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CLASS IV.

METALLIC SUBSTANCES.

T HE metallic fubftances are now to be confidered as the FourthClafs of the objects of Chemiftry.

They probably attracted the attention of mankind at firft by theirfhining furface. But when their nature and properties became betterknown, they were valued as materials with which we can eafily exe-cute many purpofes in arts which cannot be attained without them.The qualities which render them ufeful and valuable are,into , Their fufibility and malleability, by which we are enabled tomelt different maffes of them into one, or eafily to divide large onesinto fmall ones, and to mould or hammer, or otherwife work theminto the forms which our purpofes require.

2^0, The ftrong cohefion of their parts, in confequence of whichthey are the proper materials for all parts of machinery, or otherworks in which great ftrength or long duration is required.

3*0, The different degrees of hardnefs and elaflicity which fome ofthem can be made to aflume, render them highly ufeful to us on in-numerable occafions, for the fabrication of tools, fprings, and manyother implements neceffary in the arts.

4 to, The denfity of their fubftance, which is impenetrable to water,and moft other kinds of matter, is one more of their ufeful qualities.And,