The term non-metallic is one, as its name signifies, of exclusion, being founded on a previous appreciation of the term metallic. Hence the general properties of metals should be glanced at in this course. All the more common members of the metallic group possess certain external qualities, which create, we scarcely know why, an appreciation of their nature, and bespeak for them the denomination of metals, as being consistent with certain preconceived notions we had formed of them. Nevertheless it is difficult, perhaps impossible, to specify the exact nature of a metal by associating it with any one unvarying set of qualities. Thus, although great specific gravity is a characteristic of most metals, potassium and sodium are so light that they swim in water. A certain lustre, termed metallic, is also another leading quality of metals; but this is also participated by the non-metallic body, iodine, and is absent in certain metals. Opacity, again, is an almost universal characteristic of metals, as we see them; but gold has been beaten into leaves so fine* as to become partially transparent,—not in consequence of any cracks, holes, or fissures, but by the shining of light through its sub

One two hundred thousandth of an inch in thickness. The light transmitted is green, although the incident.ray was white; thus negativing the supposition of a mere passage through orifices in the gold, and proving the metal to possess a true refractive power,-unequal for different colours of light, as is the case with most transparent media. Silver leaf only one hundred thousandth of an inch in thickness is perfectly opaque.

stance. This phenomenon renders the supposition probable that other metals might also become transparent, provided they were sufficiently malleable to be beaten out into leaves of the necessary fineness; and thus we are obliged to relinquish the idea of opacity as being necessarily a quality of metallic bodies.

Power of conducting electricity is another general quality of metals; but it cannot be said to characterise this class absolutely, seeing that it is also participated by certain non-metallic elements. Although not universal for all metals, the three qualities mentioned,that is to say, great specific gravity, peculiar lustre, and facility of conducting electricity,—are the most general. Amongst the less general qualities of metals are, malleability, or power of extension under the hammer,ductility, or the property of being drawn out into wires,—brittleness, or hardness:-properties which belong to certain classes of metals, and not to others; thus enabling us to arrange them in groups. Although then it be not possible to define with logical precision the term metal, yet the possession or the absence of certain qualities has sufficed to fix with sufficient exactness the limits between the metallic and the non-metallic in our list of sixty-two or sixty-three elementary bodies.

*The ancients designated them by the names of the planets to which they were supposed to have some mysterious relation; and each was denoted by a particular symbol, representing both the metal and the planet. This planetary designation was adopted by the alchemists, and forms the basis of some chemical and medical terms now in use. Thus we have "Lunar caustic," or fused nitrate of silver; "Martial pyrites" of native sulphuret of iron; “Mercury" is even now as much a term as quicksilver; and "Saturnine paralysis" is paralysis caused by salts of lead.

Iron malleable

Iron cast.

Manganese

require the highest heat of a
smith's forge.

Nickel, nearly the same as cobalt.

Infusible

Palladium.

TABLE OF THE ACTION OF SULPHURETTED HYDROGEN (HYDROSULPHURIC ACID) AND HYDROSULPHURET OF AMMONIA ON

* Metals admit of division into three primary classes, viz., kaligenous, terrigenous, and calcigenous-the distinction between which is founded upon the different qualities of metallic oxide. Metals, which by combination with oxygen form alkalies, are termed kaligenous, and are potassium, sodium, and lithium. Those which by combination with the same form earths, are termed terrigenous, and are calcium, forming lime; barium, and strontium, forming respectively baryta and strontia. Magnesium, aluminium, yttrium, thorium, glucinium, cerium, lanthanium, didymium, zirconium; all the remaining metals, form neither alkalis nor earths by union with oxygen, but generate substances which early chemical authors termed calces. Hence the term, calcigenous. Calcigenous metals are alone affected by hydrosulphuric acid and hydrosulphate of ammonia.