Tut. That is a principal reason, no doubt. But these metals have intrinsic properties that make them highly valuable, else probably they would not have been chosen in so many countries to make money of. In 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 degrees into an earthy, scaly matter, called an oxide. You have melted lead, I dare say?
Geo. Yes, often.
Tut. Have you not, then, perceived a drossy film collect upon its surface, after it had kept melting a while?
Geo. Yes.
Tut. That is an oxide; and in time the whole lead would change to such a substance. You may see, too, when you have heated the poker red-hot, some scales separate from it, which are brittle.
Har. Yes, the kitchen poker is almost burnt away by putting into the fire.
Tut. 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.
Har. What, is it heavier than lead?
Tut. 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 discovering 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 bigger. Gold, too, is the most ductile of all metals. You have seen gold-leaf?
Geo. Yes; I bought a book of it once.