253 NINETEEN LIL EVENING.

the first place, gold and silver are both perfect metals,
that is, indestructible in the fire. Other metals, if
kept a considerable time in the fire, change by degrecs
into a powdery or scaly matter, called a calx. You
have melted lead, I dare say ?

G. Yes, often.

7. Have you not, then, perceived a arossy film
collect upon its surface, after 16 had been kept melting
a while?

G. Yes.

T. That is a calx ; and, in time, the whole lead would
change to sucha substance. You may sce, too, when
you have heated the poker red hot, some scales separate
from it, which are brittle.

H, Yes—the kitchen poker 1s almost burnt away, by
putting it mto the fire.

T. Well—all metals undergo these changes, except
gold and silver; but these, if kept ever so long in the
hottest fire, sustain no loss or change. ‘They are,
therefore, called perfect metals. Gold has several
other remarkable properties. It is the heaviest of all
metals.

HT, What, is it heavier than Icad P

Z. Yes—about half as heavy again. It is between
nineteen and twenty times as heavy as an equal bulk
of water. This great weight is a ready means of dis-
covering counterfeit gold coin from genuine; for as
gold must be adulterated with something much lighter
than itself, a false coin, if of the same weight with the
true, will be sensibly larger. Gold, too, is the most
ductile of all metals. You have seen leaf-gold ?

G. Yes; I bought a book of it once.

Z. Leat-gold is made by beating a plate of gold,
placed between pieces of skin, with heavy hammers,
till it is spread out to the utmost degree of thinness.
And, so great is its capacity for being extended, that a
single grain of the metal, which would be scarcely
larger than a large pin’s head, is beaten out to a sur-
face of fifty square inches.