, and think it much more probable that
they fall from the moon. --But we must not suffer this digression to
take up too much of our time.

The combinations of metals with each other are called alloys; thus brass
is an alloy of copper and zinc; bronze, of copper and tin, &c.

EMILY.

And is not pewter also a combination of metal?

MRS. B.

It is. The pewter made in this country is mostly composed of tin, with a
very small proportion of zinc and lead.

CAROLINE.

Block-tin is a kind of pewter, I believe?

MRS. B.

Properly speaking, block-tin means tin in blocks, or square massive
ingots; but in the sense in which it is used by ignorant workmen, it is
iron plated with tin, which renders it more durable, as tin will not so
easily rust. Tin alone, however, would be too soft a metal to be worked
for common use, and all tin-vessels and utensils are in fact made of
plates of iron, thinly coated with tin, which prevents the iron from
rusting.

CAROLINE.

Say rather _oxydating_, Mrs. B. --Rust is a word that should be exploded
in chemistry.

MRS. B.

Take care, however, not to introduce the word oxydate, instead of rust,
in general conversation; for you would probably not be understood, and
you might be suspected of affectation.

Metals differ very much in their affinity for each other; some will not
unite at all, others readily combine together, and on this property of
metals the art of _soldering_ depends.

EMILY.

What is soldering?

MRS. B.

It is joining two pieces of metal together, by a more fusible metal
interposed between them. Thus tin is a solder for lead; brass, gold, or
silver, are solder for iron, &c.

CAROLINE.

And is not _plating_ metals something of the same nature?

MRS. B.

In the operation of plating, two metals are united, one being covered
with the other, but without the intervention of a third; iron or copper
may thus be covered with gold or silver.

EMILY.

Mercury appears to me of a very different nature from the other metals.

MRS. B.

One of its greatest peculiarities is, that it retains a fluid state at
the temperature of the atmosphere. All metals are fusible at different
degrees of heat, and they have likewise each the property of freezing or
becoming solid at a certain fixed temperature. Mercury congeals only at
seventy-two degrees below the freezing point.

EMILY.

That is to say, that in order to freeze, it requires a tem