By "tenacity" or tensile strength is unders ance a body offers to an attempt to pull its p when a stretching force is applied. The tena diminished by a rise in temperature, while the the case with regard to malleability and dmetals have a feeble tenacity, and are then sa When a body resists rupture by a bending or it is said to be "tough." Elasticity is a prop in virtue of which they tend to recover their after being subjected to a disturbing force. in every solid body, beyond which it will not original form on the withdrawal of the force; the limit of perfect elasticity. "Hardne measured by resistance to a compressive ford other physical properties of a metal, is m presence of impurities, so that, in many cases test of purity. All malleable metals become pressure, and often require annealing during manufacture. The fractured surface of m characteristic, being spoken of as fibrous, crystal columnar, and conchoidal, thus: wrought-ir zinc is crystalline, steel is granular, tin is colum steel is conchoidal. Crystalline structure companied by brittleness, and fibrous struct tenacity. Most metals are much heavier th the ratio which expresses the number of tin heavier than an equal volume of water is terme gravity." The "specific heat" or the capacity heat extends over a wide range with regard to for example, being that of water, while lea 1 The oxides of metals are usually basic but this property is only relative, as an oxide v in one compound may become acid when a stronger base.

30'

CLASSIFICATION OF METALS

§ 3. Metals may be more conveniently studie

he resist-
asunder
generally

se is often

7.

Some e brittle.

Eng force, f bodies, nd shape s a limit

n to its
s termed

which is
all the
by the

ess is a
ened by
rocess of
s often

ranular, fibrous, nd hard

cen ac

y high
er, and
body is
specific
ody for
; iron,
s than
racter,
s basic

with a

assify

ing them into groups, according as they approxim general characters, based chiefly on their affiniti oxygen.

I. Noble Metals.-Gold, Platinum, Silver, and rare metals. The members of this class have little tendency to unite with oxygen in the free state, an placed in water at a red heat do not alter its comp The oxides are readily decomposed by heat in consequ the feeble affinity between the metal and oxygen.

2. Copper Group.-Copper, Mercury, Lead, and B They do not decompose water, even at a red heat, bu with oxygen when heated, forming oxides of a basic ch Mercury has the least affinity for oxygen, and in this approaches the noble metals in character.

3. Tin Group.-Tin, Antimony, Arsenic, etc. metals, except arsenic, decompose steam at a red he form some oxides of an acid character; in this resembling the non-metals. Protoxide of tin is a base.

4. Iron Group.-Iron, Chromium, Manganese, and Cobalt. Steam is decomposed when brought in with the members of this group at a red heat. TH oxides form powerful bases. Some of the higher of iron, chromium, and manganese form what may be metallic acids, which combine with bases to form soluble in water.

5. Zinc Group.-Zinc, Cadmium, and Magnesium members of this group oxidise slowly in moist air, but when heated. They are readily volatile, and burn with a bright light, producing oxides, which form p bases. At a red heat they decompose steam.

6. Aluminium Group.-Aluminium and allie metals. Aluminium does not oxidise in air or dec water, unless the metal is in a very finely divided sta forms an oxide, which is acid or basic according a allied with a stronger or weaker base.

7. Alkaline-earthy Metals.—Barium, Strontiu

Calcium. These metals rapidly decompose oxides. All the oxides are strongly basic, an with acids.

8. Alkali Metals.-Sodium, Potassium, These metals have such an intense affinity fo they require to be preserved in some liquid element. The oxides dissolve in water form caustic solutions.

NATURE OF NON-METALS

§ 4. All the chemical elements devoid of th of physical and chemical properties which metals are termed non-metals. Only a few found in nature in the free state; namely, oxy sulphur, and sometimes carbon and selenium. rule they are opposite to the metals in t relations, being electro-negative, and, consequer at the positive electrode when their comp composed by the electric current. The positiv character, however, like that of the metals, is except in the elements oxygen and fluorin according to the kind of elements existing in Thus, in the compound known as hydrochloric is negative; but when chlorine is in comb oxygen it plays the part of a positive element.

The combination of a metal with a non-n oxygen, is characterised by a much more decis properties than in the case of union between The affinity of the different metals for oxygen, is however very varied, being more intense t difference between the electrical relations of the In the case of gold the affinities are so feeble th does not unite directly with either of these noncompounds of most metals with oxygen form bodies termed bases; while the combination o with oxygen generally forms a class of bodies

ination ite the

em are

trogen,

reneral ectrical Dearing

re de

gative solute, varies

ation. lorine

with

eh as.

ge of

properties, termed acids. Those metals, however, whi hibit the metallic character in a feeble degree, more have acid than basic properties when combined with ox It is upon these chemical relations, taken in conjur with the physical properties, that a true classificati the elements into metals and non-metals is based.

CHEMICAL PRINCIPLES AND CHANGES

§ 5. Chemists have found that all bodies, whether i form of a solid, a liquid, or a gas, are either simple stances or can be resolved into simple substances, te "elements." These elements are represented by syn which are usually the initial letter or letters of their n Different elements combine together in definite propor forming an endless variety of substances termed " pounds."

Elements are classified into "metals" and "non-me the former being distinguished by well-marked prope which are absent in the latter. The ultimate partic "atoms" which compose any element differ in weight the atoms of any other element, and the relative w compared with hydrogen is termed the "atomic wei The following table gives the chemical elements their symbols, atomic weights, and specific gravities:

METALS

etals.