The following is a short description of the chief nonmetals mentioned in the present section, and which are subsequently alluded to.

8

Oxygen (0).-This is the most abundant element, forming probably one-half the solid crust of the earth, 9 of all water, and about 21 per cent by volume of the air. It is necessary for life and all ordinary processes of combustion. In the air it is a gas, but its compounds are chiefly solid or liquid. Its oxidising action has been already mentioned. It is the chief supporter of combustion, that is, it forms the active medium in which bodies burn.

Oxides, as the compounds of oxygen with other elements are termed, may be roughly divided into two groups. 1°. Those which have an acid character, chiefly oxides of the non-metals, and often termed acids, such as carbonic acid CO, and silica SiO,. 2°. Those of a basic character, chiefly oxides of the metals, which are termed bases. These two classes are opposite in character, and when united in equivalent proportions, generally neutralise each other, forming what are termed "neutral" bodies, which do not possess the characteristic properties of either kind. Thus silica SiO2 will neutralise oxide of iron FeO, forming a silicate, which is neither acid nor basic. If any compound contain an excess of acid or base, it is classified either as an acid or as a basic substance, according to the kind which predominates. Thus, 3FeO.SiO, is a basic silicate, and FeO.SiO2 an acid silicate, because in the former there is more FeO than is required to neutralise the acid SiO2, and in the latter less than is necessary for this purpose.

Hydrogen (H) is chiefly found in nature in combination with oxygen, forming water H2O, which contains its weight of hydrogen. It differs from other non-metals in not generally uniting with metals to form compounds, but metals such as palladium and iron absorb it in large quantities, when it is said to be occluded. It burns in air or in pure oxygen, forming water, and evolving great heat2H+0=H2O.

It is a constituent of wood, peat, coal, and coal-gas, part of it probably existing in these bodies as water; and in combination with carbon it forms what are termed hydrocarbons, such as marsh-gas CH4, and olefiant-gas CH4. When the latter are burnt the hydrogen forms water, thus

In some furnaces and gas-producers, steam is introduced along with air to increase the volume of combustible gases, but only a very limited amount of steam can be used for this purpose.

Nitrogen (N) forms about 79 per cent by volume of the air, its chief function being to modify the active properties of oxygen. It neither burns nor supports combustion, so that the nitrogen which enters a furnace, for the most part, comes out unchanged, thus robbing it of a large amount of heat, without contributing any itself.

Air is simply a mixture of oxygen and nitrogen along with small quantities of water and carbonic acid. Omitting the latter, its composition may be taken as—

A ton of air thus contains about 515 lbs. of oxygen. Air resembles oxygen in its properties, but is less active on account of the inactive nitrogen.

Silicon (Si). This non-metal is a grayish-black substance. It is generally present in iron and a few other metals, and supposed to exist, like carbon, in the "free" and in the "combined" state. It is of little importance as an

element, but in combination it forms about of the earth's crust. It burns in oxygen, forming silica, thus

Silica (SiO2) plays a prominent part in the reduction of metals from their ores, being the chief slag-forming substance. It exists largely as sand, and in combination with "bases" it forms silicates. The various slags are chiefly combinations of SiO2 with alumina Al2O3, lime CaO, and other metallic oxides which fuse at high temperatures. combined silica is practically infusible.

Un

Carbon (C). This non-metal is an essential constituent of all living matter, and of all ordinary fuels, such as coal. It exists in the free state as the diamond, and as graphite or black-lead. In the latter form it is used in the manufacture of crucibles, etc., because of its infusibility, and its nontendency to form fusible slags with acid or basic substances. It will burn away in contact with air, but will not melt or vaporise. It exists in pig-iron and steel in the free and in the combined state. Part of the free carbon of pig-iron sometimes rises to the surface of the molten mass when allowed to stand, and is known as "kish.” Charcoal and coke are almost entirely composed of carbon, with a little earthy matter, which is left as ash when the carbon is burnt. Either form of carbon will burn in oxygen, forming oxides. When carbon is strongly heated in the presence of steam the latter is decomposed and the carbon oxidised thus

Carbon dioxide or Carbonic acid (CO2) is a gas about 11⁄2 times the weight of air, and is formed when carbon is burned in oxygen or in a free supply of air, thus

Also when carbonic oxide is burned in air or oxygen, thus

Carbonic oxide. Oxygen. Carbonic acid.

If carbon dioxide is brought in contact with red-hot carbon, it takes up some of the latter, forming twice its volume of carbonic oxide (CO), thus—

2

In this case carbonic acid is oxidising. CO2 is not poisonous, but it will not support life or ordinary combustion.

Carbon monoxide or Carbonic oxide (CO) is a colourless gas, about the same weight as air, extremely poisonous, and burns in air or oxygen with a blue flame producing carbonic acid, and evolving considerable heat. The combustible gas formed in gas-producers is chiefly carbonic oxide. It is a powerful reducing agent, probably the chief agent in reducing oxide of iron in the blast-furnace, and zinc oxide in zinc muffles. At high temperatures CO is decomposed, especially in the presence of other bodies, such as iron, which combine with carbon.

This is probably the case in the blast-furnace, and in the cementation process for steel.

Phosphorus (P). This non-metal is generally a waxylooking crystalline solid, which readily melts and vaporises. It is highly inflammable in air, forming a white cloud of phosphorus pentoxide P2O5, also called phosphoric acid. It combines with oxygen in two proportions, forming oxides of phosphorus. One of these oxides unites with bases to form compounds termed phosphates. It probably exists in metals as an element, but in slags as a phosphate. Thus, in refining pig-iron, phosphate of iron (3FeO.P2O) is found in tapcinder, and phosphate of lime (4CaO.P,O) in basic slag.

Phosphates are decomposed by silica at high tempera

tures, because under these conditions SiO2 is non-volatile, thus

2

3FeO.PO, SiO2 = 3FeO.SiO2 + P205
Iron phosphate.

Silica.

Iron silicate. Phosphoric acid.

Phosphoric acid is reduced by carbon, or even by iron, the phosphorus uniting with the iron, thus

P205 + 5C

Phosphoric acid.

5CO

+ 2P Carbon. Carbonic oxide. Phosphorus.

Sulphur (S) is a non-metal, and solid at ordinary temperatures. It readily melts and vaporises, and unites with metals forming sulphides, such as ferrous sulphide FeS. With oxygen it forms oxides, viz. sulphur dioxide SO2, and sulphur trioxide SO.

Chlorine.—This element exists in nature mainly in combination with sodium, calcium, potassium, magnesium, etc. At ordinary temperatures and pressures chlorine is a greenish-yellow gas, having a pungent and irritating smell, but by great pressure may be liquefied to a dark greenishyellow liquid, and at low temperatures may be solidified. It is readily soluble in water. It is an active chemical agent, and combines with most metals, forming a class of bodies termed chlorides. Indirectly it acts as a powerful oxidising agent, and is thus used in bleaching and as a disinfectant. In combination with hydrogen it forms hydrochloric acid HCl.

PROPERTIES OF THE METALS

NOBLE METALS. GOLD, PLATINUM, SILVER

§ 6. Gold is usually found in the metallic state in nature (generally associated with silver, and sometimes with copper, iron, and platinum). It is often found in ores of lead, zinc, iron, and copper. Gold is a yellow metal, with a brilliant lustre; it exceeds all others with regard to malleability and ductility; its specific gravity is 19.5; its melting point about 1200° C.; and it is only volatile at very high tempera